Cerebral Blood Flow Asymmetry Research Articles

Migraine with Aura Is Associated with an Incomplete Circle of Willis: Results of a Prospective Observational Study

ObjectiveTo compare the prevalence of an incomplete circle of Willis in patients with migraine with aura, migraine without aura, and control subjects, and correlate circle of Willis variations with alterations in cerebral perfusion.MethodsMigraine with aura, migraine without aura, and control subjects were prospectively enrolled in a 1∶1∶1 ratio. Magnetic resonance angiography was performed to examine circle of Willis anatomy and arterial spin labeled perfusion magnetic resonance imaging to measure cerebral blood flow. A standardized template rating system was used to categorize circle of Willis variants. The primary pre-specified outcome measure was the frequency of an incomplete circle of Willis. The association between circle of Willis variations and cerebral blood flow was also analyzed.Results170 subjects were enrolled (56 migraine with aura, 61 migraine without aura, 53 controls). An incomplete circle of Willis was significantly more common in the migraine with aura compared to control group (73% vs. 51%, p = 0.02), with a similar trend for the migraine without aura group (67% vs. 51%, p = 0.08). Using a quantitative score of the burden of circle of Willis variants, migraine with aura subjects had a higher burden of variants than controls (p = 0.02). Compared to those with a complete circle, subjects with an incomplete circle had greater asymmetry in hemispheric cerebral blood flow (p = 0.05). Specific posterior cerebral artery variants were associated with greater asymmetries of blood flow in the posterior cerebral artery territory.ConclusionsAn incomplete circle of Willis is more common in migraine with aura subjects than controls, and is associated with alterations in cerebral blood flow.

Brain perfusion and upper limb motor function: A pilot study on the correlation between evolution of asymmetry in cerebral blood flow and improvement in Fugl–Meyer Assessment score after rTMS in chronic post-stroke patients

Few studies have explored the refinement of asymmetry in regional cerebral blood flow in relation to behavioral improvement after treatment. The purpose of this retrospective pilot study was to identify cerebral cortical regions with improved perfusion that correlated with improvement of upper limb motor function after repetitive transcranial magnetic stimulation (rTMS). The study subjects were 33 post-stroke patients with upper limb hemiparesis who underwent rTMS combined with intensive occupational therapy (mean ± SD age: 64.9 ± 11.2 years; time since onset of stroke: 57.3 ± 45.9 months). Fugl-Meyer Assessment (FMA) and the Wolf Motor Function Test (WMFT) were applied before and after treatment to evaluate motor function in the affected upper limb. Regional brain perfusion was measured by single-photon emission computed tomography, and the percentages of asymmetry values (asymmetry index [AI]) for 52 bilateral regions of interest were calculated. The change in AI was calculated as the post-intervention minus pre-intervention values. Changes in AI in the superior and middle frontal areas correlated significantly and negatively with changes in FMA score (superior: r = -0.406, P = 0.03, R(2) = 0.251; middle: r = -0.437, P < 0.001, R(2) = 0.306), but not with changes in WMFT log performance time. Changes in AI less than zero reflect improved perfusion, suggesting that upper limb motor function improvement in post-stroke patients reflects evolution of brain perfusion in the superior and middle frontal areas.

Diagnostic impact of baseline cerebral blood flow in patients with acute ischemic stroke prior to intravenous recombinant tissue plasminogen activator therapy

To determine whether severe cerebral perfusion defects measured by SPECT prior to rt-PA therapy attribute to severe intracerebral hemorrhage (SICH). We measured baseline cerebral blood flow (CBF) using technetium-99m-labeled hexamethylpropyleneamine oxime (99mTc-HMPAO) SPECT qualitatively prior to rt-PA therapy, in 52 consecutive patients (range 38-93 years). The degree and extent of the asymmetry of local CBF were analyzed semi-quantitatively. We did not administrate rt-PA in patients with severe perfusion defects. Clinical outcome and the incidence of SICH were studied. Three (5.8%) patients had severe perfusion defects that were undetected by CT and/or DWI. The other 49 (94.2%) patients had mild perfusion defects. The asymmetry of local CBF was 0.08±0.08 (n=3) and 0.3±0.15 (n=49) in the two groups, respectively. The percentages of the ipsilateral hemisphere in which perfusion was impaired severely were 17.5±9.5% (n=3) and 0.43±0.87% (n=49). Two patients were found petechial hemorrhage, but there was no patient who developed SICH in the former group following conventional antithrombotic therapy. In the latter group, SICH occurred in 1/49 (2.0%) patient following rt-PA therapy. These results suggest that rt-PA therapy for patients with severe cerebral perfusion defects may cause SICH and baseline CBF may contribute to identify patients at high risk for SICH after intravenous rt-PA therapy.

Abstract TP41: Arterial Spin-Labeled Perfusion MRI with Multi-Delay: Expanding Beyond CBF in Acute Ischemic Stroke

Background: Arterial spin-labeled (ASL) perfusion MRI can measure cerebral blood flow (CBF), yet the prolonged delays of collateral perfusion in acute ischemic stroke may impose limitations. Multiparametric maps of perfusion, including transit times and cerebral blood volume (CBV), may reveal important hemodynamic features before CBF collapse. We implemented a novel multi-delay ASL sequence to investigate multiparametric perfusion changes in acute stroke. Methods: Consecutive acute ischemic stroke patients admitted during an 8-month period were evaluated with pseudo-continuous ASL on Siemens 1.5 T and 3 T scanners within 12 hours of symptom onset. ASL was acquired using a 4-delay pCASL protocol with background suppressed 3D GRASE (postlabeling delay (PLD)=1.5/2/2.5/3s, FOV=22cm, matrix=64x64, 16x8mm slices, rate-2 GRAPPA, TE=22ms, 8 pairs of tag and control for each delay, total scan time 4min). After motion correction, arterial transit time (ATT), CBF, and arterial CBV (aCBV) maps were generated from the 4 PLDs. Results: A total of 161 ASL multi-delay perfusion MRI studies were performed in 130 acute ischemic stroke patients (mean age was 71±18 years and 56% were female). Repeated multi-delay ASL or serial studies were acquired in 19 cases, including 11 cases with 2 MRIs, 7 with 3, and 1 with 6 MRIs, depicting multiparametric blood flow changes after treatment. Correlation of multi-delay ASL (4 PLDs) and DSC MRI CBF asymmetry measures in MCA stroke patients (when available) was r=0.785 (p&lt;0.001) and r=0.683 (p=0.003) for CBV measures with limited correlation for ATT. Conclusions: Multidelay ASL with 4 PLDs is feasible in the setting of acute stroke, providing multiparametric perfusion measures (CBF, CBV, ATT) of blood flow changes with treatment.

АСИМЕТРІЯ ГОЛОВНОГО МОЗКУ ПРИ АДАПТАЦІЇ ДО УМОВ ВИСОКОГІР'Я

Association between cerebral blood flow and higher nervous activity in people at different stages of adaptation to the midlands was studied. Investigation were performed before, during and after a three-week stay in the mountains at an altitude of 2100 m, as well as during short-term ups without the physical load on the height of 3900 m. In the initial period of adaptation to hypoxia desynchronization between the nerve processes in the cerebral cortex and brain blood flow was observed. There was an inversion and an increase in the asymmetry of cerebral blood flow in the direction of the dominance of the left hemisphere of the brain. After the three-week stay in the mountains asymmetry of cerebral blood flow was disappeared, blood flow to the brain was reduced, hemispheric symmetry was formed, and blood flow synchronized with the nerve processes in the cerebral cortex again was restored.

Arterial spin labeling measurement of cerebral perfusion in children with sickle cell disease

To evaluate the applicability of arterial spin labeling (ASL) cerebral blood flow (CBF) measurements in children with sickle cell disease (SCD). We included 12 patients and five controls. Conventional magnetic resonance imaging (MRI) (T2, fluid attenuated inversion recovery [FLAIR], and MR angiography) was performed to diagnose silent infarcts, vasculopathy, or leukoencephalopathy. Pseudo-continuous ASL was performed to measure CBF using two postlabeling delays to identify transit-time effects. Perfusion estimates were corrected for hematocrit and blood velocity in the labeling plane and compared to phase-contrast MR. CBF asymmetries between the flow maps of the left and right internal carotid arteries were tested for significance using paired t-tests. Significant asymmetries were expressed in terms of an asymmetry ratio (AR = absolute difference/mean). An AR >10% was considered clinically relevant. Mean CBF was higher in patients than in controls. Agreement between CBF and flow improved after applying hematocrit and velocity corrections. At a 2100 msec postlabeling delay one patient had a clinically relevant asymmetry. No association was observed between CBF asymmetries and silent infarcts. Care must be taken in the interpretation of ASL-CBF measurements in SCD patients. A long postlabeling delay with blood velocity correction anticipates overestimation of CBF asymmetries.

Automatic Detection and Lesion Description in Cerebral Blood Flow and Cerebral Blood Volume Perfusion Maps

The paper presents a new approach of description and analysis of potential lesions in cerebral blood flow and cerebral blood volume perfusion maps. To perform such a computer analysis at first the axial position in patient's brain must be chosen. In next step the generation of brain perfusion maps connected with detection of asymmetries indicating selected pathological states, and allowing supporting diagnosis of the visible lesions are all done automatically. The constructed system uses the unified algorithm for detection of asymmetry in cerebral blood flow and cerebral blood volume perfusion maps, as well as a registration algorithm created by the authors and based on free form deformation. The tests were performed on set of dynamic perfusion computer tomography maps. Algorithms presented in this paper enable detection of pathological states like head injuries, epilepsy, brain vascular disease, ischemic and hemorrhagic stroke.

The Use of Quantitative Magnetic Resonance Perfusion for Assessment of CBF in The Perioperative Management of Carotid Stenosis: Case Illustration

Objective and Importance: Internal Carotid Artery (ICA) stenosis is a common condition with a high preva- lence in the normal population and carries a high risk of stroke. Hemodynamic impairment has been proven to be a power- ful and independent risk factor for stroke. Understanding the hemodynamics beyond a stenosis may play a role in select- ing patients who would benefit from treatment, determining the success of the treatment, and monitoring for disease recur- rence. Our group has developed a unique quantitative approach to MR perfusion. We report on the use of Quantitative Magnetic Resonance Perfusion (MRP) for assessment of Cerebral Blood Flow (CBF) pre- and post- Carotid Angioplasty and Stenting for symptomatic ICA stenosis. Clinical Presentation: A 71-year-old female with significant comorbidities presented with two episodes of left transient ischemic attacks (TIAs) over the course of one month related to high grade left ICA stenosis. Preoperative quantitative MRP showed asymmetry in CBF between the two hemispheres. Carotid angioplasty and stenting was recommended. Intervention: Left ICA angioplasty and stenting was performed and reduced the stenosis to <10%. Quantitative MRP done after the procedure revealed improved CBF to the affected side and normalization in the asymmetry of perfusion between the two hemispheres. Quantitative MRP values showed that affected regions were hypoperfused, but flow was sufficiently maintained so as to avoid infarct. Conclusion: Relative MRP images allowed us to elucidate improvement in perfusion resulting form carotid angioplasty and stenting. This novel quantitative MRP allows quantification of CBF and the potential to provide additional informa- tion on the degree of hemodynamic compromise.

Arterial spin‐labeled perfusion combined with segmentation techniques to evaluate cerebral blood flow in white and gray matter of children with sickle cell anemia

Changes in cerebral perfusion are an important feature of the pathophysiology of sickle cell anemia (SCA); cerebrovascular ischemia occurs frequently and leads to neurocognitive deficits, silent infarcts, and overt stroke. Non-invasive MRI methods to measure cerebral blood flow (CBF) by arterial spin labeling (ASL) afford new opportunities to characterize disease- and therapy-induced changes in cerebral hemodynamics in patients with SCA. Recent studies have documented elevated gray matter (GM) CBF in untreated children with SCA, but no measurements of white matter (WM) CBF have been reported. Pulsed ASL with automated brain image segmentation-classification techniques were used to determine the CBF in GM, WM, and abnormal white matter (ABWM) of 21 children with SCA, 18 of whom were receiving hydroxyurea therapy. GM and WM CBF were highly associated (R(2) = 0.76, P < 0.0001) and the GM to WM CBF ratio was 1.6 (95% confidence interval: 1.43-1.83). Global GM CBF in our treated cohort was 87 +/- 24 mL/min/100 g, a value lower than previously reported in untreated patients with SCA. CBF was elevated in normal appearing WM (43 +/- 14 mL/min/100 g) but decreased in ABWM (6 +/- 12 mL/min/100 g), compared to published normal pediatric controls. Hemispheric asymmetry in CBF was noted in most patients. These perfusion measurements suggest that hydroxyurea may normalize GM CBF in children with SCA, but altered perfusion in WM may persist. This novel combined approach for CBF quantification will facilitate prospective studies of cerebral vasculopathy in SCA, particularly regarding the effects of treatments such as hydroxyurea.

Post-carotid endarterectomy neurocognitive decline is associated with cerebral blood flow asymmetry on post-operative magnetic resonance perfusion brain scans

Objective: Up to 25% of patients experience subtle declines in post-operative neurocognitive function following, otherwise uncomplicated, carotid endarterectomy (CEA). We sought to determine if post-CEA neurocognitive deficits are associated with cerebral blood flow (CBF) abnormalities on post-operative MR perfusion brain scans.Methods: We enrolled 22 CEA patients to undergo a battery of neuropsychometric tests pre-operatively and on post-operative day 1 (POD 1). Neurocognitive dysfunction was defined as a two standard deviation decline in performance in comparison to a similarly aged control group of lumbar laminectomy patients. All patients received MR perfusion brain scans on POD 1 that were analysed for asymmetries in CBF distribution. One patient experienced a transient ischemic attack within 24 hours before the procedure and was excluded from our analysis.Results: Twenty-nine percent of CEA patients demonstrated neurocognitive dysfunction on POD 1. One hundred percent of those patients with cognitive deficits demonstrated CBF asymmetry, in contrast to only 27% of those patients without cognitive impairment. Post-CEA cognitive dysfunction was significantly associated with CBF abnormalities (RR=3.75, 95% CI: 1.62–8.67, p=0.004).Conclusion: Post-CEA neurocognitive dysfunction is significantly associated with post-operative CBF asymmetry. These results support the hypothesis that post-CEA cognitive impairment is caused by cerebral hemodynamic changes. Further work exploring the relationship between CBF and post-CEA cognitive dysfunction is needed.

Cerebral blood flow in temporal lobe epilepsy: a partial volume correction study

Previous studies in temporal lobe epilepsy (TLE) have shown that, owing to brain atrophy, positron emission tomography (PET) can overestimate deficits in measures of cerebral function such as glucose metabolism (CMR(glu)) and neuroreceptor binding. The magnitude of this effect on cerebral blood flow (CBF) is unexplored. The aim of this study was to assess CBF deficits in TLE before and after magnetic resonance imaging-based partial volume correction (PVC). Absolute values of CBF for 21 TLE patients and nine controls were computed before and after PVC. In TLE patients, quantitative CMR(glu) measurements also were obtained. Before PVC, regional values of CBF were significantly (p<0.05) lower in TLE patients than in controls in all regions, except the fusiform gyrus contralateral to the epileptic focus. After PVC, statistical significance was maintained in only four regions: ipsilateral inferior temporal cortex, bilateral insula and contralateral amygdala. There was no significant difference between patients and controls in CBF asymmetry indices (AIs) in any region before or after PVC. In TLE patients, AIs for CBF were significantly smaller than for CMR(glu) in middle and inferior temporal cortex, fusiform gyrus and hippocampus both before and after PVC. A significant positive relationship between disease duration and AIs for CMR(glu), but not CBF, was detected in hippocampus and amygdala, before but not after PVC. PVC should be used for PET CBF measurements in patients with TLE. Reduced blood flow, in contrast to glucose metabolism, is mainly due to structural changes.

Toward Objective Quantification of Perfusion-weighted Computed Tomography in Subarachnoid Hemorrhage: Quantification of Symmetry and Automated Delineation of Vascular Territories 1

Perfusion-weighted computed tomography (CTP) is a relatively recent innovation that estimates a value for cerebral blood flow (CBF) using a series of axial head CT images tracking the time course of a signal from an intravenous contrast bolus. CTP images were obtained using a standard imaging protocol and were analyzed using commercially available software. A novel computer-based method was used for objective quantification of side-to-side asymmetries of CBF values calculated from CTP images. Our method corrects for the inherent variability of the CTP methodology seen in the subarachnoid hemorrhage (SAH) patient population to potentially aid in the diagnosis of cerebral vasospasm (CVS). This method analyzes and quantifies side-to-side asymmetry of CBF and presents relative differences in a construct termed a Relative Difference Map (RDM). To further automate this process, we have developed a unique methodology that enables a computer to delineate vascular territories within a brain image, regardless of the size and shape of the brain. While both the quantification of image symmetry using RDMs and the automated assignment of vascular territories were initially designed for the analysis of CTP images, it is likely that they will be useful in a variety of applications.

Objective quantification of perfusion-weighted computed tomography in the setting of acute aneurysmal subarachnoid hemorrhage

Perfusion-weighted computed tomography (CTP) is a relatively recent innovation that estimates a value for cerebral blood flow (CBF) using a series of axial head CT images which tracks the time course of signal from an administered bolus of intravenous contrast. We introduce a novel computer-based method for objective quantification of CBF values calculated from CTP images. Our method corrects for the inherent variability of the CTP methodology seen in the subarachnoid hemorrhage (SAH) patient population to potentially aid in the diagnosis of cerebral vasospasm (CVS). This method analyzes and quantifies side-to-side asymmetry of CBF and represents relative differences in a construct termed a relative difference map (RDM). Herein, we present our preliminary results that show that analysis of histograms of the RDM in left and right hemispheres, as well as different vascular territories of the brain, can be used for detection and diagnosis of cerebral vasospasm in patients with SAH. While this method has been designed specifically to analyze postprocessed CTP images, it could be potentially applied to quantification and analysis of MR perfusion data, as well.

Evaluation of regional cerebral blood flow changes in panic disorder with Tc99m-HMPAO SPECT

The objective of this study is to investigate differences in regional cerebral blood flow (rCBF) and rCBF asymmetry index values between panic disorder patients ( n=22) and normal comparison subjects ( n=19) using Tc99m-hexamethylpropyleneamine oxime single photon emission tomography imaging. A decrease in perfusion in the bilateral frontal regions and a relative increase in perfusion in the right medial and superior frontal regions were found. There were significant positive correlations between scores on the Panic and Agoraphobia Scale and rCBF asymmetry index values of the parietal, superior temporal and lateral temporal regions in the panic disorder patients. These correlations point to a relationship between the severity of panic disorder and relative right brain activation. Activation of the amygdala, increased CBF in the frontal region, or hyperactivation of the locus ceruleus seen in panic disorder may explain the decrease in the rCBF in the inferior frontal region.

Test‐retest reproducibility of quantitative CBF measurements using FAIR perfusion MRI and acetazolamide challenge

The reproducibility of quantitative cerebral blood flow (CBF) measurements using MRI with arterial spin labeling and acetazolamide challenge was assessed in 12 normal subjects, each undergoing the identical experimental procedure on two separate days. CBF was measured on a 1.5T scanner using a flow-sensitive alternating inversion recovery (FAIR) pulse sequence, performed both at baseline and 12 min after intravenous administration of acetazolamide. T(1) was measured in conjunction with the FAIR scan in order to calculate quantitative CBF. The CBF maps were segmented to separate gray matter (GM) from white matter (WM) for region-of-interest (ROI) analyses. Post- acetazolamide CBF values (ml/100 g/min, mean +/- SD) of 87.5 +/- 12.5 (GM) and 46.1 +/- 10.8 (WM) represented percent increases of 37.7% +/- 24.4% (GM) and 40.1% +/- 24.4% (WM). Day-to-day differences in baseline CBF were -1.7 +/- 6.9 (GM) and -1.4 +/- 4.7 (WM) or, relative to the mean CBF over both days for each subject, -2.5% +/- 11.7% (GM) and -3.8% +/- 13.6% (WM) Day- to-day differences in absolute post-ACZ CBF increase were -2.5 +/- 6.8 (GM) and 2.7 +/- 9.4 (WM) or, relative to the mean CBF increase over both days for each subject, -4.7% +/- 13.3% (GM) and 9.1% +/- 26.2% (WM). Thus, FAIR- based CBF measurements show satisfactory reproducibility from day to day, but with sufficient variation to warrant caution in interpreting longitudinal data. The hemispheric asymmetry of baseline CBF and post-acetazolamide CBF increases varied within a narrower range and should be sensitive to small changes related to disease or treatment.

Relationship between Cerebral Blood Flow and Clinical Outcome in Acute Stroke

Objective: The purpose of this study was to determine the relationship between cerebral blood flow (CBF) measurements in acute stroke and early clinical outcome. Material and Methods: The xenon-enhanced computed tomography (XeCT) CBF studies performed in 50 patients in the acute stage (within 8 h) of a hemispheric stroke were retrospectively analyzed. The mean CBF of the symptomatic vascular territory was compared to the corresponding territory in the contralateral hemisphere. Clinical assessment on admission and discharge was performed using the National Institutes of Health stroke scale (NIHSS). Results: Three groups were defined according to the degree of CBF asymmetry between the symptomatic and the contralateral asymptomatic vascular region. The CBF asymmetry was mild in group A (≤20%), moderate in group B (>20% and <60%) and severe in group C (≥60%). Patients in group A (n = 18) had a good outcome with a mean NIHSS score of 2 ± 2 at discharge. In group B, the patients (n = 22) had intermediate but variable outcomes: 2 patients died and the mean NIHSS score for the survivors was variable (mean NIHSS score: 9 ± 6). The patients in group C (n = 10) had a very poor outcome: 4 patients died and the survivors had a mean NIHSS score of 15 ± 1. Conclusions: Quantitative XeCT CBF measurements may be useful for selecting subgroups of stroke patients with different clinical outcomes. The possibility of predicting patient prognosis as early as in the first hours after the ischemic event may help to identify the appropriate target population that will benefit from aggressive stroke therapy.

Magnetic resonance perfusion imaging in acute ischemic stroke using continuous arterial spin labeling.

Continuous arterial spin-labeled perfusion MRI (CASL-PI) uses electromagnetically labeled arterial blood water as a diffusible tracer to noninvasively measure cerebral blood flow (CBF). We hypothesized that CASL-PI could detect perfusion deficits and perfusion/diffusion mismatches and predict outcome in acute ischemic stroke. We studied 15 patients with acute ischemic stroke within 24 hours of symptom onset. With the use of a 6-minute imaging protocol, CASL-PI was measured at 1.5 T in 8-mm contiguous supratentorial slices with a 3.75-mm in-plane resolution. Diffusion-weighted images were also obtained. Visual inspection for perfusion deficits, perfusion/diffusion mismatches, and effects of delayed arterial transit was performed. CBF in predetermined vascular territories was quantified by transformation into Talairach space. Regional CBF values were correlated with National Institutes of Health Stroke Scale (NIHSS) score on admission and Rankin Scale (RS) score at 30 days. Interpretable CASL-PI images were obtained in all patients. Perfusion deficits were consistent with symptoms and/or diffusion-weighted imaging abnormalities. Eleven patients had hypoperfusion, 3 had normal perfusion, and 1 had relative hyperperfusion. Perfusion/diffusion mismatches were present in 8 patients. Delayed arterial transit effect was present in 7 patients; serial imaging in 2 of them showed that the delayed arterial transit area did not succumb to infarction. CBF in the affected hemisphere correlated with NIHSS and RS scores (P=0.037 and P=0.003, Spearman rank correlation). The interhemispheric percent difference in middle cerebral artery CBF correlated with NIHSS and RS scores (P=0.007 and P=0.0002, respectively). CASL-PI provides rapid noninvasive multislice imaging in acute ischemic stroke. It depicts perfusion deficits and perfusion/diffusion mismatches and quantifies regional CBF. CASL-PI CBF asymmetries correlate with severity and outcome. Delayed arterial transit effects may indicate collateral flow.

Spontaneous improvement in reduced vasodilatory capacity in major cerebral arterial occlusive disease.

Reduced vasodilatory capacity resulting from occlusive lesions of the major cerebral arteries may return to normal without surgical revascularisation. We aimed to determine prospectively the frequency and predictors of recovery of impaired haemodynamics as demonstrated by acetazolamide (ACZ) reactivity on single-photon emission computed tomography (SPECT). Vasoreactivity was measured by (123)I-IMP SPECT with an ACZ challenge, in 37 medically treated patients with unilateral occlusive disease of the internal carotid or middle cerebral artery at an interval of 1-2 years. Each ACZ challenge test was analysed semiquantitatively by calculating the degree of increase in cerebral blood flow (CBF) asymmetry after ACZ administration (DeltaAI). Vasodilatory capacity was abnormal initially in 20 patients (65 %); eight of whom (40 %) exhibited spontaneous normalisation on follow-up. Although the baseline characteristics did not differ significantly between patients with or without increase in reactivity, logistic regression analysis revealed that the initial DeltaAI (P < 0.05) and the type of vascular lesion (stenosis or occlusion) (P < 0.05) correlated significantly with a return towards normal of reduced ACZ reactivity. Spontaneous improvement of impaired vasodilatory capacity may not be a rare phenomenon. We found that mild reduction in the initial ACZ reactivity and a stenosis, but not complete occlusion, were independent factors contributing to normalisation of impaired cerebral haemodynamics.

Brain activation during dichotic presentations of consonant-vowel and musical instrument stimuli: a 15O-PET study

Dichotic listening means that two different stimuli are presented at the same time, one in each ear. This technique is frequently used in experimental and clinical studies as a measure of hemispheric specialization. The primary aim of the present study was to record regional changes in the distribution of cerebral blood flow (CBF) with the 15O-PET technique to dichotically presented consonant-vowel (CV) and musical instrument stimuli, in order to test the basic assumption of differential hemispheric involvement when stimuli presented to one ear dominate over stimuli presented in the other ear. All stimuli were 380 ms in duration with a 1000 ms interstimulus interval, and were presented in blocks of either CV-syllable or musical instrument pairs. Twelve normal healthy subjects had to press a button whenever they detected a CV-syllable or a musical instrument target in a stream of CV- and musical instrument distractor stimuli. The targets appeared equally often in the right and left ear channel. The CV-syllable and musical instrument targets activated bilateral areas in the superior temporal gyri. However, there were significant interactions with regard to asymmetry of the magnitude of peak activation in the significant activation clusters. The CV-syllables resulted in greater neural activation in the left temporal lobe while the musical instruments resulted in greater neural activation in the right temporal lobe. Within-subjects correlations between magnitude of dichotic listening and CBF asymmetry were, however, non-significant. The changes in neural activation were closely mimicked by the performance data which showed a right ear superiority in response accuracy for the CV-syllables, and a left ear superiority for the musical instruments. In addition to the temporal lobe activations, there were activation tendencies in the left inferior frontal lobe, right dorsolateral prefrontal cortex, left occipital lobe, and cerebellum.

Absence of an apolipoprotein E epsilon4 allele is associated with increased parietal regional cerebral blood flow asymmetry in Alzheimer disease.

The apolipoprotein E (Apo E) epsilon4 allele has been associated with parietal metabolic abnormalities and asymmetries in asymptomatic subjects at risk for Alzheimer disease (AD). However, previous research has shown minimal effect of the epsilon4 allele on regional cerebral blood flow (rCBF) and metabolism in patients with probable AD. To determine whether the Apo E epsilon4 allele is associated with parietal rCBF abnormalities and asymmetries in patients with probable AD. Thirty patients with AD with the epsilon4 allele (epsilon4+ AD), 22 patients with AD without the epsilon4 allele (epsilon4- AD), and 14 healthy control subjects underwent single-photon emission computed tomography (SPECT) scanning with 740 MBq technetium Tc 99m hexamethylpropyleneamine oxime. Ratios of parietal-unaffected regions and a left-right parietal asymmetry index were compared between both patient groups. The group with epsilon4- AD was younger (P = .005, Student t test) and had an earlier age of onset (P = .005) than the group with epsilon4+ AD. Analysis of covariance revealed no significant difference in the parietal rCBF ratio, controlling for age of onset and Mini-Mental State Examination score (F(1,48) = 0.06; P = .81). However, contrary to hypothesis, significantly greater parietal rCBF asymmetry was seen in patients with epsilon4- AD (mean +/- SD, 9.7% +/- 5.5%) than those with epsilon4+ AD (6.3% +/- 4.7%; F(1,50) = 5.89; P = .02; analysis of variance). When number of epsilon4 allele copies was considered, this effect appeared to accrue primarily from a difference between patients with 0 and with 2 epsilon4 allele copies. An exploratory analysis of multiple cortical structures suggested that this asymmetry extended to additional regions (superior temporal) and to combined association cortex. Greater parietal rCBF asymmetry is involved in epsilon4- AD than in epsilon4+ AD. Lack of the epsilon4 allele may be associated with other (as yet undiscovered) genetic or environmental risk factors, which confer greater neuropathological asymmetry.