Evaluation of ischaemia in obese patients: feasibility and accuracy of a low-dose protocol with a cadmium-zinc telluride camera
Obesity is a significant and independent risk factor for cardiovascular disease, and assessing ischaemia in obese patients is clinically important but sometimes difficult because of imaging artefacts. The aim of this study was to evaluate the feasibility and diagnostic accuracy of stress/rest imaging with a cadmium-zinc telluride (CZT) camera using a low-dose protocol in a series of consecutive obese patients referred for the evaluation of coronary artery disease. We considered 148 consecutive obese patients (mean BMI 39 ± 7 kg/m2) with known or suspected coronary artery disease referred to our laboratory for stress/rest myocardial perfusion imaging. A subgroup of 103 of the 148 patients underwent invasive coronary angiography for clinical reasons. All patients underwent a single-day stress/rest low-dose ultrafast protocol. Patients were injected with 99mTc-tetrofosmin at a dose in the range 185–222 MBq during bicycle exercise or dipyridamole stress, and underwent the first scan with an acquisition time of 7 min starting 15 min after the end of the stress. The rest scan with an acquisition time of 6 min was started from 30 to 45 min after 99mTc-tetrofosmin injection at a dose in the range 370–444 MBq. Images were visually inspected, and the summed stress score (SSS) and summed rest score (SRS) were obtained. Image quality was graded very good or excellent in all patients. Of the 103 patients who underwent coronary angiography, 12 (12 %), 26 (25 %) and 56 (54 %) showed one-, two- and three-vessel disease, and 9 showed normal coronary vessels. In the 103 patients submitted to coronary angiography, the mean SSS and SRS were 7±6 and 2±3, respectively. Semiquantitative regional and global SSS was a good discriminant of coronary artery disease and the area under the overall ROC curve was 0.848 (95 % CI 0.723–0.975). In obese patients, a single-day stress/rest low-dose ultrafast protocol with a CZT camera is clinically feasible and provides high image quality.