Hyperacute ischemic stroke missed by diffusion-weighted imaging.
(65/5118)
We present two cases of hyperacute ischemic stroke that were initially missed by diffusion-weighted imaging; abnormalities in locations corresponding to focal neurologic deficits were discovered by MR angiography and perfusion-weighted imaging. Within hours, follow-up diffusion-weighted scans revealed partial conversion of the hypoperfused regions to complete stroke. These cases illustrate the potential for a nonresolving stroke-in-evolution to go undetected by diffusion-weighted imaging at hyperacute timepoints. (+info)
Diffusion-negative stroke: a report of two cases.
(66/5118)
Diffusion-weighted MR imaging is generally thought to be highly sensitive for the diagnosis of acute stroke. We report two cases of hyperacute stroke with absence of changes on diffusion-weighted images within 4 hours of symptom onset. Follow-up studies, performed 4 days later, showed infarction in regions compatible with the clinical presentation and (in one case) with the initial perfusion deficit. These cases indicate that normal findings on diffusion-weighted images in patients with suspected cerebral ischemia do not rule out impending infarction. (+info)
Transcranial Doppler of a paradoxical brain embolism associated with a pulmonary arteriovenous fistula.
(67/5118)
We herein report the case of a patient who had paradoxical brain embolism owing to a pulmonary arteriovenous fistula (PAVF) who was diagnosed as having a right-to-left shunt by transcranial Doppler (TCD) with saline contrast medium. TCD with saline contrast medium failed to detect any high-intensity transient signals immediately after catheter embolization of the PAVF. Thus, TCD with saline contrast medium was useful for identifying the presence of a right-to-left shunt and for confirming that the shunt had been obliterated after endovascular treatment. (+info)
MR blood oxygenation level-dependent signal differences in parenchymal and large draining vessels: implications for functional MR imaging.
(68/5118)
BACKGROUND AND PURPOSE: One major limitation of current functional MR (fMR) imaging is its inability to clarify the relationship between sites of cortical neuronal activation, small parenchymal venules that are in close proximity to these sites, and large draining veins distant from the active parenchyma. We propose to use gradient-echo blood oxygenation level-dependent (BOLD) fMR time courses to differentiate large draining veins from parenchymal microvasculature. METHODS: In eight research subjects, five of whom presented with space-occupying lesions near the central sulcus, gradient-echo fMR imaging was performed during alternating periods of rest and motor activation. MR signal time courses from parenchymal regions and draining veins of different diameters, which were identified using contrast-enhanced T1-weighted scans, were evaluated. Percent signal changes (deltaS) and the time to the onset of MR signal rise (T0) were calculated. RESULTS: Mean delta(S) for all subjects was 2.3% (SD+/-0.7%) for parenchymal activation, 4.3% (SD +1.0%) for sulcal macrovasculature, and 7.3 (SD+/-1.1%) for large superficial bridging veins. The mean time to onset of MR signal increase was 4.4 seconds for parenchymal task-related hemodynamic changes and 6.6 seconds for venous hemodynamic changes, regardless of vessel size. Both the differences in delta(S) and T0 were statistically significant between venous and parenchymal activation (P < .0001). CONCLUSION: Gradient-echo fMR imaging reveals hemodynamic task-related changes regardless of vessel size and therefore might show macrovascular changes distal to the site of neuronal activity. MR-signal time-course characteristics (delta(S) and T0) can be used to differentiate between small parenchymal and larger pial draining vessels, which is especially important in presurgical planning of neurosurgical procedures involving functionally important brain regions. The knowledge about the differences in (delta)S and T0 between micro- and macrovasculature might lead to a more accurate description of the spatial distribution of underlying neuronal activity. (+info)
Echo-planar functional MR imaging of epilepsy with concurrent EEG monitoring.
(69/5118)
BACKGROUND AND PURPOSE: The role of functional MR (fMR) imaging in the evaluation of patients with epilepsy has not been systematically studied. Our purpose was to identify the fMR correlates of interictal epileptiform discharges. METHODS: Twenty patients with epilepsy and frequent interictal discharges were studied with concurrent EEG monitoring on a 1.5-T echo-planar magnet to acquire blood-oxygenation-level-dependent (BOLD) images in the baseline (OFF) and immediate post-discharge (ON) states. Analysis was performed using subtraction of average ON and OFF data (method I); cross-correlation analysis between the ON and OFF states (method II); and individual spike analysis (ISA), with which signal intensity in the individual ON states was statistically analyzed using a weighted comparison with the mean and variance of the OFF states (method III). Agreement of fMR activation with EEG localization was determined. RESULTS: Eighteen of 20 patients had interictal discharges during the monitoring period. Method I yielded visually detectable sites of BOLD signal differences in only one patient. Method II resulted in two patients with sites of BOLD activation. Method III, ISA, resulted in regions of increased BOLD signal corresponding to the EEG focus in nine of 10 patients. CONCLUSION: fMR studies can often reveal sites of increased BOLD signal that correspond to sites of interictal EEG discharge activity. Because of variable intensity changes associated with discharge activity, ISA resulted in increased sensitivity. (+info)
A comparison of MR imaging with fast-FLAIR, HASTE-FLAIR, and EPI-FLAIR sequences in the assessment of patients with multiple sclerosis.
(70/5118)
BACKGROUND AND PURPOSE: Fast fluid-attenuated inversion-recovery (FLAIR) sequences are sensitive for detecting lesions in patients with multiple sclerosis (MS). More rapid fast-FLAIR imaging of the brain can be achieved by the concomitant use of half-Fourier acquisition single-shot turbo spin-echo (HASTE-FLAIR) and echo-planar imaging (EPI-FLAIR). The present study was performed in a large cohort of subjects to assess and compare the number and volume of brain lesions detected by the fast-FLAIR, HASTE-FLAIR, and EPI-FLAIR sequences in patients with MS. METHODS: Fast-FLAIR, HASTE-FLAIR, and EPI-FLAIR sequences were obtained from 46 consecutive MS patients. Lesions seen on each type of sequence were counted and classified by consensus by two observers. Lesion volumes were measured using a semiautomated segmentation technique based on local thresholding. RESULTS: The quality of the fast-FLAIR images was significantly better than that of HASTE-FLAIR and EPI-FLAIR images. Fast-FLAIR revealed significantly more lesions and higher lesion volumes than did HASTE-FLAIR and EPI-FLAIR. A similar number of large lesions was detected by the three sequences, but HASTE-FLAIR and EPI-FLAIR showed significantly fewer small and intermediate lesions than did fast-FLAIR. The number of lesions seen on HASTE-FLAIR and EPI-FLAIR images was similar. CONCLUSION: HASTE-FLAIR and EPI-FLAIR sequences revealed as many large MS lesions as fast-FLAIR. Because their acquisition times are only a fraction of that needed for fast-FLAIR sequences, they may be useful for making a rapid diagnosis of MS in uncooperative patients. Their reduced ability to detect smaller lesions indicates that they should not be used as a routine approach to imaging patients with MS. (+info)
Evolution of multiple sclerosis lesions on serial contrast-enhanced T1-weighted and magnetization-transfer MR images.
(71/5118)
BACKGROUND AND PURPOSE: Magnetization-transfer imaging is a technique that could provide indirect evidence of the characteristics of multiple sclerosis (MS) lesions. The purpose of this work was to study the evolution of MS lesions on T1-weighted MR images over time and to investigate changes in magnetization-transfer ratio (MTR) values of MS lesions with different initial appearances on contrast-enhanced T1-weighted images. METHODS: Eleven patients with relapsing-remitting MS were studied with MR imaging. The MTRs were calculated for 47 lesions that had been classified according to their appearance on contrast-enhanced T1-weighted images. Each patient was examined at four time points over a 1-year period. The MTR changes observed in the selected lesions were compared with their initial T1-weighted appearance. RESULTS: The lowest MTR values were initially found in hypointense nonenhancing lesions and in ring-enhancing lesions, with both types showing a hypointense center. Changes in MTR values were more dynamic and reversible in ring-enhancing than in hypointense nonenhancing plaques. Nodular-enhancing lesions had slightly lower initial MTRs than did isointense non-enhancing lesions. CONCLUSION: The absence or presence of contrast uptake may indicate a different pathologic basis for hypointense MS lesions on T1-weighted MR images. These differences should be kept in mind when considering T1 lesion load as a surrogate marker of disability in MS. (+info)
Serial analysis of magnetization-transfer histograms and Expanded Disability Status Scale scores in patients with relapsing-remitting multiple sclerosis.
(72/5118)
BACKGROUND AND PURPOSE: Magnetization transfer ratio histogram peak height (MTR-HPH) has been shown to correlate with macroscopic and microscopic brain disease in patients with multiple sclerosis (MS). We studied the changes in MTR-HPH and in Kurtzke's Expanded Disability Status Scale (EDSS) scores over time in a group of patients with relapsing-remitting MS. METHODS: Twenty adult patients with relapsing-remitting MS (four men and 16 women) were followed up for a period of 334 to 1313 days. In all, 86 MR imaging studies of the brain were obtained, and MTR-HPH was calculated for each MR examination by using a semiautomated technique. Changes in MTR-HPH were compared between patients over the study's duration. A neurologist specialized in the care of MS patients assessed the EDSS score for each patient as a measure of clinical disability. RESULTS: Serial MR data showed a subtle but significant decline in MTR-HPH with time. No significant changes in EDSS scores were noted over the same period. CONCLUSION: Patients with relapsing-remitting MS have a significant progressive decline in normalized MTR-HPH, which is independent of EDSS score. MTR-HPH measurements can be used to monitor subclinical disease in patients with relapsing-remitting MS over a short time frame of 1 to 4 years. This parameter might be applied in future therapeutic trials to assess its usefulness. (+info)