Comparison of left anterior oblique, anterior and geometric mean methods for determining gastric emptying times.

The accurate determination of gastric emptying time requires correction or compensation for tissue attenuation. The gold standard for tissue attenuation correction for gastric emptying is the geometric mean of the gastric counts from the anterior and posterior views. For reasons of efficiency, many community hospitals acquire only the anterior projection. This study addressed the hypothesis that, using the left anterior oblique view alone, one can minimize the effect of variation in attenuation as the meal moves from the fundus to the stomach to the more anterior antrum to a degree equal to that of the geometric mean technique. We studied 42 consecutive patients using a standardized 300-g meal labeled with 650 muCi of 99mTc-sulfur colloid. The patients were imaged in the anterior (ANT), posterior (POST) and left anterior oblique (LAO) views every 15 min for 90 min. Linear regressions were obtained using the ANT, LAO and GM data. Cross-correlation of the T1/2 for 35 cases showed an R value for the GM versus LAO of 0.95 and GM versus ANT of 0.84. The p value greater than 0.49, for the paired two-tailed t-test of the LAO and GM methods. The p value for the ANT and GM methods is 0.0058 indicating a significant difference between these methods. The cross-correlation, F-test p and t-test p values support the hypothesis that there is no significant difference between the geometric mean and left anterior oblique gastric emptying times. It is therefore reasonable to substitute the left anterior oblique for routine GET when using a solid meal in patients with normal gastric anatomy, albeit altered physiology.