XVII. European Stroke Conference
Nice, France
XVII. European Stroke Conference
Nice, France
Poster Session: Brain Imaging: new
developments
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
Perfusion-Magnetic Resonance Imaging T Max and Mean Transit Time compared to Stable Xenon Computed Tomography Cerebral Blood Flow.
J.M.OLIVOT
M. MLYNASH
G. ZAHARCHUK
M. STRAKA
R. BAMMER
M.G.LANSBERG
M.E.MOSELEY
G.W.ALBERS
STANFORD STROKE CENTER
USA
Background: Accurate quantitative assessment of cerebral blood flow (CBF) is one of the challenges of bolus perfusion-weighted magnetic resonance imaging (PWI-MRI) in ischemic stroke. Stable xenon computed tomography (Xe-CT) is an accepted standard for the quantitative estimation of CBF. Patients and Methods: The Improved PWI Methodology in Acute Clinical Stroke Study is an NIH funded study of patients experiencing an acute or subacute brain infarct due to severe hypoperfusion. Nine patients (5M, 4F) with brain infarction (5 atherosclerotic, 1 cardioembolic, 2 unilateral Moya-Moya, and 1 ICA dissection) underwent stable XeCT (DDI, 4 10mm slices, 28% Xe gas) and single-shot GE EPI based PWI-MRI (1.5 T GE, TR/TE 2000/60 ms, 12 6mm slices) within a 24-hr period. Perfusion MRI maps (Tmax & MTT) were calculated using circular singular value deconvolution with an automatic arterial input function and venous output function detection. Images were co-registered using SPM2. For each patients we drew 25 ROIs of multiple sizes and locations (normal and abnormal regions of the brain) and we compared the mean value in each ROI with the corresponding XeCT assessed CBF. Comparison was done by estimating Pearson Correlation Coefficient (R). We performed ROC curve analyses to define the threshold of T Max and MTT that could predict a Xe-CT CBF <20ml.100g.min. Results: Subjects’ mean age (SD) was 50 (15) years; median (IQR) NIHSS was 2 (2; 6), and median (IQR) time between MRI and Xe CT was 12 (-7; 19) hours. Total number of ROIs was 225 and median (IQR) ROI size was 550(360; 960) pixels. The correlation coefficient, R, between Tmax and Xe-CT CBF (0.58) was significantly higher than that found between MTT and Xe-CT CBF (0.42), p<0.05. ROC curves analysis found that Tmax > 4 sec has a 78% sensitivity and 60% specificity for predicting ROIs with Xe-CT CBF <20mL/100g/min. Conclusion: Our results suggest that T Max correlate better than MTT with Xe-CT CBF and that T Max>4 sec is strongly associated with Xe-CT CBF<20ml.100g.min.
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
Stimulation of the Visual Cortex in Patients with Acute PCA Stroke as assessed by TCD and fMRI
M. Griebe
K. Szabo
M.E.Wolf
T. Jaeger
M.G.Hennerici
A. Gass
Universitätsklinikum Mannheim, University of Heidelberg
GERMANY
Introduction: fMRI is thought to demonstrate signs of electrical brain activity via neurovascular coupling. Therefore one of the major limitations of fMRI are states that might disturb a normal neurovascular coupling process. In order to understand these mechanisms and relationships better we performed a series of visual stimulation paradigms with fMRI and TCD in patients with acute infarction affecting the visual system in PCA stroke. Methods: We examined 5 patients with PCA stroke, 5 normal controls and 2 pathological controls with dorsal MCA ischemia affecting the optic radiation with fMRI (1.5T Siemens Sonata, BOLD-imaging; 1Hz, 2Hz and 4Hz flickering checkerboard, 20sec ON/OFF intervals) and TCD (moving coloured patterns, 20sec ON/OFF intervals). Results: In normal controls symmetrical activation in fMRI and symmetrical increase of flow velocity was noted. The 2 pathological controls showed, as expected, an ipsilateral reduction of visual cortex activation in fMRI and a diminished increase in flow velocity. In contrast, heterogeneous responses were found in acute PCA stroke patients: while the increase in flow velocity was diminished in the affected vessel in all patients, in fMRI one did not show an ipsilateral activation at all, two revealed a reduced activation and two had an increased activation on the side of infarction. Conclusions: These experiments indicate that neurovascular coupling in pathological situations is difficult to predict and that beyond common assumptions more heterogeneity is present in stimulation experiments of patients with acute stroke. The slightly different stimulation paradigms – the checkerboard stimulating predominantly V1 and V2, the moving coloured patterns additionally V3-V5 – may add to this heterogeneity.
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
Use of fMRI and tractography for differentiating corticospinal tract fibres depending on motor function.
R. Alibert
A. Comte
E. Medeiros
E. Revenco
L. Tatu
T. Moulin
University Hospital, Besancon
FRANCE
Introduction: Diffusion tensor imaging (DTI) carried out in the sub acute phase of a sub cortical ischemic stroke involving the pyramidal tract (PT) can help predict recovery of motor function by analysing fractional anisotropy. The aim was to obtain precise data in the acute phase of ischemic stroke by undertaking a selective analysis of PT fibres depending on motor function. This preliminary study aims to differentiate PT fibres depending on motor function in healthy subjects: we performed a precise cartography, currently under debate, of the motor cortex in functional Magnetic Resonance Imaging (fMRI) and then visualised the PT coming from each motor cortical representation (MCR) using DTI. Methods: Motor tasks were carried out in fMRI by eight healthy volunteers. A DTI was performed for one subject. Centres of geometry (COGs) of the sum of activations for each task were used as a primary region of interest (ROI) for fibre tractography. The target ROI was the basal section of the homolateral pons. Results: The COGs corresponding to major human body parts are clearly distinct. Inside each major part, the COGs are close and activation volumes overlap. In tractography, fibres passing between the two ROIs follow the whole of the PT’s path. Discussion: The MCRs of major human body parts are organised somatotopically. Inside each major part, the overlap of MCRs indicates a somatotopic gradient and COGs correspond to anchorage points. A weak inter-individual variation of these anchorage points appears to exist when compared to similar fMRI studies. Performing PT fibre tracking by identifying the fibres coming from restricted cortical regions is possible. It seems possible to realise selective fibre tracking of the PT in the acute phase of an ischemic stroke. The use of standardised ROIs shown in this study will allow for a shorter exam.
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
Changes in brain volume after carotid endarterectomy
J. Jinnouchi
S. Fujimoto
K. Toyoda
T. Inoue
M. Yasaka
K. Yasumori
S. Ibayashi
S. Sadoshima
Y. Okada
National Kyushu Medical Center
JAPAN
Background: We previously reported changes in vasoreactivity might be a good predictor for brain atrophy in patients with cerebral artery occlusive disease. Several studies have reported hemodynamic effect of carotid endarterectomy (CEA) in patients with severe stenosis of the internal carotid artery (ICA), however changes in brain volume after CEA is unclear. The purpose of this study is to examine changes in hemodynamic factors and brain volume before and after CEA. Methods: From April 2005 to November 2005, 15 consecutive patients (13 males, mean age 68.8±6.8 years) who underwent CEA were studied. All patients have unilateral high-grade ICA stenosis evaluated with intra-arterial digital subtraction angiography (average 82.1±11.4% in NASCET method) , and 14 patients were symptomatic. We examined changes in brain volume using magnetic resonance imaging before, 3months and 1 year after CEA. We also examined the association of cerebral hemodynamics, measured by single photon emission computed tomography, with the changes in brain volume. As a tracer, 99mTc-ethyl cysteinate dimmer was used. Results: Percent brain volume significantly increased in both affected (82.1±3.4% to 83.2±3.7%, p=0.029) and unaffected (83.3±2.6% to 84.7±2.8%, p=0.0004) hemisphere 3 months after CEA. Compared with the baseline values, acetazolamide reactivity showed an increase (20.7±14.8% to 27.7±15.2%, p=0.28) in the affected hemisphere 3 months after CEA. There was no changes in cerebral blood flow (43.5±4.7ml/100g/min to 42.8±4.0 ml/100g/min, p=0.77) in the affected hemisphere between baseline and 3 months after CEA. Three-month increase (decrease) in acetazolamide reactivity of the affected hemisphere showed a positive correlation with 3 month changes in percent brain volume (R = 0.60, p=0.019). Conclusions: Percent brain volume may increase 3 months after CEA in both hemisphere compared with before CEA. Especially in affected hemisphere, changes in acetazolamide reactivity may have a positive correlation with changes in brain volume 3 months after CEA.
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
Multiple DWI lesions in one carotid territory is not commonly caused by stenotic/occlusive carotid disease
M.H.Alzawahmah
A.M.Al-khathaami
A.M.Demchuk
P. Sharma
M. Eesa
C.O.Reilly
S. Tymchuk
Calgary Stroke program
CANADA
Introduction: MRI has been used to evaluate etiology of stroke. The presence of multiple DWI lesions in one vascular territory raises suspicion of proximal large vessel disease as the culprit etiology. We examined CTA of neck vessel information in a series of patients with multiple DWI lesions in the carotid vascular territory. Patients and method: 729 patients with acute stroke symptoms who had CTA neck were screened for having MRI within one week of symptoms. MRI were reviewed and patients with bilateral anterior circulation stroke, posterior circulation stroke, solitary lesion, or normal MRI were excluded. Patients with multiple DWI lesion in carotid distribution were divided in two groups based on stroke severity. TIA or mild stroke NIHSS≤7 and disabling stroke NIHSS>7. CTA abnormalities were evaluated in this multiple DWI lesion cohort. Result: 71 patients were found to have multiple DWI lesions in the unilateral carotid distribution. 47 TIA/mild stroke and 24 disabling stroke. In the TIA or mild stroke population 42.5% had stenotic/occlusive cervical carotid disease, 25.5% had non stenotic carotid abnormalities and 32% had completely normal carotids with no plaque. In the disabling stroke population 21% had stenotic/occlusive cervical carotid disease, 25% had non stenotic carotid abnormalities and 54% had completely normal carotids with no plaque. Conclusion: Stenotic or occlusive carotid disease represented a minority of patients with multiple DWI lesions in the carotid territory and was especially the case in disabling stroke. Such MRI findings should warrant close evaluation for nonstenotic carotid abnormalities and evaluation of the great vessels and intracranial circulation.
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
Diffusion Tensor Imaging and Functional Recovery after Cerebral Infarction
R. Allibert
E. Revenco
E. Medeiros
T. Moulin
University Hospital, Besancon
FRANCE
Introduction Secondary degeneration of the corticospinal tract (CT) after cerebral infarction is visualised using diffusion tensor imaging (DTI) as a progressive reduction in anisotropy indices or changes in fibre tracking. We aimed to establish a correlation between these images and functional recovery of infarcts. Methods Five patients underwent a diffusion MRI during the acute phase of a subcortical cerebral infarction as well as a DTI during follow-up. MRI parameters studied were the diffusion coefficient inside the ischemic lesion and anisotropy indices and fibre tracking of the CT under the lesion. Clinical parameters used were NIHSS at the acute phase and modified Rankin Score (mRS) and NIHSS after stroke. Results The anisotropy indice was lower for all patients except one whose NIHSS score was zero after stroke. The anisotropy indice reduction was greater among patients with a high NIHSS and mRS score. In fibre tracking, a reduction in the volume of CT in the damaged area, which seemed greater among patients with a high NIHSS and mRS score was seen in all subjects. There was a reduction in diffusion coefficient at the acute phase which was greater among patients with a slightly improved NIHSS score and a significant anisotropy indice reduction inside the CT. Discussion In this preliminary study which will be followed up on a larger cohort, the reduction in anisotropy indice inside the CT after cerebral infarction is correlated with a poorer functional recovery as well as a reduction in diffusion coefficient at the acute phase of the infarction. Fibre tracking shows that a reduction in the volume of damaged CT may be greater among patients with poorer clinical outcome.
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
Accuracy of ADC-based prediction of MCA infarct growth
C. Rosso
Y. Attal
N. Hevia-Montiel
S. Deltour
D. Dormont
S. Baillet
Y. Samson
Hôpital Pitié-Salpêtrière, Paris
FRANCE
Background: We recently developed a DWI-based prediction of infarct growth (IG) in acute stroke patients (< 6 hours) with an algorithm mimicking the real infarct growth process on the initial ADC map. This method has been validated by showing the significant correlation between predicted and real IG in 98 MCA stroke patients (J.Eur Neurol, 2007; 254 (Suppl 3). Abstract.). Here, we assess the accuracy of the method to predict IG in individual patients. Methods: The 98 patients had MRI performed within 6 hours (median delay 2.3 hours; IQR: 1.8-3 h), and a control MRI in the next few days. They were sorted in (a) 55 patients with IG (≥ 10 cm3) and (b) 43 patients without IG. We then generate the ROC curve for predicting IG in order to determine the best compromise of sensitivity/specificity. The results were compared with the accuracy of the PWI/DWI mismatch reported in the literature. Results: The ROC curve for predicting IG has an area under curve of 0.740, indicating a fair predicting performance. The method correctly classified 74 % of the patients with a sensitivity of 79 % and a specificity of 70 %. When IG was predicted, it occurred in 72 % of patients, but when not predicted, it still occurred in 29 %. The PWI/DWI mismatch accuracy has been mainly assessed in small studies, with sensitivity ranging from 52 to 91 % and specificity from 64 to 73 %. Discussion: This ADC-based method of IG prediction appears to have accuracy comparable to PWI-DWI mismatch, while reducing MRI duration, since PWI is not required. Yet, IG occurs in nearly one third of non-IG predicted patients, suggesting caution for individual therapeutic decision making.
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
Time-dependent changes of brain lactate concentrations in human acute ischaemic stroke.
B. Karaszewski
J.M.Wardlaw
I. Marshall
V. Cvoro
K. Wartolowska
K. Haga
P.A.Armitage
M.E.Bastin
M.S.Dennis
Division of Clinical Neurosciences, The University of Edinburgh
UNITED KINGDOM
Background: High lactate concentrations in human acute ischaemic brain are associated with large infarcts and possibly with worse clinical outcome. However, the time-dependent changes of lactate in different ischaemic sub-regions remain unknown. Methods: 39 patients with acute ischaemic stroke had MR DWI (tensor) and multi-voxel spectroscopy from 1.5 to 26 hrs from stroke. Voxels superimposed on DWI were coded as: “definitely” or “possibly abnormal” (DAL or PAL respectively), “infarct outer edge” (IE), “ipsi-” or “contra-lateral normal” (INL or CNL respectively) blind to all other data. Lactate concentration was calculated in standard units for each. Changes in lactate concentration by time to scan were analysed across the different ischaemic regions and normal brain. Results: Mean lactate concentration was highest in DAL (42.1u), then in PAL (26.0u) and PAL+ (14.5u), INL (10.4u) and lowest in CNL (8.7u) (p<0.05). Lactate concentration was lower in those patients who were scanned later in PAL+ and INL tissues (p=0.006 and 0.02, respectively), non-significantly lower in PAL (p=0.076), and did not change with time to scan in DAL and CNL (p>0.05). Discussion: Over the first several hours of stroke, the lactate concentration decreased in tissues of the ipsilateral hemisphere surrounding the ischaemic lesion, but remained elevated in the ischaemic lesion core and did not change in the contralateral hemisphere.
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
The Effectiveness of Using Low Cost Teleconsultation for Emergency Head Computer Tomography in Patients with Suspected Stroke
P. Kanitpong
H. siriporn
Prince of Songkhal University
THAILAND
Background: Teleradiology in an emergency situation can be used to support rapid neurological decision making when specialists are remote or distant from the hospital. Although, the technology of teleradiology is expensive and not yet available in Thailand, we have developed and adapted the cellular telephone network for teleradio-consultation. Methods: The experimental system was based on a Dell portable personal computer to send the images and a PDA phone - Hp IPAQ 6515 - for receiving data. We used AIS SMS/MMS toolbar software for transmitting information through the cellular telephone network. Results: A total of 100 images of clinically suspected strokes within the previous 24 hours were transmitted to a neurologist. The mean transmission time of a single image was 48.30 second. The comparative diagnosis between P original and P PDA were in 100% agreement in cases of acute ischemic stroke, intracerebral hemorrhage, metastasis, subdural hematoma and in normal scans but 87.5% (7 of 8 cases) in subarachnoid hemorrhage. The overall cost was 400 baht ($2.94 U.S.) average three cents U.S. per case. Conclusion: Our study indicates a good accuracy can be achieved with a low cost system used for teleradiology consultation in a stroke setting.
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
White matter diffusion tensor imaging (DTI) in
asymptomatic internal carotid artery stenosis: preliminary results
C. Herweh
N. Attigah
S. Nagel
A. Hug
P.A.Ringleb
D. Böckler
M. Bendszus
University of Heidelberg
GERMANY
Background: The clinical management of asymptomatic patients with stenosis of the internal carotid artery (ICA) remains controversial. Diffusion tensor MR imaging (DTI) probes the directionality of movement of free water molecules, thereby allowing to estimate the tissue orientation, especially in brain white matter (WM). Derived metrics such as fractional anisotropy (FA) can be used as an indicator of WM integrity. We examined WM FA of both hemispheres in patients with unilateral asymptomatic ICA stenosis to test the hypothesis that chronic hypoperfusion would lead to a FA reduction in the affected hemisphere. Materials & Methods: 8 patients with unilateral ICA stenosis underwent DTI (echo planar imaging, 20 slices with 6 mm thickness, diffusion probing gradients in 6 non-collinear directions). Regions of interest (ROI) were placed on FA maps in the lobar WM (temporal, occipital, frontal and parietal) as well as in watershed regions (fronto-parietal, parieto-occipital and in the centrum semiovale) and the thalamus. Values were compared between hemispheres using paired t-test. Results: Stenosis degrees ranged from 65 to 90% and were below than 50% in the contralateral ICA. FA was reduced in the frontal (19,01%, p=0,07) and occipital WM (14,78%, p=0,16). For watershed regions there were only slight differences between hemispheres in the parieto-occiptal (-4,75%, p=0,33) and the fronto-parietal white matter (-1,8%, p=0,62). There was no correlation between FA and the degree of stenosis. Discussion: The data show a clear trend for a reduced FA in ipsilateral WM in asymptomatic ICA stenosis. Interestingly, FA reductions are more pronounced in the lobar white matter than in watershed regions. A larger patient series to confirm and further specify these results is underway.
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
Characteristics of diffusion-weighed imaging in patients with acute multiple brain infarction
D.K. Jung
Y.H.Hwang
S.P.Park
C.K.Suh
Neurology KyungPook National University Hospital
SOUTH KOREA
While we often observe acute multiple brain infarction (AMBI), their clinical significance has not been fully investigated. We sought to determine the relationship between the characteristics of AMBI in diffusion-weighted imaging (DWI) and internal carotid artery (ICA) disease and middle cerebral artery (MCA) disease of unilateral AMBI in the anterior circulation. We studied 107 consecutive ischemic stoke patients who underwent DWI and MRI/MR angiography within 3 days of stroke onset. Patients were assigned to 1 of 5 observed lesion characteristics in DWI: (1) multiple small lesions (<1cm), (2) multiple small and medium lesions (1 to 3cm), (3) multiple small and large lesions (>3cm), (4) multiple lesions in hemodynamic risk zone, and (5) others. The involvement of insula, periventricular white matter (PVWM), basal ganglia, and cortex was also investigated. Comparisons of all these characteristics were made between ICA disease patients (ICA group, n=43) and MCA disease patients (MCA group, n=64) on MR angiography. There was no significant relationship between cerebral artery involvement and the characteristics of lesions in DWI. Between 2 groups of arterial disease, maximum diameter of lesion which is more than 3cm and PVWM involvement were significantly related with MCA group (p=0.02 and p=0.007). The pathogenic mechanisms of unilateral AMBI can be predicted by the characteristic of its size and location using DWI.
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
Perfusion Computed Tomography in Ischemic Stroke Compared to 15O-water-PET: a Case Report
S. Sorgalla
W. Moeller-Hartmann
J. Sobesky
University of Cologne
GERMANY
Background: The reliability of perfusion computed tomography (pCT) in ischemic stroke has mainly been demonstrated by follow-up CT studies or by comparative magnet resonance imaging studies. In a case report we describe the comparison of pCT with 15O-water PET, the gold standard of in vivo measurement of cerebral blood flow (CBF). Methods: A 52 years old male patient presented with dysarthria and left sided hemiparesis since 30 hours. The neurological workup revealed an occlusion of the right internal carotid artery. Noncontrast CT (Philips Brilliance 6) was followed by a perfusion CT protocol (6 mm slice thickness, cycletime 1.3 sec, 40 ml contrast agent, flow rate 4 ml/sec). Maps of cerebral blood flow and volume (CBF, CBV), mean-transit-time (MTT) and time-to peak (TTP) were calculated. Then, PET with 15O-H2O (60 mCi, data acquisition 90 sec; ECAT HRT, Siemens/CTI) was performed to assess relative CBF values. Results: CT displayed an infarction of the right anterior MCA territory (figure 1a). PET-CBF (performed 35 min after CT) showed a severe decrease of CBF within the infarct core (relative CBF 17%, corresponding to values below 12 ml/100g/min). In the adjacent tissue posterior to the hypoperfusion, a small area of postischemic hyperperfusion was seen (relative CBF 190%) (figure 1b). On perfusion CT, the central area of the infarct core (as defined by CT and PET) yielded no valuable data. This was due to an insufficient fit of the time intensity curve in severe ischemic regions. In the peripheral areas of infarction, pCT showed decreased CBF and CBV values with increased MTT and TTP values compared to the contralateral homotopic regions. The area of postischemic hyperperfusion was characterized by high CBV and CBF values and by low MTT and TTP values (figure 1c). Discussion: In the presented patient the qualitative comparison of perfusion CT and CBF-PET yielded a good agreement between the methods. Critical hypoperfusion as well as postischemic hyperperfusion were well depicted by pCT in subacute ischemic stroke. These preliminary findings should be proven in a quantitative analysis of a larger sample in order to enhance the clinical application of pCT.
Session:
Poster Session I
Date:
Wednesday 14 May 2008
Time:
12:30 - 14:00
Room:
Agora 2
Cerebrovascular Reserve Impairment is associated with Recurrent Events in Patients with Carotid Artery Occlusion
S.D.Goode
N. Altaf
S. Munshi
S.T.MacSweeney
D.P.Auer
Queens Medical Centre, Nottingham
UNITED KINGDOM
Introduction Cerebrovascular reserve (CVR) measurements have been shown to be useful in predicting haemodynamic impairment and risk of future ischaemic events in patients with carotid artery disease. CVR can be assessed by using a vasodilatory stimulus such as carbon dioxide (CO2), whereby the residual vasodilatory capacity of resistance vessels is probed. Identification of patients with carotid artery disease and a significant haemodynamic impairment is important for selection for vascular intervention. The aim of this study was to investigate the CVR of patients with carotid artery occlusion in relation to the presence of recurrent symptoms using BOLD hypercapnia fMRI. Methods 15 patients with symptomatic internal carotid artery occlusion were scanned using a clinical 1.5T Intera MR scanner. 11 patients had only a single symptomatic event and the remaining 4 patients had recurrent symptoms following their initial episode. All 15 patients underwent CO2 reactivity testing using hypercapnia BOLD fMRI. All data was analysed using FSL software. To quantify the relative signal change for each patient the mean % signal change(%SC) was extracted from the grey matter of the MCA territory of each hemisphere. The degree of side-to-side asymmetry in the brain was calculated using the Hemispheric Asymmetry Index (hAI). Results The mean %SC in the MCA territory distal to the occlusion [2.52%(SD 0.31)] was significantly lower than the mean %SC in the contralateral MCA territory [2.740%(SD 0.40)p=0.008]. hAI was significantly higher in the 4 patients with recurrent symptoms compared to those with a single event (18.5%vs.3.9%,p=0.004) Conclusion Measurement of CVR capacity using BOLD hypercapnia fMRI can provide important information on the haemodynamic status of patients with carotid artery occlusion. It is tempting to speculate that these recurrent events may be haemodynamically explained by reduced CVR in relation to the degree of compensatory vasodilatation during rest. Larger studies are needed to establish whether abnormal AI may predict haemodynamic strokes.
