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Figure 9. (A) Fixed and reversible defects. A defect (light area) present at stress and rest is termed a fixed defect and typically represents an area of infarction. A defect present at stress but not at rest is termed a reversible defect and implies ischemia. (B) Schematic showing induction of a perfusion defect at stress. One segment of the ventricle is supplied by a normal artery and a second segment by a stenoic artery. At rest, there is equal flow to both myocardial segments and equal uptake of tracer. At stress, flow to the myocardium supplied by the patent artery increases markedly. Flow to the myocardium supplied by the stenoic artery increases marginally. Less tracer will be taken up in the myocardium supplied by the stenotic vessel than in normally supplied myocardium, i.e., a perfusion defect is induced at stress.

Figure 9. (A) Fixed and reversible defects. A defect (light area) present at stress and rest is termed a fixed defect and typically represents an area of infarction. A defect present at stress but not at rest is termed a reversible defect and implies ischemia. (B) Schematic showing induction of a perfusion defect at stress. One segment of the ventricle is supplied by a normal artery and a second segment by a stenoic artery. At rest, there is equal flow to both myocardial segments and equal uptake of tracer. At stress, flow to the myocardium supplied by the patent artery increases markedly. Flow to the myocardium supplied by the stenoic artery increases marginally. Less tracer will be taken up in the myocardium supplied by the stenotic vessel than in normally supplied myocardium, i.e., a perfusion defect is induced at stress.

Figure 10. Schematic showng derivation of the polar plot. The heart is divided into one pixel slices (A). A single slice is shown on the right side of panel A. The septum and lateral wall show normal uptake while the inferior wall shows a mild defect and the anterior wall a severe defect. Information from this slice (B) and all other slices is inserted into a polar plot (C). In this example, the septum and lateral wall are normal. The entire inferior wall shows mildly diminished activity while the entire anterior wall and apex show markedly dimished uptake.

Figure 10. Schematic showng derivation of the polar plot. The heart is divided into one pixel slices (A). A single slice is shown on the right side of panel A. The septum and lateral wall show normal uptake while the inferior wall shows a mild defect and the anterior wall a severe defect. Information from this slice (B) and all other slices is inserted into a polar plot (C). In this example, the septum and lateral wall are normal. The entire inferior wall shows mildly diminished activity while the entire anterior wall and apex show markedly dimished uptake.

Figure 11. Polar plot of study shown in Figure 17. (A) Stress polar plot showing diminished activity (darker area) in the inferior wall. (B) Rest polar plot showing improved uptake in the inferior wall. (C) Using the stress polar plot, areas considered to be abnormal (based on normal population database) are highlighted in black. (D) Using this "blackout" image, areas considered to improve significantly between stress and rest (i.e., the reversible inferior wall defect) are highlighted in white.

Figure 11. Polar plot of study shown in Figure 17. (A) Stress polar plot showing diminished activity (darker area) in the inferior wall. (B) Rest polar plot showing improved uptake in the inferior wall. (C) Using the stress polar plot, areas considered to be abnormal (based on normal population database) are highlighted in black. (D) Using this "blackout" image, areas considered to improve significantly between stress and rest (i.e., the reversible inferior wall defect) are highlighted in white.

Clinical Role in the Diagnosis of Coronary Artery Disease

Indications

One of the major applications of MPI is the detection of hemodynamically significant CAD in patients with an intermediate pre-test likelihood of coronary disease. In most institutions, a GXT is the initial diagnostic test unless there are resting electrocardiographic abnormalities or the patient is on digoxin (since inducible ST segment depression in this population is of uncertain diagnostic significance). MPI is also indicated in patients who have a non-diagnostic GXT because they were unable to reach their target heart rate and did not have angina or ST segment depression (Table 3). In accordance with Bayes' theorem the predictive accuracy of a test depends not only on its sensitivity and specificity but also on the prevalence of

Figure 12. Twenty segment model used for calculation of the stress severity score (SSS). The left ventricular apex is divided into two segments (anteroapical and inferoapical). The remainder of the ventricle is divided into three cylindrical slices representing the distal, mid and basal thirds of the ventricle. Each of these thirds is divided into six segments (Ant-anterior; AL-anterolateral; PL-posterolateral; Inf-inferior; IS-inferoseptal; AS-anteroseptal) for a total of 20 segments. To calculate the SSS, each segment is assigned a score from 0 (normal) to 4 (absent) uptake. The sum of the scores for all 20 segments is the SSS.

Figure 12. Twenty segment model used for calculation of the stress severity score (SSS). The left ventricular apex is divided into two segments (anteroapical and inferoapical). The remainder of the ventricle is divided into three cylindrical slices representing the distal, mid and basal thirds of the ventricle. Each of these thirds is divided into six segments (Ant-anterior; AL-anterolateral; PL-posterolateral; Inf-inferior; IS-inferoseptal; AS-anteroseptal) for a total of 20 segments. To calculate the SSS, each segment is assigned a score from 0 (normal) to 4 (absent) uptake. The sum of the scores for all 20 segments is the SSS.

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