T2 and T2∗ mapping in ex situ porcine myocardium: myocardial intravariability, temporal stability and the effects of complete coronary occlusion.

Diagnosis of ischaemia-related sudden cardiac death in the absence of microscopic and macroscopic ischaemic lesions remains a challenge for medical examiners. Medical imaging techniques increasingly provide support in post-mortem examinations by detecting and documenting internal findings prior to autopsy. Previous studies have characterised MR relaxation times to investigate post-mortem signs of myocardial infarction in forensic cohorts. In this prospective study based on an ex situ porcine heart model, we report fundamental findings related to intramyocardial variability and temporal stability of T2 as well as the effects of permanent coronary occlusion on T2 and T2∗ relaxation in post-mortem myocardium. The ex situ porcine hearts included in this study (n= 19) were examined in two groups (Ss, n= 11 and Si, n= 8). All magnetic resonance imaging (MRI) examinations were performed ex situ, at room temperature and at 3 T. In the Ss group, T2 mapping was performed on slaughterhouse porcine hearts at different post-mortem intervals (PMI) between 7 and 26 h. Regarding the intramyocardial variability, no statistically significant differences in T2 were observed between myocardial segments (p= 0.167). Assessment of temporal stability indicated a weak negative correlation (r=- 0.21) between myocardial T2 and PMI. In the Si group, animals underwent ethanol-induced complete occlusion of the left anterior descending artery. T2 and T2∗ mapping were performed within 3 h of death. Differences between the expected ischaemic and remote regions were statistically significant for T2 (p= 0.007), however not for T2∗ (p= 0.062). Our results provide important information for future assessment of the diagnostic potential of quantitative MRI in the post-mortem detection of early acute myocardial infarction.

Post-mortem MR angiography: quantitative investigation and intravascular retention of perfusates in ex situ porcine hearts.

As the implementation of minimally invasive imaging techniques in both forensic and pathological practice increases, research in this area focuses on addressing recognised diagnostic weaknesses of current approaches. Assessment of sudden cardiac death (SCD) can be considered one such area in which post-mortem imaging still shows diagnostic weaknesses. We hypothesise that magnetic resonance imaging (MRI) with an angiographic adjunct may improve the visualisation and interpretation of cardiac pathologies in a post-mortem setting. To systematically investigate this hypothesis, selected perfusates (paraffin oil, Gadovist®;-doped physiological solution and polyethylene glycol (PEG)) were injected into the left anterior descending (LAD) artery of ex situ porcine hearts to assess the visualisation of perfusates in MRI as well as their intravascular retention over 12 h. Morphological images were acquired and quantitative T1 maps were generated from inversion recovery data. Visualisation of vascular structure and image quality were assessed using signal-to-noise and contrast-to-noise ratios. Intravascular retention was assessed both visually and statistically using a volume of interest (VOI) approach to analyse significant changes in signal intensity in and around the filled LAD artery, as well as changes in the longitudinal relaxation time (T1) in adjacent myocardium. In addition to presenting possible mechanisms explaining perfusate extravasation given the increased permeability of post-mortem vessels, the potential diagnostic consequences of this phenomenon and the importance of contrast stability and extended intravascular retention are discussed. In light of our findings and these considerations, paraffin oil emerged as the preferred perfusate for use in post-mortem MR angiography.

Clinical forensic imaging and fundamental rights in Austria.

Clinical forensic imaging encompasses the diverse application of imaging procedures that serve the same purpose: to enable the analysis and investigation of criminal activities and consequences of a crime. All kinds of imaging techniques and their corresponding images can be subsumed under "forensigraphy", a more comprehensive term for forensic imaging created by the Ludwig Boltzmann Institute for Clinical Forensic Imaging in Graz, Austria. As the word forensigraphy suggests, criminal imaging material should be of use in forensic investigations. Ideally, this can lead to new findings that would not have been revealed without the application of imaging techniques and are moreover admissible as evidence in criminal proceedings. However, the admissibility of evidence can only be facilitated through the implementation of clinical forensic imaging techniques into the forensic routine case work, which requires a precise pre-analysis of the corresponding legal framework. Because taking and displaying internal images of a person's body touches upon various aspects of one's physical and psychological integrity, imaging methods in general and clinical forensic imaging methods especially have a strong impact on and interfere regularly with the fundamental rights of the concerned person. Particularly with regard to a possible medical context, certain legal regulations have to be taken into account. Therefore, this paper examines forensic imaging in the field of radiological forensigraphy, specifically its in vivo (i.e. clinical) application. It is designed to enlighten readers as to the great significance of legal barriers that emerge from fundamental rights, as laid down in the European Convention on Human Rights (ECHR), when dealing with clinical forensic imaging. As a result, the legal framework of clinical forensic imaging procedures are comprehensively described, the relevant fundamental rights, especially the right to respect for private and family life, the right to data protection and certain procedural guarantees, are concisely presented to further raise awareness regarding the importance of fundamental rights.

Temperature dependence of viscosity, relaxation times (T1, T2) and simulated contrast for potential perfusates in post-mortem MR angiography (PMMRA).

Developments in post-mortem imaging increasingly focus on addressing recognised diagnostic weaknesses, especially with regard to suspected natural deaths. Post-mortem MR angiography (PMMRA) may offer additional diagnostic information to help address such weaknesses, specifically in the context of sudden cardiac death. Complete filling of the coronary arteries and acceptable contrast with surrounding tissue are essential for a successful approach to PMMRA. In this work, the suitability of different liquids for inclusion in a targeted PMMRA protocol was evaluated. Factors influencing cooling of paraffinum liquidum + Angiofil® (6 %) in cadavers during routine multiphase post-mortem CT angiography were investigated. The temperature dependence of dynamic viscosity (8-20 °C), longitudinal (T1) and transverse (T2) relaxation (1-23 °C) of the proposed liquids was quadratically modelled. The relaxation behaviour of these liquids and MR scan parameters were further investigated by simulation of a radiofrequency (RF)-spoiled gradient echo (GRE) sequence to estimate potentially achievable contrast between liquids and post-mortem tissue at different temperatures across a forensically relevant temperature range. Analysis of the established models and simulations indicated that based on dynamic viscosity (27-33 mPa · s), short T1 relaxation times (155-207 ms) and a minimal temperature dependence over the investigated range of these parameters, paraffin oil and a solution of paraffin oil + Angiofil® (6 %) would be most suitable for post-mortem reperfusion and examination in MRI.

Assessment of fiducial markers to enable the co-registration of photographs and MRI data.

PURPOSE: To investigate the visualisation of novel external fiducial skin markers in photography and MRI. To co-register photographs and MR images, and additionally assess the spatial accuracy of these co-registrations with the view of future application in the investigation of forensically relevant soft tissue lesions. METHODS AND MATERIALS: Strand-shaped fiducial markers were secured externally over hematomas on the thigh of 10 volunteers. The region of interest was photographed and examined using MRI at 3T in oblique and transversal orientations and the visibility of the markers assessed. Markers provided 'control points' in both sets of images, enabling the computation of an affine transform to register oblique MR images to photographs. The fiducial registration error was evaluated by calculating the root-mean-square error of nine corresponding evaluation points visible in both modalities. RESULTS: Fiducial markers were clearly visualised in both photography and MRI. The co-registration of photographs and oblique MR images was achieved for all participants. The overall root-mean-square error for registrations was 1.18mm (TIRM) and 1.46mm (TSE2D with SPAIR fat-suppression). CONCLUSIONS: The proposed approach led to the successful visualisation of non-invasive fiducial markers using photography and MRI (TIRM and TSE2D (SPAIR) sequences). This visualisation, combined with an affine transformation process provided a simple, cost-effective way to accurately co-register photographs and MR images of subcutaneous hematomas located on the thigh. Further investigation of the novel markers and the proposed co-visualisation approach holds potential to improve not only the forensic documentation of soft tissue lesions, but to also improve certain clinical applications, including the area of dermatology.