Cortical activation resulting from the stimulation of periodontal mechanoreceptors measured by functional magnetic resonance imaging (fMRI).

OBJECTIVE: To describe the normal cortical projections of periodontal mechanoreceptors. MATERIAL AND METHODS: A device using von Frey filaments delivered 1-Hz punctate tactile stimuli to the teeth during fMRI. In a block design paradigm, tooth (T) 11 and T13 were stimulated in ten volunteers and T21 and T23 in ten other subjects. Random-effect group analyses were performed for each tooth, and differences between teeth were examined using ANOVA. RESULTS: The parietal operculum (S2) was activated bilaterally for all teeth; the postcentral gyrus (S1) was activated bilaterally for T21 and T23 and contralaterally for T11 and T13. In the second-level analysis including the four teeth, we found five clusters: bilateral S1 and S2, and left inferior frontal gyrus, with no difference between teeth in somatosensory areas. However, the ANOVA performed on the S1 clusters found separately in each tooth showed that S1 activation was more contralateral for the canines. CONCLUSION: One-hertz mechanical stimulation activates periodontal mechanoreceptors and elicits bilateral cortical activity in S1 and S2, with a double representation in S2, namely in OP1 and OP4. CLINICAL RELEVANCE: The cortical somatotopy of periodontal mechanoreceptors is poorly described. These findings may serve as normal reference to further explore the cortical plasticity induced by periodontal or neurological diseases.

[Intramedullary tumours and pseudotumours]. / Moelle épinière tumorale et pseudo-tumorale.

Swelling of the spinal cord and/or enhancement after intravenous gadolinium administration are not always specific features of intramedullary tumour. These may also be seen in association with several diseases of inflammatory, infectious, granulomatous or vascular origin. A tumour is characterized by its sagittal location, axial topography: central, lateral or exophytic, its size and size of the spinal canal, macroscopic components: calcium, fat, methemoglobin, melanin, hemosiderin, vascular pedicle, cystic component, enhancement after intravenous gadolinium administration, effect on the spinal cord tracts and edema. Characteristics: astrocytoma is lateral and infiltrative, ependymoma is central with white matter tract displacement and hemosiderin cap, hemangioblastoma is postero-lateral and shows enhancement with a vascular pedicle, metastases are very edematous or leptomeningeal in location.

How to measure olfactory bulb volume and olfactory sulcus depth?

In combination with psychophysical testing and electrophysiological studies, magnetic resonance imaging plays a role in the clinical evaluation of patients with an olfactory dysfunction. Quantitative measurements of olfactory bulb volume and of olfactory sulcus depth, and the morphological depiction of structural abnormalities, make synergistic contributions to the accurate radiological diagnosis of smell dysfunction. Moreover, the plasticity of our olfactory system can be demonstrated by temporal changes in OB volumetric measurements. In this paper, we provide an outline of how to measure olfactory bulb volume and olfactory sulcus depth, with numerous illustrative cases of patients with congenital anosmia, post-infectious or posttraumatic olfactory loss and sinonasal-related olfactory dysfunction.

[Central nervous system involvement in Wegener's granulomatosis]. / Atteinte cérébrale au cours d'une maladie de Wegener.

INTRODUCTION: Wegener's granulomatosis (WG) is a systemic necrotizing vasculitis associated with c-ANCA antibodies. The involvement of the central nervous system in WG is uncommon and usually caused by in situ vasculitis, intracranial granuloma formation or contiguous invasion from extracranial sites. CASE REPORT: Here, we report on a tumour-like expansion of a severe nasosinusal WG into the brain, which was confirmed by brain biopsy examination. CONCLUSION: The positivity of positron emission tomography in our observation supports the potential role of such functional imaging in the staging, as well as in the follow-up of WG.

[Safety and efficacy of multiple subpial transections: report of a consecutive series of 30 cases]. / Sécurité et efficacité des trans-sections sous-piales multiples: analyse d'une série consécutive de 30 patients.

PURPOSE: To present our results using multiple subpial transections (MST) for the treatment of pharmacologically refractory epilepsy (PRE) with epileptogenic foci in eloquent areas. METHOD: Between January 2003 and March 2006, we treated 33 patients with PRE with epileptogenic foci in eloquent areas by MST "in rays", either isolated (MSTs group) or completing resection or disconnection of other cortical areas (MST+ group). Our first 30 patients had a follow-up of at least 24 months: eight in the MSTs group and 22 in the MST+ group. Four postoperative grades were distinguished based on a modified Engel classification: seizure-free (100% seizure reduction equals to Grade I), substantial significant seizure reduction (75% to 99% seizure reduction equals to Grade II), moderate significant reduction (50% to 74% seizure reduction equals to Grade III) and finally no significant reduction (seizure reduction less than 50% equals to Grade IV). RESULTS: In the MSTs group, two patients (25%) were in grade I and five (62%) in grade II or III. In the MST+ group, six patients (27%) were in grade I and 13 (59%) in grade II or III. All patients showed some seizure reduction and some improvement in behavior or cognitive function with no permanent neurological deficit. CONCLUSION: This series supports the notion that multiple subpial transections are associated with a significant seizure reduction (in 86.6% of the cases reported herein) and that the risk of permanent neurological deficit can be very low.

Multiple subpial transections and magnetic resonance imaging.

INTRODUCTION: Multiple subpial transection (MST) has been applied to the treatment of refractory epilepsy when epileptogenic zone involves eloquent areas since 1989. However, there is a lack of data evaluating the effect of this surgical technique on the cortex as measured by Magnetic Resonance Imaging (MRI). PATIENTS AND METHODS: Ten consecutive patients (3F/7M, average age: 18.5 years) were operated on using radiating MST (average: 39; min: 19, max: 61) alone (n=3) or associated with another technique (n=7). Seven patients underwent a post-operative 3.0T MRI while 3 had a 1.5T MRI. Three patients had an early post-operative MRI and 7 a late MRI, among which 3 previously had an intraoperative MRI. RESULTS: The MR sequences that allowed the best assessment of MST-induced changes were T2 and T2*. The traces of MST are more visible on late MRI. These discrete non-complicated stigmas of MST were observed in all 10 studied patients: on the intraoperative MRI they are seen as micro-hemorrhagic spots (hypo-T2), on the early postoperative MRI as a discreet and limited cortical edema whether associated or not with micro-hemorrhagic spots and on the late MRI as liquid micro-cavities (hyper-T2) surrounded with a fine border of hemosiderin. CONCLUSIONS: MST-induced cerebral lesions are best visualized in T2-sequences, mainly on the late postoperatively MRIs. On all the MRI examinations in this study, the MST are only associated with limited modifications of the treated cortical regions.

Comparative overview of brain perfusion imaging techniques.

Numerous imaging techniques have been developed and applied to evaluate brain hemodynamics. Among these are: Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), Xenon-enhanced Computed Tomography (XeCT), Dynamic Perfusion-computed Tomography (PCT), Magnetic Resonance Imaging Dynamic Susceptibility Contrast (DSC), Arterial Spin-Labeling (ASL), and Doppler Ultrasound. These techniques give similar information about brain hemodynamics in the form of parameters such as cerebral blood flow (CBF) or volume (CBV). All of them are used to characterize the same types of pathological conditions. However, each technique has its own advantages and drawbacks. This article addresses the main imaging techniques dedicated to brain hemodynamics. It represents a comparative overview, established by consensus among specialists of the various techniques. For clinicians, this paper should offers a clearer picture of the pros and cons of currently available brain perfusion imaging techniques, and assist them in choosing the proper method in every specific clinical setting.

Is there an apparent diffusion coefficient threshold in predicting tissue viability in hyperacute stroke?

BACKGROUND AND PURPOSE: Rapid and precise identification of the penumbra is important for decision-making in acute stroke. We sought to determine whether an early and moderate decrease in the apparent diffusion coefficient (ADC) may help to identify, within the diffusion/perfusion (DWI/PWI) mismatch, those areas that will eventually evolve toward infarction. METHODS: We reviewed 48 patients not treated by thrombolytics who had a DWI/PWI within 6 hours after onset, with infarct evolution documented by follow-up magnetic resonance on days 2 to 4. We calculated absolute values for ADC and the ADC ratio (ADCr) in (1) the initial DWI hypersignal; (2) the final volume of the infarct, ie, the follow-up fluid-attenuated inversion recovery abnormalities; (3) the infarct growth (IGR) area; and (4) the oligemic area (OLI) that remained viable despite initial hemodynamic disturbance. We tested the value of the ADC to predict tissue outcome by using discriminant analysis. RESULTS: ADC values were marginally but significantly decreased in the IGR area (ADC 782+/-82x10(-6) mm(2)/s, ADCr 0.94+/-0.08) compared with mirror values (P=0.01) and with OLI (ADC 823+/-41x10(-6) mm(2)/s, ADCr 0.99+/-0.07; P=0.001). Of all quantitative DWI and PWI parameters, the ADCr best discriminated between IGR and OLI (F(1,50)=13.6, cutoff=0.97, 64% sensitivity, 92% specificity) and between the final volume of infarct and OLI (F(1,83)=219, cutoff=0.91, 91% sensitivity, 100% specificity). CONCLUSIONS: A simple approach based on ADC alone may allow the identification of tissue at risk of infarction in acute-stroke patients.

Usefulness of magnetic resonance-derived quantitative measurements of cerebral blood flow and volume in prediction of infarct growth in hyperacute stroke.

BACKGROUND AND PURPOSE: The identification of the tissue at risk for infarction remains challenging in stroke patients. In this study, we evaluated the value of quantitative cerebral blood flow (CBF) and cerebral blood volume (CBV) measurements in the prediction of infarct growth in hyperacute stroke. METHODS: Fluid-attenuated inversion recovery (FLAIR), diffusion-weighted (DW), and gradient-echo echo-planar perfusion-weighted (PW) sequences were obtained in 66 patients within 6 hours of stroke onset; ischemia was confirmed on follow-up FLAIR images. We delineated the following: (1) the initial infarct on DW images, (2) the area of hemodynamic disturbance on mean transit time (MTT) maps, and (3) the final infarct on follow-up FLAIR images. MTT, CBF, and CBV were calculated in the following areas: area of initial infarct (INF), area of infarct growth (IGR, final minus initial infarct), the hemodynamically disturbed area that remained viable (OLI, hemodynamic disturbance minus final infarct), and all contralateral mirror regions. RESULTS: Compared with mirror regions, the MTT in abnormal areas was always prolonged. The respective mean+/-SD CBF and CBV values were as follows: for INF, 28+/-16 mL/min per 100 g and 6.9+/-2.7%; for IGR, 36+/-20 mL/min per 100 g and 8.9+/-3.1%; for OLI, 50+/-17 mL/min per 100 g and 11.2+/-3%; and for mirror regions, 64+/-23 mL/min per 100 g and 8.7+/-2.5%. The CBV and CBF values were significantly different between all abnormal areas (except for the CBF between INF and IGR). In the area of DW/PW mismatch, a combined CBF or CBV threshold of 35 or 8.2, respectively, predicted evolution to infarction with a sensitivity of 81% and a specificity of 76%. CONCLUSIONS: Quantitative measurements of CBF and CBV in hyperacute stroke may help to predict infarct growth and to select the subjects who will benefit from thrombolysis.

Cortical localization of reading in normal children: an fMRI language study.

BACKGROUND: fMRI provides a noninvasive means of identifying the location and organization of neural networks that underlie cognitive functions. OBJECTIVE: To identify, using fMRI, brain regions involved in processing written text in children. METHODS: The authors studied nine normal right-handed native English-speaking children, aged 10.2 years (range 7.9 to 13.3 years), with two paradigms: reading Aesop's Fables and "Read Response Naming" (reading a description of an object that was then silently named). Data were acquired using blood oxygen level-dependent fMRI. Group data were analyzed with statistical parametric mapping; individual data sets were analyzed with a region-of-interest approach from individual study t maps. The number of activated pixels was determined in brain regions and an asymmetry index (AI = [L - R]/[L + R]) calculated for each region. RESULTS: The authors found strong activation in the left middle temporal gyrus and left midfrontal gyrus and variable activation in left inferior frontal gyrus for both reading tasks in the group analysis (z > 5.5 to 9.1). All subjects had strong left-sided lateralization for both tasks in middle/superior temporal gyrus, inferior frontal gyrus, and middle frontal gyrus (AI = 0.76 to 1.0 for t = 4). Reading Fables activated twice as many pixels in temporal cortex as the Read Response Naming task; activation in dorsolateral prefrontal cortex was similar for both tasks. Small homologous right middle temporal region activation was seen with reading a fable. CONCLUSIONS: The neural networks that process reading appear to be lateralized and localized by middle to late childhood. Reading text paradigms may prove useful for identifying frontal and temporal language-processing areas and for determining language dominance in children experiencing epilepsy or undergoing tumor surgery.

Language dominance in partial epilepsy patients identified with an fMRI reading task.

BACKGROUND: fMRI language tasks readily identify frontal language areas; temporal activation has been less consistent. No studies have compared clinical visual judgment to quantitative region of interest (ROI) analysis. OBJECTIVE: To identify temporal language areas in patients with partial epilepsy using a reading paradigm with clinical and ROI interpretation. METHODS: Thirty patients with temporal lobe epilepsy, aged 8 to 56 years, had 1.5-T fMRI. Patients silently named an object described by a sentence compared to a visual control. Data were analyzed with ROI analysis from t-maps. Regional asymmetry indices (AI) were calculated ([L-R]/[L+R]) and language dominance defined as >0.20. t-Maps were visually rated by three readers at three t thresholds. Twenty-one patients had intracarotid amobarbital test (IAT). RESULTS: The fMRI reading task provided evidence of language lateralization in 27 of 30 patients with ROI analysis. Twenty-five were left dominant, two right, one bilateral, and two were nondiagnostic; IAT and fMRI agreed in most patients, three had partial agreement, none overtly disagreed. Interrater agreement ranged between 0.77 to 0.82 (Cramer V; p < 0.0001); agreement between visual and ROI reading with IAT was 0.71 to 0.77 (Cramer V; p < 0.0001). Viewing data at lower thresholds added interpretation to 12 patients on visual analysis and 8 with ROI analysis. CONCLUSIONS: An fMRI reading paradigm can identify language dominance in frontal and temporal areas. Clinical visual interpretation is comparable to quantitative ROI analysis.

Delineation of myocardial viability with PET.

UNLABELLED: Relative flow and metabolic imaging (the "mismatch pattern") with PET have been proposed to identify the presence of viable myocardium in patients with ischemic left ventricular dysfunction. Yet, optimal criteria to identify dysfunctional but viable myocardium and predict significant functional improvement have not been fully defined. METHODS: Dynamic PET imaging with 13N-ammonia and 18F-deoxyglucose to assess absolute myocardial perfusion and glucose uptake was performed in 25 patients (20 men, 5 women; mean age 57 +/- 12 yr, range 30-72 yr) scheduled for coronary revascularization because of coronary artery disease, anterior wall dysfunction and mildly depressed left ventricular ejection fraction (49% +/- 11%). Global and regional left ventricular function was evaluated by contrast left ventriculography at baseline and after revascularization. RESULTS: As judged from the changes in end-systolic volume and resting anterior wall motion before and after revascularization, 17 patients with improved wall motion score and decreased end-systolic volume were considered to have viable myocardium, whereas 8 patients with either no change in regional wall motion or increased end-systolic volume were considered to have nonviable myocardium. Before revascularization, viable myocardium showed higher absolute myocardial blood flow (77 +/- 20 versus 51 +/- 9 ml (min.100 g)-1, p = 0.004) and absolute regional myocardial glucose uptake (36 +/- 14 versus 24 +/- 11 mumole (min.100 g)-1, p = 0.04) than nonviable myocardium. CONCLUSION: This study identified absolute myocardial blood flow and normalized glucose extraction as the most powerful predictors of the return of contractile function after coronary revascularization in patients with ischemic anterior wall dysfunction.

Comparison of gadolinium-DTPA and polylysine-gadolinium-DTPA--enhanced magnetic resonance imaging of hepatocarcinoma in the rat.

RATIONALE AND OBJECTIVES: To compare the magnetic resonance (MR) imaging characteristics of gadolinium-DTPA (Gd-DTPA), a low-molecular-weight contrast agent, and polylysine-Gd-DTPA, a macromolecular contrast agent, in two types of hepatocarcinomas (HCC) in the rat. METHODS: T1-weighted spin-echo images were obtained in 13 rats with chemically induced HCC and 26 rats with Novikoff HCC before and 3 minutes to 60 hours after administration of either Gd-DTPA or polylysine-Gd-DTPA. RESULTS: Three minutes after polylysine-Gd-DTPA administration, the tumor-to-liver contrast of the two types of HCC increased significantly (positive contrast for chemically induced HCC and negative contrast for Novikoff HCC). At 30 minutes and 60 hours, the tumor-to-liver contrast remained above baseline values in chemically induced HCC and returned progressively to baseline values in Novikoff HCC. No significant increase in tumor-to-liver contrast was observed after Gd-DTPA administration. CONCLUSIONS: These results suggest that polylysine-Gd-DTPA provides a higher and more prolonged increase in tumor-to-liver contrast than Gd-DTPA.

Comparison of unenhanced and gadoxetate disodium-enhanced spin-echo magnetic resonance imaging for the detection of experimental hepatocellular carcinoma in the rat.

RATIONALE AND OBJECTIVES: The authors compare the potential value of unenhanced and gadoxetate disodium-enhanced spin-echo images for the detection of hepatocellular carcinoma in a rat model. METHODS: Eleven rats with chemically induced hepatocellular carcinoma underwent unenhanced T2-weighted fast spin-echo imaging followed by T1-weighted spin-echo imaging before and at 5 minutes, 30 minutes, 3 hours, 1 day, and 3 days after intravenous administration of 60 micromol/kg gadoxetate disodium at 4.7 tesla. Tumor and liver enhancement, and tumor-to-liver contrast-to-noise (C/N) ratio were calculated. RESULTS: After gadoxetate disodium administration, the tumors showed less enhancement than the liver. Tumor-to-liver C/N ratio increased from 5.5 +/- 0.8% on unenhanced T1-weighted images to 12.9 +/- 2.4% on gadoxetate-enhanced T1-weighted images (P = 0.02). However, the C/N ratio on unenhanced T2-weighted images (23.5 +/- 3.6%) remained higher than that on gadoxetate-enhanced T1-weighted images, a difference that is statistically significant (P < 0.01). CONCLUSIONS: In the experimental setting of our study, the higher tumor-to-liver C/N ratio on unenhanced T2-weighted spin-echo images suggests that unenhanced T2-weighted spin-echo images are superior to gadoxetate disodium-enhanced T1-weighted spin-echo images for the detection of hepatocellular carcinoma.

Brain energy metabolism in early blind subjects: neural activity in the visual cortex.

As an attempt to better understand the metabolic basis for the previously reported increases in glucose metabolism in the visual cortex of congenitally blind subjects, cerebral blood flow, oxygen consumption and glucose utilization were investigated with multitracer positron emission tomography. Measurements were carried out in three subjects who became blind early in life and in three age-matched blindfolded controls. Regional analysis of cerebral blood flow, metabolic rates for oxygen and glucose utilization revealed that these parameters were relatively higher in the visual cortex in case of early blindness (109.7 +/- 2.4%; 114.3 +/- 1.5%; 118.0 +/- 5.5%, respectively) than in controls (98.1 +/- 3.9%; 108.6 +/- 3.6%; 105.2 +/- 4.8%). There were slight differences, albeit statistically not significant, between early blind and control subjects in terms of oxygen-to-glucose metabolic ratios. The relatively preserved stoichiometry in the visual areas of blind subjects points to the lack of variation in the yield of glucose oxidation in this cortex. Those observations suggest that the high level of energy metabolism disclosed in early blind visual cortex is related to neural activity.

Diagnosis of intracranial aneurysms: accuracy of MR angiography at 0.5 T.

PURPOSE: Our goal was to determine the accuracy of MR angiography at 0.5 T for the diagnosis of intracranial aneurysms. METHODS: We retrospectively studied 140 patients, 70 with acute subarachnoid hemorrhage, who were either at high or low risk for intracranial aneurysm. Three-dimensional time-of-flight MR angiography was typically performed to cover the circle of Willis, with a volume thickness of 30 mm. Conventional spin-echo MR images and MR angiograms were reviewed together, and the results were compared with those obtained at intraarterial cerebral angiography to determine the sensitivity and specificity of MR angiography. RESULTS: Eighty-nine aneurysms (size range, 2 to 27 mm; 25 aneurysms < 5 mm) were identified at intraarterial cerebral angiography. Six aneurysms were missed by MR angiography and two were doubtful (sensitivity, 91% to 93%; specificity, 100%). Missed aneurysms were located outside the MR angiographic acquisition volume (n = 3) or on the carotid siphon (n = 3; size = 2, 3, and 5 mm). CONCLUSION: Even if MR angiography presents some restrictions in acquisition volume and spatial resolution, the detection rate of intracranial aneurysms is excellent at 0.5 T in both asymptomatic patients and in those with subarachnoid hemorrhage. A midfield system is not a restriction to the detection of intracranial aneurysms by MR examination.

Unusual location of an intracranial chondroma.

We describe the MR findings in a case of chondroma arising from the falx. At MR imaging, the mass appeared well defined, lobulated, hypointense to isointense on T1-weighted images, and very heterogeneous with marked hyperintense areas on T2-weighted images. After contrast administration, this tumor enhanced slightly on delayed images.

Vasospasm after subarachnoid hemorrhage: diagnosis with MR angiography.

BACKGROUND AND PURPOSE: The possibility of treating intracranial vasospasm has increased the significance of its diagnosis and follow-up; however, so far, no ideal method is available. The goal of this study was to assess the accuracy of MR angiography versus intraarterial angiography (IA-DSA) in detecting vasospasm. METHODS: The study included 42 patients with acute spontaneous subarachnoid hemorrhage (SAH). Serial MR angiograms (minimum, two per patient within 10 days after the event; total, 149) were obtained prospectively using a 3D time-of-flight technique covering the circle of Willis at 0.5 T. Forty-seven MR angiograms could be compared with intraarterial angiograms obtained within 24 hours of MR angiography. Vascular narrowing on both studies was rated consensually by two pairs of neuroradiologists using a scale from 0 (no narrowing) to 3 (severe narrowing). Categories 0 and 1 were considered an absence of vasospasm and categories 2 and 3 a presence of vasospasm. RESULTS: Agreement between MR angiography and IA-DSA (assessed with weighted kappa statistics) was substantial for the middle and anterior cerebral arteries (MCA and ACA) but moderate for the internal carotid artery (ICA). The sensitivity, specificity, accuracy, and positive and negative predictive values of MR angiography for detecting patients with vasospasm were 92%, 98%, 96%, 92%, and 98%, respectively. Considering each vessel separately, specificity was high for all locations (95-99%) and sensitivity was excellent for the ACA (100%) but poorer for the ICA (25%) and MCA (56%). CONCLUSION: MR angiography at 0.5 T is capable of identifying vasospasm after acute SAH but is less sensitive than IA-DSA for depicting vasospasm in the ICA and MCA.

Whipple disease confined to the central nervous system in childhood.

In a case of pediatric Whipple disease confined to the central nervous system, white matter lesions initially appeared as areas of very low signal intensity on T1-weighted MR images and as areas of hyperintensity on proton density-weighted and T2-weighted images, and showed slight peripheral enhancement on delayed contrast-enhanced T1-weighted images. On MR studies obtained 3 and 6 months after antibiotic therapy, the lesions had decreased in size and no longer enhanced. They became progressively less hypointense on T1-weighted images and less hyperintense on T2-weighted images.

Assessment of whole-brain vasodilatory capacity with acetazolamide challenge at 1.5 T using dynamic contrast imaging with frequency-shifted burst.

PURPOSE: To determine whether whole-brain acetazolamide-induced changes in regional cerebral blood volume (rCBV) can be assessed on a conventional gradient 1.5-T MR system using 3-D dynamic susceptibility contrast-enhanced MR imaging. METHODS: A 3-D frequency-shifted (FS) burst technique was used to assess the intravascular first pass of contrast agent. Changes in rCBV were calculated in 40 volunteers before and after acetazolamide (n = 30) or saline (n = 10) injection using customized analysis software on an independent workstation. A single-section gradient-echo technique with better spatial resolution was used in one additional volunteer to examine the effect of partial volume averaging on calculation of absolute rCBV. RESULTS: A statistically significant increase in rCBV (gray matter = 23%, white master = 32.5%) was noted after acetazolamide compared with saline. Baseline fractional CBVs were 22% +/- 3% for gray matter and 12% +/- 2% for white matter. Partial volume averaging was probably responsible for a systematic but linear overestimation of absolute rCBV. CONCLUSION: Acetazolamide-induced changes in rCBV can be assessed using 3-D dynamic susceptibility contrast-enhanced MR imaging with FS-burst on a conventional gradient 1.5-T MR system. Values obtained with this technique overestimate absolute rCBV but are systematically biased and can be used for intersubject and intrasubject ratio comparisons.