Clinical Utility and Future Applications of PET/CT and PET/CMR in Cardiology

Abstract

Over the past several years, there have been major advances in cardiovascular positron emission tomography (PET) in combination with either computed tomography (CT) or, more recently, cardiovascular magnetic resonance (CMR). These multi-modality approaches have significant potential to leverage the strengths of each modality to improve the characterization of a variety of cardiovascular diseases and to predict clinical outcomes. This review will discuss current developments and potential future uses of PET/CT and PET/CMR for cardiovascular applications, which promise to add significant incremental benefits to the data provided by each modality alone.

Keywords: PET/CMR; PET/CT; cardiovascular magnetic resonance; computed tomography; molecular imaging; myocardial; positron emission tomography.

Figure 1

Schematic cross-sectional views of potential designs for combined PET/MR imaging systems: (A) sequential design with two imagers mounted from end to end and (B) fully-integrated design with the PET imager (P) in between the radiofrequency coil (R) and the gradient set (G) of the MR imager (bottom). Adapted from Torigian et al., 2013, by permission of Radiology [23].

Figure 2

Viability imaging with PET using ¹³NH₃ and ¹⁸F-FDG. Viable tissue can be identified based on the mismatch between reduced myocardial blood flow seen by poor ¹³NH₃ uptake (left) and normal myocardial metabolism of ¹⁸F-FDG (right). Reproduced from Schinkel et al., 2007 by permission of J. Nucl. Med. [50].

Figure 3

PET/CT assessing perfusion and coronary artery anatomy. Hyperemic MBF by PET (top) was reduced in the territories supplied by the left circumflex artery (LCX) and right coronary artery (RCA) (1.8–1.9 mL/min/g), but normal in the left anterior descending (LAD) arterial territory (2.6 mL/min/g). CCTA interpretation (bottom), however, suggested significant stenoses in the LAD, LCX and RCA. Adapted from Thomassen et al., 2013, by permission of Eur. J. Nucl. Med. Mol. Imaging [96].

Figure 4

PET/CT imaging of ¹⁸F-fluoride and ¹⁸F-FDG uptake in a patient with acute myocardial infarction seen by ST-segment elevation on EKG. Invasive coronary angiography (A) demonstrates a proximal occlusion (red arrow) of the left anterior descending artery; ¹⁸F-Fluoride PET/CT imaging (B) identifies the culprit plaque (red arrow) based on (B) intense focal uptake (yellow-red); The corresponding ¹⁸F-FDG PET/CT image (C) shows no uptake at the site of the culprit. Significant uptake can be seen in myocardium next to the coronary artery (yellow arrow) and in the esophagus (blue arrow). Adapted from Joshi et al., 2014, by permission from The Lancet [55].

Figure 5

Hybrid PET/CMR imaging of three subendocardial infarctions (red arrows) with significant myocardial salvage. In all of the studies, the areas of reduced ¹⁸F-FDG uptake (black arrows) and of increased T2 mapping (white arrows) extended beyond the areas of LGE. In Study 2, the area of reduced ¹⁸F-FDG uptake is substantially larger than the area of LGE and more closely matched the T2 map. The follow-up scan confirms the presence of myocardial salvage, in which in area of reduced ¹⁸F-FDG uptake decreases in size and matches the areas of infarction. Reproduced from Bulluck et al., 2016, by permission of Circ. Cardiovasc. Imaging [123].

Figure 6

PET imaging of flow, viability and sympathetic innervation in two patients with ischemic cardiomyopathy to predict risk from sudden cardiac arrest (SCA). The subject in (A), who developed an SCA, demonstrated a larger volume of sympathetic denervation by ¹¹C-HED compared to infarct size by ¹⁸F-FDG uptake. There was also reduced perfusion by ¹³NH with preserved ¹⁸F-FDG indicating hibernating myocardium; In contrast, (B) shows a subject with matched reductions in flow, infarct volume and sympathetic denervation. ANT = anterior; INF = inferior; LAT = lateral; PET = positron emission tomography; SEP = septum. Reproduced from Fallavollita et al., 2014, by permission of J. Am. Coll. Cardiol. [133].

Figure 7

Staging of cardiac sarcoidosis using resting myocardial perfusion scintigraphy (MPS), FDG-PET and LGE-CMR. MPS shows increasing size of scarring as the disease advances. FDG-PET shows a heterogeneous pattern of inflammation in the intermediate stages, with exception to burnt-out stages in which there is no FDG uptake. LGE-CMR demonstrates the fibrotic changes, which is more prevalent in late stage sarcoidosis. Reproduced by Kouranos et al., 2015, by permission of Br. Med. Bull. [139].