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The increasing role of quantification in clinical nuclear cardiology: The Emory approach

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Single photon emission computed tomography (SPECT) myocardial perfusion imaging has attained widespread clinical acceptance as a standard of care for patients with known or suspected coronary artery disease. A significant contribution to this success has been the use of computer techniques to provide objective quantitative assessment in interpreting these studies. We have implemented the Emory Cardiac Toolbox (ECTb) as a pipeline to distribute the software tools that we and others have researched, developed, and validated to be clinically useful so that diagnosticians everywhere can benefit from our work. Our experience has demonstrated that integration of all software tools in a common platform is the optimal approach to promote both accuracy and efficiency. Important attributes of the ECTb approach are (1) our extensive number of normal perfusion databases for SPECT and positron emission tomography (PET) studies, each created with at least 150 patients; (2) our use of Fourier analysis of regional thickening to ensure proper temporal resolution and to allow accurate measurement of left ventricular function and dyssynchrony; (3) our development of PET tools to quantify myocardial hibernation and viability; (4) our development of 3-dimensional displays and the use of these displays as a platform for image fusion of perfusion and computed tomography angiography; and (5) the use of expert systems for decision support. ECTb is an important tool for extracting quantitative parameters from all types of cardiac radionuclide distributions. ECTb should continue to play an important role in establishing cardiac SPECT and PET for flow, function, metabolism, and innervation clinical applications.

Section snippets

ECTb philosophy

Our primary goal as a research team is to stay at the leading edge of scientific discovery to diagnose heart disease. We have implemented ECTb as a pipeline to distribute the software tools that we and others have researched, developed, and validated to be clinically useful so that diagnosticians everywhere can benefit from our work. We use a high-level scientific language (IDL) to shorten the time between concept and general distribution, and this frees our scientists to devote most of their

Integration

Our experience has demonstrated that integration of all software tools in a common platform is the optimal approach to promote both accuracy and efficiency. Accuracy is promoted because in the common platform, all functions are synergistic. For example, all automatic processing is performed before displaying the tomographic oblique slices for visual interpretation. Because the algorithm has already detected the apex and the base of the rest and stress MPI studies, the software automatically

Polar Map Representation

For representation of the patient’s LV myocardial perfusion distribution and for identifying hypoperfused segments, we use the polar map approach first reported by Garcia et al.1 In this approach the 3-dimensional (3D) maximal LV count distribution is synthesized onto a single 2-dimensional polar map, where the count distribution at the base of the left ventricle corresponds to the intensity at the periphery of the map and the counts at the apex to the center of the polar map. For detecting

Myocardial Thickening

All measurements of LV function in ECTb are based on our ability to measure myocardial thickening throughout the cardiac cycle. In 1990 Galt et al13 from our group showed that as a result of the limited spatial resolution of our imaging cameras compared with the myocardial thickness, partial-volume effects cause an almost linear change in maximal counts in myocardial segments as a change in thickness. Thus we determined that thickening could be measured for a myocardial segment as a change in

PET tools for quantitative analysis

Quantification of myocardial perfusion of PET tracers uses the same database quantification approach explained earlier except that the normal limits are generated by use of PET radiopharmaceuticals. Normal patterns are shown in Figure 2 for rubidium 82 and nitrogen 13 ammonia, and the PET normal databases are listed in Table 2. These have been validated clinically including the latest Rb-82 PET/computed tomography (CT) protocol.21

To quantify the perfusion/metabolism match/mismatch pattern as a

Three-Dimensional Displays

We use 3D graphics techniques to overlay results of perfusion quantification onto a representation of a specific patient’s left ventricle. This representation is generated by use of endocardial or epicardial surface points extracted from the perfusion data. Our approach for detecting the surface of the myocardium starts with the 3D coordinates of the maximal myocardial count samples created during perfusion quantification.23 The coordinates of each sampled point are filtered to remove noise. By

Summary

The inherently digital nuclear cardiology images coupled with the tremendous advances in computer hardware and software have facilitated our progress in total automatic analysis; multidimensional, multimodality display; quantification of all clinically relevant parameters; and computer-assisted decision support. Our Emory team has created ECTb as a pipeline to take advantage of this modern technology to bring to nuclear cardiology practitioners clinically validated tools to visualize and

Acknowledgment

The research that generated the science implemented in ECTb was funded in part by National Institutes of Health grants HL070422, HL068904, HL42052, and LM06726. Some of the authors receive royalties from the sale of ECTb (E.V.G., T.L.F., C.D.C., and R.D.F.) related to the research described in this article. The terms of this arrangement have been reviewed and approved by Emory University in accordance with its conflict-of-interest practice.

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