Is the 2 hr delayed Imaging really Needed in Gastric Emptying Scintigraphy ? Kyung Hoon Hwang, Wonsick Choe, Jong Ho Kim and Minki Yoon Dept. of Nuclear Medicine, Gachon Medical School, Incheon, Korea

Introduction  Gastric emptying (GE) scintigraphy is the well known physiologic study evaluating gastric motility.  GE values may be fit by adequate mathematical functions, thus, divergent mathematical models have been suggested.

Background  In most nuclear medicine practice, 2-hr delayed images are routinely taken for GE scintigraphy.  We investigated whether the 2-hr delayed GE values can be replaced by the calculated values using the simplified fitting equation in patients with normal to moderately delayed GE time.

Mathematical Models - I  Two most famous models 1) Elashoff Model - Power Exponential Function Y(t) = 2 (-t/T half ) 2) Siegel Model - Modified Power Exponential Function Y(t) = 1-(1-e -kt )  

Mathematical Models - II  Mathematical fitting of patient ’ s GE data to the known power exponential functions has been unsatisfactory. - Lag phase - Geometric change in attenuation  Besides, Known mathematical fitting models are complex and difficult to apply in practice.

Mathematical Model - III  We modified the well-known Siegel equation into more simple form fitted in only late phase. Y(t) = 1-(1-e -kt )  Y(t)  e (-kt)  A in late phase A: Y-intercept extrapolated from late emptying curve (usually >1). Modified to

Mathematical Model - IV  Then, applying Logarithm,  We can obtain the slope of the equation by linear regression from late (60 to 90 min) GE time data. - FR120 (fractional retention at 120 min) or other parameters can be predicted by this simple equation. Ln Y(t) = -kt + ln A

A h Y(t) = e (-kt)  A

Methods - I  GE time was measured using solid food (Fried eggs containing Tc-99m DTPA)  GE time data of 74 patients (M:F = 22:52) who have T 1/2 less than 200 min and FR120 less than 75% were retrospectively analyzed.

Geometric Mean Count was measured in the ROI of stomach.

Methods - II  The predicted T 1/2 and FR120 were calculated from linear regression of late GE values (60, 75 and 90 min), using modified exponential model.  The correlation between the predicted GE values and the measured ones was evaluated using Medcalc statistical software

Ln Predicted FR120 = e = (51.0%) Measured FR120 = (50.7%)

Results  A very significant correlation was found between the predicted FR120 and the measured one (r=0.95, p<0.0001).  There was also a significant correlation between the predicted T1/2 and the measured one (r=0.81, p<0.0001).

R=0.9515, p<0.0001

R=0.8137, p< T 1/2 Predicted T1/2

Conclusion  Highly reliable FR120 and T 1/2 could be predicted from the late GE time values by using the modified exponential function.  Therefore, 2-hr delayed measurement of GE time may be replaced by the values calculated from the late GE time values

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