Low-dose single acquisition rest (99m)Tc/stress (201)Tl myocardial perfusion SPECT protocol: phantom studies and clinical validation.

PURPOSE: We developed and tested a single acquisition rest (99m)Tc-sestamibi/stress (201)Tl dual isotope protocol (SDI) with the intention of improving the clinical workflow and patient comfort of myocardial perfusion single photon emission computed tomography (SPECT). METHODS: The technical feasibility of SDI was evaluated by a series of anthropomorphic phantom studies on a standard SPECT camera. The attenuation map was created by a moving transmission line source. Iterative reconstruction including attenuation correction, resolution recovery and Monte Carlo simulation of scatter was used for simultaneous reconstruction of dual tracer distribution. For clinical evaluation, patient studies were compared to stress (99m)Tc and rest (99m)Tc reference images acquired in a 2-day protocol. Clinical follow-up examinations like coronary angiography (CAG) and fractional flow reserve (FFR) were included in the assessment if available. RESULTS: Phantom studies demonstrated the technical feasibility of SDI. Artificial lesions inserted in the phantom mimicking ischaemia could be clearly identified. In 51/53 patients, the image quality was adequate for clinical evaluation. For the remaining two obese patients with body mass index > 32 the injected (201)Tl dose of 74 MBq was insufficient for clinical assessment. In answer to this the (201)Tl dose was adapted for obese patients in the rest of the study. In 31 patients, SDI and (99m)Tc reference images resulted in equivalent clinical assessment. Significant differences were found in 20 patients. In 18 of these 20 patients additional examinations were available. In 15 patients the diagnosis based on the SDI images was confirmed by the results of CAG or FFR. In these patients the SDI images were more accurate than the (99m)Tc reference study. In three patients minor ischaemic lesions were detected by SDI but were not confirmed by CAG. In one of these cases this was probably caused by pronounced apical thinning. For two patients no relevant clinical follow-up information was available for evaluation. CONCLUSION: The proposed SDI protocol has the potential to improve clinical workflow and patient comfort and suggests improved accuracy as demonstrated in the clinical feasibility study.

Intra-patient reproducibility of myocardial SPECT imaging with 201Tl.

BACKGROUND: To define the physical and clinical reproducibility of (201)Tl myocardial perfusion SPECT (MPS), this study assesses the variation between two repeated rest (201)Tl MPS with repositioning only, with a two-hour time interval and with phantom measurements as a reference. METHODS: Three anthropomorphic thorax phantoms were filled with (201)Tl. For each phantom five repeated (201)Tl MPS were obtained. In addition, in 20 patients repeated (201)Tl rest-MPS and in 26 patients early and delayed (201)Tl rest-MPS were performed. Quantitative analysis was done using MunichHeart. Statistical methods were used to calculate variability. Visual analysis was performed by 2 independent observers. RESULTS: The average variation between repeated phantom MPS was 0.5% (95% confidence interval (CI): -0.4% to 1.4%). For patient scans this was -5.0% (95% CI: -2.5% to -7.5%) and between early and delayed (201)Tl MPS -15.5% (95% CI: -11.7% to -19.3%). Visual assessment revealed no clinical significant differences between rest (201)Tl and repeated or delayed (201)Tl MPS. CONCLUSIONS: Repositioning in phantom (201)Tl MPS does not cause significant variation. Repeated (201)Tl MPS in patients shows 5.0% decrease of (201)Tl in 30 minutes, which increases to 15% during a two-hour time interval without quantitative or visual regional differences. This decrease indicates a time-related washout of (201)Tl, but does not change clinical diagnosis.