Selected interventions in nuclear medicine: gastrointestinal motor functions

Abstract

The measurement of gastrointestinal functions by the use of scintigraphy is established in clinical practice and research. The most commonly used test is the gastric-emptying test, which is acknowledged as the gold standard to measure gastric motility and is conducted according to a consensus statement from the national nuclear medicine and motility societies. Other techniques are somewhat more esoteric (eg, measurement of gastric accommodation with single-photon emission computed tomography) or the scintigraphic approach is not the acknowledged gold standard (eg, colonic transit, rectoanal angle, and emptying, esophageal transit). The performance characteristics of many of the scintigraphic measurements have been published and the pros and cons established in the literature. Pharmacologic interventions may also be used during scintigraphy to aid in diagnosis and treatment. Gastrointestinal scintigraphy is an integral and important component of the assessment of gastrointestinal function.

Figure 1

Gastric emptying, colonic filling and colonic transit in a patient with gastrointestinal symptoms. Regions of interest are drawn over the stomach and different regions of the colon in which isotope is identified. Note the delay in gastric emptying at 2 and 4 h, and the reduced colonic filling at 6 h (reflecting orocecal transit). At 6 h, note that the isotope is partly in the small bowel and partly in the colon. In the presence of delayed gastric emptying, reduced percent colonic filling should be interpreted with caution and may be normal. Colonic transit is within normal range. GC = geometric center, the weighted average of counts in the 4 colonic regions and stool.

Figure 2

Method using SPECT imaging to measure gastric volume during fasting and postprandially. After i.v. injection of ^99m Tc pertechnetate, transaxial images are obtained and subsequently 3-dimensional reconstructions of all transaxial images provides an estimate of gastric volumes.

Figure 3

Scintigraphic measurement of rectal emptying, perineal descent and recto-anal angle during simulated defecation. The instillation of radioisotope into the rectum allows measurement of the recto-anal angle with a lateral view image. Normally, at least 65% of the radiolabeled Veegum® should be excreted from the rectum; the degree of perineal descent relative to the pubococcygeal line is 5.8 cm (normal >1cm or <4.0 cm), and the rectoanal angle opening is <15°, suggesting abnormal emptying dynamics secondary to descending perineum syndrome. R-A=recto-anal angle