Cardiovascular magnetization transfer ratio imaging compared with histology: a postmortem study.

Cardiovascular magnetization transfer ratio (MTR) imaging by steady state free precession is a promising imaging method to assess microstructural changes within the myocardium. Hence, MTR imaging was correlated to histological analysis. Three postmortem cases were selected based on a suspicion of myocardial infarction. MTR and T2 -weighted (T2w ) imaging was performed, followed by autopsy and histological analysis. All tissue abnormalities, identified by autopsy or histology, were retrospectively selected on visually matched MTR and T2w images, and corresponding MTR values compared with normal appearing tissue. Regions of elevated MTR (up to approximately 20%, as compared to normal tissue), appearing hypo-intense in T2w -images, revealed the presence of fibrous tissue in microscopic histological analysis. Macroscopic observation (autopsy) described scar tissue only in one case. Regions of reduced MTR (up to approximately 20%) corresponded either to (i) the presence of edema, appearing hyperintense in T2w -images and confirmed by autopsy, or to (ii) inflammatory granulocyte infiltration at a microscopic level, appearing as hypo-intense T2w -signal, but not observed by autopsy. Findings from cardiovascular MTR imaging corresponded to histology results. In contrast to T2w -imaging, MTR imaging discriminated between normal myocardium, scar tissue and regions of acute myocardial infarction in all three cases.

Feasibility of post mortem cardiac proton density weighted fast field echo imaging in two cases of sudden death.

OBJECTIVE: The aim of this work is to investigate and compare cardiac proton density (PD) weighted fast field echo (FFE) post-mortem magnetic resonance (PMMR) imaging with standard cardiac PMMR imaging (T1-weighted and T2-weighted turbo spin-echo (TSE)), postmortem CT (PMCT) as well as autopsy. MATERIALS AND METHODS: Two human cadavers sequentially underwent cardiac PMCT and PMMR imaging (PD-weighted FFE, T1-weighted and T2-weighted TSE) and autopsy. The cardiac PMMR images were compared to each other as well as to PMCT and autopsy findings. RESULTS: For the first case, cardiac PMMR exhibited a focal region of low signal in PD-weighted FFE and T2-weighted TSE images, surrounded by a signal intense rim in the T2-weighted images. T1-weighted TSE and PMCT did not appear to identify any focal abnormality. Macroscopic inspection identified a blood clot; histology confirmed this to be a thrombus with an adhering myocardial infarction. In the second case, a myocardial rupture with heart tamponade was identified in all PMMR images, located at the anterior wall of the left ventricle; PMCT excluded additional ruptures. In PD-weighted FFE and T2-weighted TSE images, it occurred hypo-intense, while resulting in small clustered hyper-intense spots in T1-weighted TSE. Autopsy confirmed the PMMR and PMCT findings. CONCLUSIONS: Presented initial results have shown PD-weighted FFE to be a valuable imaging sequence in addition to traditional T2-weighted TSE imaging for blood clots and myocardial haemorrhage with clearer contrast between affected and healthy myocardium.

Three-dimensional strain fields in human brain resulting from formalin fixation.

Before investigating human brains post mortem, the first preparation step is often formalin fixation of the brain. As the brain consists of inhomogeneous tissues, the fixation leads to a three-dimensional strain field within the tissue. During the single case MR-based investigation of the brain, first, the starting point with the brain post mortem but still within the cranium, was examined. Then 13 MR data sets were acquired over a fixation period of 70 days and compared to the initial data set. Based on affine registration of the data sets, the global volume shrinkage was found to be 8.1%. By means of a non-rigid registration additional maximal local volume strains of 32% were determined.

A 3D in vitro bone organ model using human progenitor cells.

Three-dimensional (3D) organotypic culture models based on human cells may reduce the use of complex and costly animal models, while gaining clinical relevance. This study aimed at developing a 3D osteoblastic-osteoclastic-endothelial cell co-culture system, as an in vitro model to mimic the process of bone turnover. Osteoprogenitor and endothelial lineage cells were isolated from the stromal vascular fraction (SVF) of human adipose tissue, whereas CD14+ osteoclast progenitors were derived from human peripheral blood. Cells were co-cultured within 3D porous ceramic scaffolds using a perfusion-based bioreactor device, in the presence of typical osteoclastogenic factors. After 3 weeks, the scaffolds contained cells with endothelial (2.0±0.3%), pre/osteoclastic (14.0±1.4%) and mesenchymal/osteoblastic (44.0±8.4%) phenotypes, along with tartrate-resistant acid phosphatase-positive (TRAP+) osteoclastic cells in contact with deposited bone-like matrix. Supernatant analysis demonstrated sustained matrix deposition (by C-terminus procollagen-I propeptides), resorption (by N-terminus collagen-I telopeptides and phosphate levels) and osteoclastic activity (by TRAP-5b) only when SVF and CD14+ cells were co-cultured. Scanning electron microscopy and magnetic resonance imaging confirmed the pattern of matrix deposition and resorption. The effectiveness of Vitamin D in replacing osteoclastogenic factors indicated a functional osteoblast-osteoclast coupling in the system. The formation of human-origin bone-like tissue, blood vessels and osteoclasts upon ectopic implantation validated the functionality of the developed cell types. The 3D co-culture system and the associated non-invasive analytical tools can be used as an advanced model to capture some aspects of the functional coupling of bone-like matrix deposition and resorption and could be exploited toward the engineering of multi-functional bone substitute implants.

Influence of MT effects on T(2) quantification with 3D balanced steady-state free precession imaging.

Signal from balanced steady-state free precession is affected by magnetization transfer. To investigate the possible effects on derived T(2) values using variable nutation steady-state free precession, magnetization transfer-effects were modulated by varying the radiofrequency pulse duration only or in combination with variable pulse repetition time. Simulations reveal a clear magnetization transfer dependency of T(2) when decreasing radiofrequency pulse duration, reaching maximal deviation of 34.6% underestimation with rectangular pulses of 300 µs duration. The observed T(2) deviation evaluated in the frontal white matter and caudate nucleus shows a larger underestimation than expected by numerical simulations. However, this observed difference between simulation and measurement is also observed in an aqueous probe and can therefore not be attributed to magnetization transfer: it is an unexpected sensitivity of derived T(2) to radiofrequency pulse modulation. As expected, the limit of sufficiently long radiofrequency pulse duration to suppress magnetization transfer-related signal modulations allows for proper T(2) estimation with variable nutation steady-state free precession.

A new digital preoperative planning method for total hip arthroplasties.

Preoperative templating is an important part of a THA. The ability to accurately determine magnification of the hip on the radiograph and apply identical magnification to the radiograph and template will improve accuracy of preoperative templating of THA. We designed a templating method using a new way of determining the hip magnification with a linear relationship between magnification of the hip and the reference object on top of the pubis symphysis; the relationship was determined on 50 radiographs. We then compared our method with two other templating methods: an analog method assuming an average hip magnification of 15% and a digital method determining the hip magnification with a one-to-one relationship between the reference object and the hip. All methods were reproducible. Uniform undersizing occurred when templating with the digital method based on the one-to-one relationship; the analog method best predicted the implanted prosthesis size, closely followed by our new digital templating method; the new method will be particularly applicable for preoperative THA when analog methods are replaced by digital methods.