Association between coronary vascular dysfunction and cardiac mortality in patients with and without diabetes mellitus

Quantification of Myocardial Perfusion Reserve Using Dynamic SPECT Imaging in Humans: A Feasibility Study

Myocardial perfusion imaging (MPI) is well established in the diagnosis and workup of patients with known or suspected coronary artery disease (CAD); however, it can underestimate the extent of obstructive CAD. Quantification of myocardial perfusion reserve with PET can assist in the diagnosis of multivessel CAD. We evaluated the feasibility of dynamic tomographic SPECT imaging and quantification of a retention index to describe global and regional myocardial perfusion reserve using a dedicated solid-state cardiac camera.

METHODS

Ninety-five consecutive patients (64 men and 31 women; median age, 67 y) underwent dynamic SPECT imaging with (99m)Tc-sestamibi at rest and at peak vasodilator stress, followed by standard gated MPI. The dynamic images were reconstructed into 60-70 frames, 3-6 s/frame, using ordered-subsets expectation maximization with 4 iterations and 32 subsets. Factor analysis was used to estimate blood-pool time-activity curves, used as input functions in a 2-compartment kinetic model. K1 values ((99m)Tc-sestamibi uptake) were calculated for the stress and rest images, and K2 values ((99m)Tc-sestamibi washout) were set to zero. Myocardial perfusion reserve (MPR) index was calculated as the ratio of the stress and rest K1 values. Standard MPI was evaluated semiquantitatively, and total perfusion deficit (TPD) of at least 5% was defined as abnormal.

RESULTS

Global MPR index was higher in patients with normal MPI (n = 51) than in patients with abnormal MPI (1.61 [interquartile range (IQR), 1.33-2.03] vs. 1.27 [IQR, 1.12-1.61], P = 0.0002). By multivariable regression analysis, global MPR index was associated with global stress TPD, age, and smoking. Regional MPR index was associated with the same variables and with regional stress TPD. Sixteen patients undergoing invasive coronary angiography had 20 vessels with stenosis of at least 50%. The MPR index was 1.11 (IQR, 1.01-1.21) versus 1.30 (IQR, 1.12-1.67) in territories supplied by obstructed and nonobstructed arteries, respectively (P = 0.02). MPR index showed a stepwise reduction with increasing extent of obstructive CAD (P = 0.02).

CONCLUSION

Dynamic tomographic imaging and quantification of a retention index describing global and regional perfusion reserve are feasible using a solid-state camera. Preliminary results show that the MPR index is lower in patients with perfusion defects and in regions supplied by obstructed coronary arteries. Further studies are needed to establish the clinical role of this technique as an aid to semiquantitative analysis of MPI.

Journey in evolution of nuclear cardiology: will there be another quantum leap with the F-18-labeled myocardial perfusion tracers?

The field of nuclear cardiac imaging has evolved from being rather subjective, more "art than a science," to a more objective, digital-based quantitative technique, providing insight into the physiological processes of cardiovascular disorders and predicting patient outcome. In a mere 4 decades of its clinical use, the technology used to image myocardial perfusion has made quantum leaps from planar to single-photon emission computed tomography (SPECT) and now to a more contemporary rapid SPECT, positron emission tomography (PET), and hybrid SPECT-computed tomography (CT) and PET-CT techniques. Meanwhile, radiotracers have flourished from potassium-43 and red blood cell-tagged blood pool imaging to thallium-201 and technetium-99m-labeled SPECT perfusion tracers along with rubidium-82, ammonia N-13, and more recently F-18 fluorine-labeled PET perfusion tracers. Concurrent with this expansion is the introduction of new quantitative methods and software for image processing, evaluation, and data interpretation. Technical advances, particularly in obtaining quantitative data, have led to a better understanding of the physiological mechanisms underlying cardiovascular diseases beyond discrete epicardial coronary artery disease to coronary vasomotor function in the early stages of the development of coronary atherosclerosis, hypertrophic cardiomyopathy, and dilated nonischemic cardiomyopathy. Progress in the areas of molecular and hybrid imaging are equally important areas of growth in nuclear cardiology. However, this paper focuses on the past and future of nuclear myocardial perfusion imaging and particularly perfusion tracers.