WO2011162721A1

WO2011162721A1 - Method and system for performing tissue measurements

Info

Publication number: WO2011162721A1
Application number: PCT/SG2011/000218
Authority: WO
Inventors: Zhiwei Huang
Original assignee: National University of Singapore
Current assignee: National University of Singapore
Priority date: 2010-06-25
Filing date: 2011-06-21
Publication date: 2011-12-29
Anticipated expiration: 2012-12-25
Also published as: SG177028A1

Abstract

A method and system for performing tissue measurements. The system comprising: an endoscope for providing illumination light and for acquiring detected light from the tissue; and optical means for directing a portion of the detected light to a spectrometer and another portion of the detected light to an image capturing means.

Description

METHOD AND SYSTEM FOR PERFORMING TISSUE MEASUREMENTS

FIELD OF INVENTION The invention relates to a method and system for performing tissue measurements.

BACKGROUND Head and neck cancer is one of the most common malignancies in humans worldwide due to its high incidence rates and mortalities. For instance, in the United States, more than 35,000 new cases of head and neck malignancies were reported in 2009, accounting for approximately 3% of all newly diagnosed cancers. In Singapore, over 2,000 patients between 35-50 years old have been diagnosed with head and neck cancer from 1998 to 2002. Early diagnosis and localization of head and neck cancer with effective treatment is critical to decreasing the mortality rates.

However, identification of early cancer can be difficult by using the conventional white-light reflectance (WLR) endoscopy, which relies on visualization of tissue morphological changes associated with neoplastic transformation. Subtle tissue changes may not be apparent, limiting its diagnostic accuracy. Positive endoscopic biopsy is the standard means for head and neck cancer diagnosis, but is invasive and impractical for screening high-risk patients who may have multiple suspicious lesions.

In the past two decades, autofluorescence (AF) imaging, which is capable of detecting the changes of endogenous fiuorophores and morphological architectures of tissue, has been developed to significantly improve the diagnostic sensitivity of early neoplastic lesions at endoscopy. However, AF imaging suffers from moderate diagnostic specificities.

Optical spectroscopic techniques, such as AF spectroscopy and diffuse reflectance (DR) spectroscopy, which provide information about tissue optical properties (e.g. absorption and scattering coefficients), morphologic structures, endogenous fiuorophores distribution, blood content (e.g. hemoglobin) and oxygenation associated with neoplastic transformation, have been comprehensively investigated for in vitro or in vivo precancer and cancer diagnosis in various organs with high diagnostic specificity.

A need therefore exists to provide a method and system for performing tissue measurements that seeks to address at least one of the abovementioned problems.

SUMMARY

According to the first aspect of the present invention, there is provided a system for performing tissue measurements, comprising: an endoscope for providing illumination light and for acquiring detected light from the tissue; and optical means for directing a portion of the detected light to a spectrometer and another portion of the detected light to an image capturing means. The system may further comprise a light source for providing the illumination light.

The light source may be configured to provide white light for white-light reflectance (WLR) imaging.

The light source may be configured to provide a selected wavelength of light for autofluorescence (AF) imaging.

The optical means may comprise a substantially transparent portion and a reflective portion.

The reflective portion may be disposed substantially at the centre of the substantially transparent portion. The optical means may be coupled to an actuating means for moving the optical means when directing a portion of the detected light to the spectrometer and another portion of the detected light to the image capturing means.

The reflective portion may comprise gold.

The substantially transparent portion may comprise quartz. The reflective portion may be about 100 μιη in diameter.

The light source may comprise one or more band-pass filters for selecting the wavelength of light provided for imaging.

According to the second aspect of the present invention, there is provided a method of performing tissue measurements, comprising the steps of: providing illumination light and acquiring detected light from the tissue using an endoscope; and directing, using an optical means, a portion of the detected light to a spectrometer and another portion of the detected light to an image capturing means.

The light source may provide the illumination light. The light source may be configured to provide white light for white-light reflectance (WLR) imaging.

The reflective portion may be disposed substantially at the centre of the substantially transparent portion.

The step of directing a portion of the detected light to a spectrometer and another portion of the detected light to an image capturing means comprises moving the optical means using an actuating means.

The reflective portion may comprise gold.

The substantially transparent portion may comprise quartz.

The reflective portion may be about 00 Mm in diameter. The method may further comprise the step of selecting the wavelength of light provided for imaging using one or more band-pass filters.

According to the third aspect of the present invention, there is provided a data storage medium having stored thereon computer program code means for instructing a computer system to execute the method of performing tissue measurements as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

Figure 1 is a schematic of a system for integrated point-wise spectroscopy and autofluorescence (AF) imaging for in vivo tissue measurements during endoscopy, according to an embodiment of the present invention. Figure 2a shows in vivo white-light reflectance (WLR) images and the corresponding diffuse reflectance (DR) spectra of different tissue sites, according to an embodiment of the present invention.

Figure 2b shows in vivo tissue AF images and the corresponding point-wise AF spectra of different tissue sites, according to an embodiment of the present invention.

Figure 3a shows in vivo AF spectral differences of different sites of the cheek, according to an embodiment of the present invention.

Figure 3b shows different fluorescent intensity distributions across different spots of the same imaged tissue, according to an embodiment of the present invention. Figure 4a shows a white light image of a tumor larynx tissue and a fluorescence image of a normal larynx tissue while Figure 4b shows the corresponding point-wise autofluorescence (AF) spectra of the normal and tumor larynx tissues, according to an embodiment of the present invention.

Figure 5a shows a white light image of a tumor nasopharyngeal tissue and a fluorescence image of a normal nasopharyngeal tissue while Figure 5b shows the corresponding point-wise autofluorescence (AF) spectra of the normal and tumor nasopharyngeal tissues, according to an embodiment of the present invention.

Figure 6a shows a white light image of a tumor colonic tissue and a fluorescence image of a normal colonic tissue while Figure 6b shows the corresponding point-wise autofluorescence (AF) spectra of the normal and tumor colonic tissues, according to an embodiment of the present invention.

Figure 7 is a schematic of a computer system for implementing the system for endoscopy in example embodiments.

Figure 8 shows in vivo point-wise diffuse reflectance spectra ± standard error of normal (n=58) and cancerous (n=48) ENT tissue, obtained using embodiments of the present invention.

Figure 9 shows principal component analysis-linear discriminant analysis (PCA-LDA) classification results of normal and cancerous tissues, obtained using embodiments of the present invention. Figure 10 shows a scatter plot of posterior probability for normal and cancerous tissue using PCA-LDA with "leave-one spectrum out, cross-validation" method, obtained using embodiments of the present invention.

Figure 1 shows a Receiver Operating Characteristic (ROC) curve, obtained using embodiments of the present invention.

Figure 12 is a flow chart illustrating a method of performing tissue measurements, according to an example embodiment of the present invention. DETAILED DESCRIPTION

Embodiments of the present invention provide a system for integrated point- wise spectroscopy (autofluorescence / diffuse reflectance) (AF/DR) and AF endoscopic imaging for real-time in vivo tissue measurements during endoscopy. The in vivo point-wise AF/DR spectra can be acquired from any specific area (-100 pm in diameter) of the imaged tissue of interest under AF/WLR imaging guidance during endoscopic examination.

According to an example embodiment, there is provided a unique point spectrum optical design to realize real-time AF imaging and AF / or diffuse reflectance (DR) spectroscopy measurements from a small area of tissue of interest on the AF image. Both the AF image and the point-wise AF/DR spectra can be simultaneously acquired from an oral cavity in vivo within 0.1 s, and significant changes in AF imaging and point-wise AF spectroscopy can be observed in cancerous colonic, head and neck tissues. Accordingly, embodiments of the present invention can facilitate in vivo tissue diagnosis and characterization at endoscopy. Some portions of the description which follows are explicitly or implicitly presented in terms of algorithms and functional or symbolic representations of operations on data within a computer memory. These algorithmic descriptions and functional or symbolic representations are the means used by those skilled in the data processing arts to convey most effectively the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self- consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities, such as electrical, magnetic or optical signals capable of being stored, transferred, combined, compared, and otherwise manipulated.

Unless specifically stated otherwise, and as apparent from the following, it will be appreciated that throughout the present specification, discussions utilizing terms such as "scanning", "calculating", "determining", "replacing", "generating", "initializing", "outputting", or the like, refer to the action and processes of a computer system, or similar electronic device, that manipulates and transforms data represented as physical quantities within the computer system into other data similarly represented as physical quantities within the computer system or other information storage, transmission or display devices.

The present specification also discloses apparatus for performing the operations of the methods. Such apparatus may be specially constructed for the required purposes, or may comprise a general purpose computer or other device selectively activated or reconfigured by a computer program stored in the computer. The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general purpose machines may be used with programs in accordance with the teachings herein. Alternatively, the construction of more specialized apparatus to perform the required method steps may be appropriate. The structure of a conventional general purpose computer will appear from the description below. In addition, the present specification also implicitly discloses a computer program, in that it would be apparent to the person skilled in the art that the individual steps of the method described herein may be put into effect by computer code. The computer program is not intended to be limited to any particular programming language and implementation thereof. It will be appreciated that a variety of programming languages and coding thereof may be used to implement the teachings of the disclosure contained herein. Moreover, the computer program is not intended to be limited to any particular control flow. There are many other variants of the computer program, which can use different control flows without departing from the spirit or scope of the invention.

Furthermore, one or more of the steps of the computer program may be performed in parallel rather than sequentially. Such a computer program may be stored on any computer readable medium. The computer readable medium may include storage devices such as magnetic or optical disks, memory chips, or other storage devices suitable for interfacing with a general purpose computer. The computer readable medium may also include a hard-wired medium such as exemplified in the Internet system, or wireless medium such as exemplified in the GSM mobile telephone system. The computer program when loaded and executed on such a general-purpose computer effectively results in an apparatus that implements the steps of the preferred method. The invention may also be implemented as hardware modules. More particular, in the hardware sense, a module is a functional hardware unit designed for use with other components or modules. For example, a module may be implemented using discrete electronic components, or it can form a portion of an entire electronic circuit such as an Application Specific Integrated Circuit (ASIC). Numerous other possibilities exist. Those skilled in the art will appreciate that the system can also be implemented as a combination of hardware and software modules. Figure 1 is a schematic, designated generally as reference numeral 100, of a system for integrated point-wise spectroscopy and autofluorescence (AF) imaging for in vivo tissue measurements during endoscopy, according to an embodiment of the present invention. The system 100 comprises a dedicated 300 W xenon short arc lamp 102 which is coupled with two customized band-pass (BP) filters 103 (BP1 : 400-700 nm for WL illumination; BP2: 375-440 nm for AF excitation) for AF/DR spectroscopy and imaging, a medical endoscope 104, a sensitive three-chip charge- coupled device (CCD) camera 106 having a red (R) channel (600-700 nm); green (G) channel (500-580 nm), and blue (B) channel (400-480 nm), a spectrograph 108 equipped with a CCD detector, and an optical adaptor 1 10.

The optical adaptor 10 facilitates simultaneous in vivo endoscopic imaging and point-wise AF/DR spectral measurements on any specific areas of an imaged tissue of interest. The optical adaptor 1 10 comprises three convex lenses 1 12/1 14/1 16 (f=50 mm), a thin quartz glass plate 1 18 (30 x 30 x 1 mm³) coated with a gold mirror 20 (diameter of about 100 pm, reflection of -99% in 400-1000 nm) and a 3-D motorized transiational stage 122. The gold mirror 120 is disposed substantially at the centre of the quartz glass plate 1 18.

For simultaneous AF imaging and spectroscopy measurements, a filtered blue excitation iight (375-440 nm) is conducted into the endoscope 104 via a flexible fiber-optic Iight guide 124 and shines onto a tissue through the fiber tip 104a of the endoscope 104. Tissue AF emitted from the tissue is collected by the same fiber tip 104a of the endoscope 104. Tissue fluorescence from the endoscope 104 is coupled into the optical adapter 1 10 by passing through a long pass filter 1 1 1 (cut off at 480 nm) for removing the interference of excitation Iight scattered from the tissue, and then is focused onto the quartz glass plate 1 18 which is positioned at the interim imaging plane of lens 1 12 with an orientation of 45° with respect to the incident Iight direction. The tissue fluorescence light passes through the 45° oriented glass plate 1 18 and is focused onto the 3-chip CCD camera 106 through lens 1 14 for fluorescence imaging measurements. Simultaneously, a very small portion of tissue fluorescence is reflected from the gold mirror 120 and focused (via lens 1 16) onto a 100 Mm fiber 123 which is connected to the spectrograph 108 (e.g. USB2000 - Ocean Optics Inc, Florida) for fluorescence spectroscopic measurements.

Further, in an example embodiment, automatic motorization of the gold mirror 120 in the optical adaptor 1 10 together with the point-wise spectrograph 108 facilitates rapid movement of the 100 μηι dark spot (due to reflection of the gold mirror 120) on the image to any spot of the imaged tissue of interest. In other words, by rapidly moving the 100 m reflection mirror 120 in the optical adapter 1 10, embodiments of the present invention can advantageously pinpoint the spectral properties of the specific areas of interest on the imaged tissue quickly. The 3D motorized translational stage 122, carrying both the optics 1 16 and the mirror 1 18, synchronously moves the mirror 1 18 and the optics 116 to maintain the light collected for spectroscopy in focus.

Accordingly, AF imaging and point-wise AF spectroscopy can be simultaneously acquired from the tissue without requiring a fiber-optic probe to pass down the instrument channel of the endoscope as in conventional endoscopic spectral measurements, which prolong endoscopic operation procedures.

Similarly, simultaneous WLR imaging and point-wise DR spectroscopy on the same tissue can be realized by switching the excitation iight filter to the white light illumination mode (BP1 : 400-700 nm) and removing the 480 nm LP filter in the optical adaptor 1 10.

In another embodiment of the present invention, there is provided a Labview- based software for real-time endoscopic image (WLR/AF) acquisition and point-wise spectral acquisition and processing (e.g. wavelength calibration, system spectral response calibration, CCD dark-noise subtraction, signal saturation detection, etc). Both the live AF/WLR image and AF/DR spectrum can be displayed on a computer monitor 126 for real-time review, and stored in a computer 128 for further analysis.

Figure 2a shows an example of in vivo WLR images 202/204/206/208 and the corresponding diffuse reflectance (DR) spectra of different tissue sites (i.e., chin 203, buccal mucosa 205, dorsal of the tongue 207, and lower lip 209) simultaneously acquired from a healthy volunteer using the system 100 under the white light illumination mode. Point-wise DR spectra from different anatomical locations (dark spots in the WLR images 202/204/206/208) in the oral cavity can be acquired within 10ms, and the absorption peaks (e.g. at 420, 540 and 580 nm) attributed to hemoglobin absorptions in the vessels can be clearly identified, with large absorption variations among different tissue locations.

In vivo tissue AF images and point-wise AF spectra can also be simultaneously acquired from the head and neck by swapping the excitation filter in the xenon lamp 102 to the blue BP filter (BP2: 375-440 nm). Figure 2b shows an example of in vivo tissue AF images 210/212/214/216 and the corresponding point- wise AF spectra of different tissue sites (i.e., chin 21 1 , buccal mucosa 213, dorsal of the tongue 215, and lower lip 217) simultaneously acquired from a healthy volunteer using the system 100. High quality in vivo tissue AF spectra can be acquired within 0.1 s from the dark spot areas on the AF images. The AF spectra from different anatomical tissue locations vary, revealing the differences in concentrations of endogenous fluorophores among different tissue locations. For instance, the prominent fluorescence peak at 535 nm for flavins is observed in all different tissues, but a much stronger fluorescence at 630 nm for protoporphyrins is found, particularly in the chin and the tongue. The AF images 210/212/214/216 in Figure 2b contain information about endogenous fluorophores distributions in tissue, and provide a higher image contrast as compared to WLR images 202/204/206/208 in Figure 2a. Embodiments of the present invention can reveal the inhomogeneity of endogenous fluorophores distributions in the same tissue. For example, using the system 100, in vivo AF spectral differences of different sites of the cheek can be obtained, as shown in Figure 3a. Furthermore, different fluorescent intensity distributions across different spots of the same imaged tissue can be observed, as shown in Figure 3b. Intensity profile (I) shows the distribution of endogenous fluorophore-flavins (autofluorescehce peaking at 535 nm) in the cheek. Intensity profile (II) shows the distribution of endogenous fluorophore-protoporphyrin (autofluorescence peaking at 630 nm) in the cheek. Embodiments of the present invention also provide sensitive diagnosis and detection of neoplastic lesions in humans. For example, Figure 4a shows a white light image of a tumor larynx tissue 402 and a fluorescence image of a normal larynx tissue 404. Figure 4b, designated generally as reference numeral 406, shows the corresponding point-wise autofluorescence (AF) spectra of the normal and tumor larynx tissues. Significant spectra changes and intensity changes can be observed in tumor larynx tissues.

Similarly, Figure 5a shows a white light image of a tumor nasopharyngeal tissue 502 and a fluorescence image of a normal nasopharyngeal tissue 504. Figure 5b, designated generally as reference numeral 506, shows the corresponding point- wise autofluorescence (AF) spectra with ± 1 standard deviations of the normal (n=20) and tumor (n=20) nasopharyngeal tissues.

Similarly, Figure 6a shows a white light image of a tumor colonic tissue 602 and a fluorescence image of a normal colonic tissue 604. Figure 6b, designated generally as reference numeral 606, shows the corresponding point-wise autofluorescence (AF) spectra of the normal and tumor colonic tissues.

Using embodiments of the present invention, the simultaneous acquisition of endoscopic autofluorescence (AF) image and AF spectrum from specific areas of imaged tissue in vivo can be realized within 0.1 s without introducing an optical fiber catheter through the instrument channel of the endoscope, which may facilitate the rapid, noninvasive, in vivo tissue diagnosis and characterization in clinical settings. Besides cancer diagnosis and detection in the colon, head and neck, it is envisioned that embodiments of the present invention can be readily adapted to study other internal organs in vivo by using different flexible medical endoscopes (e.g., bronchoscope, coionoscope, gastroscope, etc.).

The method and system of the example embodiment can be implemented on a computer system 700, schematically shown in Figure 7. It may be implemented as software, such as a computer program being executed within the computer system 700, and instructing the computer system 700 to conduct the method of the example embodiment.

The computer system 700 comprises a computer module 702, input modules such as a keyboard 704 and mouse 706 and a plurality of output devices such as a display 708, and printer 710. The computer module 702 is connected to a computer network 712 via a suitable transceiver device 714, to enable access to e.g. the Internet or other network systems such as Local Area Network (LAN) or Wide Area Network (WAN).

The computer module 702 in the example includes a processor 718, a Random Access Memory (RAM) 720 and a Read Only Memory (ROM) 722. The computer module 702 also includes a number of Input/Output (I/O) interfaces, for example I/O interface 724 to the display 708, and I/O interface 726 to the keyboard 704.

The components of the computer module 702 typically communicate via an interconnected bus 728 and in a manner known to the person skilled in the relevant art.

The application program is typically supplied to the user of the computer system 700 encoded on a data storage medium such as a CD-ROM or flash memory carrier and read utilising a corresponding data storage medium drive of a data storage device 730. The application program is read and controlled in its execution by the processor 718. Intermediate storage of program data maybe accomplished using RAM 720.

Figures 8 to 1 1 show experimental results obtained using embodiments of the present invention.

Figure 8 shows in vivo point-wise diffuse reflectance spectra ± standard error of normal (n=58) and cancerous (n=48) ENT tissue, obtained using embodiments of the present invention. Figure 9 shows principal component analysis-linear discriminant analysis

(PCA-LDA) classification results of normal and cancerous tissues, obtained using embodiments of the present invention.

Figure 10 shows a scatter plot of posterior probability for normal and cancerous tissue using PCA-LDA with "leave-one spectrum out, cross-validation" method, obtained using embodiments of the present invention. Figure 1 shows a Receiver Operating Characteristic (ROC) curve, obtained using embodiments of the present invention. The area under the ROC curve is 0.973 for PCA-LDA diagnostic algorithms.

Figure 12 is a flow chart, designated generally as reference numeral 1200, illustrating a method of performing tissue measurements, according to an example embodiment of the present invention. At step 1202, an endoscope is used to provide illumination light and acquire detected light from the tissue. At step 1204, an optical means is used to direct a portion of the detected light to a spectrometer and another portion of the detected light to an image capturing means.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the embodiments without departing from a spirit or scope of the invention as broadly described. The embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

Claims

CLAIMS . A system for performing tissue measurements, comprising:

an endoscope for providing illumination light and for acquiring detected light from the tissue; and

optical means for directing a portion of the detected light to a spectrometer and another portion of the detected light to an image capturing means. 2. The system as claimed in claim 1 , further comprising a light source for providing the illumination light.

3. The system as claimed in claim 2, wherein the light source is configured to provide white light for white-light reflectance (WLR) imaging.

4. The system as claimed in claim 2, wherein the light source is configured to provide a selected wavelength of light for autofluorescence (AF) imaging.

5. The system as claimed in any of the preceding claims, wherein the optical means comprises a substantially transparent portion and a reflective portion.

6. The system as claimed in claim 5, wherein the reflective portion is disposed substantially at the centre of the substantially transparent portion. 7. The system as claimed in any of the preceding claims, wherein the optical means is coupled to an actuating means for moving the optical means when directing a portion of the detected light to the spectrometer and another portion of the detected light to the image capturing means. 8. The system as claimed in any of claims 5 to 7, wherein the reflective portion comprises gold.

9. The system as claimed in any of any of claims 5 to 8, wherein the substantially transparent portion comprises quartz.

10. The system as claimed in any of claims 5 to 9, wherein the reflective portion is about 100 μιη in diameter. 1 1 . The system as claimed in any of claims 2 to 10, wherein the light source comprises one or more band-pass filters for selecting the wavelength of light provided for imaging.

12. A method of performing tissue measurements, comprising the steps of: providing illumination light and acquiring detected light from the tissue using an endoscope; and

directing, using an optical means, a portion of the detected light to a spectrometer and another portion of the detected light to an image capturing means.

13. The method as claimed in claim . 2, wherein a light source provides the illumination light.

14. The method as claimed in claim 13, wherein the light source is configured to provide white light for white-light reflectance (WLR) imaging. 5. The method as claimed in claim 13, wherein the light source is configured to provide a selected wavelength of light for autofluorescence (AF) imaging.

16. The method as claimed in any one of claims 12 to 15, wherein the optical means comprises a substantially transparent portion and a reflective portion. 17. The method as claimed in claim 16, wherein the reflective portion is disposed substantially at the centre of the substantially transparent portion.

18. The method as claimed in any one of claims 12 to 17, wherein the step of directing a portion of the detected light to a spectrometer and another portion of the detected light to an image capturing means comprises moving the optical means using an actuating means.

19. The method as claimed in any one of claims 16 to 18, wherein the reflective portion comprises gold.

20. The method as claimed in any one of claims 16 to 19, wherein the substantially transparent portion comprises quartz. 21. The method as claimed in any one of claims 16 to 20, wherein the reflective portion is about 100 μιτι in diameter.

22. The method as claimed in any one of claims 13 to 21 , further comprising the step of selecting the wavelength of light provided for imaging using one or more band-pass filters.

23. A data storage medium having stored thereon computer program code means for instructing a computer system to execute the method of performing tissue measurements, as claimed in any one of claims 12 to 22.