Variability of DACS Antral Contraction Frequency and Ejection Fraction in Normals

Introduction: Introduction: Fourier analysis(FA) of dynamic antral contraction scintigraphy (DACS) has been used to measure antral frequency and ejection fraction(EF). We utilize DACS software (MIM Software (Cleveland, OH)) which permits visual evaluation of all sequential antral contractions from the DACS imaging and have observed spontaneous, irregularities in the frequency and amplitude of antral contractions in symptomatic patients (Fig1). FA software typically includes composite analysis of all antral contractions. The purpose of this study was to quantitate the amount of variability of antral contractions observed in normal subjects during DACS using time activity curves(TAC) analysis and the potential for such analysis to detect significant gastric dysrhythmias in patients.

Methods: Gastric emptying (GE) studies with DACS imaging were analyzed in 22 normal subjects with normal GE results. We used the solid-meal, egg-white protocol of the current SNMMI GE guideline with a minimum of 74MBq(2 mCi) Tc sulfur colloid for radiolabeling. DACS included 1 sec/frame acquisitions for 10 min at time points (TP): t =30, 60, 120 min. Each DACS TP was reviewed and motion-corrected software was applied to eliminate movement artifacts. DACS was then analyzed by two observers (PS, AM). A 2 cm ROI was placed over the mid antrum to record a TAC from each DACS TP sequence. Both observers independently reviewed the TAC and measured the number of cycles where there were irregularities in frequency(peak-peak time interval) and/or EF (peak-peak amplitude) to obtain a % of irregular antral contractions for each TP utilizing caliper based measurements and to obtain a mean value for the two readers (Fig 2). Any % differences greater than 30% between the two readers were reviewed for a final consensus measurement.

Results: Of the 66 DACS TP analyzed (3 TP in each of 22 normal subjects), the readers excluded 12 TPs due to technical issues (2 subjects due to motion artifact (6 TP) and for low counts in 6 subjects at 120 min TP (6TP) leaving 54 TP for final analysis. Using Fourier analysis, the normal mean (5%,95% Confidence Intervals) frequency(cycle/min) results were: 3.08(2.67,3.33)@30 min; 2.86(2.76,3.48)@ 60 min and EF were: 27%(14, 36%) @ 30 min; 27%(19%,40%) at 60 min; and 32%(11%, 41%) @ 120 min. Using TAC analysis, the mean % irregular contractions for the two readers were: 9.9% with range (0-34.7%) @30 min; 11.7% with range (0-35.4%)@60 min and 11.3%% with range (0-23.1%)@120min).

Conclusions: Overall, there is a low occurrence (average of 11%) of irregular antral contractions observed during DACS in normals. These periods of spontaneous, irregular contractions (which can be up to 35%) observed may affect measurements of dominant frequency and EF by composite Fourier analysis. This suggests review of the DACS TAC should be performed routinely as a part of DACS analysis. Additional studies are needed to determine if the % dysrhythmia observed in symptomatic patients when compared to these normal results yields additional information on gastric dysmotility.

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