Low dose in nuclear cardiology: state of the art in the era of new cadmium-zinc-telluride cameras.

The use of myocardial perfusion imaging has seen a tremendous growth during the last decade and has become the most commonly used non-invasive imaging tool for risk stratification in patients with suspected and known coronary artery disease. Adherence to radiation safety best practices varied significantly between laboratories but the possibility to use the new cameras in nuclear cardiology can reduce dramatically the radiation dose without losing accuracy. Moreover, the physical characteristics of ultrafast technology could be able to open new doors for the evaluation of old parameters, changing the impact of nuclear cardiology in the diagnostic strategies.

Temporal evolution of administered activity in cardiac gated SPECT and patients' effective dose: analysis of an historical series.

PURPOSE: Myocardial perfusion imaging contributes >20 % of the average medical radiation exposure to the population in the USA. Imaging protocols able to achieve a radiation exposure ≤9 mSv in 50 % of the studies by 2014 have been recommended. The aim of this study was to analyse the temporal evolution of administered activities in patients scheduled for dual-day (99m)Tc tracer gated single photon emission computed tomography (SPECT) and to compare different dose administration protocols in terms of patients' effective dose. METHODS: Patients evaluated from 1 July 2002 to 31 January 2012 were allocated according to the protocol adopted: group 1: fixed activity according to diagnostic reference level: 740 MBq up to 80 kg (adapted for weight <60 kg); 900 MBq 80-100 kg, 1,110 MBq >100 kg, standard filtered back-projection (FBP) reconstruction; group 2: weight-adjusted activity: 8 MBq/kg up to 1,110 MBq, standard FBP reconstruction; and group 3: 4 MBq/kg, UltraSPECT wide beam reconstruction (WBR) reconstruction. A dual-head Anger camera (GE Helix) was used. RESULTS: A total of 9,060 patients were allocated to different groups: 4,751 in group 1, 2,844 in group 2 and 1,465 in group 3. The stress + rest administered activity was 1,617 ± 180 in group 1, 1,136 ± 260 in group 2 and 682 ± 164 MBq in group 3 (all p < 0.001). Patients' effective dose was 13.7 ± 3 in group 1, 9.5 ± 2.8 in group 2 and 5.7 ± 1.6 mSv in group 3 (all p < 0.001). The 50th percentile was 12.6 in group 1, 9.1 in group 2 and 5.3 mSv in group 3. The effective dose received by the dedicated cardiologists was 2.1, 1.5 and 1.0 µSv/exam in group 1, group 2 and group 3 periods, respectively (all p < 0.001). CONCLUSION: A significant reduction over time in the administered activity for gated SPECT was achieved; accordingly, a significant reduction in patients' exposure was obtained. A simple weight-adjusted strategy with 8 MBq/kg immediately fulfils the recommendations to limit exposure. In selected group 3 patients, a stress-only strategy allows for studies with <3 mSv exposure. Thus, at least the adoption of a new reconstruction algorithm is strongly encouraged, and suggested tracer activities for cardiac gated SPECT are to be revised.

Prognostic value of (123)I-betamethyl-p-iodophenyl-pentadecanoic acid single-photon emission computed tomography in diabetic patients with suspected ischemic heart disease.

BACKGROUND: Because of their high risk for cardiovascular events, we investigated the role of (123)I-betamethyl-p-iodophenyl-pentadecanoic acid (BMIPP) SPECT in evaluating the prognosis of diabetic patients with suspected coronary heart disease. METHODS AND RESULTS: We retrospectively registered 186 diabetic patients with suspected coronary heart disease, but no previous diagnosis of heart disease, who had been examined by BMIPP and thallium (TL) dual SPECT. They were followed for over 2 years. The dual SPECT images were scored to obtain summed defect scores for each SPECT image (BMDS, TLDS and mismatch score [MS]). The primary endpoint was the first incidence of all-cause cardiac events. The secondary endpoint was cardiac death. Clinical classical risk factors in addition to the stage of chronic kidney disease (CKD), as well as cardiac function, were included in the prognostic analysis. Cardiac events occurred in 39 patients, including 8 cardiac deaths. Kaplan-Meier analysis revealed significantly more frequent cardiac event rates in patients with than without MS ≥5 or BMDS ≥6 (P<0.0001). Cox hazard multivariate analysis showed that MS and CKD stage or BMIPP and CKD stage were independent predictors. Only hemodialysis was a significant prognostic indicator for cardiac death. CONCLUSIONS: BMIPP SPECT when combined with CKD stage accurately predicts cardiac events among diabetic patients with suspected ischemic heart disease.

Wide beam reconstruction for half-dose or half-time cardiac gated SPECT acquisitions: optimization of resources and reduction in radiation exposure.

PURPOSE: A new iterative reconstruction algorithm (WBR™) has been recently proposed for cardiac single photon emission computed tomography (SPECT). The WBR™ technology is designed to reduce noise, improving lesion identification without affecting the image resolution, allowing SPECT studies with reduced count statistic. This allows for either half-time (HT) or half-dose (HD) cardiac SPECT, with image quality and quantitative data comparable to standard-time (ST) or standard-dose (SD) SPECT. Few data exist on the comparison between conventional filtered backprojection (FBP) and this new algorithm in a clinical setting. The aim of this study was to compare the performance of FBP and WBR™. METHODS: Phantoms studies were performed to compare spatial resolution and contrast recovery with FBP, ordered subset expectation maximization (OSEM) and WBR™. A group of 92 patients, with different cardiac pathology, scheduled for a stress-rest SPECT were studied: 52 patients (group A) were injected with a SD of tracer and underwent both ST and HT SPECT; 40 patients (group B) were injected with a half dose of tracer and underwent ST SPECT and immediately after an additional SPECT at double time/projection (DT), to compensate for the low count statistic. A 2-day (99m)Tc-sestamibi protocol was used in all patients. SD/ST and HD/DT SPECT were reconstructed with a conventional FBP; SD/HT and HD/ST SPECT were reconstructed with WBR™. The summed stress score (SSS) and summed rest score (SRS) were calculated; the left ventricular ejection fraction (LVEF) was automatically derived. RESULTS: In group A (SD), no significant differences were observed between ST FBP SPECT and HT WBR™ in SSS (11.1 and 11.7, respectively) and SRS (9.4 and 10.3, respectively, NS). LVEF on rest acquisitions was also comparable (50% on ST SPECT and 49% on HT SPECT, NS); LVEF on post-stress studies in HT SPECT (46%) was lower than ST SPECT (50%), although not statistically significant. In group B (HD), SSS (6.2 in ST and 5.3 in DT) and SRS (4.0 in ST and 3.3 in DT) were also comparable. No differences were documented between ST and DT in rest (47 and 48%, respectively) and stress (48 and 50%, respectively) LVEF. CONCLUSION: WBR™ performance and image quality were comparable to those of conventional FBP, allowing for either HT or HD studies. The former allows for an increased patient throughput and optimization of resources. The latter modalities would allow for a significant reduction in both patients' and operators' exposure. Further studies are needed to validate the clinical use of this method.