Imaging performance of a novel multi-pinhole collimator on the AnyScan TRIO triple-head SPECT/CT for nuclear cardiology applications

Introduction: In this study we evaluated the imaging capabilities of a novel Multi-pinhole collimator (MPH-Cardiac) specially designed for nuclear cardiology applications on the AnyScan TRIO, a NaI(Tl) based triple-head SPECT/CT system.

Methods: 99mTc point source measurements covering the field-of-view (FOV) were used to determine tomographic sensitivity (TSpointsource) and spatial resolution. Organ-size tomographic sensitivity (TSorgan) was measured with a left ventricle (LV) phantom filled with typical myocardial activity of a patient scan. Reconstructed image uniformity was measured with a 140 mm diameter uniform cylinder phantom. Using the LV phantom once filled with 99mTc and after with 123I, Contrast-to-noise ratio (CNR) was measured on the reconstructed images by ROI analysis on the myocardium activity and on the LV cavity. Furthermore, a polar map analysis was performed determining Spill-Over-Ratio in water (SORwater) and image noise. A 3D printed LV phantom set (20 ml, 60 ml and 140 ml with 10 mm fillable wall thickness) was filled with 99mTc-sestamibi and ecg-triggered gated SPECT acquisitions were performed with scan duration of 16 minutes. End Diastole Volume (EDV) was determined from the image sets using Cedars-Sinai QGS, Invia 4DM and Emory Toolbox. Results were compared with that of a dual-head parallel-hole low energy high resolution (LEHR) collimator SPECT system. Gated SPECT scans of 42 patients with suspected coronary artery disease (CAD) were performed on both the LEHR and MPH-Cardiac system. EDV, End Systole Volume (ESV) and LV Ejection Fraction (LVEF) were determined for both techniques with all three cardiac software suites.

Results: Peak TSpointsource was found to be 1013 cps/MBq in the axial center of the FOV while it was decreasing towards the radial edges. TSorgan in the CFOV was found to be 134 cps/MBq and 700 cps/MBq for the LEHR and MPH-Cardiac respectively. Average spatial resolution throughout the FOV was 4.38 mm FWHM for the MPH-Cardiac collimator. Reconstructed image uniformity values were found to be 0.504 % versus 0.392 % for the LEHR and MPH-Cardiac measurements respectively. CNR was found to be higher in case of MPH-Cardiac than for LEHR in case of 99mTc (15.5 vs. 11.7) as well as for 123I (13.5 vs. 8.3). SORwater values were found to be 28.83% and 21.1 % for the 99mTc measurements, and 31.44 % and 24.33 % for the 123I measurements for LEHR and MPH-Cardiac respectively. Pixel noise of the 99mTc polar maps resulted in values of 0.38 % and 0.24 % and of the 123I polar maps 0.62 % and 0.21 % for LEHR and MPH-Cardiac respectively. In case of triple-head MPH-Cardiac measurements EDV values were found to be 19 ml, 59 ml, 139 ml with QGS, 19 ml, 58 ml, 138 ml with Invia 4DM and 18 ml, 55 ml, 133 ml with Emory Toolbox. The LEHR method showed significant underestimation of EDV i.e. 12 ml, 54 ml, 123 ml with QGS, 11 ml, 49 ml, 125 ml with Invia 4DM and 11 ml, 47 ml, 117 ml with Emory Toolbox. Median values of the distribution of LVEF values for all patients were found to be lower due to significantly higher ESV values in case of MPH-Cardiac compared to the LEHR technique.

Conclusions: Higher tomographic sensitivity and better spatial resolution was achieved with dedicated MPH-Cardiac collimator on a triple-head SPECT/CT system when compared to conventional SPECT. This significant image quality improvement paves the way for short acquisition and low-dose nuclear cardiology applications. MPH-Cardiac with triple-head SPECT provides more precise volume measurements and consequently more reliable LVEF results than dual-head LEHR SPECT.