Comparison and optimization of pCASL and VSASL for rat thoracolumbar spinal cord MRI at 9.4 T.

PURPOSE: To evaluate pseudo-continuous arterial spin labeling (pCASL) and velocity-selective arterial spin labeling (VSASL) for quantification of spinal cord blood flow (SCBF) in the rat thoracolumbar spinal cord. METHODS: Labeling efficiency (LE) was compared between pCASL and three VSASL variants in simulations and both phantom and in vivo experiments at 9.4 T. For pCASL, the effects of label plane position and shimming were systematically evaluated. For VSASL, the effects of composite pulses and phase cycling were evaluated to reduce artifacts. Additionally, vessel suppression, respiratory, and cardiac gating were evaluated to reduce motion artifacts. pCASL and VSASL maps of spinal cord blood flow were acquired with the optimized protocols. RESULTS: LE of the descending aorta was larger in pCASL compared to VSASL variants. In pCASL, LE off-isocenter was improved by local shimming positioned at the label plane and the anatomical level of labeling for the thoracic cord was only viable at the level of the T10 vertebra. Cardiac gating was essential to reduce motion artifacts. Both pCASL and VSASL successfully demonstrated comparable SCBF values in the thoracolumbar cord. CONCLUSION: pCASL demonstrated high and consistent LE in the thoracic aorta, and VSASL was also feasible, but with reduced efficiency. A combination of cardiac gating and recording of actual post-label delays was important for accurate SCBF quantification. These results highlight the challenges and solutions to achieve sufficient ASL labeling and contrast at high field in organs prone to motion.

King-Devick Sensitivity and Specificity to Concussion in Collegiate Athletes.

CONTEXT: The King-Devick (K-D) test is used to identify oculomotor impairment after concussion. However, the diagnostic accuracy of the K-D test over time has not been evaluated. OBJECTIVES: To (1) examine the sensitivity and specificity of the K-D test at 0 to 6 hours postinjury, 24 to 48 hours postinjury, the beginning of a return-to-play (RTP) protocol (asymptomatic), unrestricted RTP, and 6 months postconcussion and (2) compare outcomes between athletes with and those without concussion across confounding factors (sex, age, sport contact level, academic year, learning disorder, attention-deficit/hyperactivity disorder, migraine history, concussion history, and test administration mode). DESIGN: Retrospective, cross-sectional design. SETTING: Multiple institutions in the Concussion Assessment, Research and Education Consortium. PATIENTS OR OTHER PARTICIPANTS: A total of 320 athletes with a concussion (162 men, 158 women; age = 19.80 ± 1.41 years) were compared with 1239 total collegiate athletes without a concussion (646 men, 593 women; age = 20.31 ± 1.18 years). MAIN OUTCOME MEASURE(S): We calculated the K-D test time difference (in seconds) by subtracting the baseline from the most recent time. Receiver operator characteristic (ROC) curve and area under the curve (AUC) analyses were used to determine the diagnostic accuracy across time points. We identified cutoff scores and corresponding specificity at both the 80% and 70% sensitivity levels. We repeated ROC with AUC analyses using confounding factors. RESULTS: The K-D test predicted positive results at the 0- to 6-hour (AUC = 0.724, P < .001), 24- to 48-hour (AUC = 0.701, P < .001), RTP (AUC = 0.640, P < .001), and 6-month postconcussion (AUC = 0.615, P < .001) tim points but not at the asymptomatic time point (AUC = 0.513, P = .497). The 0- to 6-hour and 24- to 48-hour time points yielded 80% sensitivity cutoff scores of -2.6 and -3.2 seconds (ie, faster), respectively, but 46% and 41% specificity, respectively. The K-D test had a better AUC when administered using an iPad (AUC = 0.800, 95% CI = 0.747, 0.854) compared with the spiral-bound card system (AUC = 0.646, 95% CI = 0.600, 0.692; P < .001). CONCLUSIONS: The diagnostic accuracy of the K-D test was greatest at 0 to 6 hours and 24 to 48 hours postconcussion but declined across subsequent postconcussion time points. The AUCs did not differentiate between groups across confounding factors. Our negative cutoff scores indicated that practice effects contributed to improved performance, requiring athletes to outperform their baseline scores.

Differential Trajectory of Diffusion and Perfusion Magnetic Resonance Imaging of Rat Spinal Cord Injury.

Traumatic spinal cord injury causes rapid neuronal and vascular injury, and predictive biomarkers are needed to facilitate acute patient management. This study examined the progression of magnetic resonance imaging (MRI) biomarkers after spinal cord injury and their ability to predict long-term neurological outcomes in a rodent model, with an emphasis on diffusion-weighted imaging (DWI) markers of axonal injury and perfusion-weighted imaging of spinal cord blood flow (SCBF). Adult Sprague-Dawley rats received a cervical contusion injury of varying severity (injured = 30, sham = 9). MRI at 4 h, 48-h, and 12-weeks post-injury included T1, T2, perfusion, and DWI. Locomotor outcome was assessed up to 12 weeks post-injury. At 4 h, the deficit in SCBF was larger than the DWI lesion, and although SCBF partially recovered by 48 h, the DWI lesion expanded. At 4 h, the volume of the SCBF deficit (R2 = 0.56, padj < 0.01) was significantly correlated with 12-week locomotor outcome, whereas DWI (R2 = 0.30, padj < 0.01) was less predictive of outcome. At 48 h, SCBF (R2 = 0.41, padj < 0.01) became less associated with outcome, and DWI (R2 = 0.38, padj < 0.01) lesion volume became more closely related to outcome. Spinal cord perfusion has unique spatiotemporal dynamics compared with diffusion measures of axonal damage and highlights the importance of acute perfusion abnormalities. Perfusion and diffusion offer complementary and clinically relevant insight into physiological and structural abnormalities following spinal cord injury beyond those afforded by T1 or T2 contrasts.

Diagnostic Imaging in Spinal Cord Injury.

In the evaluation of spinal trauma, diagnostic imaging is of paramount importance. Computed tomography (CT), flexion/extension radiographs, and MRI are complementary modalities. CT is typically obtained in the initial setting of spinal trauma and provides detailed information about osseous structures. MRI provides detailed information about structural injury to the spinal cord. Diffusion tensor imaging provides microstructural information about the integrity of the axons and myelin sheaths, but its clinical use is limited. Novel imaging techniques may be better suited for the acute clinical setting and are under development for potential future clinical use.

Diffusion-prepared fast spin echo for artifact-free spinal cord imaging.

PURPOSE: Diffusion MRI provides unique contrast important for the detection and examination of pathophysiology after acute neurologic insults, including spinal cord injury. Diffusion weighted imaging of the rodent spinal cord has typically been evaluated with axial EPI readout. However, Diffusion weighted imaging is prone to motion artifacts, whereas EPI is prone to susceptibility artifacts. In the context of acute spinal cord injury, diffusion filtering has previously been shown to improve detection of injury by minimizing the confounding effects of edema. We propose a diffusion-preparation module combined with a rapid acquisition with relaxation enhancement readout to minimize artifacts for sagittal imaging. METHODS: Sprague-Dawley rats with cervical contusion spinal cord injury were scanned at 9.4 Tesla. The sequence optimization included the evaluation of motion-compensated encoding diffusion gradients, gating strategy, and different spinal cord-specific diffusion-weighting schemes. RESULTS: A diffusion-prepared rapid acquisition with relaxation enhancement achieved high-quality images free from susceptibility artifacts with both second-order motion-compensated encoding and gating necessary for reduction of motion artifacts. Axial diffusivity obtained from the filtered diffusion-encoding scheme had greater lesion-to-healthy tissue contrast (52%) compared to the similar metric from DTI (25%). CONCLUSION: This work demonstrated the feasibility of high-quality diffusion sagittal imaging in the rodent cervical cord with diffusion-prepared relaxation enhancement. The sequence and results are expected to improve injury detection and evaluation in acute spinal cord injury.

Optimized cervical spinal cord perfusion MRI after traumatic injury in the rat.

Despite the potential to guide clinical management of spinal cord injury and disease, noninvasive methods of monitoring perfusion status of the spinal cord clinically remain an unmet need. In this study, we optimized pseudo-continuous arterial spin labeling (pCASL) for the rodent cervical spinal cord and demonstrate its utility in identifying perfusion deficits in an acute contusion injury model. High-resolution perfusion sagittal images with reduced imaging artifacts were obtained with optimized background suppression and imaging readout. Following moderate contusion injury, perfusion was clearly and reliably decreased at the site of injury. Implementation of time-encoded pCASL confirmed injury site perfusion deficits with blood flow measurements corrected for variability in arterial transit times. The noninvasive protocol of pCASL in the spinal cord can be utilized in future applications to examine perfusion changes after therapeutic interventions in the rat and translation to patients may offer critical implications for patient management.