Eliot N. Heller

Simple techniques to reduce bowel activity in cardiac SPECT imaging.

Background and aimScatter from the bowel degrades image quality in 99mTc sestamibi myocardial perfusion imaging (MPI). Iodinated oral contrast, which has been used to outline bowel in medical imaging, absorbs X-rays as well as gamma rays. The purpose of this study was to test our hypothesis that iodinated oral contrast during MPI would absorb gamma rays emitted from 99mTc sestamibi in the bowel, thereby reducing scatter and improving cardiac SPECT images. Methods and resultsThirty subjects undergoing adenosine stress 99mTc sestamibi cardiac SPECT were randomized to receive either iodinated oral contrast (IOC), water or no intervention (controls). Subjects had 1 day rest–stress MPI using the adenosine stress protocol. Images were analysed using infra-cardiac counts, image variability, image contrast and the ratios of anterior to inferior and septal to lateral walls. The improvement in image contrast and variability between first and second images were significant in both the IOC and water groups. The IOC group had a more significant improvement in variability than did the water group. The reduction in infra-cardiac counts was also more significant in the IOC group. ConclusionThe use of oral contrast and water improved the image variability and contrast by decreasing the infra-cardiac scatter. The improvement was even more significant in the oral contrast group.

Acute ischemic dysfunction alters coronary flow reserve in remote nonischemic regions: potential mechanical etiology identified in an acute canine model.

BackgroundImpaired coronary flow reserve (CFR) has been observed in remote nonischemic regions in patients after myocardial infarction. The mechanism for this impairment in remote nonischemic CFR remains undefined. This study evaluates the effect of progressive regional ischemic dysfunction on function in remote nonischemic regions, and the effect of the extent of dysfunction on remote nonischemic coronary flow and CFR.MethodsIn an anesthetized open-chest canine model (n=7) of acute progressive distal and proximal left anterior descending (LAD) coronary artery occlusion, regional myocardial thickening fraction and coronary flow and CFR were measured with Doppler probes. CFR was assessed by an intracoronary injection of 36 μg of adenosine. Changes in thickening fraction and CFR were evaluated for isovolumic, ejection, and diastolic phases. Changes in resting regional flow were also assessed using radiolabeled microspheres. The extent of the ischemic area was defined as regions of myocardium with endocardial microsphere blood flow less than 0.3 mL/min/g.ResultsThe ischemic area increased from 12%±1% of left ventricle with distal occlusion to 30%±2% of left ventricle with proximal occlusion (P<.001). The LAD thickening fraction decreased significantly from baseline (18%±1%) to distal (−8%±1%,) and proximal (−4%±1%) occlusion (P<.001 for distal and proximal vs baseline). Isovolumic bulging in the LAD region was associated with a progressive increase in thickening fraction in the remote nonischemic left circumflex (LCX) artery region (baseline 12%±1%; distal occlusion 15%±2%, P=.014 vs baseline; proximal occlusion 17%±2%, P=.02 vs baseline). Most of the increase in remote thickening fraction occurred during the isovolumic phase. There was no significant change in resting flow in remote nonischemic LCX regions or global hemodynamic parameters. However, there was a progressive decrease in remote nonischemic CFR (baseline 2.44±0.3), distal occlusion (2.19±0.31; P=.055 vs baseline), and proximal occlusion (1.79±0.22; P=0.004 vs baseline, and P=.012 vs distal occlusion). A progressive decrease in CFR was noted in each phase of the cardiac cycle.ConclusionIn a canine model of acute progressive distal and proximal coronary occlusion, we observed a progressive decrease in CFR in remote nonischemic regions concurrent with an increase in the extent of ischemia. The decrease in remote nonischemic CFR was associated with ischemia-induced isovolumic bulging, which placed the remote regions at a mechanical disadvantage. These observations suggest a potential mechanical etiology for the observed impairment in remote CFR. Alterations in remote nonischemic CFR during acute ischemia may have important clinical implications for perfusion scintigraphy.

Quantification of technetium 99m-labeled sestamibi single-photon emission computed tomography based on mean counts improves accuracy for assessment of relative regional myocardial blood flow: Experimental validation in a canine model

BackgroundQuantification of single-photon emission computed tomographic (SPECT) images is generally based on determination of maximal counts on radial sectors of short-axis slices. We hypothesized that analysis of mean counts may reduce estimation error.Methods and ResultsWe compared quantitative 99mTc-labeled sestamibi (MIBI) SPECT based on maximal myocardial counts with that based on mean myocardial counts for accuracy of quantifying relative regional myocardial perfusion in a canine model of permanent left anterior descending coronary artery occlusion. MIBI and radiolabeled microspheres were injected during left anterior descending coronary artery occlusion. Relative microsphere myocardial blood flow was expressed as a percentage of normal (left circumflex coronary artery territory) blood flow. SPECT imaging was performed in vivo and ex vivo. Relative MIBI uptake on SPECT short-axis slices was quantified with normalized circumferential profiles based on maximal and mean counts. In vivo and ex vivo SPECT relative myocardial count density was compared to relative myocardial blood flow in six dogs. In the comparisons percent errors in estimating the relative blood flow and relative flow deficit with MIBI SPECT imaging were calculated. There was an excellent correlation between absolute myocardial tissue MIBI activity and regional myocardial blood flow for each of the six dogs (r=0.90 to 0.98) The correlations between relative myocardial count density on SPECT and relative blood flow for individual sectors were similar for maximal and mean count profiles (maximal, 0.79 to 0.83; mean, 0.77 to 0.82). Comparing the nadirs of in vivo and ex vivo circumferential count profiles, the correlations were slightly better (maximal, 0.82 to 0.91; mean, 0.87 to 0.91). Average percent errors in assessing relative blood flow and relative flow deficit were decreased significantly by use of mean count profiles (p<0.05).ConclusionsRelative SPECT count density with either maximal or mean count profiles correlated well with relative myocardial blood flow. Compared with maximal count profiles, quantification with mean count profiles improved estimation of relative flow.