LAUSR

In this issue of the Journal, we are presented with a report by Barone-Rochette et al., of the diagnostic accuracy of a novel approach to myocardial perfusion imaging for stable coronary artery disease (CAD). The protocol utilized was dual isotope, stress thallium-201/ rest Tc-99m. The dose was 2 mCi of Tl-201, and around 8 mCi of Tc-99m sestamibi for patients \ 80 Kg, and weight-based for heavier patients, resulting in an average total body effective dose of 12 mSv. Strengths of the study include the use of FFR, and not just visually interpreted coronary angiography as the comparator standard, and the fact that all patients were referred for coronary angiography. While the latter fact avoids the verification bias resulting from selective angiography in patients with abnormal scans, it introduces a bias of its own by selecting only high-risk patients as subjects for the study. This selection bias was reflected in the results, with reported patient-level sensitivity, specificity, and diagnostic accuracy of 92.8%, 69.2%, and 81.4%, respectively. The protocol is novel in that it used the strengths of solid-state (Cadmium Zinc Telluride-crystal) technology to enable low-dose imaging with Tl-201, a tracer that has a higher extraction fraction than Tc-99m sestamibi or Tc-99m tetrofosmin, and thus might be expected to improve the sensitivity of detecting mild disease and identify more ischemia. While this logic is based on sound physiological concept, the study did not actually demonstrate that this is true by comparing this protocol to a single-isotope, Tc-99m-based one. Thus, it remains mostly a feasibility study of a dual isotope protocol using low-dose thallium-201. In this respect, it is not exclusive, since such an approach has been proven feasible before. In fact, like many similar studies of diagnostic performance, the manuscript leaves the reader with many unanswered questions: