Endoscopic treatment for early gastric cancer (EGC) has been rapidly progressing and become common widely in recent days. Therefore, both the accurate diagnosis of the vertical invasion especially for a depressed lesion of the stomach and the exact evaluation for the therapeutic effect are required. Though the therapeutic effect on endoscopic treatment for EGC can be judged correctly by histopathological examination, other diagnostic approaches, which are safe, prompt and reliable, are thought to be necessary. We experimentally studied the possibility of differential diagnoses among four different layers of the gastric wall by means of Pulsed Photothermal Radiometry (PPTR). We developed a new fiber-optic PPTR method, in which an argon laser by pulse wave as an excitation light source was used and the thermal radiation from the surface was delivered through a As-S infrared glass fiber and observed by Au-Ge infrared detector. The detected signals were documented by a digital storage oscilloscope and the e-folding decay time was measured. This fiber has a 2mm external diameter and a 2m effective length. After the abdomen of a rabbit was surgically opened under the anesthesia, the greater curvature of the stomach was cut about 5cm in length, and the abovementioned PPTR method was performed. As a result, the e-folding decay time in each layer of the stomach was examined as follows: 119.06 ms in the mucosa, 32.50 ms in the submucosa, 38.77 ms in the proper muscle and 33.98 ms in the serosa. It was proved that the mucosal layer can be significantly differentiated from the other layers of the gastric wall. For clinically applying this method, several problems remain to be solved, such as an effet of mucus upon the mucosa, differencies of blood flow in each area and/or a distribution of parietal cells. When such a problem becomes to be solved clinically, this new fiber-optic PPTR method will play a definite role for diagnosing the vertical invasion of a depressed lesion and evaluating the therapeutic effect due to its simplicity and safety.
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