TTP Maps Research Articles

Perfusion Deficits in Different Mechanisms of Two Subtypes of Acute Stroke with Diffusion MRI Confirmation.

Branch atheromatous disease (BAD) and lacunar infract (LI) are the different mechanisms of subtypes of acute stroke. We aimed to investigate perfusion deficits and clinical characteristics of the different mechanisms of two subtypes of acute stroke. Five hundred and ninety-nine CTP examinations were retrospectively reviewed between January and December 2021 in patients with acute stroke symptoms with CTP within 12 hours and MRI within 7 days of symptom onset. Based on diffusion MRI, the patients were assigned to one of two subtypes: BAD and LI. Lesion volumes were measured on NCCT, CTA, CBV, CBF, MTT, and TTP maps by region-of-interest analysis and were confirmed by follow-up MRI. One hundred thirty-three patients met the inclusion criteria (26.3% female). The BAD group was present in 104 of 133 (78.2%), and the LI group 29 of 133 (21.8%). Based on CT perfusion, 42 of 78 (53.8%) BAD group and 5 of 18 (27.8%) LI group had perfusion deficits in the supratentorial region. BAD had a higher proportion of abnormal perfusion than LI patients, with a significant difference (P < 0.05). The sensitivity of CTP ranged from 21.4% (CBV) to 90.5% (TTP); specificity ranged from 97.2% (TTP) to 100% (CBV, CBF, and MTT) in BAD patients. CTP has high specificity in identifying BAD. Compromised perfusion deficits are more presented in BAD patients compared with LI. CT perfusion imaging may be useful for determining the clinical significance of perfusion abnormalities in BAD occurrence.

Perfusion recovery on TTP maps after endovascular stroke treatment might predict favorable neurological outcomes.

Early recanalization and adequate collateral blood flow are surrogates for functional recovery in endovascular stroke treatment (EVT). We evaluated the prognostic value of pre- and immediate post-thrombectomy perfusion-weighted magnetic resonance imaging (PWI) parameters. Consecutive patients with acute ischemic stroke who underwent EVT were enrolled. Lesion volumes and their corresponding changes on diffusion-weighted (DWI) and PWI were assessed. Outcome was measured with modified Rankin Scale (mRS) at 90days, and early neurological improvement (> 8 points improvement on National Institutes of Health Stroke Scale [NIHSS] or 0 to 1) at 7days. Fifty-two patients were enrolled. After control of initial NIHSS and recanalization status, post-thrombectomy time-to-peak (TTP) hypoperfused volume and TTP hypoperfused volume change remained independent predictors of favorable functional outcome (odds ratio [OR] = 0.13, 95% confidence interval [CI] = 0.03-0.54, p = 0.005; OR = 1.018, 95% CI = 1.00-1.03, p = 0.017), and early neurological improvement (OR = 0.20, 95% CI 0.07-0.58, p = 0.003; OR = 1.02, 95% CI = 1.00-1.03, p = 0.010). The areas under the curve of post-thrombectomy TTP hypoperfused volume and TTP hypoperfused volume change were 0.90 and 0.82 (cutoff 68mL and 56mL) for favorable outcome and 0.86 and 0.82 (cutoff 76mL and 58mL) for early neurological improvement, which had better prognostic values than other MR parameters and recanalization grades. These results suggest a large amount of perfusion recovery on TTP is associated with favorable outcome as well as early neurological improvement after EVT, and may be a useful prognostic marker. • A large amount of perfusion recovery on TTP map is associated with favorable outcome and early neurological improvement after EVT. • The best cutoff value for favorable functional outcome was 68mL for post-EVT TTP hypoperfused volume and 56mL decrease for TTP hypoperfused volume. • Amount of perfusion recovery on TTP map has better performance on the prediction of favorable functional recovery and early neurological improvement than other diffusion- and perfusion-weighted MRI parameters and recanalization grades.

Abstract TP76: Quantitative Comparison of Multidetector CT and Cone-Beam CT Perfusion Maps in Large Vessel Occlusion Stroke Patients Undergoing Mechanical Thrombectomy

Cerebral perfusion evaluation using CT or MR perfusion is the gold standard modality to select large vessel occlusion (LVO) stroke patients presenting &gt;6 hours from symptom onset. The availability of cone beam C-arm CT perfusion (CBCTP) in angiography suites could reduce time to endovascular revascularization. We aimed to evaluate the reliability of using CBCTP when compared to multidetector CT perfusion (MDCTP). In this prospective, single-arm, interventional study, 14 LVO anterior circulation thrombectomy patients underwent both a 128 slice MDCTP in the ED and a CBCTP &lt;30 minutes apart prior to groin puncture. CBCTP was acquired using a prototype acquisition mode enabling 10 consecutive C-Arm rotations with nearly continuous data acquisition. A total of 60 cc of contrast layered with 60 cc of saline were injected covering arterial inflow, parenchymal phase and venous outflow. Image data was reconstructed into CBF, CBV, MTT and TTP maps. Three types of measurements were used to compare modalities. In measurement 1, 6 circular regions of interest (ROI) (400mm 2 ) were placed in the anterior arterial territory. In measurement 2, circular ROIs were placed in the ASPECTS regions (cortical 300mm 2 , subcortical 200mm 2 ). In measurement 3, a ROI was drawn around the entire affected area. All ROIs were placed in the basal ganglia and supraganglionic level of both brain sides. Rates (unaffected/affected area) between MDCTP and CBCTP were compared for all sequences. The intraclass correlation coefficient (ICC) was calculated using a single rater, consistency, two-way random-effects model. Measurement 1 found a moderate degree of agreement between MDCTP and CBCTP in CBF, CBV, MTT and TTP rates with ICCs of 0.58 (CI 0.42 - 0.69), 0.65 (CI 0.53 - 0.74), 0.77 (CI 0.68 - 0.83) and 0.52 (CI 0.35 - 0.65). In measurement 2, moderate agreement was found in CBF, CBV and MTT rates; with ICCs of 0.51 (CI 0.32 - 0.65), 0.57 (CI 0.4 - 0.69) and 0.62 (CI 0.47 - 0.73). The results of measurement 3 found an excellent (ICC=0.95, CI 0.88 - 0.98), good (ICC=0.83, CI 0.62 - 0.9) and moderate (ICC=0.7, CI 0.34 - 0.87), degree of agreement in the CBV, MTT and CBF rates, respectively. These results demonstrate promising accuracy of CBCTP in the evaluating ischemic tissue in patient presenting with LVO acute stroke.

Evaluation of cerebrovascular reserve in patients with cerebrovascular diseases using resting-state MRI: A feasibility study

PurposeTo demonstrate the feasibility of mapping cerebrovascular reactivity (CVR) using resting-state functional MRI (fMRI) data without gas or other challenges in patients with cerebrovascular diseases and to show that brain regions affected by the diseases have diminished vascular reactivity. Materials and methodsTwo sub-studies were performed on patients with stroke and Moyamoya disease. In Study 1, 20 stroke patients (56.3 ± 9.7 years, 7 females) were enrolled and resting-state blood‑oxygenation-level-dependent (rs-BOLD) fMRI data were collected, from which CVR maps were computed. CVR values were compared across lesion, perilesional and control ROIs defined on anatomic images. Reproducibility of the CVR measurement was tested in 6 patients with follow-up scans. In Study 2, rs-BOLD fMRI and dynamic susceptibility contrast (DSC) MRI scans were collected in 5 patients with Moyamoya disease (32.4 ± 8.2 years, 4 females). Cerebral blood flow (CBF), cerebral blood volume (CBV), and time-to-peak (TTP) maps were obtained from the DSC MRI data. CVR values were compared between stenotic brain regions and control regions perfused by non-stenotic arteries. ResultsIn stroke patients, lesion CVR (0.250 ± 0.055 relative unit (r.u.)) was lower than control CVR (0.731 ± 0.088 r.u., p = 0.0002). CVR was also lower in the perilesional regions in a graded manner (perilesion 1 CVR = 0.422 ± 0.051 r.u., perilesion 2 CVR = 0.492 ± 0.046 r.u.), relative to that in the control regions (p = 0.005 and 0.036, respectively). In the repeatability analysis, a strong correlation was observed between lesion CVR (r2 = 0.91, p = 0.006) measured at two time points, as well as between control CVR (r2 = 0.79, p = 0.036) at two time points. In Moyamoya patients, CVR in the perfusion deficit regions delineated by DSC TTP maps (0.178 ± 0.189 r.u.) was lower than that in the control regions (0.868 ± 0.214 r.u., p = 0.013). Furthermore, the extent of reduction in CVR was significantly correlated with the extent of lengthening in TTP (r2 = 0.91, p = 0.033). ConclusionOur findings suggested that rs-BOLD data can be used to reproducibly evaluate CVR in patients with cerebrovascular diseases without the use of any vasoactive challenges.

Standardized MR Perfusion Scoring System for Evaluation of Sequential Perfusion Changes and Surgical Outcome of Moyamoya Disease.

Simple-but-precise evaluation of cerebral perfusion is crucial for the treatment of Moyamoya disease. We aimed to develop a standardized scoring system for MR perfusion suitable for Moyamoya disease evaluation and investigate the postoperative serial changes and outcome predictors. From January 2013 to December 2016, patients diagnosed with Moyamoya disease and receiving indirect revascularization were recruited prospectively. Clinical data and serial imaging studies were analyzed. The TTP maps were standardized using cerebellar reference values. We developed a scoring system of standardized TTP maps: 14 points for each hemisphere with higher points indicating better perfusion. In total, 24 children (4-17 years of age, 41 hemispheres) and 20 adults (18-51 years of age, 34 hemispheres) were included. The mean preoperative TTP scores were higher in children (7.34 ± 3.90) than in adults (4.88 ± 3.24). The standardized TTP maps revealed dynamic improvement with an increase in the corresponding scores at the 1-, 3-, and 6-month postoperative follow-ups; the scores stabilized after 6 months. The mean improvement in the 6-month scores of the pediatric and adult groups was 4.15 ± 3.55 and 6.03 ± 3.04, respectively. The 6-month TTP score improvements were associated with Matsushima grades. If we took score improvement as the outcome, the preoperative TTP score was the only significant predictor in multivariable analysis. The standardized TTP maps and scoring system facilitated the quantification of the sequential perfusion changes during Moyamoya disease treatment. The preoperative perfusion status was the only predictor of indirect revascularization outcome.

Identifying perfusion deficits on CT perfusion images using temporal similarity perfusion (TSP) mapping.

Deconvolution-derived maps of CT perfusion (CTP) data may be confounded by transit delays. We propose temporal similarity perfusion (TSP) analysis to decrease CTP maps' dependence on transit times and investigate its sensitivity to detect perfusion deficits. CTP data of acute stroke patients obtained within 9h of symptom onset was analyzed using a delay-insensitive singular value decomposition method and with TSP. The TSP method applies an iterative process whereby a pixel's highest Pearson's R value is obtained through comparison of a pixel's time-shifted signal density time-series curve and the average whole brain signal density time-series curve. Our evaluation included a qualitative and quantitative rating of deconvolution maps (MTT, CBV, and TTP), of TSP maps, and of follow-up CT. Sixty-five patients (mean 68 (SD 13) years, 34 male) were included. A perfusion deficit was identified in 90%, 86%, 65%, and 84% of MTT, TTP, CBV, and TSP maps. The agreement of MTT, TTP, and TSP with CT follow-up was comparable but noticeably lower for CBV. CBV had the best relationship with final infarct volume (R2 = 0.77, p < 0.001), followed by TSP (R2 = 0.63, p < 0.001). Intra-rater agreement of an inexperienced reader was higher for TSP than for CBV/MTT maps (kappa's of 0.79-0.84 and 0.63-0.7). Inter-rater agreement for experienced readers was comparable across maps. TSP maps are easier to interpret for inexperienced readers. Perfusion deficits detected by TSP are smaller which may suggest less dependence on transit delays although more investigation is required. • Temporal similarity perfusion mapping assesses CTP data based on similarities in signal time-curves. • TSP maps are comparable in perfusion deficit detection to deconvolution maps. • TSP maps are easier to interpret for inexperienced readers.

Correlation-based perfusion mapping using time-resolved MR angiography: A feasibility study for patients with suspicions of steno-occlusive craniocervical arteries.

To explore the feasibility of using correlation-based time-delay (CTD) maps produced from time-resolved MR angiography (TRMRA) to diagnose perfusion abnormalities in patients suspected to have steno-occlusive lesions in the craniocervical arteries. Twenty-seven patients who were suspected to have steno-occlusive lesions in the craniocervical arteries underwent both TRMRA and brain single-photon emission computed tomography (SPECT). TRMRA was performed on the supra-aortic area after intravenous injection of a 0.03 mmol/kg gadolinium-based contrast agent. Time-to-peak (TTP) maps and CTD maps of the brain were automatically generated from TRMRA data, and their quality was assessed. Detection of perfusion abnormalities was compared between CTD maps and the time-series maximal intensity projection (MIP) images from TRMRA and TTP maps. Correlation coefficients between quantitative changes in SPECT and parametric maps for the abnormal perfusion areas were calculated. The CTD maps were of significantly superior quality than TTP maps (p < 0.01). For perfusion abnormality detection, CTD maps (kappa 0.84, 95% confidence interval [CI] 0.67-1.00) showed better agreement with SPECT than TTP maps (0.66, 0.46-0.85). For perfusion deficit detection, CTD maps showed higher accuracy (85.2%, 95% CI 66.3-95.8) than MIP images (66.7%, 46-83.5), with marginal significance (p = 0.07). In abnormal perfusion areas, correlation coefficients between SPECT and CTD (r = 0.74, 95% CI 0.34-0.91) were higher than those between SPECT and TTP (r = 0.66, 0.20-0.88). CTD maps generated from TRMRA were of high quality and offered good diagnostic performance for detecting perfusion abnormalities associated with steno-occlusive arterial lesions in the craniocervical area. • Generation of perfusion parametric maps from time-resolved MR angiography is clinically useful. • Correlation-based delay maps can be used to detect perfusion abnormalities associated with steno-occlusive craniocervical arteries. • Estimation of correlation-based delay is robust for low signal-to-noise 4D MR data.

FLAIR vascular hyperintensities and 4D MR angiograms for the estimation of collateral blood flow in anterior cerebral artery ischemia.

PurposeTo assess FLAIR vascular hyperintensities (FVH) and dynamic (4D) angiograms derived from perfusion raw data as proposed magnetic resonance (MR) imaging markers of leptomeningeal collateral circulation in patients with ischemia in the territory of the anterior cerebral artery (ACA).MethodsForty patients from two tertiary care university hospitals were included. Infarct volumes and perfusion deficits were manually measured on DWI images and TTP maps, respectively. FVH and collateral flow on 4D MR angiograms were assessed and graded as previously specified.ResultsForty-one hemispheres were affected. Mean DWI lesion volume was 8.2 (± 13.9; range 0–76.9) ml, mean TTP lesion volume was 24.5 (± 17.2, range 0–76.7) ml. FVH were observed in 26/41 (63.4%) hemispheres. Significant correlations were detected between FVH and TTP lesion volume (ρ = 0.4; P<0.01) absolute (ρ = 0.37; P<0.05) and relative mismatch volume (ρ = 0.35; P<0.05). The modified ASITN/SIR score correlated inversely with DWI lesion volume (ρ = -0.58; P<0.01) and positively with relative mismatch (ρ = 0.29; P< 0.05). ANOVA of the ASITN/SIR score revealed significant inter-group differences for DWI (P<0.001) and TTP lesion volumes (P<0.05). No correlation was observed between FVH scores and modified ASITH/SIR scores (ρ = -0.16; P = 0.32).ConclusionsFVH and flow patterns on 4D MR angiograms are markers of perfusion deficits and tissue at risk. As both methods did not show a correlation between each other, they seem to provide complimentary instead of redundant information. Previously shown evidence for the meaning of these specific MR signs in internal carotid and middle cerebral artery stroke seems to be transferrable to ischemic stroke in the ACA territory.

Abstract 41: Prognostic Value of Perfusion MRI in Patients with Transient Ischemic Attack or Minor Stroke

Background and purpose: We aimed to investigate the role of perfusion MRI parameters (TTP: time to peak, CBF: cerebral blood flow, CBV: cerebral blood volume) as a prognostic factor for the risk of stroke recurrence or cardiovascular outcome in patients with transient ischemic attack (TIA) or minor stroke. Methods: We retrospectively reviewed TIA or minor stroke patients who underwent our stroke MRI protocol (DWI, perfusion MRI, and MRA) in a consecutively collected stroke registry. Primary outcome was nonfatal stroke recurrence and secondary outcome was cardiovascular composite outcome. Multivariate analysis was used to examine the association of perfusion MRI parameters and angiographic findings with the risk of stroke recurrence and cardiovascular event. Results: Of the 326 patients who met inclusion criteria, we identified 15(4.6%) nonfatal strokes and 25(7.7%) cardiovascular composite events during the first 1 year after the index TIA or minor stroke. The presence of regional delayed perfusion on TTP maps (p=0.002) and regional hyperperfusion on CBV maps (p&lt;0.001) were associated with recurrent stroke. In MRA images, concomitant stenosis of the intracranial arteries and/or extracranial carotid arteries was associated with cardiovascular events (p=0.009). Using multivariate cox proportional hazard analysis, presence of regional hyperperfusion on CBV remained an independent predictor of recurrent stroke (HR 10.82, 95% CI 4.19-38.67, p&lt;0.001) and cardiovascular event (HR 6.30, 95% CI 2.67-18.25, p&lt;0.001). The AUC of the CBV maps was also greater than other parameters for the prediction of stroke recurrence (AUC=0.701, 95% CI 0.54-0.86) and cardiovascular composite outcome (AUC=0.628, 95% CI 0.50-0.76). Conclusions: Increased CBV on perfusion MRI, representing the hemodynamic status of postischemic hyperperfusion, could be more useful than other perfusion parameters in predicting poor prognosis of TIA or minor stroke patients.

Multi-site laser Doppler flowmetry for assessing collateral flow in experimental ischemic stroke: Validation of outcome prediction with acute MRI

High variability in infarct size is common in experimental stroke models and affects statistical power and validity of neuroprotection trials. The aim of this study was to explore cerebral collateral flow as a stratification factor for the prediction of ischemic outcome. Transient intraluminal occlusion of the middle cerebral artery was induced for 90 min in 18 Wistar rats. Cerebral collateral flow was assessed intra-procedurally using multi-site laser Doppler flowmetry monitoring in both the lateral middle cerebral artery territory and the borderzone territory between middle cerebral artery and anterior cerebral artery. Multi-modal magnetic resonance imaging was used to assess acute ischemic lesion (diffusion-weighted imaging, DWI), acute perfusion deficit (time-to-peak, TTP), and final ischemic lesion at 24 h. Infarct volumes and typology at 24 h (large hemispheric versus basal ganglia infarcts) were predicted by both intra-ischemic collateral perfusion and acute DWI lesion volume. Collateral flow assessed by multi-site laser Doppler flowmetry correlated with the corresponding acute perfusion deficit using TTP maps. Multi-site laser Doppler flowmetry monitoring was able to predict ischemic outcome and perfusion deficit in good agreement with acute MRI. Our results support the additional value of cerebral collateral flow monitoring for outcome prediction in experimental ischemic stroke, especially when acute MRI facilities are not available.

Left Atrial 4-Dimensional Flow Magnetic Resonance Imaging: Stasis and Velocity Mapping in Patients With Atrial Fibrillation.

Left atrial (LA) 4-dimensional flow magnetic resonance imaging (MRI) was used to derive anatomic maps of LA stasis, peak velocity, and time-to-peak (TTP) velocity in patients with atrial fibrillation (AF) and to identify relationships between LA flow with LA volume and patient characteristics. Four-dimensional flow MRI for the in vivo assessment of time-resolved 3-dimensional LA blood flow velocities was performed in 111 subjects: 42 patients with a history of AF and in sinus rhythm (AF-sinus), 39 patients with persistent AF (AF-afib), 10 young healthy volunteers (HVs), and 20 age-appropriate controls (CTRL). Data analysis included the 3-dimensional segmentation of the LA and the calculation of LA stasis, peak velocity, and TTP maps. Regional LA flow dynamics were quantified by calculating mean stasis, peak velocity, and TTP in the LA center region and the region adjacent to the LA wall. A sensitivity analysis identified thresholds for global LA stasis (<0.1 m/s) and peak velocity (top 5% LA velocities), which detected significant differences between AF patients and controls for global LA stasis (HV, 25% ± 5%; CTRL, 29% ± 10%; AF-sinus, 41% ± 13%; AF-afib, 52% ± 17%) and peak velocity (HV, 0.43 ± 0.02 m/s; CTRL, 0.37 ± 0.04 m/s; AF-sinus, 0.33 ± 0.05 m/s; AF-afib, 0.30 ± 0.05 m/s). Regional analysis revealed significantly increased stasis at both LA center and wall for AF patients compared with age-appropriate controls (29%-84% difference, P < 0.006) and for AF-afib versus AF-sinus patients (22%-30% difference, P < 0.004). In addition, stasis close to the LA wall was significantly elevated (P < 0.001) compared with the LA center for all subject groups. Multiple regressions revealed significant (RAdj = 0.45-0.50, P < 0.001) relationships between impaired global LA flow (reduced velocity and increased stasis) with age (|β| = 0.27-0.50, P < 0.002) and LA volume (|β| = 0.26-0.50, P < 0.003). Atrial 4-dimensional flow MRI detected changes in global and regional LA flow dynamics associated with AF, age, and LA volume. Longitudinal studies are needed to test the diagnostic value of LA flow metrics as potential risk factors for thromboembolic events.

Acute Stroke Syndromes with Isolated Hypoperfusion on MRI - A Clinical and MRI Study

Background: Acute stroke syndromes with negative diffusion-weighted imaging (DWI) but extensive perfusion deficits are rare and constitute a diagnostic challenge due to different operational definitions of penumbral hypoperfusion in acute stroke patients based on MRI criteria. Methods: MR profiles of 19 patients presenting with acute stroke syndromes with negative DWI in the presence of an extensive area of hypoperfusion on time-to-peak (TTP) maps of dynamic susceptibility contrast perfusion-weighted imaging (PWI) were analysed. DWI and PWI lesions were quantified and interpreted with regard to the clinical course. Results: Despite the large area of abnormal perfusion on TTP maps, the clinical course was benign (median National Institute of Health Stroke Scale 2 at admission, 0 at discharge). The volume of hypoperfused tissue was significantly smaller on postprocessed TTP maps with a TTP delay of >4 s than on unprocessed TTP maps with manual contrast adjustment. Semiquantitatively assessed TTP lesion volume was associated with the presence of DWI lesions on follow-up. Conclusion: TTP maps are highly sensitive to demonstrate even small-scale perfusion abnormalities. The additional information from TTP delay thresholds indicates critically reduced perfusion and appears to be a good prognostic indicator in combination with MR angiography and symptomatology.

WE-E-18A-12: Sampling Correction of Parametric Imaging Maps Derived From Digital Subtraction Angiography in Vascular Phantoms

Purpose: To implement corrections for system sampling distortions in parametric imaging maps derived from digital subtraction angiography and test this approach in a controlled flow experiment using a neurovascular phantom. Methods: Depending on the exposure time and frame rate, imaging system sampling can cause distortion of the time density curves (TDC) used in parametric imaging. To solve this problem we implemented a distortion correction algorithm. A flow circuit set to physiologic conditions was created using an internal carotid artery phantom. Parametric imaging maps (PIM) were derived by measuring TDC's at each pixel location in the map. Each TDC was corrected by adding its numerical derivative multiplied by the sampling interval. PIM's were derived for two different contrast bolus injection volumes (5 and 10 ml), and four injection rates (5, 10, 15 and 20 ml/s). We derived PIM's for mean-transit-time (MTT), time-to-peak (TTP) and bolus-arrival-time (BAT). Colored maps were derived for each parameter; values were recorded at precise locations and compared between corrected and uncorrected cases for all injections techniques. Results: For corrected MTT's maps, the correlation with the injection techniques was still strong but the correction resulted in 10 to 30% smaller MTT's. At the inlet location, the corrected MTT's were between 2-0.25 seconds. For corrected BAT and TTP maps, the inlet values changed 20%. Conclusion: The experiment showed that the distorted PIM's for MTT are strongly correlated with the injection conditions and they agree with the expected theoretical values. Sampling correction reduces the BAT and TTP dependence on the injection technique which is expected since these particular parameters should be mostly related to the flow conditions rather than the injection technique. Supported by NIH Grant: 2R01EB002873 and equipment grant from Toshiba Medical Systems Corporation

A comparative analysis of the dependences of the hemodynamic parameters on changes in ROI’s position in perfusion CT scans

This study performed a comparative analysis of cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), and mean time-to-peak (TTP) obtained by changing the region of interest’s (ROI) anatomical positions, during CT brain perfusion. We acquired axial source images of perfusion CT from 20 patients undergoing CT perfusion exams due to brain trauma. Subsequently, the CBV, CBF, MTT, and TTP values were calculated through data-processing of the perfusion CT images. The color scales for the CBV, CBF, MTT, and TTP maps were obtained using the image data. Anterior cerebral artery (ACA) was taken as the standard ROI for the calculations of the perfusion values. Differences in the hemodynamic average values were compared in a quantitative analysis by placing ROI and the dividing axial images into proximal, middle, and distal segments anatomically. By performing the qualitative analysis using a blind test, we observed changes in the sensory characteristics by using the color scales of the CBV, CBF, and MTT maps in the proximal, middle, and distal segments. According to the qualitative analysis, no differences were found in CBV, CBF, MTT, and TTP values of the proximal, middle, and distal segments and no changes were detected in the color scales of the the CBV, CBF, MTT, and TTP maps in the proximal, middle, and distal segments. We anticipate that the results of the study will useful in assessing brain trauma patients using by perfusion imaging.

Abstract WMP14: Perfusion Weighted Imaging Findings in Acute TIA Patients Predict Subsequent Infarction

Introduction: Perfusion weighted imaging (PWI) increases the yield of MRI for the detection of ischemic lesions in TIA patients. We investigate whether PWI predicts the occurrence of acute diffusion weighted imaging (DWI) lesions on follow-up MRI. Methods: Consecutive patients over the age of 18 who were suspected to have a TIA were prospectively enrolled. Patients with technically adequate baseline DWI/PWI and 5 day follow-up DWI were eligible. PWI lesions were identified, blinded to clinical information, as a focal delay on MTT and/or TTP maps. Lesions were confirmed by two stroke neurologists. The baseline and follow-up MRIs were then compared to determine if a new DWI lesion had developed on follow-up and if it was located in the same brain region as the baseline PWI lesion. Results: Seventy percent (94/120) of the enrolled patients were eligible for these analyses. Mean age was 63 years (SD 13) and median ABCD 2 score was 5 (IQR 3, 5). The median delay from symptom onset to baseline MRI was 261 minutes (IQR 131-587); median delay to follow-up MRI was 5 days (IQR 3, 7). Acute ischemic lesions were present on the baseline DWI in 20 patients (21%). The baseline PWI revealed an ischemic lesion in 38 patients (41%). Acute PWI lesion were detected on both MTT and TTP maps in 34 (90%); MTT alone 2 (5%) and TTP alone 2 (5%). Combining DWI and PWI revealed an acute ischemic lesion in 42 patients (45%) distributed as follows: DWI+/PWI+ =16 (17%); DWI+/PWI- 4 (4%), DWI-/PWI+ 22 (23%), DWI-/PWI- 52 (55%). Every positive DWI lesion at baseline (n=20) continued to be DWI positive at follow up. In addition, 10 new DWI lesions were detected. Seven of these were in the same location as a positive baseline PWI lesion and 2 were both outside and inside the area of the initial perfusion deficit ; 1 was in a region that was normal at baseline. Therefore, 9/22 (41%) of the solated PWI lesions at baseline progressed to infarction. Conclusions: Early DWI lesions in patients presenting with transient neurologic symptoms were not reversible at 5 days. Early isolated PWI lesions were seen in about one fourth of these patients and nearly half progressed to infarction. These results substantiate the value of PWI for confirming the diagnosis of an ischemic lesion in patients with suspected TIA.

Post-embolisation susceptibility changes in giant meningiomas: multiparametric histogram analysis using non-contrast-enhanced susceptibility-weighted PRESTO, diffusion-weighted and perfusion-weighted imaging

To investigate imaging characteristics of post-embolised meningioma and to determine if SW imaging can delineate tumour ischaemia. Sixteen patients were studied before and after preoperative embolisation therapy (8 histopathologically determined with ischaemia, 8 with non-ischaemia). In each patient, a slice-wise ROI for the entire tumour was established, and histogram variables (mean, SD, minimum, maximum, histogram width, mode, and peak height) of SW, ADC, CBV, CBF, MTT, and TTP maps were compared between ischaemic and non-ischaemic groups. Changes in SW histogram were correlated with histopathological characteristics. Signal intensity on the SW map tended to decrease in the ischaemic group and partially increased in the non-ischaemic group. A similar trend was observed on the ADC map. The PW histogram showed an MTT increase in ischaemic group; however, CBV did not show significant changes between ischaemic and non-ischaemic groups. Microhaemorrhage was slightly correlated with Δpeak height in the SW histogram. Post-embolisation changes of intrinsic T2-weighted MR contrasts on SW map are most likely associated with alterations in deoxyhaemoglobin levels and arterial blood flow.

Abstract 2972: Perfusion CT in Patients with Basilar Artery Occlusion: Diagnostic and Prognostic Value in the Basilar Artery International Cooperation Study

Background: The posterior circulation Acute Stroke Prognosis Early CT Score (pc-ASPECTS) applied to CT angiography source images (CTA-SI) predicts the functional outcome of patients with basilar artery occlusion (BAO). Compared with CTA-SI, perfusion CT (CTP) may provide added information. We assessed the diagnostic and prognostic impact of CTP compared with CTA-SI among patients in the Basilar Artery International Cooperation Study (BASICS) Methods: BASICS was a prospective observational registry of consecutive patients with acute symptomatic BAO. We applied pc-ASPECTS to CTA-SI and cerebral blood volume (CBV), cerebral blood flow (CBF), time-to-peak (TTP) and mean-transit-time (MTT) parameter maps in a 3-reader-consensus with readers blinded to clinical data. Hypoattenuation on CTA-SI, a relative reduction in CBV or CBF, or relative increase in MTT or TTP was rated as abnormal. Clinical outcome was measured with the modified Rankin Scale (mRS) score at 1 month. Results: Among 592 patients in the BASICS registry, 27 patients (4.6%) had CTP studies performed. Median (interquartile-range) pc-ASPECTS values on TTP/MTT, CTA-SI, CBF and CBV were 6 (5-8), 7 (5-9), 8 (6-9) and 10 (8.75-10), respectively (p&lt;0.001). The proportion of patients with any perfusion abnormalities in the posterior circulation was highest for TTP/MTT (93%; CI 95% 74% to 99%), compared with 78% (CI 95% 57% to 91%) for both CTA-SI and CBF and 46% (CI 95% 27% to 66%) for CBV (p&lt;0.001). At 1 month, 9 patients (33%) had a favourable outcome (mRS scores 0-3), 8 patients (30%) had an unfavourable outcome (mRS scores 4-5) and 10 patients (37%) were deceased. In univariate analysis, pc-ASPECTS scores did not correlate with outcome mRS scores for all imaging modalities (Spearman’s Rho, p&gt;0.1 for all). All three patients (100%) with a CBV pc-ASPECTS &lt;8 compared to 6 of 23 patients (26%) with a CBV pc-ASPECTS &gt;8 died (p=0.03). Conclusion: CTP was performed in a minority of patients in the BASICS registry population. Perfusion disturbances in the posterior circulation were most frequent and most pronounced on TTP and MTT parameter maps. Extensive reduction of CBV, defined as a pc-ASPECTS &lt;8, may indicate patients with a high case fatality.

Abstract 2511: Reperfusion Measured by Mean Transit Time Predicts Clinical Improvement in Hyperacute Ischemic Stroke Patients Better Than Time-to-Peak and Tmax

Background: Early reperfusion is associated with improved clinical outcome in acute ischemic stroke; however, there is no consensus regarding which perfusion parameter may best serve as a marker of clinical improvement. We compared three commonly used MRI perfusion parameters, mean transit time (MTT), time-to-peak (TTP), and Tmax, to identify which method of measuring reperfusion best predicted clinical improvement. Methods: Acute ischemic stroke patients underwent two MR scans: within 4.5 hours (tp1) and at 6 hours (tp2) after stroke onset. Co-registered MTT, TTP, and Tmax maps were generated to measure regions of perfusion deficit at tp1 and tp2. Perfusion deficit was defined as prolongation of MTT, TTP, or Tmax beyond four pre-specified thresholds for each parameter (4 thresholds were chosen to ensure results were not spuriously based on one threshold). Commonly-used thresholds (relative to contralateral median) were selected for each parameter: for MTT: &gt;3, 4, 5, or 6 seconds (s), for TTP: &gt;2, 4, 6, or 8s, and for Tmax: &gt;2, 4, 6, and 8s. The volume of reperfusion (Vreperf) was defined as the volume of tissue with perfusion deficit at tp1 and no perfusion deficit at tp2. Clinical improvement was defined as: Admission NIH Stroke Scale (NIHSS) - 1 month NIHSS (ΔNIHSS). A multivariable linear regression model identified if Vreperf as measured by MTT, TTP, or Tmax was an independent predictor of clinical improvement after adjusting for patient age, admission NIHSS, tPA treatment, and volume of tp1 perfusion deficit. Results: Thirty-nine acute ischemic stroke patients were prospectively scanned at 2.8±.8hr (tp1) and 6.4±.4hr (tp2) after stroke onset (mean age=64, 44% female, 36% Black, mean NIHSS=14, 74% received IV tPA). Across the four thresholds, mean volume of perfusion deficit ranged from 58-96ml for MTT, 56-116ml for TTP, and 51-113ml for Tmax. Mean Vreperf ranged from 15-22ml for MTT, 15-23ml for TTP, and 14-21ml for Tmax. In the multivariable linear regression analysis, after adjusting for age, admission NIHSS, tPA treatment, and volume of tp1 perfusion deficit, Vreperf predicted ΔNIHSS for MTT=4s (p=0.007), MTT=5s (p=0.005), and MTT=6s (p=0.010), whereas Vreperf did not predict ΔNIHSS for any TTP or Tmax threshold ( Table ). Conclusion: Reperfusion, defined by MTT, was an independent predictor of clinical improvement, while reperfusion defined by TTP and Tmax were not. Therefore, MTT may be the best time-based perfusion parameter to define clinically-relevant reperfusion after stroke.

A system for detecting and describing pathological changes using dynamic perfusion computer tomography brain maps

This paper presents a novel method of detecting and describing pathological changes that can be visualized on dynamic computer tomography brain maps (perfusion CT). The system was tested on a set of dynamic perfusion computer tomography maps. Each set consisted of two perfusion maps (CBF, CBV and TTP for testing the irregularity detection algorithm) and one CT brain scan (for the registration algorithm) from 8 different patients with suspected strokes. In 36 of the 84 brain maps, abnormal perfusion was diagnosed. The results of the algorithm were compared with the findings of a team of two radiologists. All of the CBF and CBV maps that did not show a diagnosed asymmetry were classified correctly (i.e. no asymmetry was detected). In four of the TTP maps the algorithm found asymmetries, which were not classified as irregularities in the medical diagnosis; 84.5% of the maps were diagnosed correctly (85.7% for the CBF, 85.7% for the CBV and 82.1% for the TTP); 75% of the errors in the CBF maps and 100% of the errors in the CBV and the TTP maps were caused by the excessive detection of asymmetry regions. Errors in the CBFs and the CBVs were eliminated in cases in which the symmetry axis was selected manually. Subsequently, 96.4% of the CBF maps and 100% of the CBV maps were diagnosed correctly.

Crossed Cerebellar Diaschisis in Acute Stroke Detected by Dynamic Susceptibility Contrast MR Perfusion Imaging

Crossed cerebellar diaschisis (CCD), the decrease in blood flow and metabolism in the cerebellar hemisphere contralateral to a supratentorial stroke, is frequently reported on positron-emission tomography (PET) and single-photon emission CT (SPECT) but is rarely described with MR perfusion techniques. This study was undertaken to determine the frequency of CCD observed in acute stroke by retrospective review of a research data base of patients with acute stroke evaluated by diffusion-weighted (DWI) and dynamic contrast susceptibility perfusion MR imaging (PWI). PWI scans of 301 consecutive patients with acute stroke and positive DWI abnormality from a research data base were reviewed. Contralateral cerebellar hypoperfusion was identified by inspection of time-to-peak (TTP) maps for asymmetry with an absence of cerebellar abnormalities on T2-weighted scans, DWI, or disease of the vertebrobasilar system on MR angiography. In a subset of the cases, quantitative analysis of perfusion scans was performed using an arterial input function and singular value decomposition (SVD) to generate cerebral blood flow (CBF) maps. A total of 47 of 301 cases (15.61%) met the criteria of CCD by asymmetry of cerebellar perfusion on TTP maps. On quantitative analysis, there was corresponding reduction of CBF by 22.75 +/- 10.94% (range, 7.45% to 52.13%) of the unaffected cerebellar hemisphere). MR perfusion techniques can be used to detect CCD, though the frequency presented in this series is lower than that commonly reported in the PET/SPECT literature. Nevertheless, with its role in acute stroke and noninvasive nature, MR perfusion may be a viable alternative to PET or SPECT to study the phenomenon and clinical consequences of supratentorial stroke with CCD.