Background: The quantitative analysis of myocardial blood flow and myocardial flow reserve (MFR) is expected to address challenges in evaluating the relative distribution of myocardial perfusion imaging. This study aimed to determine the normal range of MFR index using the myocardial uptake ratio (MUR) method in normal volunteers (NV) with an Anger-type single photon emission computed tomography/computed tomography (SPECT/CT) system and to evaluate its diagnostic accuracy for ischemic heart disease (IHD) and heart failure (HF).
Method: Two methods for calculating the MUR were evaluated. The area under the curve (AUC) method utilized the AUC of the time-activity curve (TAC) of the aortic arch as the input function (AUC-based MFR index). The DOSE method employed the dose activity (dose-based MFR index). IHD was categorized into single-vessel disease (SVD) and multivessel disease (MVD; double- and triple-vessel disease combined).
Results: Normal range of AUC-based MFR index was 1.63±0.30, 1.40±0.24 for SVD, 1.28±0.17 for MVD, and 1.11±0.12 for HF. The normal range of the dose-based MFR index was 1.18±0.14, 1.15±0.26 for SVD, 1.02±0.10 for MVD, and 0.99±0.06 for HF. Significant differences were observed among the NV, MVD, and HF groups. No significant differences were noted between NV and SVD groups. The results of the receiver operating characteristic curve (ROC) analysis in combination with NV showed that the AUC of the ROC curve was 0.732 (95%CI 0.542–0.922) for SVD, 0.841 (95%CI 0.717–0.965) for MVD, and 0.969 (95%CI, 0. 922–1.0) for HF. The AUC of dose-based MFR index were 0.667 (95%CI 0.404–0.929) for SVD, 0.817 (95%CI 0.684–0.950) for MVD, and 0.908 (95%CI 0.814–1.0) for HF. DeLong’s test showed no significant differences between the AUC of AUC-based and dose-based MFR indices.
Conclusion: The findings suggest the potential clinical application of AUC and DOSE methods for quantitative analysis of the MFR index using an Anger-type SPECT/CT system. These methods are expected to enhance the accuracy of diagnosis and prognosis in patients with IHD and HF.

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Background: In nuclear cardiology, tracer uptake and washout rate (WR) are key parameters for evaluating cardiac pathophysiology. However, WR is influenced by counts in the early image, making it difficult to evaluate pathophysiology based on WR value alone. To differentiate cardiovascular diseases involving count and WR variations, such as triglyceride deposit cardiomyovasculopathy (TGCV) and old myocardial infarction (OMI), we proposed a method to simultaneously evaluate both.
Methods: We newly developed the Count-Washout Rate Polar Map (CWRM), a graphical representation of the count and WR values in a polar coordinate system. CWRM consists of two axes: count in the early image and WR. Given the variety of diseases characterized by count and WR, Iodine-123-β-methyl-p-iodophenyl-pentadecanoic acid was selected as the radiotracer. We examined patients without cardiovascular disease (normal) and patients with TGCV, OMI, and TGCV with OMI. CWRMs for each disease were visually evaluated.
Results: In the normal case, sufficient counts were observed in the early image, and WR did not decrease; CWRM showed light blue. In TGCV, sufficient counts were observed in the early image, but WR markedly decreased; CWRM showed orange evenly. In non-TGCV with OMI, regions with decreased and preserved counts coexisted; CWRM showed light blue in the normal region and black in the OMI region. In TGCV with OMI, CWRM showed orange in the TGCV myocardium and black in the OMI region.
Conclusion: CWRM is useful for at-a-glance differentiation of patients with TGCV, OMI, and TGCV with OMI, thereby showing potential as a new diagnostic indicator.

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Purpose: The aim of this study was to validate positron emission tomography feature tracking (PETFT) for assessing endocardial wall strain by comparing it with conventional tagging-cine magnetic resonance (MR) derived strain analysis (TAG).
Methods: Consecutive 62 patients who underwent ¹³N-ammonia PETMR (52 males, mean age 66 years) were enrolled. PETFT and TAG were obtained through simultaneous acquisition with electrocardiography-gated PET and cine-MR for rest scan. Global longitudinal and circumferential strain (GLS and GCS) were calculated. Correlations and Bland-Altman plots were employed to evaluate associations, bias, and 95% limit of agreement (LOA) between PETFT and TAG.
Results: PETFT and TAG showed significant correlations (r = 0.69 [95% CI: 0.54 to 0.80], p<0.0001; r = 0.55 [95% CI: 0.33–0.80], p<0.0001 for GCS and GLS, respectively). Bland-Altman plot showed acceptable agreements (Bias 0.7±6.7, LOA -12.5 to 13.9; Bias 1.3±5.5, LOA -9.5 to 12.0 for GCS and GLS, respectively). In patients with abnormal perfusion, the correlations were still significant (r = 0.76 [95% CI: 0.62 to 0.93], p<0.0001; r = 0.59 [95% CI: 0.18 to 0.82], p=0.007 for GCS and GLS, respectively)
Conclusion: PETFT has been identified as a feasible technique compared to TAG, demonstrating its potential as a novel tool for assessing wall strain in routine clinical practice. However, discrepancies in strain values may arise due to differences in algorithms and the presence of perfusion defects.

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Background: This study aimed to evaluate the optimal region of interest (ROI) size of the heart-to-contralateral (H/CL) ratio on planar imaging for detecting myocardial technetium-99m pyrophosphate (PYP) uptake in patients with suspected transthyretin cardiac amyloidosis (ATTR-CA) and to assess the impact of ROI size on intra- and interobserver variability in the H/CL ratio.
Methods: We retrospectively analyzed 90 consecutive patients who underwent PYP imaging for ATTR-CA evaluation after excluding 20 patients without myocardial PYP uptake on planar images (i.e., Grade 0). The H/CL ratio was measured using three ROI sizes (4.5 cm, 3 cm, and 2 cm). Receiver operating characteristic (ROC) analysis was used to evaluate the performance of each ROI size in detecting positive PYP single-photon emission computed tomography (SPECT). Intra- and inter-observer variability was assessed using intraclass correlation coefficients (ICCs).
Results: Grade 2-3 myocardial PYP uptake on SPECT was observed in 41 (46%) patients. ROC analysis revealed no significant differences in the area under the curve among the various ROI sizes at 1 hour (0.68, 0.71, and 0.71 for the 4.5-, 3-, and 2-cm ROIs, respectively; P=0.44) or 3 hours (0.71, 0.72, and 0.72 for the 4.5-, 3-, and 2-cm ROIs, respectively; P=0.86). The largest ROI (4.5 cm) demonstrated the highest reproducibility, with excellent intra-observer (ICC=0.949) and inter-observer (ICC=0.906) agreement.
Conclusions: The size of the ROI used to calculate the H/CL ratio did not significantly affect the detection of myocardial PYP uptake in patients with suspected ATTR-CA. Using a larger ROI size that covers the entire heart may improve the reproducibility of the H/CL ratio measurement.

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Triglyceride deposit cardiomyovasculopathy (TGCV) (Orphanet ORPHA code: 692305) is an emerging rare adult-onset cardiovascular disease, first identified in Japan. In TGCV, defective intracellular lipolysis of long-chain triglycerides (LCTGs) results in cellular steatosis and energy failure, leading to intractable heart failure, diffuse coronary artery disease, and ventricular arrhythmia. A hallmark of TGCV diagnosis is the reduced washout rate (WR) of ¹²³I-β-methyl-p-iodophenyl pentadecanoic acid (BMIPP), a well-established radiopharmaceutical of long-chain fatty acid (LCFA). Recently, the working group of the Japanese Society of Nuclear Cardiology published the practical guideline for measuring ¹²³I-BMIPP-WR. Here, we present the diagnostic principle of TGCV using ¹²³I-BMIPP-WR based upon basic and clinical studies in nuclear cardiology as well as current biochemical insights into TG and LCFA metabolism.

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The measurement of absolute myocardial blood flow (MBF) has played a pivotal role in the development of nuclear cardiology and other perfusion imaging techniques. However, the capacity to perform such experiments may be diminished. This review examines the basic physiology of microsphere measurement of absolute MBF which was developed over 50 years ago, with multiple refinements over time. The use of different types of microspheres is presented in depth. The set-up and performance of a large animal model is detailed with tips and pitfalls explained. It is the purpose of this review to stimulate the next generation of investigators into considering this skill as part of their research tool box.

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