RU215019U1 - Optically transparent sensor for optical resolution optoacoustic microscopy - Google Patents

Abstract

The utility model relates to the field of optoacoustics, namely optical resolution optoacoustic microscopy (OAM-OR). An optically transparent sensor of ultrasonic signals for optoacoustic microscopy contains a housing with a light-transmitting receiving element made of a piezofilm fixed in it, through which a focused laser beam passes to the object under study. The receiving element is connected to a broadband amplifier, which is a two-stage amplifier. Between the first stage, which provides a high input impedance in a wide frequency band, and the second stage, which provides uniform signal amplification in the same band, a filter is installed that suppresses the low-frequency part of the input signal spectrum. The technical result consists in increasing the sensitivity of the optically transparent sensor. 5 ill.

Description

The utility model relates to the field of optoacoustics, namely optical resolution optoacoustic microscopy (OAM-OR). OAM-OR makes it possible to obtain high-contrast images of the smallest vessels of biological tissues - capillaries. The depth of images in such systems is usually limited to 1 mm, and the resolution can reach less than 1 µm. When visualizing blood vessels, tissues are probed with focused laser pulses, as a result of which ultrasonic waves appear in the medium under study, which are recorded by a piezoelectric transducer. A three-dimensional image is obtained by scanning an object with an optical beam or the entire optical focusing system together with a sensor.

The invention described in patent KR 101749602 "Optical resolution photoacoustic microscopy using non-conductive fluid, and photoacoustic image acquisition system and method using the same" (publ. 06/21/2017, IPC G01N 21/17, G01N 29/06, G01N 29/24, G02B 7/30), refers to a photoacoustic microscope and contains an external source of laser radiation, an ultrasonic transducer, an optical-acoustic unit that reflects laser radiation and transmits a photoacoustic signal generated from an object in the direction of the ultrasonic transducer.

In the patent US 9226666 "Confocaloscopy photoacoustic micr with optical lateral resolution" (publ. 01/05/2016, IPC A61B 5/00, A61B 8/00, G01N 21/17, G01N 29/06, G01N 29/24, G02B 21 /00, A61B 8/08) proposed a method for determining the absorption coefficient of hemoglobin using a device based on the reception of a photoacoustic signal emitted by an object in response to at least one light pulse.

JP 5885600 "Photoacoustic microscopes" (publ. Jan. 09, 2014, IPC G01B 11/00, G01B 11/24, G02B 21/00) describes a photoacoustic microscope capable of performing high-speed scanning, obtaining an image of a photoacoustic wave with high measurement accuracy in short time and easy to respond to changes in observation depth.

In the configurations of the above systems, either optical-acoustic combiners are used to separate the optical beam and the acoustic wave using standard ultrasonic sensors, or special configurations of the sensors themselves, allowing light to pass through the central hole or around the periphery. However, the use of a large number of optical and acoustic elements in combined systems can lead to undesirable distortions, both in the formation of an optical beam and in the reception of an ultrasonic wave. The use of ring-shaped ultrasonic detectors with a remote central part weakens the acoustic sensitivity and the signal-to-noise ratio.

The closest to the claimed device is a sensor for optoacoustic microscopy, described in the article "A focused optically transparent PVDF transducer for photoacoustic microscopy" (C. Fang, H. Hu, J. Zou, IEEE Sens. J. 20, 2313, 2020. ). It discusses the design of a transparent sensor. A transparent PVDF transducer in the form of a thin film covered with electrodes is placed on a concave glass lens. The transparent PVDF transducer, which is the receiving element, has a high (>80%) optical transmission in the wavelength range of 250-900 nm. The resulting ultrasonic pulses were received by the transducer and amplified by an amplifier built into the generator-receiver. The main disadvantage of the sensor presented in the article, according to the authors, is that the developed transducer has a low sensitivity associated with the design of the device. One of the reasons, as stated in the paper itself, is the electrical impedance mismatch between the sensor and the amplifier. To obtain clear and contrasting images, the authors of the prototype carried out 16-fold averaging of the signal, which indicates a rather large NEP value of the sensor. When comparing the sensitivity of different sensors, the NEP value is often used, which characterizes the noise level expressed in units of pressure. This value is defined as the ratio of the noise standard deviation to the average sensitivity value.

The objective of the proposed utility model is to develop an optically transparent sensor for optoacoustic microscopy, which has a high sensitivity, the average value of which is not less than 1 μV/Pa in the entire operating frequency band.

The technical result is achieved due to the fact that the developed device, as well as the prototype device, contains a housing with a light-transmitting receiving element made of piezofilm fixed in it, through which a focused laser beam passes to the object under study, while the receiving element is connected to a broadband amplifier. What is new is that the broadband amplifier is a two-stage amplifier, while between the first stage, which provides a high input impedance in a wide frequency band, and the second stage, which provides uniform signal amplification in the same band, a filter is installed that suppresses the low-frequency part of the input signal spectrum.

The developed utility model is illustrated by the following figures.

In FIG. 1 schematically shows the developed optically transparent sensor of ultrasonic signals: a) a light-transmitting receiving element, b) a sensor mounted on a lens.

In FIG. 2 shows a photograph of the developed optically transparent sensor of ultrasonic signals.

In FIG. Figure 3 shows a block diagram of the setup for optoacoustic microscopy of optical resolution using the developed optically transparent sensor of ultrasonic signals.

In FIG. 4 shows the result of 3D optoacoustic microscopy in the study of the blood vessels of the ear margin of a mouse.

In FIG. 5 shows the result of three-dimensional optoacoustic microscopy: visualization of carbon fibers with a diameter of 7 μm.

In FIG. Figure 1 shows a diagram of the construction of an optically transparent sensor 1 fixed on an objective 2. A light-transmitting receiving element 4 made of a piezofilm is fixed in the body 3 of the sensor 1, through which a focused laser beam passes to the object under study 5 (see Fig. 3). In the housing 3 of the sensor 1 there is a two-stage broadband amplifier 6, which is connected to the electrodes of this receiving element 4.

In a specific implementation, the receiving element 4 of the sensor 1 is a piezopolymer PVDF (polyvinylidene fluoride) film with light-transmitting ITO (indium tin oxide) electrodes, fixed with conductive glue 7 between two plastic washers 8 with a diameter D with an inner diameter d (diameter of the receiving area of the sensor one). In the sample made by the authors, the diameter D was 5 mm, and the inner diameter d was 2.5 mm. The signal from the receiving element 4 goes to a two-stage broadband amplifier 6 with overall dimensions of 13 mm × 7 mm × 2 mm. The first stage of the amplifier 6 provides a high input impedance in a wide frequency band (from 1 to 100 MHz). An RC filter is installed between the amplification stages, which suppresses the low-frequency part of the spectrum (below 1 MHz) of the input signal. The second stage provides directly uniform amplification (K=30) of the received signal also in the entire band up to 100 MHz. The receiving element 4 of the sensor 1, together with the amplifier 6, is hermetically placed in the housing 3, which is made of plastic and printed on a 3D printer (Shuffle, Phrozen, China). The optically transparent sensor 1 is provided with the necessary shielding from external electrical interference, including those created by the metal case of the optical lens 2. From the outside and inside, the body 3 of the sensor 1 is covered with silver ink 9 for shielding from external electrical interference. A protective layer 10 (a thin layer of lacquer) is applied over the silver ink 9 to prevent the destruction of the shielding layer. The developed sensor 1 (see Fig. 3) is fixed on the lens 2, for example, using three screws 11 (see Fig. 3). Also, an additional ground wire extends from the amplifier 6 to the lens 2, the metal case of which can create pickups and an additional noise level on the signal electrode of the piezoelectric film.

In FIG. Figure 3 shows a block diagram of the OAM-OR setup implemented using the developed optically transparent sensor 1. The setup uses a nanosecond solid-state laser (Onda 532, BrightSolutions, Italy) with a wavelength of 532 nm as the probing radiation source 12. The laser beam is controlled by 2-axis scanners 13 Galvo (6215H, Cambridge Technology/USA). After that, the beam is delivered to the objective 2 with a numerical aperture NA=1 (W-Plan Apochrom 20x/1.0 DIC, Zeiss, Germany), which focuses the laser radiation in the object under study 5 (for example, in biological tissues), thereby providing submicron resolution of the obtained images. Ultrasonic signals are recorded by a transparent sensor 1 mounted on the lens 2 itself. Then the signals are digitized by an analog-to-digital converter 14 (ADC) and recorded on a computer 15. coordinate shifts 16, controlled from a computer 15 using motion controllers 17. In the course of research, a thin layer of ultrasonic gel is applied to the object 5 for acoustic communication.

The use of a two-stage amplifier 6 makes it possible to match the impedance of the amplifier 6 with the electrical impedance of the receiving element 4. This ensures the high sensitivity of the developed sensor 1.

Focusing of laser radiation is carried out directly through the sensor 1 mounted on the optical lens 2. This method offers a simpler implementation of OAM-OR systems without the use of additional elements to separate the optical and acoustic paths. The developed sensor 1 allows combination with different lenses 2 and thus easy integration with other imaging techniques using the same optics, such as optical coherence tomography (OCT). At the same time, OAM-OR in combination with an optically transparent sensor 1 of ultrasonic signals makes it possible to obtain in vivo images with submicron resolution and a high signal-to-noise ratio. Examples of such images are shown in Fig. 4 and FIG. 5 obtained by the authors using the developed device.

The authors carried out a number of experiments to assess the sensitivity of the developed optically transparent sensor of ultrasonic signals in the frequency band from 1 to 16 MHz. To calibrate the inventive sensor, resonant emitters were used that overlap this frequency band, and a commercial needle hydrophone NH1000 (Precision Acoustic, UK) with a known sensitivity characteristic for a frequency band from 1 to 16 MHz. The average value of the sensitivity of the claimed device was 2.7 µV/Pa. The pressure noise equivalent NEP was 8.5 Pa at an optically transparent sensor noise level of 22.9 μV in the band from 1 to 100 MHz.

For example, the NEP value of the NH1000 needle hydrophone is 85 Pa. Such a small value of the pressure noise equivalent for the developed sensor makes it possible to register weak signals from the smallest capillaries and carbon fibers with a diameter of 7 μm without any signal averaging.

Claims (1)

An optically transparent sensor of ultrasonic signals for optoacoustic microscopy, comprising a housing with a light-transmitting receiving element made of piezofilm fixed in it, through which a focused laser beam passes to the object under study, while the receiving element is connected to a broadband amplifier, characterized in that the broadband amplifier is a two-stage amplifier , while between the first stage, which provides a high input impedance in a wide frequency band, and the second stage, which provides uniform signal amplification in the same band, a filter is installed that suppresses the low-frequency part of the input signal spectrum.

Images