Gastric cancer is one of the most prevalent types of cancer in the world. If gastric cancer is found early, the five-year survival rate increases nearly 90 percent. In contrast, most patients with advanced gastric cancer have a poor prognosis. Gastric cancer is classified as elevated, flat and depressed types. Despite improvements in endoscopic technologies, depressed-type early gastric cancer is challenging to diagnose because it manifests as subtle changes in colour and shape. Variations in colour, however, can also mean inflammation, so it is difficult to determine what is benign and what is malignant. Therefore, biopsies must then be taken.
"In our comparative study, the optimal band imaging system with endoscopy showed contrasting images that could delineate the depressed-type early gastric cancers more easily than conventional endoscopy," said the study's lead author Hiroyuki Osawa, MD, Jichi Medical University. "A distinct demarcation was observed endoscopically between the reddish images of the cancerous lesion and the yellowish images of the surrounding noncancerous area. This is the first report of optimal band images for early gastric cancer."
Optimal band imaging (OBI) was developed with the aim of enhancing the capillary pattern and pit patterns of lesions in endoscopic images. In contrast to narrow band imaging, in which the bandwidth of spectral transmittance is narrowed by optical filters, the OBI system is based on a new spectral estimation technique that replaces the need for optical filters. OBI takes an ordinary endoscopic image from the video processor and arithmetically processes the reflected photons to reconstitute virtual images for a choice of different wavelengths.
Patients and Methods
An OBI system with electronic endoscope for the upper-gastrointestinal tract was used in this prospective study. Twenty-seven patients between May and December 2006 who were diagnosed with conventional endoscopy as having depressed-type early gastric cancer participated in the study. The mean age of the patients was 65.3 years with 23 men and four women. Twenty-four patients were diagnosed with differentiated adenocarcinoma and three patients with undifferentiated adenocarcinoma by the histopathologic evaluation of biopsy specimens. Researchers used the OBI system without magnification to observe the entire stomach because of the ample light intensity.
Results
With the OBI system, depressed type-early gastric cancer in 26 of 27 cases were easily identified because it clearly showed contrasting demarcation lines between the reddish images of the cancerous lesions and the yellowish images of the surrounding noncancerous area. A 40-fold magnification was then applied to observe the pit pattern, the disappearance of pit pattern or an irregular microvascular pattern of the cancerous lesions. This further enhanced the demarcation of the cancer and the noncancerous areas.
Researchers concluded that OBI images were better than conventional endoscopy images in identifying depressed-type early gastric cancer, but said that further study is warranted. They noted that even medical students, who had not had considerable amounts of clinical endoscopic experience, were able to easily identify the demarcation line between cancer and noncancerous areas in optimal band images versus conventional endoscopic images. OBI is available even without magnification during routine endoscopy because the system provides the same light intensity as conventional endoscopy. The researchers stated that such non-magnified optimal band images may be ideal for screening, whereas magnified optimal band images are more suitable for detailed examination of early gastric cancer.
