Quantitation of Myocardial Blood Flow with Quantitative Dynamic SPECT/CT

Abstract

Background: Myocardial blood flow quantitation (MBFQ) with PET currently is not practical in Taiwan, China and other Asian countries due to the accessibility of PET imaging tracers. MBFQ with SPECT tracers, such as Tc-99m Sestamibi(MIBI) or Tc99m Tetrofosmin instead becomes clinically feasible when quantitative dynamic SPECT/CT (dSPECT/CT) imaging method has been developed. In this article, we depict the technical detail of dSPECT/CT imaging and demonstrate its feasibility to measure MBF in normal subjects with MIBI tracer.Methods: Dynamic SPECT images were acquired using Symbia T SPECT/CT system and reconstructed with 3D-OSEM with correction for attenuation, scatter, resolution, isotope decay and image noise. A coke bottle experiment was performed to obtain the calibration factor for converting pixel value to the unit of Bq/ml. A cardiac phantom experiment was performed to test the accuracy of activity measurement in myocardial wall, left ventricle cavity and torso regions. Five consecutive patients with low likelihood of coronary artery disease ＜5%) were recruited for rest/dipyridamole-stress fast MIBI dSPECT/CT scan. A net-retention flow model was employed to calculate Kl for MBF value with correction for partial volume in myocardium and MIBI extraction fraction adopted from animal data. Coronary flow reserve (CFR) was then computed as the ratio of stress and rest MBF values.Results: The calibration factor was 60264 Bq/ml. In cardiac phantom, the accuracy of activity prediction in torso region was 99.3% for 600 sec and remained 91.1% with reduced acquisition duration to 10 sec. Due to spillover and partial volume effects, the accuracy for left ventricle cavity was 87% and 54% for myocardium, likely independent to duration. The partial volume correction was 1.83. Mean MBF at rest for normal subjects was 0.57±0.14 (ml/g/min) and increased to 2.69±0.57 with DS. Mean CFR value was 4.67±0.61 which matched closely with the known CFR value of N13Ammonia PET (4.3±1.3).Conclusion: Quantitative imaging with dynamic SPECT is an effective method to measure myocardial blood flow with Tc-99m labeled tracers. Its clinical utilization can also be extended to other applications which require fast dynamic imaging to study physiological parameters with SPECT tracers.