Patent Grant
7627365
The present invention relates to imaging and qualitative or quantitative characterization of biological tissue using visible or infra-red radiation, and more particularly to detection, imaging and characterization of breast tumors.
Traditionally, potentially harmful ionizing radiation (for example X-ray or γ-ray) has been used to image biological tissue. This radiation propagates in the tissue on straight, ballistic tracks, i.e., scattering of the radiation is negligible. Thus, imaging is based on evaluation of the absorption levels of different tissue types. For example, in roentgenography the X-ray film contains darker and lighter spots. In more complicated systems, such as computerized tomography (CT), a cross-sectional picture of human organs is created by transmitting X-ray radiation through a section of the human body at different angles and by electronically detecting the variation in X-ray transmission. The detected intensity information is digitally stored in a computer which reconstructs the X-ray absorption of the tissue at a multiplicity of points located in one cross-sectional plane.
Near infra-red radiation (NIR) has been used to study non-invasively the oxygen metabolism in tissue (for example, the brain, finger, or ear lobe). Using visible, NIR and infra-red (IR) radiation for medical imaging could bring several advantages. In the NIR or IR range the contrast factor between a tumor and a tissue is much larger than in the X-ray range. In addition, the visible to IR radiation is preferred over the X-ray radiation since it is non-ionizing and thus, potentially causes fewer side effects. However, the visible or IR radiation is strongly scattered and absorbed in biological tissue, and the migration path cannot be approximated by a straight line, making inapplicable certain aspects of cross-sectional imaging techniques.
Computerized Tomography using NIR spectrometry has been used for in vivo imaging. This technique utilizes NIR radiation in an analogous way to the use of X-ray radiation in an X-ray CT. The X-ray source is replaced by several laser diodes emitting light in the NIR range. The NIR-CT uses a set of photodetectors that detect the light of the laser diodes transmitted through the imaged tissue. The detected data are manipulated by a computer similarly as the detected X-ray data would be in an X-ray CT. Different NIR-CT systems have recognized the scattering aspect of the non-ionizing radiation and have modified the X-ray CT algorithms accordingly.
The above-mentioned X-ray or γ-ray techniques have been used to detect a tissue tumor. Under the term “angiogenesis” I mean the generation of new blood vessels into a tissue or organ. Under normal physiological conditions humans or animals undergo angiogenesis only in very specific restricted situations. For example, angiogenesis is normally observed in wound healing, fetal and embryonal development and formation of the corpus luteum, endometrium and placenta.
Both controlled and uncontrolled angiogenesis are thought to proceed in a similar manner. Persistent, unregulated angiogenesis occurs in a multiplicity of disease states, tumor metastasis and abnormal growth by endothelial cells and supports the pathological damage seen in these conditions. The diverse pathological disease states in which unregulated angiogenesis is present have been grouped together as angiogenic dependent or angiogenic associated diseases. The hypothesis that tumor growth is angiogenesis dependent was first proposed in 1971. (Folkman J., Tumor angiogenesis: Therapeutic implications, N. Engl. Jour. Med. 285: 1182-1186, 1971) In its simplest terms it states: “Once tumor ‘take’ has occurred, every increase in tumor cell population must be preceded by an increase in new capillaries converging on the tumor.” Tumor ‘take’ is understood to indicate a prevascular phase of tumor growth in which a population of tumor cells occupying a few cubic millimeters volume and not exceeding a few million cells, can survive on existing host microvessels. Expansion of tumor volume beyond this phase requires the induction of new capillary blood vessels. This explanation was directly or indirectly observed and documented in numerous publications.
Breast cancer is among the most common and the most feared malignancies in women. It has an unpredictable course, the treatment is frequently physically and emotionally draining and the risk of metastatic spread persists for many years. Due to its high occurrence rate, routine breast cancer screening, which includes physical examination and x-ray mammography, plays an important role in current health care. X-ray mammography can detect perhaps 90% of all masses and increases the 10-year survival rate to about 95% for patients with cancers solely detected by mammography. Although the modern mammography uses a low-dose of x-rays, it still involves some very small risk of inducing cancers by the radiation. Other tests, such as magnetic resonance imaging (MRI) and gadolinium enhanced MRI, have been used successfully for detection of breast tumors and may be used routinely for screening in the future.
After a small suspicious mass is detected in the breast non-invasively, an excisional biopsy is usually performed to exclude or diagnose malignancy. The biopsy specimen is removed under local anesthesia and is used for histopathological diagnosis. The statistics show that up to 75% of the excisional biopsies, the biopsied tissue is diagnosed to be benign. Thus, a majority of patients undergoes this unpleasant and costly procedure unnecessarily.
Therefore, a non-invasive, relatively inexpensive technique that can detect and characterize breast tumors may find its place in today's health care alone or in conjunction with the above-mentioned techniques.
The present invention includes different novel apparatuses and methods for optical examination of biological tissue, in general, and breast tissue, specifically, using visible or infra-red light. The optical examination technique can be used alone to detect and characterize a breast tumor, or can be used in combination with X-ray mammography, ultrasound examination, fMRI, or a needle biopsy. Furthermore, the optical examination technique can be used to examine women of any age.
The technique can employ one or several optical modules positioned on the right or left breast of a female patient placed in different positions. The patient may be sitting upright supporting the examined breast by the optical module, or may be lying face down with the breast on the optical module pad. Alternatively, the patient may be lying supine face up with the breast spread over the chest as evenly as possible. If a suspicious mass is detected, the technique can non-invasively characterize the mass by taking optical data at different wavelengths and by measuring one or several tissue specific characteristics related to the tissue metabolism (or hypermetabolism), biochemistry, pathophysiology (including angiogenesis) or another characteristic of a pathological tissue condition.
In one aspect, the optical examination technique employs an optical system for in vivo non-invasive examination of a volume of biological tissue of a subject. The optical examination system includes an optical module, a controller and a processor. The optical module includes an array of optical input ports and optical detection ports located in a selected geometrical pattern to provide a multiplicity of source-detector paths of photon migration inside the biological tissue. Each optical input port is constructed to introduce into the tissue volume visible or infrared light emitted from a light source. Each optical detection port is constructed to provide light from the tissue to a light detector. The controller is constructed and arranged to activate one or several light sources and light detectors so that the light detector detects light that has migrated over at least one of the source-detector migration paths. The processor receives signals corresponding to the detected light and creates a defined spatial image of the examined tissue.
The optical examination system may generate single wavelength or multiple wavelength images of the examined tissue, wherein the employed wavelength is sensitive to absorption or scattering by a tissue constituent (e.g., an endogenous or exogenous pigment, tissue cells, chemical compounds) or is sensitive to structural changes in the tissue. The optical images may display tissue absorption, tissue scattering, or both. The optical imaging system may also generate blood volume hemoglobin oxygenation images and hemoglobin deoxygenation images (or images of any other tissue constituent) based on a single wavelength optical data or a multiple wavelength optical data. A processor may use different image processing and enhancing algorithms known in the art. The processor may correlate several images taken on the same tissue or taken on symmetrical tissue regions such as the left breast and the right breast, or the left arm and the right arm. Based on this correlation, the system detects a suspicious tissue mass and characterize the detected mass. The correlation includes determining congruency of the structures detected in different images. The processor may employ different types of combined scoring, based on several optical images alone or in combination with X-ray mammography, ultrasound examination, or fMRI, to characterize a suspicious tissue mass.
The optical imaging system may generate the above-described images by examining symmetrical tissue regions of the right breast and the left breast, or may generate images of both the entire right breast and the entire left breast. To identify and characterize a suspicious tissue mass, the processor may employ the different types of combined scoring by correlating the right breast image with the left breast image.
The optical imaging system may collect single wavelength or multiple wavelength data of a breast tissue model for calibration or for detection of background data. In the calibration procedure, the optical module is placed on the model, and the imaging system can collect a limited number of optical data or can collect optical data using the same sequences as used during the tissue examination. The system may either collect and store the model data for subsequent digital processing, or may adjust the source or detector gains to detect optical data according to a predetermined optical pattern. The imaging system may use different breast models having the same scattering coefficient and the same absorption coefficient as the normal breast tissue of a female, for example, below 40 years or above 40 years. Furthermore, the models may have different sizes and have a shape of a female breast during examination. For example, the model has a shape of the breast (or the breast and a portion of the chest) of a woman lying on her back during examination.
According to another aspect, the optical examination technique employs an optical system for in vivo, non-invasive examination of biological tissue of a subject. The optical system includes an optical module, a controller, and a processor. The optical module includes an array of optical input ports and detection ports located in a selected geometrical pattern to provide a multiplicity of photon migration paths inside an examined region of the biological tissue. Each optical input port is constructed to introduce visible or infrared light emitted from a light source. Each optical detection port is constructed to receive photons of light that have migrated in the examined tissue region from at least one of the input ports and provide the received light to a light detector. The controller is constructed and arranged to control operation of the light source and the light detector to detect light that has migrated over at least one of the photon migration paths. The processor is connected to receive signals from the detector and arranged to form at least two data sets, a first of the data sets representing blood volume in the examined tissue region and a second of the data sets representing blood oxygenation in the examined tissue region. The processor is arranged to correlate the first and second data sets to detect abnormal tissue in the examined tissue region.
Preferably, the second data set includes hemoglobin deoxygenation values. The processor may be arranged to form a third data set being collected by irradiating a reference tissue region.
According to another aspect, the optical examination technique employs an optical system for in vivo, non-invasive examination of biological tissue of a subject. The optical system includes an optical module, a controller, and a processor. The optical module includes an array of optical input ports and detection ports located in a selected geometrical pattern to provide a multiplicity of photon migration paths inside an examined region of the biological tissue. Each optical input port is constructed to introduce visible or infrared light emitted from a light source. Each optical detection port is constructed to receive photons of light that have migrated in the tissue from at least one of the input ports and provide the received light to a light detector. The controller is constructed and arranged to control operation of the light source and the light detector to detect light that has migrated over at least one of the photon migration paths. The processor is connected to receive signals from the detector and arranged to form at least two data sets, a first of the data sets being collected by irradiating an examined tissue region of interest and a second of the data sets being collected by irradiating a reference tissue region having similar light scattering and absorptive properties as the examined tissue region. The processor is arranged to correlate the first and second data sets to detect abnormal tissue in the examined tissue region.
According to another aspect, the optical examination technique employs an optical system for in vivo, non-invasive examination of biological tissue of a subject. The optical system includes an optical module, a controller, and a processor. The optical module includes an array of optical input ports and detection ports located in a selected geometrical pattern to provide a multiplicity of photon migration paths inside an examined region of the biological tissue or a model representing biological tissue. Each optical input port is constructed to introduce visible or infrared light emitted from a light source. Each the optical detection port is constructed to receive photons of light that have migrated in the tissue or the model from at least one of the input ports and provide the received light to a light detector. The controller is constructed and arranged to control operation of the light source and the light detector to detect light that has migrated over at least one of the photon migration paths. The processor is connected to receive signals from the detector and arranged to form at least two data sets of two tissue regions, a first of the data sets being collected by irradiating an examined tissue region and a second of the data sets being collected by irradiating a region of a tissue model having selected light scattering and absorptive properties. The processor is arranged to correlate the first and second data sets to detect abnormal tissue in the examined tissue region.
Preferred embodiments of these aspects of the inventions have one or more of the following features.
The processor may be arranged to correlate the first and second data sets by determining congruence between data of the two sets.
The processor may be programmed to order the first and second data sets as two-dimensional images and to determine the congruence using the two-dimensional images. The processor may be programmed to order the first and second data sets as two-dimensional images and to determine the congruence using the following formula:
The processor may be further arranged to determine a location of the abnormal tissue within the examined tissue region.
The processor may be adapted to produce from the data set an image data set by implementing an optical tomography algorithm. The optical tomography algorithm may use factors related to determined probability distribution of photons attributable to the scattering character of the tissue being imaged.
The controller may be arranged to activate the source and the detector to obtain a first selected distance between the input and detection ports, and the processor may be arranged to form the data set for the first distance. The processor may produce an image data set from the data set formed for the first distance. The controller may further be arranged to activate the source and the detector to obtain a second selected distance between the input and detection ports and is arranged to form another data set for the second distance.
The optical system may further include a display device constructed to receive the image data set from the processor and to display an image.
The optical system may further include a first oscillator and a phase detector. The first oscillator is constructed to generate a first carrier waveform at a first frequency on the order of 108 Hz, the first frequency having a time characteristic compatible with the time delay of photon migration from the input port to the detection port. The light source is coupled to the first oscillator and constructed to generate the light modulated by the first carrier waveform. The phase detector is constructed to determine change in waveform of the detected light relative to the waveform of the introduced light and measure therefrom the phase shift of the detected light at the wavelength, wherein the phase-shifted light is indicative of scattering or absorptive properties of the examined tissue region. The processor is arranged to form the data set based on the measured phase shift. This optical system may further include a second oscillator constructed to generate a second waveform at a second frequency. The detector is then arranged to receive a reference waveform at a reference frequency offset by a frequency on the order of 103 Hz from the first frequency and to produce a signal, at the offset frequency, corresponding to the detected radiation. The phase detector is adapted to compare, at the offset frequency, the detected radiation with the introduced radiation and to determine therefrom the phase shift.
The optical system may further include an oscillator, a phase splitter, and first and second double balanced mixers. The oscillator is constructed to generate a first carrier waveform of a selected frequency compatible with time delay of photon migration from the input port to the detection port The light source is connected to receive from the oscillator the carrier waveform and is constructed to generate optical radiation modulated at the frequency. The phase splitter is connected to receive the carrier waveform from the oscillator and produce first and second reference phase signals of predefined substantially different phases. The first and second double balanced mixers are connected to receive from the phase splitter the first and second reference phase signals, respectively, and are connected to receive from the detector the detector signal and to produce therefrom a in-phase output signal and a quadrature output signal, respectively. The processor being connected to the double balanced mixers and arranged to receive the in-phase output signal and the quadrature output signal and form therefrom the data set.
The processor may be arranged to calculate a phase shift (Θλ) between the light introduced at the input port and the light detected at the detection port prior to forming the data set.
The processor may arranged to calculate an average migration pathlength of photons scattered in the examined tissue between the optical input port and the optical detection port prior to forming the data set.
The processor may further employ the pathlength in quantifying hemoglobin saturation (Y) of the examined tissue.
The processor may be arranged to calculate a signal amplitude (Aλ) determined as a square root of a sum of squares of the in-phase output signal and the quadrature output signal prior to forming the data set.
The optical system may further include a narrow band detector connected to receive from the optical detector the detector signal and to produce a DC output signal therefrom. The processor then further determines a modulation index (Mλ) as a ratio of values of the signal amplitude and the signal amplitude plus the DC output signal.
The optical system may further include at least one oscillator connected to at least one light source. The oscillator is constructed to generate a carrier waveform of a selected frequency. The light source generate slight of a visible or infrared wavelength being intensity modulated at the frequency to achieve a known light pattern. The controller is constructed to control the emitted light intensity or phase relationship of patterns simultaneously introduced from multiple input ports, wherein the introduced patterns form resulting radiation that possesses a substantial gradient of photon density in at least one direction. This resulting radiation is scattered and absorbed over the migration paths. The detector is constructed and arranged to detect over time the resulting radiation that has migrated in the tissue to the detection port. The processor is further arranged to process signals of the detected resulting radiation in relation to the introduced radiation to create the data sets indicative of influence of the examined tissue upon the substantial gradient of photon density of the resulting radiation.
The optical system may further include a phase detector constructed to detect the phase of the detected radiation and provide the phase to the processor.
The optical system may further include an amplitude detector constructed to detect the amplitude of the detected radiation and provide the amplitude to the processor.
The phase relationship of light patterns introduced from two input ports may be 180 degrees.
The optical system may be constructed as described in U.S. Pat. Nos. 5,119,815 or 5,386,827. This system includes a light source constructed to generate pulses of radiation of the wavelength, the pulses having a known pulse wave form of a duration on the order of a nanosecond or less. An optical detector is constructed to detect over time photons of modified pulses that have migrated in the tissue from the input ports. This system also includes an analyzer connected to the detector and adapted to determine a change in the pulse waveform shape of the detected pulses relative to the introduced pulses, at the employed wavelength. The processor then creates the data set based on the determined pulse waveform change. The processor may also be constructed and arranged to calculate the effective pathlength of photons of the wavelength migrating between the input and detection ports in conjunction with creating the data set. The processor may also be constructed and arranged to calculate the scattering coefficient at the wavelength in conjunction with creating the image data set The processor may also be constructed and arranged to calculate the absorption coefficient at the wavelength in conjunction with creating the data set.
The optical system may use the light source that produces relatively long light pulses and the processor that forms the data set by subtracting amplitude of two the pulses emitted from two input ports located symmetrically relative to one detection port.
The optical system may be constructed to introduce and detect photons at two wavelengths selected to be sensitive to a tissue constituent. The tissue constituent may be an endogenous pigment or an exogenous pigment. The endogenous pigment may be hemoglobin. The exogenous pigment may be a selected contrast agent.
Other advantages and features of the invention will be apparent from the following description of the preferred embodiment and from the claims.
Referring to
In one embodiment, optical module 12 includes nine laser diodes S1, S2, . . . , S9 and four photomultiplier tubes (PMTs) D1, D2, D3, D4. The laser diodes and PMTs are embedded in a pliable rubber-like material positioned in contact with the examined breast. There may be a Saran® wrap or similar material located between the laser diodes and the skin, and between the PMTs and the skin. Similarly, optical module 14 includes four laser diodes S1, S2, S3, S4 and 27 silicon diode detectors D1, D2, . . . , D27 embedded in a pliable rubber-like material. The optical systems shown in
Furthermore, the optical systems shown in
Referring to
Controller 19, connected to a personal computer (not shown), sequences laser diodes S1, S2, . . . , S9 so that two diodes receive 0° phase and 180° phase signals from splitter 20, every 0.1 sec. At the same time, controller 19 connects a symmetrically located PMT to SSB receiver 26. As shown in a timing diagram 40 (
In the next cycle, controller 19 directs switch 18 to connect laser diodes 2 (S2) and 3 (S3), which emit modulated light of a 0° phase and a 180° phase, respectively, and detector 2 (D2) detects light that has migrated in the breast tissue. Controller 19 also directs switch 27 to connect detector 2 to SSB receiver 26, which receives detection signal corresponding to the photons that have migrated from laser diodes 2 and 3 to detector 2. Again, phase detector 32 measures the phase (36) of the detected light, and SSB receiver 26 provides the amplitude (38) of the detected light. The duration of each pair of light flashes is 100 msec. The complete set of data for all source detector combinations is collected every 30 sec. A computer (not shown) stores the phase values and the amplitude values measured for the different combinations shown in timing diagram 40 and employs these values to create images of the examined tissue, as is described below. The computer uses the ADA2210 board for data acquisition.
Before or after the above-described measurement, phased array imaging system 15 may be calibrated on one or several models of the female breast. In the calibration procedure, the optical module is placed on the model and the imaging system collects the phase data and the amplitude data using the sequences shown in the timing diagram 40. The imaging system may use different breast models having the same scattering coefficient and the same absorption coefficient as the normal breast tissue of a female, for example, below 40 years and above 40 years. Due to the nature of the visible or infrared optical radiation, the described optical imaging systems may be used for breast tissue examination of a woman of any age. Furthermore, the models may have different sizes and have a shape of a female breast during examination. For example, the model has a shape of the breast (or the breast and a portion of the chest) of a woman lying on her back during examination.
Phased array imaging system 15 generates a “model” image for each wavelength employed. The model image may later be subtracted from the breast images to calibrate the system and also account for the boundary conditions of the light migrating in the tissue. Alternatively, phased array imaging system 15 is calibrated prior to taking measurement data and the gain on the light sources or the detectors is adjusted to obtain selected values.
Referring to
As shown in timing diagram 40 (
Initially the system takes quick pictures to find the area of interest so that the optical module can be moved around to find an optimal geometry. Once found, the 780 nm and 830 nm data (i.e., both the phase and amplitude data) is acquired and saved on a disk.
Several phased array systems were described in the PCT application PCT/US 93/05868 (published as WO 93/2514 on Dec. 23, 1993), which is incorporated by reference. This PCT publication also describes the basic principles of phase and amplitude cancellation. The phased array imaging system uses a detector for detecting light emitted from equidistant sources located symmetrically with respect to the detector (or one source and several equidistant detectors located symmetrically). If two sources S1 and S2 emit modulated light having equal amplitude and a 0° phase and a 180° phase, detector D1 located in the middle detects a null in the amplitude signal and detects a crossover between the 0° and 180° phase, i.e., a 90° phase, for substantially homogeneous tissue. That is, the detector is located on the null plane. In heterogeneous tissue, the null plane is displaced from the geometric midline. Nevertheless, the null establishes an extremely sensitive measure to perturbation by an absorber or scatterer. Furthermore, at the null condition, the system is relatively insensitive to amplitude fluctuations common to both light sources, and insensitive to inhomogeneities that affect a large tissue. The system has a high sensitivity to scattering provided that the scattering contrast is the same as the absorbing contrast. The system can readily observe shifts of 50 to 60° of phase under altered blood volume or blood oxygenation conditions, where the phase noise is less than a 0.1° (s/n>400) for a 1 Hz bandwidth. The amplitude signal is little less useful in imaging since the position indication is somewhat ambiguous, i.e., an increase of signal is observed regardless of the displacement of the absorbing object with respect to the null plane, although this is remedied by further encoding of the sources.
As described in the PCT application PCT/US 93/05868, the light sources excite a photon diffusion wave, which due to cancellation effects has a relatively long wavelength (˜10 cm), determined by the scattering (μs′=10 cm−1) and absorption (μa=0.04 cm−1) properties of the tissue. The photon diffusion wavelength of about 10 cm provides imaging in the “near field.” The imaging system may use light sources of one or several optical wavelengths in the visible to infrared range, depending on the characteristic to be imaged (i.e., blood volume, blood oxygenation, a distribution of a contrast agent in the tissue, an absorbing constituent of the tissue, a fluorescing constituent of the tissue, or other) The phase signal at zero crossing detection is essentially a square wave “overloaded” signal. It is moderately insensitive to the changes of signal amplitude that may occur in imaging from proximal to distal source-detector pairs and is also moderately insensitive to ambient light.
Referring to
A controller 140, connected to a personal computer, sequences laser diodes S1, S2, . . . , S9 using switch 102 so that two diodes receive modulate signal at a 0° phase and a 180° phase signals from splitter 104. At the same time, a controller 140 connects a symmetrically located PMT using a switch 130 to an amplifier 134. Amplifier 134 provides a detection signal (136) to double balance mixers 122 and 124, and to a DC detector 138. Double balance mixer 122 receives the detection signal (136) and the 0° phase reference signal (118) and provides an in-phase signal I (144). Double balance mixer 124 receives the detection signal (136) and the 90° phase reference signal (120) and provides a quadrature signal R (142). DC detector 138 provides DC signal (146). The in-phase signal I and quadrature signal R specify the phase (θ=tan−1 I/R) of the detected optical radiation and the amplitude (A=(R2+I2)1/2) of the detected optical radiation. This phase detection circuit was described in U.S. Pat. No. 5,553,614, which is incorporated by reference.
Similarly as for imaging systems 15 and 45, imaging system 100 directs controller 140 to sequence the laser diodes and the PMT detectors using timing diagram 40. The computer stores the phase value and the amplitude value measured for each of the combinations and generates images described below.
When no time multiplexing is performed, oscillator 106 operates in the 100 MHz region. Splitter 104 splits the oscillator waveform into 0° and 180° signals that are then attenuated by digitally controlled attenuators 107A and 107B by 0% to 10% in amplitude. The phase of the attenuated signals is appropriately shifted by digitally controlled phase shifters 109A and 109B in the range of 10°-30°, and preferably 20° in phase. Laser drivers 108A and 108B drive LD1 and LD2, respectively, which emit light of the same wavelength, for example, 780 or 800 nm. After the introduced light migrates in the examined tissued, a PMT detector D1 amplifies the detected signals having initially the 0 and 180° phases. As described above, for homogeneous tissue and symmetric locations of LD1, LD2 and D1, the output of the PMT is 90°, i.e., halfway between 0° and 180° and the amplitude is close to zero. The personal computer (PC) adjusts the attenuation provided by attenuator 107B and the phase shift provided by phase shifter 109B so that detector D1 detects phase nominally around 25° and amplitude nominally around ≦10 millivolts for homogeneous tissue. This signal is connected to amplifier 134 and to the IQ circuit 139. The cosine and sine signals are fed into the personal computer, which takes the amplitude (the square root of the sum of the squares of I and Q) and the phase angle (the angle whose tangent is I/Q) to give outputs of phase around 25° and amplitude signals around 10 millivolts. The personal computer also adjusts the reference signal to the IQ to have the phase φ3 between 10° to 30° and preferably around 25°, i.e., phase shifter 114 provides to the IQ circuit 139 the reference phase having a value selected by the combination of phase shifters 109A and 109B.
In a currently preferred embodiment, splitter 104 is a two way 180° power splitter model number ZSCJ-21, available from Mini-Circuits (P.O. Box 350186, Brooklyn, N.Y. 11235-0003). The phase shifters 109A, 109B and 114 and attenuators 107A, and 107B are also available from Mini-Circuits, wherein the attenuators can be high isolation amplifier MAN-1AD. IQ demodulator 139 is a demodulator MIQY-140D also available from Mini-Circuits.
The system obtains the initial values of attenuator 107B (A2) and phase shifter 109B (φ2) on a model or a symmetric tissue region (e.g., the contralateral breast that is tumor free). The entire probe is calibrated on a tissue model by storing the calibration values of A2 and φ2 for the various source-detector combinations (i.e., the baseline image). The probe is then moved to the breast, for example, and the phases and amplitudes are detected for the various source and detector combinations. When the contralateral tumor free breast is used as a model, the probe is transferred to the contralateral breast (taking note to rotate the probe because of the mirror image nature of the breast physiology) and then the images are read out from all the source-detector combinations to acquire the tissue image. There is no limitation on multiplexing as long as the bandwidth of F1 and F2 is recognized as being the limiting condition in the system normalization. It should be noted that normalization must be accurate and without “dither” and therefore, a significant amount of filtering in F1 and F2, i.e., less than 10 Hz bandwidth. If φ2 is adjusted over a large range, there will be an amplitude-phase crosstalk. Thus, the system may adjust phase and then amplitude and repeat these adjustments iteratively because of the amplitude phase crosstalk. The control of A1 and φ1 provides even a greater range of control, where obviously inverse signals would be applied to them, i.e., as the A1φ1 signals are increased, the A2, φ2 signals would be decreased. Both A2 and φ2 can be controlled by PIN diodes, to achieve an extremely wideband frequency range. However, since signal processing controls the bandwidth of the feedback system, that either PIN diode or relay control of the phase and amplitude is feasible for automatic compensation. If, in addition, dual wavelength or triple wavelength sources are used, each one of them must be separately calibrated because no two light sources can be in the same position relative to the imaged tissue (unless, of course, they are combined with optical fibers).
Referring to
Similarly as described above, controller 175, connected to a personal computer, sequences laser diodes S1, S2, . . . , S9 or laser diodes S1a, S2a, . . . , S9a using switch 152 so that two diodes emitting the same wavelength receive 0° phase and 180° phase signals from splitter 154. At the same time, controller 175 connects a symmetrically located PMT using a switch 178 to filter 180 and adjustable gain controller 182. Phase detector 184 provides the measured phase. Imaging system employs timing diagram 40 (
Referring to
Optical module 212 is connected to an analog circuit 202, which includes a source circuit 204 for controlling sources S1, S2, . . . S12. Optical module 212 is connected to a detector circuit 206, which controls diode detectors D1, D2, D3 and D4. In general, imaging system 200 can turn ON each source for a selected period in the range of 10−6 sec. to 0.1 sec., and one or several symmetrically located detectors are turned on simultaneously or sequentially to collect optical data. Specifically, as provided in Appendix B, one of sources S1, S2, . . . S12 is turned ON for 500 msec and the emitted light is introduced into the tissue from the corresponding input port. The introduced photons migrate over banana shaped paths in the examined tissue to a detection port. The corresponding detector is triggered 200 msec. after the source and collects light for 200 msec. A detection circuit 206 receives a detector signal from the diode detector. Detection circuit 206 enables correction for the dark current/noise that comprises background light, DC offset of the operational amplifiers, photodiode dark current, temperature effects on the outputs of individual components and variations due to changing environment.
Imaging system 200 performs data acquisition in four steps synchronized by its internal oscillator. The first step is performed by having the light sources OFF. The detector output is directed to an integrator 216 and integration capacitor 218 is charged to the dark level voltage. In the second step, the light source is turned ON and after 200 msec the preamplifier output that corresponds to the intensity of the detected light is directed to integrator 216 in a way to charge capacitor 218 with current of polarity opposite to the polarity of the charging current in the first step. This is achieved using an appropriate ON/OFF combination of switches A and B. The voltage of capacitor 218 is charging to a value that, after 200 msec., represents the total detected intensity minus the dark level noise signal. In the third step, both switches A and B are turned OFF to disconnect both the positive unity gain and the negative unity gain operational amplifiers (220 and 222). Then, the output of integrator 218 is moved via switch C to an analog-to-digital converter and the digital signal is stored in the memory of a computer. In the fourth step, the switches A, B and C are open and switch D is closed in order to discharge capacitor 218 through a 47K resistor. At this point, the circuit of integrator 216 is reset to zero and ready for the first step of the detection cycle.
Alternatively, analog circuit 202 may be replaced by a computer with an analog-to-digital converter and appropriate software that controls the entire operation of optical module 212. An algorithm that controls the sources and the detectors of optical module 212 in a similar way as described above. The detected dark level noise signal is digitally subtracted from the detected intensity of the introduced light.
The collected data sets are processed using an imaging algorithm. The imaging algorithm calculates the blood volume of the examined tissue for each source-detector combination for each data set. The imaging algorithm can also calculate the oxygenation of the examined tissue for each source-detector combination.
The blood volume or oxygenation images can be subtracted from “model” images. The blood volume image can be subtracted from the oxygenation image to create congruence data to localize and characterize a tissue anomaly. That is, the imaging algorithm creates an image using the differential image data sets. Prior to creating the image, an interpolation algorithm is employed to expand the differential image data set, containing 16 (4×4) data points, to an imaging data set containing 32×32 image points.
Alternatively, the computer uses a back-projection algorithm known in computed tomography (CT), which is modified for light diffusion and refraction and the banana like geometry employed by the optical imaging system. In the optical back-projection algorithm, the probabilistic concept of the “photon migration density” replaces the linear relationship of ballistically transmitted X-rays, for the beam representing pixels. The photon migration density denotes a probability that a photon introduced at the input port will occupy a specific pixel and reach the detection port. For different types of tissue, the phase modulation spectrophotometer provides the values of the scattering and absorption coefficients employed in the probability calculations. In the image reconstruction program, the probability is translated into a weight factor, when it is used to process back-projection. Back-projection algorithms known in CT may be used. The back-projection averages out the values of information that each beam carries with the weighting in each pixel. A weighting algorithm for creating a photon density image may be used in the back-projection reconstruction algorithm described above.
A method for correcting blurring and refraction used in the back-projection algorithm was described by S. B. Colak, H. Schomberg, G. W.'t Hooft, M. B. van der Mark on Mar. 12, 1996, in “Optical Back-projection Tomography in Heterogeneous Diffusive Media” which is incorporated by reference as if fully set forth herein. The references cited in this publication provide further information about the optical back-projection tomography and are incorporated by reference as if fully set forth herein.
Another embodiment of the amplitude cancellation imaging system 200 uses optical module 14 shown in
Alternatively, the amplitude cancellation imaging system uses light modulated at frequencies in the range of 0.1 to 100 kHz. The system employs the above-described algorithm, but the light sources emit frequency modulated light and the detectors, each connected to a lock-in amplifier, detect light modulated at the same frequency. This lock-in detection may further increase the signal to noise ratio by eliminating external noise. The detected light intensities are processed the same way as described above to image the examined tissue.
The intensity regulations for delivering continuous otherwise noncoherent light to the skin often depend on the temperature rise of the skin itself. For examination of large tissue volumes or deep tissues (i.e., where there is a large separation between the optical input and optical detection ports) relatively large light intensities are needed. Under conditions of prolonged even low level illumination, the skin may become uncomfortably warm and may blister. However, the erythemic effects are much smaller in the NIR, where the delivered heat is a factor, than they are in UVA and UVB, where cancer-producing damage may occur (but is not known for the NIR). The effect of the cooling air is not just convection of warm air away from the skin, but it enhances the evaporation of perspiration from the skin. Thus, as soon as the skin temperature rises and perspiration is initiated, greatly enhanced cooling is obtained with the forced air increasing the evaporation.
Referring to
Also referring to
Amplitude cancellation imaging system 260 is normalized on a tissue model by detecting signals for the individual source-detector combinations and appropriately normalizing the detected signal using the AGC control. The individual normalization/calibration amplitudes form a baseline image that is stored in the computer. As described above, the baseline image may also be acquired on a symmetric tissue region, such as the contralateral breast for breast tissue examination or the contralateral brain hemisphere for brain tissue examination. The normalization process can be repeated several times to account for drifts in the individual elements. During the measurement process, the personal computer can adjust the gain of each AGC 314 based on the calibration values that account only for the electronic drift. Then, the defected image is subtracted from the baseline image of the examined tissue. Alternatively, while collecting the measurement data on the examined tissue, the measurement image is subtracted from the baseline image to create the tissue image that includes any tissue in homogeneities such as a tumor or bleeding. The sample-and-hold circuit may be an analog circuit or the sample-and-hold function, including the filtering, may be performed digitally.
In the amplitude cancellation system 310, all light sources emit light at the same time into a selected tissue region. Each light source is modulated at a distinct frequency in the range of 1 kHz to 100 kHz. In order to resolve the modulated light signals and attribute them to the individual light sources, the oscillators operate at frequencies 1 kHz, 2 kHz, 4 kHz, 8 kHz, 16 kHz, . . . Filters 312 and 318 are designed to provide only the detection signal from a selected light source, and lock-in amplifier 312 provides the amplitude of the signal at the selected frequency. Frequency multiplex system 300 is calibrated the same way as the time multiplex system 260, and the normalization/calibration amplitude values are also stored in the personal computer. The images are processed as described above.
All above-described imagers will achieve a higher spacial resolution of the imaged tissue by increasing the number of sources and detectors. Furthermore, the sources and detectors may form various 1 dimensional, 1.5 dimensional, or 2 dimensional arrays as described in the above-referenced documents.
In a clinical study, which is provided only as an illustrative example, a number of female patients were examined using three different positions. First, the patients were sitting upright supporting the breast by the imager optical module. Second, the patients were lying face down with the breast on the optical module pad, and third, the patients were lying supine, on examination table 11, face up with the breast spread over the chest as evenly as possible as shown in
Initially, the imager was first calibrated on a breast model. During the examination, the patient or the attendant held optical probe 14 over a designated portion of the breast. The mirror image region on the contralateral breast was also recorded. The images were acquired in 8 sec from each breast taking advantage of a priori information obtained by palpation, X-ray mammography, ultrasound examination, fMRI, or a needle biopsy. Other images were taken having only palpation information so that the 10×10 cm2 active area of optical probe 14 covered the suspicious mass. The positioned probe may or may have not included the nipple, which is clearly visible on the optical images.
The optical images were created using a back-projection algorithm. The images may be displayed in the format of the left breast data minus the model data, the right breast data minus the model data for each wavelength (e.g., 750 and 830 nm). Alternatively, the model calibration may be performed by adjusting the detector gains prior to the breast measurements. Furthermore, the images may be the differential between the right breast and the left breast for each wavelength to emphasize any tissue difference, such as a suspicious mass, which is unlikely located symmetrically in both breasts. The images may also be processed to image blood volume and blood oxygenation of the examined tissue of each breast. The blood volume image is the sum of 0.3 times the 750 nm data and 1.0 times the 830 nm data. The blood deoxygenation image is the difference of the 750 nm and the 830 nm data. The above coefficients were derived from blood tests in model systems. The images have the highest specificity and sensitivity when the contralateral breast data is used as a baseline and both the blood volume data and the hemoglobin deoxygenation data is imaged and positional compared.
The blood volume and hemoglobin deoxygenation images provide an important tool in characterizing a suspicious anomaly in the examined breast. While the blood volume, hemoglobin oxygenation images and hemoglobin deoxygenation images, as well as the single wavelength images, are useful in locating an abnormal tissue region (i.e., detecting the abnormal structure), these images are also used to characterize the metabolism or pathology of the suspicious tissue anomaly. Specifically, an increased blood volume signal is observed with respect to the adipose tissue background due to the increased vascularity of a tumor as a consequence of angiogenetic factors. These factors include actively metabolizing regions and necrotic/apoptotic regions of the tumor. On the other hand, the hemoglobin deoxygenation signal is related to metabolic intensity. That is, the balance between oxygen delivery and oxygen uptake, which in tumors is usually balanced in favor of oxygen uptake exceeding oxygen delivery. The increased oxygen uptake occurs particularly for those tumors that are aggressively growing, and may well be metastatic.
By selecting an appropriate wavelength, or several wavelengths, sensitive to an optically active tissue property, the imaging system can non-invasively characterize a tissue anomaly. The above-mentioned wavelengths are sensitive to hemoglobin and hemoglobin oxygenation, but other wavelengths sensitive to absorption by any tissue constituent may be used. Furthermore, an optical contrast agent (e.g., cardiogreen, indocyanine green) may be injected intravenously. The imaging system will then use a wavelength sensitive to the administered contrast agent. The regions of increased blood volume will also have a higher content of the contrast agent.
Alternatively, differences in tissue scattering may be imaged. Due to differences in the optical refractive index, different types of tissue and different tissue solutes scatter light differently. The above-described imaging systems are also sensitive to scattering changes. The imaging system may use a wavelength that does not exhibit absorption changes for different types of tissue and different tissue solutes, but exhibits differences in scattering.
The following are examples of clinical data acquired by the amplitude cancellation system of
Discussion of the Images
The two-dimensional nature of
Bilateral Signals.
In these cases, bilateral congruence affords a diagnostic aid. In some cases, particularly in cancer bearing breast (point 13 (GR)), the left and right breast signals measured with respect to the model showed similar shapes and thus subtraction of the left and right mammographically dense breasts failed to give a recognizable object in the designated outer, lower portion of the left breast. While indeed a residual shape was seen at the bottom of the image, the region was not intense; the blood volume and the deoxygenation signals were about 0.9 and 0.4 V. However, when the model is used as a reference, the middle, left portion of the image gives signals 2 and 0.9 V. In this case, the signal is placed in Zone II in
Subject No. 30 (likely normal) showed distinctive signals in the left portion of the right breast, but showed no distinctive signals in the region of the right breast, which was heterogeneous and dense. This subject (No. 30) showed no significant features in the data of the left breast minus model, but the data of the right breast minus model showed a clear anomaly in both blood volume and deoxygenation. This anomaly appeared on the data of the right breast on the inner side along the midline providing a highly significant signal from a congruent volumes. This subject was scored at 2.5 V and 1.9 V having heterogeneously dense breast (43 year old) but no mammographically detected tumor.
Studies Referenced to the Model Breast.
No. 25 (KS) was found to have a mass near the nipple, 9-11 o'clock in the left breast. Both breasts were characterized by significant blood volume and deoxygenation signals as if the breast had unusual glandular or active metabolic characteristics. However, there was a very clear spot at the mammographically indicated region in the deoxygenation image with respect to the models, but little signal in the congruent position in the blood volume minus model image. On subtraction two, there is poor congruence, again a small image in deoxygenation, and large non-congruent image at the mammographic indication. Thus, I scored the optical data of subject 25 against the model (i.e., the left breast minus model) because of background interference from the contralateral breast. Subject 15 lacks the optical data on the model, but a shape in the blood volume with no congruence in oxygenation was detected.
The optical images of subject 8 (LA) had a “suspicious mass” below the nipple in both left breast and right breast. In fact, there was rather good congruence between the left and right breasts in the blood volume images but the “oxygenation mass” was distant from the “suspicious mass”. Thus, in the difference blood volume image the mass disappeared with no image left in the suspicious region.
A 23 year old subject (No. 9) showed a mammographically designated lower middle mass in the left breast. There is a congruent blood volume middle breast signal in both left and right breast showing a wide diffuse area of low intensity of deoxygenation in both breasts (about 1.8 V). The subject had similar anomalies in both breasts, with congruent deoxygenation. This subject was scored on the left breast only providing the values of about 1.8 and 0.5 V, respectively.
A 27 year old patient (No. 28) with fibroadenoma in the left breast near the midline displayed a very large blood volume signal of 3.8 V and a relatively small and diffuse deoxygenation signal with very poor congruence (0.7 V) placing the signal in Zone III.
Nipple Signal
In the contralateral (the right breast), the nipple shows as about a 1 cm shape in both the blood volume and deoxygenation images proving low signal levels of about 1 and 1.2 V, respectively (see
Two Dimensional Charts
Histograms shown in
Quantitation of Co-Registration.
In principle, vasculogenesis (blood volume) and hypermetabolism (tissue hypoxia) occur in similar and often identical tissue locations. Therefore, I evaluated the congruence of the blood volume and deoxygenation images to further reinforce the identity of a suspicious mass. The following method for quantitation of the congruence was performed pixel by pixel. The first step was the normalization of the two images to equalize the maximum signals. A computer program was used to select the area and obtain the integrated value for the spatial congruence residual and for the blood volume signal. Then, subtraction pixel-by-pixel provided a residual value on which to base an estimate of the congruence of the two shapes, blood volume and deoxygenation. This was carried out for those shapes which appear by inspection to be congruent and the integral of the residual non-zero pixels is compared to the total signal. A simpler evaluation procedure can take the maximum value of the difference and divide it by the maximum value of the normalized value for the two images.
The following test was applied to those images in the upper right region of
The diagram is summarized as follows:
For example, a red dot of a given size in the upper right hand quadrant of the diagram indicates a suspicious mass, having a large blood volume and a large deoxygenation with a high spatial congruence of the two parameters. Several measurements in this diagram either lacked congruence, lacked high blood volume, or lacked large blood deoxygenation. These are mainly in the lower left quadrant.
This preliminary study has employed a combination of angiogenesis and hypermetabolism as indices of tumor regenesis. While the study has been guided by mammographic/ultrasound location of the tumor volume, only in one case has that information been required to identify the site at which the optical measurements were to be taken, the resolution of the images of blood volume and deoxygenation is adequate to determine their congruence. The congruence level is at the >70% level for the images of cancer. Thus, morphology is an asset of these studies and a 2D projection of the tumor size is indicated by the images.
Localized increases of blood volume and of deoxygenation have been used as the principle criteria of this study, others may add to the sensitivity/specificity. The first one of these is an estimate of congruence which is over 80% for those studies in the upper right hand corner of the diagram and poor for those in the lower left sector.
Breast Matching Medium
In other studies we have employed the breast immersed in a liquid of μa, μs′ approximately matching the tumor, intending to render it optically invisible except for the inhomogeneity introduced by the tumor. This has been found to be quite important when transmission measurements are made through the breast. In the above study, however, each patient was lying on her back placing the breast against the chest, the body wall and ribcage, which created a matching background for the optical radiation. In the case of fatty breasts, the soft tissue “runs” over the chest and forms a thinner and optically more acceptable system, where the suspicious mass may be much better detected than in pendant breasts. The lymphatics could also be studied by this method.
Higher Resolution Images
In previous studies, optical tomography has attempted to mimic the X-ray image by a 2D projection of absorbance usually in 2 planes as shown, for example, by Fantini, et al. using a compressed breast and transmission time or frequency domain methods. The success of this techniques is based upon the ability of the radiologist to identify the structures of either scattering or absorbing material that differ from the normal breast.
However, a high resolution is required to delineate such structural features on which mammographic identification of cancer is usually based, and high resolution is time intensive as well as apparatus intensive, i.e., numerous source detector combinations are required to achieve resolution comparable to PET/MRI. In this study, imaging resolution is employed mainly to increase the signal to noise ratio in quantifying optical properties of the tumor with respect to the normal, often adipose tissue.
In the above systems, imaging resolution is employed mainly to increase the signal to noise ratio in quantifying optical properties of the tumor with respect to normal tissue, or with trespect to a model of a normal tissue. However, the blood volume, oxygenation and deoxygenation data collected by the optical systems do not depend critically upon high resolution imaging.
An optical system with an increased number of sources and detectors will render higher spatial resolution. Furthermore, a larger source-detector separation (i.e., the input port to detection port separation) achieves deeper penetration of the introduced optical radiation. By using selected separation values, the above-described imaging systems can collect three-dimensional optical data that are used for three dimensional reconstruction.
Additional embodiments are within the following claims:
This application is a continuation of U.S. application Ser. No. 09/622,184 filed on Jan. 24, 2001, now abandoned which is a 371 of PCT/US99/02953, filed Feb. 11, 1999, which claims priority from U.S. Provisional Application Ser. No. 60/074,504 filed on Feb. 11, 1998 and from U.S. Provisional Application Ser. No. 60/098,018 filed on Aug. 26, 1998, all of which are incorporated by reference as if fully set forth herein.
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