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Nuclear Cardiology: Where Do We Stand? (1)

Daniel S. Berman, MD
Guido Germano, PhD

Introduction

Between 1993 and 1997 there has been a significant growth overall in nuclear medicine procedures performed in the United States from 11 million in 1993 to 13 million in 1997, and the major growth that has occurred in nuclear cardiology. In fact, a sustained growth pattern in nuclear cardiology has been observed for approximately 20 years now.
The predominant factor behind this growth is the demonstration that assessing myocardial perfusion, function, and viability with nuclear cardiology is an effective method for defining patients at risk for cardiac events who may benefit from treatment. Despite this growth, we are now witnessing increased competition by other modalities for limited health care dollars. The challenge for nuclear medicine is to demonstrate that nuclear tests are more effective than other modalities in answering important questions at similar costs.

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Myocardial Perfusion Assessment

The principal tools of nuclear cardiology are called myocardial perfusion tracers, but in fact they are tracers of both perfusion and viability. We have an intrinsic advantage of our technology in that the perfusion tracers require viable myocardium in order for them to be extracted, i.e., so the measurement of the amount of thallium, tetrofosmin or sestamibi in the myocardium provides an assessment of myocardial viability as well as myocardial perfusion. Another important competitive advantage of nuclear cardiology is the availability of operator-independent quantitative assessment of myocardial perfusion and function which can be performed in an automatic and objective fashion. It decreases reliance on the expertise of the interpreter and improves reproducibility, facilitates serial assessments, and standardizes results from center to center. (Table 1) Because of the digital nature of the nuclear data, it is possible for the post-acquisition processes of nuclear cardiology to be completely automated, including filtering, reorientation, and reconstruction, as well as analysis of perfusion, analysis of function. (Figure 1) Finally even development of the expert report at the end could have a great deal of input of automatic analysis.

Table 1: Advantages of Quantitative Nuclear Cardiology

Fig. 1: Cardiac perfusion SPECT: quantitative analysis. Quantitative parameters that are derivable from a rest/stress gated perfusion SPECT protocol

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In addition to having this kind of quantitative perfusion defect measurement, the newer programs from various different manufacturers allow the interpreter to use an automatic computer scoring system which can then be modified by the observer to allow the scoring of summed stress score and summed rest score, scores that have been shown to be of major importance for prognostic purposes (Figure 2).

Fig. 2: QPS in AutoQUANT, quantitative perfusion SPECT (QPS) program developed by Cedars-Sinai
Medical Center. An extensive, largely reversible defect is noted throughout the left anterior descending
coronary artery territory. In addition to the quantitative defect extent, 57% in this patient, the QPS display
also provides a computer-derived 20-segment score which can be visually verified or modified.
(adapted with permission from Clinical Gated Cardiac SPECT,
eds. Germano, Berman. Futura Publishing Co., Armonk, NY, p.165).

Ventricular Function Assessment (click here)

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