Thickness of the gastric wall determined by megavoltage roentgenography.

Abstract

Diagnostic roentgenograms obtained with the use of generators of 1,000 or higher kvp have potential advantages over conventional roentgenograms. The coefficients of absorption of bone and soft tissue are nearly the same when exposed to rays of the megavoltage range. A wide separation, however, still remains between these coefficients and that of air (or other gas). These factors should have the effect of diminishing contrast between soft tissues and bone, thus enhancing the visualization of structures outlined by gas. The enhanced delineation more than compensates for the loss of contrast. The advantages of megavoltage have been observed in films of the chest and mediastinum (6, 7, 9, 10), the skull (4), and the pharynx and trachea, as well as in air myelograms and retroperitoneal air studies (6). A review of the literature revealed that the technic had not been applied in the diagnosis of gastrointestinal lesions, but one author has suggested its use (5). An experiment was designed to determine whether, in examining the air-outlined gastric wall, megavoltage roentgenograms offered advantages over conventional x-ray examinations. More specifically, a comparison was made between plain films, tomograms, and megavoltage roentgenograms. Method One or more artificial tumors were implanted in the gastric wall of 24 New Zealand white rabbits and 10 mongrel cats. The “tumors” were of two types. One was a small Lucite ovoid or sphere, 4 to 6 mm in diameter, sewn into the gastric wall through a small incision in the serosa and intended to simulate a localized tumor. The other was a measured volume (0.5 to 3.0 cc) of a heated, concentrated solution of clear gelatin injected beneath the serosa through a 17-gauge needle and intended to simulate an infiltrating tumor. The distal esophagus and proximal duodenum were ligated with umbilical tape, and the stomach was moderately distended by the introduction of air through a 25-gauge needle. The abdominal incision was sutured in 3 layers to ensure an airtight closure. The peritoneal space was then filled with gas through a 25-gauge needle inserted through the abdominal wall, and conventional films, tomograms, and megavoltage roentgenograms were obtained (Figs. 1, 2). The Massiot-Philips polytome was used with hypocycloidal movement. A 1 MeV-peak Maxitron generator was employed with a lead-screen cassette. DuPont Cronex Safety I film was used for all 3 of the procedures. The precise position of the “tumor” was recorded at the time of its insertion. Roentgenograms obtained by each of the 3 procedures were evaluated by an experienced radiologist. Those of the rabbits were evaluated twice, allowing a thirty-day interval between readings. The presence or absence of tumor, the type of tumor (localized or infiltrating), and the position were noted and recorded. Results In the experiments in rabbits, the “tumors” were detected with equal success on plain and megavoltage roentgenograms during the first reading (Table I).