Comparison of left anterior oblique and geometric mean gastric emptying.

A left anterior oblique image (LAO) and the geometric mean of anterior and posterior counts have both been proposed as methods for acquiring gastric emptying data. Both approaches are used to correct for the changes in attenuation that occur as the depth of radiolabeled solids changes during gastric emptying. These two methods were compared by using a power exponential curve fit to calculate a lag phase, an equilibrium emptying rate, and a half-time for gastric emptying in 20 patients. There were no significant differences (mean +/- 1 s.e.m.) in the measured half-emptying time (115 +/- 10 versus 104 +/- 7 min) (p = 0.08) or rate of gastric emptying (0.015 +/- 0.002 versus 0.015 +/- 0.002 min-1) (p = 0.56) for LAO imaging versus the geometric mean. However, the LAO measurements of the lag phase were significantly higher (69 +/- 7 min) than the geometric mean (53 +/- 6 min) measurements (p = 0.004). This resulted in 4/20 (20%) of patients with normal geometric mean lag phase measurements who would have been reclassified as abnormal using the LAO method.