Is the CZT technology the future of nuclear cardiology?

Optimization of the Pixel Design for Large Gamma Cameras Based on Silicon Photomultipliers

Most single-photon emission computed tomography (SPECT) scanners employ a gamma camera with a large scintillator crystal and 50-100 large photomultiplier tubes (PMTs). In the past, we proposed that the weight, size and cost of a scanner could be reduced by replacing the PMTs with large-area silicon photomultiplier (SiPM) pixels in which commercial SiPMs are summed to reduce the number of readout channels. We studied the feasibility of that solution with a small homemade camera, but the question on how it could be implemented in a large camera remained open. In this work, we try to answer this question by performing Geant4 simulations of a full-body SPECT camera. We studied how the pixel size, shape and noise could affect its energy and spatial resolution. Our results suggest that it would be possible to obtain an intrinsic spatial resolution of a few mm FWHM and an energy resolution at 140 keV close to 10%, even if using pixels more than 20 times larger than standard commercial SiPMs of 6 × 6 mm2. We have also found that if SiPMs are distributed following a honeycomb structure, the spatial resolution is significantly better than if using square pixels distributed in a square grid.

Assessing the diagnostic value of left ventricular synchrony indices derived from phase analysis by D-SPECT in identifying obstructive coronary artery disease

This study aimed to assess the diagnostic efficacy of left ventricular synchrony (LVS) for detecting coronary artery disease (CAD). We explored whether the LVS index derived from phase analysis of D-SPECT provides superior diagnostic value compared to conventional perfusion analysis in identifying obstructive CAD. Patients with suspected or confirmed CAD underwent drug-stress/rest gated D-SPECT myocardial perfusion imaging (MPI) and coronary angiography (CAG). A 50% stenosis was set as the threshold for obstructive CAD. 110 participants were enrolled in this analysis. There were significant differences in phase standard deviation (PSD), phase histogram bandwidth (PHB) and entropy among the four groups. Patients without cardiac disease and those with mild-moderate stenosis exhibited no noticeable contraction asynchrony. However, LVS indices demonstrated a gradual increase with the progression of coronary stenosis when compared to NC (P < 0.001). Obstructive CAD was identified in 43 out of 110 participants (39%). Optimal cutoff values for diagnosing obstructive CAD during stress were determined as 7.6° for PSD, 24° for PHB, and 37% for entropy, respectively. Notably, PSD, PHB, and entropy indices exhibited higher sensitivity compared to MPI. The integration of the stress-induced LVS indices into routine MPI analysis resulted in a significantly greater area under the curve (AUC), leading to improved diagnostic performance and enhanced differential capacity. Stress-induced LVS indices increase with the severity of coronary artery stenosis by D-SPECT phase analysis. Further, the indices-derived phase analysis exhibits superior sensitivity and discriminatory ability compared to MPI in detecting obstructive CAD.

Review of cardiovascular imaging in the Journal of Nuclear Cardiology 2022: single photon emission computed tomography

In this review, we will summarize a selection of articles on single-photon emission computed tomography published in the Journal of Nuclear Cardiology in 2022. The aim of this review is to concisely recap major advancements in the field to provide the reader a glimpse of the research published in the journal over the last year. This review will place emphasis on myocardial perfusion imaging using single-photon emission computed tomography summarizing advances in the field including in prognosis, non-perfusion variables, attenuation compensation, machine learning and camera design. It will also review nuclear imaging advances in amyloidosis, left ventricular mechanical dyssynchrony, cardiac innervation, and lung perfusion. We encourage interested readers to go back to the original articles, and editorials, for a comprehensive read as necessary but hope that this yearly review will be helpful in reminding readers of articles they have seen and attracting their attentions to ones they have missed.

Feasibility of Imaging Small Animals on a 360° Whole-Body Cadmium Zinc Telluride SPECT Camera: a Phantom Study

PURPOSE

Single-photon emission computed tomography has found an important place in preclinical cancer research. Nevertheless, the cameras dedicated to small animals are not widely available. The present study aimed to assess the feasibility of imaging small animals by a newly released 360° cadmium zinc telluride camera (VERITON, Spectrum Dynamics, Israel) dedicated to human patients.

PROCEDURES

A cylindrical phantom containing hot spheres was used to evaluate the intrinsic performance of the camera first without the presence of background activity and then with two contrasts between background and hot spheres (1/4 and 1/10). Acquisitions were repeated with different scan durations (10 and 20 min), two tested radioisotopes (Tc-99 m and I-123), and a set of reconstruction parameters (10 iterations [i] 8 subsets [s], 10i16s, 10i32s). A 3D-printed phantom mimicking a rat with four subcutaneous tumours was then used to test the camera under preclinical conditions.

RESULTS

The results obtained from the micro-hollow sphere phantom showed that it was possible to visualize spheres with an inner diameter of 3.95 mm without background activity. Moreover, spheres with diameters of 4.95 mm can be seen in the condition of high contrast between background and spheres (1/10) and 7.86 mm with lower contrast (1/4). The rat-sized phantom acquisitions showed that 10- and 8-mm subcutaneous tumours were visible with a good contrast obtained for the two radioisotopes tested in this study. Both Tc-99 m and I-123 measurements demonstrated that a 10-min acquisition reconstructed with an ordered subset expectation maximization algorithm applying 10i32s was optimal to obtain sufficient image quality in terms of noise, resolution, and contrast.

CONCLUSION

Phantom results showed the ability of the system to detect sub-centimetre lesions for various radioisotopes. It seemed feasible to image small animals using a 360° cadmium zinc telluride gamma camera for preclinical cancer research purposes.

Relationship between left ventricular mechanical synchrony and left ventricular systolic function: a CZT-SPECT analysis

BACKGROUND

CZT-SPECT has good agreement in the evaluation of mechanical synchronization compared with conventional SPECT. The aim of this study was to evaluate the correlation between left ventricular mechanical contraction synchrony and left ventricular systolic function by gated myocardial perfusion imaging (GMPI) using cadmium-zine-telluride (CZT) single photon emission computed tomography (SPECT).

METHODS

This retrospective study involved 371 patients (239 males and 132 females, mean age 61.06 ± 11.78 years old) who underwent GMPI at the Nuclear Medicine Department of Shanxi Cardiovascular Hospital from January 2020 to August 2020. Systolic synchrony parameters and left ventricular systolic function parameters were calculated via Emory Cardiac Toolbox, including PP, PSD, PHB, HS, HK, EDV, ESV, and LVEF. Based on LVEF value, patients were divided into the severe reduction group (group 1, 127 cases, EF < 35%), moderate reduction group (group 2, 47 cases, 35% ≤ EF < 45%), mild reduction group (group 3, 50 cases, 45% ≤ EF < 50%) and normal group (group 4, 147 cases, EF ≥ 50%). Differences in PP, PSD, PHB, HS and HK among the four groups were compared using one-way ANOVA. Differences between two groups were compared using LSD-t test. The correlation among functional and mechanical contraction synchrony factors were analyzed using Pearson test.

RESULTS

PP, PSD, PHB, HS and HK were significantly different among the four groups (F = 5.20, 188.72, 202.88, 171.05, 101.36, P < 0.001). Pairwise comparison tests showed significant differences in PSD and PHB in each two groups, and HS and HK in each two groups except for group 2 and 3 (t = 0.28 and 0.39, both P > 0.001). PP was significantly higher in group 1, relative to group 3 (t = 2.43, P < 0.001) and group 4 (t = 3.67, P < 0.001). Pearson correlation analysis revealed that LVEF negatively correlates with PP, PSD, PHB (r = 0.194, - 0.790, - 0.799, all P < 0.001). HS and HK showed positive correlation for LVEF (r = 0.778 and 0.795, P < 0.001), PSD, PHB and ESV were had good positive correlation (r = 0.778, 0.795, P < 0.001), PSD, PHB and EDV had good positive correlation (r = 0.722, 0.732, P < 0.001). However, PP had poor correlation with EDV (r = 0.095, P > 0.001). HS and HK were negatively correlated with EDV and ESV (r =  - 0.700 to - 0.594, P < 0.001).

CONCLUSION

CZT SPECT GMPI provided left ventricular mechanical contraction synchrony parameters that correlated well with left ventricular systolic function. Worse left ventricular mechanical contraction synchrony lead to decreased LVEF, making the systolic synchrony parameters valuable in the prediction of left ventricular systolic function.

Complementary role of computed tomography angiography with fixed perfusion defects on SPECT myocardial perfusion imaging

Purpose

We present this case series exploring the complementary role of coronary computed tomography angiography (CCTA) to SPECT myocardial perfusion imaging (MPI) in the detection of myocardial necrosis.

Methods

A cardiac hybrid imaging database search identified 144 patients with a previous history of ST-segment elevation myocardial infarction treated with coronary revascularization. CCTA and MPI scans were evaluated to determine whether CCTA had an added value to MPI in detecting myocardial necrosis.

Results

Five patients with patent stents and/or bypass grafts and both fixed perfusion defects on MPI and sub-endocardial hypo-perfusion on CCTA were identified. The extent and location of the perfusion defects were closely correlated between the CCTA and SPECT MPI images.

Conclusion

In this series, CCTA and SPECT MPI were found to play a complementary role in the assessment of fixed perfusion defect, with CCTA adding specificity to the diagnosis of myocardial necrosis.