Abstract
Previously, we reported human traumatic brain injury cases demonstrating acute to subacute microbleed appearance changes in susceptibility-weighted imaging (SWI—magnetic resonance imaging [MRI]). This study aims to confirm and characterize such temporal microbleed appearance alterations in an experimental model. To elicit microbleed formation, brains of male Sprague Dawley rats were pierced in a depth of 4 mm, in a parasagittal position bilaterally using 159 μm and 474 μm needles, without the injection of autologous blood or any agent. Rats underwent 4.7 T MRI immediately, then at multiple time points until 125 h. Volumes of hypointensities consistent with microbleeds in SWI were measured using an intensity threshold-based approach. Microbleed volumes across time points were compared using repeated measures analysis of variance. Microbleeds were assessed by Prussian blue histology at different time points. Hypointensity volumes referring to microbleeds were significantly decreased (corrected p < 0.05) at 24 h compared with the immediate or the 125 h time points. By visual inspection, microbleeds were similarly detectable at the immediate and 125 h imaging but were decreased in extent or completely absent at 24 h or 48 h. Histology confirmed the presence of microbleeds at all time points and in all animals. This study confirmed a general temporary reduction in visibility of microbleeds in the acute phase in SWI. Such short-term appearance dynamics of microbleeds should be considered when using SWI as a diagnostic tool for microbleeds in traumatic brain injury and various diseases.
Highlights
The term cerebral microbleed refers to small extravascular collections of blood or blood products in the brain that are visible as signal voids in magnetic susceptibility sensitive magnetic resonance imaging (MRI) techniques.[1,2]
Hypointensities referring to microbleeds along both the left and right brain parenchymal injury sites were present in the immediate minimum intensity projection (minIP) images of all animals (Fig. 2A, 3)
Histopathological findings confirmed that microbleeds did not vanish, because microbleeds were present in all time points of animal euthanasia
Summary
The term cerebral microbleed (or microhemorrhage) refers to small extravascular collections of blood or blood products in the brain that are visible as signal voids in magnetic susceptibility sensitive magnetic resonance imaging (MRI) techniques.[1,2] Such techniques include T2* gradient echo (T2* GRE) and most sensitively susceptibility-weighted imaging (SWI).[3]. In acute traumatic brain injury, microbleed detection may aid the diagnosis, severity, and prognosis assessment of hemorrhagic diffuse axonal injury.[4,5,6,7,8,9,10,11,12] results are heterogeneous, which detains clinical feasibility.[13,14] A potential confounding factor may be the inconsistent MRI appearance of microbleeds over time, as a result of the different possible biophysical states of blood
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