An arterial map is overlaid on the 3-D topographic display of rest perfusion images (upper row) of Figure 1. Alternatively, a map of the coronary artery distribution regions is overlaid on the myocardial perfusion images after dipyridamole stress (lower row) of Figure 1. These overlays of the coronary arteries or their regions were developed as a precise, detailed perfusion atlas for every coronary artery and all secondary branches by correlating myocardial perfusion defects objectively quantified on PET perfusion images, with stenosis in every specific coronary artery and their individual branches, on coronary arteriograms for over 1,000 patients.
Figure 1 illustrates the remarkable accuracy of PET for assessing the location and severity of mild or severe stenosis of specific coronary arteries and secondary branches. In this example, the PET shows a severe stenosis of the second diagonal branch, a milder stenosis of a small first obtuse marginal branch, and mild diffuse disease of the left circumflex coronary artery, all confirmed by arteriography. Every coronary artery and secondary branches have been mapped like this example. Sub-endocardial underperfusion manifests as milder decreased activity in the 3-D topographic display compared with a more severe defect for transmural perfusion defects.
Cardiac PET and CT for Coronary Calcification or CT Arteriography
Coronary calcium by CT scanning is an important marker of coronary atherosclerosis. However, early lipid-rich coronary atheroma in young people with premature CAD may cause plaque rupture and coronary events without calcification. At the other extreme, heavy coronary calcification with no flow-limiting stenosis is common in the authorÔÇÖs experience. While valuable as a marker of atherosclerosis, the question of associated stenosis with asymptomatic coronary calcification remains, for which invasive arteriography may not be justified.
The non-invasive CT coronary arteriogram is generating interest for assessing the presence and severity of stenoses. However, the best resolution achievable with a static ideal phantom using the most advanced CT is 1.2 line pairs per millimeter measured personally by the author compared with three- to four-line pairs/mm resolution of invasive cine arteriography that is necessary for assessing stenosis severity quantitatively. Consequently, careful comparisons of non-invasive CT arteriograms with invasive cine arteriograms demonstrate that severity of coronary artery stenosis cannot be reliably determined by CT angiography for definitive clinical purposes. Smaller detector size in CT scanners would improve resolution but would incur prohibitively increased radiation exposure and cost.