Perfusion-weighted Imaging Volumes Research Articles

Estimation of Diffusion Weight Imaging and Perfusion-Weighted Imaging Volume by Texture Methods

Estimation of Diffusion Weight Imaging and Perfusion-Weighted Imaging Volume by Texture Methods

Estimating Perfusion Deficits in Acute Stroke Patients Without Perfusion Imaging.

Perfusion weighted imaging (PWI) is critical for determining whether stroke patients presenting in an extended time window are candidates for mechanical thrombectomy. However, PWI is not always available. Fluid-attenuated inversion recovery hyperintense vessels (FHVs) are seen in patients with a PWI lesion. We investigated whether a scale measuring the extent FHV could serve as a surrogate for PWI to determine eligibility for thrombectomy. The National Institutes of Health (NIH) FHV score was developed to quantify the burden of FHV and applied to magnetic resonance imaging scans of stroke patients with fluid-attenuated inversion recovery and perfusion imaging. The NIH-FHV was combined with the diffusion weighted image volume to estimate the diffusion-perfusion mismatch ratio. Linear regression was used to compare PWI volumes and mismatch ratios with estimates from the NIH-FHV score. Receiver operating characteristic analysis was used to test the ability of the NIH-FHV score to identify a significant mismatch. There were 101 patients included in the analysis, of whom 78% had a perfusion deficit detected on PWI with a mean lesion volume of 47 (±59) mL. The NIH-FHV score was strongly associated with the PWI lesion volume (P<0.001; R2=0.32; β-coefficient, 0.57). When combined with diffusion weighted image lesion volume, receiver operating characteristic analysis testing the ability to detect a mismatch ratio ≥1.8 using the NIH-FHV score resulted in an area under the curve of 0.94. The NIH-FHV score provides an estimate of the PWI lesion volume and, when combined with diffusion weighted imaging, may be helpful when trying to determine whether there is a clinically relevant diffusion-perfusion mismatch in situations where perfusion imaging is not available. Further studies are needed to validate this approach.

Predictive value of Alberta stroke program early CT score for perfusion weighted imaging - diffusion weighted imaging mismatch in stroke with middle cerebral artery occlusion.

This study aimed to quantitatively assess the consistency and correlation between perfusion weighted imaging (PWI)/ diffusion weighted imaging (DWI) Alberta Stroke Program Early CT Score (ASPECTS) mismatch and PWI/DWI mismatch.Sixty-eight acute ischemic stroke with middle cerebral artery occlusion who underwent magnetic resonance imaging before thrombectomy were eligible. DWI volume, PWI volume and PWI-DWI mismatch were measured. DWI-, PWI-, PWI-DWI ASPECTS were evaluated. Statistical analysis was performed to compare the correlation between volume and ASPECTS of DWI-, PWI- and PWI-DWI mismatch. Receiver operating characteristic curve analysis was used to assess the predictive value of the PWI-DWI ASPECTS mismatch for the occurrence of PWI-DWI mismatch in acute ischemic stroke patients with middle cerebral artery occlusion.Of 68 patients, the DWI volume, PWI volume and PWI-DWI mismatch volume were (27.76 ± 17.53) mL, (167.09 ± 59.64) mL and (139.33 ± 58.18) mL respectively. DWI-ASPECTS was 6.75 ± 1.90 with the interobserver agreement was κ=0.98 (95% CI, 0.95–0.99); PWI-ASPECTS was 3.09 ± 2.11 with the interobserver agreement was κ=0.95 (95% CI, 0.91–0.99); PWI-DWI ASPECTS mismatch was 6.75 ± 1.90. Spearman's rank correlation analysis revealed that PWI-DWI mismatch volume was negatively correlated with PWI-DWI ASPECTS mismatch (r = −0.802; P = .000). Receiver operating characteristic analysis showed that when the PWI-DWI ASPECTS mismatch cut point was ≥ 2, the under curve of PWI-DWI ASPECTS mismatch for predicting PWI-DWI mismatch was 0.954 (95%CI, 0.911–0.998), with the sensitivity and specificity were 84.00% and 100% respectively.PWI-DWI ASPECTS mismatch may represent a convenient surrogate for penumbra in clinical trials.

ASPECTS (Alberta Stroke Program Early CT Score) Assessment of the Perfusion-Diffusion Mismatch.

Rapid and reliable assessment of the perfusion-weighted imaging (PWI)/diffusion-weighted imaging (DWI) mismatch is required to promote its wider application in both acute stroke clinical routine and trials. We tested whether an evaluation based on the Alberta Stroke Program Early CT Score (ASPECTS) reliably identifies the PWI/DWI mismatch. A total of 232 consecutive patients with acute middle cerebral artery stroke who underwent pretreatment magnetic resonance imaging (PWI and DWI) were retrospectively evaluated. PWI-ASPECTS and DWI-ASPECTS were determined blind from manually segmented PWI and DWI volumes. Mismatch-ASPECTS was defined as the difference between PWI-ASPECTS and DWI-ASPECTS (a high score indicates a large mismatch). We determined the mismatch-ASPECTS cutoff that best identified the volumetric mismatch, defined as VolumeTmax>6s/VolumeDWI≥1.8, a volume difference≥15 mL, and a VolumeDWI<70 mL. Inter-reader agreement was almost perfect for PWI-ASPECTS (κ=0.95 [95% confidence interval, 0.90-1]), and DWI-ASPECTS (κ=0.96 [95% confidence interval, 0.91-1]). There were strong negative correlations between volumetric and ASPECTS-based assessments of DWI lesions (ρ=-0.84, P<0.01) and PWI lesions (ρ=-0.90, P<0.01). Receiver operating characteristic curve analysis showed that a mismatch-ASPECTS ≥2 best identified a volumetric mismatch, with a sensitivity of 0.93 (95% confidence interval, 0.89-0.98) and a specificity of 0.82 (95% confidence interval, 0.74-0.89). The mismatch-ASPECTS method can detect a true mismatch in patients with acute middle cerebral artery stroke. It could be used for rapid screening of patients with eligible mismatch, in centers not equipped with ultrafast postprocessing software.

Effect of Collateral Blood Flow on Patients Undergoing Endovascular Therapy for Acute Ischemic Stroke

Our aim was to determine the relationships between angiographic collaterals and diffusion/perfusion findings, subsequent infarct growth, and clinical outcome in patients undergoing endovascular therapy for ischemic stroke. Sixty patients with a thrombolysis in cerebral infarction (TICI) score of 0 or 1 and internal carotid artery/M1 occlusion at baseline were evaluated. A blinded reader assigned a collateral score using a previous 5-point scale, from 0 (no collateral flow) to 4 (complete/rapid collaterals to the entire ischemic territory). The analysis was dichotomized to poor flow (0-2) versus good flow (3-4). Collateral score was correlated with baseline National Institutes of Health Stroke Scale, diffusion-weighted imaging volume, perfusion-weighted imaging volume (Tmax ≥6 seconds), TICI reperfusion, infarct growth, and modified Rankin Scale score at day 90. Collateral score correlated with baseline National Institutes of Health Stroke Scale (P=0.002) and median volume of tissue at Tmax ≥6 seconds (P=0.009). Twenty-nine percent of patients with poor collateral flow had TICI 2B-3 reperfusion versus 65.5% with good flow (P=0.009). Patients with poor collaterals who reperfused (TICI 2B-3) were more likely to have a good functional outcome (modified Rankin Scale score 0-2 at 90 days) compared with patients who did not reperfuse (odds ratio, 12; 95% confidence interval, 1.6-98). There was no difference in the rate of good functional outcome after reperfusion in patients with poor collaterals versus good collaterals (P=1.0). Patients with poor reperfusion (TICI 0-2a) showed a trend toward greater infarct growth if they had poor collaterals versus good collaterals (P=0.06). Collaterals correlate with baseline National Institutes of Health Stroke Scale, perfusion-weighted imaging volume, and good reperfusion. However, target mismatch patients who reperfuse seem to have favorable outcomes at a similar rate, irrespective of the collateral score. http://www.clinicaltrials.gov. Unique identifier: NCT01349946.

Factors that determine penumbral tissue loss in acute ischaemic stroke

The goal of acute stroke treatment with intravenous thrombolysis or endovascular recanalization techniques is to rescue the penumbral tissue. Therefore, knowing the factors that influence the loss of penumbral tissue is of major interest. In this study we aimed to identify factors that determine the evolution of the penumbra in patients with proximal (M1 or M2) middle cerebral artery occlusion. Among these factors collaterals as seen on angiography were of special interest. Forty-four patients were included in this analysis. They had all received endovascular therapy and at least minimal reperfusion was achieved. Their penumbra was assessed with perfusion- and diffusion-weighted imaging. Perfusion-weighted imaging volumes were defined by circular singular value decomposition deconvolution maps (Tmax > 6 s) and results were compared with volumes obtained with non-deconvolved maps (time to peak > 4 s). Loss of penumbral volume was defined as difference of post- minus pretreatment diffusion-weighted imaging volumes and calculated in per cent of pretreatment penumbral volume. Correlations between baseline characteristics, reperfusion, collaterals, time to reperfusion and penumbral volume loss were assessed using analysis of covariance. Collaterals (P = 0.021), reperfusion (P = 0.003) and their interaction (P = 0.031) independently influenced penumbral tissue loss, but not time from magnetic resonance (P = 0.254) or from symptom onset (P = 0.360) to reperfusion. Good collaterals markedly slowed down and reduced the penumbra loss: in patients with thrombolysis in cerebral infarction 2 b-3 reperfusion and without any haemorrhage, 27% of the penumbra was lost with 8.9 ml/h with grade 0 collaterals, whereas 11% with 3.4 ml/h were lost with grade 1 collaterals. With grade 2 collaterals the penumbral volume change was -2% with -1.5 ml/h, indicating an overall diffusion-weighted imaging lesion reversal. We conclude that collaterals and reperfusion are the main factors determining loss of penumbral tissue in patients with middle cerebral artery occlusions. Collaterals markedly reduce and slow down penumbra loss. In patients with good collaterals, time to successful reperfusion accounts only for a minor fraction of penumbra loss. These results support the hypothesis that good collaterals extend the time window for acute stroke treatment.

Clinical Outcomes Strongly Associated With the Degree of Reperfusion Achieved in Target Mismatch Patients

Background and Purpose— To investigate relationships between the degree of early reperfusion achieved on perfusion-weighted imaging and clinical outcomes in the Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution studies. We hypothesized that there would be a strong correlation between the degree of reperfusion achieved and clinical outcomes in target mismatch (TMM) patients. Methods— The degree of reperfusion was calculated on the basis of the difference in perfusion-weighted imaging volumes (time to maximum of tissue residue function [Tmax]&gt;6 s) between the baseline MRI and the early post-treatment follow-up scan. Patients were grouped into quartiles, on the basis of degree of reperfusion achieved, and the association between the degree of reperfusion and clinical outcomes in TMM and no TMM patients was assessed. Favorable clinical response was determined at day 30 on the basis of the National Institutes of Health Stroke Scale and good functional outcome was defined as a modified Rankin Scale score ≤2 at day 90. Results— This study included 121 patients; 98 of these had TMM. The median degree of reperfusion achieved was not different in TMM patients (60%) versus No TMM patients (64%; P =0.604). The degree of reperfusion was strongly correlated with both favorable clinical response ( P &lt;0.001) and good functional outcome ( P =0.001) in TMM patients; no correlation was present in no TMM. The frequency of achieving favorable clinical response or good functional outcome was significantly higher in TMM patients in the highest reperfusion quartile versus the lower 3 quartiles (88% versus 41% as odds ratio, 10.3; 95% confidence interval, 2.8–37.5; and 75% versus 34% as odds ratio, 5.9; 95% confidence interval, 2.1–16.7, respectively). A receiver operating characteristic curve analysis identified 90% as the optimal reperfusion threshold for predicting good functional outcomes. Conclusion— The degree of reperfusion documented on perfusion-weighted imaging after reperfusion therapies corresponds closely with clinical outcomes in TMM patients. Reperfusion of ≥90% of the perfusion lesion is an appropriate goal for reperfusion therapies to aspire to.

Loss of Penumbra by Impaired Oxygen Supply Decreasing Hemoglobin Levels Predict Infarct Growth after Acute Ischemic Stroke

Background: The association of mortality and poor outcome with reduced levels of hemoglobin (Hb) and hematocrit (Hct) in patients admitted for ischemic stroke was recently demonstrated. The mechanisms behind this have remained unclear. Aims: Here, we aimed to investigate a putative association between low Hb and Hct levels and infarct growth. Methods: All consecutive patients who received intravenous thrombolysis based on multimodal magnetic resonance imaging during the years 1998–2009 were screened. Laboratory data as well as admission magnetic resonance images and follow-up computed tomography scans of 257 patients were assessed. Overall, data of 100 patients were of sufficient quality and further analyzed. Results: Decrease in Hb and Hct as well as perfusion-weighted imaging volume, mismatch volume, and final infarct size on follow-up computed tomography were associated with infarct growth. A linear regression model revealed Hb decrease (β = 0.23, p = 0.02) to be a predictor of infarct growth, independent of mismatch volume (β = 0.27, p = 0.004) and minimum sodium (β = -0.21, p = 0.03), and adjusted to the non-predicting variables age, National Institute of Health Stroke Scale score, maximum leucocytes and C-reactive protein, blood glucose, and Hct decrease. Conclusion: Hb levels that decrease after admission independently predict infarct growth in thrombolyzed stroke patients. The clinical implications of this relationship remain to be investigated.

Evidence-based guideline: The role of diffusion and perfusion MRI for the diagnosis of acute ischemic stroke: Report of the Therapeutics and Technology Subcommittee of the American Academy of Neurology

Objective: To assess the evidence for the use of diffusion-weighted imaging (DWI) and perfusionweighted imaging (PWI) in the diagnosis of patients with acute ischemic stroke. Methods: We systematically analyzed the literature from 1966 to January 2008 to address the diagnostic and prognostic value of DWI and PWI. Results and Recommendations: DWI is established as useful and should be considered more useful than noncontrast CT for the diagnosis of acute ischemic stroke within 12 hours of symptom onset. DWI should be performed for the most accurate diagnosis of acute ischemic stroke (Level A); however, the sensitivity of DWI for the diagnosis of ischemic stroke in a general sample of patients with possible acute stroke is not perfect. The diagnostic accuracy of DWI in evaluating cerebral hemorrhage is outside the scope of this guideline. On the basis of Class II and III evidence, baseline DWI volumes probably predict baseline stroke severity in anterior territory stroke (Level B) but possibly do not in vertebrobasilar artery territory stroke (Level C). Baseline DWI lesion volumes probably predict (final) infarct volumes (Level B) and possibly predict early and late clinical outcome measures (Level C). Baseline PWI volumes predict to a lesser degree the baseline stroke severity compared with DWI (Level C). There is insufficient evidence to support or refute the value of PWI in diagnosing acute ischemic stroke (Level U). Neurology ® 2010;75:177–185

Effect of baseline magnetic resonance imaging (MRI) apparent diffusion coefficient lesion volume on functional outcome in ischemic stroke

<title/>Objective: We explored the relationship between predicted infarct core, predicted ischemic penumbras and predicted final infarct volumes obtained though apparent diffusion coefficient (ADC)-based method, as well as other clinical variables, and functional outcome.Methods: Patients with acute cerebral ischemic stroke were retrospectively recruited. The National Institutes of Health Stroke Scale score was evaluated at baseline and the modified Rankin Scale (mRS) at day 90. Favorable outcome was defined as an mRS score of 0 to 2, and unfavorable outcome as 3 to 6. Multimodal stroke magnetic resonance imaging was carried out at presentation. The volumes of diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) were measured using the regions of interest (ROI) method. The volumes of predicted infarct core, predicted ischemic penumbra and predicted final infarct were obtained by an automated image analysis system based on baseline ADC maps. The association between baseline magnetic resonance imaging volumes, baseline clinical variables, and functional outcome was statistically analyzed.Results: The study included 30 males and 20 females (mean±SD age, 56±10 years). Baseline DWI, PWI and PWI-DWI mismatch volumes were not correlated with day-90 mRS (P>0·05). Predicted infarct core, predicted ischemic penumbra and predicted final infarct through ADC-based method were all correlated with day-90 mRS (P<0·05). A better outcome was associated with a smaller predicted volume. Low baseline National Institutes of Health Stroke Scale and recanalization also demonstrated a trend toward a favorable outcome. Receiver operating characteristic analysis showed that the area under the curve of predicted final infarct volume and recanalization were higher with statistical significance (P<0·001).Discussion: Predicted volumes obtained from ADC-based methods, especially predicted final infarct volume, as well as baseline National Institutes of Health Stroke Scale and recanalization may have effect on functional outcome in acute ischemic stroke.

The Hidden Mismatch

In ischemic stroke, MR perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) mismatch represents tissue at risk for infarction. Infarct growth should only take place in the presence of mismatch, although there have been reports of this occurring. We hypothesized that this observation may be attributable to the presence of undetected "hidden mismatch," which may become obvious when coregistration techniques are used. MR PWI/DWI was performed within 48 hours of stroke onset and a final T2-weighted image at ≈3 months. Volumetric-subtraction mismatch volume was defined as PWI minus DWI volume and infarct growth was defined as T2 minus DWI volume. Coregistration mismatch volume was PWI not overlapped by DWI. Mismatch salvage was the proportion of coregistered mismatch tissue that had not progressed to infarction. Thirty-four patients were studied with MR at a median of 4.9 hours (interquartile range, 2.9-21.1 hours). With the volumetric-subtraction technique, 5 patients (14.7%; 95% CI, 0.05%-0.31%) had infarct growth exceeding mismatch volume, 11 patients (32.0%) had no mismatch and, among these, 3 (27.3%) had infarct growth (median volume, 2.2 mL; interquartile range, 1.0-6.5 mL). All patients had mismatch volume identified by coregistration method that was greater than infarct growth volume. The proportion of this volume salvaged was 77.7% (interquartile range, 63.0%-98.9%). The illogical finding of infarct growth volume being greater than the presence of mismatch volume can be explained by the presence of "hidden mismatch," which may be detected by coregistration methods.

Pathophysiological Determinants of Worse Stroke Outcome in Atrial Fibrillation

Background: The reasons for worse outcome following ischemic stroke in patients with atrial fibrillation (AF) remain unclear. We aimed to elucidate the pathophysiological determinants of poorer stroke outcome in patients with AF using systematic MRI data from the Echoplanar Imaging Thrombolytic Evaluation Trial (EPITHET). Methods: Comparisons of infarct size, hypoperfusion volume, infarct growth, arterial occlusion, recanalization, reperfusion, hemorrhagic transformation and stroke severity were made between patients with and without AF enrolled in the EPITHET study. Results: AF was present in 42 of 101 patients. At baseline, AF patients were older (79 vs. 73 years, p = 0.02), had more severe neurological impairment (National Institutes of Health Stroke Scale score 16 vs. 11, p = 0.006), larger infarcts (29 vs. 15 ml, p = 0.04) and greater volumes of more severe hypoperfusion (T_max ≧8 s, perfusion-weighted imaging volume 70 vs. 43 ml, p = 0.01) compared to patients without AF. There were no significant differences in arterial occlusion site, infarct growth, recanalization or reperfusion. At outcome, AF patients had larger infarcts (52 vs. 16 ml, p = 0.05), more severe hemorrhagic transformation (29 vs. 5%, p = 0.002 for parenchymal hematomas), greater disability (modified Rankin Scale score 4 vs. 3, p = 0.03) and higher mortality rates (31 vs. 12%, p = 0.04). AF was an independent predictor of parenchymal hematoma (OR = 6.90, 95% CI = 1.57–30.25), but not mortality (OR = 2.56, 95% CI = 0.83–7.85). Conclusions: Patients with AF have worse clinical and imaging outcomes following ischemic stroke. This study suggests that the adverse effect of AF is due to greater volumes of more severely hypoperfused tissue, leading to larger infarct size and greater risk of severe hemorrhagic transformation.

Evidence-based guideline: The role of diffusion and perfusion MRI for the diagnosis of acute ischemic stroke [RETIRED

To assess the evidence for the use of diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) in the diagnosis of patients with acute ischemic stroke. We systematically analyzed the literature from 1966 to January 2008 to address the diagnostic and prognostic value of DWI and PWI. DWI is established as useful and should be considered more useful than noncontrast CT for the diagnosis of acute ischemic stroke within 12 hours of symptom onset. DWI should be performed for the most accurate diagnosis of acute ischemic stroke (Level A); however, the sensitivity of DWI for the diagnosis of ischemic stroke in a general sample of patients with possible acute stroke is not perfect. The diagnostic accuracy of DWI in evaluating cerebral hemorrhage is outside the scope of this guideline. On the basis of Class II and III evidence, baseline DWI volumes probably predict baseline stroke severity in anterior territory stroke (Level B) but possibly do not in vertebrobasilar artery territory stroke (Level C). Baseline DWI lesion volumes probably predict (final) infarct volumes (Level B) and possibly predict early and late clinical outcome measures (Level C). Baseline PWI volumes predict to a lesser degree the baseline stroke severity compared with DWI (Level C). There is insufficient evidence to support or refute the value of PWI in diagnosing acute ischemic stroke (Level U).

Clinical-Diffusion Mismatch Predicts the Putative Penumbra With High Specificity

Perfusion-diffusion (PWI-DWI) mismatch may represent the ischemic penumbra. The complexities associated with perfusion-weighted imaging (PWI) have restricted its use. Mismatch between stroke severity, assessed with the National Institutes of Health Stroke Scale (NIHSS), and the volume of the diffusion-weighted imaging (DWI) lesion (clinical-diffusion mismatch; CDM) has been suggested as a surrogate for PWI-DWI mismatch. We compared CDM with PWI and DWI in acute stroke. Seventy-nine hemispheric stroke patients were imaged within 24 hours of symptom onset and subacutely (3 to 5 days). CDM was defined as NIHSS > or =8 and DWI < or =25 mL. DWI lesion and PWI (Tmax+4s) volumes were measured by planimetric techniques. Acute PWI-DWI mismatch was examined as a continuous variable (mismatch volume=PWIvol-DWIvol) and a categorical variable (mismatch=PWIvol-DWIvol/DWIvol x 100>20%). Early infarct expansion was calculated as DWI(subacute vol/DWI(acute vol). In the 54 sub-6-hour patients, CDM detected PWI-DWI mismatch with a specificity of 93% (95% confidence interval [CI], 62% to 99%), a positive predictive value of 95% (95% CI, 77% to 100%), but a sensitivity of only 53% (95% CI, 34% to 68%). Alternate DWI and NIHSS cutpoints did not improve test performance characteristics. In addition, subacute DWI expansion was significantly greater in patients with CDM (P=0.01) compared with those without. CDM (NIH > or =8, DWI < or =25 mL) predicts the presence of PWI-DWI mismatch with high specificity and low sensitivity. CDM also predicts DWI expansion. CDM may be a useful selection tool in acute stroke therapies, including thrombolysis.

Refining the Perfusion–Diffusion Mismatch Hypothesis

The Echoplanar Imaging Thrombolysis Evaluation Trial (EPITHET) tests the hypothesis that perfusion-weighted imaging (PWI)-diffusion-weighted imaging (DWI) mismatch predicts the response to thrombolysis. There is no accepted standardized definition of PWI-DWI mismatch. We compared common mismatch definitions in the initial 40 EPITHET patients. Raw perfusion images were used to generate maps of time to peak (TTP), mean transit time (MTT), time to peak of the impulse response (Tmax) and first moment transit time (FMT). DWI, apparent diffusion coefficient (ADC), and PWI volumes were measured with planimetric and thresholding techniques. Correlations between mismatch volume (PWIvol-DWIvol) and DWI expansion (T2(Day 90-vol)-DWI(Acute-vol)) were also assessed. Mean age was 68+/-11, time to MRI 4.5+/-0.7 hours, and median National Institutes of Health Stroke Scale (NIHSS) score 11 (range 4 to 23). Tmax and MTT hypoperfusion volumes were significantly lower than those calculated with TTP and FMT maps (P<0.001). Mismatch > or =20% was observed in 89% (Tmax) to 92% (TTP/FMT/MTT) of patients. Application of a +4s (relative to the contralateral hemisphere) PWI threshold reduced the frequency of positive mismatch volumes (TTP 73%/FMT 68%/Tmax 54%/MTT 43%). Mismatch was not significantly different when assessed with ADC maps. Mismatch volume, calculated with all parameters and thresholds, was not significantly correlated with DWI expansion. In contrast, reperfusion was correlated inversely with infarct growth (R=-0.51; P=0.009). Deconvolution and application of PWI thresholds provide more conservative estimates of tissue at risk and decrease the frequency of mismatch accordingly. The precise definition may not be critical; however, because reperfusion alters tissue fate irrespective of mismatch.

Acute Basilar Artery Occlusion

Diffusion-perfusion MRI in patients with anterior circulation occlusions has demonstrated salvage of threatened tissue after thrombolytic therapy. Similar studies have not been reported with posterior circulation occlusions. Patients with acute basilar artery occlusion treated with intra-arterial thrombolytics were studied with multimodal MRI before treatment, several hours after treatment, and at day 7. Ten patients were studied (9 men, 1 woman). Mean age was 70 years, and median pretreatment National Institutes of Health Stroke Scale (NIHSS) score was 14. In 6 patients imaged before treatment and at day 7, mean pretreatment diffusion-weighted imaging (DWI) lesion volume was 11 cm(3), and day 7, lesion volume was 2.6 cm(3). Significant mismatch was visualized in all 5 patients with pretreatment perfusion-diffusion imaging (mean, 73%; range, 49% to 99%). Late imaging obtained in 4 of these 5 patients demonstrated that mean posttreatment DWI lesion volume (21 cm(3)) was less than the mean initial perfusion lesion volume (62 cm(3)). Although there was no direct correlation between pretreatment DWI volume and initial NIHSS (r=-0.113), there was good correlation between pretreatment perfusion-weighted imaging volume and initial NIHSS (r=0.72). In this first report of diffusion-perfusion MRI in patients with acute basilar artery occlusions treated with intra-arterial thrombolysis, significant mismatch was visualized on pretreatment studies, suggesting that large volumes of salvageable tissue were present. Final infarct volumes were smaller than pretreatment perfusion volumes, suggesting that substantial volumes of tissue were salvaged by thrombolytic reperfusion.

Prediction of early neurological deterioration using diffusion- and perfusion-weighted imaging in hyperacute middle cerebral artery ischemic stroke.

Early neurological deterioration (END) occurs in approximately one third of all ischemic stroke patients and is associated with a poor outcome. Our study sought to assess the value of ultra-early MRI in the prediction of END in stroke patients. Between August 1999 and November 2001, 38 stroke patients with a proven middle cerebral artery (MCA) or intracranial internal carotid artery (ICA) occlusion on MR angiography underwent perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) within 6 hours after onset, and 30 fulfilled all inclusion criteria. Control DWI and MR angiography were performed between days 3 and 5. Cranial CT was performed to rule out hemorrhagic transformation. Vascular risk factors, temperature, blood pressure, glycemia, and blood count were assessed on admission. National Institutes of Health Stroke Scale (NIHSS) scores were obtained at baseline and at 6, 12, 24, and 48 hours. At the same time points, transcranial Doppler (TCD) examinations were conducted to assess arterial recanalization. END was defined as an increase in the NIHSS score >4. A logistic regression model was applied to detect independent predictors of END. The Kruskal-Wallis test was used to evaluate the relationship between infarct growth and duration of vessel occlusion. Initial MR angiography showed an occlusion of intracranial ICA in 7 patients (23.3%), of proximal MCA in 14 (46.6%), and of distal MCA in the remaining 9 (30%). A PWI-DWI mismatch >20% was observed in 28 patients (93.3%). END occurred in 7 patients (23.3%). Baseline NIHSS score (P=0.05), proximal site of occlusion (P=0.002), initial DWI (P=0.002) and PWI (P=0.003) volumes, and reduced PWI-DWI mismatch (P=0.038) were associated with END in the univariate analysis. Only hyperacute DWI volume remained as a predictor of END when a logistic regression model was applied (odds ratio, 11.5; 95% CI, 2.31 to 57.10; P=0.0028). A receiver operator characteristic curve identified a cutoff point of DWI >89 cm(3) (sensitivity, 85.7%; specificity, 95.7%) to predict END. A graded response was seen in DWI lesion expansion in relation to duration of arterial occlusion (P=0.017). Ultra-early DWI is a powerful predictor of END after MCA or intracranial ICA occlusion.

Clinical and Radiological Correlates of Reduced Cerebral Blood Flow Measured Using Magnetic Resonance Imaging

Methods for determining cerebral blood flow (CBF) using bolus-tracking magnetic resonance imaging (MRI) have recently become available. Reduced apparent diffusion coefficient (ADC) values of brain tissue are associated with reductions in regional CBF in animal stroke models. To determine the clinical and radiological features of patients with severe reductions in CBF on MRI and to analyze the relationship between reduced CBF and ADCs in acute ischemic stroke. Case series. Referral center. We studied 17 patients with nonlacunar acute ischemic stroke in whom perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) were performed within 7 hours of symptom onset. A PWI-DWI mismatch of more than 20% was required. We compared patients with ischemic lesions that had CBF of less than 50% relative to the contralateral hemisphere with patients with lesions that had relative CBF greater than 50%. Characteristics analyzed included age, time to MRI, baseline National Institutes of Health Stroke Scale score, mean ADC, DWI and PWI lesion volumes, and 1-month Barthel Index score. Patients with low CBF (n = 5) had lower ADC values (median, 430 x 10 (-6) mm(2)/s vs. 506 x 10 (-6) mm(2)/s; P =.04), larger DWI volumes (median, 41.8 cm(3) vs. 14.5 cm(3); P =.001) and larger PWI lesions as defined by the mean transit time volume (median, 194.6 cm(3) vs. 69.3 cm(3); P =.01), and more severe baseline National Institutes of Health Stroke Scale scores (median, 15 vs. 9; P =.02). Ischemic lesions with severe CBF reductions, measured using bolus-tracking MRI, are associated with lower mean ADCs, larger DWI and PWI volumes, and higher National Institutes of Health Stroke Scale scores.

Clinical Utility of CMRO2 Obtained with MRI in Determining Ischemic Brain Tissue at Risk

P16 It has been suggested that the relationship between oxygen delivery and oxygen demand defines brain tissue at risk during cerebral ischemia. We have recently demonstrated that a quantitative estimate of cerebral blood oxygen saturation (and thereby oxygen extraction fraction, OEF) can be obtained using MRI in vivo. When combined with MR estimated cerebral blood flow (CBF), a quantitative measure of MR-CMRO2 can be calculated. In this study, we sought to explore the potential clinical utility of MR-CMRO2 in determining brain tissue at risk during cerebral ischemia. Seven patients with acute ischemic strokes were imaged at 4.5±.9 hrs (tp1) and 6 of the patients were imaged 3–5 days after stroke onset (tp2) with diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI). In addition, a 2D multiecho gradient/spin echo sequence was employed to acquire images which were subsequently used to estimate MR-OEF. Singular value decomposition was used to obtain a quantitative estimate of CBF to calculate MR-CMRO2 (= MR-OEF x MR-CBF). At tp1, 5/7 patients showed a DWI-PWI mismatch (PWI&gt;DWI) while 2/7 patients exhibited match. At tp2, only 1 patient showed PWI&lt;DWI, and the remaining patients had matched defects. In addition, 4/6 patients had DWI lesion volumes similar to tp1 abnormal PWI volumes, while 2/6 had smaller lesion volumes at tp2. Regional measurements of MR-CMRO2 were obtained in the regions where PWI and DWI abnormalities coincided (“core”), regions where PWI were abnormal (“core+penumbra”), and the corresponding regions on the contralateral hemisphere. In patients who demonstrated mismatched PWI-DWI defects at tp1, CMRO2 in the “core” regions was 35.3±3.4% of the contralateral region. In contrast, CMRO2 in the “core+penumbra” was 48.9±5.4% of the contralateral region, which was significantly different from “core” CMRO2 (p&lt;0.003). Furthermore, the two patients with matched DWI-PWI at tp1 had CMRO2 values 16.6±14.1% of the contralateral regions. Analysis of tp2 images revealed that all “core” regions became infarcted. These results suggest that brain regions with CMRO2 above 35.3% of the contralateral hemisphere may represent salvageable tissue.

Evaluation of early reperfusion and i.v. tPA therapy using diffusion- and perfusion-weighted MRI.

To characterize the effects of recombinant tissue plasminogen activator (rt-PA) therapy and early reperfusion on diffusion-weighted (DWI) and perfusion-weighted imaging (PWI) changes observed following acute ischemic injury. Twelve patients were evaluated prospectively using echo planar DWI and bolus tracking PWI. Six patients received i.v. rt-PA 0.9 mg/kg and were compared with six patients who did not. Patients receiving rt-PA were initially imaged (T1) 3 to 5 hours postictus (mean, 4 hours 20 minutes) whereas those not treated with tissue plasminogen activator (tPA) were imaged 4 to 7 hours postictus (mean, 5 hours, 25 minutes). Follow-up imaging was performed 3 to 6 hours (T2), 24 to 36 hours (T3), 5 to 7 days (T4), and 30 days (T5) after the first scan in all patients. Lesion volumes were measured on both DWI and time-to-peak maps constructed from PW images. PWI was performed successfully at T1 and T3 in 11 of 12 patients. In the group that received i.v. tPA, initial PWI volumes were less than DWI volumes in five of six patients (83%), whereas only one of five patients (20%) not receiving tPA had PWI < DWI volume (p = 0.08). PWI normalized by 24 to 36 hours (T3) in 6 of 11 patients (early reperfusers), with 5 of 6 of these early reperfusers having received tPA. The aggregate apparent diffusion coefficient (ADC) values for the early reperfusers were consistently higher at T2 (p = 0.04), T3 (p = 0.002), and T4 (p = 0.0005). Five of six patients with early reperfusion demonstrated regions of elevated ADC within the ischemic zone (mean ipsilateral ADC/contralateral ADC, 1.46 +/- 0.19) by 24 to 36 hours, whereas none of the nonearly reperfusers showed these regions of elevated ADC (p = 0.015). Early reperfusion is seen more frequently with i.v. tPA therapy. In addition, the study showed that ADC may undergo early increases that are tied closely to reperfusion, and marked ADC heterogeneity may exist within the same lesion. Early reperfusion is seen more frequently with i.v. tPA therapy.