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Objective: Estimation of myocardial blood flow (MBF) and coronary flow reserve (CFR) by SPECT myocardial perfusion imaging (MPI) remains challenging. Our aim was to approximate MBF and CFR by quantifying the absolute Tc-99m tetrofosmin retention in the myocardium via gated-SPECT/CT MPI., Methods: Tracer retention was calculated on the basis of the microsphere kinetic model and served as an index of MBF at stress and rest (sMBFi, rMBFi). CFR was given by the sMBFi/rMBFi ratio. A planar first-pass acquisition during dipyridamole stress and at rest provided the data for tracer input determination. The input was represented by the integral of a gamma variate fitted on the time-activity curve of the left ventricle. Gated-SPECT/CT was performed 1 h post tracer injection and myocardial activity was measured in attenuation-corrected transaxial slices by a threshold VOI. The input was also compensated for tissue attenuation by measuring the distance from the centre of the left ventricle to the body surface on fused SPECT/CT slices. Input and uptake results were adjusted for planar-SPECT counting geometry differences by the aid of a phantom experiment. Thirty-nine subjects with low probability of coronary artery disease (CAD), age lower than 75 years and normal MPI (control group) were compared with 57 patients with documented CAD (CAD group)., Results: CFR and sMBFi values of CAD patients (1.39 ± 0.37 and 1.42 ± 0.35 ml/min/g) were considerably lower (p < 0.0001) than controls (1.68 ± 0.25 and 1.72 ± 0.37 ml/min/g). Significant difference in CFR (p = 0.03) was also noted between CAD patients with normal MPI (1.48 ± 0.38) and controls. However, sMBFi managed to discriminate certain CAD subgroups (normal MPI/ischemia/scar/scar and ischemia) more efficiently than CFR. Maximum heart rate-blood pressure product (RPP) during stress was an independent predictor of sMBFi and CFR. The other independent CFR correlates were resting RPP and diabetes mellitus, while sMBFi was associated with age, sex, smoking, and stress perfusion defects., Conclusions: Despite the low myocardial extraction fraction of Tc-99m tetrofosmin, an approximation of MBF and CFR is feasible with gated-SPECT/CT MPI. These flow indices together were able to discriminate CAD patients from controls and stratify different patient subgroups.

Objective: Previous studies indicate that the quality of single photon emission tomography/computed tomography (SPET/CT) myocardial perfusion imaging (MPI) is degraded by even mild transmission-emission misregistrations. The purpose of the current study was to investigate the impact of SPET/CT misalignment on the interpretation of MPI and examine the value of a commercial software application for registration correction., Subjects and Methods: A total of 255 technetium-99m ((99m)Tc)-tetrofosmin stress/rest MPI examinations in 150 patients were reviewed for SPET/CT misalignment. After registration correction by the software, images were reassessed for interpretation differences from the misregistered study. The diagnostic benefit of reregistration was determined by taking into account the non-attenuation compensated image pattern, combined stress-rest evaluation, gated-SPET data and patient's history. In a phantom experiment and in 3 representative clinical cases, SPET/CT misalignment was purposely created by the software by sequential slice shifts and its effect was evaluated quantitatively., Results: Misregistration ≥1 pixel in at least one direction was observed in 24% of studies. Interpretation of MPI changed after registration correction in 11% of cases with misalignment <1 pixel, in 18% with 1-2 and in 73% with ≥2 pixels. The diagnostic information seemed to improve after registration correction in 58% of studies irrespective of the degree of misregistration. Software-simulated misregistration had dissimilar effects in the phantom and the 3 selected clinical cases., Conclusions: The impact of SPET/CT misregistration on MPI interpretation although influenced by the degree and direction of slice misplacement, it is also case-specific and hardly predictable. Registration restoration by the software seems worthwhile regardless of misregistration magnitude.

Background: Previous studies advocate the use of attenuation correction in myocardial perfusion scintigraphy (MPS) for patient risk stratification., Methods: Six-hundred and thirty-seven unselected patients underwent Tl-201 MPS by a hybrid SPECT/CT system. Attenuation-corrected (AC) and non-corrected (NAC) images were interpreted blindly and summed stress scores (SSS) were calculated. Study endpoints were all-cause mortality and the composites of death/non-fatal acute myocardial infarction (AMI) and death/AMI/late revascularization., Results: During a follow-up of 42.3 ± 12.8 months 24 deaths, 13 AMIs and 28 revascularizations were recorded. SSS groups formed according to event rate distribution across SSS values were: 0-4, 5-13, >13 for NAC and 0-2, 3-9, >9 for AC. Kaplan-Meier functions were statistically significant between NAC SSS groups for all study endpoints. AC discriminated only between SSS 0-2 and >9 for death/AMI and between 0-2 and 3-9 for death/AMI/revascularization. In the univariate Cox regression abnormal NAC (SSS > 4) was accompanied with much higher hazards ratios than abnormal AC (SSS > 2). In the multivariate model abnormal AC yielded no significance for either endpoint whereas abnormal NAC proved independent from other covariates for the composite endpoints., Conclusion: Our results challenge the effectiveness of CT-based AC for risk stratification of patients referred for MPS.