When the only gated sestamibi scan is the post-stress scan, global and regional LV function will not represent basal LV function in all patients with stress-induced ischemia.

Objectives We sought to evaluate the accuracy and reproducibility of visual estimation of coronary artery calcium (CAC) from CT attenuation correction (CTAC) scans performed for hybrid PET/CT and SPECT/CT myocardial perfusion imaging (MPI). Background At the time of MPI, hybrid systems obtain a low-dose, non-ECG-gated CT scan that is used to perform attenuation correction. Utility of this CTAC scan in estimating actual CAC as measured by Agatston score (AS) on standard ECG-gated scans has not been previously studied. Methods 492 patients from 3 centers receiving both MPI with CTAC and a standard CAC scan were studied. At each site, experienced readers blinded to AS reviewed CTAC images, visually estimating CAC on a six-level scale: classifying patients as estimated AS of 0, 1-9, 10-99, 100-300, 400-999, or ≥1000. Agreement between visually-estimated CAC (VECAC) on CTAC and AS, measured standardly and converted to the same scale, was evaluated, as was inter-reader agreement. Results Although CTAC images are low-dose and non-gated, a high degree of association was observed between VECAC and AS, with 63% of VECACs in the same category as the AS category and 93% within one category. Weighted kappa was 0.89 (95% confidence interval 0.88 to 0.91, p<0.0001). High weighted kappa statistics were observed for each site, scanner type, and gender. Readers reported identical scores in 65% of cases and scores within one category in 93%. Conclusions CAC can be visually assessed from low-dose CTAC scans with high agreement with AS. CTAC scans should be routinely assessed for VECAC.

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TILIZATION OF MEDICALimaging has grown rapidly in recent years. 1 Along with the benefits patients have received from medical imaging has come an increase in the burden of ionizing radiation associated with many such tests and the attendant potential risks of cancer. The National Council on Radiation Protection and Measurements has estimated that the per capita dose of medical radiation in the United States increased nearly 6-fold from the early 1980s to 2006. 2 This increased medical radiation burden has raised public health concerns, leading to a US Food and Drug Administration initiative to reduce unnecessary radiation exposure from medical imaging, 3 with one of its focuses being nuclear imaging, and discussion in Congress of new legislation to regulate medical radiation. 4 Although much attention has been paid to radiation from computed tomography (CT) scans, 5,6 a recent study demonstrated that the single test with the highest radiation burden, accounting for 22% of cumulative effective dose from medical sources, is myocardial perfusion imaging (MPI). 7 Volume of MPI increased from less than 3 million procedures in the United States in 1990 to 9.3 million in 2002, 8 and it is now estimated to account for more than 10% of the entire cumulative effective dose to the US population from all sources, excluding radiotherapy. 2

A r t i c l e A m e n d m e n t s5 5 2 1

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Attenuation correction applied to studies with stress-only Tc-99m ECG-gated single photon emission computed tomography images significantly increases the ability to interpret studies as definitely normal or abnormal and reduces the need for rest imaging. These findings may improve laboratory efficiency and diagnostic accuracy.

Identifying patients at high risk for an acute cardiovascular event such as myocardial infarction or stroke and assessing the total atherosclerotic burden are clinically important. Currently available imaging modalities can delineate vascular wall anatomy and, with novel probes, target biologic processes important in plaque evolution and plaque stability. Expansion of the vessel wall involving remodeling of the extracellular matrix can be imaged, as can angiogenesis of the vasa vasorum, plaque inflammation, and fibrin deposits on early nonocclusive vascular thrombosis. Several imaging platforms are available for targeted vascular imaging to acquire information on both anatomy and pathobiology in the same imaging session using either hybrid technology (nuclear combined with CT) or MRI combined with novel probes targeting processes identified by molecular biology to be of importance. This article will discuss the current state of the art of these modalities and challenges to clinical translation.