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Is the 2 hr delayed Imaging really Needed in Gastric Emptying Scintigraphy ?

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.

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Is the 2 hr delayed Imaging really Needed in Gastric Emptying Scintigraphy ?

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  1. 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

  2. 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.

  3. 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.

  4. Mathematical Models - I • Two most famous models 1) Elashoff Model - Power Exponential Function Y(t) = 2(-t/Thalf) 2) Siegel Model - Modified Power Exponential Function Y(t) = 1-(1-e-kt) 

  5. 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.

  6. 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 Modified to -------- A: Y-intercept extrapolated from late emptying curve (usually >1).

  7. 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

  8. Y(t) = e(-kt)A A h

  9. 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 T1/2 less than 200 min and FR120 less than 75% were retrospectively analyzed.

  10. Geometric Mean Count was measured in the ROI of stomach.

  11. Methods - II • The predicted T1/2 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

  12. Ln Predicted FR120 = e-0.673 = 0.510 (51.0%) Measured FR120 = 0.507 (50.7%)

  13. 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).

  14. R=0.9515, p<0.0001

  15. R=0.8137, p<0.0001 Predicted T1/2 T1/2

  16. Conclusion • Highly reliable FR120 and T1/2 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

  17. THE END

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