Impact of low dose myocardial perfusion imaging on patient radiation effective dose and imaging time in real world clinical practice.

Objectives To demonstrate proof of concept/practicality of reducing medical radiation exposure from myocardial perfusion imaging (MPI) by adopting low dose protocols in real world clinical practice.

Methods A cohort of 100 consecutive patients who were referred for MPI to our nuclear medicine service was imaged with a low dose rest-stress MPI protocol. Traditionally used doses of 10 millicuries (mCi) or 370 megabecquerel (MBq) at rest and 30 mCi (1110 MBq) at stress were decreased to half for the low dose protocol, 5 mCi (185 MBq) at rest and 15 mCi (555MBq) at stress. This decision was based on the principle of lowering the injected dose as much as practically feasible while obtaining good diagnostic quality images with similar 1 million count threshold for image acquisition in a reasonable, patient comfortable imaging time ^[1]. All imaging was performed using an ultrafast, high resolution, dedicated cardiac camera (D-SPECT, Spectrum Dynamics) ^[2] in upright position for rest and stress. An additional supine stress image was additionally acquired ^[3]. The low dose patient cohort was retrospectively compared to a cohort of 100 consecutive patients referred to our service for MPI who were imaged using the traditional dose protocol immediately preceding the adoption of the low dose protocol. Comparison between the two groups in different protocols was made using the average values of administered doses in mCi, radiation effective dose in millisieverts (mSv) and the imaging time in minutes: seconds for each rest, stress and total MPI. All patients were imaged using a single day, rest-stress protocol with technetium99m-sestamibi using either exercise or pharmacological stress as determined clinically by the cardiology team.

Results A total of 200 patients with 100 patients in each cohort were evaluated. Traditional dose patients had an average age of 69.8 years (y), male: female ratio of 59:41, weight of 85 kilograms (kg), received a dose of 10.4 mCi (385 MBq) at rest, 31.1 mCi (1151 MBq) at stress. Low dose patients had an average age of 66.6 y, male: female ratio of 52:48, weighed 83.3 kg, and received a dose of 5.28 mCi (195 MBq) at rest, 16.0 mCi (592 MBq) at stress. High dose imaging time in minutes: seconds was 8:17 (rest), 1:46 (stress) and 10:03 (total). Low dose imaging time was 14:36 (rest), 3:24 (stress) and 18:00 (total). As compared to traditional dose protocols, low dose protocols demonstrated significant reduction in average radiation effective dose of 49.1% in rest, 48.5% in stress and 48.7% in total rest-stress MPI. As expected, an increase in imaging time was noted in the low dose protocol, with an average increase of 07:20 min in rest, 03:14 min in stress and 10:34 min in total imaging time, which did not significantly impact patient throughput. No patient complaints were encountered with regards to imaging time by the imaging team. All images were of diagnostic quality, acquired by identical parameters of 1 million count threshold for image acquisition and deemed clinically interpretable by a team of board certified clinical nuclear medicine providers.

Conclusions MPI contributes significantly to medical radiation exposure ^[4]. Low dose MPI can be easily implemented clinically using newer high resolution cardiac specific cameras to achieve markedly lower radiation effective doses to the patient population without significantly impacting patient throughput or diagnostic quality of images. Low dose MPI leads to decreasing medical radiation exposure to the patients, their caregivers, medical staff ^[5] and to the community as a whole. RESEARCH SUPPORT: