Multimodal MR examination in acute ischemic stroke

In recent years, combined diffusion-weighted imaging (DWI) with perfusion imaging (PI) has become an important investigational tool in the acute phase of ischemic stroke, as it may differentiate reversible from irreversible brain tissue damage. We consecutively examined 20 subjects within 12 h of stroke onset using a multiparametric magnetic resonance (MR) examination consisting of DWI, mean transit time (MTT) as PI parameter, and MR angiography (MRA). T2-weighted and fluid-attenuated inversion recovery (FLAIR) on day 7 were also acquired in order to obtain final infarct volume. The following MR parameters were considered: volumetric measures of lesion growth and MTT abnormalities, quantification of regional apparent diffusion coefficient (ADC) and visual inspection of MRA findings. Our results showed: (1) an acute DWI lesion was not predictive of lesion growth and the DWI abnormality did not represent the irreversibly infarcted tissue; (2) ADC values in the ischemic penumbra could not predict tissue at risk; (3) the DWI–PI mismatch did not predict lesion growth, and the PI abnormality overestimated the amount of tissue at risk; and (4) patients with proximal middle cerebral artery occlusion had greater initial and final infarct volumes. This study did not demonstrate the prognostic value of a multimodal MR approach in early ischemic stroke; MRA alone provided predictive information about the volumetric evolution of the lesion.     

Acute ischemic stroke: predictive value of 2D phase-contrast MR angiography--serial study with combined diffusion and perfusion MR imaging

PURPOSE: To evaluate phase-contrast magnetic resonance (MR) angiography and diffusion- and perfusion-weighted imaging in predicting evolution of infarction and clinical outcome. MATERIALS AND METHODS: Phase-contrast angiographic and diffusion-weighted images obtained 1 and 2 days after acute middle cerebral artery (MCA) stroke were assessed in 43 patients; 39 underwent perfusion-weighted imaging on day 1. Follow-up phase-contrast angiographic and T2-weighted images (n = 38) were obtained on day 8. Clinical outcome was assessed at 3 months. Patients were assigned to three groups according to angiographic findings on day 1: group 1, absence of flow in proximal MCA (M1 segment); group 2, internal carotid artery (ICA) occlusion with collateral M1 flow; group 3, flow in ICA and M1. Differences in lesion volumes on diffusion- and perfusion-weighted maps among groups were compared with one-way analysis of variance with Tukey post hoc multiple comparisons. RESULTS: Patients in group 1 had significantly larger infarct growth, volumes of hypoperfusion on relative cerebral blood volume (rCBV) and relative cerebral blood flow maps, and initial and final infarct volumes than did other patients (P <.05). Initial perfusion deficits on mean transit time maps were significantly (P =.002) larger in group 2 than in group 3, but there were no significant differences in infarct growth (P =.977), final infarct volume on day 8 (P =.947), and clinical outcome (P =.969). Absence of M1 flow on day 1 was significantly associated with unfavorable clinical outcome (modified Rankin score > or = 3) at 3 months (P =.010, chi(2) test). Discriminant analysis revealed that rCBV maps alone and combination of diffusion-weighted imaging and MR angiography yielded the highest accuracy in predicting an unfavorable clinical outcome. CONCLUSION: Phase-contrast MR angiography can provide complementary information to that with diffusion- and perfusion- weighted imaging in predicting the outcome of patients with acute stroke.     

Multiphasic perfusion computed tomography in hyperacute ischemic stroke: comparison with diffusion and perfusion magnetic resonance imaging

PURPOSE: The purpose of this study was to compare multiphasic perfusion computed tomography (CT) with diffusion and perfusion magnetic resonance imaging (MRI) in predicting final infarct volume, infarct growth, and clinical severity in patients with hyperacute ischemia untreated by thrombolytic therapy. METHOD: Multiphasic perfusion CT was performed in 19 patients with ischemic stroke within 6 hours of symptom onset. Two CT maps of peak and total perfusion were generated from CT data. Diffusion-weighted imaging (DWI) and perfusion MRI were obtained within 150 minutes after CT. Lesion volumes on CT and MRI were compared with final infarct volume and clinical scores, and mismatch on CT or MRI was compared with infarct growth. RESULTS: The lesion volume on the CT total perfusion map strongly correlated with MRI relative cerebral blood volume (rCBV), and that on the CT peak perfusion map strongly correlated with MRI relative cerebral blood flow (rCBF) and rCBV (P < 0.001). The lesion volume on unenhanced CT or DWI moderately correlated with final infarct volume, but only lesion volume on unenhanced CT weakly correlated with baseline clinical scores (P = 0.024). The lesion volumes on the CT peak perfusion map and MRI rCBF similarly correlated with final infarct volume and clinical scores and more strongly than those on mean transit time (MTT) or time to peak (TTP). DWI-rCBF or CT mismatch was more predictive of infarct growth than DWI-MTT or DWI-TTP mismatch. CONCLUSION: Multiphasic perfusion CT is useful and of comparable utility to diffusion and perfusion MRI for predicting final infarct volume, infarct growth, and clinical severity in acute ischemic stroke.     

MR imaging in acute stroke: diffusion-weighted and perfusion imaging parameters for predicting infarct size

PURPOSE: To investigate the predictive value of the ischemic lesion size, as depicted in the acute stroke phase on diffusion-weighted magnetic resonance (MR) images and time-to-peak (TTP) maps of tissue perfusion imaging, for infarct size, as derived from T2-weighted imaging in the postacute phase. MATERIALS AND METHODS: Fifty patients who underwent diffusion-weighted and perfusion imaging within 1-24 hours after stroke onset and a follow-up T2-weighted investigation after about 8 days were included. Lesion volumes were evaluated by using a semiautomatic thresholding technique. Volumetric results of acute diffusion-weighted and perfusion imaging were analyzed in comparison with follow-up T2-weighted images and in terms of the time difference between symptom onset and initial MR imaging. RESULTS: At diffusion-weighted imaging, the acute lesion defined by a signal intensity increase of more than 20%, compared with the contralateral side, showed the best correlation with the infarct size after 1 week. At perfusion imaging, the best predictor relative to the contralateral side was a delay of more than 6 seconds on TTP maps. Temporal analysis of volumetric results, which depended on the time difference between symptom onset and examination, revealed two patient subgroups. CONCLUSION: Diffusion-weighted imaging helped to predict the size of the lesion on T2-weighted images obtained after about 8 days in patients with a symptom onset of more than 4 hours (r = 0.96), while in patients with a symptom onset of less than 4 hours, perfusion imaging provided important additional information about brain tissue with impaired perfusion.     

Which MR-derived perfusion parameters are the best predictors of infarct growth in hyperacute stroke? Comparative study between relative and quantitative measurements

PURPOSE: To compare predictors of infarct growth in hyperacute stroke from a retrospective review of various relative and quantitative parameters calculated at perfusion-weighted magnetic resonance (MR) imaging performed within 6 hours after ictus. MATERIALS AND METHODS: Fluid-attenuated inversion recovery and diffusion- and perfusion-weighted images were obtained in 66 patients. The initial infarct was delineated on diffusion-weighted images; the hemodynamic disturbance, on apparent mean transit time (MTT) maps; and the final infarct, on follow-up fluid-attenuated inversion recovery images. Relative (without and with deconvolution) and quantitative values of the bolus arrival time, time to peak (TTP), apparent MTT or MTT, cerebral blood volume (CBV), peak height, and cerebral blood flow (CBF) index or CBF were calculated for initial infarct, infarct growth (final minus initial infarct contour), viable hemodynamic disturbance (apparent MTT minus final infarct contour), and contralateral mirror regions. Univariate and multivariate analyses (receiver operating characteristic curves and discriminant analysis) were performed to compare the diagnostic performance of these parameters for predicting infarct growth. RESULTS: At univariate analysis, relative peak height and quantitative CBF were the best predictors of infarct growth; at multivariate analysis, a function of peak height and TTP for relative measurements and CBF alone for quantitative measurements. Quantitative and relative measurements (without or with deconvolution) worked equally well. A combined relative peak height or TTP threshold (<54% or >5.2 seconds, respectively) had a sensitivity of 71% and a specificity of 98%. A quantitative CBF threshold (<35 mL/min/100 g) had a sensitivity of 69% and a specificity of 85%. CONCLUSION: A combination of relative peak height and TTP measurements allowed the best prediction of infarct growth, which obviates more complex quantitative calculation.     

Automatic prediction of infarct growth in acute ischemic stroke from MR apparent diffusion coefficient maps

RATIONALE AND OBJECTIVES: We introduce a new approach to the prediction of final infarct growth in human acute ischemic stroke based on image analysis of the apparent diffusion coefficient (ADC) maps obtained from magnetic resonance imaging. Evidence from multiple previous studies indicate that ADC maps are likely to reveal brain regions belonging to the ischemic penumbra, that is, areas that may be at risk of infarction in the few hours following stroke onset. MATERIALS AND METHODS: In a context where "time is brain," and contrarily to the alternative-and still-debated-perfusion-diffusion weighted image (PWI/DWI) mismatch approach, the DWI magnetic resonance sequences are standardized, fast to acquire, and do not necessitate injection of a contrast agent. The image analysis approach presented here consists of the segmentation of the ischemic penumbra using a fast three-dimensional region-growing technique that mimics the growth of the infarct lesion during acute stroke. RESULTS: The method was evaluated with both numerical simulations and on two groups of 20 ischemic stroke patients (40 patients total). The first group of patient data was used to adjust the parameters of the model ruling the region-growing procedure. The second group of patient data was dedicated to evaluation purposes only, with no subsequent adjustment of the free parameters of the image-analysis procedure. Results indicate that the predicted final infarct volumes are significantly correlated with the true final lesion volumes as revealed by follow-up measurements from DWI sequences. CONCLUSION: The DWI-ADC mismatch method is an encouraging fast alternative to the PWI-DWI mismatch approach to evaluate the likeliness of infarct growth during the acute stage of ischemic stroke.     

Multiphasic Perfusion CT in Acute Middle Cerebral Artery Ischemic Stroke: Prediction of Final Infarct Volume and Correlation with Clinical Outcome

Objective

To assess the utility of multiphasic perfusion CT in the prediction of final infarct volume, and the relationship between lesion volume revealed by CT imaging and clinical outcome in acute ischemic stroke patients who have not undergone thrombolytic therapy.

Materials and Methods

Thirty-five patients underwent multiphasic perfusion CT within six hours of stroke onset. After baseline unenhanced helical CT scanning, contrast-enhanced CT scans were obtained 20, 34, 48, and 62 secs after the injection of 90 mL contrast medium at a rate of 3 mL/sec. CT peak and total perfusion maps were obtained from serial CT images, and the initial lesion volumes revealed by CT were compared with final infarct volumes and clinical scores.

Results

Overall, the lesion volumes seen on CT peak perfusion maps correlated most strongly with final infarct volumes (R²=0.819, p<0.001, slope of regression line=1.016), but individual data showed that they were less than final infarct volume in 31.4% of patients. In those who showed early clinical improvement (n=6), final infarct volume tended to be overestimated by CT peak perfusion mapping and only on total perfusion maps was there significant correlation between lesion volume and final infarct volume (R²=0.854, p=0.008). The lesion volumes depicted by CT maps showed moderate correlation with baseline clinical scores and clinical outcomes (R=0.445-0.706, p≤0.007).

Conclusion

CT peak perfusion maps demonstrate strong correlation between lesion volume and final infarct volume, and accurately predict final infarct volume in about two-thirds of the 35 patients. The lesion volume seen on CT maps shows moderate correlation with clinical outcome.     

Combined perfusion- and diffusion-weighted MR imaging in acute ischemic stroke during the 1st week: a longitudinal study

PURPOSE: To compare findings with different magnetic resonance (MR) perfusion maps in acute ischemic stroke. MATERIALS AND METHODS: Combined diffusion-weighted (DW) and perfusion-weighted (PW) MR imaging was performed in 49 patients with acute (<24 hours) stroke, on the 1st and 2nd days and 1 week after stroke. Volumes of hypoperfused tissue on maps of relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF), and mean transit time (MTT) were compared with the volume of infarcted tissue at DW imaging. RESULTS: The mean infarct volume increased from 41 to 65 cm(3) between the 1st and 2nd days (P: <.001; n = 49). On the 1st day, all perfusion maps on average showed hypoperfusion lesions larger than the infarct at DW imaging (P: <.001; n = 49). MTT maps showed significantly (P: <.001) larger hypoperfusion lesions than did rCBF maps, which showed significantly (P: <.001) larger hypoperfusion lesions than did rCBV maps. The sizes of the initial perfusion-diffusion mismatches correlated significantly with the extent of infarct growth (0.479 < r < 0.657; P: 相似文献   

Accuracy of dynamic perfusion CT with deconvolution in detecting acute hemispheric stroke

BACKGROUND AND PURPOSE: Dynamic perfusion CT (PCT) with deconvolution produces maps of time-to-peak (TTP), mean transit time (MTT), regional cerebral blood flow (rCBF), and regional cerebral blood volume (rCBV), with a computerized automated map of the infarct and penumbra. We determined the accuracy of these maps in patients with suspected acute hemispheric stroke. METHODS: Forty-six patients underwent nonenhanced CT and dynamic PCT, with follow-up CT or MR imaging. Two observers reviewed the nonenhanced studies for signs of stroke and read the PCT maps for TTP, MTT, rCBF, and rCBV abnormalities. Sensitivity, specificity, accuracy, and interobserver agreement were compared (Wilcoxon tests). Nonenhanced CT and PCT data were reviewed for stroke extent according to previously reported methods. Sensitivity, specificity, and accuracy of the computerized maps in detecting ischemia and its extent were determined. RESULTS: Compared with nonenhanced CT, PCT maps were significantly more accurate in detecting stroke (75.7-86.0% vs. 66.2%; P <.01), MTT maps were significantly more sensitive (77.6% vs. 69.2%; P <.01), and rCBF and rCBV maps were significantly more specific (90.9% and 92.7%, respectively, vs. 65.0%; P <.01). Regarding stroke extent, PCT maps were significantly more sensitive than nonenhanced CT (up to 94.4% vs. 42.9%; P <.01) and had higher interobserver agreement (up to 0.763). For the computerized map, sensitivity, specificity, and accuracy, respectively, were 68.2%, 92.3%, and 88.1% in detecting ischemia and 72.2%, 91.8%, and 87.9% in showing the extent. CONCLUSION: Dynamic PCT maps are more accurate than nonenhanced CT in detecting hemispheric strokes. Despite limited spatial coverage, PCT is highly reliable to assess the stroke extent.     

Time course of cerebral infarction in the middle cerebral arterial territory: deep watershed versus territorial subtypes on diffusion-weighted MR images

PURPOSE: To examine possible differences between the evolution of cerebral watershed infarction (WI) and that of territorial thromboembolic infarction (TI) by using diffusion-weighted (DW) and T2-weighted magnetic resonance (MR) images and apparent diffusion coefficient (ADC) maps. MATERIALS AND METHODS: Fourteen patients with TI and nine with WI underwent MR imaging from the acute to chronic infarction stages. ADC maps were derived from DW images. Lesion-to-normal tissue signal intensity ratios on ADC maps (rADC), echo-planar T2-weighted images, and DW images were calculated. Lesion volumes at acute or early subacute infarction stages were measured on DW images, and final lesion volumes were estimated on fluid-attenuated inversion-recovery images. RESULTS: Analysis of variance revealed a significant difference in temporal evolution patterns of rADC between WI and TI (P <.001). rADC pseudonormalization following TI began about 10 days after symptom onset, but that following WI did not occur until about 1 month after symptom onset. The Pearson correlation coefficient between final and initial infarct volumes was 0.9899 for both infarction subtypes, indicating that the initial ischemic injury volume measured at the acute or early subacute stage predicted the final lesion volume fairly well. CONCLUSION: The evolution time of ADC is faster for TI than for WI. This difference, which likely originates from the different pathophysiologic and hemodynamic features of the two infarction types, might account for the relatively large range of ADC values reported for the time course of ischemic strokes.     

Intraobserver variability in the MR determination of tumor volume in squamous cell carcinoma of the pharynx

BACKGROUND AND PURPOSE: If tumor volumes are to be used for evaluating responses to treatment and long-term outcomes of patients with primary pharyngeal carcinomas, the reproducibility of these measurements must be established. We determined the intraobserver variability of MR imaging-based volume measurements of these cancers and their regional metastases. METHODS: We used an interactive computer program (IDL) that enables the extraction of tumor volumes from 3D MR data to obtain 202 volume measurements in 17 patients with pharyngeal carcinoma (two to five time points each). The primary cancer and largest nodal mass were manually outlined on every T2-weighted image of each MR study. The same neuroradiologist reanalyzed this MR dataset 2-41 weeks later. Measurement error and percentage measurement error (intraobserver variability) were determined. Differences in intraobserver variability between primary lesions and nodes, as well as between stages of treatment were tested with a Wilcoxon rank sum test. RESULTS: The mean and median percentage measurement errors, respectively, were 13% and 12% (range, 0-53%; 95% CI: 10%, 16%) for primary tumors and 9% and 7% (range, 0-37%; 95% CI: 7%, 12%) for nodal metastases. The difference in the percentage measurement error between primary lesions and cervical nodes approached statistical significance (P =.07). Differences in the variation of volume measurements based on the stage of therapy were significant (P =.01). CONCLUSION: Our results suggest that MR imaging-based tumor volumes are reliably reproducible. Such measurements may be important in predicting patient outcome, determining appropriate therapy, and conducting patient follow-up.     

Effect of the arterial input function on the measured perfusion values and infarct volumetric in acute cerebral ischemia evaluated by perfusion computed tomography

OBJECTIVES: We sought to evaluate the accuracy of the perfusion computed tomography (PCT) deconvolution-based brain perfusion measurements and the lesions' (infarct and penumbra) volumetric with regard to arterial input function (AIF) selection in patients with acute stroke. MATERIALS AND METHODS: Eighteen consecutive patients with symptoms of acute stroke underwent PCT at admission. Follow-up magnetic resonance imaging was obtained in all patients after 3.6 +/- 1.7 days (range, 1.5-6 days). PCT maps were generated focusing on the anterior cerebral artery (ACA) and branches of the middle cerebral artery (MCA) ipsilateral and contralateral to the ischemic lesion as AIFs. Infarct, penumbra, and total ischemic lesion were delineated on cerebral blood flow (CBF) maps. CBF, cerebral blood volume (CBV), and mean transit time (MTT) were calculated in the ischemic regions as provided by the 3 different AIFs, the normality test was applied for the obtained parameters, and the values were correlated (Pearson's correlation coefficient). Volumes of the ischemic regions (as obtained by the different AIFs) also were correlated and compared (paired t test) to the follow-up infarct volume. RESULTS: The CBF and CBV values obtained by the different AIFs in the infarct, penumbra, and total ischemic lesion were significantly correlated (r=0.94-0.96, P相似文献   

CT perfusion identifies increased salvage of tissue in patients receiving intravenous recombinant tissue plasminogen activator within 3 hours of stroke onset

BACKGROUND AND PURPOSE: In spite of the advent of thrombolytic therapy, CT-perfusion imaging is currently not fully used for clinical decision-making and not included in published clinical guidelines for management of ischemic stroke. We investigated whether lesion volumes on cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) maps predict final infarct volume and whether all these parameters are needed for triage to intravenous recombinant tissue plasminogen activator (rtPA). We also investigated the effect of intravenous rtPA on affected brain by measuring salvaged tissue volume in patients receiving intravenous rtPA and in controls.MATERIALS AND METHODS: Forty-four patients receiving intravenous rtPA and 19 controls underwent CT perfusion (CTP) studies in the emergency department within 3 hours of stroke onset. Lesion volumes were measured on MTT, CBV, and CBF maps by region-of-interest analysis and were compared with follow-up CT volumes by correlation and regression analysis. The volume of salvaged tissue was determined as the difference between the initial MTT and follow-up CT lesion volumes and was compared between intravenous rtPA-treated patients and controls.RESULTS: No significant difference between the groups was observed in lesion volume assessed from the CTP maps (P > .08). Coefficients of determination for MTT, CBF, and CBV versus follow-up CT lesion volumes were 0.3, 0.3, 0.47, with intravenous rtPA; and 0.53, 0.55, and 0.81 without intravenous rtPA. Regression of MTT on CBF lesion volumes showed codependence (R² = 0.98, P < .0001). Mean salvaged tissue volumes with intravenous rtPA were 21.8 ± 17.1 and 13.2 ± 13.5 mL in controls; these were significantly different by using nonparametric (P < .03) and Fisher exact tests (P < .04).CONCLUSIONS: Within 3 hours of stroke onset, CBV lesion volume does not necessarily represent dead tissue. MTT lesion volume alone can be used to identify the upper limit of the size of abnormally perfused brain. More brain is salvaged in patients with intravenous rtPA than in controls.

CT with physiologic imaging of cerebral perfusion (CTP) is routinely used at many centers around the world to assist in the triage of patients with acute stroke into various therapies, including intravenous thrombolysis with recombinant tissue plasminogen activator (rtPA). The use of CT in the triage process has been driven by the rapidity and wide availability of this imaging technique. Functional maps of cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) are readily constructed on a CT workstation and provide important information about the status of regional brain perfusion. Because giving intravenous rtPA is optimal within 3 hours of stroke ictus, it would be helpful to avoid spending time on those CTP parameters that do not provide critical information and to evaluate only those that directly impact the therapeutic decision.A key consideration in the assessment process of patients having acute stroke symptoms is how much affected brain tissue was already infarcted, how much is inevitably going to die, and how much could be potentially salvaged by therapy. It is this functional information that is being sought by using perfusion imaging and mapping of vascular physiology.^1-5 In the literature, it has been shown that lesion volumes on physiologic maps constructed from initial perfusion imaging in patients assessed in the 6- to 72-hour time window predict the final infarct volume.^6-9 Furthermore, several authors have shown that the volume of the initial CBV deficit approximates the final infarct size and likely represents already irreversibly infarcted tissue.^10,11Because the development of infarction is a dynamic time-dependent process, interpretation of the maps may well vary with the time from ictus. It was our aim in this study to investigate whether the lesion volumes observed on CBV, CBF, and MTT CTP maps, obtained within 3 hours of ictus, also predicted the final infarct volume and whether all these parameters are needed for triage. In addition, we investigated the effect of intravenous rtPA on affected brain tissue by measuring the final salvaged tissue volume in patients receiving intravenous rtPA and in a control group not receiving thrombolytic therapy.     

Improving the prediction of final infarct size in acute stroke with bolus delay-corrected perfusion MRI measures

PURPOSE: To investigate whether bolus delay-corrected dynamic susceptibility contrast (DSC) perfusion MRI measures allowed a more accurate estimation of eventual infarct volume in 14 acute stroke patients using a predictive tissue classifier algorithm. MATERIALS AND METHODS: Tissue classification was performed using a expectation maximization and k-means clustering algorithm utilizing diffusion and T2 measures (diffusion-weighted imaging [DWI], apparent diffusion coefficient [ADC], and T2) combined with uncorrected perfusion measures cerebral blood flow ((CBF) and mean transit time [MTT]), bolus delay-corrected perfusion measures (cCBF and cMTT), and bolus delay-corrected perfusion indices (cCBF and cMTT with bolus delay). RESULTS: The mean similarity index (SI), a kappa-based correlation statistic reflecting the pixel-by-pixel classification agreement between predicted and 30-day T2 lesion volumes, were 0.55 +/- 0.19, 0.61 +/- 0.15 (P < 0.02) and 0.60 +/- 0.17 (P <0.03), respectively. Spearman's correlation coefficients, comparing predicted and final lesion volumes were 0.56 (P < 0.05), 0.70 (P < 0.01), and 0.84 (P < 0.001), respectively. We found a more significant correlation between predicted infarct volumes derived from bolus delay-corrected perfusion measures than from conventional perfusion measures when combined with diffusion measures and compared with final lesion volumes measured on 30-day T2 MRI scans. CONCLUSION: Bolus delay-corrected perfusion measures enable an improved prediction of infarct evolution and evaluation of the hemodynamic status of neuronal tissue in acute stroke.     

Predicting cerebral ischemic infarct volume with diffusion and perfusion MR imaging

BACKGROUND AND PURPOSE: Diffusion and perfusion MR imaging have proved useful in the assessment of acute stroke. We evaluated the utility of these techniques in detecting acute ischemic infarction and in predicting final infarct size. METHODS: Diffusion and hemodynamic images were obtained in 134 patients within a mean of 12.3 hours of onset of acute ischemic stroke symptoms. We retrospectively reviewed patient radiology reports to determine the presence or absence of lesion identification on initial diffusion- (DW) and perfusion-weighted (PW) images. Radiologists were not blinded to the initial clinical assessment. For determination of sensitivity and specificity, the final discharge diagnosis was used as the criterion standard. Neurologists were not blinded to the DW or PW imaging findings. In 81 patients, acute lesions were compared with final infarct volumes. RESULTS: Sensitivities of DW imaging and cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) perfusion parameters were 94%, 74%, 84%, and 84%, respectively. Specificities of DW imaging, CBV, CBF, and MTT were 96%, 100%, 96%, and 96%, respectively. Results were similar in 93 patients imaged within 12 hours. In 81 patients with follow-up, regression analysis yielded r(2) = 0.9, slope = 1.24 for DW imaging; r(2) = 0.84, slope = 1.22 for CBV; r(2) = 0.35, slope = 0.44 for CBF; and r(2) = 0.22, slope = 0.32 for MTT, versus follow-up volume. A DW-CBV mismatch predicted additional lesion growth, whereas DW-CBF and DW-MTT mismatches did not. Results were similar in 60 patients imaged within 12 hours. CONCLUSION: Diffusion and hemodynamic images are sensitive and specific for detecting acute infarction. DW imaging and CBV best predict final infarct volume. DW-CBV mismatch predicts lesion growth into the CBV abnormality. CBF and MTT help identify additional tissue with altered perfusion but have lower correlation with final volume.     

Functional MR of brain activity and perfusion in patients with chronic cortical stroke.

PURPOSE(1) To determine whether functional MR can reliably map functional deficits in patients with stroke in the primary visual cortex; (2) to determine whether functional MR can reliably map perfusion deficits; and (3) to determine whether functional MR can give any additional diagnostic information beyond conventional MR.METHODSSeven patients who had had a stroke in their primary visual system were examined using two functional MR techniques: (1) dynamic susceptibility contrast imaging, and (2) cortical activation mapping during full-field visual stimulation. Maps of relative cerebral blood volume and activation were created and compared with visual field examinations and conventional T2-weighted images on a quadrant-by-quadrant basis in five of these patients.RESULTSVisual field mapping matched with both T2-weighted conventional images and activation mapping of 16 of 18 quadrants. In two quadrants, the activation maps detected abnormalities that were present on the visual field examination but not present on the T2-weighted images nor on the relative cerebral blood volume maps, which may indicate abnormal function without frank infarction. In addition, the activation maps demonstrated decreased activation in extrastriate cortex and had normal T2 signal and relative cerebral blood volume but was adjacent to infarcted primary cortex, mapping in vivo how stroke in one location can affect the function of distant tissue.CONCLUSIONFunctional MR techniques can accurately map functional and perfusion deficits and thereby provide additional clinically useful information. Additional studies will be needed to determine the prognostic utility of functional MR in stroke patients.     

Development of brain infarct volume as assessed by magnetic resonance imaging (MRI): follow-up of diffusion-weighted MRI lesions

PURPOSE: To investigate the development of ischemic brain lesions, as present in the acute stroke phase, by diffusion-weighted magnetic resonance imaging (DWI), and in the subacute and chronic phases until up to four months after stroke, in fluid-attenuated inversion recovery (FLAIR)- and T2-weighted (T2W) magnetic resonance (MR) images. MATERIALS AND METHODS: Twelve consecutive patients with their first middle cerebral artery (MCA) infarction were included. Lesion volumes were assessed on T2W images recorded with a turbo spin echo (TSE) and on images recorded with the FLAIR sequence on average on day 8 and after about four months. They were compared with acute lesion volumes in perfusion and DWI images taken within 24 hours of stroke onset. RESULTS: On day 8, lesion volumes in images obtained with FLAIR exceeded the acute infarct volumes in DWI. The chronic lesion volumes were almost identical in T2W and FLAIR images but significantly reduced compared with the acute DWI lesions. The lesion volumes assessed on DWI images correlated highly with the lesions in the images obtained with TSE or FLAIR, as did the lesions in the images obtained with FLAIR and TSE. The secondary lesion shrinkage was accompanied by ventricular enlargement and perilesional sulcal widening, as most clearly visible in the images obtained with FLAIR. CONCLUSION: Our results show that the acute DWI lesions are highly predictive for the infarct lesion in the chronic stage after stroke despite a dynamic lesion evolution most evident in MR images obtained with FLAIR.     

CT perfusion scanning with deconvolution analysis: pilot study in patients with acute middle cerebral artery stroke.

PURPOSE: To measure mean cerebral blood flow (CBF) in ischemic and nonischemic territories and in low-attenuation regions in patients with acute stroke by using deconvolution-derived hemodynamic imaging. MATERIALS AND METHODS: Twelve patients with acute middle cerebral artery stroke and 12 control patients were examined by using single-section computed tomography (CT) perfusion scanning. Analysis was performed with a deconvolution-based algorithm. Comparisons of mean CBF, cerebral blood volume (CBV), and mean transit time (MTT) were determined between hemispheres in all patients and between low- and normal-attenuation regions in patients with acute stroke. Two independent readers examined the images for extent of visually apparent regional perfusion abnormalities. The data were compared with extent of final infarct in seven patients with acute stroke who underwent follow-up CT or magnetic resonance imaging. RESULTS: Significant decreases in CBF (-50%, P =.001) were found in the affected hemispheres of patients with acute stroke. Significant changes in CBV (-26%, P =.03) and MTT (+111%, P =.004) were also seen. Significant alterations in perfusion were also seen in low- compared with normal-attenuation areas. Pearson correlation between readers for extent of CBF abnormality was 0.94 (P =.001). Intraobserver variation was 8.9% for CBF abnormalities. CONCLUSION: Deconvolution analysis of CT perfusion data is a promising method for evaluation of cerebral hemodynamics in patients with acute stroke.     

Predicting final infarct size using acute and subacute multiparametric MRI measurements in patients with ischemic stroke

PURPOSE: To identify early MRI characteristics of ischemic stroke that predict final infarct size three months poststroke. MATERIALS AND METHODS: Multiparametric MRI (multispin echo T2-weighted [T2W] imaging, T1-weighted [T1W] imaging, and diffusion-weighted imaging [DWI]) was performed acutely (<24 hours), subacutely (three to five days), and at three months. MRI was processed using maps of apparent diffusion coefficient (ADC), T2, and a self-organizing data analysis (ISODATA) technique. Analyses began with testing for individual MRI parameter effects, followed by multivariable modeling with assessment of predictive ability (R(2)) on final infarct size. RESULTS: A total of 45 patients were studied, 15 of whom were treated with tissue plasminogen activator (tPA) before acute MRI. The acute DWI and DWI-ISODATA mismatch lesion size, and the interactions of ADC, T2, and T2W imaging lesion with tPA remained in the final multivariable model (R(2) = 70%). A large acute DWI lesion or DWI < ISODATA lesion independently predicted increase in the final infract size, with predictive ability 68%. Predictive ability increased (R(2) = 83%) when subacute MRI parameters were included along with acute DWI, DWI-ISODATA mismatch, and acute T2W image lesion size by tPA treatment interaction. Subacute DWI > acute DWI lesion size predicted an increased final infarct size (P < 0.01). CONCLUSION: Acute-phase DWI and DWI-ISODATA mismatch strongly predict the final infarct size. An acute-to-subacute DWI lesion size change further increases the predictive ability of the model.     

Normalization of cerebral volumes by use of intracranial volume: implications for longitudinal quantitative MR imaging

BACKGROUND AND PURPOSE: MR-based volumetric measures of cerebral structures are increasingly used for diagnostic purposes and to measure progression of atrophy. Variations in individual head size may be corrected by normalization with use of a total intracranial volume (TIV) measurement. The TIV also may be used to correct for voxel size fluctuations in serial studies. The TIV should be measured from the same images used for structural volumetry, usually T1-weighted imaging. The objectives were to show that normalization with TIV reduces interindividual variation, to develop and validate a simple protocol for measuring TIV from T1-weighted MR images, and to apply TIV normalization to serial brain measures in controls and subjects with Alzheimer disease (AD). METHODS: We measured TIV with a semiautomated segmentation technique on T1- and T2-weighted MR images in 55 controls, 10 AD patients, and two persons at risk of familial AD. Whole-brain volumes also were measured and normalized with TIVs. RESULTS: The TIV normalization of cross-sectional brain volumes significantly reduced interindividual variation; the coefficient of variation (CV) was reduced from 10.0% to 6.0% in controls (P <.001). The TIVs measured on T1-weighted images had low variability (CV, 0.16%) and did not differ significantly from those measured on T2-weighted images (P =.16). The TIV normalization of serial brain-volume measurements reduced interimage differences caused by voxel-scaling variations (CV reduced from 1.3% to 0.5%, P =.002) in 10 controls and five AD patients. CONCLUSION: Structural volumes should be normalized with a TIV, measured cross-sectionally, to reduce interindividual variation, and longitudinally with a concurrent measurement, to reduce subtle interimage differences. This may have important implications in progression studies.