Cardiac PET•CT: Integrated CT Angiography and PET Myocardial Perfusion in Multivessel Disease
Noninvasive investigation of CAD using ammonia N 13 injection and multislice CT and PET
Partha Ghosh, MD, Siemens Healthcare, Hoffman Estates, Ill., USA
Case study data provided by Erick Alexanderson, MD, UNAM, Mexico City, Mexico
A 31-year-old man (86.64 kg; 191 lbs) with history of early onset diabetes presented with occasional shortness of breath during exertion. A treadmill stress ECG study showed borderline ST depression in the inferior leads. The patient was referred for a myocardial perfusion PET•CT study. A stress myocardial perfusion PET•CT study was performed on a Biograph™ 64 TruePoint system using 13N NH3 with adenosine infusion stress. Immediately following the PET•CT study, the patient underwent a CT coronary angiography on the same system per-formed as an integrated study.
This study illustrates the potential of comprehensive noninvasive investigation of coronary artery disease using a Biograph scanner with integrated state-of-the-art multislice CT and PET.
Fig. 1: 13N NH3 adenosine stress myocardial perfusion study shows moderate to severe perfusion defect in the inferior wall as well as anterior wall, septum and apex. The lateral and inferolateral walls show normal perfusion. Left ventricle shows significant post-stress dilatation. From the stress PET study, the impression was of LAD and RCA territory ischemia with relatively better perfusion in the left circumflex area, suggesting significant coronary artery disease involving LAD and RCA. The inferior wall appears more severely ischemic than the anterior wall and septum, suggesting more severe stenosis in the RCA. Examination Protocol: 20 mCi 13N NH3 injection following adenosine infusion, 7 minute dynamic PET acquisition. CT angiography performed at conclusion of stress PET acquisition.
Demonstration of severe myocardial perfusion defect on stress perfusion prompted the integrated CT angiography study performed immediately without change in patient position, thereby demonstrating the stenotic coronary artery lesions corresponding to the ischemic zones. The location and severity of the coronary artery lesions correlate perfectly with the ischemic zones and the degree of ischemia (Fig 2 and 3).
Fig. 2: Integrated CT angiography performed following PET perfusion shows multiple stenotic lesions in the proximal and mid LAD and RCA. Multiple mixed plaques (calcified and soft plaques combined) are visualized with severe stenosis in proximal RCA and moderate stenosis in the proximal and mid LAD. There is calcified plaque in mid left circumflex without significant vessel lumen stenosis with normal distal vessel. The distal vessels for both LAD and RCA do not show stenosis (top row).
Fusion of CT angiography and stress PET perfusion using syngo® Circulation demonstrates the relationship of the LAD and RCA stenosis to the large anterior wall and inferior wall ischemia with normal lateral wall perfusion corresponding to healthy left circumflex and OM1 (rows 2 and 3).
Technical advancements of Siemens Biograph scanners in the integration of high-end PET and premium CT make such a single combined modality cardiac workflow possible. Several studies have shown the benefits of such a combined approach. Kajander et al (Circulation 2010, 122: 603-613) performed integrated CT angiography and PET myocardial perfusion using O15 water with quantification of myocardial blood flow in 102 consecutive patients with intermediate pretest probability of coronary artery disease. The results were compared with catheter angiography. PET perfusion and CT angiography alone both demonstrated 97% negative predictive value. However, CTA alone was suboptimal in evaluating the severity of stenosis (81% positive predictive value). PET perfusion was highly sensitive in delineation of functionally significant ischemia. PET in combination with CT angiography was able to clarify the diagnosis in all cases with borderline ischemia and together was accurate in 98% of cases when correlated with catheter angiography and post revascularization follow up. It is in this context that a combination of PET perfusion and CT angiography can have a major impact in characterization of coronary artery disease.
PET perfusion imaging can rule out significant CAD with high negative predictive value. It also is very sensitive for detection of functionally significant ischemia. A combination of perfusion and coronary morphology in a single integrated procedure enabled by the Biograph PET•CT scanner can clarify the significance of perfusion defects as well as characterize coronary artery lesions and define their hemodynamic significance. Such an integrated approach also can help assign a culprit vessel to the zone of ischemia which may help define the appropriate therapy approach regarding which lesion to stent or perform angioplasty and which lesion to spare. Overall, such combined approaches have the potential of significantly improving diagnostic confidence in coronary artery disease evaluation.