RU2787527C2 - System for quantitative image generation and its use - Google Patents

Abstract

FIELD: medical equipment.

SUBSTANCE: systems and methods for image generation are proposed, in particular a quantitative tomography system and a laser optoacoustic ultrasonic imaging system assembly (LOUISA) for generation of images of a tissue area, for example, subject’s breast. In general, system components are a laser, which emits instant laser radiation pulses in a wavelength changing mode, fiber-optic bundles, or arc-shaped fiber-optic bundles made with the possibility of delivery of laser radiation, an image generation module with image generation capacity, optoacoustic arrays of super-broadband ultrasound converters, and ultrasound arrays of ultrasound converters. In methods for generation of an image of quantitative functional parameters and/or molecular parameters and anatomical structures, in a subject, in a volume of tissue of interest, such as breast, the claimed systems for quantitative tomography and image generation are used.

EFFECT: inventions allow for implementation and use of three-dimensional tomography systems providing full visibility and automatic screening of the entire breast with quantitatively accurate and easily interpretated volumetric images.

30 cl, 8 dwg

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[001] This international application claims priority under Section 35 U.S.C. §119(e) of U.S. provisional application serial number 62/652,337, filed April 4, 2018, which is hereby incorporated by reference in its entirety.

Federal Funding Statement

[002] The present invention was made with government support under grant number R01CA167446 from the National Institutes of Health. The government has certain rights to the present invention.

BACKGROUND OF THE INVENTION

FIELD OF TECHNOLOGY

[003] The present invention relates to the field of biomedical imaging and tomography systems that can provide medical information about a volumetric area of interest of the body being examined. More specifically, the present invention provides a Laser Optoacoustic Ultrasonic Imaging System Assembly (LOUISA) for quantitative 3D imaging of a tissue region of interest in a subject to obtain anatomical, functional and molecular imaging.

BACKGROUND OF THE INVENTION

[004] As discovered by Judah Folkman (1), aggressive cancer cannot develop into a life-threatening disease without the support of nutrition and oxygen from microvessels. The optical absorption spectra of oxygenated and deoxygenated hemoglobin in the human body are such that they allow a selection of two near-infrared wavelengths which, when used with optoacoustic tomography imaging, can establish an oxyhemoglobin/deoxyhemoglobin contrast useful for functional imaging capabilities (2). The difference between these two states of hemoglobin oxygenation makes it possible to localize the arteries that feed the tumors and the veins that exit the tumors. With this capability, it is expected that the radiologist will distinguish between highly vascularized tissues and tissues with hypoxic malignant growth and recommend a biopsy with greater confidence than is currently expected, with 7-8 out of 10 biopsies being negative (3). These optoacoustic images can improve the detection sensitivity and specificity of medical diagnosis compared to using ultrasound alone by providing functional information about total hemoglobin (tHb) and blood oxygen saturation (s02) within tumors and displayed in morphology. tissue structures of the breast (4).

[005] Due to the great medical need and the large market for advanced breast imaging systems, since the beginning of the 21st century, a number of clinical prototype systems based on the principles of optoacoustic tomography (5-12) have been developed, and all of them are reported to have sufficient technical ability to detect breast cancer. However, the only system tested in statistically significant multicenter studies with reported clinical viability is the IMAGIO system (Seno Medical Instruments, San Antonio, Texas, USA) (3). This dual opto-acoustic/ultrasonic imaging system has the advantage of the convenience and real-time video frame rate display capability associated with the hand-held sensor (13) design. However, the limited field-of-view hand-held transducer provides two-dimensional slices that only highly trained radiologists can interpret, with reduced lateral resolution and incomplete tomographic reconstruction of quantitative images.

[006] Therefore, there is a recognized need in the art for full view 3D tomography systems that provide automatic screening of the entire breast with quantitatively accurate and easily interpretable volumetric images. In particular, the prior art lacks a quantitative functional anatomical imaging system for breast screening with simultaneous diagnosis of cancerous tumors. More specifically, the inventive quantitative imaging system design, in which functional and molecular images are displayed in anatomical tissue structures visualized by superimposed ultrasound images, has numerous applications in cancer and vascular disease detection. The present invention satisfies this longstanding need and need in the art.

DISCLOSURE OF THE INVENTION

[007] The present invention relates to a quantitative tomography system. In this system, the laser is configured to emit instantaneous pulses of laser radiation with wavelengths in the spectral range from the red part of the spectrum to the near infrared region, and the laser is configured to operate in the mode of changing wavelengths. The fiber optic bundle is configured to deliver instantaneous pulses of laser radiation to the entire tissue area of interest with maximum transmission. The imaging module comprises an imaging container shaped to correspond to the area of interest in the tissue, at least one optoacoustic array of ultra-wideband ultrasonic transducers, and at least one ultrasonic array of ultrasonic transducers. The optoacoustic array of ultra-wideband ultrasonic transducers is configured to detect ultrasonic signals within an ultra-wide band of ultrasonic frequencies generated in a tissue area of interest by instantaneous pulses of laser radiation. Said at least one ultrasonic array of ultrasonic transducers is configured to transmit ultrasound pulses to a tissue region and detect ultrasonic signals reflected from said tissue region or transmitted through said tissue region. The imaging module also contains a bonding medium that fills the imaging container and through which instantaneous laser radiation pulses and ultrasound pulses are transmitted. The multichannel electronic data acquisition system contains analog preamplifiers, analog-to-digital converters and boards for digital data storage, processing and transmission. Said data acquisition system is microprocessor-controlled (microprocessors) with a user-programmable gate array. With a multi-channel electronic data acquisition system, a computer is electronically connected, which contains a multi-core central processing unit (CPU) and a multi-core graphic processor (graphics processing unit, GPU), and software stored in material means, configured to control these CPU processors and GPU, for system control, signal processing, image reconstruction and image fusion. A high-resolution display is electronically connected to the computer to present the reconstructed image to the operator of the quantitative tomography system.

[008] The present invention also relates to a method for imaging quantitative or functional parameters in a tissue region of interest in a subject. Said area of tissue is placed in an imaging vessel of the quantitative tomography system described herein, and an optoacoustic ultra-wideband ultrasonic transducer array and an ultrasonic array of ultrasonic transducers are positioned within the imaging vessel. Laser radiation wavelengths are selected in the spectral range from the red part of the spectrum to the near infrared region for delivery as instantaneous pulses to the specified tissue area in the mode of changing wavelengths, and the changing instantaneous pulses of laser radiation with the selected wavelength are delivered to the specified tissue area. For each selected wavelength, signals within the ultra-wide band of ultrasonic frequencies generated within a specified area of tissue are detected using an optoacoustic array, and optoacoustic images from the detected signals are obtained for each selected wavelength and superimposed. Images of quantitative functional parameters or molecular parameters are generated from the combined optoacoustic images, and the generated quantitative images are displayed.

[009] The present invention relates to a corresponding imaging method. Said method also includes transmitting ultrasonic pulses from an ultrasonic array to said tissue region and detecting, by means of an ultrasonic array, signals reflected from said tissue region or transmitted through said tissue region. The sound speed images are generated based on the sound speed distribution within the specified tissue area and anatomical images based on the reflection or attenuation of ultrasound from the detected ultrasound signals. The images of quantitative functional parameters or molecular parameters are combined with anatomical structures, and the combined images are displayed as an overlay of images of quantitative or functional parameters with anatomical images or sound speed images. The present invention relates to another suitable method further comprising enhancing optoacoustic images and ultrasound reflection or attenuation images with sound speed images. The present invention relates to another relevant method further comprising diagnosing cancer based on quantitative functional parameters or molecular parameters and anatomical structures displayed on said overlay.

[0010] The present invention also relates to a Laser Optoacoustic Ultrasonic Imaging System Assembly (LOUISA) for imaging the breast of a subject. The laser is configured to emit instantaneous pulses of laser radiation with wavelengths in the spectral range from the red part of the spectrum to the near infrared region, and said laser is configured to operate in the mode of changing two or three wavelengths in the specified spectral range. The arcuate fiber optic bundle is rotatable around the chest to deliver instant pulses of laser radiation to the entire chest. The imaging container has a shape with a spherical surface corresponding to the breast. At least one arc-shaped optoacoustic array of ultra-wideband ultrasonic transducers is configured to detect ultrasonic signals within an ultra-wide band of 50 kHz to 6 MHz, generated in the chest by instantaneous laser radiation pulses and at least one arc-shaped ultrasonic array of ultrasonic transducers, configured to transmit pulses of ultrasound into the chest and detection of ultrasound signals reflected from the chest or transmitted through the chest. An optically transparent and sound-permeable bonding medium fills the imaging container through which instantaneous laser pulses and ultrasound pulses are transmitted. The electronics in the LOUISA system comprise a multi-channel electronic data acquisition system, a computer in electronic communication with the multi-channel electronic data acquisition system, and a high resolution display electronically connected to the computer. The multichannel electronic data acquisition system contains analog preamplifiers, analog-to-digital converters and boards for digital data storage, processing and transmission, while said data acquisition system is controlled by a microprocessor (microprocessors) with a user-programmable gate array. The computer contains a multi-core central processing unit (CPU) and a multi-core graphic processor (graphics processing unit, GPU), and software stored in material means, configured to control the specified CPU and GPU processors, for system control, signal processing, reconstruction images and image alignment. The high resolution display presents the reconstructed breast image to the LOUISA operator.

[0011] Other and additional aspects, features, benefits and advantages of the present invention will be apparent from the following description of the presently preferred embodiments of the invention presented for the purpose of disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Thus, in the manner in which the above features, advantages, and objects of the invention, as well as other features, advantages, and objects of the invention that become clear, achieved, and can be understood in detail, more detailed descriptions of the invention summarized above can be obtained by reference to some embodiments of their implementation shown in the accompanying drawings. These drawings are part of said disclosure. It should be noted, however, that the accompanying drawings illustrate preferred embodiments of the invention and should therefore not be construed as limiting their scope.

[0013] FIG. 1A is a basic schematic diagram for OAT 1D Optoacoustic Tomography, and FIG. 1B-1E show a Laser Optoacoustic Ultrasonic Imaging System Assembly (LOUISA) for breast scanning. FIG. 1A shows rotating arc-shaped fiber optic irradiators that generate ultrasonic waves from optical absorption by the tumor, which can then be detected by an independently rotating optoacoustic transducer, providing a complete set of signal data for accurate volumetric reconstruction. FIG. 1B shows a fiber optic bundle with a single arcuate fiber optic blade (see 7 in FIG. 1C). FIG. 1C shows a fiber optic bundle with two arcuate fiber optic vanes. FIG. 1D shows an imaging module for scanning a large breast. The imaging module has an imaging module platform 1 placed on a large base 2 for a motor to rotate the entire imaging container 3 around the breast. The imaging module contains an imaging container filled with an acoustic bonding medium, while the breast is stabilized inside the imaging module using a breast stabilizer (see FIG. 1E), which is a very thin optically transparent and sound-permeable plastic cup with a spherical surface, concave arc-shaped array 4 ultrasonic transducers, concave arc-shaped array 5 opto-acoustic transducers, boards 6 pre-amplifiers directly connected to the opto-acoustic sensor, expanding the bandwidth of opto-acoustic transducers, arc-shaped fiber optic bundle (fiber optic blade) 7 for irradiating the chest with a homogeneous beam of light, this the fiber optic system may have one (see FIG. 1B), two (see FIG. 1C), or more arcuate fiber optic vanes for faster exposure to the entire chest, and a small motor 8 to rotate the arc shaped fiber optic vane around the imaging bowl. FIG. 1E shows a chest stabilizer.

[0014] FIG. 2A-2B are views showing a structure having a spherical shape of an imaging vessel with a single arcuate transducer composed of three planar 2D arrays of UWB ultrasonic transducers. One transducer array serves both anatomical (ultrasonic) and molecular (optoacoustic) imaging.

[0015] FIG. 3 is a schematic representation of an array of optoacoustic ultrasonic transducers for a cylindrical 3D tomography system in which either a half ring or a full ring of optoacoustic transducers with attached fiber optic feeds translates along the z-axis of the cylinder to produce a 3D image.

[0016] FIG. 4A-4B is a photograph of a breast phantom made of PVC-plastisol with the optical properties of a medium breast (m _eff ~ 1.15/cm) (FIG. 4A) and a functional image of blood oxygen saturation within the phantom reconstructed from two combined optoacoustic images obtained by irradiating the phantom with two alternating wavelengths of 757 nm and 797 nm (FIG. 4B). FIG. 5A-5B are 2D optoacoustic images of an artery/vein pair taken with the LOUISA system's hand-held transducer. FIG. 5A shows that the vein is clearly visible under irradiation at a wavelength of 757 nm. FIG. 5B shows that the artery is clearly visible at a wavelength of 1064 nm.

[0017] FIG. 6A-6C are examples of maximum intensity projections on the frontal x-y plane (FIG. 6A), on the sagittal x-z plane (FIG. 6B) and y-z (FIG. 6C) three-dimensional optoacoustic images demonstrating the capabilities of the LOUISA system for imaging blood vessels, breast nipple filled with microvessels and small tumor growth.

[0018] FIG. 7A-7C are maximum intensity projection images of the chest of a healthy volunteer obtained from a 3D optoacoustic image taken at a wavelength of 757 nm. FIG. 7A shows the original raw image, which shows only superficial blood vessels due to the non-uniform distribution of optical energy across the chest. FIG. 7B is an optoacoustic (OA) image processed by normalizing (flattening) the distribution of laser light energy on the chest surface, which depicts a greater depth of imaging. FIG. 7C shows an optoacoustic image processed by compensation for effective optical attenuation as a function of depth, which depicts the full depth of imaging in the chest.

[0019] FIG. 8 is an example of a sagittal 2D slice of combined 3D optoacoustic and ultrasound images. An optoacoustic image slice is shown with a brightness threshold to display only the maximum brightness superimposed on the corresponding gray scale values of the ultrasound image.

IMPLEMENTATION OF THE INVENTION

[0020] As used herein, singular grammatical means may mean one or more. As used herein in claims, when used in conjunction with the word "comprising", singular grammatical means may mean one or more than one.

[0021] As used herein, "another" or "another" may refer to at least the second or more of the same or a different claim element or components thereof. Likewise, the word "or" is intended to include "and" unless the context clearly indicates otherwise. "Contain" means "to include".

[0022] As used herein, the term "approximately" refers to a numerical value, including, for example, whole numbers, fractions, and percentages, whether explicitly stated or not. The term "about" generally refers to a range of numerical values (eg, +/- 5-10% of a specified value) that a person skilled in the art would consider equivalent to a given value (eg, having the same function or result). In some cases, the term "approximately" may include numerical values rounded to the nearest significant number.

[0023] In one embodiment of the present invention, a quantitative tomography system is provided, comprising a laser configured to emit instantaneous pulses of laser radiation with wavelengths in the spectral range from the red part of the spectrum to the near infrared region, and the specified laser is configured to operate in a shift mode wavelengths; a fiber optic bundle configured to deliver instantaneous pulses of laser radiation to the entire tissue area of interest with maximum transmission; an imaging module comprising an imaging container shaped according to the region of interest in the tissue; at least one ultra-wideband ultrasonic transducer optoacoustic array configured to detect ultrasonic signals within a ultra-wide band of ultrasonic frequencies generated in a tissue region of interest by instantaneous pulses of laser radiation; at least one ultrasonic array of ultrasonic transducers, configured to transmit ultrasound pulses to a tissue region and detect ultrasonic signals reflected from said tissue region or transmitted through said tissue region; and a bonding medium that fills the imaging container and through which instantaneous laser radiation pulses and ultrasound pulses are transmitted; a multichannel electronic data acquisition system containing analog preamplifiers, analog-to-digital converters and boards for digital data storage, processing and transmission, while said data acquisition system is controlled by a microprocessor (microprocessors) with a user-programmable gate array; a computer in electronic communication with a multi-channel electronic data acquisition system and containing a multi-core central processing unit (CPU) and a multi-core graphic processor (graphics processing unit, GPU), and software stored in tangible means, configured to control these CPU processors and GPU, for system control, signal processing, image reconstruction and image alignment; and a high resolution display electronically connected to a computer for presenting the reconstructed image to an operator of the quantitative tomography system.

[0024] In this embodiment, the spectral wavelength range from red to near infrared is about 650 nm to about 1250 nm. Also, the wavelength change mode can include two or three wavelengths in the spectral range from the red part of the spectrum to the near infrared region. According to an aspect of this embodiment, the two alternate wavelengths are 757 nm and 850 nm. According to this aspect, the laser may be a pumped Nd:YAG OPO laser for quantitative molecular imaging. In yet another aspect, the three alternate wavelengths are 757 nm, 800 nm, and 850 nm, or 757 nm, 800 nm, and 1064 nm. In this aspect, the laser may be a Cr:LICAF quantitative functional imaging laser. In addition, maximum transmission of instantaneous laser pulses can be realized with a hot alloy entry tip that gives the fibers in the tow a honeycomb shape.

[0025] Also in this embodiment, the UWB ultrasonic transducers in the array can detect ultrasonic signals within the UWB from 50 kHz to 6 MHz. According to one aspect, an optoacoustic array of ultra-wideband ultrasonic transducers and an ultrasonic array of ultrasonic transducers are combined into one array.

[0026] In addition, the imaging container in the imaging unit has a spherical surface shape or a cylindrical shape. An example of a tissue region of interest is the breast tissue region. In addition, in this embodiment, the software provides processor-executable signal processing and image processing instructions to obtain images of quantitative concentrations of molecules or functional parameters within a region of interest in tissue or anatomical structures. According to aspects, these instructions may be configured to: restore the original profiles of the optoacoustic signal generated in the specified region of the tissue by instantaneous laser pulses, using the deconvolution of the acoustic-electrical and spatial impulse response functions of the ultra-wideband ultrasonic transducer from the detected optoacoustic signals; reconstruction of three-dimensional images of optoacoustic tomography of the specified area of tissue by strict direct algorithms or iterative algorithms using a complete set of data obtained with a geometry that provides full visibility; normalizing the distribution of the incident optical energy density on the surface of the specified tissue area by equalizing the brightness of the image of all surface voxels; normalizing the distribution of the incident optical energy density over the entire area of the tissue by compensation for effective attenuation of the optical radiation; displaying images of the optical absorption coefficient after normalization of the incident optical energy density through the specified tissue area on optoacoustic images of optical energy absorbed in the specified tissue area; obtaining combined optoacoustic images obtained at two or three alternating laser wavelengths to obtain quantitative functional or molecular images; and obtaining images of the distribution of the speed of sound within the specified area of tissue, which are used to improve the contrast and resolution of the combined optoacoustic images or ultrasound reflection and attenuation images.

[0027] In a related embodiment of the present invention, there is provided a Laser Optoacoustic Ultrasonic Imaging System Assembly (LOUISA) for imaging the chest of a subject, comprising a laser configured to emit instantaneous pulses of laser radiation at wavelengths in the spectral range from the red part of the spectrum to the near infrared region, and the specified laser is configured to operate in the mode of changing wavelengths with two or three wavelengths in the specified spectral range; an arcuate fiber optic bundle rotatable around the chest to deliver instant pulses of laser radiation to the entire chest; an imaging container having a shape with a spherical surface corresponding to a breast; at least one arc-shaped optoacoustic array of ultra-wideband ultrasonic transducers, configured to detect ultrasonic signals within an ultra-wide band of 50 kHz to 6 MHz, generated in the chest by instantaneous pulses of laser radiation; at least one arc-shaped ultrasonic array of ultrasonic transducers, configured to transmit ultrasound pulses to the chest and detect ultrasonic signals reflected from the chest or transmitted through the chest; an optically transparent and sound-transmitting binding medium which fills the imaging container and through which instantaneous laser pulses and ultrasound pulses are transmitted; and an electronic subsystem containing a multi-channel electronic data acquisition system containing analog preamplifiers, analog-to-digital converters and boards for digital data storage, processing and transmission, while said data acquisition system is controlled by a microprocessor (microprocessors) with a user-programmable gate array; a computer in electronic communication with a multi-channel electronic data acquisition system and containing a multi-core central processing unit (CPU) and a multi-core graphic processor (graphics processing unit, GPU), and software stored in tangible means, configured to control these CPU processors and GPU, for system control, signal processing, image reconstruction and image alignment; and a high resolution display electronically connected to a computer for presenting the reconstructed breast image to a LOUISA system operator.

[0028] In this embodiment, the two alternating wavelengths may be 757 nm and 850 nm. Also in this embodiment, the three alternate wavelengths are 757 nm, 800 nm, and 850 nm, or 757 nm, 800 nm, and 1064 nm. In addition, the optoacoustic array of ultra-wideband ultrasonic transducers and the ultrasonic array of ultrasonic transducers can be combined into one array. In addition, the arcuate fiber bundle, the arcuate optoacoustic array, and the arcuate ultrasonic array are configured to independently rotate around the chest to irradiate the entire chest for each position of the optoacoustic array and the ultrasonic array.

[0029] In yet another embodiment, the present invention provides a method for imaging quantitative or functional parameters in a tissue region of interest in a subject, comprising the steps of: placing said tissue region in a container for imaging a quantitative tomography system as described above; positioning the optoacoustic array of ultra-wideband ultrasonic transducers and the ultrasonic array of ultrasonic transducers inside the imaging container; selection of wavelengths of laser radiation in the spectral range from the red part of the spectrum to the near infrared region for delivery as instantaneous pulses to the specified tissue area in the mode of changing wavelengths; delivery to the volume of the specified tissue changing instantaneous pulses of laser radiation with a selected wavelength; detecting with an optoacoustic array, for each selected wavelength, signals within an ultra-wide band of ultrasonic frequencies generated within a specified tissue area; obtaining optoacoustic images from the detected signals for each selected wavelength; combination of optoacoustic images; generating images of quantitative functional parameters or molecular parameters from the combined optoacoustic images; and displaying the generated quantitative images.

[0030] In addition to this embodiment, the method includes transmitting to the specified area of the tissue pulses of ultrasound from the ultrasound array; detecting, using an ultrasonic array, signals reflected from said tissue region or transmitted through said tissue region; generating images at the speed of sound based on the distribution of the speed of sound within the specified region of the tissue; generation of anatomical images based on the reflection or attenuation of ultrasound from the detected ultrasound signals; aligning images of a quantitative functional parameter or molecular parameters within anatomical structures; and displaying the combined images as an overlay of the quantitative or functional parameters images with anatomical or sound velocity images. In yet another further implementation, the method includes enhancing optoacoustic and ultrasonic reflection or attenuation images with sound speed images. In yet another further embodiment, the method includes diagnosing cancer based on functional parameters or molecular parameters and anatomical images displayed on said overlay. An example of cancer is breast cancer.

[0031] In all implementations, the detection of signals generated at each selected wavelength may occur simultaneously. Also, in all embodiments, the quantitative functional parameter may comprise the concentration of a protein, a receptor protein, or a molecule associated with breast cancer, or a combination of these. In addition, the molecular parameter may be total hemoglobin or blood oxygen saturation, or a combination of these.

[0032] In one aspect of all embodiments, the tissue region of interest may be spherical and the transducer arrays arcuate, the transducer arrays rotating around the region of interest by a computer controlled motor. Also, for a spherical tissue region of interest, the fiber tow rotates around the region of interest independently of the rotating transducer arrays so that during scanning, complete exposure of the tissue region of interest is achieved for each position of the transducer arrays.

[0033] According to another aspect of all embodiments, the tissue region of interest may be cylindrical in shape and the transducer arrays may be arcuate or full ring shaped and translate along the region of interest by a computer controlled motor. Also for a cylindrical tissue region of interest, the fiber tow is translated along the axis of the cylinder along with the transducer arrays.

[0034] A three-dimensional (3D) medical volumetric imaging system providing full visibility was developed to meet the needs of radiologists-diagnostics in a quantitative tomography system (quantitative tomography system, QT-System), capable of providing quantitative molecular information in specific anatomical structures, such as like tumors and their environment. One of the many important applications of such a system is the detection and diagnosis of cancer. Thus, the present invention provides a Laser Optoacoustic Ultrasonic Imaging System Assembly (LOUISA) for detecting and diagnosing breast cancer.

[0035] The technical features of this system contribute to improving the low detection sensitivity of mammography x-rays and tomographic reconstruction in dense and heterogeneous breasts and the low diagnostic specificity of magnetic resonance imaging. In our opinion, the combination of quantitatively accurate molecular images of the breast, showing the functional parameters of total hemoglobin (tHb) and blood oxygen saturation (sO2), in the morphological structures of the breast, including tumors and their environment, will provide a clinically useful solution for management of breast cancer. Quantitative molecular imaging in the LOUISA system is supported by unique hardware features and software methods, as well as the algorithms of the optoacoustic subsystem, described below. Anatomical imaging of specific structures within a region of interest (ROI) tissue, such as tumors, is enabled by unique hardware and software techniques, as well as the algorithms of the ultrasound subsystem described below. What makes this system not only clinically viable but also practical is a novel signal acquisition and scanning design that provides fast 3D volumetric scanning of the entire region of interest, adding a fourth dimension of time to the system's 3D capabilities. Ultimately, the system is able to create 3D images with temporal resolution, not just spatial resolution.

System overview

[0036] The quantitative tomography system has six main components that provide its operation and new functions and capabilities:

[0037] 1. A pulsed laser that emits instantaneous pulses of optical energy in the spectral range from the red part of the spectrum to the near infrared region with the possibility of changing the wavelength. "Instantaneous pulses" as used herein means that the duration of these laser pulses is much less than the time required for an acoustic wave to propagate at the speed of sound through a voxel to provide resolution in optoacoustic images. For example, if the desired image resolution, i.e. the voxel size is 0.15 mm, then given that the speed of sound is 1.5 mm per microsecond, the time required for an acoustic wave to propagate through this voxel is 0.1 microsecond. "Much less" means at least three times less. Therefore, for this particular example, the laser pulses will be less than 30 nsec. Too short pulses are also unacceptable, since they can damage the optical elements of the system, primarily the fiber-optic subsystem for delivering light.

[0038] The spectral range from the red part of the spectrum to the near infrared region is the wavelength range from 650 nm to 1250 nm. This wavelength range is important for deep penetration of optical energy into biological tissue and at the same time for strong optical absorption by medically important molecules such as hemoglobin, oxyhemoglobin, lipids, water and exogenous contrast agents used in medical diagnostics and therapy. The ability to change wavelengths means that the emitted wavelength changes with each laser pulse. The optimal number of wavelengths to select for quantitative molecular imaging is two, which corresponds to two unknown concentrations of molecules or two unknown functional parameters.

[0039] When the molecules of interest are hemoglobin and oxyhemoglobin, images showing functional parameters of total hemoglobin (tHb) and blood oxygen saturation (sO2) are called functional images. These images can be calculated from optoacoustic images taken at two wavelengths, one corresponding to the optical absorption peak of hemoglobin, eg 757 nm, and the other corresponding to the optical absorption peak in oxyhemoglobin, eg 850 nm. Two wavelengths are also needed to measure and display the concentration of an endogenous molecule or exogenous contrast agent. In this case, one wavelength is chosen at the optical absorption peak of the molecule of interest, and the second wavelength is chosen outside the optical absorption peak of the molecule of interest.

[0040] Three alternating wavelengths can be used to increase the accuracy of quantitative information from molecular or functional waveform images. For example, a third wavelength of 800 nm can be used for functional imaging of total hemoglobin and blood oxygen saturation. This third wavelength can be used to normalize functional images because it corresponds to the isosbestic point in the optical absorption spectrum where the absorption coefficients of hemoglobin and oxyhemoglobin are equal. Using more than three wavelengths per cycle is not practical for medical imaging because the total imaging time for quantitative imaging should be as short as possible.

[0041] The ability to change wavelengths is critical for optoacoustic image alignment, which allows molecular (functional) images to be generated using mathematical operations such as addition, subtraction, and division. Only merged images can be subjected to mathematical operations, otherwise the resulting image will have a very high level of errors. Image registration is performed when each voxel of one image has the same location (coordinates) as in the second image, which can only be achieved if living tissues are not moving at the time when both images are acquired. Therefore, two images must be acquired at the same time or as soon as possible one after the other in order to perform registration. The desired laser pulse repetition rate is from 10 Hz to 50 Hz, which allows a time delay of 100 ms to 20 ms between images taken at two different wavelengths. However, it is possible to reduce the time delay between acquisition of two images to a minimum, which is equal to the propagation time of ultrasound from the farthest voxel in the area of interest to the ultrasound transducers in the detector array (approximately 0.15 ms). This final alignment can be achieved with a dual laser design that allows emission to be triggered at two alternating wavelengths with any given delay. This, in turn, allows two successive optoacoustic signals acquired at two alternating wavelengths to be recorded as a single signal recorded by the data acquisition system, with the first sample positions in each optoacoustic signal precisely determined by the synchronization trigger.

[0042] 2. Fiberoptic Light Delivery (FLD) subsystem. The fiber optic bundle has a round entrance that matches the shape of the incident laser beam. The fibers at the tip are hot welded to form a honeycomb shape. The hexagonal shape of the fibers in the bundle minimizes light losses between the fibers and achieves maximum light transmission to the output (up to 85%). The exit shape corresponds to the shape of the area of interest in the tissue. Since most areas of interest in human organs are either spherical or cylindrical, the most advantageous form of fiber optic output is an arc. An arc can be well approximated by a series of flat lines arranged in an arc shape. A plurality of arcuate fiber optic bundles can be used to enlarge the portion of the area of interest that is exposed to the same laser pulse at the same time. For example, the breast is an area of interest for diagnostic imaging of breast cancer. Since the natural shape of the female breast is a hemisphere, the design of the fiber optic light delivery subsystem is a 90 degree arc or multiple arcs emanating from the same center like flower petals (FIGS. 1A-1C). For other organs and areas of interest such as the neck, arms, legs, fingers, the output of the fiber optic light delivery is also in the form of an arc, and a plurality of fiber arcs may be in the form of cylindrical surfaces. The fiber optic light delivery subsystem is mounted on a computer controlled motor so that it can be rotated or translated to illuminate the entire area of interest (FIG. 1D).

[0043] 3. An imaging module with two sensors represented by arrays of ultrasonic transducers sensitive to transient pressure changes. The first sensor is an optoacoustic (OA) sensor represented by an arcuate array of ultrawide-band ultrasonic transducers (UBT) operating in receive mode. The second sensor is an ultrasonic (US) sensor, represented by an arcuate array of ultrasonic transducers operating in transmit and receive modes. The arcuate shape of the sensors can be represented by a series of flat lines along the arc. The arcuate shape of the transducers makes it possible to significantly increase the acoustic aperture at small physical dimensions and, in turn, provides high image resolution in the lateral direction.

[0044] Both sensors are placed in an optically transparent sound-permeable container, which, in turn, is connected to a computer-controlled motor (regardless of the motor used to rotate or translate the fiber optic light delivery subsystem), which can rotate around a spherical area tissue of interest, or to carry out translational movement along the axis of symmetry of the cylindrical region of the tissue of interest. The rotation and translation of the sensors around the area of interest in the tissue allows you to collect complete sets of data for imaging, providing full visibility, and, in turn, to reconstruct quantitative tomographic images. The independence of the engine of the fiber optic light delivery subsystem and the engine of the imaging container allows complete illumination of the entire area of interest in the tissue for each position of the sensors. This full irradiation of the entire large organ is achieved with a less expensive laser with lower pulsed energy, which makes the quantitative tomography system more practical.

[0045] Alternatively, optoacoustic and ultrasonic sensors can be combined into a single sensor that serves both molecular imaging and anatomical imaging purposes, making the quantitative tomography system less expensive and more compact. In addition, the goal of superimposing molecular (optoacoustic) images with anatomical (ultrasound) images is achieved more easily and naturally when optoacoustic and ultrasonic transducers are combined into one. The sensor can be either a linear array of transducers or a two-dimensional array of ultrasonic transducers. A 2D array of ultrasonic transducers is the most advantageous for a quantitative tomography system because it allows flexible control of the directivity of the sensors, eliminates the need for an acoustic lens, increases the sensitivity of the sensors, allows reconstruction of 3D images at video rate, and reduces the overall scanning time of a large area of tissue of interest. Materials for transducers in transducers are selected from those that allow the creation of ultra-wideband ultrasonic transducers, which is critical for a quantitative tomography system. Without UWB acoustic transducers, the detected optoacoustic signals are significantly distorted, which in turn leads to much lower accuracy of quantitative information in molecular and functional images. Examples of transducer materials for designing and manufacturing ultra-wideband ultrasonic transducers include, but are not limited to, single crystal piezoelectric composites such as PZT and PMN-PT. Micromachined capacitive ultrasonic transducers (cMUTs) are also good candidates for ultra-wideband acoustic transducer array design. However, the most sensitive ultra-wideband acoustic transducer arrays, with the widest ultrasonic detectable bandwidth spanning both the high and low frequency ranges, have been designed and fabricated from micromachined piezoelectric ultrasonic transducers (pMUTs) that can provide maximum ultra-wide bandwidth. detected ultrasonic frequencies from 50 kHz to 20 MHz and, in turn, optoacoustic images with the highest quantitative accuracy, the highest contrast and at the same time the highest resolution. Optical detectors of transient ultrasonic waves can also be used as ultra-wideband ultrasonic transducers. The most promising optical ultrawideband acoustic transducer designs are based on Fabry-Perot etalons that measure tissue displacement and balanced photodiode arrays that measure the deflection angle of a laser beam.

[0046] 4. Multi-channel electronic data acquisition system (Data Acquisition System, DAS) with low-noise analog preamplifiers, analog-to-digital converters and boards for digital data storage, processing and transmission, made by controlled microprocessors with a field programmable gate array and fast transmission data to a computer via fast data ports such as USB3 or PCI express. Important features of this data acquisition system are (i) a high dynamic range (at least 14 bits), which allows detecting strong signals from the surface of the tissue region of interest and simultaneously weak signals from deep tissue, (ii) a high sampling rate (at least 30 MHz) allowing for accurate digitization of analog signals, and (iii) a large detectable signal length (at least 8000 samples) allowing the use of a new design for detecting two optoacoustic signals simultaneously as a single signal, thus reducing imaging time and providing conditions for perfect alignment.

[0047] 5. A computer with a processor, memory, and at least one network connection, as well as software for system management, data post-processing and image reconstruction, image conversion, image alignment, and image post-processing. Signal processing and image processing in a quantitative tomography system represents a critical novelty in system design, which uses a complete set of optoacoustic signals recorded with minimal distortion using ultra-wideband ultrasonic transducers. The following mathematical processing provides accurate quantitative tomography that satisfies a long-standing need in medical diagnostics (and cancer diagnostics in particular) to measure functional parameters such as total hemoglobin and blood oxygen saturation, as well as the concentrations of specific receptor proteins and other physiologically important molecules:

a. Reconstruction of the original profiles of an optoacoustic signal generated in a tissue region of interest by instantaneous laser pulses using deconvolution of the acoustic-electrical and spatial impulse response functions of an ultra-wideband ultrasonic transducer from the detected optoacoustic signals.

b. Reconstruction of 3D optoacoustic tomography images of a tissue region of interest using rigorous algorithms using a complete set of data acquired with a geometry that provides full visibility

Iterative methods of optoacoustic tomography can be used to further increase image accuracy.

c. Normalization of the distribution of the incident optical energy density on the surface of the tissue region of interest by equalizing the brightness of the image of all surface voxels. If the optical absorption coefficient of the voxels of the surface of the region of interest is not uniform, perform this step of normalizing the falling absorbance of energy using the stabilizer of the tissue region of interest. A tissue region of interest stabilizer is a thin, spherical or cylindrical shaped plastic cup that is placed on the tissue region of interest to ensure that the region of interest has a specific and well-defined shape and dimensions. Such a stabilizer, made of optically transparent and sound-permeable plastic, greatly increases the accuracy of the reconstruction of the combined images, preventing any movement of the tissue during scanning and providing accurate surface coordinates of the region of interest. An example of a tissue region of interest stabilizer is the breast cup shown in FIG. 1D, with spherical surface parameters selected individually for each patient.

d. Normalization of the distribution of optical energy density throughout the volume of tissue area of interest by compensation for effective attenuation of optical radiation. The fiber optic light delivery subsystem is designed to deliver optical energy orthogonally to the surface of the tissue region of interest along a radius vector connecting each surface voxel to the focal point of the spherical imaging container or the axis of symmetry of the cylindrical imaging container. Therefore, compensation for the effective attenuation of optical radiation can be performed along these radius vectors, R. A typical effective attenuation of optical radiation in biological tissues can be described by Beer's law as ~ exp-(mu _eff R), where mu _eff is the coefficient of effective attenuation of optical radiation at a given laser wavelength, and R is the depth in tissue measured from the surface voxel along the light propagation radius vector. A more accurate function of the effective attenuation of optical radiation can be measured experimentally from the gradually decreasing brightness of the background voxels in the images reconstructed in step (b). Although such a measurement is not possible with the current state of the art, the proposed quantitative tomography system uses ultra-wideband ultrasonic transducers that allow such slopes of low-frequency signals in optoacoustic images to be measured as the slope of the effective attenuation of optical radiation by biological tissues. After normalization (alignment) of the optical energy density over the volume of the region of interest of the tissue, the brightness of the voxels of the image, first reconstructed in step (b), becomes proportional to the optical absorption coefficient.

e. Performing signal processing step (a) and image processing steps (b), (c), (d) for each of the alternating laser wavelengths selected for image examination.

f. Use of combined optoacoustic images obtained in step (d) for two or three alternating laser wavelengths to calculate quantitative molecular or functional images.

g. Use of complete sets of ultrasonic signals to reconstruct images from reflection or attenuation of ultrasound, or the speed of sound and ensure their registration with molecular (functional) images. Both optoacoustic and ultrasound imaging require knowledge of the sound velocity distribution in the tissue region of interest. Therefore, sound speed imaging can be used to improve the fidelity (contrast and resolution) of optoacoustic and ultrasonic reflection or attenuation imaging.

h. Display of molecular (functional) images overlaid with superimposed anatomical images based on reflection, ultrasound attenuation, or sound velocity. These final image overlays display in color quantitative values of molecular concentrations and functional parameters in anatomical tissue structures displayed in gray scale contrast on ultrasound images.

i. The computer also has an operator interface for sending commands to the system through the keyboard or by voice using artificial intelligence software.

[0048] 6. High resolution screen for displaying images. The display may be physical (such as LCD, LED) or represent a holographic display. The display may have a touch screen for transmitting commands to a computer.

Application of two tools for molecular anatomical imaging

Limitations of current technologies for breast cancer management

[0049] Currently used x-ray tools for breast screening and diagnostic imaging tools for mammography and tomographic reconstruction have serious limitations in sensitivity and specificity, especially in the case of dense and heterogeneous breasts in young women. Based on the optimal balance between the risk of exposure to ionizing radiation and the benefits of early detection, the American Cancer Society recommends a mammogram every two years and only after age 50 (14). Thus, ultrasound for breast examination is used as an adjunct to X-ray screening tools (15). Ultrasound in its 2D and 3D versions is used as a diagnostic imaging tool due to the very high false positive rate. However, even when both mammography and ultrasound suggest cancer and recommend a biopsy, the rate of negative biopsy results exceeds 70% (16).

Optoacoustic (OA) functional imaging

[0050] From the very beginning of research in the field of optoacoustic imaging of breast cancer, this was considered as functional imaging of tumor angiogenesis (17). When using optoacoustic means, the main chromophore is hemoglobin, therefore, if the tumor is completely filled with blood, the network of vessels and, therefore, the tumor will be more visible. The use of ultrasound alone can also lead to false positive diagnoses, which can be further refined with additional optoacoustic imaging (10). In the initial study of the previous system, the LOUISA system, in which the transducers were larger (2 cm), the vessel networks were assembled together. The current system has smaller transducers (1.1 mm) as well as spherical objects, as opposed to the linear ones in the previous system. In the past, tumors could be seen with some vascular network, but now tumors and a highly articulated vascular network can be seen, indicating readiness to start clinical trials.

[0051] Functional imaging that distinguishes between hemoglobin and oxyhemoglobin using tissue irradiation with at least two near-infrared optical waveforms was first demonstrated by Chance (18).

[0052] Using the same formulas applied to data collected by photoacoustic microscopy, Wang demonstrated functional changes in blood oxygen saturation in a live rat (19). A number of research groups are currently developing methods to improve the quantitative accuracy of functional imaging, especially challenging for deep tissue volumetric imaging (20).

Quantitative Imaging by Compensating for Attenuated Energy Density

[0053] The LOUISA Rotating Fiber Optic Light Delivery System is designed to provide the most uniform integral breast exposure as experimentally possible. On the other hand, it is impossible to avoid the attenuation of the optical emission of light in the near infrared region in the tissues of the breast, which leads to a spherically symmetric gradient of the effective optical energy density in the hemisphere of the breast. It is interesting to note that the reduced effective optical energy density at the focal point of the chest hemisphere is partially compensated by the improved resolution in the focal region of the transducer array. The brightness of microvessels with diameters less than the spatial resolution will be lower due to the limited penetration of light into the tissues, but will be higher due to the increased resolution of the system.

[0054] To reconstruct volumetric images with brightness regardless of depth from the exposed surface, the brightness of voxels increases exponentially in radial directions from the skin surface to the focal center of the chest. It has been found that the average attenuation of optical radiation in the chest in the range from 755 nm to 800 nm is approximately meff~1.15/CM. Therefore, the function exp(1.15R) is applied to the brightness palette of optoacoustic images, where R is the radius of the hemisphere. This approach was sufficient to reconstruct binary functional oxygen saturation images showing either oxygenated blood in red or deoxygenated blood in blue.

Combination of functional and anatomical images

[0055] Although breast ultrasound has low specificity in diagnosing breast cancer, this tool is quite sensitive and provides a good overview of anatomical features, which allows you to get a general idea of \u200b\u200bthe morphology of the breast. Ultrasound can provide a certain level of specificity based on the shape of the tumor shadow, ie. benign tumors are round in shape, while cancerous lesions have a heterogeneous morphology and an "ugly" shape, often with sprouts. Ultrasound lacks functional/molecular information, such as angiogenesis density and blood oxygen saturation, which is characteristic for distinguishing malignant tumors from benign lesions and cysts (21). In other words, the combination of optoacoustic and ultrasound images is quite justified, especially considering that the same sensor and the same electronic means can be used for both means (22-23).

[0056] An earlier study demonstrated that the tumor morphology seen on optoacoustic images closely resembles that seen on B-mode ultrasound (5). The next step is to display the functional parameters of total hemoglobin and blood oxygen saturation (within and near the tumor, as shown on gray scale ultrasound images. diagnostic specificity of the two agents compared with the use of ultrasound alone (3).

[0057] Three-dimensional optoacoustic images providing full visibility and two-dimensional optoacoustic images providing partial visibility are obtained at two rapidly changing laser wavelengths in the spectral region of the near infrared region. Two-dimensional anatomical images of the breast were obtained by B-mode ultrasound using an arcuate transducer to achieve a wider acoustic aperture and greater resolution in the lateral direction. Three-dimensional images of the anatomical background of the breast can be obtained in the LOUISA system by means of a sequence of B-mode breast ultrasound slices obtained with an array of transducers rotating around the breast. This creates the possibility of visualizing the distributions of total hemoglobin and blood oxygen saturation (in specific morphological structures, such as angiogenesis of the tumor microvessel network and the network of large vessels in the vicinity of the tumor.

Problems of two-dimensional optoacoustic tomography

[0058] Optoacoustic imaging systems based on hand-held transducer ultrasonic transducers are becoming increasingly popular in the biomedical imaging community. These systems provide 2D imaging at standard video frequencies in applications related to the detection of cancer and vascular anomalies. Due to the compact size of hand-held transducers, these real-time imaging systems can be useful for guiding needle insertion to the most aggressive part of a tumor during a biopsy, and for mapping circulation and neural networks during surgery. On the other hand, hand-held transducers have significant limitations related to their small size and thus the small acoustic aperture of the ultrasound transducer array: (i) providing an incomplete data set, making it theoretically impossible to display true brightness/contrast using reconstruction tomography ; (ii) poor resolution in the lateral direction in the image plane, (iii) poor rejection of signals out of the image plane, especially those containing low ultrasonic frequencies emitted by large objects. The reverse mode of optoacoustic imaging using laser irradiation and ultrasound detection within the same sensor on the same side of the skin introduces complex requirements for the design of the sensor housing for hypoechoic lesions, notch filters for scattered laser radiation illuminating the acoustic lens and suppressing ultrasonic converters. This creates signal artifacts and non-zero signal slope, which makes it very difficult to distinguish the corresponding signals from the background. The proposed design of the hand-held sensor solved the problems of imaging in reverse mode (8). With improved transducer design and ultra-wideband ultrasound transducers, the optoacoustic system can achieve higher volumetric contrast of breast tumors and greater imaging depth, which in turn has made the system clinically useful (3). However, a 2D system based on a hand held transducer cannot be used for breast screening due to excessive time and operator dependency. Thus, a 3D automatic system that provides full visibility should be used for screening in conjunction with a 2D system that serves to image the lymph nodes surrounding the breast and potentially drain cancer cells from the underlying breast tumor.

Improvements in the LOUISA system

[0059] All of the aforementioned limitations have been relaxed or compensated for in the LOUISA 3D full view tomography system. In the LOUISA system, the laser irradiation is separated from the transducer array, and the optoacoustic sensor is separated from the ultrasonic sensor.

Quantitative tomography system

3D opto-acoustic system for full visibility

[0060] Many of the limitations of a 2D limited view optoacoustic imaging system can be avoided in a 3D full view system. Previously, the benefits of full-view 3D optoacoustic tomography were demonstrated in the development of the Laser Optoacoustic Imaging System (LOIS-3D) for preclinical studies in mice. The LOIS-3D system uses an arc-shaped array of 96 UWB ultrasonic transducers and rotates the subject 360 degrees, creating a sphere with 96×360=34560 virtual detectors (24). The LOIS-3D system design has been scaled up and enhanced with a number of advanced design features, resulting in the present LOUISA system design. These enhancements include a new hemispherical imaging module, a chest-rotating array of amplified ultra-wideband ultrasound transducers sensitive to a frequency range of approximately 50 kHz to approximately 6 MHz, an arcuate fiber-optic irradiation vane that rotates independently around the chest, and a new dual-wavelength pulsed an alexandrite laser with two alternating wavelengths of approximately 757±2 nm and approximately 797±2 nm. The basic principles of operation of the optoacoustic tomography subsystem, providing full visibility, the design of the imaging module and a photograph of the system are shown in F. 1A-1D.

[0061] The imaging module of the breast scanning system, LOUISA, like the previously clinically studied LOIS-3D system, contains an array of 96 ultra-wideband (from 50 kHz to 6 MHz) ultrasound transducers, while the array has a 90 degree arc shape. The noise equivalent pressure (NEP) of approximately 1.5 Pa of these transducers enables high sensitivity deep tissue imaging. The increased spatial resolution of approximately 0.3 mm for this system is due to three factors, namely: (i) a high cutoff frequency of 6 MHz, (m) a three-dimensional representation of the hemispherical shape of the breast using an optically transparent sound-transmitting thin plastic stabilizer in the form of a bowl and (ii) irradiating the entire chest and combining all optoacoustic signals for each of the 320 rotational positions of the sensor. The alexandrite laser (Light Age, Somerset, NJ, USA) used in the system emits pulses of 50 nm at two alternating wavelengths of 757 nm and 797 nm, separated by a time delay of 50 ms or 100 ms, which ensures accurate alignment of two optoacoustic images and calculation of functional images of total hemoglobin and blood oxygen saturation (25). The pulsed laser radiation energy available from this laser is up to 800 mJ, which makes it possible to achieve an optimal (safe) optical energy density of F~20 mJ/cm ² for breast irradiation with a total beam area of 40 cm ² . Therefore, up to 10 stages are required to irradiate the entire large breast with a surface area of approximately 400 cm ² (corresponding to a hemisphere with a radius of 8 cm). Considering two wavelengths and a setting of 10 exposure steps per wavelength for full breast exposure per transducer step, the theoretical minimum time to scan at two wavelengths alternately at 10 Hz is: 320×10×2×0.1 s \u003d 640 s ~ 10.6 minutes per chest. Improvements are currently being tested to speed up clinical scanning by increasing the pulse rate to 20 Hz, increasing the number of fiber optic blades to 2, and thus reducing the number of exposure steps to 5, resulting in a reduction in scan time to approximately 2.5 minutes. .

Rotational scan versus translational scan

[0062] A full view tomography system may be configured to perform rotational scanning and reconstruct images in spherical coordinates (FIGS. 1A-1D) or, alternatively, it may be configured to perform translational scanning and reconstruct images in cylindrical coordinate system (FIG. 2A-2B). The advantage of a rotational scanning system is that it can obtain a true 3D volumetric image with a spatial 3D resolution equal in all three directions of the Cartesian coordinate system (x, y, z).

[0063] The advantage of the translational scanning system is that it uses a full ring of transducers and can acquire and reconstruct 2D images of circular slices at video frequency (10-40 Hz), i.e. in real time with physiological events. The translational scanning system has excellent resolution in a circular 2D (x-y) slice, but the resolution in the vertical (along the z-axis) direction, which can be obtained by superimposing 2D slices in a cylindrical volume, is approximately 2-5 times worse than with what can be obtained in two-dimensional circular slices.

Ultra wideband ultrasonic transducers

[0064] Standard medical ultrasound transducers can only detect in a relatively narrow frequency range and generate electrical reverberations in response to a pulse emitted by biological tissues irradiated with a short laser pulse. This means that the detected optoacoustic signal can be significantly distorted by commercial ultrasonic detectors, which in turn limits the contrast and resolution of optoacoustic images. More importantly, self-pressure profiles generated in tissue by short laser pulses can be severely distorted by standard transducers, impairing the ability of an optoacoustic imaging system to reproduce the true brightness of image voxels and thus blocking the ability of functional imaging. Particular efforts have been made in the development of ultrawide-band ultrasonic transducers (UBT) for optoacoustic tomography systems.

[0065] The distribution of absorbed optical energy is used to visualize and quantify various tissue structures and their physiological functions based on changes in the optical properties of tissues. To associate tissue structure with optoacoustic images, acoustic detectors must be able to recognize not only fast changes in optoacoustic signals associated with sharp edges and boundaries in tissues, but also to reproduce slow changes associated with smooth changes in optical properties within a tissue of the same type. In other words, acoustic detectors must be able to detect both high and low ultrasonic frequencies of acoustic pressure signals. These types of acoustic detectors are called ultrawideband acoustic transducers. The best ultra-wideband acoustic transducers have relatively uniform detection sensitivity over the entire ultrasonic range from 20 kHz to 20 MHz, but practical and clinically useful ultra-wideband acoustic transducers for deep tissue imaging have a bandwidth of about 50 kHz to about 10 MHz. The ultrasonic detection bandwidth of acoustic transducers determines the limits of axial resolution. The lateral resolution of optoacoustic tomography (OAT), on the other hand, is given by the dimensions of each acoustic transducer, the pitch between two adjacent transducers in an array (or the distance between two measurement points in scan mode), the overall aperture, and the geometry of the transducer array (measurement surface) . To obtain an accurate tomographic image, the object of interest must be surrounded by transducers (FIG. 3) so that all detector positions form a closed surface. Otherwise, the reconstruction will be performed using an incomplete set of measurement data that is not quantitatively accurate. Complete time-resolved optoacoustic datasets can be obtained using either 2D transducer arrays, 1D scans of a linear array of transducers, or 2D scans of a single transducer.

[0066] Polyvinylidene difluoride (PVDF) copolymers have previously been used to develop ultra-wideband ultrasound transducers and arrays of these transducers have been used for imaging in breast cancer diagnosis (5). However, due to the low electrical capacitance of the PVDF transducers, they could not be made small enough, which limited the spatial resolution in early prototypes of the breast imaging system. In recent years, advances in piezoelectric materials such as composite material, single crystal piezoelectric ceramics PMN-PT or single crystal piezoelectric ceramics PZT embedded in a polymer matrix, or micromachined piezoelectric ultrasonic transducers have made it possible to fabricate linear and two-dimensional arrays of ultra-wideband acoustic transducers with high electrical capacitance (approximately 100 pF) and small size (approximately 1 mm ² ). These piezocomposite transducers are both sensitive in the high ultrasonic frequency range to provide high resolution imaging and in the low ultrasonic frequency range to provide high contrast for optoacoustic imaging of large objects such as large blood vessels and tumors. While standard commercial transducers can only visualize the edges of large objects in the chest, ultra-wideband acoustic transducers can visualize the volumetric brightness of large objects with a quantitatively accurate representation of their brightness, resulting in accurate functional images.

Sensitivity and imaging depth

[0067] The acoustic-electrical and spatial impulse responses of the ultrasonic transducers used in the LOUISA system were measured using a previously developed Delta laser ultrasound source (26). Also, measurements of optoacoustic signals detected from well-characterized phantoms having spherical inclusions with a known optical absorption coefficient have shown an equivalent noise pressure of approximately 1.3 Pa and a transducer sensitivity that gives an electrical voltage increase of 16 pV/Pa for the equivalent noise pressure. With an analog gain of 70 dB, the amplitude of the noise becomes 47 mV recorded by the analog-to-digital converters (ADCs), which is significantly averaged due to the addition of signals from 30,720 converters to each image voxel. With this sensitivity, the LOUISA system can detect relatively large (approximately 1 cm) blood containing objects, such as tumors, with a typical optical absorption coefficient of 1/cm, exposed to an effective optical energy density of 0.01 mJ/cm ² . Such an effective optical energy density can be achieved at a depth of Z~50 mm with a safe incident laser energy density (27) of 20 mJ/cm ² and an effective attenuation of optical radiation in the chest of approximately exp(-115Z) (28).

Examples of the ultrasonic subsystem

[0068] B-mode ultrasound is used to visualize and define morphological tissue structures.

Rotary scanning system

[0069] The ultrasound subsystem for rotational scanning is based on a 90-degree arc-shaped array of ultrasound transducers with a radius of 80 mm optimized for B-mode breast ultrasound. An array of 192 transducers with a center frequency of 7 MHz and a wide bandwidth of ±3.5 MHz. The ultrasound subsystem provides two-dimensional sections of the breast structure, which can be easily superimposed on corresponding optoacoustic sections selected from three-dimensional functional images.

Progressive scanning system

[0070] The ultrasound subsystem for translational scanning is based on either a 180 degree arc-shaped ultrasound transducer array or a 360-degree full ring ultrasound transducer array with a radius of 80 mm optimized for B-mode breast ultrasound. An array of 256 (half ring) or 512 (full ring) ultrasonic transducers centered at 5 to 10 MHz with a bandwidth of ±3.5 MHz. The ultrasound subsystem provides two-dimensional sections of the breast structure, which can be easily superimposed on the corresponding optoacoustic sections. The transducer ring is translated into a stack of 2D images including 3D ultrasound images.

EXAMPLE 1

Verification of functional imaging in phantoms

[0071] The most important improvement of this latest system design over previously known systems is the whole breast exposure performed for each stage of rotation of the optoacoustic transducer array using a fiber optic feed rotating around the chest independently of the rotation of the detector sensor. This paper presents the results of a pilot study of one healthy volunteer and a patient with a suspicious small chest lesion. The deoxygenated veins and oxygenated arteries of a healthy volunteer visualized using the LOUISA system demonstrate its ability to visualize hypoxic microvessels in cancerous tumors. The small lesion found on the optoacoustic image of the patient was not visible on ultrasound, potentially indicating a high systemic sensitivity of the optoacoustic subsystem to small but aggressively growing cancerous lesions with a high angiogenesis density of the microvessel network. At a safe level of optical energy density in the near infrared region, the network of the main vessels of the chest (0.5-1 mm) can be seen at a depth of up to 50 mm with a resolution of 0.3 mm. The results of a pilot clinical test of the LOUISA system, demonstrating the readiness of the system for a statistically significant clinical study of its feasibility.

[0072] By changing two wavelengths of laser irradiation in one incremental revolution, it is possible to physically match images obtained at these wavelengths with an accuracy better than 1 voxel (0.2 mm). The distinction between arteries and veins on optoacoustic images, as well as the distinction between malignant lesions with hypoxia and normally oxygenated benign lesions, provides valuable functional information for radiologists in addition to publicly available breast morphology. The ability of the LOUISA system to visualize arteries and veins, cancerous and benign tumors has been experimentally tested using realistic phantoms of breast tissue made of PVC-plastisol, TiO ₂ powder for optical scattering, and plastic dyes for optical absorption (29).

[0073] FIG. 4A-4B show a chest phantom photograph and a functional image of blood oxygen saturation, where red was set for blood oxygen saturation of more than 80% and blue was set for blood oxygen saturation of less than 75%. The range from 75% to 80% has been given zero (black) brightness. The optical properties of six embedded objects were chosen to represent realistic vasculature and tumors: (1) artery (red) with 100% oxygen saturation, (2) vein (blue) with approximately 70% oxygen saturation of benign tumors (red) with blood oxygen saturation of approximately 95% and blood oxygen saturation of approximately 85%, aggressive malignant tumor with blood oxygen saturation of approximately 65%, and mixed non-aggressive tumor with blood oxygen saturation of approximately 80%.

[0074] The image in FIG. 4B confirms the sufficient accuracy of the LOUISA3D system in functional imaging, given the chosen optical properties of the objects in this phantom. The artery and vein are clearly visible and correctly stained. Two benign tumors are seen, correctly stained. One malignant deep tumor with hypoxia is clearly visible and correctly stained. The second "mixed" tumor with borderline oxygen saturation is partly invisible and partly stained red.

EXAMPLE 2

Clinical validation of the LOUISA system

[0075] The LOUISA system includes a 3D imaging module and a handheld 2D imaging sensor. Although the LOIS-3D system, the predecessor of the LOUISA system, used a half-period reconstruction algorithm in spherical coordinates (30), it was necessary to use full-period reconstruction for the hemispherical geometry of the 3D image reconstruction in order to maintain an accurate reconstruction solution that provides full visibility for breast imaging (31). This patient was imaged at a single wavelength, 757 nm, so oxygenation of the blood vessels and tumor was not possible. The nature of the relatively small (3.5 mm) tumor seen in two of the three views (FIGS. 6A-6B, not FIG. 6C) has not been conclusively established. FIG. 6A-6C show the sensitivity of the LOUISA system, but not the specificity of discriminating tumors.

[0076] A number of improvements in imaging module design and improvements in signal processing and image reconstruction algorithms have resulted in high-contrast, high resolution breast images showing the breast vasculature in detail. FIG. 7A shows a sagittal plane projection of a volume optoacoustic image of a normal breast at a wavelength of 757 nm. Veins are likely the dominant vessels in this image. FIG. 7B-7C show a frontal plane view of a 3D functional image of blood oxygen saturation, which allowed the separation of veins (blue) with reduced oxygen saturation and arteries (red) with full oxygenation. This functional image was reconstructed using equations 1 and 2 on two combined optoacoustic images taken at 757 nm and 797 nm. The threshold value for the blue/red binary color palette was chosen at a blood oxygen saturation level of 80%. The number of detailed features in the vessels and microvessels visualized in the images presented in FIG. 7A-7C demonstrate the potential readiness of the LOUISA system to perform clinical trials in screening and imaging for the diagnosis of breast cancer.

[0077] FIG. Figure 8 shows an example of overlapping of sections of optoacoustic and ultrasound images taken along the central axis of a hemispherical chest volume obtained from a healthy volunteer. This type of image, which provides information regarding the distribution of the vascular network, will be most valuable to the radiologist in the presence of a tumor, since the density of the vascular network and microvascular network and their geometry in the vicinity of the tumor provides diagnostic information. Similarly, functional images of blood oxygen saturation and total hemoglobin can provide discrimination between benign and malignant tumors with particularly high specificity when it comes to tumor and adjacent tissue morphology from a superimposed ultrasound image.

EXAMPLE 3

The LOUISA-3D system for breast cancer management as an example of a quantitative tomography system

[0078] Full view optoacoustic tomography based on a laser optoacoustic ultrasound system assembly for 3D imaging combined with ultrasound tomography has been developed for use in screening and imaging for the diagnosis of breast cancer. The system was tested on one patient with a tumor in the breast with suspected cancer and on one normal volunteer as a control subject or a healthy control patient. The performance of the LOUISA system during validation showed a number of technical improvements that make this combined functional and anatomical imaging system a potentially viable solution to unmet needs in breast cancer management.

[0079] The following features of the LOUISA system have been found to be important for clinical effect: (i) ultra-wideband ultrasound transducers sensitive in the frequency range of 50 kHz to 6 MHz; (ii) ultra-low noise transducers and electronics with an equivalent noise pressure of approximately 1.3 Pa and a sensitivity of S~0.012 mV/Pa; (iii) irradiating the entire chest/acquisition of data providing partial visibility, which allowed for an accurate reconstruction in spherical coordinates; (iv) applying the inverse function of effective optical attenuation to provide depth independent of image brightness. The LOUISA system offers hybrid imaging with sufficient tumor and blood vessel contrast and adequate resolution of 0.3 mm to 0.5 mm in all three dimensions (depending on breast size). Rapid switching between 757 nm and 850 nm near-infrared pulses allows functional imaging of the vascular network, although clinical discrimination between normally oxygenated and hypoxic tissues may require changing from 850 nm to 1064 nm. The scan duration is approximately 10 minutes with "single pulse" exposure in 20 steps at each wavelength, producing 320 angled images of an array of 96 transducers in an 80° arc. The image reconstruction time is approximately 4 minutes for over 100 million voxels and 1,536 data samples from each of 30,720 virtual transducers.

[0080] A combined 3D optoacoustic and ultrasound imaging system with spatial alignment of functional and anatomical information demonstrates clinically sufficient accuracy of quantitative information. The LOUISA system provides automatic examination and screening of the entire breast, regardless of the experience of the operator. Clinical applications in the screening and diagnostic differentiation of breast cancer are expected to be useful as a substitute for costly, sensitive, but non-specific MRI, especially for young women's dense and heterogeneous breasts.

The following are references to sources cited in this document.

1. Folkman, J., New Engl. J. Med., 333:1757-1763, 1995.

2 Savateeva et al., Proc. SPIE, 4618:63-75, 2002.

3. Neuschler et al., Radiology, 285:xxx, 2017.

4. Gartlehner et al., Int J Evid Based Healthc., 11(2):87-93, 2013.

5. Ermilov et al., J Biomed Opt. 14(2):024007(1-14), 2009.

6. Heijblom et al., Eur Radiol. DOI 10.1007/s00330-016-4240-7dd

7. Kruger et al., Med Phys., 40(11):1 13301, 2013.

8. Zalev et al., Proc. SPIE, 2013; 8581, 858103.

9. Fakhrejahani et al., PLoS One 2015; 10(10):e01391 13, 2015.

10. Toil et al., Scientific Reports, 7:41970, 2017.

11. Dean-Ben et al., J. Biophotonics 9(3):253-259, 2016.

12. Diot et al., Clin Cancer Res., 23(22):6912-6922, 2017.

13. Oraevsky, A.A., Optoacoustic Tomography: From Fundamentals to Diagnostic Imaging of Breast Cancer", in Biomedical Photonics Handbook, Second Edition: Fundamentals, Devices, and Techniques, ed. by T. Vo-Dinh, CRC Press, Boca Raton, Florida , 2014, vol.PM222, Ch.21, pp.715-757.

14. Oeffinger et al., JAMA, 314(15):1599-1614 2015.

15. Gartlehner et al., Int J Evid Based Healthc. 11(2):87-93, 2013.

16. Burkett et al., Acad. Radiol. 23(12):1604-1609, 2016.

17. Oraevsky et al., Proc. SPIE, 3597: 352-363, 1999.

18. Liu et al., Phys. Med. Biol., 40:1983-1993, 1995.

19. Wang et al., Nature Biotech., 21(7):803-806, 2003.

20. Dean-Ben et al., J Vis Exp. 2014; 4(93):e51864, 2014.

21. Zhu et al., Radiology; 256(2), 367-378 (2010).

22. Emelianov et al., Proc. SPIE, 5320:101-112, 2004.

23 Niederhauser et al., IEEE Trans. Med. Imaging, 24(4):436-440, 2005.

24. Brecht et al., J. Biomed. Optics, 14(6):0129061-8, 2009.

25. Klosner et al., Proc. SPIE, 9708:97085 B, 2016.

26. Conjusteau et al., Rev. sci. Inst., 80:093708(1-5), 2009.

27. American National Standard for Safe Use of Lasers, ANSI Z136.1-2014. Publication by American Laser Institute, New York, NY.

28. Taroni et al., Sci Rep. 7:40683, 2017.

29. Spirou et al., Phys. Med. Biol., 50:141-153, 2005.

30. Pan et al., IEEE Transactions on Image Processing, 12:784-795, 2003.

31. Wang et al., Phys Med Biol., 57(17):5399-5423, 2012.

Claims (81)

1. A quantitative tomography system, comprising: - a laser configured to emit instantaneous pulses of laser radiation with wavelengths in the spectral range from the red to the near infrared region of the spectrum, and said laser is configured to operate in the mode of changing wavelengths; - a fiber optic bundle configured to deliver instantaneous pulses of laser radiation to the entire tissue area of interest with maximum transmission; - an imaging module comprising: an imaging container having a shape corresponding to the area of interest of the tissue; at least one ultra-wideband ultrasonic transducer optoacoustic array configured to detect ultrasonic signals within a ultra-wide band of ultrasonic frequencies generated in a tissue region of interest by instantaneous pulses of laser radiation; at least one ultrasonic array of ultrasonic transducers, configured to transmit ultrasonic pulses to said tissue region and detect ultrasonic signals reflected from said tissue region and transmitted through said tissue region; and a bonding medium that fills the imaging container and through which instantaneous laser pulses and ultrasound pulses are transmitted; - a multi-channel electronic data acquisition system containing analog preamplifiers, analog-to-digital converters and boards for digital data storage, processing and transmission, while said data acquisition system is microprocessor-controlled with a user-programmable gate array; - a computer in electronic communication with a multi-channel electronic data acquisition system and containing a multi-core central processing unit (CPU) and a multi-core graphic processing unit (GPU), and software stored in tangible means, configured to control said CPU and GPU processors, to control the system, signal processing, image reconstruction and image alignment; wherein said software is capable of executing processor-executable instructions configured to: a. restoring the original profiles of the optoacoustic signal generated in the specified region of the tissue by instantaneous laser pulses, using the deconvolution of the acoustic-electrical and spatial impulse response functions of the ultra-wideband ultrasonic transducer from the detected optoacoustic signals; b. reconstruction of three-dimensional images of optoacoustic tomography of the specified area of tissue by means of rigorous direct algorithms using a complete set of data obtained with a geometry that provides full visibility; c. increasing image accuracy through iterative algorithms; d. normalizing the distribution of the incident optical energy density on the surface of the specified tissue area by equalizing the brightness of the image of all surface voxels; e. normalizing the distribution of the incident optical energy density over the entire area of the tissue by compensation for effective attenuation of the optical radiation; f. displaying images of the optical absorption coefficient after normalization of the incident optical energy density through the specified tissue area on optoacoustic images of optical energy absorbed in the specified tissue area; g. obtaining combined optoacoustic images obtained at two alternating laser wavelengths with obtaining quantitative functional images; h. obtaining combined optoacoustic images obtained at three alternating laser wavelengths with obtaining quantitative functional images and i. obtaining images of the distribution of the speed of sound within the specified region of the tissue, which are used to improve the contrast and resolution of the combined optoacoustic images and images of the reflection and attenuation of ultrasound; and a high resolution display electronically connected to a computer for presenting the reconstructed image to the operator of the quantitative tomography system. 2. The system of claim. 1, in which the spectral wavelength range from red to near infrared spectral region is from about 650 nm to about 1250 nm. 3. The system of claim. 2, in which the change in wavelength mode has two wavelengths in the spectral range from the red to the near infrared region of the spectrum. 4. The system of claim 3, wherein the two alternating wavelengths are 757 nm and 850 nm. 5. The system of claim. 2, in which the change in wavelength mode has three wavelengths in the spectral range from the red to the near infrared region of the spectrum. 6. The system of claim 5, wherein the three alternating wavelengths are 757 nm, 800 nm, and 850 nm. 7. The system of claim 5, wherein the three alternating wavelengths are 757 nm, 800 nm, and 1064 nm. 8. The system of claim 1, wherein the ultra-wideband ultrasonic transducers in the array are configured to detect ultrasonic signals within an ultra-wide band of 50 kHz to 6 MHz. 9. The system of claim. 1, in which the optoacoustic array of ultra-wideband ultrasonic transducers and the ultrasonic array of ultrasonic transducers are combined into one array. 10. The system of claim. 1, wherein the imaging container in the imaging module has the shape of a spherical surface. 11. The system of claim 1, wherein the imaging container in the imaging module is cylindrical. 12. The system of claim 1, wherein the tissue region of interest is a breast tissue region. 13. A method for imaging quantitative functional parameters in a tissue area of interest in a subject, comprising the following steps: placing said area of tissue in a container for imaging the quantitative tomography system of claim 1; positioning the optoacoustic array of ultra-wideband ultrasonic transducers and the ultrasonic array of ultrasonic transducers inside the imaging container; selection of wavelengths of laser radiation in the spectral range from red to near infrared region of the spectrum for delivery as instantaneous pulses to the specified area of the tissue in the mode of changing wavelengths; delivery to the specified volume of tissue changing instantaneous pulses of laser radiation with a selected wavelength; detecting with an optoacoustic array, for each selected wavelength, signals within an ultra-wide band of ultrasonic frequencies generated within a specified tissue area; obtaining optoacoustic images from the detected signals for each selected wavelength; combination of optoacoustic images; generation of images of quantitative functional parameters from combined optoacoustic images and display of generated quantitative images. 14. The method of claim 13, wherein the signals generated at each selected wavelength are detected simultaneously. 15. The method according to claim 13, wherein the quantitative functional parameter is blood oxygen saturation. 16. The method of claim 13, wherein the quantitative functional parameter is total hemoglobin and blood oxygen saturation. 17. Laser Optoacoustic Ultrasonic Imaging System Assembly (LOUISA) for imaging a tissue volume in a subject, comprising: a laser configured to emit instantaneous pulses of laser radiation with wavelengths in the spectral range from the red to the near infrared region of the spectrum, and said laser is configured to operate in a mode of changing wavelengths in the specified spectral range; arcuate fiber-optic bundle, made with the possibility of rotation around the volume of tissue to deliver instantaneous pulses of laser radiation; an imaging container having a surface shape corresponding to the tissue volume; an arcuate array containing a combination of an optoacoustic array of ultra-wideband ultrasonic transducers and an ultrasonic array of ultrasonic transducers operating in transmit and receive modes, and is configured to detect ultrasonic signals within an ultra-wide band of 50 kHz to 6 MHz generated in the tissue volume and transmit pulses of ultrasound into the tissue volume and detecting ultrasound signals reflected from the tissue volume and transmitted through the tissue volume, said signals being processed and superimposed as functional images within the anatomical structures of the tissue volume; an optically transparent and sound-transmitting binding medium which fills the imaging container and through which instantaneous laser pulses and ultrasound pulses are transmitted; and electronic subsystem containing: a multi-channel electronic data acquisition system containing analog pre-amplifiers, analog-to-digital converters and boards for digital data storage, processing and transmission, while said data acquisition system is microprocessor-controlled with a user-programmable gate array; a computer in electronic communication with a multi-channel electronic data acquisition system and containing a multi-core central processing unit (CPU) and a multi-core graphics processing unit (GPU), and software stored in tangible means, configured to control said CPU and GPU processors, to control the system, process signals, image reconstruction and image alignment; and a high resolution display electronically connected to a computer for presenting the reconstructed breast image to the operator of the LOUISA system. 18. The LOUISA system of claim 17, wherein the red to near infrared spectral wavelength range is from about 650 nm to about 1250 nm. 19. The LOUISA system of claim 18, wherein the wavelength changing mode has two changing wavelengths in the red to near infrared spectral range. 20. The LOUISA system of claim 19, wherein the two alternating wavelengths are 757 nm and 850 nm. 21. The LOUISA system of claim 18 wherein the wavelength changing mode has three changing wavelengths in the red to near infrared spectral range. 22. The LOUISA system of claim 21, wherein the three alternating wavelengths are 757 nm, 800 nm, and 850 nm. 23. The LOUISA system of claim 22, wherein the three alternating wavelengths are 757 nm, 800 nm, and 1064 nm. 24. The LOUISA system of claim 17, wherein the arcuate fiber bundle and the arcuate array are configured to independently rotate around a tissue volume to fully irradiate it for each position of the arcuate array. 25. A method for forming an image of quantitative functional parameters in a tissue volume in a subject, including the following steps: placing said volume of tissue in the LOUISA imaging container of claim 17; selection of wavelengths of laser radiation in the spectral range from red to near infrared region of the spectrum for delivery as instantaneous pulses to the specified volume of tissue in the mode of changing wavelengths; delivery to the specified volume of tissue changing instantaneous pulses of laser radiation with selected wavelengths; transmission to the specified amount of tissue pulses of ultrasound from the arcuate array; detection using an arcuate array for each selected wavelength of signals within an ultra-wide band of ultrasonic frequencies generated within a specified volume of tissue; detecting ultrasonic signals reflected from said tissue volume and transmitted through said tissue volume; generating images of quantitative functional parameters from the signals detected within the ultra-wide band of ultrasonic frequencies; generating anatomical images from the detected ultrasound signals; generating images at the speed of sound based on the distribution of the speed of sound within the specified volume of tissue; improvement of images of quantitative functional parameters and anatomical images by means of sound speed images; combination of images of quantitative functional parameters within anatomical structures and display of combined images as an overlay of images of quantitative functional parameters with anatomical images. 26. The method of claim 25, further comprising: diagnosing cancer based on quantitative functional parameters and anatomical structures displayed on said overlay. 27. The method of claim 25 wherein the cancer is breast cancer. 28. The method of claim 25, wherein the signals generated at each selected wavelength are detected simultaneously. 29. The method of claim 25, wherein the quantitative functional parameter is blood oxygen saturation. 30. The method of claim 25, wherein the quantitative functional parameter is total hemoglobin and blood oxygen saturation.

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