High-resolution 3D-MRI of postmortem brain specimens fixed by formalin and gadoteridol

Two medicolegal autopsy cases of multinodular and vacuolating neuronal tumor revealed by postmortem MRI

The multinodular and vacuolating neuronal tumor (MVNT) is a recently recognized brain lesion. MVNT has a characteristic appearance in MRI images and is potentially epileptogenic. To the best of our knowledge, no report has yet described this pathological entity in the forensic medicine literature. We present two medicolegal autopsy cases where postmortem MRI (PMMR) was useful to detect this lesion. Case 1: a man in his 30s, with about a 7-year history of intractable epilepsy and known MVNT died suddenly. Although MVNT was not detected in the initial morphological evaluation during autopsy, PMMR of the formalin-fixed brain revealed the lesion in the left frontal lobe. Histopathology confirmed it as a MVNT. Case 2: a man in his 20s hanged himself to death. PMMR prior to autopsy revealed MVNT in his brain, and the diagnosis was confirmed by a detailed histopathological evaluation. In both cases, postmortem CT was not useful for evaluation. The cases suggested that MVNT can cause sudden, unexpected epileptic death, and pre- or post-autopsy PMMR may be useful to detect it.

Comparison of histological procedures and antigenicity of human post-mortem brains fixed with solutions used in gross anatomy laboratories

Background

Brain banks provide small tissue samples to researchers, while gross anatomy laboratories could provide larger samples, including complete brains to neuroscientists. However, they are preserved with solutions appropriate for gross-dissection, different from the classic neutral-buffered formalin (NBF) used in brain banks. Our previous work in mice showed that two gross-anatomy laboratory solutions, a saturated-salt-solution (SSS) and an alcohol-formaldehyde-solution (AFS), preserve antigenicity of the main cellular markers (neurons, astrocytes, microglia, and myelin). Our goal is now to compare the quality of histology and antigenicity preservation of human brains fixed with NBF by immersion (practice of brain banks) vs. those fixed with a SSS and an AFS by whole body perfusion, practice of gross-anatomy laboratories.

Methods

We used a convenience sample of 42 brains (31 males, 11 females; 25-90 years old) fixed with NBF (N = 12), SSS (N = 13), and AFS (N = 17). One cm3 tissue blocks were cut, cryoprotected, frozen and sliced into 40 μm sections. The four cell populations were labeled using immunohistochemistry (Neurons = neuronal-nuclei = NeuN, astrocytes = glial-fibrillary-acidic-protein = GFAP, microglia = ionized-calcium-binding-adaptor-molecule1 = Iba1 and oligodendrocytes = myelin-proteolipid-protein = PLP). We qualitatively assessed antigenicity and cell distribution, and compared the ease of manipulation of the sections, the microscopic tissue quality, and the quality of common histochemical stains (e.g., Cresyl violet, Luxol fast blue, etc.) across solutions.

Results

Sections of SSS-fixed brains were more difficult to manipulate and showed poorer tissue quality than those from brains fixed with the other solutions. The four antigens were preserved, and cell labeling was more often homogeneous in AFS-fixed specimens. NeuN and GFAP were not always present in NBF and SSS samples. Some antigens were heterogeneously distributed in some specimens, independently of the fixative, but an antigen retrieval protocol successfully recovered them. Finally, the histochemical stains were of sufficient quality regardless of the fixative, although neurons were more often paler in SSS-fixed specimens.

Conclusion

Antigenicity was preserved in human brains fixed with solutions used in human gross-anatomy (albeit the poorer quality of SSS-fixed specimens). For some specific variables, histology quality was superior in AFS-fixed brains. Furthermore, we show the feasibility of frequently used histochemical stains. These results are promising for neuroscientists interested in using brain specimens from anatomy laboratories.

Optimization of the fluid-attenuated inversion recovery (FLAIR) imaging for use in autopsy imaging of the brain region using synthetic MRI

BACKGROUND

The failure of cerebrospinal fluid (CSF) signal suppression in postmortem fluid-attenuated inversion recovery (FLAIR) of the brain is a problem.

OBJECTIVE

The present study was to clarify the relationship between the temperature of deceased persons and CSF T1, and to optimize the postmortem brain FLAIR imaging method using synthetic MRI.

METHODS

Forehead temperature was measured in 15 deceased persons. Next, synthetic MRI of the brain was performed, the CSF T1 was measured, and the optimal TI was calculated. Two types of FLAIR images were obtained with the clinical and optimal TI. The relationship between forehead temperature and the CSF T1 and optimal TI was evaluated. The optimized FLAIR images were physically and visually evaluated.

RESULTS

The CSF T1 and optimal TI were strongly correlated with forehead temperature. Comparing the average SNR and CNR ratios and visual evaluation scores of the two FLAIR images, those captured with the optimal TI showed statistically lower SNR, higher CNR, and higher visual evaluation scores (p< 0.01).

CONCLUSIONS

Synthetic MRI enables the quantification of the CSF T1 resulting from postmortem temperature decreases and calculation of the optimal TI, which could aid in improving the failure of CSF signal suppression and in optimizing postmortem brain FLAIR imaging.

Changes in magnetic resonance imaging relaxation time on postmortem magnetic resonance imaging of formalin-fixed human normal heart tissue

Background

Postmortem magnetic resonance imaging (MRI) has been used to investigate the cause of death, but due to time constraints, it is not widely applied to the heart. Therefore, MRI analysis of the heart after formalin fixation was previously performed. However, the changes in MRI signal values based on the fixation time of formalin were not investigated. The objective was to investigate changes over time in the T1- and T2-values of MRI signals in normal areas of hearts removed during autopsy, hearts subsequently fixed in formalin, and heart specimens sliced for the preparation of pathological specimens.

Methods

The study subjects were 21 autopsy cases in our hospital between May 26, 2019 and February 16, 2020 whose hearts were removed and scanned by MRI. The male:female ratio was 14:7, and their ages at death ranged from 9 to 92 years (mean age 65.0 ± 19.7 years). Postmortem (PM)-MRI was conducted with a 0.3-Tesla (0.3-T) scanner containing a permanent magnet. A 4-channel QD head coil was used as the receiver coil. Scans were performed immediately after removal, post-formalin fixation, and after slicing; 7 cases were scanned at all three time points.

Results

The T1- and T2-values were calculated from the MRI signals of each sample organ at each scanning stage. Specimens were sliced from removed organs after formalin fixation, and the changes in T1- and T2-values over time were graphed to obtain an approximate curve. The median T1-values at each measurement time point tended to decrease from immediately after removal. The T2-values showed the same tendency to decrease, but this tendency was more pronounced for the T1-values.

Conclusion

MRI signal changes in images of heart specimens were investigated. Formalin fixation shortened both T1- and T2-values over time, and approximation formulae were derived to show these decreases over time. The shortening of T1- and T2-values can be understood as commensurate with the reduction in the water content (water molecules) of the formalin-fixed heart.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12880-021-00666-5.

The choice of embedding media affects image quality, tissue R2 * , and susceptibility behaviors in post-mortem brain MR microscopy at 7.0T

PURPOSE

The quality and precision of post-mortem MRI microscopy may vary depending on the embedding medium used. To investigate this, our study evaluated the impact of 5 widely used media on: (1) image quality, (2) contrast of high spatial resolution gradient-echo (T₁ and T₂ ^* -weighted) MR images, (3) effective transverse relaxation rate (R₂ ^* ), and (4) quantitative susceptibility measurements (QSM) of post-mortem brain specimens.

METHODS

Five formaldehyde-fixed brain slices were scanned using 7.0T MRI in: (1) formaldehyde solution (formalin), (2) phosphate-buffered saline (PBS), (3) deuterium oxide (D₂ O), (4) perfluoropolyether (Galden), and (5) agarose gel. SNR and contrast-to-noise ratii (SNR/CNR) were calculated for cortex/white matter (WM) and basal ganglia/WM regions. In addition, median R₂ ^* and QSM values were extracted from caudate nucleus, putamen, globus pallidus, WM, and cortical regions.

RESULTS

PBS, Galden, and agarose returned higher SNR/CNR compared to formalin and D₂ O. Formalin fixation, and its use as embedding medium for scanning, increased tissue R₂ ^* . Imaging with agarose, D₂ O, and Galden returned lower R₂ ^* values than PBS (and formalin). No major QSM offsets were observed, although spatial variance was increased (with respect to R₂ ^* behaviors) for formalin and agarose.

CONCLUSIONS

Embedding media affect gradient-echo image quality, R₂ ^* , and QSM in differing ways. In this study, PBS embedding was identified as the most stable experimental setup, although by a small margin. Agarose and Galden were preferred to formalin or D₂ O embedding. Formalin significantly increased R₂ ^* causing noisier data and increased QSM variance.

Oesophageal carcinoma: comparison of ex vivo high-resolution 3.0 T MR imaging with histopathological findings

High-resolution magnetic resonance (MR) images clearly depict the normal oesophageal wall as consisting of eight layers, which correlates well with histopathological findings. In 56 (91.8%) of 61 lesions, the depth of oesophageal wall invasion determined through MR imaging was consistent with histopathological staging (r = 0.975, P < 0.001). The sensitivity, specificity and accuracy for the mucosa were 71.4%, 98.1%, and 95.1%, respectively, and the corresponding values for the submucosa were 82.4%, 95.5%, and 91.8%; for the muscularis propria, the sensitivity, specificity and accuracy were 100%, 95.7%, and 96.7%, respectively, and for the adventitia, these values were 100%, 100%, and 100%. The Cohen k values for interobserver agreement were excellent: K = 0.839, P < 0.001 (observer 1 vs. observer 2); K = 0.908, P < 0.001 (observer 1 vs. observer 3); and K = 0.885, P < 0.01 (observer 2 vs. observer 3). High-resolution ex vivo MR images obtained with a 3.0 T scanner can be used to precisely evaluate oesophageal carcinoma invasion and provide good diagnostic sensitivity, specificity and accuracy.

Optimization of Inversion Time for Postmortem Fluid-attenuated Inversion Recovery (FLAIR) MR Imaging at 1.5T: Temperature-based Suppression of Cerebrospinal Fluid

PURPOSE

Signal intensity (SI) and image contrast on postmortem magnetic resonance (MR) imaging are different from those of imaging of living bodies. We sought to suppress the SI of cerebrospinal fluid (CSF) sufficiently for fluid-attenuated inversion recovery (FLAIR) sequence in postmortem MR (PMMR) imaging by optimizing inversion time (TI).

MATERIALS AND METHODS

We subject 28 deceased patients to PMMR imaging 3 to 113 hours after confirmation of death (mean, 27.4 hrs.). PMMR imaging was performed at 1.5 tesla, and T1 values of CSF were measured with maps of relaxation time. Rectal temperatures (RT) measured immediately after PMMR imaging ranged from 6 to 32°C (mean, 15.4°C). We analyzed the relationship between T1 and RT statistically using Pearson's correlation coefficient. We obtained FLAIR images from one cadaver using both a TI routinely used for living bodies and an optimized TI calculated from the RT.

RESULTS

T1 values of CSF ranged from 2159 to 4063 ms (mean 2962.4), and there was a significantly positive correlation between T1 and RT (r = 0.96, P < 0.0001). The regression expression for the relationship was T1 = 74.4 * RT + 1813 for a magnetic field strength of 1.5T. The SI of CSF was effectively suppressed with the optimized TI (0.693 * T1), namely, TI = 0.693 * (77.4 * RT + 1813).

CONCLUSION

Use of the TI calculated from the linear regression of the T1 and RT optimizes the FLAIR sequence of PMMR imaging.