Abstract

Cardiac PET/MR is a relatively new imaging technique that promises to combine multi-contrast and multi-parametric cardiac MRI that provides information on heart anatomy, left ventricular function, myocardial viability, perfusion, oxygenation, fibrosis (T1), inflammation (T2) and iron content (T2*) with the high sensitivity of PET for radiotracer detection¹. Thus, it promises to enable simultaneous assessment of molecular and cellular processes related to cardiovascular diseases such as atherosclerosis, post infarct remodelling, cardiomyopathy or heart failure. Current clinical interest in cardiac PET/MR has mainly focused on the diagnosis of patients with sarcoidosis², aortic calcification³, amyloidosis⁴ and coronary artery disease by exploiting several radiotracers including 18F-FDG (glucose metabolism), 18F-NaF (microcalcification), 68Ga-DOTATATE (inflammation), 18F-flutemetamol (amyloid). Among those cardiovascular diseases, sarcoidosis is considered an ideal application for PET/MR, as it benefits from the simultaneous assessment of myocardial inflammation with 18F-FDG and T2 mapping in concert with late gadolinium enhancement (LGE) for scar detection. Other applications include detection of amyloidosis with 18F-flutemetamol PET in concert with MR-based native T1 mapping and extracellular volume quantification or assessment of high-risk coronary plaque with 18F-NaF PET and coronary MR angiography. Most cardiac PET/MR exams however do not take full advantage of the simultaneous data acquisition and typically perform 2D cardiac MR scans in several standardized views (long axis, short axis, 2, 3 and 4 chamber view) during multiple breathholds while the PET acquisition is performed in 3D during free-breathing, which can lead to mis-registration artefacts between the MR and PET emission and attenuation correction data, even though they are simultaneously acquired, potentially leading to e.g. PET quantification errors or image artefacts. In the last 3-5 years attempts have been made to obtain motion information from MRI, either by using calibration scans in concert with motion surrogates such as bellows⁵ or by performing fully diagnostic MRI scans in concert with self-navigation or image-navigation techniques that allow to motion correct both the free-breathing 3D MRI and 3D PET emission and attenuation data and thus improve image quality and quantification of radiotracer uptake⁶. In this presentation, we will discuss the latest technical developments in PET-MR and review clinical studies with different radiotracers.

Acknowledgements

This work was supported by the following grants: (1) EPSRC EP/P032311/1, EP/P001009/1 and EP/P007619/1, (2) BHF programme grant RG/20/1/34802, (3) King’s BHF Centre for Research Excellence RE/18/2/34213 (4) Wellcome EPSRC Centre for Medical Engineering (NS/A000049/1), and (5) the Department of Health via the National Institute for Health Research (NIHR) Cardiovascular Health Technology Cooperative (HTC) and comprehensive Biomedical Research Centre awarded to Guy’s & St Thomas’ NHS Foundation Trust in partnership with King’s College London and King’s College Hospital NHS Foundation Trust.