Patent Application
20160058295
1. Field of the Invention
The present invention relates to a photoacoustic wave measurement apparatus and a photoacoustic wave measurement method.
2. Description of the Related Art
An optical imaging apparatus causes light, irradiated from a light source such as laser, to be propagated through a subject and detects a signal based on the propagated light to thereby acquire information on the inside of the subject. This technique has been actively studied in medical fields as an in vivo examination technique. Photoacoustic imaging is known as one of such optical imaging technologies.
Photoacoustic imaging is a technology which irradiates pulsed light generated from a light source to a subject, detects acoustic waves (hereinafter, also referred to as “photoacoustic waves”) generated from a biological tissue having absorbed energy of light diffused within the subject, and visualizes information relating to an optical characteristic value of inside of the subject. Thus, an optical characteristic value distribution of inside of the subject, particularly, a light energy absorption density distribution may be acquired.
Using light having a wavelength which may be absorbed by hemoglobin as the pulsed light, for example, allows non-invasive imaging of an angiogram of inside of a living body. Using light having a wavelength different from that absorbed by hemoglobin allows imaging of other parameters such as collagen and elastin under the skin. The use of a contrast medium responsive to a specific wavelength also allows highlighting of an angiogram and imaging of a lymphatic vessel.
A representative technology of three-dimensional visualization technologies applying photoacoustic imaging detects photoacoustic waves generated from a light absorber by using an ultrasonic transducer placed on a two-dimensional plane and performs image reconstruction computing thereon to generate three-dimensional data relating to optical characteristic values. Such a three-dimensional visualization technology is called a photoacoustic tomography (PAT).
Furthermore, in recent years, a photoacoustic microscope attracts attention as an apparatus which allows visualization with a high spatial resolution by applying the photoacoustic imaging. A photoacoustic microscope uses an optical lens or an acoustic lens to focus light or sound so that a high-resolution image may be acquired.
However, it is known that the depth for visualization and the spatial resolution are trade-offs in an apparatus using PAT and a photoacoustic apparatus such as a photoacoustic microscope. In other words, PAT has a feature that information acquired by PAT has a spatial resolution which decreases as the depth of tissue of a living body increases. This is because light is easily diffused within a living body and photoacoustic waves at a high frequency generated from the living body attenuate largely as the depth of tissue of a living body increases. Because of this characteristic, a photoacoustic microscope with a high spatial resolution, for example, is mainly applicable for visualizing a light absorber within the skin present in a relatively shallower part of a living body. For example, in a case where a photoacoustic microscope may be used to visualize blood hemoglobin, a blood vessel present in a dermal layer of the skin may be visualized. A non-patent literature “In vivo dark-field reflection-mode photoacoustic microscopy,” by Maslov et al., OPTICS LETTERS Vol. 30, No. 6, March 2005, discloses a photoacoustic microscope capable of capturing at a high resolution an image of a blood vessel present in a region close to the skin by using an acoustic lens.
Generally, a mole or a body hair present on the skin or in an epidermal layer exhibit a high light absorbing quantity. A “mole” is a cluster of pigmented cells called melanocytes. Moles, freckles, skin tags, seborrheic keratosis, and lentigines are formed when pigmented cells grow in clusters on the skin. Thus, photoacoustic waves generated based on light absorbed by a mole or a body hair have a higher intensity than that of photoacoustic waves acquired from other regions of the skin. Therefore, using the photoacoustic microscope disclosed in the above-mentioned non-patent literature may provide wrong information from photoacoustic waves based on a mole or a body hair, which may possibly prevent correct evaluation of biological information of a dermal layer present under a cluster of pigmented cells or body hair.
Accordingly, an aspect of the present invention provides a photoacoustic apparatus capable of properly visualizing information relating to optical characteristic values of a tissue to be visualized even in a case where an object which highly absorbs light, such as a mole or body hair, exists on the skin or in an epidermal layer.
A photoacoustic wave measurement apparatus according to one aspect of the present invention includes an image pickup unit configured to capture a surface image of an object, a light source configured to generate light, a photoacoustic wave detection unit configured to detect photoacoustic waves propagated from an object irradiated with the light, a specific region detection unit configured to detect a specific region within the captured surface image of the object, and a control unit which sets a measurement region of the object to perform irradiation of the light and controls detection of the photoacoustic waves based on positional information of the specific region detected by the specific region detection unit.
A photoacoustic wave measurement apparatus according to another aspect of the present invention includes an image pickup unit, a light source configured to generate light, a photoacoustic wave detection unit configured to detect photoacoustic waves propagated from an object irradiated with the light, a specific region detection unit configured to detect a specific region within a captured image obtained by the image pickup unit, and an image processing unit that generates image data from the photoacoustic waves detected by the photoacoustic wave detection unit based on positional information of the specific region detected by the specific region detection unit.
A photoacoustic wave measurement method according to still another aspect of the present invention includes obtaining a captured image of an object, detecting a specific region within the captured image, setting a measurement region of the object based on a position of the specific region within the captured image, and irradiating light to the measurement region and detecting photoacoustic waves propagated from the measurement region of the object in response to the irradiation of the light.
A photoacoustic wave measurement method according to still another aspect of the present invention includes obtaining a captured image of an object, detecting a specific region within the captured image, irradiating light to the object and detecting photoacoustic waves propagated from the object in response to the irradiation of the light, and generating image data from the detected photoacoustic waves based on a position of the specific region within the captured image.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
A photoacoustic wave measurement apparatus according to a first embodiment is an ultrasonic-focus photoacoustic microscope, for example. According to this embodiment, an ultrasonic-focus photoacoustic microscope refers to a photoacoustic microscope configured such that a focal point region of pulsed light may be wider than a focal point region of ultrasound. The present invention is applicable not only to an ultrasonic-focus photoacoustic microscope but also to a light-focus photoacoustic microscope configured such that a focal point region of pulsed light may be smaller than a focal point region of ultrasound.
An example of material to be visualized by photoacoustic measurement is tissue or a phantom having light absorption coefficient and scattering coefficient equivalent to tissue. An example of the specific region reference material is a pre-identified non-measuring tissue of photoacoustic measurement according to this embodiment. According to this embodiment, in a region where photoacoustic measurement is to be executed, pulsed light 104 is irradiated to the region, and photoacoustic waves are detected. On the other hand, in a region where photoacoustic measurement is not executed, at least one of irradiation of pulsed light 104 and photoacoustic wave detection is not performed.
An overall configuration of a photoacoustic microscope, an example of photoacoustic wave measurement apparatus, according to this embodiment will be described.
A pulsed light source 101 emits pulsed light under control of a measurement control unit 102. The pulsed light passes through an optical fiber 103 and is guided to an optical system for irradiating excited light to a living body. According to this embodiment, the optical system includes a lens 105, a beam splitter 106, a conical lens 107, and a lens 108. The pulsed light 104 emitted from the optical fiber 103 is collimated by the lens 105, and a part of the light passes through the beam splitter 106 and another part of the light is reflected by the beam splitter 106. The pulsed light having passed through the beam splitter 106 spread in a ring shape by the conical lens 107 and is launched into a mirror 111. On the other hand, the pulsed light reflected by the beam splitter 106 is collected by a lens 108 and is detected by a photodetector 109. A digital signal acquired by converting the detected signal by a data acquisition unit (DAQ unit) 110 is stored in an internal memory of the DAQ unit. The pulsed light detected by the photodetector 109 may be used for correcting an error due to a variation in light quantity of the photoacoustic signal and may be usable as a trigger signal for determining measurement timing of photoacoustic waves.
The pulsed light 104 spreads into a ring shape by the conical lens 107, and is then collected by being reflected by the mirror 111. The mirror 111 mainly contains a member made of transparent material such as glass and is configured to reflect the pulsed light 104 at the boundary between the mirror 111 and the outside of the mirror 111 (such as air or water, which will be described below). A metal film may be evaporated on the outer surface of the member forming the mirror 111 for a higher light reflectance. The mirror 11 is set such that the position of the focal point of light collected by the mirror 111 may be located in an internal part of the subject 113 for measurement of photoacoustic waves. According to this embodiment, the lens 105, conical lens 107, and mirror 111 function as an optical unit configured to guide the pulsed light 104 to the subject 113. The pulsed light diffused by an internal part of the subject 113 is absorbed by a light absorber 112 (e.g., blood) located within the subject 113. Some types of light absorber 112 may have a specific or predetermined light absorption coefficient. When the light absorber 112 absorbs light, photoacoustic waves 114 are generated due to the well-known photoacoustic effect. The photoacoustic waves 114 are detected by a transducer 115 functioning as a photoacoustic wave detection unit placed near the center of the mirror 111, and a change in sound pressure intensity is converted to an electric signal. The transducer 115 includes an ultrasonic transducer (of one or more transducer elements) sensitive to an ultrasonic frequency band. The transducer 115 may have an acoustic lens. According to the present embodiment, the transducer 115 having an acoustic lens is capable of detecting sound waves generated from its focal position with high sensitivity. The focal point of the acoustic lens may be set to the focal position of the pulsed light collected by the mirror 111 so that sound waves generated from the focal position of the pulsed light may be detected with high sensitivity. Water stored in a tank 116 is present between the transducer 115 and the subject 113 for acoustic impedance matching with the subject. The material for acoustic impedance matching to be stored in the tank 116 is not limited to water but may contain other substances. A gel acoustic impedance matching material may be coated between a bottom of the tank 116 and the subject 113. The photoacoustic waves 114 are detected by the transducer 115 and are converted to an electric signal. The electric signal acquired by the transducer 115 is transmitted to a signal amplifier 117, and its signal intensity is amplified. After that, the electric signal is converted to a digital signal by the DAQ unit 110 and is stored in an internal memory of the DAQ unit 110. The data stored in the DAQ unit 110 undergo signal processing performed by the signal processing unit 118. After that, the data undergo image processing performed by the image processing unit 119 and are displayed as image data by the display unit 120. The signal processing unit 118 and image processing unit 119 may be configured as an integral processing unit.
According to the present embodiment, members enclosed within a box 121 are mounted on a movable stage (not illustrated) capable of scanning two-dimensionally. Two-dimensional relative movement of the movable stage about the subject 113 may move positions of the focal point of the pulsed light 104 focused on the subject 113 and the focal point of the transducer 115. By detecting photoacoustic waves at two-dimensionally scanned measurement positions, two-dimensional photoacoustic signal data of the subject may be acquired.
An image pickup unit (camera) 122 is further provided adjacent to the transducer 115 for capturing a surface image of the subject 113. The mirror 111 including a transparent member for a wavelength band of light to which the image pickup unit 122 is sensitive may acquire an image of a surface of the subject 113. The illumination for capturing an image of the subject 113 may be light from an external environment or light generated from the pulsed light source 101. Alternatively, an illumination unit may be provided separately from the pulsed light source 101, and the illumination unit may be used to illuminate the subject 113. In a case where the pulsed light source 101 is used as an illumination unit for image capturing, light having an identical wavelength characteristic to that of the light generated when a photoacoustic measurement is performed may be used as the illumination light. Apparently, light having a wavelength characteristic different from that of light generated when a photoacoustic measurement is performed may be used as illumination light. When image data acquired by the image pickup unit 122 is transmitted to a specific region detection unit 123, the specific region detection unit 123 detects data on a non-measuring tissue of a photoacoustic measurement among image data. Based on the detected data, the measurement control unit 102 functioning as a control unit sets a region where a photoacoustic measurement is to be executed.
Referring to
The measurement control unit 102 may perform light emission control of the pulsed light source 101, control over the movable stage (not illustrated), control regarding data sampling of the DAQ unit 110, control over image capturing performed by the image pickup unit 122 and illumination therefor and so on.
In the aforementioned configuration, the focal point region of the pulsed light 104 contains a focal point of ultrasonic waves of an acoustic lens included in the transducer 115, for example. However, the relationship may be reversed, as in the configuration of a light-focus photoacoustic microscope. In other words, a focal point region of focus of the pulsed light 104 through an objective lens may contain a region of a focal point of ultrasonic waves of the acoustic lens in the transducer 115. When a light-focus photoacoustic microscope is used, the resolution of the photoacoustic microscope depends on the size of the focal point of light. Thus, a photoacoustic image at a higher resolution may be acquired.
Next, with reference to the timing chart in
Next, a method will be described more specifically which uses the ultrasonic-focus photoacoustic microscope as described above to acquire two-dimensional plane data of a photoacoustic signal generated from inside of the subject 113 and display a corresponding image.
A measurement procedure will be described with reference to the flowchart for a measurement in
In step 201, a measurement parameter such as a measurement region for a photoacoustic measurement is set in the measurement control unit 102. Other concrete examples of the measurement parameter may include a measurement pitch of a photoacoustic measurement, a storage/sampling frequency of a photoacoustic signal at one point, a storage time, a scanning rate of a movable stage, acceleration, a light emission frequency of the pulsed light source 101, a light quantity, and a wavelength.
In step 202, an image of a surface of the subject 113 is acquired. The movable stage is moved based on information on the measurement region set in step 201, and the subject 113 is captured by the image pickup unit 122 such that the measurement region for acquiring a photoacoustic image may be included to acquire image data. The moving amount of the movable stage is calculated in consideration of a relative distance between the positions where the image pickup unit 122 and the transducer 115 are placed. Data on a surface image of the subject 113 captured by the image pickup unit 122 are transmitted to the specific region detection unit 123.
In step 203, a mole or a body hair present on a surface of the subject 113 are detected. The specific region detection unit 123 locates a position on a captured image of a tissue of a mole or a body hair present on a subject surface. In this case, the tissue has a significant light absorbing quantity from blood hemoglobin to be visualized by a photoacoustic measurement. A specific method for detecting a mole or a body hair from a captured image will be described below.
In step 204, the photoacoustic measurement region is reset. The measurement control unit 102 adjusts the alignment of the positions of the image of the subject surface and the photoacoustic measurement region set in step 201 and then resets a new photoacoustic measurement region excluding a position of at least one of a mole and a body hair detected in step 203. In step 201, the setting of a measurement region may be omitted. A photoacoustic wave measurement region may be set in step 204.
The method for adjustment of the alignment of the positions may be implemented by grasping coordinates of the image pickup unit 122 and transducer 115 and an imaging region of the image pickup unit with reference to the coordinates managed within the movable stage. Also in a case where no camera is mounted on the movable stage, the alignment of a captured image and a photoacoustic measurement region may be adjusted with reference to a subject or a marking around the subject. Details of the method for re setting a photoacoustic measurement region will be described below.
In step 205, based on the measurement region reset in step 204, a photoacoustic signal is acquired for each measurement position within the measurement region. Operations for a photoacoustic measurement are performed as described above.
Acquisition of a photoacoustic signal at each measurement position will be described. Through the procedure described with reference to
In step 206, signal processing is performed by the signal processing unit 118 on the electric signals based on the photoacoustic signals acquired at the measurement positions. Specific processes of the signal processing may include deconvolution in consideration of a pulse width of the pulsed light source 101 and envelop line detection. In a case where a distinctive frequency of noise added to a signal is known in advance and can be separated from a main frequency of a photoacoustic signal, a specific frequency component due to noise can also be removed. A component based on a photoacoustic wave reaching the transducer 115 with a delay from a wave directly transmitted from a sound source of a photoacoustic wave due to reflection by a surface of the subject 113 or a bottom of the tank 116 may be removed from the signal. In a case where a component based on a photoacoustic wave generated on a surface of the subject 113 is significant, the component may be deleted by performing this flow.
In step 207, image processing is performed. The image processing unit 119 generates voxel data based on a position on a scanning plane of the movable stage and a signal intensity distribution in a depth direction of a subject of a photoacoustic signal having undergone the signal processing in step 206 and generates an image data for visualization. In this case, a known artifact if any may be removed from the voxel data. In a case where an oxygen saturation of a light absorber within a subject is calculated, for example, voxel data storing oxygen saturation values may be generated from voxel data on intensities of photoacoustic signals acquired at a plurality of wavelengths of pulsed light. In a case where the measurement is performed by setting a wavelength of pulsed light such that blood hemoglobin within a subject may be a main light absorber, an image of a blood vessel is binarized and extracted from the acquired voxel data, for example.
In step 208, voxel data generated from the intensity distribution of photoacoustic signals in step 207 are displayed by a display method desired by a user. For example, the voxel data may be displayed by a method which displays a vertical cross section on three-dimensional axes or a method which displays voxel data as a two-dimensional distribution of the highest value, minimum value or average value of the voxel data in axis directions. Alternatively, a user may set an ROI (region of interest) within voxel data, and a user interface program may be configured to display statistical information regarding a shape of light absorber within the region and oxygen saturation information. In this case, in step 204, the value calculated based on a photoacoustic measurement does not exist with respect to the region from which a mole or a body hair is detected and thus excluded from the measurement region. Therefore, calculations are performed with reference to a region excluding the region from which a mole or body hair is detected. Dummy data on a region having a mole or a body hair excluded from the measurement region in step 204 may be displayed on the display unit 120.
In the measurement flow as described above, after whether a photoacoustic measurement is to be performed over all of the measurement region set in step 201 or not is determined, a measurement region is reset, and a photoacoustic measurement is performed thereon. However, during the photoacoustic measurement step 205, scanning may be performed with a movable stage capable of moving relatively to the subject 113, and the determination on whether a measurement is to be performed or not (and resetting of a measurement region) may be performed on positions one by one. The determination may be repeated until the scanning on the measurement region set in step 201 ends.
Next, a specific method will be described which detects a non-measuring tissue of the photoacoustic measurements present on a subject surface and excludes it from a measurement region of a photoacoustic measurement. For example, this method is applicable to a case where a mole or a body hair, for example, having a high light absorbing quantity on the skin surface is excluded from a measurement region in order to image a blood vessel under the skin by performing a photoacoustic measurement.
According to the present embodiment, a camera is used as an image pickup unit for acquiring a surface image of the subject 113. The image pickup unit may be an apparatus including a two-dimensional array type sensor in which pixels are arranged two-dimensionally.
The surface image may be acquired by using one kind of monochromatic light as illumination light or may be acquired for each of a plurality of kinds of monochromatic light switched to irradiate the subject 113.
First, a unit for using a monochromatic wavelength as the illumination light will be described.
Assume a case in which a non-measuring tissue is identified in advance to the measurement. Here, such a non-measuring tissue has a significantly higher light absorbing quantity than that of a tissue to be visualized by performing a photoacoustic measurement. For example, it may correspond to a mole or a body hair on the skin when an object of the visualization by photoacoustic measurement is blood hemoglobin. A difference in light absorbing quantity between a tissue to be visualized by performing a photoacoustic measurement and another tissue may be acquired by, for example, acquiring photoacoustic signals of tissue samples thereof and comparing the light absorbing quantities at a specific wavelength based on their signal intensities. Alternatively, a non-measuring tissue may be identified from information on known light absorption coefficients of the tissues.
In a case where one kind of monochromatic light is used as the illumination light, a wavelength of the illumination light may be selected which provides sufficient contrast on a captured image between a non-measuring tissue of a photoacoustic measurement and a subject surface tissue which is an object.
In order to acquire wavelength dependencies of intensities on a captured image of tissues, images of the tissues may be captured previously, or the wavelength dependencies may be calculated in consideration of wavelength dependencies of reflectances of the tissues and a wavelength dependency of an optical element of a camera to be used. In a case where the wavelength dependencies of images are acquired by performing a calculation or an experiment, an incident angle dependency of illumination light is also considered as required. Alternatively, a diffusing plate may be used for a lower incident angle dependency to diffuse and irradiate illumination light to a subject.
Also in a case where a non-measuring tissue is not identified previously, the tissue may be detected from an image captured by using illumination light having a monochromatic wavelength. The method will be described below.
An example will be described in which a non-measuring tissue of a photoacoustic measurement has a relatively higher light absorbing quantity, on a surface of the subject 113, at a wavelength of pulsed light to be irradiated to the subject 113 for a photoacoustic measurement. A tissue having a relatively higher light absorption at a certain wavelength than that of a surrounding tissue has a lower reflectance at the wavelength than that of the surrounding tissue. Therefore, its luminance on a captured image is relatively low, that is, its signal level is relatively low. For example, in a case where the wavelength to be used for a photoacoustic measurement is in a visible light region and light having the wavelength is used as illumination for capturing an image, a mole or a body hair generally has a higher light absorbing quantity than that of surrounding skin. Thus, signal levels of the pigmented tissues, e.g., where a cluster of pigmented cells called melanocytes are captured in an image, are relatively lower than the surrounding skin. Therefore, a captured image can be acquired which has a signal level dependent on the magnitude of the light absorbing quantity at a wavelength used for a photoacoustic measurement, which allows detection of a non-measuring tissue.
Next, a case will be described in which a non-measuring tissue of photoacoustic measurements has a significantly higher light absorbing quantity than that of an object of visualization by the photoacoustic measurements. In this case, a material to be visualized in the photoacoustic measurements includes a tissue or a prepared phantom having an equal light absorption coefficient and scattering coefficient as that of the tissue. To that end, light having a wavelength used for the photoacoustic measurements may be used as illumination light to acquire in advance the signal level on the captured image. The prepared signal level corresponding to the tissue to be visualized among captured images of a subject surface in the measurement region are defined as a threshold to identify a region having an intensity equal to or lower than the threshold as a non-measuring region. Thus, at a wavelength usable for performing the photoacoustic measurements, a region having a tissue having a higher light absorbing quantity than the light absorbing quantity of the tissue to be visualized can be identified as a non-measuring region of the photoacoustic measurements. The opposite may also be true. That is, a region of tissue having a lower light absorbing quantity than the light absorbing quantity of the tissue to be visualized can be identified as a non-measuring region of the photoacoustic measurements.
Next, a method will be described which uses illumination light having a plurality of monochromatic wavelengths to identify the position of a non-measuring tissue of the photoacoustic measurements. In a case where illumination light having a plurality of monochromatic wavelengths is used, the kind of non-measuring tissue of photoacoustic measurements may be identified in advance. For example, when a region having a mole is a non-measuring tissue of photoacoustic measurements, the wavelength dependency of the intensity of the reflected light from the mole may be known in advance. For example, an image of a subject surface tissue including a mole is captured for each wavelength of illumination light having a plurality of monochromatic wavelengths, and the signal level of the region having the mole on the captured image is acquired for each wavelength of the illumination light. Thus, the dependency of the mole on the wavelengths of the illumination light may be acquired a priori. When the dependency of the mole on the wavelengths of the illumination light is unknown, the wavelength dependency of the reflectance of the mole and the wavelength dependency of the signal levels of the captured image may be possible to be obtained by calculation or experimentation.
After the data on the wavelength dependency of the mole with respect to the illumination light on the captured image are prepared, images of a subject surface may be captured by using illumination light having a plurality of monochromatic wavelengths so that a signal level of each of pixels of the captured image for each of the wavelengths may be acquired. After that, a correlation coefficient for each pixel is calculated between the acquired signal level on the captured image and the prepared data on the wavelength dependency of the mole on the captured image with respect to the illumination light. For example, as a result of the calculation of the correlation coefficient by using the prepared data on the wavelength dependency of the mode on the captured image, it may be considered that there is a high possibility that a pixel having a high correlation coefficient is a result of the capturing an image of the mole. This may give high contrast between a non-measuring mole of photoacoustic measurements and the other subject surface tissue within a captured image for identification. When a subject is illuminated with light at different wavelengths, the light quantity of the illumination light may be monitored to correct the light quantity and to correct a signal level on a captured image.
Having described above the example in which a correlation coefficient is calculated for each pixel of a captured image, the correlation coefficient may be calculated based on a value acquired by adding or averaging signal levels of a plurality of pixels.
The method has been described above for identifying a non-measuring tissue of photoacoustic measurements by using a mole as an example. On the other hand, for a tissue on which photoacoustic measurements are to be performed, wavelength dependency data on a captured image may be prepared to identify a region on which photoacoustic measurements are to be performed and a non-measuring region of photoacoustic measurements.
Next, supplementary explanation will be given on the method with reference to drawings.
In this case, n is the number of used wavelengths and is an integer equal to or higher than 2. Thus, a pixel having a high correlation coefficient with a wavelength dependency of a mole is highly possibly a pixel corresponding to the mole on the captured image data. Therefore, the mole may be detected from the captured image.
This method allows acquisition of image data displaying a non-measuring biological tissue of photoacoustic measurements and a biological tissue surface which is an object at a sufficiently high contrast ratio. Thus, the position of a non-measuring biological tissue of photoacoustic measurements may be identified from an image captured by an image pickup unit. For some characteristics of biological tissues, the aforementioned methods may be used in combination to secure a sufficiently high contrast ratio.
The method has been described which uses light having a single monochromatic wavelength or a plurality of monochromatic wavelengths as illumination light if the aforementioned methods use such light. However, a subject may be irradiated with non-monochromatic light as illumination light such as light having a broad wavelength band. In this case, an optical filter allowing only light having a monochromatic wavelength to pass through may be used.
Therefore, the illumination light is not limited to light having a monochromatic wavelength but may be light having a broad wavelength characteristic such as white light. For example, the illumination light may be light in a room where the ultrasonic-focus photoacoustic microscope according to the present embodiment is placed. Alternatively, if a camera includes a white light illumination, the provided white light illumination may be used. A sensor capable of outputting in color may be used as a sensor of the camera. In this illumination method, a non-measuring tissue of photoacoustic measurements is identified in advance.
Next, a method will be described which extracts pixels capturing a non-measuring tissue of photoacoustic measurements from a captured image of a subject surface acquired by one of the aforementioned methods.
A method applicable to the present embodiment may extract an image region of the tissue by binarizing intensity data of the image. This method is applicable in a case where a non-measuring tissue of photoacoustic measurements is detected by using illumination light having a monochromatic wavelength as described above. In this case, for the binarization, a user may be required to set a threshold of the intensity of image data. For example, the threshold may be set in advance in the measurement control unit 102 when the measurement parameter setting is performed in step 201 in
As an alternative extraction method, a user may select a region manually from a captured image of a subject. In this case, a user refers to a distinctive shape of a non-measuring tissue to extract an image of the tissue. This process may be performed by the specific region detection unit 123 in step 203, for example. This extraction method is applicable to all of the illumination methods described above.
Next, with reference to
The measurement region may not be divided into a grid manner but may be divided into any arbitrary shape. The method for selecting a non-measuring region of a photoacoustic wave measurement, including a tissue such as a mole or a body hair, is not limited to the method described above, but a wider region may be selected if a tissue such as a mole or a body hair is included.
The configurations and operations of the aforementioned embodiment are given for illustration purpose only and may be changed. For example, the pulsed light 104 to be irradiated to the subject 113 may be light having a wavelength absorbed by a specific one of components of the subject 113. The pulse width of the pulsed light 104 is in the order of several picoseconds to several hundred nanoseconds. If the subject is a living body, the subject may preferably absorb light having a pulse width of several to several tens nanoseconds. Though the pulsed light source 101 which generates pulsed light 104 may be a laser or may be a light emitting diode or a photographic flash lamp instead of a laser.
A laser as the pulsed light source 101 may vary such as a solid-state laser, a gas laser, a dye laser, a semiconductor laser. If pigments in which oscillation wavelengths can be changed or OPOs (Optical Parametric Oscillators) are used as light sources, differences among optical characteristic value distributions depending on wavelengths can be measured.
The wavelength of the pulsed light source 101 may be in a wavelength region of 400 nm to 1600 nm or in ranges of terahertz wave, microwave, and radio waves.
In a case where light with a plurality of wavelengths is used as the pulsed light 104, a coefficient relating to an optical characteristic within a living body is calculated and is compared with a wavelength dependency inherent to a substance (such as glucose, collagen, oxidation-reduction hemoglobin) contained in a biological tissue for each of the wavelengths. This allows imaging of concentration distributions of substances contained in the living body.
Use of the acoustic signal receiving unit allows proper visualization of a tissue that is a visualization object even in a case where a substance having a high light absorbing quantity such as a mole or a body hair is present on the skin or in an epidermal layer.
According to a second embodiment, a method different from the first embodiment will be described which excludes measurement data of a tissue such as a mole or a body hair, which is a non-measuring of photoacoustic measurements according to the first embodiment, from data constructing an image. According to the first embodiment, a photoacoustic measurement is not performed on a non-measuring tissue. In other words, at least one of irradiation of pulsed light and detection of photoacoustic waves is not performed. According to the present embodiment on the other hand, photoacoustic measurements are performed on all of measurement regions which are initially set, and measurement data acquired from a region including a non-measuring tissue of the measurements are excluded so that the data are not to be used for constructing an image. Descriptions on the same parts as those of the first embodiment will be omitted though details will be described below, and differences from the first embodiment will be described mainly.
First, an overall configuration of the present embodiment will be described with reference to
Next, a data acquisition process will be described with reference to the flowchart illustrated in
In this flow, data based on a non-measuring tissue is excluded from data constructing an image. The data excluded from data constructing an image may not be stored in a memory or may be stored in a memory. The region excluded from data constructing an image may be separated such that data on the region has lower reliability than measurement data on other regions and may be replaced by dummy data, for example.
Because the method for detecting a non-measuring tissue such as a mole or a body hair in image data to be displayed in step 208 and the method for extracting pixel data showing such a tissue from an image captured by the image pickup unit 122 are the same as those in the first embodiment, the description will be omitted.
Next, a method for excluding non-measuring data from the voxel data generated from a measured photoacoustic signal in step 1002 will be described with reference to
First, like the first embodiment, the positional alignment of an image captured by the image pickup unit 122 and a region set as a photoacoustic measurement region is adjusted.
The method for dividing a measurement region is not limited to the aforementioned example, but a measurement region may be divided into arbitrary shapes. The method for selecting a region excluded from the voxel data, including a tissue such as a mole or a body hair, is not limited to the method described above, but a wider region may be selected if a tissue such as a mole or a body hair is included.
The present embodiment may also apply the configuration according to the first embodiment.
The acoustic signal receiving unit according to the present embodiment allows proper visualization of a tissue that is a visualization object even in a case where a substance having a high light absorbing quantity such as a mole or a body hair is present on the skin or in an epidermal layer.
According to a third embodiment, photoacoustic tomography (PAT) is applied which acquires a sound pressure of a photoacoustic wave generated from a subject at a plurality of positions on a two-dimensional plane and performs an image reconstruction calculation based on it to generate three-dimensional information relating to optical characteristic values of inside of the subject. This is different from the method applied in a photoacoustic microscope which performs photoacoustic measurements at a plurality of positions within a limited measurement region from which photoacoustic waves may be measured in the measurements by focusing light or sound waves to generate three-dimensional information as in the first embodiment and the second embodiment.
A configuration of the present embodiment will be described with reference to
Next, a data acquisition process will be described with reference to
According to the present embodiment, measurement data not to be measured are excluded from the voxel data. The data excluded from data constructing an image may not be stored in a memory or may be stored in a memory. The excluded region may be separated such that data on the region has lower reliability than measurement data on other regions and may be replaced by dummy data, for example.
Because the method for detecting a non-measuring tissue, such as a mole or a body hair, in image data to be displayed finally and the method for extracting pixel data showing such a tissue from an image captured by the image pickup unit 122 are the same as those in the first embodiment, the description will be omitted.
Next, a method for excluding data not to be measured from the voxel data generated from a measured photoacoustic signal in step 1301 will be described with reference to
First, the positional alignment of an image captured by the image pickup unit 122 and voxel data generated by the image reconstruction calculation in step 1301 is adjusted.
Having described above that measurement data on a non-measuring tissue are excluded from the voxel data, the excluded data may not be stored in a memory or may be stored in a memory. The region on which the excluded data are based may be separated such that data on the region has lower reliability than measurement data on other regions, and dummy data, for example, may be included. The method for dividing a measurement region into voxels used for the reconstruction calculation is not limited to the aforementioned method, but a measurement region may be divided into arbitrary shapes. The method for selecting a region excluded from the voxel data, including a tissue such as a mole or a body hair, is not limited to the method described above, but a wider region may be selected if a tissue such as a mole or a body hair is included.
The present embodiment may also apply the configuration according to the first embodiment. According to the present embodiment, the transducer 1203 is moved on a two-dimensional plane by a movable stage (not illustrated) to perform a photoacoustic measurement. However, a plurality of transducers may be arranged as a two-dimensional array to measure photoacoustic signals on the two-dimensional plane without performing the scanning by the movable stage. Use of this configuration may increase the speed of the measurements.
Use of the acoustic signal receiving unit according to the present embodiment allows proper visualization of a tissue that is a visualization object even in a case where a substance having a high light absorbing quantity such as a mole or a body hair is present on the skin or in an epidermal layer.
The aforementioned embodiments are given for illustration purpose only and may be combined with each other without departing from the spirit and scope of the present invention.
The aforementioned photoacoustic measurement apparatus may be utilized as a medical diagnostic imaging apparatus in a case where a subject is a biological substance. More specifically, for diagnoses and follow-up studies of chemical treatments performed on tumors and vascular diseases, an optical characteristic value distribution within a living body and a concentration distribution of a substance contained in a biological tissue from the information may be imaged.
The present invention is applicable to a non-destructive test to be performed on a non-biological substance.
The present invention allows proper visualization of the skin or an epidermal layer even in a case where a substance having a high light absorbing quantity such as a mole or a body hair is present on the skin or in the epidermal layer.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-178561, filed Sep. 2, 2014, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-178561 | Sep 2014 | JP | national |
