Masakazu Tsujimoto

This study aimed to determine the optimal measurement conditions for accurate standardized uptake value (SUV) analysis of iodine-123 metaiodobenzylguanidine (¹²³I-MIBG) by examining the relationship between image convergence and quantitation. Single-photon emission computed tomography/computed tomography images were acquired using JS-10 and National Electrical Manufacturers Association (NEMA) body phantoms, with acquisition time per view varied (10, 30, 50, and 100 s/view). Image reconstruction was performed using three-dimensional-ordered subset expectation maximization, adjusting the product of subset and iteration (SI product; 60, 120, 180) and Gaussian filter parameters (8, 10, 12 mm). For the JS-10 phantom, we evaluated the dose linearity (DL), the recovery coefficient (RC) of individual rods, the scatter ratio (SR), and the coefficient of variation (CV). For the NEMA body phantom, we assessed the contrast-to-noise ratio (CNR) of the 17-mm-diameter hot sphere. We also evaluated the maximum and mean SUVs for all its hot spheres, and their relative standard error (RSE), using SUVs obtained at 100 s/view as reference. In the JS-10 phantom, the DL remained stable under all conditions. The RC decreased when the Gaussian filter was large and the SI product was small. A trade-off between the CV and the SR emerged, depending on the acquisition time and the SI product; optimal results were observed at 50 − 100 s/view and an SI product of 120 − 180. In the NEMA body phantom, contrast improved with acquisition times of ≥30 s/view, and the CNR increased as noise declined with longer acquisition times. At ≥50 s/view, variation in the maximum and mean SUVs decreased, with the RSE remaining below 5%. In conclusion, accurate SUV measurement with ¹²³I-MIBG requires an acquisition time of ≥50 s/view, an SI product of approximately 120, and a Gaussian filter of 10 − 12 mm. These findings provide a foundation for future studies comparing this method with the heart-to-mediastinum ratio, supporting its clinical application.

Abstract Background Cardiac amyloidosis requires quantitative assessment using technetium-99m pyrophosphate (^99mTc-PYP) single-photon emission computed tomography (SPECT)/computed tomography (CT) for adequate discrimination and evaluation of disease extent. This study aimed to evaluate the utility of standardized uptake value (SUV) analysis using ^99mTc-PYP SPECT/CT in pathologically-confirmed transthyretin amyloid cardiomyopathy (ATTR-CM). The study also explored the relationship between local uptake heterogeneity and indicators of cardiac impairment. Methods Forty patients diagnosed via heart biopsy and genetic analysis (20 ATTR-CM; 4 light-chain amyloidosis, 16 non-amyloidosis) were enrolled. The mean SUVs of the heart and aorta were measured using SPECT images. Discrimination performance was evaluated by comparing each SUV, the heart-to-aorta ratio (rSUV_H/Ao), and the heart-to-contralateral-lung ratio with pathological findings serving as the gold standard. Polar maps were analyzed to assess local SUV distribution in patients with ATTR-CM. The coefficient of variation (COV) of myocardial uptake, difference score between the septum and lateral wall (%DS), base-to-apex variability, and total cardiac SUV were calculated and compared with echocardiographic parameters. Results All metrics were significantly different between the ATTR-CM and non-amyloidosis groups. The rSUV_H/Ao effectively differentiated patients with ATTR-CM from those with light-chain or non-amyloidosis. Local myocardial SUV distribution correlated with impaired cardiac function. Notably, COV showed significant correlations with e' (R = 0.782) and E/e' (R =  − 0.625), linking heterogeneity to myocardial stiffness and diastolic dysfunction. Larger %DS, which predominantly reflected the ATTR-CM pattern of high septal uptake, correlated significantly with thinner walls (average wall thickness, R =  − 0.655; relative wall thickness, R =  − 0.486). As the total cardiac SUV increased, the %DS decreased (reflecting more homogeneous distribution), and global longitudinal strain worsened (R = 0.614). These observations indicated that greater impairment was associated with a higher disease burden. Conclusions This study demonstrated that quantitative SPECT analysis provides a valuable tool for the diagnostic evaluation and differentiation of ATTR-CM. The rSUV_H/Ao offers high discriminatory performance. Local heterogeneity and total myocardial uptake are closely related to the disease burden and extent, as reflected by structural and functional abnormalities on echocardiography. These findings suggest potential relevance to the non-invasive assessment of these aspects of the disease at a single time point. Graphical abstract