Motion Corrected Reconstruction for 3D Cardiac Simultaneous PET-MR Imaging: Towards Efficient Assessment of Coronary Artery Disease

Coronary artery disease (CAD) is the leading single cause of morbidity and mortality in the Western world. CAD reduces the blood supply to the cardiac muscle and can lead to chest pain (angina) or heart attack. CAD diagnosis is currently performed by a wide range of invasive and non-invasive tests. However in current practice a non-negligible number of patients that may not need the intervention are referred to invasive, ionizing, and potentially harmful x-ray cardiac catheterization procedures. Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) are two very promising non-invasive imaging technologies for early risk assessment, guidance of therapy and treatment monitoring of CAD. Both technologies provide complementary information, thus the recent introduction of simultaneous PET-MR systems offers great potential for accurate interpretation of findings of PET and MR images and new perspectives for better CAD diagnosis and treatment. For example three-dimensional fusion of PET perfusion images with non-invasive coronary MR images may allow the exact localization of stenosis, causing ischemia, to guide required interventions. However, inevitable patient motion (such as that caused by breathing and heart beating) during the acquisition degrades the image quality of both PET and MR images. Currently, commercial simultaneous PET-MR scanners do not feature technology for efficient and accurate correction of such motion.

Current research developments that deal with the motion problem in cardiovascular PET-MR concentrate mainly on improving the quality of PET images based on MR information. Moreover these approaches do not allow truly simultaneous PET and MR acquisitions leading to prolonged scan times, since diagnostic MR images need to be acquired after the simultaneous PET-MR acquisition. The reason is that dedicated MR acquisitions need to be performed concurrently with the PET imaging in order to correct for motion in the PET data. This means that MR is being used as an expensive motion-correction device limiting its diagnostic utility. In this proposal we aim to develop, implement and test the clinical feasibility of an efficient PET-MR acquisition and reconstruction framework that enables truly simultaneous acquisition of complementary PET and MR diagnostic information. We hypothesize that this can be achieved using synergistic information of both modalities i.e. functional, anatomic and motion MR information, and quantitative perfusion PET data in a motion corrected reconstruction approach. The proposed approach is foreseen as an important step towards clinical adoption of PET-MR cardiovascular imaging and lastly towards an efficient and accurate non-invasive assessment of CAD.

The beneficiaries of this research will be patients with suspected or known coronary artery disease, who will benefit from efficient and accurate non-invasive diagnostic tests. Secondary beneficiaries will be clinicians involved in the diagnosis and treatment of CAD. Complementary information provided by both imaging technologies will enable more reliable diagnosis. In the long term this project will also help reducing NHS healthcare costs by a) reducing the number of examinations: both PET and MR images will be acquired in a single-test, in a shorter scan time (from 60 min each scan to ~30 min for the simultaneous PET-MR) and will require one integrated reporting from the clinicians; and b) improving hospital discharge rates by providing more accurate diagnosis. Moreover the technology developed in this project may also have an impact in PET-MR cancer imaging where respiratory motion is a known major challenge. Through commercialisation, the research will be of benefit to the imaging manufacturers and subsequently to the healthcare system by improving patient management through improved treatment outcome and reduced healthcare costs on a national and international level.

Our goal is to maximise the impact of our work through dissemination of our ideas and results to the academic and clinical communities and potential industrial partners. The scientific methodology results from this research will be output as research publications in high-impact journals in the field of medical imaging. A large amount of phantom and in-vivo PET-MR data will be generated during the lifetime of the grant. After the studies are published in scientific journals, and after they are patented if patenting is a viable option, this data will be made publicly available for research use. We also plan to use the data to organise a "Motion Correction Challenger" in relevant Scientific Conferences. Moreover the data and reconstruction codes generated during the lifetime of the grant will be used in different teaching, networking and software development activities planned within the EP/M022587/1 "Computational Collaborative Project in Synergistic PET-MR Reconstruction" grant. Dr. Prieto (PI of this proposal) and Dr. Reader (CoI of this proposal) are both CoIs in this recently awarded Computational Collaborative Project PET-MR grant.

Clinical simultaneous PET-MR systems have been available for only a few years with two installations in the UK, one of them at the Division of Imaging Sciences at KCL. However, the UK government is expected to announce funding for five new PET-MR systems. Current commercial PET-MR scanners do not feature advanced techniques to deal with the problem of motion in cardiovascular imaging, therefore this project is foreseen as an important step towards clinical translation and validation of cardiovascular PET-MR. At the completion of this project we plan to work closely together with industrial partner to transfer the developed methodology into the product software to allow wide spread clinical use of this research.