Is the 2 hr delayed Imaging really Needed in Gastric Empt

ying 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 models1) Elashoff Model- Power Exponential Function

Y(t) = 2(-t/Thalf)

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 mod

els 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

Ah 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 T1/2 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 T1/2 and FR120 were calcu

lated 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

y = - 0.0076x + 0.23930

- 1

- 0.9

- 0.8

- 0.7

- 0.6

- 0.5

- 0.4

- 0.3

- 0.2

- 0.1

00 20 40 60 80 100 120 140

Ln

Predicted FR120 = e-0.673 = 0.510 (51.0%)

Measured FR120 = 0.507 (50.7%)

Results A very significant correlation was found b

etween 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).

0 10 20 30 40 50 60 70 80

Pred_FR120

80

70

60

50

40

30

20

10

0

120min

R=0.9515, p<0.0001

0 50 100 150 200 250 300

T0.5

500

400

300

200

100

0

-100

-200

predicted_0.5T

R=0.8137, p<0.0001

T1/2

Pred

icte

d T

1/2

Conclusion Highly reliable FR120 and T1/2 could be pred

icted 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

THE END