Clinical evaluation of a new low dose Tc-rest, Tl-stress single-scan cardiac SPECT protocol indicating improved accuracy

Objectives Our aim is to evaluate the diagnostic value of a one-hour single-scan dual isotope protocol (SDI) in comparison to a standard two-day protocol.

Methods The proposed SDI protocol starts with an injection of 250MBq Technetium (Tc) at rest. After 20 min waiting time, followed by stress with 70-111MBq Thallium (Tl) injection at peak stress, tracer distributions are acquired by a single dual isotope SPECT scan. Images are reconstructed by an OSEM reconstruction code including attenuation correction, fast Monte Carlo based correction of scatter and cross-contamination, and resolution recovery. Tc images acquired in a 2-day protocol in the same patient at same stress level are used as reference. SDI and reference images are evaluated blinded, and interpretation is done by experienced cardiologists and nuclear physicians.

Results In 30 of the first 53 patient (57%) the interpretation of the SDI and the reference images leads to comparable clinical outcome (SSS-score and area). In 18 patients the interpretation of the SDI images differs from Tc reference. In 10 patients a coronary angiography was performed and in 9/10 SDI results are proven to be more accurate with regard to severity and extent of the lesions. For the remaining 8 patients no clinical follow-up is available, yet. For 5 obese patients (BMI >32) the injected Tl-dose seems to be not sufficient and images are hardly interpretable. This was recognized during the study and Tl-dose for obese patients has since been adapted to a maximum of 131MBq.

Conclusions Originally the proposed SDI protocol aimed at optimized clinical workflow and patient comfort due to single acquisition of rest and stress images. The preliminary outcome of the study indicates that in most cases the results are highly comparable to the reference data. Moreover, enhanced diagnostic value is indicated in almost all cases where follow-up examinations are applicable