In vivo laser-induced fluorescence imaging of a rat pancreatic cancer with pheophorbide-a.

Laser-induced fluorescence (LIF) of pheophorbide-a (Ph-a) was used for imaging of a rat pancreatic tumor. Using a dimensionless function (the ratio of Ph-a fluorescence by bluish autofluorescence), the fluorescence contrasts between excised tumors and their paired pancreas were investigated up to 48 h after a 9 mg kg-1 Ph-a intravenous administration. Among five tested excitation wavelengths, 355 and 610 nm excitations gave the best distinctive contrasts, both 48 h after dye injection. The LIF imaging of six intrapancreatic tumors and six healthy pancreas was carried out in vivo using two laser excitations: 355 nm (Nd:YAG + tripling) for bluish autofluorescence and 610 nm (rhodamine 6G dye) for reddish autofluorescence and dye emission. Images were recorded through bandpass filters at 470 and 640 nm (autofluorescence) and at 680 nm (dye + autofluorescence) with an intensified charged-coupled device camera. Autofluorescence as Ph-a fluorescence images did not allow accurate LIF diagnosis of pancreatic carcinoma. An image processing, including for each pixel a computed division of Ph-a fluorescence (after subtraction of reddish autofluorescence) by bluish autofluorescence intensity generated poorly contrasted tumor images in five of six and false tumor localization in one of three of the tumor-bearing pancreas. A fitting of the digital 640 nm autofluorescence up to the mean 680 nm fluorescence intensity in pancreas prior to subtraction allowed a safe diagnosis to be made with well-contrasted tumor images. To assess automation ability of the processing, a same fitting coefficient (mean of individual values) was applied. In this way, false-negative (one of six) and false-positive (two of six) images were present in tumor-bearing animals as false-positive in one-half of the controls. A successful standardized procedure was then applied with a normalization of 640 and 680 nm pancreas intensities to a same set threshold prior processing. In opposition to thin-layered hollow organs, such as bronchial tube or digestive tract, LIF imaging of carcinoma inserted in a compact organ is exhausting. The use of a dye excitable in the red wavelength range (610 nm for Ph-a) may partly solve this problem, rendering LIF imaging more accurate and potentially automated.

KAMEDIN: a telemedicine system for computer supported cooperative work and remote image analysis in radiology.

The software system KAMEDIN (Kooperatives Arbeiten und MEdizinische Diagnostik auf Innovativen Netzen) is a multimedia telemedicine system for exchange, cooperative diagnostics, and remote analysis of digital medical image data. It provides components for visualisation, processing, and synchronised audio-visual discussion of medical images. Techniques of computer supported cooperative work (CSCW) synchronise user interactions during a teleconference. Visibility of both local and remote cursor on the conference workstations facilitates telepointing and reinforces the conference partner's telepresence. Audio communication during teleconferences is supported by an integrated audio component. Furthermore, brain tissue segmentation with artificial neural networks can be performed on an external supercomputer as a remote image analysis procedure. KAMEDIN is designed as a low cost CSCW tool for ISDN based telecommunication. However it can be used on any TCP/IP supporting network. In a field test, KAMEDIN was installed in 15 clinics and medical departments to validate the systems' usability. The telemedicine system KAMEDIN has been developed, tested, and evaluated within a research project sponsored by German Telekom.

Image transfer and computer-supported cooperative diagnosis.

The KAMEDIN system was designed as a low-cost communication tool as part of a computer-supported cooperative work project that included synchronized user interaction, telepointing and audioconferencing. During a five-month field trial, it was used for medical image transfer and cooperative diagnosis in 14 clinics and medical departments in Germany. During the field test, 297 teleconsultations were performed via ISDN and 875 MByte of data were transferred. An image compression ratio of 2-3 was obtained, so that the total quantity of data transferred corresponded to 14,000-21,000 magnetic resonance images or 3500-5250 computerized tomography images. Furthermore, 694 local sessions were conducted for the preparation of teleconsultations and the review of transferred images. Participants learned to handle the KAMEDIN system in a few hours. This was mainly owing to the design of the user-oriented graphical user interface and the restriction of the system to a set of essential image-processing functions.

Photodynamic imaging of a rat pancreatic cancer with pheophorbide a.

Laser-induced fluorescence of pheophorbide a (Ph-a) was used for in vitro photodynamic imaging (PDI) of a rat pancreatic acinar tumor. A 400 nm excitation induced a 470 nm autofluorescence and a 678 nm dye fluorescence in tumors and their surrounding pancreas 24 h after a 9 mg kg-1 body weight Ph-a intravenous administration. With lower intensities in these blood-rich tumors than in pancreas, Ph-a fluorescence signals are unable to provide tumor images. A dimensionless function (the ratio of Ph-a fluorescence by autofluorescence, called Rt for the tumor and Rp for the pancreas) was used for fluorescence contrast calculation (C = Rt/Rp) between six tumors and their paired pancreas. Among five available laser excitation wave-lengths, only the 355 nm excitation gave a distinctive contrast (C = 1.5). The PDI of six intrapancreatic tumors and their intraperitoneal metastasis and of two control normal pancreas was thus performed ex vivo using a 355 nm excitation source delivered by a tripled Nd:YAG laser and a charged-coupled device camera. Fluorescence images were recorded at 680 nm (dye), 640 nm (background) and 470 nm (autofluorescence) through three corresponding 10 nm width bandpass filters. Computed division for each pixel of Ph-a fluorescence values by autofluorescence generated false color image. In this way, contrasted tumor images were obtained. But in five out of six animals false-positive images were present due to an autofluorescence decrease in some normal pancreatic areas. A 470 nm autofluorescence imaging on the same tumors gave in all cases false-positive image and false-negative in half of the cases. These observations suggest that autofluorescence alone is unable to achieve accurate PDI of pancreatic carcinoma and that using Ph-a as a PDI dye needs strong improvements.

ISDN based teleradiology and image analysis with the software system KAMEDIN.

This contribution describes the software system KAMEDIN (Kooperatives Arbeiten und MEdizinische Diagnostik auf Innovativen Netzen) that is designed as an ISDN based computer supported cooperative work (CSCW) tool for usage in medical diagnostics. Medical image data from various sources (for example CT and MR) can be interchanged and analyzed in bilateral teleconferences via ISDN. During a cooperative session, user interactions for image processing etc., are synchronized and performed on both workstations, Features like telepointing, remote control, and audio connection enhance communication quality. With ISDN as a transmission line, widespread availability and low communication costs are achieved. Further, automatic tissue labeling in intracranial MR data can be invoked. For this purpose, artificial neural network classifiers such as multilayer perceptron and Kohenen feature map are integrated. Classification results can be viewed as 3D-reconstructions.

Experimental photodynamic therapy with a copper metal vapor laser in colorectal cancer.

In an attempt to define the best conditions for an adjunctive treatment of residual colonic microtumors by photodynamic therapy (PDT), an experimental model has been defined. S.c. HT29 colonic-cancer-cell tumors grown in nude mice were used and, 48 hr after i.p. administration of 30 mg/kg Photofrin (PH), laser illumination was performed with 75 or 150 Joules/cm2. The efficiencies of 2 lasers, the classically used rhodamine laser (RL) and a copper metal vapor laser (CMVL), were compared. The effects of PDT were assessed by histological and immunocytochemical (detection of a digestive enzyme, dipeptidyl-peptidase IV, as a marker of cell viability) follow-up and by the growth curve of the tumors after illumination. We conclude that, although the depth of necrosis resulting from PDT was nearly 3 mm at 75 J/cm2 and nearly 4-5 mm at 150 J/cm2 with both lasers, complete necrosis was obtained only with the CMVL at 150 J/cm2 (in 50% of the tumors). Under the other conditions, a layer of unaffected cells persisted at the pole opposite to laser illumination, resulting in growth curves lower than but parallel to those of the controls. Analysis of drug concentrations in the tumors and various organs, 48 hr after injection, i.e., at the time of laser illumination, revealed the presence of 21 micrograms/g dry weight PH in the tumors. The tumor vs. host-organ ratios were equal to or higher than 1 for the small bowel, colon, stomach, lung, skin and muscle. In contrast, the ratios were below 1 for the spleen, pancreas, kidney and liver.

[Photodynamic therapy in oncological digestive tract surgery]. / La thérapie photodynamique en chirurgie digestive oncologique.

Photodynamic therapy is a useful new antitumoral treatment, since it is relatively selective and noniatrogenic. The photosensitizers become preferentially localized in the tumoral tissue, where their excitation by light causes the production of free cytotoxic radicals. If haematoporphyrin derivatives are the most widely used photosensitizers, numerous molecules are being tested. Now used as a palliative photodynamic therapy could logically be used as adjuvant treatment in curative surgical excision. The practical utility of peroperative photodynamic therapy in gastroenterological surgery is being evaluated experimentally and clinically.