Post-mortem MR imaging techniques for the assessment of sudden cardiac death: Quantitative and angiography-based approaches

Assessment of sudden cardiac death (SCD), specifically SCD related to acute coronary events and acute myocardial infarction, represents the diagnostic context for the evaluation of post-mortem magnetic resonance imaging (PMMR) techniques presented in this thesis. To date, research in this area has primarily focussed on visualising vessels and calcifications using post-mortem computed tomography angiography (PMCTA) and on the quantification of tissue alterations in post-mortem myocardium using accelerated quantitative PMMR. Through systematic investigation of the premises and considerations for performance of post-mortem MR angiography (PMMRA) and presentation of additional quantitative MR imaging techniques for the assessment of acute myocardial infarction, this thesis advances research regarding the radiological assessment of cardiac causes of death. Systematic evaluation commenced with the characterisation of viscosity and MR relaxation properties (T1, T2) of candidate perfusates for PMMRA at temperatures between 1-23°C. Perfusates demonstrating stable, medium dynamic viscosity (20-100 mPa·s) and T1 relaxation times at least 100 ms below corresponding cadaveric tissue (myocardium, fat) were preferred for angiography-based post-mortem MR of the coronary arteries. Clinically available MR sequences such as T2w SPACE and T1w gradient echo (GRE) delivered high contrast between perfusates and surrounding tissue as well as good spatial resolution for the assessment of filled vessel-like structures similar in size to human coronary arteries. The visualisation and intravascular retention of three selected perfusates (paraffin oil, polyethylene glycol (PEG) 200 and Gadovist®-doped physiological solution) were quantitatively investigated in an ex situ porcine heart model. At 23-25°C all perfusates demonstrated an excellent contrast-to-noise ratio with post-mortem myocardium and epicardial fat using a 3D T1w GRE sequence. Fast perfusate extravasation (< 1 hour) was observed for PEG200 and the Gadovist® solution, as evidenced by statistically significant changes in the signal intensity of the filled vessel and T1 relaxation times in adjacent myocardium in this time. Conversely, paraffin oil remained intravascular for the entire duration of the experiment (12 hours). The technical feasibility of paraffin oil as perfusate in combination with 3D T1-weighted imaging sequences could be successfully demonstrated in a forensic cohort, where PMMRA was performed directly following PMCTA using 6% paraffin oil & Angiofil®. Additionally, quantitative MR imaging was applied in a preclinical porcine heart model to characterise early tissue alterations in post-mortem myocardium following fatal induced myocardial infarction. Longitudinal and transverse relaxation times, as well as diffusion parameters such as fractional anisotropy (FA) and mean diffusivity (MD) were examined in infarcted and remote regions of the myocardium. While observed trends in FA and MD were not found to be statistically significant in this study, T1 and T2 relaxation times were found to be shortened in the infarcted regions compared with remote regions (p-value < 0.05).