Objectives We validated the effectiveness of adaptive statistical iterative reconstruction (ASIR, GE Healthcare (GE)) for minimising image noise in low dose quantitative myocardial perfusion (MP) imaging against microspheres MP measurement.
Methods Iodinated contrast (Isovue 370, 0.7 mgI × kg-1) was injected at 3 to 4 mls-1 into 68 ± 25 kg normal pigs via an ear vein and the heart was scanned using a GE Discovery 750HD scanner with a prospectively ECG triggered dynamic protocol (Snapshot Pulse (SSP), GE): axial scan every 1–2 heart beats for 22 scans using 140 kV, 0.35 s gantry period and 80 mA (normal dose). MP measurement was repeated with the x-ray tube current reduced to 20 mA (low dose). The normal- and low-dose SSP images were reconstructed using filtered backprojection (FBP) (SSP80) and both FBP (SSP20FBP) and ASIR (SSP20ASIR) respectively. All images were corrected for beam hardening from which MP maps were generated using CT Perfusion (GE). After the CT perfusion studies, fluorescent microspheres were injected into the left atrial appendage of the heart to measure MP. Mean MP measured with microspheres and the three CT image sets in 45 segments from the lateral, apical and septal wall in 15 slices from three pigs were compared using linear regression and Bland-Altman analysis. Effective dose (ED) of each SSP protocol was estimated from the dose-length product provided by the scanner.
Results SSP80 images exhibited the highest correlation with microspheres (R = 0.69) compared to SSP20ASIR (R = 0.60) and SSP20FBP (R = 0.57). SSP80 images also showed the smallest difference in mean MP from microspheres and narrowest limits of agreement with microspheres (7.0 and -32.9 to 46.8 ml × min-1 × 100g-1 (80)) compared to SSP20ASIR (11.3 and -35.3 to 57.8 (93)) and SSP20FBP (15.7 and -32.8 to 64.1 (97)). ED of the SSP80 and SSP20 protocols were 4.5 and 1.1 mSv respectively.
Conclusions Noise in low dose SSP images reconstructed with FBP was excessive which led to less accurate and reproducible MP estimation with CT Perfusion but such errors could be reduced with ASIR. With the proposed image acquisition and reconstruction approaches, MP measurement with low dose CT Perfusion is a feasible alternative to MRI and SPECT for studying ischemic heart disease.