Three-dimensional Time-of-flight Research Articles

Transition of intracranial aneurysmal wall enhancement from high to low wall shear stress mediation with size increase: A hemodynamic study based on 7T magnetic resonance imaging

BackgroundWall shear stress (WSS) has been proved to be related to the formation, development and rupture of intracranial aneurysms. Aneurysm wall enhancement (AWE) on magnetic resonance imaging (MRI) can be caused by inflammation and have confirmed its relationship with low WSS. High WSS can also result in inflammation but the research of its correlation with AWE is lack because of the focus on large aneurysms limited by 3T MRI in most previous studies.This study aimed to assess the potential association between high or low WSS and AWE in different aneuryms. Especially the relationship between high WSS and AWE in small aneurysm. MethodsForty-three unruptured intracranial aneurysms in 42 patients were prospectively included for analysis. 7.0 T MRI was used for imaging. Aneurysm size was measured on three-dimensional time-of-flight (TOF) images. Aneurysm-to-pituitary stalk contrast ratio (CRstalk) was calculated on post-contrast black-blood T1-weighted fast spin echo sequence images. Hemodynamics were assessed by four-dimensional flow MRI. ResultsThe small aneurysms group had more positive WSS–CRstalk correlation coefficient distribution (dome: 78.6 %, p = 0.009; body: 50.0 %, p = 0.025), and large group had more negative coefficient distribution (dome: 44.8 %, p = 0.001; body: 69.0 %, p = 0.002). Aneurysm size was positively correlated with the significant OSI–CRstalk correlation coefficient at the dome (p = 0.012) and body (p = 0.010) but negatively correlated with the significant WSS–CRstalk correlation coefficient at the dome (p < 0.001) and body (p = 0.017). ConclusionAWE can be mediated by both high and low WSS, and translate from high WSS- to low WSS-mediated pathways as size increase. Additionally, AWE may serve as an indicator of the stage of aneurysm development via different correlations with hemodynamic factors.

Simultaneous time-of-flight MR angiography and quantitative susceptibility mapping with key time-of-flight features.

A technique for combined time-of-flight (TOF) MR angiography (MRA) and quantitative susceptibility mapping (QSM) was developed with key features of standard three-dimensional (3D) TOF acquisitions, including multiple overlapping thin slab acquisition (MOTSA), ramped RF excitation, and venous saturation. The developed triple-echo 3D TOF-QSM sequence enabled TOF-MRA, susceptibility-weighted imaging (SWI), QSM, and R2* mapping. The effects of ramped RF, resolution, flip angle, venous saturation, and MOTSA were studied on QSM. Six volunteers were scanned at 3 T with the developed sequence, conventional TOF-MRA, and conventional SWI. Quantitative comparison of susceptibility values on QSM and normalized arterial and venous vessel-to-background contrasts on TOF and SWI were performed. The ramped RF excitation created an inherent phase variation in the raw phase. A generic correction factor was computed to remove the phase variation to obtain QSM without artifacts from the TOF-QSM sequence. No statistically significant difference was observed between the developed and standard QSM sequence for susceptibility values. However, maintaining standard TOF features led to compromises in signal-to-noise ratio for QSM and SWI, arising from the use of MOTSA rather than one large 3D slab, higher TOF spatial resolution, increased TOF background suppression due to larger flip angles, and reduced venous signal from venous saturation. In terms of vessel contrast, veins showed higher normalized contrast on SWI derived from TOF-QSM than the standard SWI sequence. While fast flowing arteries had reduced contrast compared with standard TOF-MRA, no statistical difference was observed for slow flowing arteries. Arterial contrast differences largely arise from the longer TR used in TOF-QSM over standard TOF-MRA to accommodate additional later echoes for SWI. In conclusion, although the sequence has a longer TR and slightly lower arterial contrast, provided an adequate correction is made for ramped RF excitation effects on phase, QSM may be performed from a multiecho sequence that includes all key TOF features, thus enabling simultaneous TOF-MRA, SWI, QSM, and R2* map computation.

Intraluminal arterial transit artifact as a predictor of intracranial large artery stenosis on 3D time of flight MR angiography: Expanding the application of arterial spin labeling MRI in ischemic stroke.

The objective of this study was to evaluate the diagnostic value of "intraluminal arterial transit artifact" in the prediction of intracranial large artery stenosis and to determine if this finding is predictive of ischemic stroke in the territory of the involved artery. The presence of arterial transit artifact (ATA) within the lumen of an intracranial large vessel was noted on three-dimensional time of flight (3D-TOF) magnetic resonance angiography (MRA) (ATA group). The patients with stenosis but with no ATA (no-ATA group), patients with total occlusion (total occlusion group), and patients with no stenosis/occlusion (normal group) were included in the analysis. There were four groups of patients included in the final analysis, the ATA group (n = 22), the no-ATA group (n = 23), the normal group (n = 25), and the total occlusion group (n = 9). Among patients with any demonstrable stenosis (n = 45), the presence of ATA within the stenotic segment was predictive of stenosis of ≥56% (Sensitivity of 100% [85.2-100, 95% CI], specificity of 100% [86.4-100, 95% CI]), with area under curve of 1.0 (0.92-.0, 95% CI). The presence of intra-arterial ATA signal was significantly associated with ischemic stroke as compared with the no-ATA group (86.36% vs. 26.08%, P = 0.0003). Intraluminal ATA was found to be an independent predictor of infarction in the territory of the involved artery. Intraluminal ATA is predictive of stenosis of at least 56% in the involved artery on 3D-TOF MRA. Intraluminal ATA sign may be an independent predictor of infarction in the territory of the involved artery.

Comparison of Carotid Plaque Characteristics Between Men and Women Using Magnetic Resonance Vessel Wall Imaging: A Chinese Atherosclerosis Risk Evaluation Study.

Carotid vulnerable plaque is a major cause of stroke and differs between men and women. Few studies have investigated the differences in carotid plaque features between sexes in a Chinese population. To compare carotid atherosclerotic plaque features between men and women in a Chinese population using magnetic resonance imaging. Cross-sectional. A total of 567 patients (mean age: 61.5 ± 10.1 years; 404 men) who had recent stroke or transient ischemia attack and atherosclerotic plaque in at least one carotid artery. A 3.0 T. T1- and T2-weighted turbo spin echo, three-dimensional time-of-flight (TOF) fast field echo and magnetization-prepared rapid acquisition gradient echo sequences. Plaque characteristics including lumen area (LA), wall area (WA), total vessel area (TVA), mean wall thickness (MWT), and mean normalized wall index (NWI); presence of calcification, lipid-rich necrotic core (LRNC), intraplaque hemorrhage (IPH), and fibrous cap rupture (FCR); and percent composition area (%area) were evaluated and compared between men and women. Independent-sample t test, Mann-Whitney U test, chi-square test, and multiple linear and logistic regressions. In symptomatic arteries, men had significantly greater LA (46.2 ± 15.6 mm2 vs. 40.7 ± 12.9 mm2 , P < 0.05), WA (33.9 ± 11.5 mm2 vs. 26.3 ± 7.5 mm2 , P < 0.05), and TVA (80.1 ± 20.4 mm2 vs. 67.0 ± 18.0 mm2 , P < 0.05); higher MWT (1.2 ± 0.4 mm vs. 1.0 ± 0.2 mm, P < 0.05); and higher prevalence of LRNC (72.3% vs. 46.0%, P < 0.05) and IPH (18.6% vs. 4.9%, P < 0.05) compared with women. In asymptomatic arteries, men had significantly greater LA (48.3 ± 16.9 mm2 vs. 42.1 ± 12.6 mm2 , P < 0.05), WA (32.9 ± 11.0 mm2 vs. 25.8 ± 6.1 mm2 , P < 0.05), and TVA (81.2 ± 22.1 mm2 vs. 67.9 ± 16.5 mm2 , P < 0.05); higher MWT (1.2 ± 0.3 mm vs. 1.0 ± 0.2 mm, P < 0.05); higher prevalence of LRNC (67.8% vs. 42.9%, P < 0.05), IPH (14.9% vs. 1.2%, P < 0.05), and FCR (6.4% vs. 1.2%, P < 0.05); and higher %LRNC area (24.8 ± 17.2% vs. 17.8 ± 14.1%, P < 0.05) compared with women. Men have similar plaque burden but more vulnerable atherosclerotic plaques compared with women in both symptomatic and asymptomatic carotid arteries in a Chinese population. 4 TECHNICAL EFFICACY: Stage 3.

Segmentation of Cerebrovascular Anatomy from TOF-MRA Using Length-Strained Enhancement and Random Walker.

Cerebrovascular rupture can cause a severe stroke. Three-dimensional time-of-flight (TOF) magnetic resonance angiography (MRA) is a common method of obtaining vascular information. This work proposes a fully automated segmentation method for extracting the vascular anatomy from TOF-MRA. The steps of the method are as follows. First, the brain is extracted on the basis of regional growth and path planning. Next, the brain's highlighted connected area is explored to obtain seed point information, and the Hessian matrix is used to enhance the contrast of image. Finally, a random walker combined with seed points and enhanced images is used to complete vascular anatomy segmentation. The method is tested using 12 sets of data and compared with two traditional vascular segmentation methods. Results show that the described method obtains an average Dice coefficient of 90.68%, and better results were obtained in comparison with the traditional methods.

Tertiary electrons in single-event time-of-flight Rutherford backscattering spectrometry

An effect of sample bias voltage on analysis time and time resolution of a single-event three-dimensional time-of-flight (ToF) Rutherford backscattering spectrometry (RBS) was evaluated with both experiment and simulation. Fluctuations of trajectories of secondary electrons were suppressed by positive sample bias voltage and most of the secondary electrons were collected by a secondary electron detector, resulting in short analysis-time and high time-resolution in the single-event three-dimensional ToF-RBS. On the contrary, negative sample bias voltage induced tertiary electrons at a focused ion beam (FIB) column by incident of the secondary electrons which accelerated by an electric field between the sample and the FIB column. The tertiary electrons improve analysis time, but deteriorate time resolution in the single-event three-dimensional ToF-RBS with negative sample bias voltage.

Variation in Calibre of Arteries of Circle of Willis with Age: An MRA Based Study

Objective: To establish reference range for the diameters of arteries forming the Circle of Willis (CoW) and to correlate it with age.&#x0D; Methods: This cross-sectional study was conducted at the Radiology Department from January to July 2018. It comprises of patients referred for MR imaging of brain without any manifestation of cere- brovascular diseases. Patients who were claustrophobic or had a history of atherosclerosis, vasculi- tis, thrombus, aneurysm, arteriovenous malformation (AVM), intracranial tumour, diabetes and hypertension were excluded. 300 individuals comprising both males and females with mean age of 45 ± 11.6 (years) were recruited via non-probability sampling technique. Three-dimensional Time of Flight (TOF) Magnetic Resonance Angiography (MRA) was performed. Diameters of all component vessels forming the Circle of Willis were measured.&#x0D; Results: The diameter of the anterior cerebral, anterior communicating, internal carotid, posterior communicating, posterior cerebral and basilar arteries were found to be 1.51 ± 0.28 mm, 1.05 ± 0.37 mm, 3.69 ± 0.23 mm, 1.10 ± 0.11 mm, 1.85 ± 0.23 mm, 3.00 ± 0.11 mm respectively. Spearman correlation demonstrated that the diameters of the arteries were significantly correlated with age in different ways. Significant moderate positive correlations of internal carotid and basilar artery diameters were seen with age. Significant weak negative correlations were seen in anterior and posterior cerebral arteries. Significant very weak negative correlations were seen in anterior and posterior commu- nicating artery diameters and age.&#x0D; Conclusion: The normal reference values for vessels diameter of CoW were determined in general population living in Karachi. Diameter of the arteries showed statistically significant correlation with age in different ways. Knowledge of calibre of the arteries is helpful in cerebrovascular surgeries and radiological neuro interventions.

Accelerated Time-of-Flight Magnetic Resonance Angiography with Sparse Undersampling and Iterative Reconstruction for the Evaluation of Intracranial Arteries

ObjectiveTo compare the image quality of three-dimensional time-of-flight (TOF) magnetic resonance angiography (MRA) with sparse undersampling and iterative reconstruction (sparse TOF) with that of conventional TOF MRA.Materials and MethodsThis study included 56 patients who had undergone sparse TOF MRA for intracranial artery evaluation on a 3T MR scanner. Conventional TOF MRA scans were also acquired from 29 patients with matched acquisition times and another 27 patients with matched scanning parameters. The image quality was scored using a five-point scale based on the delineation of arterial vessel segments, artifacts, overall vessel visualization, and overall image quality by two radiologists independently, and the data were analyzed using the non-parametric Wilcoxon signed-rank test. Contrast ratios (CRs) of vessels were compared using the paired t test. Interobserver agreement was calculated using the kappa test.ResultsCompared with conventional TOF at the same spatial resolution, sparse TOF with an acceleration factor of 3.5 could reduce acquisition time by 40% and showed comparable image quality. In addition, when compared with conventional TOF with the same acquisition time, sparse TOF with an acceleration factor of 5 could also achieve higher spatial resolution, better delineation of vessel segments, fewer artifacts, higher image quality, and a higher CR (p < 0.05). Good-to-excellent interobserver agreement (κ: 0.65–1.00) was obtained between the two radiologists.ConclusionCompared with conventional TOF, sparse TOF can achieve equivalent image quality in a reduced duration. Furthermore, using the same acquisition time, sparse TOF could improve the delineation of vessels and decrease image artifacts.

Usefulness of the Principle of Selective Excitation Technique Non-electrocardiogramgated 3D-TOF Method in Lower-extremity MRA Using a Whole-body Coil

Generally, non-contrast, lower-extremity, magnetic resonance angiography (MRA) uses electrocardiography; thus, examination is difficult in patients who exhibit arrhythmia. However, the use of electrocardiography can be avoided by using the selective excitation technique in non-electrocardiogram-gated three-dimensional time-of-flight (TOF) (pNon-Gate) MRA. Therefore, patients who exhibit arrhythmia can be examined with pNon-Gate MRA. The purpose of this study was to assess the usefulness of pNon-Gate MRA by using a whole-body coil. Images acquired using pNon-Gate MRA were compared with images acquired using electrocardiogram-gated two-dimensional TOF (Gate) MRA. Comparisons comprised visual evaluation, as well as comparisons of contrast-to-noise ratio and imaging time. In visual evaluation of the pelvic region, Gate MRA showed better results than pNon-Gate MRA. In terms of contrast-to-noise ratio, there were no significant differences in either region. Imaging time showed no significant differences between the two methods. However, it exceeded 30 minutes frequently for Gate MRA, but rarely for pNon-Gate MRA. pNon-Gate MRA is useful in patients with frequent arrhythmia and in those with difficulty in maintaining long-term postures. By using a whole-body coil, pNon-Gate MRA enables easier patient positioning and setting. Therefore, pNon-Gate MRA can be used in routine examinations.

Circle of Willis variations and artery diameter measurements in the Turkish population.

The aim of this study was to evaluate the frequency of circle of Willis (COW) variations and the measurements of the COW vessel diameters in the Turkish population. The patient population for this single-centre, retrospective study was formed of patients who had brain magnetic resonance angiography (MRA). A total of 384 subjects were included in the study. The three-dimensional time-of-flight (TOF) technique was used for MRA imaging to evaluate the anatomy of the COW. Variations in the COW were recorded. The diameters of the critical arteries of the COW were measured. Adult configuration of the COW was determined in 326 (85%) cases, foetal configuration in 50 (13%) cases and transitional configuration in 8 (2%) cases. The COW was normal in 328 (85.4%). In the remaining 56 (14.6%) cases, agenesis was determined in 62 vessels. The mean calibrations of the vessels were measured as 2.85 mm in the basilar artery, 4.24 mm in the right internal carotid artery (ICA), 4.32 mm in the left ICA, 1.58 mm in the right A1, 1.64 mm in the left A1, 2.13 mm in the right M1, 2.10 mm in the left M1, 1.80 mm in the right P1, 1.88 mm in the left P1, 1.12 mm in the right posterior communicating artery, and 1.12 mm in the left posterior communicating artery. Circle of Willis variations may show geographic and ethnic differences. Knowledge of the frequency and types of variation in the population is important for neurosurgeons and in radiological interventional procedures as a guide for entry and in respect of collateral which could develop later.

Super-resolution intracranial quiescent interval slice-selective magnetic resonance angiography.

To evaluate the combination of nonenhanced quiescent-interval slice-selective (QISS) magnetic resonance angiography (MRA) with super-resolution reconstruction for portraying the intracranial arteries. The intracranial arteries of seven volunteers were imaged at 3T using QISS MRA acquired with a flow-compensated fast low-angle shot (FLASH) readout and thin overlapping slices. The impacts of super-resolution reconstruction and various acquisition parameters on the delineation of intracranial arteries were quantified using four metrics: arterial-to-background contrast-to-noise ratio (CNR), arterial-to-background contrast, arterial sharpness, and arterial full-width-at-half-maximum (FWHM). Three-dimensional time-of-flight (TOF) MRA was also acquired. For similar voxel sizes, QISS MRA displayed the intracranial arteries with an arterial-to-background contrast that exceeded 3D TOF MRA by 59-84%, depending on the k-space sampling trajectory (P < 0.001). Super-resolution reconstruction improved CNR, contrast, and sharpness, while reducing arterial FWHM (P < 0.001). Cardiac triggering provided minimal benefits, while Cartesian sampling provided higher CNR than radial sampling for multishot QISS (P < 0.05). Scan time for a complete intracranial MRA was <90 s using an ungated single-shot QISS acquisition. Thin, overlapping-slice QISS leveraging super-resolution reconstruction is a flexible approach for intracranial MRA that provides competitive image quality to standard-of-care 3D TOF, with the potential for reduced sensitivity to in-plane flow saturation and motion artifacts. Magn Reson Med 79:683-691, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Subarachnoid Hemorrhage in Patients with Good Clinical Grade: Accuracy of 3.0-T MR Angiography for Detection and Characterization.

Purpose To evaluate the diagnostic accuracy of aneurysm detection and the fidelity of morphologic characterization of three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography at 3.0 T in patients with a Glasgow coma score of 15 and noncontrast material-enhanced computed tomography (CT) findings that showed acute nontraumatic subarachnoid hemorrhage. Materials and Methods The institutional review board approved this prospective study, and patients provided informed consent. A total of 277 patients who had not experienced trauma but in whom nonenhanced CT showed subarachnoid hemorrhage, who had a Glasgow coma score of 15, and who underwent both 3D TOF MR angiography and digital subtraction angiography (DSA) (the reference standard) were included. Three observers who were blinded to clinical and DSA results independently analyzed all 3D TOF MR angiographic data sets. The receiver operating characteristic curve was applied to analysis of the detection of aneurysms with 3D TOF MR angiography by using patient- and aneurysm-based evaluations. Multivariate logistic regression analysis was performed to identify aneurysm-specific variables, including size, shape (daughter sac/lobulation/margin), neck width (wide if > 4 mm or if fundus-to-neck ratio was < 2), and relation to adjacent artery, that significantly affected morphologic assessment with 3D TOF MR angiography. Results Aneurysms were depicted with DSA in 225 patients. In patient- and aneurysm-based evaluations, respectively, 3D TOF MR angiography yielded accuracies of 96.8% (268 of 277) and 96.6% (309 of 320), sensitivities of 98.2% (219 of 223) and 98.1% (260 of 265), specificities of 91% (49 of 54) and 89% (49 of 55), positive predictive values of 97.8% (219 of 224) and 97.7% (260 of 266), and negative predictive values of 92% (49 of 53) and 91% (49 of 54). Accuracy of display of morphologic features was 92.5% (236 of 255) for size, 86.3% (220 of 255) for neck width, 94.5% for shape (241 of 255), and 96.9% (247 of 255) for relationship to adjacent vessel. Width of aneurysm neck was the only variable that significantly affected the morphologic assessment of 3D TOF MR angiography (odds ratio, 0.378; 95% confidence interval: 0.337, 8.347; P = .004). Conclusion Three-dimensional TOF MR angiography can accurately depict cerebral aneurysms and accurately display their morphologic features in stable patients with subarachnoid hemorrhage and a Glasgow coma score of 15. © RSNA, 2017.

Abstract TMP33: High Intensity Signal in the Plaque on 3DTOF MRA is Associated With Ischemic Stroke in the Patients With Low Grade Carotid Artery Stenosis

Background: Carotid artery stenosis is one of the major causes of ischemic strokes. However, degree of stenosis is not always correlated with frequency of ischemic strokes. Recently, it was reported that carotid intraplaque hemorrhage (IPH) was associated with accelerated plaque growth, luminal narrowing and development of symptomatic events. Maximum intensity projection (MIP) images are easily reformatted within from 5 minute, routine time-of-flight (TOF) sequences. The aim of this study was to evaluate the relationships between high intensity signal (HIS) in the carotid plaques on MIP images detected by routine three-dimensional TOF magnetic resonance angiography (3D-TOF MRA) and ischemic strokes. Materials and Methods: One hundred fifty two patients with low-grade carotid artery stenosis (North American Symptomatic Carotid Endarterectomy Trial criteria: 30% - 49%) were included. IPH was defined as the presence of HIS in the carotid plaques on MIP images of 3D-TOF MRA using the previously reported criteria. We analyzed the relationship between the presence of HIS in the plaques and prior ischemic strokes defined as ischemic lesions on diffusion weighed images of the brain. Results: HIS in the carotid plaque was present in 56 (37%) of 152 carotid arteries. Prior ipsilateral ischemic strokes were observed more frequently in HIS-positive group (12 of 56, 21.4%) than HIS-negative group (1 of 34: 2.9%) [p&lt;0.001]. In multivariate logistic regression analysis, HIS (Odds ratio: 77.7, 95%CI: 6.4 - 944.0, p&lt;0.001) and diabetes mellitus type 2 (odds ratio: 10.45, 95%CI: 1.6 - 67.9, p=0.014) were independent determinants of prior ischemic strokes after adjustment for age. Conclusions: HIS in the carotid plaques on MIP images of 3D-TOF MRA was an independent determinant of prior ischemic stroke in patients with low-grade carotid artery stenosis, and this finding may provide a reliable risk stratification of future stroke in patients with low-grade carotid artery stenosis.

Conventional T2-Weighted Imaging to Detect High-Grade Stenosis and Occlusion of Internal Carotid Artery, Vertebral Artery, and Basilar Artery

To evaluate the reliability of conventional T2-weighted imaging (WI) for detecting high-grade stenosis and occlusion of cerebral arteries by disappearance of artery flow void signals. Our hospital's neuroimaging data on patients with ischemic stroke or transient ischemic attack were collected, including only those from patients who underwent both conventional brain T2WI and three-dimensional time-of flight magnetic resonance angiography (3D-TOF MRA). Flow void signals of conventional axial T2WI were analyzed by 2 young neurologists and compared with 3D-TOF MRA as the gold standard to determine the specificity for detection of high-grade stenosis and occlusion of cerebral arteries. Interobserver agreement was evaluated by calculating kappa (κ) coefficients. Of the 1765 patients included, disappearance of flow void signals was detected in 445 major cerebral arteries in 320 patients on conventional axial T2WI. The specificity of disappearance of flow void signal for the diagnosis of high-grade stenosis and occlusion was 94% for internal carotid arteries, 96.2% for vertebral arteries, and 92% for basilar arteries. K coefficients were greater than .94 for all arteries. Disappearance of flow void signal on conventional axial T2WI is a reliable indicator of high-grade stenosis or occlusion of major cerebral arteries. Conventional axial T2WI is a useful tool in the diagnosis of cerebral artery steno-occlusive disease.

Improvement of depth resolution and detection efficiency by control of secondary-electrons in single-event three-dimensional time-of-flight Rutherford backscattering spectrometry

An improvement of a depth resolution and a detection efficiency in single-event three-dimensional time-of-flight (TOF) Rutherford backscattering spectrometry (RBS) is discussed on both simulation and experiment by control of secondary electron trajectories using sample bias voltage. The secondary electron, used for a start signal in single-event TOF-RBS, flies more directly to a secondary electron detector with the positive sample bias voltage of several tens of volt than that without sample bias voltage in the simulation. The simulated collection efficiency of the secondary electrons also increases with the positive sample bias voltage of several tens of volt. These simulation results indicate the possibility of a smaller depth resolution and a shorter measurement time in single-event TOF-RBS with positive sample bias voltage. The measurement time for the Pt-stripe sample using single-event three-dimensional TOF-RBS with the sample bias voltage of +100V is 65% shorter than that without sample bias voltage, resulting in a less sample damage by a probe beam. The depth resolution for the Pt stripes under the 50-nm-thick SiO2 cover-layer with the sample bias voltage of +100V is 4nm smaller than that without sample bias voltage. Positive sample bias voltage improves the depth resolution and the detection efficiency in single-event three-dimensional TOF-RBS without an influence on the beam focusing.

3D-FIESTA Magnetic Resonance Angiography Fusion Imaging of Distal Segment of Occluded Middle Cerebral Artery.

Middle cerebral artery (MCA) occlusion was examined with basi-parallel anatomical scanning (BPAS) using three-dimensional fast imaging employing steady-state acquisition (3D-FIESTA), and 3D-FIESTA and magnetic resonance angiography (MRA) fusion images were created. We expected that an incidence of hemorrhagic complications due to vessel perforations would be decreased by obtaining vascular information beyond the occlusion and thus acute endovascular revascularization could be performed using such techniques. We performed revascularization for acute MCA occlusion for five patients who were admitted in our hospital from October 2012 to October 2014. Patients consisted of 1 man and 4 women with a mean age of 76.2 years (range: 59–86 years). Fusion images were created from three-dimensional time of flight (3D-TOF) MRA and 3D-FIESTA with phase cycling (3D-FIESTA-C). Then thrombectomy was performed in all the 5 patients. Merci retriever to 1 patient, Penumbra system to 1, urokinase infusion to 2, and Solitaire to 1 using such techniques. In all cases, a 3D-FIESTA-MRA fusion imaging could depict approximately clear vascular information to at least the M3 segment beyond the occlusion. And each acute revascularization was able to perform smoothly using these imaging techniques. In all cases, there was no symptomatic hemorrhagic complication. It showed that 3D-FIESTA MRA fusion imaging technique could obtain vascular information beyond the MCA occlusion. In this study, no symptomatic hemorrhagic complications were detected. It could imply that such techniques were useful not only to improve treatment efficiency but also to reduce the risk of development of hemorrhagic complications caused by vessel perforations in acute revascularization.

Accurate Diagnosis of Small Cerebral Aneurysms ≤5 mm in Diameter with 3.0-T MR Angiography

To evaluate the diagnostic accuracy of three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography at 3.0 T in the detection of small cerebral aneurysms. The institutional review board approved the study protocol, and patients or qualifying family members provided informed consent. A total of 403 consecutive patients undergoing 3D TOF MR angiography and digital subtraction angiography (DSA) were prospectively enrolled. Small aneurysms were those 5 mm in diameter or smaller. DSA served as the reference standard. Three observers were blinded to clinical and DSA results, and they independently analyzed all 3D TOF MR angiographic data sets. Interobserver agreement was expressed in terms of Cohen κ value for categorical variables. Accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 3D TOF MR angiography in the detection of cerebral aneurysms were determined by using patient-, aneurysm-, and location-based evaluations. Of 403 patients, 273 aneurysms were detected with DSA in 230 patients. Patient-based evaluation with 3D TOF MR angiography at 3.0 T yielded an accuracy of 96%-97%, a sensitivity of 98.2%-98.7%, a specificity of 93.2% -94.8%, a PPV of 94.9%-96.2%, and an NPV of 97.6%-98.2% in the detection of cerebral aneurysms. Aneurysm-based evaluation yielded an accuracy of 96.4%-97.3%, a sensitivity of 98.5%-98.9%, a specificity of 93.2%-94.9%, a PPV of 95.7%-96.8%, and an NPV of 97.6%-98.2%. Aneurysm-location evaluations yielded similar results. Three-dimensional TOF MR angiography is a noninvasive method that shows promising diagnostic accuracy in the detection of small cerebral aneurysms.

Signal Intensity Ratio as a Novel Measure of Hemodynamic Significance for Intracranial Atherosclerosis

Dear Editor Factors affecting hemodynamic significance of symptomatic intracranial arterial stenosis (ICAS), for instance, collateralization, could alter subsequent stroke risk (1), so hemodynamic significance of ICAS may yield a good predictor for stroke risk in patients with symptomatic ICAS. Based on the signal contrast mechanism, flow-related enhancement (2) of time-of-flight (TOF) magnetic resonance angiography (MRA), and hemodynamic features of flowing blood in the case of stenosis, we assumed that changes of signal intensities (SIs) across an arterial stenosis might yield information on its hemodynamic significance. Therefore, in a pilot study, we developed and evaluated a novel index, named SI ratio (SIR), to quantify the hemodynamic significance of ICAS using TOF MRA. The index SIR was calculated as follows: SIR = (mean poststenotic SI – mean background SI)/(mean prestenotic SI – mean background SI), where mean prestenotic, mean poststenotic (Fig. 1a), and left/right background SIs (Fig. 1b) were measured as shown in Fig. 1. SIRs of 26 arteries (18 middle cerebral arteries and eight intracranial internal carotid arteries) selected from patients with 50–99% symptomatic ICAS identified by three-dimensional TOF MRA (3·0 T) were measured and calculated by the same expert twice, and reproducibility of repeated measures was evaluated. Figure 1 MRA maximum intensity projections (MIPs) of an ischemic stroke patient with a short flow void of right MCA. Mean prestenotic and poststenotic SIs were measured using regions of interest (ROI) on the MIP showing the greatest degree of stenosis as follows ... Mean SIRs were both 0·84 for repeated measures, with ranges of 0·35–1·25 and 0·39–1·25, respectively. Mean absolute and relative differences between repeated measures were 0·037 and 5%, respectively. Intrarater agreement was 88% for the 26 arteries studied, and Pearson’s correlation coefficient for repetitive measures was 0·975. Measurement and calculation of the index SIR on TOF MRA were easy to perform and highly reproducible, which makes it feasible to be carried out in clinical practice. Future studies are warranted to further test this novel method for evaluating hemodynamic significance of ICAS and to find out whether it is related to outcomes of patients with symptomatic ICAS.

Studies on new MR venography in cerebral areas

Three-dimensional time of flight (3D TOF) venography images that had been used in magnetic resonance (MR) venography were compared with venography images in which the three-dimensional spoiled gradient-recalled (3D SPGR) sequence had been applied to evaluate the utility of the new MR venography images. From September 2010 to May 2011, venography images with 3D TOF venography or 3D SPGR sequence applied were obtained in 30 healthy individuals without a prior disease history and without brain diseases using 3·0 T MR imaging equipment. The acquired images were analysed qualitatively. On the sagittal images, the level of anatomical description of the internal cerebral vein (IVC), basal vein (BV), vein of Galen (VG), superior cerebral veins and sinus confluence (SC) was evaluated. On the coronal images, the level of anatomical description of the superior sagittal sinus (SSS), inferior sagittal sinus (ISS), sagittal sinus (SS) and transverse sinus (TS) was evaluated. The results show that the anatomical descriptions of the IVC, BV and SCV were comparable on the sagittal images, whereas the anatomical description of the VG was superior on the 3D SPGR venography images. On the coronal images, the anatomical descriptions of the SSS, ISS, SS and TS were comparable.

Contrast enhancement in TOF cerebral angiography at 7 T using saturation and MT pulses under SAR constraints: Impact of VERSE and sparse pulses

Cerebral three-dimensional time of flight (TOF) angiography significantly benefits from ultrahigh fields, mainly due to higher signal-to-noise ratio and to longer T(1) relaxation time of static brain tissues; however, specific absorption rate (SAR) significantly increases with B(0). Thus, additional radiofrequency pulses commonly used at lower field strengths to improve TOF contrast such as saturation of venous signal and improved background suppression by magnetization transfer typically cannot be used at higher fields. In this work, we aimed at reducing SAR for each radiofrequency pulse category in a TOF sequence. We use the variable-rate selective excitation principle for the slab selective TOF excitation as well as the venous saturation radiofrequency pulses. In addition, magnetization transfer pulses are implemented by sparsely applying the pulses only during acquisition of the central k-space lines to limit their SAR contribution. Image quality, angiographic contrast, and SAR reduction were investigated as a function of variable-rate selective excitation parameters and of the total number of magnetization transfer pulses applied. Based on these results, a TOF protocol was generated that increases the angiographic contrast by more than 50% and reduces subcutaneous fat signal while keeping the resulting SAR within regulatory limits.