Sugako Kanayama

Myocardial distribution of (18)F-FDG and (99m)Tc-sestamibi on dual-isotope simultaneous acquisition SPET compared with PET.

Abstract. A dual-isotope simultaneous acquisition (DISA) single-photon emission tomography (SPET) protocol with fluorine-18 fluorodeoxyglucose (18F-FDG) and a technetium-99m labelled flow tracer is attractive because it permits assessment of both myocardial glucose utilisation and flow within a single study. Differences in physical and physiological characteristics between 18F-FDG and the 99mTc-labelled flow tracer, however, may cause differences in myocardial activity distribution between the agents. The aim of this study was to investigate the relation between the myocardial distribution of 18F-FDG and a 99mTc-labelled flow tracer on DISA SPET in comparison with nitrogen-13 ammonia/18F-FDG positron emission tomography (PET). Nine normal volunteers without cardiac disease and ten patients with known coronary artery disease (CAD) underwent 13N-ammonia/18F-FDG PET and 99mTc-sestamibi/18F-FDG DISA SPET. Using a semiquantitative polar map approach, the left ventricular myocardium was divided into nine segments, and relative regional activity was calculated for each segment. A segment was considered to have concordant uptake between 18F-FDG and flow tracer if the difference in measured regional activity between the tracers was ≤10% of peak activity, and the percentage of concordant segments was calculated for each subject. There was a good overall concordance of myocardial activity between the agents on DISA SPET (84.0%±14.8%) in normals, which was comparable to that seen on PET (86.4%±14.5%, NS vs DISA SPET). However, the myocardial activity distributions of 18F-FDG and flow tracer were not identical in that reduced flow tracer activity was seen in the basal segments on DISA SPET in both normals and CAD patients. It is concluded that there is good overall concordance of activity between 18F-FDG and flow tracer in normal myocardium on DISA SPET, which is comparable to that on PET, supporting the use of combined 99mTc-flow tracer/18F-FDG imaging for the detection of viable myocardium. However, there is a difference in the myocardial activity distribution between the agents in both normals and CAD patients, the difference being particularly evident in the basal segments. Therefore, careful image interpretation that takes into consideration the different normal activity distribution between the tracers and/or a tracer-specific normal database is necessary for comparison with patient studies.

Electrocardiographic-gated dual-isotope simultaneous acquisition SPECT using 18F-FDG and 99mTc-sestamibi to assess myocardial viability and function in a single study

PurposeDual-isotope simultaneous acquisition single-photon emission computed tomography (DISA SPECT) with 18F-fluorodeoxyglucose (FDG) and 99mTc-sestamibi appears attractive for the detection of viable myocardium because it permits simultaneous assessment of glucose utilisation and perfusion. Another potential benefit of this approach is that the measurement of left ventricular (LV) function may be possible by ECG gating. The aim of this study was to test the hypothesis that both myocardial viability and LV function can be assessed by a single ECG-gated 18F-FDG/99mTc-sestamibi DISA SPECT study, based on comparison with 18F-FDG/13N-ammonia positron emission tomography (PET) and magnetic resonance imaging (MRI) as reference techniques.MethodsThirty-three patients with prior myocardial infarction underwent ECG-gated 18F-FDG/99mTc-sestamibi DISA SPECT and 18F-FDG/13N-ammonia PET on a single day. Of these, 25 patients also underwent cine-MRI to assess LV function. The LV myocardium was divided into nine regions, and each region was classified as viable or scar using a semiquantitative visual scoring system as well as quantitative analysis. The global and regional LV function measured by gated SPECT was compared with the results of MRI.ResultsThere was good agreement in respect of viability (90–96%, κ 0.74–0.85) between DISA SPECT and PET by either visual or quantitative analysis. Furthermore, although both global and regional LV function measured by gated SPECT agreed with those by MRI, 99mTc-sestamibi showed a closer correlation with MRI than did 18F-FDG.ConclusionIn conclusion, ECG-gated DISA SPECT provides information on myocardial viability, as well as global and regional LV function, similar to that obtained by PET and MRI.

Effect of left ventricular function on diagnostic accuracy of FDG SPECT

ObjectivesFluorine-18 fluorodeoxyglucose (FDG) SPECT has emerged as an alternative to dedicated PET imaging. However, it remains uncertain whether FDG SPECT is an as accurate for viability assessment as FDG PET in patients with severely reduced left ventricular function. The aim of the study was to assess the diagnostic accuracy of FDG SPECT in a head-to-head comparison with FDG PET, and divide the patients according to the severity of left ventricular dysfunction.MethodsA total of 47 patients, with a history of myocardial infarction underwent FDG/perfusion (99mTc-sestamibi or201T1) SPECT as well as FDG/13N-ammonia PET. The patients were divided into 2 subgroups based on the left ventricular ejection fraction (LVEF) (35% cutoff). The left ventricular myocardium was divided into 13 segments, and each segment was classified as viable or scar using a semi-quantitative scoring system based on defect severity and the presence or absence of perfusion-FDG mismatch.ResultsOf the 47 patients studied, 23 had LVEF < 35% (low LVEF group; mean 25 ± 7%), whereas the remaining 24 had LVEF > 35% (high LVEF group; mean 47 ± 6%). In the low LVEF group, 213 segments (71%) were dysfunctional, as compared to 102 (33%) in the high LVEF group. The agreement for detection of viability between PET and SPECT in the low LVEF group was 82% (kappa 0.63), which was not different from the agreement in the high LVEF group (85%, kappa 0.66, p = 0.42 versus low LVEF group).ConclusionsThe results indicate that FDG SPECT can be used for tissue viability assessment regardless of the severity of left ventricular dysfunction.

Accuracy of cardiac PET imaging using post-injection transmission scan

The purpose of this study was to investigate the accuracy of cardiac PET with post-injection transmission scans.MethodsWe performed a phantom study using18F solution as well as13N-ammonia PET study of ten patients. The average activities of no myocardial defect phantom model were estimated, and myocardial defect sizes of 12 phantom models were measured by pre- and post-injection transmission methods at various18F activities. In13N-ammonia PET at rest and during adenosine triphosphate (ATP) stress studies, measured defect sizes were compared between both methods.ResultsThe ratios of average activity estimated by both methods (post/pre value) were almost 1.00 at each18F activity and segment. Measured defect sizes by both methods showed an excellent correlation with true defect sizes (r = 0.98, p < 0.01 for pre vs. true value: r = 0.98, p < 0.01 for post vs. true value). The mean absolute errors of measurements were minimal up to 3.5% LV, and were similar between both methods. Inl3N-ammonia PET, measured defect sizes by both methods also showed a good correlation (r = 0.97, p < 0.01).ConclusionThe results indicate that cardiac PET imaging with post-injection transmission scan provides information on myocardial tracer activity as well as myocardial defect size as does conventional pre-injection transmission method.

Case report: unstable angina with flow-fatty acid metabolism mismatch and reverse flow-glucose metabolism mismatch patterns.

A 79-year-old man with unstable angina underwent an emergency coronary angiography, and percutaneous balloon angioplasty was performed for LCX. Left ventriculography showed hypokinesis in the posterior wall, inferior and apical wall immediately after the PCI therapy. The defects on123I-BMIPP SPECT seen in the inferior, posterior and lateral wall were more extensive than those observed on99mTc-MIBI SPECT, and a flow-fatty acid metabolism mismatch pattern was observed. The18F-FDG PET showed reduced uptake in the lateral segment, although13N-NH3 PET showed normal perfusion, and a reverse flow-glucose metabolism mismatch pattern was observed. Left ventriculography showed significant improve to normal contraction on the 3-month follow up, and there was not significantly reduced uptake in99mTc-MIBI SPECT,123I-BMIPP SPECT,13N-NH3 PET or18F-FDG PET.