Ex-vivo quantitative susceptibility mapping of human brain hemispheres

Abstract

Ex-vivo brain quantitative susceptibility mapping (QSM) allows investigation of brain characteristics at essentially the same point in time as histopathologic examination, and therefore has the potential to become an important tool for determining the role of QSM as a diagnostic and monitoring tool of age-related neuropathologies. In order to be able to translate the ex-vivo QSM findings to in-vivo, it is crucial to understand the effects of death and chemical fixation on brain magnetic susceptibility measurements collected ex-vivo. Thus, the objective of this work was twofold: a) to assess the behavior of magnetic susceptibility in both gray and white matter of human brain hemispheres as a function of time postmortem, and b) to establish the relationship between in-vivo and ex-vivo gray matter susceptibility measurements on the same hemispheres. Five brain hemispheres from community-dwelling older adults were imaged ex-vivo with QSM on a weekly basis for six weeks postmortem, and the longitudinal behavior of ex-vivo magnetic susceptibility in both gray and white matter was assessed. The relationship between in-vivo and ex-vivo gray matter susceptibility measurements was investigated using QSM data from eleven older adults imaged both antemortem and postmortem. No systematic change in ex-vivo magnetic susceptibility of gray or white matter was observed over time postmortem. Additionally, it was demonstrated that, gray matter magnetic susceptibility measured ex-vivo may be well modeled as a linear function of susceptibility measured in-vivo. In conclusion, magnetic susceptibility in gray and white matter measured ex-vivo with QSM does not systematically change in the first six weeks after death. This information is important for future cross-sectional ex-vivo QSM studies of hemispheres imaged at different postmortem intervals. Furthermore, the linear relationship between in-vivo and ex-vivo gray matter magnetic susceptibility suggests that ex-vivo QSM captures information linked to antemortem gray matter magnetic susceptibility, which is important for translation of ex-vivo QSM findings to in-vivo.

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

“…Our results were consistent with previous findings in that we also observed a steep reduction in R 2 * after washing out formalin with PBS which was, however, not accompanied by a corresponding QSM offset, but by a decrease in QSM variability. These results are partially consistent with another study that found no effect of formalin fixation on bulk tissue susceptibility . These observations, supported by results from our vial experiment (Figure ; Supporting Information Table ), suggest that the short‐T 2 * behavior of the formalin solution used in the present study might not have been driven by its magnetostatic properties alone.…”

“…These results are partially consistent with another study that found no effect of formalin fixation on bulk tissue susceptibility. 55 These observations, supported by results from our vial experiment (Figure 7; Supporting Information Table S3), suggest that the short-T 2 * behavior of the formalin solution used in the present study might not have been driven by its magnetostatic properties alone. An alternative explanation, supported by a previous microwave spectroscopy study, 56 is that the formaldehyde molecule has counteracting paramagnetic and diamagnetic components at the microscopic level, although this is only a hypothesis at present time.…”

Characterization of Carotid Plaque Components by Quantitative Susceptibility Mapping

“…38 Future studies using in vivo carotid QSM are needed to clarify the usefulness of the in vivo imaging. Evia et al 39 showed the strong linear correlation in susceptibility on QSM between in vivo and ex vivo brain tissues. Therefore, our results may be valuable for translation of ex vivo QSM findings to in vivo ones.…”

“…The time from fixation of samples to MR imaging was relatively long; the mean time was 36 days. Evia et al 39 reported that susceptibility in gray and white matter measured ex vivo with QSM does not change in the first 6 weeks after death and fixation. Therefore, the effect of the time from fixation to MR imaging may have been small.…”

Imaging diamagnetic susceptibility of collagen in hepatic fibrosis using susceptibility tensor imaging

“…However, Evia et al showed that the magnetic susceptibility measurements of the same participants between in vivo and fixed ex vivo brains immersed in PBS can be modeled as a linear function. 37 Our previous study showed that collagen fibers in the cartilage have anisotropic susceptibility under physiological conditions. Therefore, we expect that a linear correlation between MSA and fibrosis still exists in physiological conditions, although the correlation coefficient may be altered by fixation.…”