Fast macromolecular proton fraction mapping from a single off-resonance magnetization transfer measurement

Neuroimaging, behavioral, and psychological sequelae of repetitive combined blast/impact mild traumatic brain injury in Iraq and Afghanistan war veterans

Abstract Whether persisting cognitive complaints and postconcussive symptoms (PCS) reported by Iraq and Afghanistan war veterans with blast- and/or combined blast/impact-related mild traumatic brain injuries (mTBIs) are associated with enduring structural and/or functional brain abnormalities versus comorbid depression or posttraumatic stress disorder (PTSD) remains unclear. We sought to characterize relationships among these variables in a convenience sample of Iraq and Afghanistan-deployed veterans with (n=34) and without (n=18) a history of one or more combined blast/impact-related mTBIs. Participants underwent magnetic resonance imaging of fractional anisotropy (FA) and macromolecular proton fraction (MPF) to assess brain white matter (WM) integrity; [(18)F]-fluorodeoxyglucose positron emission tomography imaging of cerebral glucose metabolism (CMRglu); structured clinical assessments of blast exposure, psychiatric diagnoses, and PTSD symptoms; neurologic evaluations; and self-report scales of PCS, combat exposure, depression, sleep quality, and alcohol use. Veterans with versus without blast/impact-mTBIs exhibited reduced FA in the corpus callosum; reduced MPF values in subgyral, longitudinal, and cortical/subcortical WM tracts and gray matter (GM)/WM border regions (with a possible threshold effect beginning at 20 blast-mTBIs); reduced CMRglu in parietal, somatosensory, and visual cortices; and higher scores on measures of PCS, PTSD, combat exposure, depression, sleep disturbance, and alcohol use. Neuroimaging metrics did not differ between participants with versus without PTSD. Iraq and Afghanistan veterans with one or more blast-related mTBIs exhibit abnormalities of brain WM structural integrity and macromolecular organization and CMRglu that are not related to comorbid PTSD. These findings are congruent with recent neuropathological evidence of chronic brain injury in this cohort of veterans.

Cross-relaxation imaging of human patellar cartilage in vivo at 3.0T

OBJECTIVE

To compare quantitative magnetization transfer (qMT) parameters of patellar cartilage measured using cross-relaxation imaging (CRI) in asymptomatic volunteers and patients with osteoarthritis.

DESIGN

The study was performed with Institutional Review Board approval and with all subjects signing informed consent. CRI of the knee joint was performed at 3.0T on 20 asymptomatic volunteers and 11 patients with osteoarthritis. The fraction of macromolecular bound protons (f), the exchange rate constant between macromolecular bound protons and free water protons (k), and the T2 relaxation time of macromolecular bound protons (T2(B)) of patellar cartilage were measured. Mann-Whitney-Wilcoxon rank-sum tests were used to compare qMT parameters between asymptomatic volunteers and patients with osteoarthritis.

RESULTS

Average f, k, and T2(B) of patellar cartilage was 12.46%, 7.22 s(-1), and 6.49 μs respectively for asymptomatic volunteers and 12.80%, 6.13 s(-1), and 6.80 μs respectively for patients with osteoarthritis. There were statistically significant differences between groups of subjects for k (P < 0.01) and T2(B) (P < 0.0001) but not f (P = 0.38) of patellar cartilage.

CONCLUSION

Patients with osteoarthritis had significantly lower k and significantly higher T2(B) of patellar cartilage than asymptomatic volunteers which suggests that qMT parameters can detect changes in the macromolecular matrix of degenerative cartilage.

Multi-modal MRI of mild traumatic brain injury

Multi-modal magnetic resonance imaging (MRI) that included high resolution structural imaging, diffusion tensor imaging (DTI), magnetization transfer ratio (MTR) imaging, and magnetic resonance spectroscopic imaging (MRSI) were performed in mild traumatic brain injury (mTBI) patients with negative computed tomographic scans and in an orthopedic-injured (OI) group without concomitant injury to the brain. The OI group served as a comparison group for mTBI. MRI scans were performed both in the acute phase of injury (~24 h) and at follow-up (~90 days). DTI data was analyzed using tract based spatial statistics (TBSS). Global and regional atrophies were calculated using tensor-based morphometry (TBM). MTR values were calculated using the standard method. MRSI was analyzed using LC Model. At the initial scan, the mean diffusivity (MD) was significantly higher in the mTBI cohort relative to the comparison group in several white matter (WM) regions that included internal capsule, external capsule, superior corona radiata, anterior corona radiata, posterior corona radiata, inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, forceps major and forceps minor of the corpus callosum, superior longitudinal fasciculus, and corticospinal tract in the right hemisphere. TBSS analysis failed to detect significant differences in any DTI measures between the initial and follow-up scans either in the mTBI or OI group. No significant differences were found in MRSI, MTR or morphometry between the mTBI and OI cohorts either at the initial or follow-up scans with or without family wise error (FWE) correction. Our study suggests that a number of WM tracts are affected in mTBI in the acute phase of injury and that these changes disappear by 90 days. This study also suggests that none of the MRI-modalities used in this study, with the exception of DTI, is sensitive in detecting changes in the acute phase of mTBI.

Rapid, high-resolution quantitative magnetization transfer MRI of the human spinal cord

Quantitative magnetization transfer (qMT) imaging can provide indices describing the interactions between free water protons and immobile macromolecular protons. These indices include the macromolecular proton fraction (MPF), which has been shown to correlate with myelin content in white matter. Because of the long scan times required for high-resolution spinal cord imaging, qMT studies of the human spinal cord have not found wide-spread application. Herein, we investigated whether these limitations could be overcome by utilizing only a single MT-weighted acquisition and a reference measurement, as was recently proposed in the brain. High-resolution, in vivo qMT data were obtained at 3.0T in the spinal cords of healthy volunteers and patients with relapsing remitting multiple sclerosis (MS). Low- and high-resolution acquisitions (low/high resolution=1×1×5mm(3)/0.65×0.65×5mm(3)) with clinically acceptable scan times (12min/7min) were evaluated. We also evaluated the reliability over time and the sensitivity of the model to the assumptions made in the single-point method, both in disease and healthy tissues. Our findings suggest that the single point qMT technique can provide maps of the MPF in the spinal cord in vivo with excellent grey/white matter contrast, can be reliably obtained within reasonable scan times, and are sensitive to MS pathology. Consistent with previous qMT studies in the brain, the observed MPF values were higher in healthy white matter (0.16±0.01) than in grey matter (0.13±0.01) and in MS lesions (0.09±0.01). The single point qMT technique applied at high resolution provides an improved method for obtaining qMT in the human spinal cord and may offer a reliable outcome measure for evaluating spinal cord disease.

MRI outcomes in the diagnosis and disease course of multiple sclerosis

Despite major advances in MRI, including practical implementations of multiple quantitative MRI methods, the conventional measures of focal, macroscopic disease remain the core MRI outcome measures in clinical trials. MRI enhancing lesion counts are used to assess inflammation, and new T2-lesions provide an index of (interval) activity between scans. These simple MRI measures also have immediate significance for early diagnosis as components of the 2010 revised dissemination in space and time criteria, and they provide a mechanism to monitor the subclinical disease in patients, including after treatment is initiated. The focal macroscopic injury, which includes demyelination and axonal damage, is at least partially linked to the diffuse injury through pathophysiologic mechanisms, such as secondary degeneration, but the diffuse diseases is largely independent. Quantitative measures of the more widespread pathology of the normal appearing white and gray matter currently remain applicable to populations of patients rather than individuals. Gray matter pathology, including focal lesions of the cortical gray matter and diffuse changes in the deep and cortical gray has emerged as both early and clinically relevant, as has atrophy. Major technical improvements in MRI hardware and pulse sequence design allow more specific and potentially more sensitive treatment metrics required for targeting outcomes most relevant to neuronal degeneration, remyelination and repair.

Quantitative magnetization transfer MRI of desmoplasia in pancreatic ductal adenocarcinoma xenografts

Quantitative assessment of desmoplasia in pancreatic ductal adenocarcinoma (PDAC) may be critical for staging or prediction of response to therapy. We performed quantitative magnetization transfer (qMT) MRI measurements in 18 mouse xenograft tumors generated from three PDAC cell lines. The qMT parameter bound proton fraction (BPF) was found to be significantly higher in tumors grown using the BxPC-3 cell line (5.31 ± 0.87, mean ± standard deviation) compared with the BPF measured for tumors grown from Panc-1 (3.65 ± 0.60) and Capan-1 (1.50 ± 0.58) cell lines (P < 0.05 for each comparison). Histologic measurements demonstrated a similar trend; BxPC-3 tumors had significantly higher fibrosis levels (percentage of fibrotic tissue area, 6.21 ± 2.10) compared with Panc-1 (2.88 ± 1.13) and Capan-1 (1.69 ± 1.01) tumors. BPF was well correlated with quantitative fibrosis levels (r = 0.77, P < 0.01). Our results indicate that qMT measurements offer the potential to noninvasively quantify fibrosis levels in PDAC mouse xenograft models and thus serve as a valuable in vivo biomarker of desmoplasia in PDAC.