However, small changes in coronary artery diameter of tenths of millimeters that cannot be assessed by a CT arteriogram or even by an invasive arteriogram may cause significant changes in coronary flow reserve because flow depends on the fourth power of the arterial radius. PET perfusion images of relative coronary flow reserve, without attenuation artifacts, provide a magnified signal of small changes in arterial diameter as a sensitive specific way of assessing stenosis severity. Therefore, the combination of PET perfusion imaging with CT as a PET-CT scanner has unique strengths for the comprehensive assessment of CAD or its risk factors.
PET Imaging of Early Coronary Atherosclerosis
With attention to technical details of imaging, PET images small differences in perfusion that reflect mild stenosis of diffuse CAD in the absence of significant flow-limiting stenosis. Diffuse coronary atherosclerosis causes a graded base to apex, longitudinal perfusion gradient along the long axis of the heart.This pattern of abnormal perfusion is distinctly different from the circumscribed, regional perfusion defects typical of segmental coronary artery stenosis.
The single view rest-stress perfusion images of Figure 2 show mildly reduced relative perfusion after dipyridamole stress in an asymptomatic lean runner with a father having heart disease and mildly elevated cholesterol levels. The automated quantitative analysis compared with 50 healthy control subjects shows this mild defect to be approximately four standard deviations outside normal limits, indicating diffuse non-obstructive coronary atherosclerosis.
The patient refused lipid or beta-blocker treatment, had a cardiac arrest six months later, and was successfully resuscitated by a physician with him at the time. A coronary arteriogram showed no stenosis but severe coronary atherosclerosis by intravascular ultrasound (IVUS) and a potential site of plaque rupture with probable prior thrombosis dislodged during resuscitation and treatment before the arteriogram.
Management Decisions and Second Opinions in CAD Based on PET
Most major management decisions and second opinions in CAD can be satisfactorily resolved based on PET imaging as illustrated in Figure 3. Each PET image of Figure 3 is a single view of perfusion during stress with normal resting images (not shown) except for the example of hibernating myocardium where the resting images are shown (panels G and H).