TOF Images Research Articles

Impact of Various Non-Contrast-Enhanced MRA Techniques on Lumen Visibility in Vascular Flow Models with a Surpass Evolve Flow Diverter.

Silent MRA has shown promising results in evaluating the stents used for intracranial aneurysm treatment. A deep learning-based denoising and deranging algorithm was recently introduced by GE HealthCare. The purpose of this study was to compare the performance of several MRA techniques regarding lumen visibility in silicone models with flow diverter stents. Two Surpass Evolve stents of different sizes were implanted in two silicone tubes. The tubes were placed in separate boxes in the straight position and in two different curve configurations and connected to a pulsatile pump to construct a flow loop. Using a 3.0T MRI scanner, TOF and silent MRA images were acquired, and deep learning reconstruction was applied to the silent MRA dataset. The intraluminal signal intensity in the stent (SIin-stent), in the tube outside the stent (SIvessel), and of the background (SIbg) were measured for each scan. The SIin-stent/SIbg and SIin-stent/SIv ratios were higher in the silent scans and DL-based reconstructions than in the TOF images. The stent tips created severe artefacts in the TOF images, which could not be observed in the silent scans. Our study demonstrates that the DL reconstruction algorithm improves the quality of the silent MRA technique in evaluating the flow diverter stent patency.

Time-of-Flight PET/CT Imaging of Ga-68-Dotatate: Normal Pattern, SUV Quantification, and Differences from Non-Time-of-Flight Imaging

Purpose The biodistribution of gallium-68-dotatate (Ga-68-dotatate) and standardized uptake values (SUVs) using non-time-of-flight (TOF) positron emission tomography/computed tomography (PET/CT) cameras is well established. However, with the eventual retirement of older PET cameras and their replacement with newer, highly sensitive TOF PET/CT cameras, where SUVmax measurements are reportedly higher, updated knowledge of normal SUVmax range is needed and, to our knowledge, not previously reported. Our objectives are as follows: Methods Fifty consecutive patients referred routinely to our nuclear medicine service (20 men, 30 women; median age 55 years) with presumed neuroendocrine tumors underwent Ga-68-dotatate scans on a PET-CT camera having capability of reconstructing both TOF/non-TOF images. Region of interests (ROIs) were drawn around 24 normal structures as well as the primary lesion with abnormal radiotracer uptake and SUVmax was measured. The same ROI was analyzed using both algorithms simultaneously and both TOF and non-TOF SUVmax values were compared. Results Twelve hundred ROIs were evaluated. Non-TOF Ga-68-dotatate uptake in normal structures was in alignment with previously published studies. As compared to non-TOF, TOF images had better target to background ratios visually. TOF SUVmax was higher for all structures except for lung and brain. TOF SUVmax was more than double in adrenals/uncinate process of the pancreas; approximately 1.8 times in abnormal lesions, lymph nodes, pineal gland; and greater than 1.5 times in thyroid, breast, and pancreatic head. Conclusion Normal database of Ga-68-dotatate TOF SUVmax is provided for common structures to aid visual detection of abnormalities objectively. Overall, TOF SUVmax measures higher in identical ROIs, with abnormal lesions measuring approximately 1.8 times higher versus non-TOF technology. These findings need to be taken in consideration when comparing patient scans imaged on different PET/CT technologies.

Deep Learning-Based Synthetic TOF-MRA Generation Using Time-Resolved MRA in Fast Stroke Imaging.

Time-resolved MRA enables collateral evaluation in acute ischemic stroke with large-vessel occlusion; however, a low SNR and spatial resolution impede the diagnosis of vascular occlusion. We developed a CycleGAN-based deep learning model to generate high-resolution synthetic TOF-MRA images using time-resolved MRA and evaluated its image quality and clinical efficacy. This retrospective, single-center study included 397 patients who underwent both TOF- and time-resolved MRA between April 2021 and January 2022. Patients were divided into 2 groups for model development and image-quality validation. Image quality was evaluated qualitatively and quantitatively with 3 sequences. A multireader diagnostic optimality evaluation was performed by 16 radiologists. For clinical validation, we evaluated 123 patients who underwent fast stroke MR imaging to assess acute ischemic stroke. The diagnostic confidence level and decision time for large-vessel occlusion were also evaluated. Median values of overall image quality, noise, sharpness, venous contamination, and SNR for M1, M2, the basilar artery, and posterior cerebral artery are better with synthetic TOF than with time-resolved MRA. However, with respect to real TOF, synthetic TOF presents worse median values of overall image quality, sharpness, vascular conspicuity, and SNR for M3, the basilar artery, and the posterior cerebral artery. During the multireader evaluation, radiologists could not discriminate synthetic TOF images from TOF images. During clinical validation, both readers demonstrated increases in diagnostic confidence levels and decreases in decision time. A CycleGAN-based deep learning model was developed to generate synthetic TOF from time-resolved MRA. Synthetic TOF can potentially assist in the detection of large-vessel occlusion in stroke centers using time-resolved MRA.

Evaluation of methemoglobin as an intravascular contrast agent: T1 relaxation time effect in a rabbit model

ObjectiveAlternative contrast agents for MRI are needed for individuals who may respond adversely to gadolinium, and need an intravascular agent for specific indications. One potential contrast agent is intracellular methemoglobin, a paramagnetic molecule that is normally present in small amounts in red blood cells. An animal model was used to determine whether methemoglobin modulation with intravenous sodium nitrite transiently changes the T1 relaxation of blood. MethodsFour adult New Zealand white rabbits were treated with 30 mg intravenous sodium nitrite. 3D TOF and 3D MPRAGE images were acquired before (baseline) and after methemoglobin modulation. T1 of blood was measured with 2D ss EPl acquisitions with inversion recovery preparation performed at two-minute intervals up to 30 min. T1 maps were calculated by fitting the signal recovery curve within major blood vessels. ResultsBaseline T1 was 1758 ± 53 ms in carotid arteries and 1716 ± 41 ms in jugular veins. Sodium nitrite significantly changed intravascular T1 relaxation. The mean minimum value of T1 was 1126 ± 28 ms in carotid arteries 8 to 10 min after the injection of sodium nitrite. The mean minimum value of T1 was 1171 ± 52 ms in jugular veins 10 to 14 min after the injection of sodium nitrite. Arterial and venous T1 recovered to baseline after a period of 30 min. ConclusionMethemoglobin modulation produces intravascular contrast on T1-weighted MRI in vivo. Additional studies are needed to safely optimize methemoglobin modulation and sequence parameters for maximal tissue contrast.

Clinical Implications of Internal Carotid Arterial Tortuosity in Patients with White Matter Hyperintensities

AbstractBackgroundWhite matter hyperintensities (WMHs) are observed frequently on MRI in elderly and associated with cognitive dysfunction. Many studies focused on intracranial small vessel disease (SVD), however, few studies linked WMHs with changes of extracranial large feeding arteries. We aimed to investigate the effects of internal carotid artery (ICA) tortuosity changes through quantitative MR Angiography.MethodFifty‐seven patients (age: 72.98±5.62; 32 females/25 males) with WMHs were included. WMHs lesions were semi‐automatically segmented on FLAIR images. ICAs were segmented on the TOF images to generate tortuosity quantitative metrics, including tortuosity index (TI), inflection count metric (ICM), and ICA angle (Figure 1). According to the Fazekas scores, patients were categorized into mild, moderate and severe groups as summarized in Table 1. One‐way ANOVA analyses were applied to reveal the difference of averaged bilateral ICAs' tortuosity measurements. Pearson's correlation coefficients were calculated to quantitatively investigate the relationship between tortuosity and volumes of lesions that are apart from the ventricle in subcortical white matter, i.e., deep white matter lesions (DWMLs), as well as the lesions attached with the ventricular system, i.e., periventricular white matter lesions (PVWMLs).ResultPatients with higher Fazekas scores have higher TI and ICM, indicating higher tortuosity (Figure 2). The correlation results showed that TI and ICM were positively correlated with DWMLs volumes (r = 0.33, P< 0.05; r = 0.4, P< 0.01), however, they did not show associations with PVWMLs. While there's no correlation between averaged bilateral ICA angles and DWMLs or PVWMLs, we found significant correlations between left ICA angles and DWML volumes on left brain (r =0.56, P < 0.005) as well as between right ICA angles and DWML volumes on right brain (r = 0.49, P < 0.05) (Figure 3).ConclusionTortuosity measurements derived from TOF images showed that subjects with higher degree of ICA tortuosity had higher lesion volumes of DWMLs not PVWMLs, indicating DWMLs may have different etiologies such as ischemic origin. The findings also highlight the importance of ICA angle as a risk factor for WMHs development which might be associated with the local hemodynamic shear stress at the bulb, where the ICA plaques are often developed.

Age-Related Tortuosity of Carotid and Vertebral Arteries: Quantitative Evaluation With MR Angiography.

Background and PurposeThe vascular tortuosity (VT) of the internal carotid artery (ICA), and vertebral artery (VA) can impact blood flow and neuronal function. However, few studies involved quantitative investigation of VT based on magnetic resonance imaging (MRI). The main purpose of our study was to evaluate the age and gender effects on ICA and VA regarding the tortuosity and flow changes by applying automatic vessel segmentation, centerline tracking, and phase mapping on MR angiography.MethodsA total of 247 subjects (86 males and 161 females) without neurological diseases participated in this study. All subjects obtained T1-weighted MRI, 3D time-of-flight MR angiography, and 2D phase-contrast (PC) MRI scans. To generate quantitative tortuosity metrics from TOF images, the vessel segmentation and centerline tracking were implemented based on Otsu thresholding and fast marching algorithms, respectively. Blood flow and velocity were measured using PC MRI. Among the 247 subjects, 144 subjects (≤ 60 years, 49 males/95 females) were categorized as the young group; 103 subjects (>60 years, 37 males/66 females) were categorized as the old group.ResultsIndependent t-test showed that older subjects had higher tortuosity metrics, whereas lower blood flow and velocity than young subjects (p < 0.0025, Bonferroni-corrected). Cerebral blood flow calculated using the sum flux of four target arteries normalized by the brain mass also showed significantly lower values in older subjects (p < 0.001). The age was observed to be positively correlated with the VT metrics. Compared to the males, the females demonstrated higher geometric indices within VAs as well as faster age-related vascular profile changes. After adjusting age and gender as covariates, maximum blood velocity is negatively correlated with geometric measurements. No association was observed between blood flux and geometric measures.ConclusionsVascular auto-segmentation, centerline tracking, and phase mapping provide promising quantitative assessments of tortuosity and its effects on blood flow. The neck arteries demonstrate quantifiable and significant age-related morphological and hemodynamic alterations. Moreover, females showed more distinct vascular changes with age. Our work is built upon a comprehensive quantitative investigation of a large cohort of populations covering adult lifespan using MRI, the results can serve as reference ranges of each decade in the general population.

Estimation of Body Weight for Korean Cattle Using Three-Dimensional Image

This study was conducted to estimate the body weight of Korean cattle (Hanwoo) using three-dimensional image. A time-of-flight camera and a stereo vision camera were used to acquire top-view images for Hanwoo. Multiple linear regression model incorporating body dimensions and age was developed to estimate the body weight. The prediction models with or without age variable were determined. Incorporating age variable that correlates with body weight improved the coefficient of determination for both TOF images and stereo vision images. The weight estimation error was greatly reduced under the condition that calves less than 6 months old were excluded. It was concluded that 3-D image is a promising technique for estimating the body weight of Hanwoo cattle.

Signal of Carotid Intraplaque Hemorrhage on MR T1-Weighted Imaging: Association with Acute Cerebral Infarct.

Identifying the mere presence of carotid intraplaque hemorrhage would be insufficient to accurately discriminate the presence of acute cerebral infarct. We aimed to investigate the association between signal intensity ratios of carotid intraplaque hemorrhage on T1-weighted MR imaging and acute cerebral infarct in patients with hemorrhagic carotid plaques using MR vessel wall imaging. Symptomatic patients with carotid intraplaque hemorrhage were included. The signal intensity ratios of carotid intraplaque hemorrhage against muscle on T1-weighted, TOF, and MPRAGE images were measured. The acute cerebral infarct was determined on the hemisphere ipsilateral to the carotid intraplaque hemorrhage. The association between signal intensity ratios of carotid intraplaque hemorrhage and acute cerebral infarct was analyzed. Of 109 included patients (mean, 66.8 ± 9.9 years of age; 96 men), 40 (36.7%) had acute cerebral infarct. Patients with acute cerebral infarct had significantly higher signal intensity ratios of carotid intraplaque hemorrhage on T1-weighted images than those without (Median, 1.44; 25-75 Percentiles, 1.14-1.82 versus Median, 1.27; 25-75 Percentiles, 1.06-1.55, P = .022). Logistic regression analysis revealed that the signal intensity ratio of carotid intraplaque hemorrhage on T1-weighted images was significantly associated with acute cerebral infarct before (OR, 4.08; 95% CI, 1.34-12.40; P = .013) and after (OR, 3.34; 95% CI, 1.08-10.31; P = .036) adjustment for clinical confounding factors. However, this association was not significant when further adjusted for occlusion of the carotid artery (P = .058) and volumes of intraplaque hemorrhage and lipid-rich necrotic core (P = .458). The signal intensity ratio of carotid intraplaque hemorrhage on T1-weighted images is associated with acute cerebral infarct in symptomatic patients with carotid hemorrhagic plaques. This association is independent of traditional risk factors but not of the size of plaque composition. The possibility of applying T1 signals of carotid intraplaque hemorrhage to predict subsequent cerebrovascular ischemic events needs to be prospectively verified.

Processing of MRI Images Weighted in TOF for Blood Vessels Analysis: 3-D Reconstruction

In this work a novel approach based on differences of intensities is presented for vascular structures identification in MRI studies such as the time of flight method (TOF). The plating method states that given the high intensities belonging to the vascular system, TOF images can be segmented by thresholding of the histogram. The enhancement of vascular structures is performed by applying a Vesselness filter, and upon completion of a decision based on fuzzy thresholding the error is minimized in the selection of vascular structures. A brief introduction to vascular system problems and how images have helped diagnosis is summarized as well as the history of the different imaging modalities and the evolution of digital images with computers. Segmentation and 3-D reconstruction became image type time of flight; these images are typically used in medical diagnosis of cerebrovascular diseases. The proposed method has less error in segmentation and reconstruction of volumes related to the vascular system, represented in clearer images and less noise compared to edge detection methods.

Abstract WP526: Molecular Imaging of Carotid Plaques Using a Fibrin-Binding PET Probe

Objectives: We aim to develop molecular fibrin imaging as a tool to stratify high risk atherosclerotic carotid plaques. Here, we describe our results with a fibrin-specific probe [ 68 Ga]CM-246 in two different experimental settings: ex vivo imaging of carotid endarterectomy specimens and in vivo / ex vivo imaging of atherosclerotic plaque rupture in rabbits. Methods: We incubated discarded endarterectomy specimens (n=11) from asymptomatic patients with [ 68 Ga] CM-246 or a scrambled peptide control probe and measured uptake by autoradiography and a tissue binding assay. In a rabbit plaque rupture model of high cholesterol diet followed by abdominal aorta balloon injury (n=13) and subsequent pharmacological plaque rupture, in vivo and ex vivo PET-MR with [ 68 Ga]CM-246 was performed. Tissues were processed for autoradiography and histology to verify presence of fibrin and plaque rupture. Results: Autoradiography (A-B) and tissue binding assays (C) with [ 68 Ga]CM-246 with human carotid plaques show increased tissue binding compared with non-specific control probe. Carstair’s staining (D) verified the presence of fibrin in the specimens (red stained areas). Rabbits with plaque rupture had an increase in [ 68 Ga]CM-246 signal in the abdominal aorta compared with the control group. At 105-120 min post probe injection, there was a clear PET uptake on the aorta in plaque rupture rabbit (E) compared with control rabbit (F). MR images were used to differentiate abdominal aorta (green arrows) and the inferior vena cava (blue arrows). T2-dark blood images confirmed the plaques in rupture (G) and control rabbits (H). ToF images were used to visualize aortic lumen in plaque rupture (I) and control rabbits (J). Ex-vivo PET imaging, autoradiography, and histology confirmed in vivo results. Conclusions: We demonstrated that [ 68 Ga]CM-246 detects high-risk plaque in human and rabbits and can be a useful tool for the stratification of atherosclerotic plaques in patients.

Abstract 324: Molecular Imaging of High Risk Atherosclerotic Plaque Using Fibrin-Binding PET Probe

Objectives: There is a need for better stratification of atherosclerotic patients to identify individuals at high risk for a cardiovascular event. Two key hallmarks of plaque at high risk for rupture are intraplaque hemorrhage and evidence of prior rupture. The protein fibrin is strongly associated with both hemorrhage and rupture but it is not present in earlier stages of plaque development, suggesting that fibrin imaging would be sensitive for high risk plaque versus stable/early disease. Here, we describe imaging properties of a fibrin-specific PET probe for atherosclerotic plaque rupture in rabbits. Methods: Rabbits were fed with high cholesterol diet (HCD) for 8 weeks followed by 2 weeks of normal diet. Two weeks after the initiation of HCD, endothelial denudation of abdominal aorta was performed using balloon catheter. At 10 weeks, rabbits were randomly divided into plaque rupture (n=8; triggered by Russell’s viper venom and histamine) and control group (n=4), injected with fibrin-binding probe [ 68 Ga]CM-246, and scanned on a PET/MRI. Then, vessels of interest were removed for ex-vivo PET, autoradiography, and histology. Results: Rabbits with plaque rupture had &gt;2-fold increase in [ 68 Ga]CM-246 signal in the abdominal aorta compared with the control group (A). At 105-120 min post probe injection, there was a clear PET uptake on the aorta in plaque rupture rabbit (B) compared with control rabbit (C). MR images were used to differentiate abdominal aorta (green arrows) and the inferior vena cava (blue arrows). T2-dark blood images confirmed the atherosclerotic plaques in plaque rupture (D) and control rabbits (E). ToF images were used to visualize aortic lumen in plaque rupture (F) and control rabbits (G). Ex vivo PET imaging (H) and autoradiography confirmed in vivo results. Conclusions: We demonstrated that [ 68 Ga]CM-246 detects atherosclerotic plaque rupture in a rabbit model and can be a useful tool for the diagnosis of high-risk atherosclerotic plaque in patients.

Clinical Significance of Intraluminal Contrast Enhancement in Patients with Spontaneous Cervical Artery Dissection: ABlack-Blood MRI Study.

Purpose Recent studies have suggested that intraluminal thrombi show contrast enhancement on carotid black-blood T1w MRI. The aim of this study was to evaluate the significance of intraluminal contrast enhancement (iCE) regarding symptom status in patients with spontaneous cervical artery dissection (sCAD). Methods 33 consecutive patients (19 men) with sCAD received a brain MRI (DIFF, T2w, T2*w, FLAIR) and a multi-sequence 3T-MRI with fat-saturated high-resolution black-blood T1w-sequences pre- and post-contrast, contrast-enhanced MR angiography and TOF images of carotid and vertebral arteries. Presence/absence of iCE, vessel occlusion and vessel wall hematoma (hyperintense in T1w pre-contrast) were analysed by two radiologists in consensus decision. Results 44 of 132 analysed vessels had a vessel wall hematoma, consistent with sCAD. In 17 of 44 dissected vessels an acute ischemic stroke was found. 16 of 17 (94.1 %) vessels ipsilateral to ischemic stroke demonstrated iCE, compared to 9 of 44 (20.4 %) dissected vessels without stroke (P< 0.001). The presence/absence of iCE resulted ina sensitivity, specificity, positive and negative predictive value and accuracy for ischemic stroke of 0.94, 0.67, 0.64, 0.95, and 0.77, respectively, and an odds ratio of 32.0. Conclusion iCE, which is suggestive of intraluminal thrombus formation, is strongly correlated with ischemic symptoms in patients with sCAD. Key points · Intraluminal contrast enhancement is associated with cerebral ischemia in corresponding vessel territories in patients with cervical artery dissection.. · Our results suggest that intraluminal contrast enhancement represents intraluminal thrombus formation.. · Black-blood imaging might be useful to identify those patients with cervical artery dissection at higher risk for initial or recurrent stroke.. Citation Format · Coppenrath E, Lenz O, Sommer N et al. Clinical Significance of Intraluminal Contrast Enhancement in Patients with Spontaneous Cervical Artery Dissection: A Black-Blood MRI Study. Fortschr Röntgenstr 2017; 189: 624 - 631.

Prevalence and distribution of calcified nodules in carotid arteries in correlation with clinical symptoms.

Calcified nodules ("CN") are responsible for up to 5% of coronary-infarcts and, therefore, classified as minor criteria of "vulnerable" atherosclerotic plaque. We sought to evaluate prevalence and distribution of CN in carotid arteries in correlation with clinical symptoms. 178 consecutive patients with unilateral ischemic stroke and carotid plaques ≥2mm by duplex ultrasound underwent a carotid-black-blood-3T-MRI with fat-saturated pre- and post-contrast T1w-, PDw-, T2w- and TOF images using dedicated surface-coils. CN were defined as distinct calcification with an irregular, protruding, and convex luminal surface. Prevalence of CN was determined in common carotid artery ("CCA") and internal carotid artery ("ICA") in consensus by two reviewers blinded to clinical information. Thirty seven CN in 28 arteries of 26 patients were identified. Prevalence of CN in CCA compared to ICA was slightly higher (59 vs. 41%), but nearly similar in 66 arteries with ≥30% compared to 290 arteries with <30% stenosis (9.1 vs. 7.6%) and in the artery ipsilateral versus contralateral to stroke (7.9 vs. 7.9%; P values n.s.). Prevalence of CN was significantly higher in 40 symptomatic arteries with ≥30% stenosis compared to asymptomatic 26 arteries (15.6 vs. 0%; P=0.04). There was a significantly higher prevalence of hypercholesterolemia and hypertension in patients with CN (57.7 vs. 36.0 and 88.5 vs. 66.7%; P values <0.05). CN were found in 7.9% of arteries with carotid-plaques ≥2mm by duplex-ultrasound; prevalence was significantly higher in symptomatic arteries with ≥30% stenosis compared to asymptomatic with <30% stenosis, suggesting that CN play a role in pathogenesis of ischemic stroke in a small subset of patients.

Expansive arterial remodeling of the carotid arteries and its effect on atherosclerotic plaque composition and vulnerability: an in-vivo black-blood 3T CMR study in symptomatic stroke patients.

BackgroundBased on intravascular ultrasound of the coronary arteries expansive arterial remodeling is supposed to be a feature of the vulnerable atheroslerotic plaque. However, till now little is known regarding the clinical impact of expansive remodeling of carotid lesions. Therefore, we sought to evaluate the correlation of expansive arterial remodeling of the carotid arteries with atherosclerotic plaque composition and vulnerability using in-vivo Cardiovascular Magnetic Resonance (CMR).MethodsOne hundred eleven symptomatic patients (74 male/71.8 ± 10.3y) with acute unilateral ischemic stroke and carotid plaques of at least 2 mm thickness were included. All patients received a dedicated multi-sequence black-blood carotid CMR (3Tesla) of the proximal internal carotid arteries (ICA). Measurements of lumen, wall, outer wall, hemorrhage, calcification and necrotic core were determined. Each vessel-segment was classified according to American Heart Association (AHA) criteria for vulnerable plaque. A modified remodeling index (mRI) was established by dividing the average outer vessel area of the ICA segments by the lumen area measured on TOF images in a not affected reference segment at the distal ipsilateral ICA. Correlations of mRI and clinical symptoms as well as plaque morphology/vessel dimensions were evaluated.ResultsSeventy-eight percent (157/202) of all internal carotid arteries showed atherosclerotic disease with AHA Lesion-Type (LT) III or higher. The mRI of the ICA was significantly different in normal artery segments (AHA LT I; mRI 1.9) compared to atherosclerotic segments (AHA LT III-VII; mRI 2.5; p < 0.0001). Between AHA LT III-VII there was no significant difference of mRI. Significant correlations (p < 0.05) of the mRI with lumen-area (LA), wall-area (WA), vessel-area (VA) and wall-thickness (WT), necrotic-core area (NC), and ulcer-area were observed. With respect to clinical presentation (symptomatic/asymptomatic side) and luminal narrowing (stenotic/non-stenotic) no relevant correlations or significant differences regarding the mRI were found.ConclusionExpansive arterial remodeling exists in the ICA. However, no significant association between expansive arterial remodeling, stroke symptoms, complicated AHA VI plaque, and luminal stenosis could be established. Hence, results of our study suggest that expansive arterial remodeling is not a very practical marker for plaque vulnerability in the carotid arteries.

Abstract W P37: Laterality of the Posterior Cerebral Artery is Associated With a Smaller Volume of Brain Tissue at Risk in Patients With Acute Anterior Circulation Arterial Occlusion

Background: Laterality of the posterior cerebral artery (LPCA) in acute stroke has been related with a better leptomeningeal collateral circulation and with improved functional outcome at 6 months in patients treated with IV tPA. We aim to study the association between LPCA and the amount of brain tissue at risk of infarction in patients with anterior circulation arterial occlusion. Methods: From our prospective database of ischemic stroke we selected patients with anterior circulation arterial occlusion who underwent multimodal MRI &lt; 12h of symptom onset. We considered LPCA when the following criteria were accomplished: a) ipsilateral PCA to the occlusion site was extended in 1 or more segments compared to the contralateral PCA and b) ipsilateral P4 segment was visible on axial TOF images. Two independent readers blinded to clinical data retrospectively assessed the presence of LPCA (k=0.65). We analyzed the association between LPCA and the volume of ischemic penumbra at baseline (Tmax&gt;6s) and the final infarct volume (CT 24h). Good outcome was defined as mRS ≤ 2 at 90 days. Results: Seventy-two patients were included in the study (mean age 67y, 45% male). LPCA was present in 39 (54.1%). There were no differences between groups with or without LPCA, except a lower baseline NIHSS in the LPCA group (15 vs 19; p=0.003). Proportion of patients treated with reperfusion therapies was similar between groups. Patients with LPCA had a smaller lesion in Tmax&gt;6s (54 vs 79cc; p=0.02), smaller final infarct volume (47 vs 111cc; p=0.013), and higher proportion of good outcome (52.8% vs 27.3%; p=0.03). In a multivariate analysis, LPCA was independently associated with smaller lesion volume on Tmax&gt;6s (B -18, IC95% [-36,-0.3]), smaller final infarct volume (B -64.8, IC95% [-100,-29]) and better clinical outcome (OR 4.66, IC95% [1.04,20.8]). Conclusion: LPCA sign in patients with anterior circulation arterial occlusion is associated with smaller volume of brain tissue at risk resulting in smaller infarct volume and better clinical outcome. These findings suggest favorable leptomeningeal collaterals.

Comparison of 3D TOF-MRA and 3D CE-MRA at 3 T for imaging of intracranial aneurysms

PurposeTo compare 3T elliptical-centric CE MRA with 3T TOF MRA for the detection and characterization of unruptured intracranial aneurysms (UIAs), by using digital subtracted angiography (DSA) as reference. Materials and methodsTwenty-nine patients (12 male, 17 female; mean age: 62 years) with 41 aneurysms (34 saccular, 7 fusiform; mean diameter: 8.85mm [range 2.0–26.4mm]) were evaluated with MRA at 3T each underwent 3D TOF-MRA examination without contrast and then a 3D contrast-enhanced (CE-MRA) examination with 0.1mmol/kg bodyweight gadobenate dimeglumine and k-space elliptic mapping (Contrast ENhanced Timing Robust Angiography [CENTRA]). Both TOF and CE-MRA images were used to evaluate morphologic features that impact the risk of rupture and the selection of a treatment. Almost half (20/41) of UIAs were located in the internal carotid artery, 7 in the anterior communicating artery, 9 in the middle cerebral artery and 4 in the vertebro-basilar arterial system.All patients also underwent DSA before or after the MR examination. ResultsThe CE-MRA results were in all cases consistent with the DSA dataset. No differences were noted between 3D TOF-MRA and CE-MRA concerning the detection and location of the 41 aneurysms or visualization of the parental artery. Differences were apparent concerning the visualization of morphologic features, especially for large aneurysms (>13mm). An irregular sac shape was demonstrated for 21 aneurysms on CE-MRA but only 13/21 aneurysms on 3D TOF-MRA. Likewise, CE-MRA permitted visualization of an aneurismal neck and calculation of the sac/neck ratio for all 34 aneurysms with a neck demonstrated at DSA. Conversely, a neck was visible for only 24/34 aneurysms at 3D TOF-MRA. 3D CE-MRA detected 15 aneurysms with branches originating from the sac and/or neck, whereas branches were recognized in only 12/15 aneurysms at 3D TOF-MRA. ConclusionFor evaluation of intracranial aneurysms at 3T, 3D CE-MRA is superior to 3D TOF-MRA for assessment of sac shape, detection of aneurysmal neck, and visualization of branches originating from the sac or neck itself, if the size of the aneurysm is greater than 13mm. 3T 3D CE-MRA is as accurate and effective as DSA for the evaluation of UIAs.

Image quality improvement in three-dimensional time-of-flight magnetic resonance angiography using the subtraction method for brain and temporal bone diseases

BackgroundTime-of-flight (TOF) magnetic resonance (MR) angiography is based on flow-related enhancement using the T1-weighted spoiled gradient echo, or the fast low-angle shot gradient echo sequence. However, materials with short T1 relaxation times may show hyperintensity signals and contaminate the TOF images. The objective of our study was to determine whether subtraction three-dimensional (3D) TOF MR angiography improves image quality in brain and temporal bone diseases with unwanted contaminations with short T1 relaxation times. MethodsDuring the 12-month study period, patients who had masses with short T1 relaxation times noted on precontrast T1-weighted brain MR images and 24 healthy volunteers were scanned using conventional and subtraction 3D TOF MR angiography. The qualitative evaluation of each MR angiogram was based on signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and scores in three categories, namely, (1) presence of misregistration artifacts, (2) ability to display arterial anatomy selectively (without contamination by materials with short T1 relaxation times), and (3) arterial flow-related enhancement. ResultsWe included 12 patients with intracranial hematomas, brain tumors, or middle-ear cholesterol granulomas. Subtraction 3D TOF MR angiography yielded higher CNRs between the area of the basilar artery (BA) and normal-appearing parenchyma of the brain and lower SNRs in the area of the BA compared with the conventional technique (147.7 ± 77.6 vs. 130.6 ± 54.2, p < 0.003 and 162.5 ± 79.9 vs. 194.3 ± 62.3, p < 0.001, respectively) in all 36 cases. The 3D subtraction angiography did not deteriorate image quality with misregistration artifacts and showed a better selective display of arteries (p < 0.0001) and arterial flow-related enhancement (p < 0.044) than the conventional method. ConclusionSubtraction 3D TOF MR angiography is more appropriate than the conventional method in improving the image quality in brain and temporal bone diseases with unwanted contaminations with short T1 relaxation times.

237 IN-VIVO QUANTITATIVE T2 MAPPING OF CAROTID PLAQUES IN PATIENTS WITH RECENT CEREBROVASCULAR EVENTS: AHA PLAQUE TYPE CLASSIFICATION AND CORRELATION WITH PLAQUE HISTOLOGY

<h3>Introduction</h3> Although in-vivo multicontrast MRI is capable of characterizing atherosclerotic plaques in carotid arteries, its non-quantitative nature and the need for extensive post-acquisition interpretation limit its widespread clinical application. Quantitative T2 mapping is a promising alternative since it can provide an absolute physical measure of plaque components that can be standardised among different MRI systems and widely adopted in multi-centre studies. The purpose of this pilot study is to seek the potential of in-vivo T2 mapping and its correlation with different plaque components <i>ex-vivo</i> on histology. <h3>Methods</h3> <i>3T-MRI</i>: 15 asymptomatic patients (11 males, 71±10 years) and 13 patients scheduled for endarterectomy (9 males, 70±17 years) were imaged at 3T using the conventional multicontrast protocol and Multiple-Spin-Echo (Multi-SE). T2 maps were generated by mono-exponential fitting to the series of images acquired by Multi-SE using non-linear least-squares regression. Two reviewers independently classified plaque types according to the MRI-modified AHA scheme, one using T2 maps+TOF images, the other using multicontrast MRI. <h3>Histology</h3> Carotid plaques were freshly obtained at time of endarterectomy. Plaques were divided at the level of maximal stenosis and 4mm-segments on either side of the cut were processed for formalin-fixed, paraffin-embedded (FFPE) sections and cryosections, respectively. FFPE sections were stained for H&amp;E and Masson’s trichrome, while cryosections were used for Oil-Red-O/adipophilin (foam cells marker) staining to visualize lipid. MRI-histology matching was performed for each segment using the carotid bifurcation as the common anatomical landmark. AHA plaque type was determined by an independent reviewer. <h3>Results</h3> In the 15 asymptomatic patients, AHA plaque type classified on multicontrast MRI and on T2 maps (+TOF) showed good agreement (76% of matching classifications and Cohen’s κ=0.68). 4 of the 13 patients scheduled for endarterectomy were excluded due to severe MRI motion artefacts. AHA type classification of the remaining 9 plaques using T2 maps (+TOF) vs. histology is presented in Table&nbsp;1. Figure&nbsp;1 shows a type VI and Figure&nbsp;2 a type IV-V plaque. T2 maps were able to differentiate lipid-rich necrotic core (LRNC), fibrous tissue, calcification, and recent intraplaque-haemorrhage (IPH). <h3>Conslusions</h3> These preliminary results show the potential of in-vivo T2 mapping for atherosclerotic plaque characterization. Agreement between AHA plaque types classified by T2 maps (+TOF) and by conventional multicontrast MRI was good. The ability of T2 maps to discriminate LRNC, fibrous tissue and recent IPH was confirmed by histology. Further prospective quantitative validation study is now underway.

Development of a high-speed camera system for neutron imaging at a pulsed neutron source

A neutron energy resolved imaging system with a time-of-flight technique has been newly developed and installed at Japan Proton Accelerator Research Complex (J-PARC) with the aim to investigate more preciously and rapidly a spatial distribution of several elements and crystals in various kinds of materials or substances. A high-speed video camera (CMOS, 1300k frame/s) equipped system allows to obtain TOF images consecutively resolved into narrow energy ranges with a single pulsed neutrons while conventional CCD camera imaging system could obtain only one TOF image in an arbitral neutron energy region in the pulsed neutron energy region from 0.01eV to a few keV. Qualities of the images obtained with the system, such as spatial resolution (defined by modulation transfer function, 0.8 line-pairs/mm at En∼0.01eV), dependence of the brightness on the neutron energy and measurement errors (∼2%) of the system were examined experimentally and evaluated by comparison with those of conventional imaging system. The results obtained in the experiments show that the system can visualize the neutron energy resolved images within a small error even at high speed.

High-resolution TOF MR angiography at 4.7 Tesla for volumetric and morphologic evaluation of coiled aneurysm neck remnants in a rat model

Detection of morphologic and volumetric changes in aneurysm necks is important when evaluating the effects of endovascular devices for aneurysm occlusion. To optimize high-resolution 3D-TOF MRA at 4.7 T in order to achieve the best aneurysm-to-background contrast in experimental rat aneurysms, and to quantify the volume of the aneurysm neck by imaging. Saccular aneurysms in the abdominal aorta of rats were coiled with platinum coils. Tissue relaxation times were measured, and used in a mathematical simulation. To optimize 3D-TOF angiography, imaging parameters were varied within the range obtained from the simulations. Tissue contrast and contrast-to-noise ratio were measured from MR images. TOF images were compared to conventional spin echo and gradient echo images and to endoscopic and histological analyses. Parameters yielding the best aneurysm-to-background contrast and contrast-to-noise ratio were determined. The agreement between the results from in vivo imaging and simulation was good. The optimized 3D-TOF MRA sequence (TR/TE/FA = 60 ms/6.6 ms/20°) had an isotropic voxel size of 117 µm, which enabled measurement of the aneurysm neck volume. High-resolution 3D-TOF angiography enables non-invasive quantification of changes in neck remnants of endovascularly coiled experimental aneurysms. In this model innovations like bioactive coils can be accurately tested for their efficacy for aneurysm occlusion.