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Biomedical subjects

G Schlaug

Publications and source records attributed to G Schlaug.

At least 19 recordsLinked to original sources
PubMed2000

Multiple acute stroke syndrome: marker of embolic disease?

OBJECTIVE: To determine the frequency and etiologic significance of multiple acute ischemic lesions in stroke. BACKGROUND: Although patients may have more than one stroke during the course of their lives, acute ischemic stroke is usually thought of as a single event. Using diffusion-weighted imaging (DWI), an MRI technique that detects ischemic injury within minutes after onset, we have often observed multiple acute ischemic lesions. METHODS: The MRI scans of 59 consecutively studied patients were reviewed to determine the frequency and etiologic significance of multiple acute ischemic lesions on DWI. RESULTS: Multiple acute ischemic lesions were present in 10 (17%) of 59 patients. The lesions usually occurred within one major circulation (anterior or posterior), but in two patients (3%), lesions occurred in both cerebral hemispheres or in the anterior and the posterior circulations. The lesions often were small and resulted from presumed multiple emboli or the break-up of an embolus. Two patients had internal carotid artery occlusive disease and four had a cardiac or aortic source. In the other four patients the source was not determined. Lesions larger than 1 cm in diameter progressed to infarction, but some smaller lesions were not seen on follow-up T2-weighted imaging. CONCLUSIONS: Multiple acute stroke lesions on DWI are common and could be caused by multiple emboli or the breakup of an embolus. In some cases it might become possible to make early inferences concerning the stroke mechanism that could be of use for immediately directing the clinical work-up and treatment of the patient.

Acute Disease↗
PubMed2000

Diffusion- and perfusion-weighted MRI patterns in borderzone infarcts.

BACKGROUND AND PURPOSE: The pathophysiology of borderzone infarcts is not well understood. We investigated whether combined diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) could identify pathophysiologically meaningful categories of borderzone infarcts. METHODS: Seventeen patients with borderzone infarcts were identified from the Beth Israel Deaconess Medical Center Stroke Database. All patients had DWI and PWI, the majority of them within the first 24 hours of symptom onset. RESULTS: Three patterns of perfusion abnormalities were associated with the diffusion lesions: 1, normal perfusion (5 patients); 2, localized perfusion deficits matching the area of restricted diffusion (5 patients); and 3, extensive perfusion deficits involving 1 or more vascular territories (7 patients). All but 1 patient with pattern 1 had transient peri-infarct hypotension as the presumed stroke mechanism. Two patients with pattern 2 had cardiac or aortic embolic sources; none had large-artery disease or arterial hypotension. Reperfusion was detected in all patients with this pattern who submitted to a follow-up study. All patients with pattern 3 had severe stenosis or occlusion of a large artery: the internal carotid, anterior cerebral, or middle cerebral. CONCLUSIONS: We postulate that the perfusion abnormality varies according to the mechanism of the borderzone infarction. Transient perfusion deficits occurring with hypotension in the absence of significant large-artery disease may not be revealed by PWI. Embolism may cause some cases of small borderzone perfusion deficits. Critical large-artery disease may cause large territorial perfusion deficits and predispose to borderzone infarction.

Aged↗
PubMed1999

The ischemic penumbra: operationally defined by diffusion and perfusion MRI.

BACKGROUND: Identifying tissue at risk for infarction is important in deciding which patients would benefit most from potentially harmful therapies and provides a way to evaluate newer therapies with regard to the amount of ischemic tissue salvaged. OBJECTIVE: To operationally define and characterize cerebral tissue at risk for stroke progression. METHODS: We retrospectively selected 25 patients with an acute onset of a hemispheric stroke from our database who had undergone a combination of two diffusion-weighted MRI studies and a perfusion-weighted MRI study. We applied a logistic regression model using maps of the relative mean transit time and relative cerebral blood flow (rCBF) as well as three different maps of the relative cerebral blood volume (rCBV) to predict an operationally defined penumbra (region of mismatch between the diffusion lesion on day 1 and its extension 24 to 72 hours later). RESULTS: Maps of the rCBF and initial rCBV were significant predictors for identifying penumbral tissue. Our operationally defined penumbral region was characterized by a reduction in the initial rCBV (47% of contralateral control region [CCR]), an increase (163% of CCR) in the total rCBV, and a reduction (37% of CCR) in the rCBF, whereas the operationally defined ischemic core showed a more severe reduction in the rCBF (12% of CCR) and in the initial rCBV (19% of CCR). CONCLUSION: These MR indexes may allow the identification and quantification of viable but ischemically threatened cerebral tissue amenable to therapeutic interventions in the hyperacute care of stroke patients.

Aged↗
PubMed1998

Multimodal output mapping of human central motor representation on different spatial scales.

1. Non-invasive mapping by focal transcranial magnetic stimulation (TMS) is frequently used to investigate cortical motor function in the intact and injured human brain. We examined how TMS-derived maps relate to the underlying cortical anatomy and to cortical maps generated by functional imaging studies. 2. The centres of gravity (COGs) of TMS maps of the first dorsal intersosseus muscle (FDI) were integrated into 3-D magnetic resonance imaging (MRI) data sets in eleven subjects. In seven of these subjects the TMS-derived COGs were compared with the COG of regional cerebral blood flow increases using positron emission tomography (PET) in an index finger flexion protocol. 3. Mean TMS-derived COG projections were located on the posterior lip of the precentral gyrus and TMS-derived COG projections were in close proximity to the mean PET-derived COG, suggesting that the two methods reflect activity of similar cortical elements. 4. Criteria for a reliable assessment of the COG and the number of positions with a minimum amplitude of two-thirds of the maximum motor-evoked potential (T3Ps) were determined as a function of the number of stimuli and extension of the stimulation field. COGs and T3Ps were compared with an estimate of the size of the human motor cortex targeting alpha-motoneurons of forearm muscles. This comparison suggests that TMS can retrieve spatial information on cortical organization below the macroanatomic scale of cortical regions. 5. Finally, we studied the cortical representation of hand muscles in relation to facial and foot muscle representations and investigated hemispherical asymmetries. We did not find any evidence for a different ipsi- or contralateral representation of the mentalis muscle. Also, no difference was found between FDI representations on the dominant versus the non-dominant hemisphere.

Adult↗
PubMed1998

Functional burst imaging.

A quiet magnetic resonance (MR) imaging technique for detecting changes in cerebral activity functions is presented. This single-shot method, functional Burst imaging (FBI), combines elements of Burst imaging with an offset technique known as asymmetric spin echo (ASE). The FBI sequence has the unique feature of being nearly silent, because of the low number of gradient switching steps involved. Furthermore, this approach has the key advantage that it can be implemented on conventional MR systems. Established auditory and visual paradigms were used to evaluate whether FBI can detect changes in cerebral activity using a 1.5 Tesla MR system. In a second set of experiments, the FBI technique was used to evaluate cerebral activity changes during different sleep stages in humans. The results obtained demonstrate that the FBI sequence provides an alternative approach for functional imaging of brain activity in primary and secondary sensory areas of the human brain. Furthermore, in using this quiet MR technique, it was possible to scan continuously during different stages of human sleep without acoustic noise perturbation.

Acoustic Stimulation↗
PubMed1998

Unsolved problems in comparing brain sizes in Homo sapiens.

When brain size is compared across taxonomic levels, there is a clear relation between body parameters and brain size. It is generally stated that the correlation between brain size and body parameters becomes very small at the species level (Aboitiz, 1996), but this is not the case for Homo sapiens where there is a strong correlation between brain size and body size across racial groups that differ in body size. The control for body size across racial groups (and sexes) is rendered difficult because bodies do not just differ only in height and weight. Within groups different studies show weak and inconsistent brain size/body height correlations. A better understanding of brain size/body height relations must await better quality data and a better understanding of how exactly body parameters should be scaled between groups and sexes. We attribute the clear between-group and weak within-group correlations to the large variety of body sizes and body types in our species, a variety which is only equalled in selectively bred species of animals. At present, there is no meaningful basis for the comparison of brain sizes within and between racial groups and sexes.

Adult↗
PubMed1998

Differential magnetic resonance signal change in human sensorimotor cortex to finger movements of different rate of the dominant and subdominant hand.

Functional magnetic resonance tomography (fMRI) analysis of unimanual and bimanual sequential movements in righthanders showed the following effects. First, a rate-dependent activation of the somato-motor cortex was confirmed, with faster movement rates producing higher activation both in terms of signal intensity and number of activated voxels. Second, the right hemisphere showed more activation than the left hemisphere during unimanual tasks. Third, during bimanual movements, the left hemisphere showed greater activation than the right hemisphere. Finally, while the left hemisphere showed a marked change in activation patterns from unimanual to bimanual task, the right hemisphere activation patterns were not sensitive to task changes. The hemispheric asymmetries suggest substantial left hemisphere involvement in the coordination of bimanual tasks.

Adult↗
PubMed1998

Turbo spin-echo diffusion-weighted MR of ischemic stroke.

PURPOSE: Our objective was to determine whether a multisection technique, diffusion-weighted half-Fourier single-shot turbo spin-echo (HASTE) imaging, can compensate for the drawbacks common to other diffusion-weighted techniques; specifically, the need for echo-planar technology and the presence of susceptibility artifacts in areas close to the skull base. METHODS: Forty subjects who were referred to the stroke service with signs of acute (less than 24 hour) neurologic dysfunction were included in this prospective study. MR imaging of the brain was performed with diffusion-weighted echo-planar and diffusion-weighted HASTE sequences. The images obtained with both sequences were analyzed for the presence of hyperintensities corresponding to ischemic lesions as well as for the presence of image artifacts and distortions. RESULTS: Diffusion-weighted HASTE images showed areas of hyperintensity corresponding to the infarcts present on diffusion-weighted echo-planar imaging studies without distortion or susceptibility artifacts in all the patients who had a stroke. Twelve patients had no acute ischemic lesions; of these, five had other findings, six had normal findings, and in one patient, a hyperintensity seen on diffusion-weighted echo-planar images proved to be an artifact on diffusion-weighted HASTE images. CONCLUSIONS: Diffusion-weighted HASTE is equal to diffusion-weighted echo-planar imaging in the detection of early ischemia. Because of the absence of significant image distortions and other artifacts, diffusion-weighted HASTE permits fast multiplanar imaging in artifact-prone regions, such as the posterior fossa and the inferior frontal and temporal lobes. Diffusion imaging can be performed on conventional systems with strengths of 1.5 T that do not have echo-planar imaging capabilities.

Acute Disease↗
PubMed1997

Prefrontal cortex fMRI signal changes are correlated with working memory load.

We investigated whether a nonspatial working memory (WM) task would activate dorsolateral prefrontal cortex (DLPFC) and whether activation would be correlated with WM load. Using functional magnetic resonance imaging we measured regional brain signal changes in 12 normal subjects performing a continuous performance, choice reaction time task that requires WM. A high WM load condition was compared with a non-WM choice reaction time control condition (WM effect) and a low WM load condition (load effect). Significant changes in signal intensity occurred in the DLPFC, frontal motor regions and the intraparietal sulcus (IPS) in both comparisons. These findings support the role of DLPFC and IPS in WM and suggest that signal changes in DLPFC correlate with WM load.

Adult↗
PubMed1997

Enlargement of human cerebral ischemic lesion volumes measured by diffusion-weighted magnetic resonance imaging.

We aimed to determine the frequency and time course of the enlargement of ischemic cerebral lesions following human stroke and to study the effect of the state of perfusion on lesion enlargement. Acute lesion volumes were measured on diffusion-weighted magnetic resonance images and compared with lesion volumes measured on T2-weighted images at 7 days or later. Forty-four measurements were performed between 2 and 53 hours after stroke onset in 28 patients. Thirteen patients also had magnetic resonance perfusion imaging performed. In 12 (43%) of 28 patients the initial lesion volume increased by 20% or more. The number of studies showing enlargement of the ischemic lesion volume ranged from 12 (43%) of 28 at or after 2 hours to 10 (38%) of 26 at or after 6 hours, 5 (33%) of 15 at or after 24 hours, and 2 (33%) of 6 at or after 48 hours. In 7 of the 10 patients in whom the hypoperfusion volume acutely exceeded the volume of the abnormality on diffusion-weighted images, lesion volume increased by 20% or more. This study provided evidence that substantial enlargement of human cerebral ischemic lesion volumes can occur beyond the first 6, 12, or 24 hours after onset. A mismatch acutely between the region of hypoperfusion (larger) and the region of diffusion abnormality (smaller) may be predictive of ischemic lesion enlargement.

Adult↗
PubMed1997

Ischemic lesion volumes in acute stroke by diffusion-weighted magnetic resonance imaging correlate with clinical outcome.

Diffusion-weighted magnetic resonance imaging detects ischemic injury within minutes after onset, and has been used to demonstrate drug efficacy in animal models of stroke. In 50 patients diagnosed with acute ischemic stroke (<24-hour duration) within the middle cerebral artery territory, lesion volume was measured by diffusion-weighted imaging. Thirty-four patients also had volumes measured by T2-weighted imaging chronically (median time, 7.5 weeks; mean, 15.9 weeks). Clinical severity was measured by the National Institutes of Health Stroke Scale Score and the Barthel index. Acute lesion volumes correlated with the acute stroke scale score (r = 0.56), the chronic stroke scale score (r = 0.63), and chronic lesion volumes (r = 0.84). Chronic volumes correlated with the chronic stroke scale score (r = 0.86) and the Barthel index (r = -0.60). When only cortically based lesions were considered, the correlations relating acute lesion volume measured by diffusion-weighted imaging (r = 0.61) and chronic lesion volume measured by T2-weighted imaging (r = 0.90) to the chronic stroke scale score were higher. These results provide evidence that lesion volumes determined by diffusion-weighted imaging acutely may be predictive of clinical severity and outcome, and may support a role for diffusion-weighted imaging in the assessment of acute stroke therapies in clinical trials.

Adult↗
PubMed1997

Hand skill asymmetry in professional musicians.

Hand skill asymmetry on two handedness tasks was examined in consistent right-handed musicians and nonmusicians as well as mixed-handed and consistent left-handed nonmusicians. Musicians, although demonstrating right-hand superiority, revealed a lesser degree of hand skill asymmetry than consistent right-handed nonmusicians. Increased left-hand skill in musicians accounted for their reduced asymmetry. Musicians predominantly playing keyboard instruments demonstrated superior tapping performance than musicians playing predominantly string instruments, although they did not differ with respect to hand skill asymmetry. Since the diminished tapping asymmetry in musicians was related to early commencement but not duration of musical training, results are interpreted as an adaptation process due to performance requirements interacting with cerebral maturation during childhood.

Adult↗
PubMed1997

A case of callosal agenesis with strong anatomical and functional asymmetries.

A 30-year-old right-handed man (W.D.) with total callosal agenesis was examined neuropsychologically and with magnetic resonance imaging. Basic neuropsychological testing revealed normal intelligence and average attentional capabilities. Anatomically, W.D. shows strong leftward perisylvian asymmetry both for the planum temporale and planum parietale, an unusual pattern not found in our database of more than 200 brains of young and healthy individuals. Functionally, W.D. has strong right hand superiority for hand skill and tactile object recognition, indicating unusual left hemisphere dominance for both functions. Our observations could support the hypothesis that callosal connectivity and hemispheric asymmetry may be inversely related.

Adult↗
PubMed1997

STAR MR angiography for rapid detection of vascular abnormalities in patients with acute cerebrovascular disease.

BACKGROUND AND PURPOSE: We undertook to investigate the usefulness of signal targeting with alternating radiofrequency magnetic resonance angiography (STAR MRA) in the diagnosis of acute cerebrovascular disease. The potential advantage of the technique is that angiographic images can be acquired in less than 1 minute. METHODS: We studied 19 patients (11 men and 8 women, ranging in age from 36 to 84 years [mean age, 66 years]) presenting with signs and symptoms of acute stroke. Patients underwent STAR MRA and three-dimensional fast imaging with steady-state precession (3D FISP) MRA. The MRAs were analyzed as to image quality and vascular abnormalities in the vascular territory of stroke as defined by diffusion-weighted imaging abnormalities and compared using a Wilcoxon signed-rank test. RESULTS: STAR MRAs had slightly inferior image quality compared with 3D FISP MRA (P < .05). STAR MRA and 3D FISP MRA agreed in 18 of 19 cases regarding vascular abnormalities in the territory of the infarct (occlusion, n = 8; stenosis, n = 4; no abnormality, n = 6). In one patient, the techniques disagreed, when 3D FISP MRA was normal and STAR MRA demonstrated a vessel occlusion in the vascular territory of a stroke as defined by diffusion-weighted imaging abnormalities (P > .05). CONCLUSIONS: Despite slightly inferior image quality compared with 3D FISP MRA, STAR MRA is comparable with 3D FISP MRA in depicting abnormalities in the proximal parts of the cerebral arteries corresponding to ischemic regions on diffusion-weighted imaging, in a strikingly shorter acquisition time. Further studies are necessary to confirm that the smaller branches are better shown by using longer inversion times.

Acute Disease↗
PubMed1997

Comparison of EPISTAR and T2*-weighted gadolinium-enhanced perfusion imaging in patients with acute cerebral ischemia.

PURPOSE: To compare echo-planar imaging with signal targeting and alternating radiofrequency (EPISTAR), an arterial spin-labeling technique, to a T2*-weighted gadolinium-enhanced (T2*-WGE) MR perfusion technique for the evaluation of acute cerebrovascular disease. METHOD: Twenty-one EPISTAR and T2*-WGE perfusion studies were performed on 18 patients with the clinical diagnosis of acute stroke (12 men, 6 women, age range 34 to 89 years, mean age 68 years). For qualitative analysis, perfusion studies of both techniques were grouped into categories (hyperperfusion, normal perfusion, delayed perfusion, or absent perfusion) and compared with a Wilcoxon signed rank test. Quantitative analysis was performed using signal intensity measurements in a region of interest that was defined by diffusion-weighted imaging abnormalities. These signal intensity measurements were compared with a mirror region in the contralateral unaffected hemisphere. Signal intensity ratios (infarcted region versus the unaffected contralateral region) were calculated and compared using a paired t test. RESULTS: Qualitative analysis demonstrated agreement between the two techniques in 17 of 21 studies (hyperfusion, n = 3 patients; normal perfusion, n = 3; delayed perfusion, n = 4; and absent perfusion, n = 7). In four studies, the two techniques disagreed when EPISTAR demonstrated absent and T2*-WGE perfusion demonstrated delayed perfusion (p > 0.05). Quantitative analysis revealed a mean signal intensity ratio of 0.73 +/- 0.79 for the T2*-WGE perfusion technique and 0.69 +/- 0.68 for the EPISTAR technique (p > 0.05). CONCLUSION: The noninvasive EPISTAR technique can assess perfusion abnormalities similarly to the T2*-WGE perfusion technique and may provide a valuable alternative in the diagnosis of acute stroke patients. Differences between the two techniques can be explained by the applied inflow times in the EPISTAR technique.

Adult↗
PubMed1997

Time course of the apparent diffusion coefficient (ADC) abnormality in human stroke.

Diffusion-weighted MRI can rapidly detect acute cerebral ischemic injury as hyperintense signal changes, reflecting a decline in the apparent diffusion coefficient (ADC) of water through brain parenchyma, whereas ADC is elevated in the chronic stage because of increased extracellular water content. To determine the time course of these ADC changes, we analyzed 157 diffusion-weighted MRI studies performed at varying time points from the initial ischemic event from 101 patients. Data were expressed as the relative ADC (rADC), the ratio of lesion to control regions of interest. We observed two phases in the time course of rADC changes in acute human stroke: a significant (p < 0.005) reduction in rADC lasting for at least 96 hours from stroke onset (mean, 58.3% of control; SEM, 1.47) and an increasing trend from reduction to pseudonormalization to elevation of rADC values at later subacute to chronic time points (> or = 7 days). We suggest that the persistent reduction of rADC within the first four days may reflect ongoing or progressive cytotoxic edema to a greater degree than extracellular edema and cell lysis.

Adult↗
PubMed1997

Ictal motor signs and interictal regional cerebral hypometabolism.

Early motor manifestations are the main components of focal seizures involving the frontal lobe. We examined the relationship between the initial ictal motor manifestations and interictal abnormalities of cerebral glucose consumption (rCMRGlc) as assessed by PET in 48 consecutive patients with focal seizures of neocortical origin. Group data analysis revealed that patients with predominantly unilateral clonic seizures had a significant contralateral perirolandic hypometabolism and to a lesser degree a contralateral frontomesial hypometabolism. Patients with predominantly focal tonic manifestations showed a hypometabolism within the frontomesial and perirolandic regions that was unilateral in all patients with lateralized tonic seizures. Patients with versive seizures had mainly contralateral metabolic depressions without a consistent regional pattern. Patients with hypermotor seizures had metabolic depressions involving frontomesial, anterior cingulate, perirolandic, and anterior insular/frontal operculum areas. In all patient groups, bilateral and symmetric hypometabolism of the thalamus and cerebellum was observed. We propose that this pattern of distinctly abnormal metabolic brain regions demonstrates not only possible epileptogenic zones but also symptomatogenic brain regions as shown by the associations between clinical manifestations and sets of abnormal brain regions, particularly if epileptogenic zones are in a clinically silent neocortical brain region. The detection and possible differentiation of symptomatogenic and epileptogenic zones might improve the effectiveness of presurgical noninvasive studies.

Adult↗