Background: We determined an appropriate noise equivalent count per volume (NEC_density) for cardiac spot acquisition and optimized the scan time of cardiac spot acquisition by utilizing NEC_density in ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography imaging for the diagnosis of cardiac sarcoidosis.
Method: We evaluated the relationship between visual score and NEC_density. Based on this result, an appropriate NEC_density for cardiac spot acquisition was determined. The correlation between the minimum acquisition time that satisfied the appropriate NEC_density and the patient’s physical index (body weight, body mass index [BMI], and lean body mass) was evaluated and we optimized scan time using BMI. Finally, we compared quantitative parameters of images obtained with optimized scan time.
Results: There was a statistically significant linear trend in the mean NEC_density, according to the advancement of visual score from 1 to 5 (p < 0.0001). From the above and receiver operating characteristic analysis, we determined that NEC_density of 1.0 was an appropriate NEC_density for cardiac spot acquisition. The correlation coefficient value between the minimum acquisition time meeting the appropriate NEC_density and BMI, body weight, or lean body mass was 0.82 (p < 0.0001), 0.78 (p < 0.0001), or 0.45 (p = 0.0001), respectively. There were no significance between 10-minute and optimized scan time for quantitative parameters.
Conclusion: We defined NEC_density of 1.0 as an appropriate NEC_density for cardiac spot acquisition. Our retrospective study using NEC_density revealed that optimization of acquisition time according to BMI could help reduce examination time for patients with BMI ≤ 28.

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Background: Quantitative images reflecting myocardial blood flow can be generated with conventional myocardial perfusion imaging (MPI) using an Anger-type gamma camera (AG) through the myocardial uptake ratio (MUR) method. This approach is reportedly useful for detecting the presence of coronary artery disease (CAD), but its prognostic value for predicting major adverse cardiovascular events (MACE) remains unclear. The aim of this study was to evaluate whether quantitative MPI using AG improves the predictive accuracy for MACE compared to conventional MPI.
Methods: Participants comprised 105 patients who underwent a 1-day adenosine stress/rest ^99mTc-sestamibi protocol and had follow-up data for over 5 years. Conventional MPI parameters assessed included perfusion scores, left ventricular ejection fraction (LVEF), left ventricular end-diastolic volume, left ventricular end-systolic volume, phase standard deviation (phase SD), bandwidth (BW), and entropy. Quantitative MPI parameters included stress MUR, area under the time–activity curve (AUC)-based myocardial flow reserve (MFR), and coronary flow capacity as a combination of stress MUR and AUC-based MFR. The ability of these parameters to predict MACE was evaluated using receiver operating characteristic analysis.
Results: Rest entropy (AUC = 0.80) was the strongest predictor among conventional MPI parameters, followed by rest phase SD, BW (both AUCs = 0.79), and LVEF (AUC = 0.78). Quantitative MPI parameters showed stress MUR (AUC = 0.85) and AUC-based MFR (AUC = 0.83). Further, the combination of stress MUR and AUC-based MFR showed an AUC of 0.90, significantly superior to that of rest entropy (p < 0.05).
Conclusions: Quantitative MPI parameters using AG may improve the ability to predict MACE compared with conventional MPI parameters.

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Background: Response to cardiac resynchronization therapy (CRT) in patients with mechanical dyssynchrony shows that echocardiographic indices alone poorly predict outcomes, highlighting the need for alternative markers. Phase standard deviation (PhSD) and histogram bandwidth (PhHB), used in the “Heart Function View (HFV) ” software, are effective left ventricle dyssynchrony indicators. Therefore, we assessed clinical characteristics associated with PhSD and PhHB from HFV and evaluated the utility of phase analysis in CRT patients.
Methods: Patients underwent quantitative-gated myocardial perfusion single-photon emission computed tomography with ^99mTc-tetrofosmin. Data were stratified by sex, age, and presence/absence of ischemic heart disease.
Results: Fifty-five patients were included. Primary CRT indications were heart failure with reduced ejection fraction (HFrEF), atrioventricular (AV) block, and sick sinus syndrome. Most patients had non-ischemic cardiomyopathy, with significant differences in phase analysis between patients with ischemic and non-ischemic cardiomyopathy. QRS duration demonstrated a significant reduction following CRT implementation. A strong positive correlation was observed between PhSD and PhHB. Multiple linear regression models revealed that functional parameters significantly predicted both PhSD and PhHB, with end-diastolic volume having the strongest standardized effect in both models. Furthermore, patients with HFrEF exhibited the highest and largest PhSD values and ventricular volumes, respectively, whereas patients with AV block had the highest ejection fraction.
Conclusions: PhSD and PhHB were strongly positively correlated among patients who had undergone CRT. Evaluating phase parameters based on a history of ischemic heart disease and other coronary indications, rather than age or sex, may be essential for optimizing CRT outcomes.

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Purpose: Although ¹³N-Ammonia (NH₃) positron emission tomography (PET) has been increasingly applied in clinical practice, its long examination time remains a limitation, primarily due to the required interval for sufficient radioactive decay. This study aimed to validate a low-dose rest scan to reduce the required interval and shorten the overall examination time.
Methods: This prospective study enrolled 24 patients (age 65±12, 15 male) with known or suspected coronary artery disease. To validate the low-dose approach, each patient underwent two separate rest scans consecutively: a low-dose scan (approximately one-third the standard dose) and a standard-dose scan (555 to 740 MBq), immediately followed by standard pharmacological stress scan. PET parameters, including end-diastolic/systolic volumes (EDV/ESV, mL), ejection fraction (EF, %), summed rest score (SRS), and rest myocardial blood flow (MBF, mL/g/min), were compared between the two rest protocols.
Results: EF, EDV, ESV, SRS, and MBF showed significant correlation between low and standard-dose (r=0.99, 0.99, 0.99, 0.99, and 0.93 for EF, EDV, ESV, SRS, and MBF; p<0.0001 for all). Bland-Altman plot showed a good agreement (bias 0.30±3.64, -0.30±1.89, -0.47±2.04, -0.21±0.78, and 0.033±0.096; limits of agreement -4.86 to 5.47, -4.02 to 3.41, -3.52 to 4.48, -1.7 to 1.3, and -0.22 to 0.15 for EF, EDV, ESV, SRS, and MBF).
Conclusion: A low-dose NH3 rest PET protocol is feasible and provides quantitative results highly comparable to the standard-dose. Implementing this approach can shorten examination times and improve clinical throughput.

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Background: Conventional non-breath-hold pulmonary perfusion single-photon emission computed tomography (SPECT) suffers from respiratory motion artifacts that deteriorate image quality and limit prognostic utility. To address these limitations, we developed a novel short-time deep-inspiratory breath-hold (STDIBH) pulmonary perfusion SPECT/computed tomography (CT) acquisition protocol, which has not been previously reported in the literature. This study evaluated the prognostic stratification ability of our newly developed STDIBH pulmonary perfusion SPECT/CT method compared with conventional quantitative methods in patients with pulmonary thromboembolism (PTE).
Methods: This prospective observational study initially enrolled 117 consecutive patients with suspected PTE who underwent pulmonary perfusion SPECT/CT between January 2011 and July 2018. After application of inclusion and exclusion criteria, 100 patients were included in the imaging analysis (40 men [40%] and 60 women [60%]; mean age 68 ± 15 years). Fifty patients underwent imaging under spontaneous breathing (non-breath-hold [NBH] group) and 50 under STDIBH (10-second breath-holds repeated 12 times with recovery intervals). Three quantitative indices were calculated: Meyer score on planar images, NBH percentage of pulmonary perfusion defect (%PPD), and STDIBH-%PPD on SPECT/CT images. Patients were followed for 3 years to evaluate major adverse events (MAE), including all-cause mortality, recurrent PTE, and hospitalization due to respiratory failure or heart failure exacerbation. Kaplan-Meier analysis and Cox regression assessed prognostic stratification ability.
Results: Only STDIBH-%PPD demonstrated statistically significant prognostic stratification (P = 0.001, cut-off: 58.2%), while Meyer score (P = 0.123, cut-off: 31.8%) and NBH-%PPD (P = 0.069, cut-off: 48.7%) did not achieve significance. In univariate Cox regression analysis, high STDIBH-%PPD (HR: 4.002, 95% CI: 1.504–10.646, P = 0.006), high tricuspid regurgitation pressure gradient (HR: 3.395, 95% CI: 1.294–8.907, P = 0.013), and high Mastora score (HR: 2.848, 95% CI: 1.076–7.541, P = 0.035) were identified as significant prognostic factors. Multivariate analysis confirmed high STDIBH-%PPD as the sole independent prognostic factor (HR: 3.376, 95% CI: 1.289–8.845, P = 0.013).
Conclusions: STDIBH pulmonary perfusion SPECT/CT demonstrates superior and independent prognostic value compared to conventional methods in PTE patients. The quantitative functional assessment by STDIBH-%PPD may facilitate improved risk stratification and guide therapeutic decision-making in clinical practice.

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An 80-year-old man presented with heart failure, left ventricular hypertrophy, and reduced ejection fraction (EF) (12.3%) with normal biomarkers. Non-contrast cardiac magnetic resonance imaging (MRI), performed for renal impairment, showed asymmetric septal hypertrophy but normal native T1 (1089 ms). Although hypertrophic cardiomyopathy (HCM) was initially suspected, ^99mTc-pyrophosphate (^99mTc-PYP) scintigraphy demonstrated Grade 3 uptake; biopsy confirmed transthyretin amyloid cardiomyopathy (ATTR-CM). This case illustrates that native T1 mapping can yield “pseudonormal ” values as significant myocyte hypertrophy offsets amyloid-induced T1 prolongation. In renal impairment and reduced EF, ^99mTc-PYP scintigraphy is an indispensable diagnostic tool—rather than a mere option—to avoid missing advanced ATTR-CM when non-contrast MRI is inconclusive.

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Background: The aim of this study was to assess myocardial metabolic activity and cardiac function in asymptomatic health checkup subjects before and after COVID-19 vaccination.
Methods: We retrospectively analyzed clinical records of 67 asymptomatic subjects who underwent whole-body ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography / computed tomography before and after COVID-19 vaccination. Cardiac metabolic activity was assessed using myocardial standardized uptake value (SUVmax). Echocardiography and cardiac magnetic resonance imaging (MRI), including cine-based strain analysis, were used to evaluate cardiac function. The Wilcoxon signed-rank test and Bland-Altman plots were applied to assess changes between pre- and post-vaccination data.
Results: No significant differences in myocardial FDG uptake (SUVmax: 3.29 [interquartile ranges ‹IQR›: 2.84–6.45] vs. 3.21 [IQR: 2.76–7.25], P = 0.63) was observed. Similarly, echocardiographic parameters, including left ventricular ejection fraction, left ventricular end-diastolic volume, and left ventricular end-systolic volume, remained unchanged. MRI-based circumferential strain also showed no significant alterations (-21.27 ± 3.63 vs. -21.90 ± 3.60, P = 0.088).
Conclusions: This study, the first to systematically evaluate myocardial FDG uptake alongside MRI strain analysis in the same subjects pre- and post-vaccination, suggests that vaccination is not associated with meaningful changes in myocardial metabolic activity or cardiac function. These findings lend support to the cardiac safety of COVID-19 vaccination and provide a robust basis for future research in broader populations.

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Background: Technetium-99m pyrophosphate (PYP) imaging is an established non-invasive tool for detecting transthyretin cardiac amyloidosis (ATTR-CA). Although the absence of myocardial uptake on single photon emission computed tomography (SPECT) generally rules out ATTR-CA, early-stage disease may yield false-negative results, and the value of follow-up imaging for such cases is unclear. Therefore, this study aimed to examine whether follow-up PYP imaging could detect the development of myocardial uptake in cases with initially negative findings.
Methods: This single-center retrospective study included 12 of 446 consecutive patients who underwent PYP imaging for suspected ATTR-CA, showed no myocardial uptake on initial SPECT, and underwent repeat PYP imaging. Myocardial PYP uptake was visually assessed using the Perugini classification on planar and SPECT images solely, and quantitatively by the heart-to-contralateral lung uptake (H/CL) ratio. Pretest probability for ATTR-CA was estimated using the Kumamoto criteria.
Results: The median interval between the initial and second PYP imaging was 473 days (interquartile range, 312-848 days). All patients had a low pretest probability of ATTR-CA (Kumamoto score 0-1) at baseline, and only one patient showed an increase in the Kumamoto score from 1 to 2 during follow-up. However, no patient developed myocardial PYP uptake on SPECT at the second PYP imaging. The H/CL ratio did not significantly change between the two scans (1.32 ± 0.10 vs. 1.28 ± 0.15, P = 0.37).
Conclusions: Patients with initially negative PYP SPECT and a low pretest probability of ATTR-CA did not develop myocardial PYP uptake over 1-2 years, suggesting that routine follow-up PYP imaging may be unnecessary unless new clinical indicators of ATTR-CA arise.

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