Scintigraphic assessment of proximal and distal phasic antral contraction synchronicity for evaluation of patients with suspected gastroparesis

Introduction: Conventional gastric emptying(GE) studies which measure only total GE fail to identify abnormal GE in approximately 50% of patients with a high clinical suspicion of gastropareis(GP). Antral hypomotility is a key component of gastroparesis(GP) with antral manometry showing reduced amplitude and frequency of antral contractions(AC) in the distal antrum. GE can be supplemented by cine images to record dynamic antral contraction scintigraphy (DACS). While DACS has been used to measure AC frequency and ejection fraction(EF) it has not previously been used to assess phasic proximal and distal AC.

Objectives: The purpose of this study was to assess the potential clinical utility of DACS for measuring synchronous, in-phase proximal and distal AC in patients with symptoms of GP.

Methods: DACS was performed on 21 normal subjects(NLS)(13M,8F; aged 36.5±13.2SD) and 50 patients(pts)(41F, 9M;aged 43.3±16.9SD)with suspected GP with a minimum dose of 74 MBq (2 mCi) Tc-99m sulfur colloid and 1 sec images obtained for 10 minutes after meal ingestion(t=0,30,60 min). The GE meal utilized the current standard adult-solid, liquid eggwhite and toast meal as per the SNNMI Adult GE Guideline 3.0. A MIM Encore(ver7.1) Software(Cleveland, OH) workflow was developed. A 2 cm region of interest was placed over the mid antrum to record a time activity curve(TAC) of AC. From the TAC the software calculates antral frequency and EF and formats a composite cine image set for Fourier(F) harmonic and amplitude analysis. Antral pixels are color-coded for F in-phase angles(Figure 1). A semi-automated thresholding calculates the % of pixels which are in-phase in the (distal + proximal)/total antrum(%Total) and the ratio of synchronous, in-phase proximal/distal pixels (RP/D). Clinical studies of pts with suspected GP were compared to NLS and correlated with results of conventional GE including: % total GE and power exponential fit of the t1/2 of GE.

Results: Of 50 pts, 30 had normal GE(NLP) by GE T1/2 and % GE @ 2hr and 4hr and 20 had delayed GE(ABNP). For NLS the antral EF @ 60 min(mean±2SD)=28±8% with a frequency =2.99±0.28 cycle/min. AC frequency did not correlate with GE measurements in the NLS or pts. NLS phase images show in-phase AC in the proximal and distal antrum separated by a band of peak amplitude which corresponds to visual to and fro bolus movement thru the mid antrum(Figure 1). At 1 hr NLS had excellent correlation of the %Total antral pixels with the % GE emptying at 2 hr(r = 0.97, p=0.04) with a mean %Total in-phase pixels = 44±11%(1 hr). The RP/D in NLS was not normally distributed with mean±95% confidence = 2.95±0.87(1hr). While not statistically significant for ABNP there was a trend in the linear correlation of the %Total at 1 hr with the GE at 1hr (r = 0.92, p=NS). Antral EF at 1 hr also had a similar linear correlation with %GE at 1 hr (r= 0.84, p=NS). Only 1 ABNP had an EF < 2 SD. None of the ABNP had an abnormal %Total but 14/20(70%) had an abnormal RP/D with 9 decreased and 5 increased. NLP also had a correlation of %GE and %Total (r=0.92,p=NS)) and EF(r = 0.85,p=NS)(1hr). None of the NLP had an abnormal EF or %Total however 20/30(67%) had an abnormal RP/D (18 decreased and 2 increased).

Conclusions: Antral EF and %Total of synchronous, in-phase proximal and distal antral pixels correlate with conventional GE % emptying in NLS and symptomatic patients. A majority(70%) of symptomatic patients with delayed GE demonstrate an abnormal ratio of in-phase proximal and distal AC. A similar percentage(67%) of symptomatic patients with otherwise normal GE also show an abnormal ratio of in-phase proximal and distal AC. These results show that enhanced GE with DACS can provide for an improved understanding of the underlying pathophysiology of antral dyssynergy and hypomotility which may help explain symptoms in patients with otherwise normal conventional GE results.

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