Faculty Bibliography

OBJECTIVE: To assess cerebral blood flow (CBF) changes in patients with mild traumatic brain injury (MTBI) using an arterial spin labelling (ASL) perfusion MRI and to investigate the severity of neuropsychological functional impairment with respect to haemodynamic changes. MATERIALS AND METHODS: Twenty-one patients with MTBI and 20 healthy controls were studied at 3T MR. The median time since the onset of brain injury in patients was 24.6 months. Both patients and controls underwent a traditional consensus battery of neurocognitive tests. ASL was performed using true fast imaging with steady state precession and a flow-sensitive alternating inversion recovery preparation. Regional CBF were measured in both deep and cortical gray matter as well as white matter at the level of basal ganglia. RESULTS: The mean regional CBF was significantly lower in patients with MTBI (45.9 +/- 9.8 ml/100 g min(-1)) as compared to normal controls (57.1 +/- 8.1 ml/100 g min(-1); p = 0.002) in both sides of thalamus. The decrease of thalamic CBF was significantly correlated with several neurocognitive measures including processing and response speed, memory/learning, verbal fluency and executive function in patients. CONCLUSIONS: Haemodynamic impairment can occur and persist in patients with MTBI, the extent of which is more severe in thalamic regions and correlate with neurocognitive dysfunction during the extended course of disease

Cerebral metabolic rate of oxygen (CMRO(2)) is an important marker for brain function and brain health. Existing techniques for quantification of CMRO(2) with positron emission tomography (PET) or MRI involve special equipment and/or exogenous agents, and may not be suitable for routine clinical studies. In the present study, a noninvasive method is developed to estimate whole-brain CMRO(2) in humans. This method applies phase-contrast MRI for quantitative blood flow measurement and T(2)-relaxation-under-spin-tagging (TRUST) MRI for venous oxygenation estimation, and uses the Fick principle of arteriovenous difference for the calculation of CMRO(2). Whole-brain averaged CMRO(2) values in young, healthy subjects were 132.1 +/- 20.0 micromol/100 g/min, in good agreement with literature reports using PET. Various acquisition strategies for phase-contrast and TRUST MRI were compared, and it was found that nongated phase-contrast and sagittal sinus (SS) TRUST MRI were able to provide the most efficient and accurate estimation of CMRO(2). In addition, blood flow and venous oxygenation were found to be positively correlated across subjects. Owing to the noninvasive nature of this method, it may be a convenient and useful approach for assessment of brain metabolism in brain disorders as well as under various physiologic conditions.

PURPOSE: To study the feasibility of using the MRI technique of segmented true-fast imaging with steady-state precession arterial spin-labeling (True-FISP ASL) for the noninvasive measurement and quantification of local perfusion in cerebral deep gray matter at 3T. MATERIALS AND METHODS: A flow-sensitive alternating inversion-recovery (FAIR) ASL perfusion preparation was used in which the echo-planar imaging (EPI) readout was replaced with a segmented True-FISP data acquisition strategy. The absolute perfusion for six selected regions of deep gray matter (left and right thalamus, putamen, and caudate) were calculated in 11 healthy human subjects (six male, five female; mean age = 35.5 years +/- 9.9). RESULTS: Preliminary measurements of the average absolute perfusion values at the six selected regions of deep gray matter are in agreement with published values for mean absolute cerebral blood flow (CBF) baselines acquired from healthy volunteers using positron emission tomography (PET). CONCLUSION: Segmented True-FISP ASL is a practical and quantitative technique suitable to measure local tissue perfusion in cerebral deep gray matter at a high spatial resolution without the susceptibility artifacts commonly associated with EPI-based methods of ASL. J. Magn. Reson. Imaging 2009;29:1425-1431. (c) 2009 Wiley-Liss, Inc

Multiple sclerosis (MS) is a disease of the central nervous system characterized by widespread demyelination, axonal loss and gliosis, and neurodegeneration; susceptibility-weighted imaging (SWI), through the use of phase information to enhance local susceptibility or T2* contrast, is a relatively new and simple MRI application that can directly image cerebral veins by exploiting venous blood oxygenation. Here, we use high-field SWI at 3.0 Tesla to image 15 patients with clinically definite relapsing-remitting MS and to assess cerebral venous oxygen level changes. We demonstrate significantly reduced visibility of periventricular white matter venous vasculature in patients as compared to control subjects, supporting the concept of a widespread hypometabolic MS disease process. SWI may afford a noninvasive and relatively simple method to assess venous oxygen saturation so as to closely monitor disease severity, progression, and response to therapy

PURPOSE: To investigate whether the variable forms of putative iron deposition seen with susceptibility weighted imaging (SWI) will lead to a set of multiple sclerosis (MS) lesion characteristics different than that seen in conventional MR imaging. MATERIALS AND METHODS: Twenty-seven clinically definite MS patients underwent brain scans using magnetic resonance imaging including: pre- and postcontrast T1-weighted imaging, T2-weighted imaging, FLAIR, and SWI at 1.5 T, 3 T, and 4 T. MS lesions were identified separately in each imaging sequence. Lesions identified in SWI were reevaluated for their iron content using the SWI filtered phase images. RESULTS: There were a variety of new lesion characteristics identified by SWI, and these were classified into six types. A total of 75 lesions were seen only with conventional imaging, 143 only with SWI, and 204 by both. From the iron quantification measurements, a moderate linear correlation between signal intensity and iron content (phase) was established. CONCLUSION: The amount of iron deposition in the brain may serve as a surrogate biomarker for different MS lesion characteristics. SWI showed many lesions missed by conventional methods and six different lesion characteristics. SWI was particularly effective at recognizing the presence of iron in MS lesions and in the basal ganglia and pulvinar thalamus

Noninvasive measurement of cerebral venous oxygenation can serve as a tool for better understanding fMRI signals and for clinical evaluation of brain oxygen homeostasis. In this study a novel technique, T2-Relaxation-Under-Spin-Tagging (TRUST) MRI, is developed to estimate oxygenation in venous vessels. This method uses the spin labeling principle to automatically isolate pure blood signals from which T2 relaxation times are determined using flow-insensitive T2-preparation pulses. The blood T2 is then converted to blood oxygenation using a calibration plot. In vivo experiments gave a baseline venous oxygenation of 64.8 +/- 6.3% in sagittal sinus in healthy volunteers (n = 24). Reproducibility studies demonstrated that the standard deviation across trials was 2.0 +/- 1.1%. The effects of repetition time and inversion time selections were investigated. The TRUST technique was further tested using various physiologic challenges. Hypercapnia induced an increase in venous oxygenation by 13.8 +/- 1.1%. On the other hand, caffeine ingestion resulted in a decrease in oxygenation by 7.0 +/- 1.8%. Contrast agent infusion (Gd-DTPA, 0.1 mmol/kg) reduced venous blood T2 by 11.2 ms. The results of this study show that TRUST MRI is a useful technique for quantitative assessment of blood oxygenation in the brain

Although BOLD functional MRI (fMRI) provides a useful tool for probing neuronal activities, large intersubject variations in signal amplitude are commonly observed. Understanding the physiologic basis for these variations will have a significant impact on many fMRI studies. First, the physiologic modulator can be used as a regressor to reduce variations across subjects, thereby improving statistical power for detecting group differences. Second, if a pathologic condition or a drug treatment is shown to change fMRI responses, monitoring this modulatory parameter is useful in correctly interpreting the fMRI changes to neuronal deficits/recruitments. Here we present evidence that the task-evoked fMRI signals are modulated by baseline blood oxygenation. To measure global blood oxygenation, we used a recently developed technique, T(2) relaxation under spin-tagging (TRUST) MRI, which yielded baseline oxygenation of 63.7% +/- 7.2% in the sagittal sinus with an estimation error of 1.3%. It was found that individuals with higher baseline oxygenation tend to have a smaller fMRI signal, and vice versa. For every 10% difference in baseline oxygenation across subjects, BOLD and cerebral blood flow (CBF) signals differ by -0.4% and -30.0%, respectively, when using visual stimulation. TRUST MRI is a useful measurement for fMRI studies to control for the modulatory effects of baseline oxygenation that are unique to each subject

BACKGROUND: Although the role of vascular pathology in multiple sclerosis (MS) lesions was suggested long ago, the derivation of these lesions from the vasculature has been difficult to assess in vivo. Ultrahigh-field (eg, 7-T) magnetic resonance imaging (MRI) has become a tool for assessing vascular involvement in MS lesions owing to markedly increased image resolution and susceptibility contrast of venous blood. OBJECTIVE: To describe the perivenous association of MS lesions on high-resolution and high-contrast 7-T susceptibility-sensitive MRI. DESIGN: Case study. SETTING: University hospital. PATIENTS: Two women with clinically definite relapsing-remitting MS. RESULTS: We demonstrated markedly enhanced detection of unique microvascular involvement associated with most of the visualized MS lesions with abnormal signals on and around the venous wall on 7-T compared with 3-T MRI. CONCLUSIONS: These findings, which have never been shown on conventional fields of MRI, not only allow for direct evidence of vascular pathogenesis in MS in vivo but also have important implications for monitoring lesion activity and therapeutic response