Kevin T. Schomacker

Colonic polyp differentiation using time-resolved autofluorescence spectroscopy

BACKGROUND Steady-state autofluorescence spectroscopy has been examined previously as a technique for distinguishing polyp types during colonoscopy. Although time-resolved methods have shown promise for tissue diagnosis in vitro, they have never been applied endoscopically. The aim of this study was to examine the feasibility of performing time-resolved autofluorescence spectroscopy in vivo and to determine the diagnostic accuracy of the technique as applied to colonic dysplasia. METHODS A time-resolved spectrometer was used to measure the spectrally resolved transient decay of laser-induced autofluorescence emission from colonic tissue in vivo. RESULTS Seventeen patients with 24 polyps (13 adenomatous, 11 non-adenomatous) were studied. The autofluorescence decay from adenomas was faster than that from non-adenomas. The measured decay time provided a means of distinguishing adenomas from non-adenomas with a sensitivity of 85%, a specificity of 91%, a positive predictive value of 92%, and a negative predictive value of 83%. CONCLUSIONS Time-resolved autofluorescence spectroscopy is a promising optical diagnostic technique for determining polyp types in vivo.

Diagnosis of bladder carcinoma using protoporphyrin IX fluorescence induced by 5-aminolaevulinic acid.

To report the results of a clinical study investigating the diagnosis of malignant and dysplastic bladder lesions by protoporphyrin IX (PPIX) fluorescence and to compare them with those from earlier studies.

Identification of Colonic Dysplasia and Neoplasia by Diffuse Reflectance Spectroscopy and Pattern Recognition Techniques

Diffuse reflectance spectroscopy of colonic tissue was employed to determine whether the spectra can be used to distinguish between neoplastic and non-neoplastic tissue in vivo. A total of 224 spectra were obtained in the wavelength range of 350–800 nm from 107 non-neoplastic tissue samples (84 normal mucosa, 23 hyperplastic polyps) and 53 neoplastic tissue samples (44 adenomatous polyps, 9 adenocarcinomas). Pattern recognition algorithms including multiple linear regression (MLR), linear discriminant analysis (LDA), and backpropagating neural network (BNN) were used to distinguish between the two tissue classes. The spectra were randomly separated into training and prediction sets for data analyses. The mean predictive accuracies of distinguishing neoplastic tissue from non-neoplastic tissue with MLR, LDA, and BNN were 85, 82, and 85%, respectively. In a similar fashion, the more clinically relevant problem of distinguishing adenomatous polyps from hyperplastic polyps was assessed. The mean predictive accuracies of distinguishing adenomatous polyps from hyperplastic polyps with MLR, LDA, and BNN were 85, 81, and 82%, respectively. The major spectral differences between tissues were attributed to changes in blood volume, oxygen saturation of hemoglobin, mean vessel depth within tissue, and tissue scattering.

Multiple-fiber probe design for fluorescence spectroscopy in tissue

The fiber-optic probe is an essential component of many quantitative fluorescence spectroscopy systems, enabling delivery of excitation light and collection of remitted fluorescence in a wide variety of clinical and laboratory situations. However, there is little information available on the role of illumination--collection geometry to guide the design of these components. Therefore we used a Monte Carlo model to investigate the effect of multifiber probe design parameters--numerical aperture, fiber diameter, source--collection fiber separation distance, and fiber-tissue spacer thickness--on light propagation and the origin of detected fluorescence. An excitation wavelength of 400 nm and an emission wavelength of 630 nm were simulated. Noteworthy effects included an increase in axial selectivity with decreasing fiber size and a transition with increasing fiber-tissue spacer size from a subsurface peak in fluorophore sensitivity to a nearly monotonic decrease typical of single-fiber probes. We provide theoretical evidence that probe design strongly affects tissue interrogation. Therefore application-specific customization of probe design may lead to improvements in the efficacy of fluorescence-based diagnostic devices.

Determination of Teflon thickness with laser speckle. I. Potential for burn depth diagnosis

A quantitative method for determining the depth of burn eschar would aid surgeons in determining whether to excise and subsequently graft a burn wound. We hypothesize that tissue viability could be assessed by an analysis of the spatial modulation of near-field laser speckle by flowing blood. A feasibility study of the technique was performed with two-layer tissue phantoms used to simulate a burn wound. A sheet of polytetrafluoroethylene (PTFE) was used to simulate nonperfused burn eschar, and tissue perfusion within deeper layers was represented by Brownian motion from a scattering solution. A low-power He-Ne laser was focused onto the target, and the resulting speckle image was captured with a CCD camera and stored on a computer for further processing. The diameter of the speckle pattern was found to be directly proportional to the thickness of the overlying layer. These data suggest that the thickness of PTFE can be determined to ±100-μm accuracy with 95% confidence and may be suitable for burn depth detection in vivo.

Use of the Er:YAG laser for improved plating in maxillofacial surgery: Comparison of bone healing in laser and drill osteotomies

Surgical reconstruction of bony defects in the maxillofacial region involves fixation of bony fragments with mini and micro plates. Bone stabilization during hole drilling is often challenging due to the need to apply pressure when using a conventional mechanical Hall drill. In addition, fragmentation of the fragile bones may occur and complicate the reconstruction. The pulsed Er:YAG laser offers an attractive alternative drilling modality because it does not require physical contact with the bone in order to drill holes, cuts bone with minimal thermal damage, and allows precise control of bone cutting. The objective of this study was to investigate the pulsed Er:YAG laser as an alternative to the mechanical bur by comparing bone healing using both modalities.

Laser induced autofluorescence diagnosis of bladder cancer.

PURPOSE We assessed the ability of laser induced autofluorescence to differentiate malignant from nonmalignant bladder lesions. MATERIALS AND METHODS We studied 53 patients with bladder cancer undergoing mucosal biopsies or transurethral resection of a bladder tumor. A quartz optical fiber was advanced through the working channel of a cystoscope and placed in gentle contact with the bladder. Tissue fluorescence was excited by 337 nm. light pulses (nitrogen laser). One fiber was used for transmission of the excitation and emission (fluorescence) light. An optical multichannel analyzer system was used to record fluorescence spectra of the sites of interest. RESULTS We analyzed the fluorescence spectra of 114 bladder areas (1 carcinoma in situ as well as 28 malignant, 35 inflammatory, 7 dysplastic, 1 squamous metaplastic and 42 normal areas). These lesions included 44 difficult to diagnose suspicious tumors (11 malignant and 33 nonmalignant). We developed an algorithm that used the I385:I455 nm. fluorescence ratio to distinguish malignant from nonmalignant lesions, including inflammatory areas. By analyzing the data on all 114 lesions, we noted the sensitivity, specificity, and positive and negative predictive values of this method for differentiating malignant from nonmalignant bladder lesions to be 97, 98, 93 and 99%, respectively. CONCLUSIONS Under excitation with 337 nm. light a clear differentiation between malignant and nonmalignant bladder tissues can be made using the I385:I455 nm. autofluorescence ratio.

Detection of high-grade dysplasia in Barrett's esophagus by spectroscopy measurement of 5-aminolevulinic acid-induced protoporphyrin IX fluorescence.

BACKGROUND Preliminary studies with qualitative detection methods suggest that 5-aminolevulinic acid-induced protoporphyrin IX fluorescence might improve the detection of dysplastic Barretts epithelium. This study used quantitative methods to determine whether aminolevulinic acid-induced protoporphyrin IX fluorescence can differentiate between Barretts mucosa with and without dysplasia. METHODS Patients were given 10 mg/kg of aminolevulinic acid orally 3 hours before endoscopy. Quantitative fluorescence spectra were acquired by using a nitrogen-pumped dye laser (l 400 nm) spectrograph system. The protoporphyrin IX fluorescence intensity at 635 nm was compared with the histopathologic diagnosis for mucosal biopsy specimens taken immediately after the fluorescence measurements. RESULTS Ninety-seven spectra were obtained from 20 patients. The mean (+/- standard error) standardized protoporphyrin IX fluorescence intensity was significantly greater (p < 0.05) for high-grade dysplastic Barretts epithelium (0.29 +/- 0.07, n = 13) than for nondysplastic Barretts epithelium (0.11 +/- 0.02, n = 43). By using protoporphyrin IX fluorescence alone, high-grade dysplasia was distinguished from nondysplastic tissue types with 77% sensitivity and 71% specificity. Decreased autofluorescence was particularly found in nodular high-grade dysplasia. By using the fluorescence intensity ratio of 635 nm/480 nm, nodular high-grade dysplasia could be differentiated from nondysplastic tissue with 100% sensitivity and 100% specificity. CONCLUSION Protoporphyrin IX fluorescence may be useful for identifying areas of high-grade dysplasia in Barretts esophagus and for targeting of biopsies.

Kinetics of cortical bone demineralization: Controlled demineralization—a new method for modifying cortical bone allografts

We investigated the kinetics of hydrochloric acid demineralization of human cortical bone with the objective of developing a method of controlled demineralization for structural bone allografts. It is known that the demineralization of cortical bone is a diffusion rate limited process with a sharp advancing reaction front. The demineralization kinetics of human cortical bone, described as the advance of the reaction front versus immersion time, were determined by measuring extraction of bone mineral in both planar and cylindrical geometries. Mathematical models based on diffusional mass transfer were developed to predict this process. The experimental data fit well with the behavior predicted by the model. The model for planar geometry is applicable to controlled demineralization of cortical bone allografts of irregular shapes such as cortical struts. The model for cylindrical geometry is appropriate when curved surfaces are involved such as in diaphyseal bone allografts. This method of demineralization has direct application to clinical modification of cortical bone allografts to potentially enhance their osteoinductive properties.

Light propagation in tissue during fluorescence spectroscopy with single-fiber probes

Fluorescence spectroscopy systems designed for clinical use commonly employ fiberoptic probes to deliver excitation light to a tissue site and collect remitted fluorescence. Although a wide variety of probes have been implemented, there is little known about the influence of probe design on light propagation and the origin of detected signals. In this study, we examined the effect of optical fiber diameter, probe-tissue spacing and numerical aperture on light propagation during fluorescence spectroscopy with a single-fiber probe. A Monte Carlo model was used to simulate light transport in tissue. Two distinct sets of excitation-emission wavelength pairs were studied (337/450 nm and 400/630 nm). Simulation results indicated that increasing fiber diameter or fiber-tissue spacing increased the mean excitation-emission photon pair pathlength and produced a transition from high selectivity for superficial fluorophores to a more homogeneous probing with depth. Increasing numerical aperture caused an increase in signal intensity, but axial emission profiles and pathlengths were not significantly affected for numerical aperture values less than 0.8. Tissue optics mechanisms and implications for probe design are discussed. This study indicates that single-fiber probe parameters can strongly affect fluorescence detection and should be considered in the design of optical diagnostic devices.