lumen and also to distend its cavity, it is necessary that the patient ingest contrast medium. Many contrast media are now available. The choice depends on indications and the possible sequence of imaging. In cases with revealed or suspected spread of infiltration to the esophagus and adjacent organs and structures, the zone of examination is expanded (D Fig. 44).
In order to rule out false results, MRI should be conducted at least 1 day (or two) after the X-ray examination, because the presence of minute traces of barium suspension in the stomach alters the signal (makes it less intensive) in spin echo pulse sequences, which may be mistaken for wall thickening. It must be noted here that the presence of barium sulphate in the intestinal loops does not cause artifacts (as is the case with computed tomography) and cannot be regarded as an absolute contraindication to MRI of the stomach on the day ofX-ray examination in cases where this is necessary for diagnostic indications.
The intensity of signals received from various tissues during MRI depends on factors such as proton rotation speed, time constants of longitudinal (Ti) and transverse (T2) relaxation, resonance sig nal frequencies characteristic of each particular tissue, chemical changes, magnetic sensitivity, associated current, perfusion, and other molecular processes. Signal intensity increases with the proton rotation speed or T2, or with decreasing Ti; signal intensity decreases with proton movement speed or T2, or with increasing Ti. Contrast substances thus influence signal intensity during MRI in the following three ways, viz., by changing the proton rotation speed, and also Ti or T2.
Water, the cheapest substance, increases the signal in T2 images homogeneously. Signal intensity in Ti images is intermediate. In order to distend the stomach adequately (depending on its size according to the findings ofthe traditional X-ray examination), the patient has to drink 500-800 ml of water in the horizontal position with his head tilted slightly upwards. It should be remembered that the rate of stomach evacuation slows down in a supine patient.
Air is a negative contrast medium immiscible with other substances. Air can be blown into the stomach through a thin elastic gastric tube or using special granulated powders. However, air intensifies peristalsis of the stomach and can therefore produce significant artifacts. When air is used as the contrast
□ Fig. 45a-d. Patient T., age 62. Diagnosis: gastric cancer. Anamnesis: The patient had complained of difficult swallowing for 3 months. Endoscopy revealed an infiltrative tumor in the abdominal segment of the esophagus, which significantly narrowed its lumen. It was impossible to examine the stomach because of the marked narrowing. In order to establish the initial location of the process, X-ray examination was recommended. a Stomach roentgenogram (tight filling, vertical position, anterior projection) at the moment of contrast medium passage through the gastroesophageal junction: marked narrowing of the abdominal segment of the esophagus due to circular infiltration (arrow). b Stomach roentgenogram (double contrast, horizontal position, left lateral projection): the anterior wall of the upper part of the stomach is thick, rigid; the relief of the cardiac rosette (cardioesophageal junction) is leveled, its specific radial pattern is absent (arrows). Conclusion: Infiltrative cancer of the upper part of the stomach with expansion to the esophagus. To verify the spread of the process, MRI was indicated. c MRI of the stomach (coronary projection, at level of upper part of the stomach, T2 image): uneven thickening of the fundus walls (black arrow) due to intramural infiltration with transition to the abdominal segment of the esophagus. The involved walls of the esophagus are markedly thickened due to circular infiltration (white arrow). d MRI of the stomach (sagittal projection, level of the upper part of the stomach and its body, T2 image): intramural infiltration of the anterior wall of the stomach body (arrows) with heterogeneous MR signal. In this particular case, diagnostic information was obtained only by radiological methods of examination in view of the objective infeasibility of adequate endoscopy with sampling of the necessary amount of material. MRI helped to detect the primary location of the tumor in the stomach and its spread to the esophagus
medium, it is necessary to medicate the patient in order to decrease peristalsis. Thus, the clinical use of air as a contrast medium in MRI is limited.
Solutions of contrast substances (1 ml/100 ml water) used in MRI are suitable for drinking because they are stable in the highly acid stomach conditions. Omniscan and Magnevist are not absorbed in the stomach walls, nor do they have any appreciable effect on peristalsis.
The second stage should be started with axial projection in conditions of Ti and T2 (the standard study protocol). For evaluation of the upper part of the stomach, the examination is supplemented with the coronary projection, and in order to estimate changes in the posterior and anterior walls in more detail, the study also includes an additional projection in the sagittal plane using the program with a delay, synchronization of respiration, and highspeed programs. For better visualization of the py-loric part, the sagittal projection with the patient in supine position is best; also good is positioning on the right side with an axial scanning plane, usually with administration of an additional portion of water for better filling of this part of the stomach. The section thickness and section spacing are selected in each individual case depending on the size and volume of the tumor (O Fig. 45) [69, 216].
Radiological diagnosis has been enriched with many new techniques which have significantly strengthened the potential of diagnosing gastric cancer. Ultrasonography, CT, and MRI are among these. Traditional X-ray methods also have high diagnostic potential owing to technical developments in digital X-ray technology. They should be returned to their rightful role in gastroenterology and, together with endoscopy, become the basic method of diagnosing gastric cancer.
In view of the changed accents in morphogenesis of gastric cancer and also in the location of primary cancer in various parts of the stomach, and above all, in view of an increased incidence of proximal cancer, new technologies - ultrasonography, CT, and MRI - must be actively employed as additional methods in verifying the diagnosis of gastric cancer. Each of these methods has its own advantages, which can help to clarify many cases.
While new technologies inevitably raise the problem of additional expenses, we and our colleagues have actively used new technologies in the radiological diagnosis of gastric cancer, and our experience shows that diagnostic problems can be solved by simple technologies at reasonable expenses.
Was this article helpful?