Cardiac PET/CT for the evaluation of known or suspected coronary artery disease

Abstract

Positron emission tomography (PET) is increasingly being applied in the evaluation of myocardial perfusion. Cardiac PET can be performed with an increasing variety of cyclotron- and generator-produced radiotracers. Compared with single photon emission computed tomography, PET offers lower radiation exposure, fewer artifacts, improved spatial resolution, and, most important, improved diagnostic performance. With its capacity to quantify rest-peak stress left ventricular systolic function as well as coronary flow reserve, PET is superior to other methods for the detection of multivessel coronary artery disease and, potentially, for risk stratification. Coronary artery calcium scoring may be included for further risk stratification in patients with normal perfusion imaging findings. Furthermore, PET allows quantification of absolute myocardial perfusion, which also carries substantial prognostic value. Hybrid PET-computed tomography scanners allow functional evaluation of myocardial perfusion combined with anatomic characterization of the epicardial coronary arteries, thereby offering great potential for both diagnosis and management. Additional studies to further validate the prognostic value and cost effectiveness of PET are warranted.

Figure 1

State-of-the-art hybrid cardiac PET/CT protocol for delineation of the extent and functional consequences of atherosclerosis. With use of an integrated PET/CT imaging system, both anatomic CAD and resulting myocardial ischemia can be characterized in a single setting. In patients with known CAD, the coronary artery calcium (CAC) scan may be omitted (although its use may be helpful for identifying patients who have extensive coronary calcification and are thus poor candidates for nonenhanced CT angiography [CTA] performed with a relatively low radiation dose). Alternatively, if detailed delineation of the extent of CAD is not required, the CAC scan alone, without coronary CT angiography, may allow additional risk stratification at lower radiation doses without iodinated contrast material. Because the attenuation-correction CT is not electrocardiographically (ECG) gated and is performed during free breathing to best match the PET study, it is not useful for quantitative ascertainment of the calcium score. However, approximate evaluation of the calcium score from attenuation-correction CT images may be possible (15).

Figure 2a

PET artifact caused by transmission-emission misalignment. (a) Misalignment of CT transmission and emission (⁸²Rb) images (top) is a result of the anterior and anterolateral walls overlapping the lung field (arrow). Consequently, the stress-rest myocardial perfusion PET scans (bottom) show an apparent reversible anterior and anterolateral perfusion defect (arrowhead). This typical perfusion defect results from applying low-attenuation coefficients (corresponding to air) to the myocardial region overlapping the lung field on the CT transmission scan during tomographic reconstruction. (b) Correctly aligned transmission-emission images (top) result in a normal perfusion study (bottom).

Figure 2b

PET artifact caused by transmission-emission misalignment. (a) Misalignment of CT transmission and emission (⁸²Rb) images (top) is a result of the anterior and anterolateral walls overlapping the lung field (arrow). Consequently, the stress-rest myocardial perfusion PET scans (bottom) show an apparent reversible anterior and anterolateral perfusion defect (arrowhead). This typical perfusion defect results from applying low-attenuation coefficients (corresponding to air) to the myocardial region overlapping the lung field on the CT transmission scan during tomographic reconstruction. (b) Correctly aligned transmission-emission images (top) result in a normal perfusion study (bottom).

Figure 3a

Underestimation of CAD extent at PET in a 63-year-old man who was referred for evaluation of atypical chest pain. (a) Stress-rest myocardial perfusion PET scans demonstrate a small reversible perfusion defect involving the inferolateral wall (arrow), a finding that is consistent with single-vessel ischemia in the left circumflex–obtuse marginal coronary artery territory. Although PET helped correctly identify the patient as having obstructive CAD, it led to severe underestimation of the amount of myocardium at risk. (b) Left anterior oblique coronary angiogram reveals severe stenosis (yellow arrow) of the left main artery (white arrow).

Figure 3b

Underestimation of CAD extent at PET in a 63-year-old man who was referred for evaluation of atypical chest pain. (a) Stress-rest myocardial perfusion PET scans demonstrate a small reversible perfusion defect involving the inferolateral wall (arrow), a finding that is consistent with single-vessel ischemia in the left circumflex–obtuse marginal coronary artery territory. Although PET helped correctly identify the patient as having obstructive CAD, it led to severe underestimation of the amount of myocardium at risk. (b) Left anterior oblique coronary angiogram reveals severe stenosis (yellow arrow) of the left main artery (white arrow).

Figure 4

Relationship between the extent of CAD and LVEF reserve. Bar graph demonstrates the inverse relationship between the extent of angiographic CAD (>70% stenosis) and the stress-induced change in LVEF. Each bar represents the mean LVEF reserve (ie, change in LVEF from rest to peak stress) on gated perfusion PET scans obtained in patients with 0- (green), 1- (yellow), 2- (red), or 3-vessel or left main (blue) CAD at invasive coronary angiography. (Reprinted, with permission, from reference .)

Figure 5a

Use of CFR to identify disease not visible at perfusion PET in a 61-year-old man who was referred for evaluation of chest pain. (a, b) Stress-rest myocardial perfusion PET scans (a) demonstrate a small reversible perfusion defect involving the left ventricular apex and inferoapical segments, a finding that is consistent with single-vessel ischemia in the distal left anterior descending coronary artery territory. Although PET helped correctly identify the patient as having obstructive CAD, it led to severe underestimation of the amount of myocardium at risk. However, quantitative CFR (b) was markedly impaired in all vascular territories (normal CFR >2), a finding that is consistent with extensive ischemic myocardium. LAD = left anterior descending artery, LCX = left circumflex artery, RCA = right coronary artery. (c, d) Left anterior oblique coronary angiograms (d, caudal view) demonstrate a complex plaque causing 70% stenosis involving the distal left main, proximal LAD, and LCX arteries (arrowheads). The right coronary artery had nonobstructive atherosclerosis.

Figure 5b

Use of CFR to identify disease not visible at perfusion PET in a 61-year-old man who was referred for evaluation of chest pain. (a, b) Stress-rest myocardial perfusion PET scans (a) demonstrate a small reversible perfusion defect involving the left ventricular apex and inferoapical segments, a finding that is consistent with single-vessel ischemia in the distal left anterior descending coronary artery territory. Although PET helped correctly identify the patient as having obstructive CAD, it led to severe underestimation of the amount of myocardium at risk. However, quantitative CFR (b) was markedly impaired in all vascular territories (normal CFR >2), a finding that is consistent with extensive ischemic myocardium. LAD = left anterior descending artery, LCX = left circumflex artery, RCA = right coronary artery. (c, d) Left anterior oblique coronary angiograms (d, caudal view) demonstrate a complex plaque causing 70% stenosis involving the distal left main, proximal LAD, and LCX arteries (arrowheads). The right coronary artery had nonobstructive atherosclerosis.

Figure 5c

Use of CFR to identify disease not visible at perfusion PET in a 61-year-old man who was referred for evaluation of chest pain. (a, b) Stress-rest myocardial perfusion PET scans (a) demonstrate a small reversible perfusion defect involving the left ventricular apex and inferoapical segments, a finding that is consistent with single-vessel ischemia in the distal left anterior descending coronary artery territory. Although PET helped correctly identify the patient as having obstructive CAD, it led to severe underestimation of the amount of myocardium at risk. However, quantitative CFR (b) was markedly impaired in all vascular territories (normal CFR >2), a finding that is consistent with extensive ischemic myocardium. LAD = left anterior descending artery, LCX = left circumflex artery, RCA = right coronary artery. (c, d) Left anterior oblique coronary angiograms (d, caudal view) demonstrate a complex plaque causing 70% stenosis involving the distal left main, proximal LAD, and LCX arteries (arrowheads). The right coronary artery had nonobstructive atherosclerosis.

Figure 5d

Use of CFR to identify disease not visible at perfusion PET in a 61-year-old man who was referred for evaluation of chest pain. (a, b) Stress-rest myocardial perfusion PET scans (a) demonstrate a small reversible perfusion defect involving the left ventricular apex and inferoapical segments, a finding that is consistent with single-vessel ischemia in the distal left anterior descending coronary artery territory. Although PET helped correctly identify the patient as having obstructive CAD, it led to severe underestimation of the amount of myocardium at risk. However, quantitative CFR (b) was markedly impaired in all vascular territories (normal CFR >2), a finding that is consistent with extensive ischemic myocardium. LAD = left anterior descending artery, LCX = left circumflex artery, RCA = right coronary artery. (c, d) Left anterior oblique coronary angiograms (d, caudal view) demonstrate a complex plaque causing 70% stenosis involving the distal left main, proximal LAD, and LCX arteries (arrowheads). The right coronary artery had nonobstructive atherosclerosis.

Figure 6

Relationship between predicted mortality and stress perfusion defects. Bar graph demonstrates the increased unadjusted annualized rate of cardiac death (blue) and myocardial infarction (red) with increasing extent and severity of perfusion defects at stress PET in patients with known or suspected CAD. (Adapted, with permission, from reference .)

Figure 7a

Potential added value of a CAC score in patients with normal myocardial perfusion who had been referred for evaluation of atypical angina. (a) Stress-rest myocardial perfusion PET images (top) and a representative transverse section from a nonenhanced gated cardiac CT scan (middle) obtained in a 61-year-old man with dyslipidemia and hypertension demonstrate no evidence of coronary artery calcifications (Agatston score = 0 [bottom]). (b) Stress-rest myocardial perfusion PET images (top) and a representative transverse section from a nonenhanced gated cardiac CT scan (middle) obtained in a 59-year-old man with dyslipidemia and a family history of CAD demonstrate coronary artery calcifications that are, however, not extensive (Agatston score = 1348 [bottom]). In both a and b, the normal myocardial perfusion PET scans indicate no evidence of flow-limiting CAD, suggesting an equally low risk in both patients. However, the CAC scores indicate very different degrees of atherosclerosis, suggesting a higher risk in the patient with extensive coronary calcifications. LAD = left anterior descending artery, LCX = left circumflex artery, LM = left main coronary artery, RCA = right coronary artery.

Figure 7b

Potential added value of a CAC score in patients with normal myocardial perfusion who had been referred for evaluation of atypical angina. (a) Stress-rest myocardial perfusion PET images (top) and a representative transverse section from a nonenhanced gated cardiac CT scan (middle) obtained in a 61-year-old man with dyslipidemia and hypertension demonstrate no evidence of coronary artery calcifications (Agatston score = 0 [bottom]). (b) Stress-rest myocardial perfusion PET images (top) and a representative transverse section from a nonenhanced gated cardiac CT scan (middle) obtained in a 59-year-old man with dyslipidemia and a family history of CAD demonstrate coronary artery calcifications that are, however, not extensive (Agatston score = 1348 [bottom]). In both a and b, the normal myocardial perfusion PET scans indicate no evidence of flow-limiting CAD, suggesting an equally low risk in both patients. However, the CAC scores indicate very different degrees of atherosclerosis, suggesting a higher risk in the patient with extensive coronary calcifications. LAD = left anterior descending artery, LCX = left circumflex artery, LM = left main coronary artery, RCA = right coronary artery.

Figure 8

Potential added value of myocardial perfusion CT in a 62-year-old man with atypical chest pain. Curved multiplanar reformatted coronary CT angiographic images (top) demonstrate mixed plaques with moderately significant stenosis in the proximal left anterior descending (LAD) artery (70%) and right coronary artery (RCA) (50%–70%) (arrow). LCx = left circumflex artery. Stress-rest short-axis PET scans (middle) show normal regional myocardial perfusion, and a parametric polar map (bottom) shows normal CFR (>2) in all three coronary territories, reflecting no evidence of flow-limiting CAD.

Figure 9

Positive predictive value of CT angiography for identifying flow-limiting coronary stenoses. Bar graph illustrates the frequency with which inducible ischemia occurs at myocardial perfusion imaging in territories with over 50% stenosis at coronary CT angiography. Yellow = positive predictive value, blue = negative predictive value, * = Di Carli study used PET, ^† = Hacker study used 64-section multidetector CT. (Reprinted, with permission, from reference .)