One short-axis slice from a single mouse. a) End diastolic LGE image, areas of hyperenhancement correspond to non-viable tissue. b) End systolic DENSE-derived Displacement map: a hypokinetic area (marked in red) is present larger than the infarct. c) End diastolic FDG-PET uptake is reduced in the infarcted areas, although small infarcts are not visualized in the PET image. Complementary information from multi-modality imaging can provide an accurate assessment of different aspects of a myocardial infarction: a) LGE MRI shows non-viable tissue. b) Cine MRI evaluates global heart function. c) DENSE MRI interrogates local muscle performance, and d) PET is used for cell viability by monitoring metabolism. Ejection fraction, DENSE-derived strain and PET infarct size plotted against LGE MRI infarct size.

Simultaneous Measurements of Heart Failure is Ideal

Heart failure (HF) is a common condition that develops after the heart becomes damaged or weakened by diseases of the heart including heart attacks and other medical conditions. Damage and recovery can be assessed on the cellular, tissue, organ or whole animal scale but these are rarely measured in concert. Ideally, recovery can be measured on long term studies of animals following the infraction with imaging techniques that monitor these scales simultaneously.

The combination of simultaneous PET and MRI present a combination of four complementary measures of heart function on multiple levels. Standard volumetric measurements of ventricle size at each phase of the heart (cine MRI) can be used to measure end-systolic and end-diastolic volumes (ESV, EDV respectively). The difference between these gives the blood volume ejected in each heart beat (SV) and the ratio of SV to EDV gives the ejection fraction (EF).

PET/MRI Measures Animal, Whole-Organ, Tissue, and Cellular Response to Myocardial Infarction

A University of Cambridge study presented data obtained using complementary techniques, including PET and MRI, for multi-modal characterization of the hearts of infarcted mice1. Mice were studied whose left anterior descending (LAD) coronary artery was occluded for 30 minutes to induce an ischemic insult with imaging being performed after 24 hours of reperfusion.

Although the protocol utilized MRI followed by PET imaging using 18F-fluorodeoxyglucose (FDG) as a direct marker of cellular viability and image co-registration in a sequential manner, the authors state that similar studies would “benefit substantially” from simultaneous PET/MRI imaging. As described in the published work, shorter imaging times mean less anesthetic stress and would result in reduced mortality, and the co-registration of the PET and MRI images would be “further improved” and would allow for better PET data through the use of such techniques as partial-volume and motion correction utilizing the MRI data. Each modality provides complementary information about heart disease and treatment to give a fuller picture of the response of the heart in response to injury and to therapy.

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