CZT Detectors-Based SPECT Imaging: How Detector and Collimator Arrangement Can Determine the Overall Performance of the Tomograph

A technical comparison is described between two SPECT systems, one dedicated to cardiovascular studies and one general-purpose, to evaluate the advantages and disadvantages of their use in an organ-specific clinical setting. The comparison was made between a dedicated cardiac SPECT (Alcyone, Discovery NM 530c, GE Healthcare) scanner and a general-purpose one (Discovery NM/CT 670 CZT, GE Healthcare). The two scanners differ in terms of hardware, mainly in the arrangement of the detectors and collimators, which are the main components of SPECT. A standard NEMA phantom was used to characterize the energy resolution, spatial resolution, and sensitivity for the two systems. Then, using a custom-made cardiac phantom, more specific indices were computed to evaluate the quality of cardiac images, such as signal-to-background noise ratio (SBNR), tissue-background contrast-to-noise ratio (TBCNR), and uniformity. Finally, the same indices were computed for clinical images acquired with the two systems from 11 subjects. Alcyone showed superior performance for dedicated cardiac imaging; however, its excellent qualities are aimed only at the study of the heart and only at patients with a low body-mass index, unlike Discovery NM/CT 670 CZT, which can be used for every anatomic district area and for every type of patient.

Incremental prognostic value of SPECT CT based visual calcium score burden for outcomes prediction

Funding Acknowledgements Type of funding sources: Other. Main funding source(s): Astellas Pharma US Background Coronary calcium is an important non-perfusion finding on SPECT CT attenuation correction (AC) and has been shown to help decrease equivocal interpretation and identifying atherosclerosis despite normal perfusion. Although correlations with measured calcium score have been good, an easy visual calcium score (VCS) for CT AC calcium and its prognostic value has not been well established. Purpose We aimed to evaluate the role of VCS calculated from low-dose CT for AC in predicting outcomes stratified by SPECT (normal versus abnormal). Methods A retrospective data review of patients who underwent cardiac SPECT CT at our center from January 2009 -August 2012 with a mean follow up of 4.5 years. Baseline characteristics and outcomes were collected. VCS scoring was established as follows and was completed on all scans by three senior cardiology fellows. When not congruent, consensus with third reader was established. Presence of visual calcium in any of the following arteries was recorded as a score of 1 with VCS range 0-6: left main, left anterior descending, left circumflex, right coronary, ascending aorta, and descending thoracic aorta. Subjects were divided into 3 groups based on the VCS of <2, 2-4, and >4. Normal versus abnormal SPECT was defined as summed stress score/summed difference score of <4/<2 and > =4/> =2 respectively. Major adverse cardiac events (MACE) defined as presence of heart failure, myocardial infarction, and/or cardiac death. Results 538 consecutive patients with SPECT CT were evaluated. Mean age was 63.3 years with 54% females. There were 463 (86%) normal SPECT and 75 (14%) abnormal SPECT. Using VCS, there was a statistically significant increase in the percentage of MACE over the period of follow-up with step wise increase in VCS severity in normal SPECT group (p-value = 0.001), although not significant in the abnormal MPI group (Figure 1). There was a higher mortality with increasing VCS in both normal and abnormal SPECT (p= <0.001 and p = 0.014 respectively). Using a multivariate logistic regression model in patients with normal SPECT, there were higher odds of death (OR 1.26) with every 1 point of VCS increase controlling for age, sex, baseline heart rate, history of dialysis, diabetes and stroke (95% confidence interval 1.09, 1.45; p-value = 0.002). Conclusion This study highlights the importance of factoring CT AC calcium in risk assessment of SPECT. CT AC calcium represents an easily available and important adjunctive risk marker during SPECT interpretation. A simple VCS as derived in this study can help with the additive risk stratification in both normal and abnormal SPECT and is of an incremental prognostic value for MACE. Clinicians interpreting SPECT should include coronary calcification on AC CT routinely in reports to help management and prognostication decisions. Our study shows that VCS can be a simple easily adopted tool for consistent reporting.

Quality and utility of [123I]I-metaiodobenzylguanidine cardiac SPECT imaging in nondiabetic postinfarction heart failure patients qualified for implantable cardioverter defibrillator

Objective Impaired cardiac adrenergic activity has been demonstrated in heart failure (HF) and in diabetes mellitus (DM). [123I]I-metaiodobenzylguanidine (MIBG) enables assessment of the cardiac adrenergic nervous system. Tomographic imaging of the heart is expected to be superior to planar imaging. This study aimed to determine the quality and utility of MIBG SPECT in the assessment of cardiac innervation in postinfarction HF patients without DM, qualified for implantable cardioverter defibrillator (ICD) in primary prevention of sudden cardiac death. Methods Consecutive patients receiving an ICD on the basis of contemporary guidelines were prospectively included. Planar MIBG studies were followed by SPECT. The essential analysis was based on visual assessment of the quality of SPECT images (“high”, “low” or “unacceptable”). The variables used in the further analysis were late summed defect score for SPECT images and heart-to-mediastinum rate for planar images. MIBG images were assessed independently by two experienced readers. Results Fifty postinfarction nondiabetic HF subjects were enrolled. In 13 patients (26%), the assessment of SPECT studies was impossible. In addition, in 13 of 37 patients who underwent semiquantitative SPECT evaluation, the assessment was equivocal. Altogether, in 26/50 patients (52%, 95% confidence interval 38–65%), the quality of SPECT images was unacceptable or low and was limited by low MIBG cardiac uptake and by comparatively high, interfering MIBG uptake in the neighboring structures (primarily, in the lungs). Conclusions The utility of MIBG SPECT imaging, at least with conventional imaging protocols, in the qualification of postinfarction HF patients for ICD, is limited. In approximately half of the postinfarction HF patients, SPECT assessment of cardiac innervation can be impossible or equivocal, even without additional damage from diabetic cardiac neuropathy. The criteria predisposing the patient to good-quality MIBG SPECT are: high values of LVEF from the range characterizing the patients qualified to ICD (i.e., close to 35%) and left lung uptake intensity in planar images comparable to or lower than heart uptake.