Hayato Ishimura

Novel Cardiac SPECT Technology with Semiconductor Detectors: Emerging Trends and Future Perspective

Recently, two vendors have introduced novel SPECT scanners with solid-state semiconductor detectors: Discovery NM530c(D530c)and D-SPECT utilizing the same cadmium zinc-telluride(CZT) detectors, with a different combination of high-sensitivity multi-pinhole or parallel-hole collimator which focuses on the myocardium. The physical performance is dramatically higher than that of conventional Anger cameras, however, 2 CZT cameras are inherently different. Spatial resolution and contrast-to-noise ratio are better with the D530c, whereas detection sensitivity is higher with the D-SPECT. Although Tc-labeled myocardial perfusion tracers might not be ideal, estimation of absolute myocardial blood flow or coronary flow reserve using dynamic CZT SPECT is of great interest and a challenging subject.

Estimation of myocardial flow reserve utilizing an ultrafast cardiac SPECT: Comparison with coronary angiography, fractional flow reserve, and the SYNTAX score

BACKGROUND Quantitative assessment of myocardial flow reserve (MFR) by single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is challenging but may facilitate evaluation of multi-vessel coronary artery disease (CAD). METHODS We enrolled 153 patients with suspected or known CAD, referred for pharmacological stress MPI. They underwent a 99mTc-perfusion stress/rest SPECT with an ultrafast cadmium-zinc-telluride (CZT) camera. Dynamic data were acquired and time-activity curves fitted to a 1-tissue compartment analysis with input function. K1 was assigned for stress and rest data. The MFR index (MFRi) was calculated as K1 stress/K1 at-rest. The findings were validated by invasive coronary angiography in 69 consecutive patients. RESULTS The global MFRi was 1.46 (1.16-1.76), 1.33 (1.12-1.54), and 1.18 (1.01-1.35), for 1-vessel disease (VD), 2-VD, and 3-VD, respectively. In the 3-VD, global MFRi was lower than that in 0-VD (1.63 [1.22-2.04], P<0.0001) and 1-VD (P=0.003). Multivariate logistic regression analysis for 3-VD showed significant associations with smoking history (odds ratio [OR]: 4.4 [0.4-8.4]), left ventricular ejection fraction (OR: 61.6 [57.5-66.0]), and global MFRi (OR: 119.6 [111.5-127.7], P=0.002). A cut-off value of 1.3 yielded 93.3% sensitivity and 75.9% specificity for diagnosing 3-VD. Fractional flow reserve positively correlated with regional MFRi (r=0.62, P=0.008), and the SYNTAX score correlated negatively with global MFRi (r=0.567, P=0.0003). CONCLUSION We developed and validated a clinically available method for MFR quantification by dynamic 99mTc-perfusion SPECT utilizing a CZT camera, which improves the detectability of multi-vessel CAD.

Diagnostic performance of a semiconductor gamma-camera system as studied by multicenter registry

BACKGROUND Despite the introduction of the novel cadmium-zinc-telluride (CZT) single-photon emission computed tomography (SPECT) in Japan; its diagnostic value in clinical practice remains largely unknown. METHODS The Semiconductor SPECT Study group is a multicenter Japanese registry which registered 1000 patients to evaluate the diagnostic utility of the CZT camera system (Discovery NM530c; GE Healthcare, Haifa, Israel). The patients underwent stress myocardial SPECT and coronary angiography within a 3-month interval. A significant stenosis was defined as ≥75% diameter narrowing based on the American Heart Association classification. RESULTS Technetium (99mTc) radiotracer (555-1110MBq) was used in 71% and thallium-201 (201Tl) (74-148MBq) in 29%. The scan times with 99mTc-radiotracer were 5-10min for stress and 3-10min for rest, whereas those with 201Tl were 5-9min for stress and 8-10min for rest. To detect individual coronary stenosis, the respective sensitivities, specificities, and accuracies were 74%, 85%, and 81% for left anterior descending coronary artery (LAD) stenosis, 76%, 89%, and 85% for left circumflex stenosis, and 72%, 86%, and 82% for right coronary artery stenosis. However, 66% sensitivity and 91% specificity for LAD stenosis were observed with 99mTc-radiotracer, whereas 88% sensitivity and 63% specificity were found with 201Tl. CONCLUSIONS The novel CZT SPECT system facilitated a short scan time with reduced radiotracer dose, yielding an acceptable diagnostic performance for angiographical coronary artery disease, although the low sensitivity for LAD detection with 99mTc-radiotracer needs to be refined.

Emerging Trends and Future Perspective of Novel Cardiac SPECT Technology

In response to concerns about overuse and increasing radiation exposure of myocardial perfusion imaging, nuclear medicine societies have declared statements aimed at lowering its radiation dose and costs. Simultaneously, two vendors have launched novel SPECT scanners with solid-state semiconductor detectors. Discovery NM 530c and D-SPECT utilize the same cadmium zinc telluride (CZT) detectors with a different combination of high-sensitivity multi-pinhole or parallel-hole collimator which focuses on the heart. The physical performance of those is dramatically higher than that of conventional Anger cameras; however, 2 CZT cameras are inherently different.

Quantification of Coronary Flow Reserve by 15 O-Water PET with ATP Stress; from a Practical Application Perspective

15 O-water has been considered to be a near-perfect and the most ideal myocardial blood flow (MBF) tracer because it is freely diffusible, metabolically inert, and independent of the myocardial metabolic state, which results in the highest extraction fraction. Absolute coronary flow reserve (CFR) is the ratio of MBF during maximal hyperemia in a coronary artery to MBF in the same artery under resting conditions and can be quantified noninvasively by positron emission tomography (PET). A growing body of literature is accumulating to show that the prognostic value of absolute MBF or CFR, which is quantified by cardiac PET. ATP infusion protocol of 0.16mg/kg/min for 5minutes and its safety profile have been established in humans and it has been widely applied in many clinical and investigative studies including 15 O-water PET. With the use of the 3-min acquisition data, the regions of interest in the left ventricular chamber and myocardium could be set for all of the subjects. Six-min CFR data could be used to separate the CAD patients and controls. A 3-min, but not 2min, scan with 15 O-water PET can be used for the quantitative evaluation of MBF and CFR. A shorter scan time will result in a reduction of body motion of patients, which may lead to the more precise quantification of MBF and CFR.