Mean Transit Time Maps Research Articles

Quantitative Pulmonary Perfusion Imaging with 3-dimensional, Contrast-enhanced MR: Regional Difference in the Perfusion Parameters of Healthy Volunteers

Purpose: We wanted to evaluate the regional differences in such perfusion parameters as pulmonary blood flow (PBF), mean transit time (MTT) and pulmonary blood volume (PBV) in the entire lung of healthy volunteers with using three-dimensional, contrast-enhanced MR imaging (3D CEMRI). Materials and Methods: Six healthy volunteers underwent dynamic 3D CEMRI (TR/TE 2.7/0.6 msec; flip angle 40° matrix 128×96; reconstructed matrix 256×192; rectangular field of view 450×315 mm; coronal 100- 150mm-thick×10 slabs; temporal resolution 1.0 sec; 35 dynamic phases) For all subjects, 2 mL of Gd-DTPA mixed with 3 ml of physiologic saline was administered as a bolus at a rate of 5 mL/sec, and this was followed by 20 mL of physiologic saline flush. From the signal intensity-time curves, the PBF, MTT and PBV maps were generated using indicator dilution theories and the central volume principle on a pixel-by-pixel basis. A total of 54 round, 1-cm sized ROIs were placed in the lung in each subject (6 ROIs per slab×9 slices except for the most posterior slab). The regional differences of the measured parameters were statistically evaluated in the gravitational direction and in the upper-mid-lower direction by one-way ANOVA tests. Results: The calculated PBF, MTT and PBV in the entire lung were 141.8±53.4 mL/100 mL/min (mean±SD), 5.35±1.38 sec, and 13.4±6.48 mL/100mL, respectively. In the gravitational direction, there was a significant increase in the PBF and PBV as it goes to the posterior direction (p

Utility of computed tomography perfusion in detection of cerebral vasospasm in patients with subarachnoid hemorrhage

Digital subtraction (DS) angiography is the gold standard for detecting cerebral vasospasm after subarachnoid hemorrhage (SAH). Computed tomography (CT) perfusion is a recently developed modality for the evaluation of cerebral hemodynamics. This study was conducted to evaluate the potential of using CT perfusion to detect vasospasm in patients with SAH. Fourteen patients between the ages of 41 and 66 years with aneurysmal SAH underwent 23 CT perfusion scans for suspected vasospasm. All patients underwent DS angiography within 12 hours of the CT perfusion scans. The presence of vasospasm on CT perfusion images was determined based on qualitative reading using color maps of mean transit time, cerebral blood flow, and cerebral blood volume as criteria. The presence or absence of vasospasm as retrospectively determined using CT perfusion was compared with DS angiography findings. Of the 23 CT perfusion scans performed, 21 (91%) were concordant with angiography findings in predicting the presence or absence of vasospasm. In 15 of 23 scans, the presence of vasospasm was detected on CT perfusion scans and confirmed on DS angiography studies. In two cases, vasospasm was revealed on DS angiography but was not confirmed on CT perfusion. The degree of agreement between CT perfusion and DS angiography for detection of vasospasm was high (K = 0.8, p , 0.0001). Computed tomography perfusion is an accurate, reliable, and noninvasive method to detect the presence or absence of vasospasm. It can be used as a tool to help guide the decision to pursue DS angiography with the intent to treat vasospasm.

Acute Anterior Circulation Stroke: Recanalization Using Clot Angioplasty

Different strategies have been employed to recanalize acutely occluded middle cerebral and internal carotid arteries (ICA) in the setting of acute stroke including intravenous and intra-arterial tPA. However, pharmaceutical thrombolysis alone, may not be effective in patients with a large amount of clot volume (complete M1, terminal internal carotid artery). We report our initial experience with endovascular clot disruption using a soft silicone balloon in addition to intravenous or intra-arterial thrombolysis with tPA. This is a retrospective review of nine patients with symptoms of acute stroke from clot in the middle cerebral or internal carotid territories who were treated with intracranial balloon angioplasty. All patients presented with symptoms of acute anterior circulation stroke less than six hours from onset. Patients in whom computed tomography (CT) angiography confirmed the presence of large vessel clot (terminal ICA, M1 or proximal M2) were included in the study. A CT perfusion was performed providing maps of cerebral blood volume, flow and mean transit time. If the patient presented less than three hours from onset then intravenous tissue plasminogen activator (tPA) was also administered. Intra-arterial tPA was delivered into the clot. If the volume of clot was judged to be significant by the treating neurointerventionist, then a limited trial of tPA was administered intra-arterially followed by balloon angioplasty of persistant clot. The time from imaging to vessel recanalization was recorded. Clinical outcomes were assessed using the modified Rankin scale and Barthel Index. Diagnostic CT perfusion studies were performed in 7 (78%), all of which showed a significant amount of salvageable tissue as judged by the treating neurointerventionist and neurologist. Recanalization (TIMI 2 or 3) was possible in 8 (89%). There were no cases of symptomatic intracranial hemorrhage and 2 (22%) asymptomatic hemorrhages. The average time from performance of the initial emergency CT to vessel recanalization was 2.1 hours with mean time from symptom onset to vessel recanalization of 4.1 hours. Five (56%) patients had good outcomes, 1 (11%) had mild and 3 (33%) had moderate to severe disability. Clot angioplasty can potentially shorten recanalization times in well-selected patients and can be an effective complimentary procedure in patients with tPA resistant clot. Angioplasty can be performed with a very low complication rate using the technique described and may be associated with good outcomes.

The Application of Diffusion‐ and Perfusion‐Weighted Magnetic Resonance Imaging in the Diagnosis and Therapy of Acute Cerebral Infarction

Diffusion- and perfusion-weighted magnetic resonance imaging (DWI and PWI) was applied for stroke diagnose in 120 acute (< 48 h) ischemic stroke patients. At hyperacute (< 6 h) stage, it is difficult to find out the infarction zone in conventional T1 or T2 image, but it is easy in DWI, apparent diffusion coefficient (ADC) map; when at 3–6-hour stage it is also easy in PWI, cerebral blood flow (CBF) map, cerebral blood volume (CBV) map, and mean transit time (MTT) map; at acute (6–48 h) stage, DWI or PWI is more sensitive than conventional T1 or T2 image too. Combining DWI with ADC, acute and chronic infarction can be distinguished. Besides, penumbra which should be developed in meaning was used as an indication or to evaluate the therapeutic efficacy. There were two cases (< 1.5 h) that broke the model of penumbra because abnormity was found in DWI but not that in PWI, finally they recovered without any sequela.

Apparent Diffusion Coefficient Thresholds Do Not Predict the Response to Acute Stroke Thrombolysis

Apparent diffusion coefficient (ADC) thresholds for tissue infarction have been identified in acute stroke. IV tissue plasminogen activator (tPA) is associated with tissue salvage. We hypothesized that tPA would lower the ADC threshold for infarction. ADC and mean transit time (MTT) maps were generated for 26 patients imaged within 6 hours of stroke onset (12 tPA and 14 conservatively managed controls). MTT maps and day-90 T2-weighted images were coregistered to ADC maps. Relative ADC (rADC) values were calculated for initial diffusion-weighted imaging (DWI) lesions, infarct growth regions (final infarct volume-the acute DWI lesion volume), and hypoperfused salvaged regions (HS; MTT map abnormality-the final infarct volume). When relevant, the DWI lesion was subdivided into DWI reversal and DWI infarct regions. Mean DWI lesion rADC was 0.79 in tPA and 0.74 in untreated patients (P=0.097). Mean rADC in HS and infarct growth regions were similar in tPA patients (0.950 and 0.946) and untreated patients (0.957, P=0.76; 0.970, P=0.08, respectively). The rADC in HS tissue was directly correlated with the time to treatment with tPA (r=0.685; P=0.029). DWI reversal was seen in 67% of tPA-treated patients and in 36% of those conservatively managed (Fisher exact test; P=0.238). In the 13 patients with DWI reversal, the mean rADC in these regions (0.81+/-0.07) was significantly higher than in the acute DWI region that infarcted (0.74+/-0.07; P=0.02), although no absolute thresholds could be identified. The peri-DWI lesion region contains tissue with intermediate ADC values. The fate of this tissue is variable and cannot be predicted based on the ADC alone. DWI expansion occurs in bioenergetically normal tissue, and this is attenuated by tPA in a time-dependent fashion.

Conversion of Ischemic Brain Tissue Into Infarction Increases With Age

Brain regions normal on diffusion-weighted imaging (DWI) but abnormal on mean transit time (MTT) maps represent tissue at risk of infarction, yet the fate of these regions is quite variable. The imperfect correlation between tissue outcome and initial imaging parameters suggests that each patient's brain may have different susceptibility to ischemic stress. We hypothesize that age is a marker for tissue susceptibility to ischemia and thus plays a role in determining tissue outcome in human stroke. Sixty patients with acute ischemic stroke and a region of DWI/MTT mismatch that was >20% of the DWI volume were included. All patients were scanned twice, within 12 hours of symptom onset and on day 5 or later. The percentage mismatch lost (PML) was calculated as percentage of initial DWI/MTT mismatch volume that was infarcted on the follow-up MRI. The statistical analysis explored relationships among the covariates age, Trial of Org 10172 in Acute Stroke Treatment (TOAST) subtypes, time-to-MRI, and initial DWI, MTT volume, mean arterial blood pressure and blood glucose level at admission, and previous history of hypertension and diabetes mellitus. Univariate comparisons showed that age (P=0.003), hypertension (P=0.009), and diabetes mellitus (P=0.0002) were significantly associated with PML. Regression analyses showed age to be a significant covariate (P=0.02). The regression model predicted a change in PML of approximately 0.65% per year. The adjusted proportion of variance (R2) in PML that could be explained by age alone was 14%. Age-dependent increase in conversion of ischemic tissue into infarction suggests that age is a biological marker for the variability in tissue outcome in acute human stroke.

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The effect of varying user-selected input parameters on quantitative values in CT perfusion maps 1

Deconvolution-based software can be used to calculate quantitative maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) from first-pass computed tomography perfusion (CTP) datasets. The application of this software requires the user to select multiple input variables. The purpose of this study was to investigate the degree to which both major and minor variations of these user-defined inputs would affect the final quantitative values of CBF, CBV, and MTT. A neuroradiologist constructed CBF, CBV, and MTT maps using standard methodology with commercially available software (GE Functool Version 1.9s) from CTP datasets of three acute stroke patients. Each map was reconstructed multiple times by systematically and independently varying the following parameters: postenhancement and preenhancement cutoff values, arterial and venous region-of-interest (ROI) placement, and arterial and venous ROI size. The resulting quantitative CTP values were compared using identical ROIs placed at the infarct core. Major variations of either arterial ROI placement or arterial and venous ROI size had no significant effect on the mean CBF, CBV, and MTT values at the infarct core (p > .05). Even minor variations, however, in the choice of venous ROI placement or in pre- and postenhancement cutoff values significantly altered the quantitative values for each of the CTP maps, by as much as threefold. Even minor variations of user-defined inputs can significantly influence the quantitative, deconvolution-based CTP map values of acute stroke patients. Although quantitation was robust to the choice of arterial ROI placement and arterial or venous ROI size, it was strongly dependent on the choice of venous ROI location and pre- and postenhancement cut-off values. Awareness of these results by clinicians may be important in the creation of quantitatively accurate CTP maps.

Quantitative assessment of regional pulmonary perfusion in the entire lung using three-dimensional ultrafast dynamic contrast-enhanced magnetic resonance imaging: Preliminary experience in 40 subjects.

To assess regional differences in quantitative pulmonary perfusion parameters, i.e., pulmonary blood flow (PBF), mean transit time (MTT), and pulmonary blood volume (PBV) in the entire lung on a pixel-by-pixel basis in normal volunteers and pulmonary hypertension patients. Three-dimensional ultrafast dynamic contrast-enhanced MR imaging was performed in 15 normal volunteers and 25 patients with pulmonary hypertension. From the signal intensity-time course curves, PBF, MTT and PBV maps were generated using deconvolution analysis, indicator dilution theories, and the central volume principle, on a pixel-by-pixel basis. From pulmonary perfusion parameter maps of normal volunteers and pulmonary hypertension patients, regional PBF, MTT, and PBV were statistically evaluated. Regional PBF, MTT, and PBV showed significant differences in the gravitational and isogravitational directions (P < 0.05). The quantitative pulmonary perfusion parameter maps demonstrated significant differences between normal volunteers and pulmonary hypertension patients (P < 0.05). Three-dimensional ultrafast dynamic contrast-enhanced MR imaging is feasible for the assessment of regional quantitative pulmonary perfusion parameters in the entire lung on a pixel-by-pixel basis in normal volunteers and pulmonary hypertension patients.

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Carbon dioxide reactivity of computed tomography functional parameters in rabbit VX2 soft tissue tumour

Tumour blood flow is one of the important factors limiting the efficacy of radiation therapy (hypoxic radioresistance), chemotherapy (drug delivery) and thermal therapy (heat dissipation) in treating cancer. The modification of tumour blood flow has been an area of intense investigation. In the current study, the arterial carbon dioxide tension (PaCO2) was changed in order to investigate the tumour vascular response to carbon dioxide. Functional maps of blood flow, blood volume and mean transit time were generated at four PaCO2 levels in VX2 tumour in the rabbit thigh and normal soft tissue. The PaCO2 levels investigated were normocapnia (PaCO2 = 40.9 ± 1.2 mmHg), hypocapnia (27.2 ± 2.3 and 33.5 ± 2.3 mmHg) and hypercapnia (54.9 ± 4.4 mmHg). The carbon dioxide reactivity of the global tumour blood flow and mean transit time showed significant differences between normocapnia and the two levels of hypocapnia, but not between normocapnia and hypercapnia. The average fractional change of blood flow from normocapnia for the two levels of hypocapnia was −0.41 ± 0.06 and −0.29 ± 0.08, respectively (P < 0.05). In the case of mean transit time the fractional change was +0.39 ± 0.30 and +0.23 ± 0.24, respectively (P < 0.05). The fractional change of blood volume from normocapnia, however, was not significantly different at any capnic level, as was the case with respect to each of the functional parameters in normal tissue. The ability to reduce blood flow and increase mean transit time through hypocapnia has significant implications in thermal therapy, since heat dissipation is a major factor in limiting the effectiveness of treatment.

The Utility of First-Pass Perfusion CT in Hyperacute Ischemic Stroke: Early Experience

Purpose: To evaluate the findings of first-pass perfusion CT in hyperacute stroke patients and to determine the relationship between a perfusion map and final infarct outcome. Materials and Methods: Thirty-five patients admitted with ischemic stroke within six hours of the onset of symptoms underwent conventional cerebral CT immediately followed by first-pass perfusion CT. Nineteen underwent follow-up CT or MRI, and three types of dynamic perfusion map - cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) - were evaluated by two radiologists. In these 19 patients, initial perfusion maps correlated with final infarct size, determined during follow-up studies. Results: In all 35 patients, major large vessel perfusion abnormalities [middle cerebral artery - MCA MCA and anterior cerebral artery - ACA (n=2); posterior cerebral artery - PCA (n=8)] were detected. On first-pass perfusion maps depicting CBF and MTT, all lesions were detected, and CBF and delayed MTT values were recorded. CBV maps showed variable findings. In all 19 patients who were followed up, the final infarct size of perfusion abnormalities was less than that depicted on CBF and MTT maps, and similar to or much greater than that seen on CBV maps. Conclusion: First-pass perfusion CT scanning is a practical, rapid and advanced imaging technique. In hyperacute stroke patients, it provides important and reliable hemodynamic information as to which brain tissue is salvageable by thrombolytic therapy, and predicts outcome of such treatment.

Final infarct size after acute stroke: prediction with flow heterogeneity.

To compare acute measurements of flow heterogeneity (FH) and mean transit time (MTT) with follow-up data to determine which method yields better predictive measures of final infarct volumes. Twenty-three patients with symptoms of stroke underwent magnetic resonance (MR) imaging during the acute stage, and the tissue at risk was estimated from MTT maps and maps generated by means of detecting abnormal FH. Final infarct volumes were calculated from T2-weighted follow-up MR image measurement. The Wilcoxon signed rank test was performed to compare the two predictive maps (MTT and FH) with T2-weighted follow-up maps. Eleven (48%) patients experienced infarct growth. Both the MTT and the FH maps enabled prediction of 10 of these cases. There were five false-positive cases with MTT measurement but three with FH measurement. In terms of predicting final infarct volumes, the final infarct size on the MTT maps was overestimated by 75%. The final infarct size on the FH maps also was overestimated, but by only 15%. MTT map measurements were significantly different from follow-up MR image measurements (P =.005), but FH map measurements were not (P =.059). FH maps may enable more precise prediction of final infarct volume in stroke patients.

Viability thresholds of ischemic penumbra of hyperacute stroke defined by perfusion-weighted MRI and apparent diffusion coefficient.

The penumbra of ischemic stroke consists of hypoperfused, but not irreversibly damaged, tissue surrounding the ischemic core. The purpose of this study was to determine viability thresholds in the ischemic penumbra, defined as the perfusion/diffusion mismatch in hyperacute stroke, by the use of diffusion- and perfusion-weighted MRI (DWI and PWI, respectively). DWI and PWI were performed in 11 patients </=6 hours after the onset of symptoms of acute ischemic stroke. Regions of interest (ROIs) were placed covering the ischemic core (ROI 1), the penumbra that progressed to infarction on the basis of follow-up scans (ROI 2), and the penumbra that recovered (ROI 3). The ratios of relative cerebral blood flow (rCBF), relative cerebral blood volume (rCBV), mean transit time (MTT), and apparent diffusion coefficient were calculated as lesion ROIs relative to the contralateral mirror ROIS: The post hoc analysis showed that the penumbra progressed to infarction at the following cutoff values: rCBF <0.59 and MTT >1.63. Higher sensitivity and accuracy in predicting outcome of the penumbra were obtained from the rCBF maps compared with the rCBV and MTT maps. The initial rCBV and apparent diffusion coefficient ratios did not differentiate between the part of the penumbra that recovered and the part that progressed to infarction. The mean rCBF ratio was optimal in distinguishing the parts of the penumbra recovering or progressing to infarction. The thresholds found in this study by combined DWI/PWI might aid in the selection of patients suitable for therapeutic intervention within 6 hours. However, these hypothesized thresholds need to be prospectively tested at the voxel level on a larger patient sample before they can be applied clinically.

Dynamic CT perfusion for acute cerebral ischemia: increasing anatomical coverage with the “toggling table” technique

P17 Computed tomography (CT) has experienced a revival for perfusion assessment in acute stroke. However, so far it is limited by its small anatomical coverage. We studied a toggling table approach to (multislice) dynamic perfusion CT for extended coverage in patients with suspected acute MCA ischemia. In 20 patients with suspected acute MCA ischemia, a dynamic CT perfusion scan was performed on a multidetector scanner. To increase anatomical coverage, 2 distinct “toggling” table positions (each consisting of two 1cm slices) were chosen to represent the MCA territory and scanned in an alternating fashion during the bolus injection of 40mL contrast agent. Dynamic images were evaluated on a ROI and pixel-by-pixel basis, estimating peak density change, time to peak (TTP), integral (rCBV), mean transit time (MTT), and flow (rCBF). Acutely acquired CT perfusion data were compared with follow-up CT or MR (perfusion and diffusion) images. With the toggling table approach, temporal resolution is reduced to approximately 5 secs. Four imaging slices at two distinct locations can be obtained, covering the MCA territory. In 15 patients, perfusion CT revealed focal abnormalities in at least one slice, most commonly on MTT maps. In 14 of these 15 patients, the area of perfusion abnormality was a good predictor of the ultimate infarct. A single table location approach would have underestimated or missed the involved tissue in most cases. In 5 of the 20 patients, perfusion maps failed to delineate any abnormality: in 4 cases, MRI confirmed the absence of ischemia, in 1 case, CT failed to reveal a small ischemic injury visible on diffusion MRI. Addition of the dynamic CT perfusion scan adds less than 5 minutes to a CT stroke protocol and can be coupled with CTA studies to image the cervical and cerebral vasculature in acute stroke. The dynamic CT perfusion technique is a practical and useful tool for the emergency assessment of acute stroke patients. By employing the toggling table approach, perfusion information can be obtained over an extended anatomic area and thus reveal the presence and the extent of presumed tissue ischemia.

Dynamic CT perfusion for acute cerebral ischemia: increasing anatomical coverage with the “toggling table” technique

P17 Computed tomography (CT) has experienced a revival for perfusion assessment in acute stroke. However, so far it is limited by its small anatomical coverage. We studied a toggling table approach to (multislice) dynamic perfusion CT for extended coverage in patients with suspected acute MCA ischemia. In 20 patients with suspected acute MCA ischemia, a dynamic CT perfusion scan was performed on a multidetector scanner. To increase anatomical coverage, 2 distinct “toggling” table positions (each consisting of two 1cm slices) were chosen to represent the MCA territory and scanned in an alternating fashion during the bolus injection of 40mL contrast agent. Dynamic images were evaluated on a ROI and pixel-by-pixel basis, estimating peak density change, time to peak (TTP), integral (rCBV), mean transit time (MTT), and flow (rCBF). Acutely acquired CT perfusion data were compared with follow-up CT or MR (perfusion and diffusion) images. With the toggling table approach, temporal resolution is reduced to approximately 5 secs. Four imaging slices at two distinct locations can be obtained, covering the MCA territory. In 15 patients, perfusion CT revealed focal abnormalities in at least one slice, most commonly on MTT maps. In 14 of these 15 patients, the area of perfusion abnormality was a good predictor of the ultimate infarct. A single table location approach would have underestimated or missed the involved tissue in most cases. In 5 of the 20 patients, perfusion maps failed to delineate any abnormality: in 4 cases, MRI confirmed the absence of ischemia, in 1 case, CT failed to reveal a small ischemic injury visible on diffusion MRI. Addition of the dynamic CT perfusion scan adds less than 5 minutes to a CT stroke protocol and can be coupled with CTA studies to image the cervical and cerebral vasculature in acute stroke. The dynamic CT perfusion technique is a practical and useful tool for the emergency assessment of acute stroke patients. By employing the toggling table approach, perfusion information can be obtained over an extended anatomic area and thus reveal the presence and the extent of presumed tissue ischemia.

Does the Severity of the Early Perfusion Deficit in Ischemic Stroke Predict the Fate of The PWI/DWI Mismatch?

9 The degree of expansion of the early DWI lesion into the volume of the baseline PWI lesion is variable. In some patients partial recruitment of the DWI lesion volume occurs, while other patients develop a DWI lesion that equals or exceeds the size of the initial PWI volume. We investigated whether a quantitative analysis of the severity of the early perfusion deficit predicted the evolution of the PWI/DWI mismatch. Methods We studied patients with acute ischemic stroke in whom PWI and DWI MRI were performed within 7 hours after symptom onset and after 4–5 days. Maps of CBF, CBV and Mean Transit Time(MTT)were created after deconvolution of the arterial input function with the time-concentration curve. We compared the lesion volume on DWI at f/u with the baseline MTT volume. Patients in whom the lesion volume on DWI at f/u was smaller than the initial PWI deficit (group 1) were compared with patients in whom the DWI lesion at f/u (group 2) was ≥ than the initial PWI volume. Characteristics analysed included age, NIHSS, time to MRI, initial DWI volume, initial PWI volume, absolute mismatch volume, relative MTT(rMTT), CBF(rCBF) and CBV (rCBV) of the baseline PWI. Results Thirteen patients had an initial PWI>DWI mismatch of >20%. Seven of these patients (group 1) had DWI lesions at f/u that were smaller than the initial PWI lesion (mean 55% of PWI volume), while in 4 patients (group 2) the f/u DWI volume was larger than the PWI volume (mean 121% of initial PWI volume). Only the median rMTT (2.7 [group 1] versus 5.2 [group 2], p=0.006) and the median rCBV (1.4 [group 1] versus 2.7 [group 2], p=0.006) differed between the two groups. The initial rMTT and rCBV correlated significantly with the degree of expansion of the DWI lesion (ρ= 0.918 for rMTT and 0.864 for rCBV, p DWI, who do not have early reperfusion, the degree of expansion of the initial DWI lesion correlates with the severity of the initial perfusion deficit as measured by the rMTT and the rCBV.

Does the Severity of the Early Perfusion Deficit in Ischemic Stroke Predict the Fate of The PWI/DWI Mismatch?

9 The degree of expansion of the early DWI lesion into the volume of the baseline PWI lesion is variable. In some patients partial recruitment of the DWI lesion volume occurs, while other patients develop a DWI lesion that equals or exceeds the size of the initial PWI volume. We investigated whether a quantitative analysis of the severity of the early perfusion deficit predicted the evolution of the PWI/DWI mismatch. Methods We studied patients with acute ischemic stroke in whom PWI and DWI MRI were performed within 7 hours after symptom onset and after 4–5 days. Maps of CBF, CBV and Mean Transit Time(MTT)were created after deconvolution of the arterial input function with the time-concentration curve. We compared the lesion volume on DWI at f/u with the baseline MTT volume. Patients in whom the lesion volume on DWI at f/u was smaller than the initial PWI deficit (group 1) were compared with patients in whom the DWI lesion at f/u (group 2) was ≥ than the initial PWI volume. Characteristics analysed included age, NIHSS, time to MRI, initial DWI volume, initial PWI volume, absolute mismatch volume, relative MTT(rMTT), CBF(rCBF) and CBV (rCBV) of the baseline PWI. Results Thirteen patients had an initial PWI&gt;DWI mismatch of &gt;20%. Seven of these patients (group 1) had DWI lesions at f/u that were smaller than the initial PWI lesion (mean 55% of PWI volume), while in 4 patients (group 2) the f/u DWI volume was larger than the PWI volume (mean 121% of initial PWI volume). Only the median rMTT (2.7 [group 1] versus 5.2 [group 2], p=0.006) and the median rCBV (1.4 [group 1] versus 2.7 [group 2], p=0.006) differed between the two groups. The initial rMTT and rCBV correlated significantly with the degree of expansion of the DWI lesion (ρ= 0.918 for rMTT and 0.864 for rCBV, p&lt;0.01). Two patients, who were excluded because of early reperfusion, had no substantial increase in the size of the initial DWI lesion despite severely increased rMTT and rCBV. Conclusion Among acute stroke patients with PWI&gt;DWI, who do not have early reperfusion, the degree of expansion of the initial DWI lesion correlates with the severity of the initial perfusion deficit as measured by the rMTT and the rCBV.

MR Perfusion Studies of Brain for Patients with Unilateral Carotid Stenosis or Occlusion: Evaluation of Maps of “Time to Peak” and “Percentage of Baseline at Peak”

Maps of "time to peak" (TTP) and "percentage of baseline at peak" (PBP) were compared with maps of conventional brain perfusion parameters, namely, mean transit time (MTT) and relative cerebral blood volume (rCBV). We performed MR perfusion studies in 11 patients. All of them had occlusion or high-grade stenosis of the unilateral carotid artery. Three areas of old infarct, 4 areas of new infarct, and 10 areas of brain without infarct were evaluated specifically. In all these cases, the TTP maps appeared similar to the MTT maps. They showed increases, normal values, or decreases at the same time in all areas evaluated. Most areas of abnormally decreased CBV had increased signal in PBP maps. In conclusion, the TTP map provided the same qualitative information as MTT. PBP seemed correlated inversely to CBV and was less sensitive in demonstrating abnormality.