Small mammal MRI imaging in spinal cord injury: A novel practical technique for using a 1.5T MRI

Correlation of in vivo and ex vivo (1)H-MRI with histology in two severities of mouse spinal cord injury

Spinal cord injury (SCI) is a debilitating neuropathology with no effective treatment. Magnetic resonance imaging (MRI) technology is the only method used to assess the impact of an injury on the structure and function of the human spinal cord. Moreover, in pre-clinical SCI research, MRI is a non-invasive method with great translational potential since it provides relevant longitudinal assessment of anatomical and structural alterations induced by an injury. It is only recently that MRI techniques have been effectively used for the follow-up of SCI in rodents. However, the vast majority of these studies have been carried out on rats and when conducted in mice, the contusion injury model was predominantly chosen. Due to the remarkable potential of transgenic mice for studying the pathophysiology of SCI, we examined the use of both in and ex vivo¹H-MRI (9.4 T) in two severities of the mouse SCI (hemisection and over-hemisection) and documented their correlation with histological assessments. We demonstrated that a clear distinction between the two injury severities is possible using in and ex vivo¹H-MRI and that ex vivo MR images closely correlate with histology. Moreover, tissue modifications at a remote location from the lesion epicenter were identified by conventional ex vivo MRI analysis. Therefore, in vivo MRI has the potential to accurately identify in mice the progression of tissue alterations induced by SCI and is successfully implemented by ex vivo MRI examination. This combination of in and ex vivo MRI follow-up associated with histopathological assessment provides a valuable approach for further studies intended to evaluate therapeutic strategies on SCI.

Echo planar diffusion tensor imaging of the mouse spinal cord at thoracic and lumbar levels: A feasibility study

Diffusion tensor imaging is increasingly used for probing spinal cord (SC) pathologies, especially in mouse models of human diseases. However, diffusion tensor imaging series requires a long acquisition time and mouse experiments rarely use rapid imaging techniques such as echo planar imaging. A recent preliminary study demonstrated the feasibility and robustness of the echo planar imaging sequence for mouse cervical SC diffusion tensor imaging investigations. The feasibility of echo planar imaging at thoracic and lumbar levels, however, remained unknown due to bulk motion, field inhomogeneities, and off-centering of the SC in the axial plane. In the present study, the feasibility and the robustness of an echo planar imaging-based diffusion tensor imaging sequence for mouse thoracic and lumbar SC investigations is demonstrated. Quantitative and accurate diffusion tensor imaging metrics, as well as high spatially resolved images, have been obtained. This successful demonstration may open new perspectives in the field of mouse SC imaging. Echo planar imaging is used in several imaging modalities, such as relaxometry or perfusion, and may prove to be very attractive for multimodal MR investigations to acquire a more detailed characterization of the SC tissue.

Traumatic thoracic ASIA A examinations and potential for clinical trials

STUDY DESIGN

Retrospective review of prospective database.

OBJECTIVE

To define the variability of neurologic examination and recovery after nonpenetrating complete thoracic spinal cord injuries (American Spinal Injury Association [ASIA] A).

SUMMARY OF BACKGROUND DATA

Neurologic examinations after spinal cord injury (SCI) can be difficult and inconsistent. Unlike cervical SCI patients, alterations in thoracic (below T1) complete SCI (ASIA A-based on the ASIA Impairment Scale [AIS]) patients' examinations are based only on sensory testing, thus changes in the neurologic level (NL) are determined only by sensory changes.

METHODS

A retrospective review of the placebo control patients in a multicenter prospective database used for the pharmacologic trial of Sygen. Patients were included if they had a complete thoracic SCI on initial evaluation, with completed ASIA examinations at follow-up weeks 4, 8, 16, 26, and 52. Specifically, pin prick (PP) and light touch (LT) were assessed and the absolute change was calculated as the number of spinal levels at a given observation time.

RESULTS

Three thousand one hundred sixty-five patients were initially screened for the Sygen clinical trial, of which 51 were the control placebo patients used in this analysis. Alterations from the baseline examination (PP and LT) were fairly consistent and the median change/recovery in neurologic examination was 1 spinal level. Across all observations postbaseline, the average change for PP was 1.48 +/- 0.13 (mean +/- SE), and for LT, 1.40 +/- 0.13. There were equal proportions of directional changes (none, improved, lost).

CONCLUSION

Changes in a thoracic complete (ASIA A) SCI patients ASIA examination as measured through sensory methods (PP/LT) are fairly uncommon. The overall examination had only 1- to 2-level variability across patients, indicating minimal change in the sensory examination over the follow-up period. Stability in the ASIA examination as measured through sensory methods has thus been demonstrated over time, making it an excellent tool to monitor changes in neurologic function.