Accuracy and Reproducibility of Myocardial Blood Flow Quantification by Single Photon Emission Computed Tomography Imaging in Patients With Known or Suspected Coronary Artery Disease.

BACKGROUND: Single photon emission computed tomography (SPECT) has limited ability to identify multivessel and microvascular coronary artery disease. Gamma cameras with cadmium zinc telluride detectors allow the quantification of absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR). However, evidence of its accuracy is limited, and of its reproducibility is lacking. We aimed to validate 99mTc-sestamibi SPECT MBF and MFR using standard and spline-fitted reconstruction algorithms compared with 13N-ammonia positron emission tomography in a cohort of patients with known or suspected coronary artery disease and to evaluate the reproducibility of this technique. METHODS: Accuracy was assessed in 34 participants who underwent dynamic 99mTc-sestamibi SPECT and 13N-ammonia positron emission tomography and reproducibility in 14 participants who underwent 2 99mTc-sestamibi SPECT studies, all within 2 weeks. A rest/pharmacological stress single-day SPECT protocol was performed. SPECT images were reconstructed using a standard ordered subset expectation maximization (OSEM) algorithm with (N=21) and without (N=30) application of spline fitting. SPECT MBF was quantified using a net retention kinetic model' and MFR was derived as the stress/rest MBF ratio. RESULTS: SPECT global MBF with splines showed good correlation with 13N-ammonia positron emission tomography (r=0.81, P<0.001) and MFR estimates (r=0.74, P<0.001). Correlations were substantially weaker for standard reconstruction without splines (r=0.61, P<0.001 and r=0.34, P=0.07, for MBF and MFR, respectively). Reproducibility of global MBF estimates with splines in paired SPECT scans was good (r=0.77, P<0.001), while ordered subset expectation maximization without splines led to decreased MBF (r=0.68, P<0.001) and MFR correlations (r=0.33, P=0.3). There were no significant differences in MBF or MFR between the 2 reproducibility scans independently of the reconstruction algorithm (P>0.05 for all). CONCLUSIONS: MBF and MFR quantification using 99mTc-sestamibi cadmium zinc telluride SPECT with spatiotemporal spline fitting improved the correlation with 13N-ammonia positron emission tomography flow estimates and test/retest reproducibility. The use of splines may represent an important step toward the standardization of SPECT flow estimation.

Collimator optimization for detection and quantitation tasks: application to gallium-67 imaging.

We describe a new approach to the problem of collimator optimization in nuclear medicine; our methodology is illustrated for the challenging case of gallium-67 imaging. Collimator-design methods based on empirical rules, such as specification of an allowable level of single-septal penetration (SSP) at a fixed energy, are especially inappropriate for radionuclides characterized by an abundance of high-energy contaminant photons that scatter in the patient, collimator, and/or detector before detection within one of a few photopeak energy windows. Lead X-rays produced in the collimator are an additional source of contamination. We designed optimal collimation for 67Ga based on relevant clinical imaging tasks and a realistic simulation of photon transport in a phantom, collimator, and detector. Collimator designs were compared on the basis of performance in lesion detection, as predicted by a three-channel Hotelling observer (CHO), as well as in tumor and background activity estimation (EST), quantified by task-specific signal-to-noise ratios (SNRs). The optimal values of collimator lead content were 22.0 and 23.8 g/cm2, respectively, for CHO and EST, while the optimal geometric resolution values were 1.8 and 1.6 cm full-width at half-maximum (FWHM), respectively, at a distance of 23.5 cm. The resolution of a commercially available medium-energy low-penetration collimator (MELP) is 1.9 cm FWHM at this distance. The optimal values for SSP at 300 keV were 7.3% and 5.8% based on CHO and EST, respectively, compared to 5.2% for the MELP collimator. Compared with the commercial MELP collimator, the 67Ga collimator optimized for tumor detection or activity estimation tasks provided improved geometric spatial resolution with reduced geometric efficiency and, surprisingly, allowed an increased level of single-septal penetration.