Recent Advances in Gastric Function Testing
contractions by computer-generated scoring systems (ranging from 0% for no contractions to 100% for complete lumen occlusion), including changes induced by prokinetic agents.41
MRI has several advantages that make it appealing as a novel modality. MRI can measure gastric emptying and accommodation globally as well as in specific regions. As opposed to ultrasonography, MRI can reliably measure both liquid and solid meal emptying42
and has the ability to
separately assess emptying of fat and water from the stomach. Finally, MRI is non-invasive, does not expose subjects to radiation, and can provide prolonged measurements of gastric emptying, volume, and wall motion in proximal and distal stomach regions simultaneously. However, MRI is limited by availability, cost, and time needed for interpretation of the study. Subjects must also remain in the supine position, which may slow gastric emptying, especially liquid emptying, as gravity is an important factor and so it may not be as physiologic. Because of its limited availability and cost, MRI may remain a tool employed mainly in academic centers and research until further clinical correlations can be made.
Single Photon Emission Computed Tomography Single photon emission computed tomography (SPECT) has been used to measure gastric volume and accommodation. 99mTc-pertechnate administered intravenously is taken up and secreted by the gastric mucosa (parietal and mucin-secreting cells). Tomographic images in an axial plane are then obtained with the patient in a supine position with a large field-of-view dual-head gamma camera system. The images are then processed to create three-dimensional images, which allows for total gastric volumes to be measured43
volume as well as accommodation of the entire stomach. However, SPECT remains a modality used primarily in research as it is not widely available in clinical practice and also exposes patients to radiation. SPECT can only assess gastric sensation in a dichotomous manner whereas gastric barostat can provide incremental measurements of gastric sensation. SPECT is also less responsive to changes in gastric volume because of the image capture time. Finally, similar to MRI, SPECT is performed with the patient in the supine position, which eliminates the force of gravity on gastric emptying. SPECT likely will be utilized mainly as a research tool given its lack of widespread availability.
Conclusion
Novel modalities to assess gastric function are currently available that can measure gastric emptying, motor function, and volume. These tests generally improve upon previous modalities in that they are less invasive and add valuable information regarding gastric physiology and pathophysiology. Most of these tests fail to address the issue of gastric sensitivity, which is one key area that needs further development, while gastric accommodation will also need further innovation. However, more common utilization of these tests will lead to further correlation of non-specific symptoms with underlying pathophysiology, which can then be used to treat gastric motility issues. n
(see Figure 5). Comparison of fasting and
There was excellent correlation (r = 0.8) between SPECT and gastric barostat in measuring gastric volume and accommodation. However, gastric volumes measured by SPECT were significantly greater than those by gastric barostat, although the volumes were significantly correlated. This is not surprising given that SPECT measures total gastric volume, while gastric barostat can only measure volume in the proximal or distal stomach, but not both simultaneously.44
SPECT has also shown good
Key advantages of this test over gastric barostat are that it is a non-invasive test that allows for measurement of total gastric
correlation with MRI in measurements of fasting and postprandial gastric volumes, but postprandial changes measured by SPECT were larger compared with MRI.45
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postprandial gastric volumes allows for estimation of gastric accommodation.44
Braden Kuo, MD, MSc, is Assistant in Medicine at Massachusetts General Hospital and Harvard Medical School. He is director of the GI Motility Laboratory at the GI Unit. He graduated from Jefferson Medical College and completed his internal medicine residency at University of Texas Southwestern and GI fellowship at Massachusetts General Hospital. He is an active member with the American Gastroenterology Association (AGA), American Neurogastroenterology Motility Society (ANMS), and the
International Foundation of Functional GI Disorders (IFFGD). He is supported by National Institutes of Health (NIH) grant K23 DK069614 and a grant from the IFFGD.
Allen Lee, MD, is a clinical fellow in the Department of Gastroenterology at Tufts Medical Center. He received his medical degree from New York Medical College in 2005. He completed his internship and residency in internal medicine at University of Michigan Hospital.
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