Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
  • A61B5/0073—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence by tomography, i.e. reconstruction of 3D images from 2D projections
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/0093—Detecting, measuring or recording by applying one single type of energy and measuring its conversion into another type of energy
  • A61B5/0095—Detecting, measuring or recording by applying one single type of energy and measuring its conversion into another type of energy by applying light and detecting acoustic waves, i.e. photoacoustic measurements
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
  • A61B5/026—Measuring blood flow
  • A61B5/0261—Measuring blood flow using optical means, e.g. infrared light
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue
  • A61B5/1455—Measuring characteristics of blood in vivo, e.g. gas concentration or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
  • A61B5/14551—Measuring characteristics of blood in vivo, e.g. gas concentration or pH-value ; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid or cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases

Definitions

• the present invention relates to an apparatus for
• Imaging apparatuses using one of X-rays and ultrasound are used in many fields requiring nondestructive
• diagnosis using ultrasound echo involves an advantage of being noninvasive and thus is used in many situations. It is important to derive biofunctional information within a living body, that is, physiological information, for discovery of a disease site, such as a cancer. But in conventional diagnosis using X-ray or ultrasound echo, only shape information within a living body is derived. Therefore,
• in vivo information is imaged by irradiating a subject with pulsed light generated from a light source and detecting an acoustic wave (typically ultrasound) which is generated from a living body tissue absorbing the energy of the light propagated and which is
• Information related to optical properties inside the subject can be made three-dimensionally visible by detecting a temporal change in acoustic waves received at a plurality of places surrounding the subject, and mathematically analyzing (that is, reconstructing) the derived signals.
• a profile of optical properties such as a profile of light absorption coefficient
• Examples of "the detection of biofunctional information using PAT include measurement of oxygen saturation.
• Oxygen saturation is content of hemoglobin bound to
• oxygen with respect to an amount of total hemoglobin in blood can be measured by detecting oxygen saturation.
• oxygen saturation is an indicator for distinguishing the benignancy/malignancy of a tumor, and therefore is expected as a measure for efficient discovery of a malignant tumor.
• Hemoglobin in a living body includes two states:
• oxygen saturation can be found by performing measurement a plurality of times using pulsed lights having different wavelengths in the near-infrared region, and subjecting calculated light absorption coefficients to comparison operation.
• oxygen saturation as a biofunctional information can also be imaged in addition to a blood vessel image as a shape information of the living body.
• Patent Literature 1 For the problem of the comparison of a plurality of measurements, such a technique as disclosed in Patent Literature 1 has been mentioned.
• a moving vector between images, measured for a particular region in the images, is extracted.
• an adjustment such as zooming, rotation, and shift, of the image is performed based on the vector to correct position displacement (i.e.
• a first problem is that the extraction of a moving
• characteristic structures presumed to be the same place is found out on a plurality of images to be compared, and a moving vector is extracted based on the point or the structure.
• characteristic structures presumed to be the same place is found out on a plurality of images to be compared, and a moving vector is extracted based on the point or the structure.
• a second problem is that it is difficult to completely match all pixels.
• a moving vector is derived only with a representative point, such as a characteristic
• the apparatus in an aspect of the present invention, the apparatus
• an acoustic wave detector for receiving a plurality of acoustic waves generated when a subject is irradiated with a plurality of lights having different wavelengths, and for converting the plurality of acoustic waves to a plurality of signals corresponding to the plurality of lights; and a processing apparatus for deriving
• the processing apparatus includes: a first unit for deriving, from a signal corresponding to light having a first wavelength, first data showing a profile of first absorption coefficient corresponding to the light having the first wavelength, and deriving, from a signal corresponding to light having a second
• second data showing a profile of second absorption coefficient corresponding to the light having the second
• biofunctional information using the first data and the second data, and wherein the second data has lower image spatial resolution than the first data.
• second data showing a profile of second absorption coefficient corresponding to the light having the second wavelength, and having lower image spatial resolution than the first data; and deriving the biofunctional information using the first data and the second data.
• oxygen saturation can be calculated with a minor error even if the position displacement of a subject occurs during measurements.
• Fig. 1 is a schematic diagram illustrating the configuration of an apparatus according to one
• FIG. 2 is a schematic diagram illustrating the flow of the data processing of the apparatus according to one embodiment of the present invention.
• Fig. 3 is a flow chart illustrating the operation of the apparatus according to one embodiment of the present invention.
• Figs. 4A, 4B and 4C are schematic diagrams illustrating the concept of the present invention .
• FIG. 5 is a schematic diagram illustrating the flow of the data processing of the apparatus according to one embodiment of the present invention.
• FIG. 6 is a diagram illustrating oxygen saturation when position displacement does not occur.
• Fig. 7 is a diagram illustrating oxygen saturation when position displacement occurs.
• Fig. 8 is a diagram of oxygen saturation calculated by applying the present invention when position displacement occurs.
• biofunctional information to be measured with the photoacoustic imaging apparatus of the present invention is not limited to oxygen saturation, and the total amount of hemoglobin or the like may also be measured.
• biofunctional information inside a subject can be derived by irradiating the subject with at least two or more lights having different wavelengths to detect the difference between acoustic waves generated within the subject, the biofunctional information acquirement
• photoacoustic imaging apparatus of the present invention can be used for the measurement of any biofunctional information.
• the present invention is not limited to a single
• the present invention is also implemented by the use of a method for implementing functions described in this embodiment, and by processing in which software
• Fig. 1 illustrates a first embodiment of the
• An photoacoustic imaging apparatus in this embodiment includes a light source 1 which irradiates a subject 3 with light 2 having a single wavelength, optical devices 4, such as lenses, which guides, the light 2 ' from the light source 1 to the subject 3, an acoustic detector 7 which detects an acoustic wave 6 generated when an optical absorber 5 absorbs the energy of the light propagated and diffused inside the subject 3, and converts the acoustic wave 6 to an electrical signal, a controlling apparatus 8 which allows the acoustic detector 7 to scan, an electrical signal processing circuit 9 which performs the amplification, digital conversion, and the like of the electrical signal, an apparatus 10 for data processing which constructs an image regarding in vivo information (generates image data) , an apparatus 11 for inputting misplacement amount which inputs the position displacement amount of the subject, and a display 12 which displays the image.
• the light source 1 which irradiates a subject 3 with light 2 having a single wavelength
• optical devices 4 such as lenses, which guides,
• the light 2 having a wavelength A (first wavelength) is pulsed, and the subject is irradiated with the pulsed light 2 (SI) .
• SI pulsed light 2
• the temperature of the absorber increases due to the absorption of the pulsed light.
• a volume expansion of the absorber occurs due to the temperature increase, and thus, an acoustic wave 6 is excited from the optical absorber 5.
• the generated acoustic wave 6 is received by an acoustic detector 7 acoustically coupled to the subject, and is converted to an electrical signal (S2).
• An acoustic wave detector may be
• acoustically coupled to the subject and a shape retention member, such as a compression plate which constantly keeps the shape of the subject, may be provided between the subject and the acoustic wave detector.
• the acoustic detector 7 can be controlled by the controlling apparatus 8, and can measure the acoustic wave 6 in various places, while mechanically moving on a surface of the subject. More than two acoustic detectors may be simultaneously used in detecting an acoustic wave generated in a single irradiation.
• the detected electrical 1 signal is
• the electrical signal processing circuit 9 such as an amplifier and an analog-to-digital converter, and then reconstructed for profile A of absorption coefficient (profile of first absorption coefficient) of light having the wavelength A within the subject at a site of the subject
• the apparatus 10 for data processing such as a PC (S3).
• the above operations are also performed for a case where light having a wavelength B (second wavelength) is used, to derive profile B of absorption coefficient (profile of second absorption coefficient) of the wavelength B within the subject at the site of the subject irradiated with the light (S4 to S6) . Further, as described later,
• Profiles C, D, and so on of absorption coefficients may also be calculated using more lights having different
• Fig. 2 and Fig. 3 show the internal processing of the apparatus 10 for data processing for carrying out the present invention.
• the apparatus for data processing 10 includes a unit 109 (first unit) for deriving an absorption coefficient, a unit 106 for calculating oxygen saturation as a unit for deriving biofunctional information (second unit) , and a unit 107 (sixth unit/ tenth unit) for composing.
• the unit 109 includes a unit 101 for calculating the absorption coefficient
• the unit 104 reduces image spatial resolution, by the determined amount for changing resolution, in at least one data among the data showing the profiles of absorption coefficient stored in the memories, to thereby derive a profile of absorption coefficient after the reduction (S8).
• the data to which the image spatial resolution is reduced is reduced
• (second data) is used in calculating information on the subject such as oxygen saturation.
• Image spatial resolution in this invention is resolution in an image space, rather than resolution determined by the size of the element of the acoustic detector 7.
• spatial resolution in three-dimensional image data is referred to as voxel spatial resolution
• spatial resolution in two-dimensional image data is referred to as pixel spatial resolution.
• voxel spatial resolution is referred to as voxel spatial resolution
• profile B of absorption coefficient (the profile of absorption coefficient that can be calculated in the irradiation with the light having the wavelength B) stored in the memory B103 is reduced.
• image spatial resolution of any of the data among the plurality of profiles of absorption coefficient may be reduced.
• more than two profiles of absorption coefficient may also be reduced.
• the image of the optical absorber in the data showing the profile A of absorption coefficient is included in the image of the optical absorber in the data showing the profile ' B of absorption coefficient of which the resolution is reduced.
• the oxygen saturation is derived by lowering the resolution and it is an average value of oxygen saturation in the image of the optical absorber (the image of the optical absorber in the profile of absorption coefficient before the resolution is reduced) and of oxygen saturation in the periphery of the image of the optical absorber, the utility value of the derived oxygen saturation is still large.
• the place where the optical absorber is actually present can be identified (that is, the resolution can be increased) in a
• he amount for changing (the extent of reducing) the image spatial resolution at this time is determined according to a position displacement amount input to the apparatus 11 for inputting misplacement amount or a method used for the resolution reduction processing.
• the portion where the images of the optical absorber are composed is created by reducing the image spatial resolution, and therefore, it is not necessary to grasp a position displacement amount for each voxel.
• the image of the optical absorber after the reduction of the image spatial resolution must be enlarged in an amount more than the actual position displacement.
• the position displacement amount input to the apparatus 11 for inputting misplacement amount may be a rough amount, a value certainly larger than the actual position
• the amount for changing the image spatial resolution with respect to the position displacement amount is determined so that the image of the optical absorber in the profile of absorption coefficient whose resolution is not reduced is at least included (when the
• the resolution may be independently determined for each profile of absorption coefficient whose image spatial resolution is to be reduced, or the amount for changing the image spatial resolution may be equally determined for all profiles of absorption coefficient whose image spatial resolution is to be reduced.
• the method for deriving the position displacement amount is not particularly limited, and the position displacement amount can be derived with any publicly known method.
• the position displacement amount may be derived from mechanical measurement or measurement from images, and the input may be either manual or automatic.
• the amount of image spatial resolution to be changed with respect to the position displacement amount is
• resolution may be previously obtained for each method for changing resolution and prepared as a table or a relation, and the amount for changing resolution may be determined using this previously prepared table or relation .
• the method for reducing the image spatial resolution is not limited, and the reduction of the image spatial resolution can be achieved, for example, by the
• the calculation amount is not large, and practically extendable to three dimensions.
• a filter that reduces resolution such as a moving average filter or a gaussian filter is used.
• the size of the image of the optical absorber in voxel data can be adjusted by changing the size of the filter. At this time, it is necessary to perform adjustment so that the images of the optical absorber overlap each other, as illustrated in Fig. 4B.
• the position displacement amount between the images of the optical absorber is measured, and the amount for changing the size of the filter to overlap each other the images of the optical absorber is
• the profile of absorption coefficient subjected to the resolution reduction processing is stored in a
• each profile of absorption coefficient is stored in a different temporary memory.
• oxygen saturation is derived using at least a profile of absorption coefficient whose resolution is reduced (S9)
• the profile of absorption coefficient whose image spatial resolution is reduced is used for at least one of the plurality of profiles of absorption coefficient used for obtaining the oxygen saturation.
• the oxygen saturation may be obtained using two or more profiles of absorption coefficient whose image spatial resolutions are reduce or all profiles of absorption coefficient used may be the ones whose image spatial resolution is reduced.
• the derived oxygen saturation is the value of a region including the periphery of the image of the optical absorber.
• the derived information on the subject e.g. oxygen saturation
• the profile of absorption coefficient whose image spatial resolution is not reduced as illustrated in Fig. 4C, and only the region of the image of the optical absorber (the image of the optical absorber in the case where the resolution is not reduced) is extracted (S10) .
• Fig. 2 it is possible to use the data showing the profile A of absorption coefficient whose resolution is not reduced for the profile of absorption coefficient used for the composing.
• the method for extracting only the region of the image of the optical absorber is not particularly limited.
• only the portion of the optical absorber can be extracted in the profile of absorption
• an absorption coefficient ⁇ ⁇ ( ⁇ ) derived by measurement using light having a wavelength ⁇ is the sum of the product of the absorption coefficient ⁇ 3 ⁇ 4 ( ⁇ ) of deoxyhemoglobin and the abundance ratio C H b of deoxyhemoglobin, and the product of the absorption coefficient ⁇ 3 ⁇ 4 ⁇ 2 ( ⁇ ) of oxyhemoglobin and the abundance ratio C H o2 of
• ⁇ 3 ⁇ 4 ( ⁇ ) and ⁇ ⁇ >02 ( ⁇ ) are physical properties with a determined value, and previously measured by other methods.
• the unknowns in the formula (1) are two, C H b and C H bo2- Therefore, by performing measurement at least twice, using lights having different wavelengths, a
• C H b and C H bo2 can be derived, for example, by fitting using the method of least squares.
• Oxygen saturation SO2 is the ratio of oxyhemoglobin in total hemoglobin and therefore calculated by a formula (2) .
• the profile A of absorption coefficient is calculated in the unit 101, using a digital signal which is sent from the
• the amount for changing the resolution of a digital signal to be reduced is determined in the unit 108, based on a value derived from the apparatus 11 for inputting misplacement amount.
• the amount for changing the resolution is determined as in Embodiment 1.
• the amount of the resolution of the digital signal to be changed with respect to the misplacement amount is different for each method for changing the resolution. Therefore, the relationship between the position
• resolution may be previously obtained for each method for changing resolution and prepared as a table or a relation, and the amount for changing resolution may be determined using this previously prepared table or relation .
• the image spatial resolution of the derived profile of absorption coefficient is reduced by processing a time- series digital signal which is sent from the electrical signal processing circuit 9 in the unit 104.
• the resolution of the signal is reduced according to the amount for changing the resolution to derive a reduced signal (first reduced signal) .
• wavelengths is reduced more than resolution of other signals corresponding to light having a wavelength different from the at least one wavelength, to derive a reduced signal corresponding to light having the at least one wavelength.
• images of the optical absorber whose image spatial resolution is reduced by limiting the band of a signal are superimposed on each other.
• a reduced signal can also be calculated by summing signals of the acoustic detector derived at a plurality of positions and using the summed signals as a signal at one place, and image spatial resolution can be reduced.
• only signal processing may be performed on the time-series signal, and processing in a three-dimensional space is not necessary. Therefore, the processing amount in the entire process is small.
• the amount of the resolution of the digital signal to be changed ' with respect to the position displacement amount is different for each method for changing the resolution. Therefore, the relationship between the position displacement amount and the amount for changing resolution may be
• a spherical optical absorber having a diameter of 2 mm, in which 40% of oxyhemoglobin and 60% of
• deoxyhemoglobin were mixed to simulate blood, was placed at the center of a subject and irradiated with 800 nm and 850 nm lights, and signals thereof were derived by simulation.
• the concentration of the portion of the spherical optical absorber was about 0.4, and the calculated oxygen saturation was 40%. It was shown that by using the present invention, oxygen saturation can be calculated with a minor error even if position displacement occurs. In addition, the increase in calculation time at this time was negligible compared with the conventional method.
• Example 2 Similar to the simulation of Example 1 was performed and a method for summing acoustic signals derived at a plurality of positions and using the summed signals as a signal at one place was used as a method for reducing the voxel spatial resolution of a profile of absorption coefficient .

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• 2011
  • 2011-01-21 JP JP2011010534A patent/JP5818444B2/ja not_active Expired - Fee Related
  • 2011-01-31 WO PCT/JP2011/052453 patent/WO2011096551A1/en not_active Ceased
  • 2011-01-31 US US13/515,037 patent/US20120289812A1/en not_active Abandoned
  • 2011-01-31 EP EP11705049A patent/EP2531094A1/en not_active Withdrawn
  • 2011-01-31 CN CN201180007827.XA patent/CN102740765B/zh not_active Expired - Fee Related
• 2019
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