Cardiovascular 18F-fluoride positron emission tomography-magnetic resonance imaging: A comparison study.

BACKGROUND: 18F-Fluoride uptake denotes calcification activity in aortic stenosis and atherosclerosis. While PET/MR has several advantages over PET/CT, attenuation correction of PET/MR data is challenging, limiting cardiovascular application. We compared PET/MR and PET/CT assessments of 18F-fluoride uptake in the aortic valve and coronary arteries. METHODS AND RESULTS: 18 patients with aortic stenosis or recent myocardial infarction underwent 18F-fluoride PET/CT followed immediately by PET/MR. Valve and coronary 18F-fluoride uptake were evaluated independently. Both standard (Dixon) and novel radial GRE) MR attenuation correction (AC) maps were validated against PET/CT with results expressed as tissue-to-background ratios (TBRs). Visually, aortic valve 18F-fluoride uptake was similar on PET/CT and PET/MR. TBRMAX values were comparable with radial GRE AC (PET/CT 1.55±0.33 vs. PET/MR 1.58 ± 0.34, P = 0.66; 95% limits of agreement - 27% to + 25%) but performed less well with Dixon AC (1.38 ± 0.44, P = 0.06; bias (-)14%; 95% limits of agreement - 25% to + 53%). In native coronaries, 18F-fluoride uptake was similar on PET/MR to PET/CT regardless of AC approach. PET/MR identified 28/29 plaques identified on PET/CT; however, stents caused artifact on PET/MR making assessment of 18F-fluoride uptake challenging. CONCLUSION: Cardiovascular PET/MR demonstrates good visual and quantitative agreement with PET/CT. However, PET/MR is hampered by stent-related artifacts currently limiting clinical application.

Assessing the qualitative and quantitative impacts of simple two-class vs multiple tissue-class MR-based attenuation correction for cardiac PET/MR.

BACKGROUND: Hybrid PET/MR imaging has significant potential in cardiology due to its combination of molecular PET imaging and cardiac MR. Multi-tissue-class MR-based attenuation correction (MRAC) is necessary for accurate PET quantification. Moreover, for thoracic PET imaging, respiration is known to lead to misalignments of MRAC and PET data that result in PET artifacts. These factors can be addressed by using multi-echo MR for tissue segmentation and motion-robust or motion-gated acquisitions. However, the combination of these strategies is not routinely available and can be prone to errors. In this study, we examine the qualitative and quantitative impacts of multi-class MRAC compared to a more widely available simple two-class MRAC for cardiac PET/MR. METHODS AND RESULTS: In a cohort of patients with cardiac sarcoidosis, we acquired MRAC data using multi-echo radial gradient-echo MR imaging. Water-fat separation was used to produce attenuation maps with up to 4 tissue classes including water-based soft tissue, fat, lung, and background air. Simultaneously acquired 18F-fluorodeoxyglucose PET data were subsequently reconstructed using each attenuation map separately. PET uptake values were measured in the myocardium and compared between different PET images. The inclusion of lung and subcutaneous fat in the MRAC maps significantly affected the quantification of 18F-fluorodeoxyglucose activity in the myocardium but only moderately altered the appearance of the PET image without introduction of image artifacts. CONCLUSION: Optimal MRAC for cardiac PET/MR applications should include segmentation of all tissues in combination with compensation for the respiratory-related motion of the heart. Simple two-class MRAC is adequate for qualitative clinical assessment.

3T MRI of Peripheral Vascular Malformations: Characteristics and Comparison of Two Fat-Saturated sequences: Short Tau Inversion Recovery Versus Three-Dimensional High-Resolution Volume Interpolated Gradient Recalled Echo.

PURPOSE: To assess morphological and hemodynamic characteristics of peripheral vascular malformations on 3 T magnetic resonance imaging (MRI) including qualitative comparison of two fat-saturated sequences: short tau inversion recovery (STIR) and three-dimensional high-resolution volume interpolated gradient recalled echo (GRE). MATERIALS AND METHODS: During 9 months, 100 patients with suspected or known vascular malformations were prospectively assessed on a 3 T scanner using T2-weighted STIR and turbo spin echo (TSE), T1-weighted TSE, time-resolved contrast-enhanced magnetic resonance angiography (MRA) with interleaved stochastic trajectories (TWIST) and T1-weighted volume interpolated breath-hold examination (VIBE) after contrast enhancement. The analysis included signal behavior and morphologic and hemodynamic characteristics. Additionally, the image quality of the fat-saturated sequences was evaluated by 2 radiologists. RESULTS: 86 patients (14 dropouts; 57 female, 29 male; mean age 26.8 years, age range 1-56) were analyzed. 22 had high-flow and 64 low-flow malformations, including 14 with a lymphatic component. In 21 of 22 patients with high-flow malformations, typical characteristics (flow voids, hyperdynamic arteriovenous fistula, dilated main/feeder-arteries and draining veins) were documented. Patients with low-flow malformations had phleboliths in 35 cases, fluid-fluid levels in 47 and dilated draining veins in 23. Lymphatic malformations showed peripheral contrast enhancement of cyst walls in the volume interpolated GRE. The comparison of fat-saturated sequences showed significantly better results of the volume interpolated GRE in all categories except the presence of artifacts which were significantly reduced in the STIR (p < 0.05). CONCLUSION: 3 T MRI with MRA provides detailed morphological and hemodynamic information of different types of peripheral vascular malformations. Contrast-enhanced high-resolution volume interpolated GRE proved superior to STIR in differentiating morphologic features and to be diagnostic in the differentiation of lymphatic parts and joint involvement. KEY POINTS: · 3 T MRI with MRA offers detailed information about vascular malformations.. · Fat-saturated MRI provides especially information about morphological characteristics, extent and tissue involvement.. · Volume interpolated GRE proved superior in almost all categories compared to STIR.. · Volume interpolated GRE showed more artifacts.. · Volume interpolated GRE additionally allows differentiation of lymphatic parts and evaluation of joint involvement.. CITATION FORMAT: · Höhn F, Hammer S, Fellner C et al. 3T MRI of Peripheral Vascular Malformations: Characteristics and Comparison of Two Fat-Saturated sequences: Short Tau Inversion Recovery Versus Three-Dimensional High-Resolution Volume Interpolated Gradient Recalled Echo. Fortschr Röntgenstr 2021; 193: 446 - 458.

Discrepancy between MRA and DSA in identifying the shape of small intracranial aneurysms.

OBJECTIVE: The authors evaluated the sensitivity and accuracy of MRA in identifying the shape of small-sized unruptured intracranial aneurysms. METHODS: Small (< 7 mm) unruptured intracranial aneurysms initially detected by MRA and confirmed by DSA between January 2017 and December 2018 were morphologically reviewed by neuroradiologists. Regularity or irregularity of aneurysm shape was analyzed by two independent reviewers using MRA without DSA results. DSA findings served as the reference standard for aneurysm shape. Irregular shape, which in small aneurysms is associated with a higher likelihood of rupture, was defined as positive, and MRA sensitivity, specificity, and accuracy were determined by using evaluations based on location, size, and MRA magnetic strength (1.5T vs 3T MRA). Multivariate analysis was performed to determine risk factors for false-negative MRA results for irregularly shaped aneurysms. RESULTS: In total, 652 unruptured intracranial aneurysms in 530 patients were reviewed for this study. For detecting aneurysm shape irregularity, the overall MRA sensitivity was 60.4% for reviewer 1 and 60.9% for reviewer 2. Anterior cerebral artery aneurysms had the lowest sensitivity for location (36.7% for reviewer 1, 46.9% for reviewer 2); aneurysms sized < 3 mm had the lowest sensitivity for size (26.7% for both reviewers); and 1.5T MRA had lower sensitivity and accuracy than 3T MRA. In multivariate analysis, location, size, and magnetic strength of MRA were independent risk factors for false-negative MRA results for irregularly shaped aneurysms. CONCLUSIONS: MRA had a low sensitivity for detecting the irregular shape of small intracranial aneurysms. In particular, anterior cerebral artery location, aneurysm size < 3 mm, and detection with 1.5T MRA were associated with a higher risk of irregularly shaped aneurysms being misjudged as regular.

Arterial Spin Labeling in Pediatric Neuroimaging.

Perfusion imaging using arterial spin labeling noninvasively evaluates cerebral blood flow utilizing arterial blood water as endogenous tracer. It does not require the need of radiotracer or intravenous contrast and offers unique complimentary information in the imaging of pediatric brain. Common clinical applications include neonatal hypoxic ischemic encephalopathy, pediatric stroke and vascular malformations, epilepsy and brain tumors. Future applications may include evaluation of silent ischemia in sickle cell patients, monitor changes in intracranial pressure in hydrocephalus, provide additional insights in nonaccidental trauma and chronic traumatic brain injury (TBI) and in functional Magnetic resonance imaging (MRI). The purpose of this review article is to evaluate the technical considerations including pitfalls, physiological variations, clinical applications and future directions of arterial spin labeling imaging.

Radiomics prognostication model in glioblastoma using diffusion- and perfusion-weighted MRI.

We aimed to develop and validate a multiparametric MR radiomics model using conventional, diffusion-, and perfusion-weighted MR imaging for better prognostication in patients with newly diagnosed glioblastoma. A total of 216 patients with newly diagnosed glioblastoma were enrolled from two tertiary medical centers and divided into training (n = 158) and external validation sets (n = 58). Radiomic features were extracted from contrast-enhanced T1-weighted imaging, fluid-attenuated inversion recovery, diffusion-weighted imaging, and dynamic susceptibility contrast imaging. After radiomic feature selection using LASSO regression, an individualized radiomic score was calculated. A multiparametric MR prognostic model was built using the radiomic score and clinical predictors. The results showed that the multiparametric MR prognostic model (radiomics score + clinical predictors) exhibited good discrimination (C-index, 0.74) and performed better than a conventional MR radiomics model (C-index, 0.65, P < 0.0001) or clinical predictors (C-index, 0.66; P < 0.0001). The multiparametric MR prognostic model also showed robustness in external validation (C-index, 0.70). Our results indicate that the incorporation of diffusion- and perfusion-weighted MR imaging into an MR radiomics model to improve prognostication in glioblastoma patients improved its performance over that achievable using clinical predictors alone.

Test-retest reliability and sample size estimates after MRI scanner relocation.

OBJECTIVE: Many factors can contribute to the reliability and robustness of MRI-derived metrics. In this study, we assessed the reliability and reproducibility of three MRI modalities after an MRI scanner was relocated to a new hospital facility. METHODS: Twenty healthy volunteers (12 females, mean age (standard deviation) â€‹= â€‹41 (11) years, age range [25-66]) completed three MRI sessions. The first session (S1) was one week prior to the 3T GE HDxt scanner relocation. The second (S2) occurred nine weeks after S1 and at the new location; a third session (S3) was acquired 4 weeks after S2. At each session, we acquired structural T1-weighted, pseudo-continuous arterial spin labelled, and diffusion tensor imaging sequences. We used longitudinal processing streams to create 12 summary MRI metrics, including total gray matter (GM), cortical GM, subcortical GM, white matter (WM), and lateral ventricle volume; mean cortical thickness; total surface area; average gray matter perfusion, and average diffusion tensor metrics along principal white matter pathways. We compared mean MRI values and variance at the old scanner location to multiple sessions at the new location using Bayesian multi-level regression models. K-fold cross validation allowed identification of important predictors. Whole-brain analyses were used to investigate any regional differences. Furthermore, we calculated within-subject coefficient of variation (wsCV), intraclass correlation coefficient (ICC), and dice similarity index (SI) of cortical segmentations across scanner relocation and within-site. Additionally, we estimated sample sizes required to robustly detect a 4% difference between two groups across MRI metrics. RESULTS: All global MRI metrics exhibited little mean difference and small variability (bar cortical gray matter perfusion) both across scanner relocation and within-site repeat. T1- and DTI-derived tissue metrics showed â€‹< â€‹|0.3|% mean difference and <1.2% variance across scanner location and <|0.4|% mean difference and <0.8% variance within the new location, with between-site intraclass correlation coefficient (ICC) â€‹> â€‹0.80 and within-subject coefficient of variation (wsCV) â€‹< â€‹1.4%. Mean cortical gray matter perfusion had the highest between-session variability (6.7% [0.3, 16.7], estimate [95% uncertainty interval]), and hence the smallest ICC (0.71 [0.44,0.92]) and largest wsCV (13.4% [5.4, 18.1]). No global metric exhibited evidence of a meaningful mean difference between scanner locations. However, surface area showed evidence of a mean difference within-site repeat (between S2 and S3). Whole-brain analyses revealed no significant areas of difference between scanner relocation or within-site. For all metrics, we found no support for a systematic difference in variance across relocation sites compared to within-site test-retest reliability. Necessary sample sizes to detect a 4% difference between two independent groups varied from a maximum of n â€‹= â€‹362 per group (cortical gray matter perfusion), to total gray matter volume (n â€‹= â€‹114), average fractional anisotropy (n â€‹= â€‹23), total gray matter volume normalized by intracranial volume (n â€‹= â€‹19), and axial diffusivity (n â€‹= â€‹3 per group). CONCLUSION: Cortical gray matter perfusion was the most variable metric investigated (necessitating large sample sizes to identify group differences), with other metrics showing substantially less variability. Scanner relocation appeared to have a negligible effect on variability of the global MRI metrics tested. This manuscript reports within-site test-retest variability to act as a tool for calculating sample size in future investigations. Our results suggest that when all other parameters are held constant (e.g., sequence parameters and MRI processing), the effect of scanner relocation is indistinguishable from within-site variability, but may need to be considered depending on the question being investigated.

Usefulness of high-resolution three-dimensional proton density-weighted turbo spin-echo MRI in distinguishing a junctional dilatation from an intracranial aneurysm of the posterior communicating artery: a pilot study.

BACKGROUND: Discriminating a junctional dilatation from a true saccular aneurysm is clinically important. PURPOSE: To evaluate the usefulness of high-resolution three-dimensional proton density-weighted turbo spin-echo magnetic resonance imaging (PD MRI) in distinguishing a junctional dilatation from an aneurysm of the posterior communicating artery (PcomA). METHODS: Eighty-two consecutive patients with 83 PcomA lesions, which were evaluated by time-of-flight (TOF) MR angiography (MRA), PD MRI, and digital subtraction angiography (DSA), were enrolled. These radiologic data were retrospectively and independently reviewed by two neurosurgeons, and each diagnosis based on TOF MRA, PD MRI, and DSA was compared. The diagnostic efficacy (interobserver agreement, intermodality agreement, and diagnostic performance) of PD MRI was compared with that of TOF MRA. RESULTS: PD MRI showed higher AC1 (Gwet's agreement coefficient, PD MRI: 0.8942, 95% CI 0.8204 to 0.968; TOF MRA: 0.7185, 95% CI 0.5753 to 0.8617) and prevalence-adjusted bias-adjusted kappa coefficient (PABAK) (PD MRI: 0.8554, TOF MRA: 0.5904) than TOF MRA for interobserver agreement. For intermodality agreement, PD MRI also showed higher AC1 (PD MRI: 0.9069, 95% CI 0.8374 to 0.9764; TOF MRA: 0.7983, 95% CI 0.6969 to 0.8996) and PABAK (PD MRI: 0.8735, TOF MRA: 0.7289) than TOF MRA. The diagnostic performance of PD MRI was statistically superior to that of TOF MRA in sensitivity, specificity, positive predictive value, and negative predictive value. CONCLUSIONS: PD MRI could provide excellent diagnostic accuracy and better information in distinguishing a junctional dilatation from a true saccular aneurysm of the PcomA compared with TOF MRA.

Neurovascular findings in children and young adults with Loeys-Dietz syndromes: Informing recommendations for screening.

INTRODUCTION: Loeys-Dietz Syndromes (LDS) are a group of connective tissue disorders associated with vascular abnormalities, including arterial tortuosity, aneurysms, and dissections. While neurovascular involvement is common, no pediatric or young adult recommendations for screening exist. We aimed to review our institution's experience with special focus on neurovascular imaging to better understand the pathology and guide screening. METHODS: A retrospective cohort study of patients with LDS was performed. Demographics, genetic subtype, clinical and radiographical data were analyzed. Primary outcome measures included pathology on neurovascular imaging, time to progression, and arterial tortuosity indexes for bilateral cervical internal carotid arteries (ICA) and vertebral arteries (VA). RESULTS: Of 47 patients with LDS identified, 39 (83.0%) were found to have neuroimaging. Intracranial and cervical vascular tortuosity were seen in 79.5% and 64.1%, respectively. Twenty-one patients (44.7%) received follow-up screening, of which 3 were found to have progression. Time to progression was an average of 2.1 years. Average follow-up was 607 days (range 123-3070 days). Mean Arterial Tortuosity Index for the right ICA, left ICA, right VA, and left VA were 18, 20, 49, and 47, respectively. Comparison of interval percent change in Arterial Tortuosity Index over the course of follow-up demonstrated small changes in the right ICA (mean 5%), left ICA (mean 1%), right VA (mean 1%), and left VA (mean 2%). CONCLUSIONS: Arterial tortuosity was most prevalent, though it did not progress significantly over time. We suggest an algorithm for management and serial screening to guide management of pediatric and young adults with LDS.

A novel computer-aided diagnosis system for the early detection of hypertension based on cerebrovascular alterations.

Hypertension is a leading cause of mortality in the USA. While simple tools such as the sphygmomanometer are widely used to diagnose hypertension, they could not predict the disease before its onset. Clinical studies suggest that alterations in the structure of human brains' cerebrovasculature start to develop years before the onset of hypertension. In this research, we present a novel computer-aided diagnosis (CAD) system for the early detection of hypertension. The proposed CAD system analyzes magnetic resonance angiography (MRA) data of human brains to detect and track the cerebral vascular alterations and this is achieved using the following steps: i) MRA data are preprocessed to eliminate noise effects, correct the bias field effect, reduce the contrast inhomogeneity using the generalized Gauss-Markov random field (GGMRF) model, and normalize the MRA data, ii) the cerebral vascular tree of each MRA volume is segmented using a 3-D convolutional neural network (3D-CNN), iii) cerebral features in terms of diameters and tortuosity of blood vessels are estimated and used to construct feature vectors, iv) feature vectors are then used to train and test various artificial neural networks to classify data into two classes; normal and hypertensive. A balanced data set of 66 subjects were used to test the CAD system. Experimental results reported a classification accuracy of 90.9% which supports the efficacy of the CAD system components to accurately model and discriminate between normal and hypertensive subjects. Clinicians would benefit from the proposed CAD system to detect and track cerebral vascular alterations over time for people with high potential of developing hypertension and to prepare appropriate treatment plans to mitigate adverse events.

High-resolution magnetic resonance imaging of intracranial vessel walls: Comparison of 3D T1-weighted turbo spin echo with or without DANTE or iMSDE.

BACKGROUND: The black-blood (BB) technique was developed to suppress the signal from blood and cerebrospinal fluid (CSF) to provide improved depiction of vessel walls. PURPOSE: The aim was to compare three-dimensional turbo spin echo T1-weighted imaging (3D TSE T1WI) with or without two BB techniques (delay alternating with nutation for tailored excitation [DANTE], and improved motion-sensitized driven equilibrium [iMSDE]) for high-resolution magnetic resonance imaging (HR-MRI) of the vessel walls of intracranial arteries. STUDY TYPE: Prospective. POPULATION: Fourteen healthy volunteers who underwent 3D T1WI for examination of intracranial vessel walls. FIELD STRENGTH/SEQUENCE: 3 Tesla, 3D TSE T1WI (SPACE and BrainVIEW) and BB (DANTE and iMSDE). ASSESSMENT: SPACE with or without DANTE, and BrainVIEW with or without iMSDE, were acquired in each subject. Two neuroradiologists independently assessed image quality, vessel wall delineation, BB effect, CSF, and acceptability using visual scoring systems, and measured signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in vessel walls, lumen, and CSF, while blinded to the presence and type of BB technique used. STATISTICAL TESTS: Repeated measures ANOVA or Friedman tests were performed for the comparisons, followed by Bonferroni correction. RESULTS: The 3T T1WI sequences without BB are significantly superior in vessel wall delineation (P = 0.001). Black CSF scores were lower in SPACE with DANTE than SPACE without DANTE, and in BrainVIEW without iMSDE than SPACE without DANTE (P < 0.001). However, there were no significant differences in BB effect, image quality, and acceptability between the four 3D T1WI sequences (p > .05). The SNRVessel wall, CNRWall-Lumen, and CNRWall-CSF were higher (all p < .001) on SPACE with and without DANTE than on BrainVIEW with and without iMSDE. SNRLumen were higher (all p < .001) on BrainVIEW with and without iMSDE than on SPACE with and without DANTE. SNRCSF was higher (all p < .001) on BrainVIEW with iMSDE than on SPACE with DANTE. DATA CONCLUSION: Both 3D TSE T1WI sequences were acceptable for intracranial vessel wall evaluation, with or without BB techniques. Therefore, BB techniques may not necessarily be required with 3D TSE T1WI with a long ETL and TR (below 1160 ms).

Systematic review with network meta-analysis: Diagnostic values of ultrasonography, computed tomography, and magnetic resonance imaging in patients with ischemic stroke.

BACKGROUND AND OBJECTIVE: Ischemic stroke is a foremost cause for disability and death worldwide. This study is conducted in order to compare the diagnostic values between transcranial Doppler ultrasound (ultrasonography), computed tomography (CT), and magnetic resonance imaging (MRI) in patients suffering from ischemic stroke by performing a network meta-analysis. METHODS: We made use of Cochrane Library, PubMed, and Embase in order to obtain literature and papers. The combination analysis of both direct and indirect evidence in terms of sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy was conducted so as to assess the odds ratios (ORs) and surface under the cumulative ranking curve (SUCRA) values of the seven different imaging methods. These imaging techniques include ultrasonography, computed tomography (traditional CT, computed tomography angiography [CTA], computed tomography perfusion [CTP]), and MRI (traditional MRI, diffusion-weighted imaging [DWI], magnetic resonance angiography), in order to properly diagnose ischemic stroke patients. RESULTS: Thirteen eligible diagnostic trials were enrolled into this network meta-analysis. The results of the traditional meta-analysis showed that among CT methods, CTP showed higher sensitivity, NPV, and accuracy; among MRI methods, DWI had relatively higher sensitivity, NPV, and accuracy. The results of network meta-analysis showed that DWI had relatively higher sensitivity, NPV, and accuracy when compared with traditional CT, CTA, magnetic resonance angiography and traditional MRI. CTP showed higher SUCRA among CT methods while DWI showed higher SUCRA among MRI methods. A cluster analysis revealed that DWI had the highest diagnostic value in terms of sensitivity, PPV, NPV, and accuracy amongst the aforementioned seven imaging techniques. CONCLUSION: This network meta-analysis provides supporting evidence to the idea that DWI has a higher diagnostic value regarding ischemic stroke among MRI methods, and CTP has a poor diagnostic value among CT methods, which provide therapeutic considerations for Ischemic stroke intervention.

Off-resonance correction for pseudo-continuous arterial spin labeling using the optimized encoding scheme.

Pseudo-continuous arterial spin labeling (PCASL) MRI has become a popular tool for non-invasive perfusion imaging and angiography. However, it suffers from sensitivity to off-resonance effects within the labeling plane, which can be exacerbated at high field or in the presence of metallic implants, leading to spatially varying signal loss and cerebral blood flow underestimation. In this work we propose a prospective correction technique based on the optimized encoding scheme, which allows the rapid calculation of transverse gradient blips and RF phase modulations that best cancel phase offsets due to off-resonance at the locations of the feeding arteries within the labeling plane. This calculation is based upon a rapidly acquired single-slice fieldmap and is applicable to any number and arrangement of arteries. In addition, this approach is applicable to both conventional PCASL and a vessel-selective variant known as vessel-encoded PCASL (VEPCASL). Through simulations and experiments in healthy volunteers it was shown that in the presence of off-resonance effects a strong bias in the strength of the perfusion signal across vascular territories can be introduced, the signal-to-noise ratio (SNR) efficiency of PCASL and VEPCASL can be severely compromised (∼40% reduction in vivo), and that vessel-selective signal in VEPCASL can be incorrectly assigned. Distortion of the spatial regions placed in the label or control conditions in the presence of off-resonance effects was confirmed in phantom experiments. The application of the proposed correction restored SNR efficiency to levels present in the absence of off-resonance effects and corrected errors in the vascular territory maps derived from VEPCASL. Due to the rapid nature of the required calculations and fieldmap acquisition, this approach could be inserted into protocols with minimal effect on the total scan time.

Standardized Evaluation of Cerebral Arteriovenous Malformations Using Flow Distribution Network Graphs and Dual-venc 4D Flow MRI.

BACKGROUND: Cerebral arteriovenous malformations (AVMs) are pathological connections between arteries and veins. Dual-venc 4D flow MRI, an extended 4D flow MRI method with improved velocity dynamic range, provides time-resolved 3D cerebral hemodynamics. PURPOSE: To optimize dual-venc 4D flow imaging parameters for AVM; to assess the relationship between spatial resolution, acceleration, and flow quantification accuracy; and to introduce and apply the flow distribution network graph (FDNG) paradigm for storing and analyzing complex neurovascular 4D flow data. STUDY TYPE: Retrospective cohort study. SUBJECTS/PHANTOM: Scans were performed in a specialized flow phantom: 26 healthy subjects (age 41 ± 17 years) and five AVM patients (age 27-68 years). FIELD STRENGTH/SEQUENCE: Dual-venc 4D flow with varying spatial resolution and acceleration factors were performed at 3T field strength. ASSESSMENT: Quantification accuracy was assessed in vitro by direct comparison to measured flow. FDNGs were used to quantify and compare flow, peak velocity (PV), and pulsatility index (PI) between healthy controls with various Circle of Willis (CoW) anatomy and AVM patients. STATISTICAL TESTS: In vitro measurements were compared to ground truth with Student's t-test. In vivo groups were compared with Wilcoxon rank-sum test and Kruskal-Wallis test. RESULTS: Flow was overestimated in all in vitro experiments, by an average 7.1 ± 1.4% for all measurement conditions. Error in flow measurement was significantly correlated with number of voxels across the channel (P = 3.11 × 10-28 ) but not with acceleration factor (P = 0.74). For the venous-arterial PV and PI ratios, a significant difference was found between AVM nidal and extranidal circulation (P = 0.008 and 0.05, respectively), and between AVM nidal and healthy control circulation (P = 0.005 and 0.003, respectively). DATA CONCLUSION: Dual-venc 4D flow MRI and standardized FDNG analysis might be feasible in clinical applications. Venous-arterial ratios of PV and PI are proposed as network-based biomarkers characterizing AVM nidal hemodynamics. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:1718-1730.

MRA versus DSA for the follow-up imaging of intracranial aneurysms treated using endovascular techniques: a meta-analysis.

BACKGROUND: Treated aneurysms must be followed over time to ensure durable occlusion, as more than 20% of endovascularly treated aneurysms recur. While digital subtraction angiography (DSA) remains the gold standard, magnetic resonance angiography (MRA) is attractive as a non-invasive follow-up technique. Two different MRA techniques have traditionally been used: time-of-flight (TOF) and contrast-enhanced (CE) MRA. We analysed data from studies comparing MRA techniques with DSA for the follow-up of aneurysms undergoing endovascular treatment. Subgroup analysis of stent-assisted coiling (SAC) and flow diversion (FD) techniques was completed. METHODS: Comprehensive searches using the Embase, PubMed, and Cochrane databases were performed and updated to November 2018. Pooled sensitivity and specificity were calculated using aneurysm occlusion status as defined by the Raymond-Roy occlusion grading scale. RESULTS: The literature search yielded 1579 unique titles. Forty-three studies were included. For TOF-MRA, sensitivity and specificity of all aneurysms undergoing endovascular therapy were 88% and 94%, respectively. For CE-MRA, the sensitivity and specificity were 88% and 96%, respectively. For SAC and FD techniques, sensitivity and specificity of TOF-MRA were 86% and 95%, respectively. CE-MRA had sensitivity and specificity of 90% and 92%. CONCLUSION: MRA is a reliable modality for the follow-up of aneurysms treated using endovascular techniques. While the data are limited, MRA techniques can also be used to reliably follow patients undergoing FD and SAC. However, clinical factors must be used to optimize follow-up regimens for individual patients.

Use of cardiac magnetic resonance imaging and single photon emission computed tomography for the diagnosis of stable coronary artery disease in Switzerland.

BACKGROUND: Direct invasive testing in the diagnosis of stable coronary artery disease (CAD) involves high costs and relevant risks. By comparison, single-photon emission computed tomography (SPECT) and cardiac magnetic resonance imaging (CMR) are noninvasive diagnostic tests. SPECT is currently the most widely used diagnostic technique, but new medical and economic evidence favours CMR. Guidelines do not recommend one technique in preference to the other, and their use in Switzerland is poorly documented, as a scoping study by the Swiss Medical Board reported. We aimed at a quantitative and qualitative analysis of the use of these diagnostic techniques in Swiss hospitals. METHODS: We contacted nine Swiss hospitals to obtain the number of SPECT/CMR investigations used to diagnose stable CAD in 2014–2016 and submitted a questionnaire to investigate the advantages and limitations of the two imaging techniques. In addition, two experts in SPECT and CMR, respectively, at two university hospitals were interviewed, using open questions. RESULTS: Data were obtained from 8 hospitals, and 22 questionnaires were returned. In Switzerland, both techniques have been implemented very differently in different hospitals, but the overall number of diagnostic procedures has increased. The questionnaires reported lower scores for CMR regarding the availability of the scans, contraindications and the suitability of the technique for the diagnosis of CAD. The experts described potential conflicts of interest in some institutions, depending on how the cardiology and radiology departments collaborated, and highlighted the debated results of studies comparing CMR with SPECT for the diagnosis of CAD. The main conclusion drawn from the interviews was the recommendation of a patient-centred evaluation. CONCLUSION: The use of SPECT versus CMR in Switzerland for the diagnosis of stable CAD is heterogeneous, but reflects the guidelines, which do not distinguish between the two diagnostic techniques. Expert opinions underlined that discussion should not be so much about the choice of the diagnostic modality but about how a clinical question in a patient can best be answered.

Ungated nonenhanced radial quiescent interval slice-selective (QISS) magnetic resonance angiography of the neck: Evaluation of image quality.

BACKGROUND: Standard-of-care time-of-flight (TOF) techniques for nonenhanced magnetic resonance angiography (NEMRA) of the carotid bifurcation and other cervical arteries often provide nondiagnostic image quality due to motion and flow artifacts. PURPOSE: To perform an initial evaluation of an ungated radial quiescent-interval slice-selective (QISS) technique for NEMRA of the neck, in comparison with 2D TOF and contrast-enhanced magnetic resonance angiography (CEMRA). STUDY TYPE: Retrospective. POPULATION: Sixty patients referred for neck MR angiography. FIELD STRENGTH/SEQUENCE: Ungated radial QISS at 3T. ASSESSMENT: Three radiologists scored image quality of 18 arterial segments using a 4-point scale (1, nondiagnostic; 2, fair; 3, good; 4, excellent), and two radiologists graded proximal internal carotid stenosis using five categories (<50%, 50-69%, 70-99%, occlusion, nondiagnostic). STATISTICAL TESTS: Friedman tests with post-hoc Wilcoxon signed-rank tests; unweighted Gwet's AC1 statistic; tests for equality of proportions. RESULTS: Ungated radial QISS provided image quality that significantly exceeded 2D TOF (mean scores of 2.7 vs. 2.0, 2.7 vs. 2.2, and 2.9 vs. 2.3; P < 0.001, all comparisons), while CEMRA provided the best image quality (mean scores of 3.6, 3.7, and 3.5 for the three reviewers). Interrater agreement of image quality scores was substantial for CEMRA (AC1 = 0.70, P < 0.001), and moderate for QISS (AC1 = 0.43, P < 0.001) and TOF (AC1 = 0.41, P < 0.001). Compared with TOF, QISS NEMRA provided a significantly higher percentage of diagnostic segments for all three reviewers (91.0% vs. 71.7%, 93.5% vs. 72.9%, 95.5% vs. 85.2%; P < 0.0001) and demonstrated better agreement with CEMRA for grading of proximal internal carotid stenosis (AC1 = 0.94 vs. 0.73 for reviewer 1, P < 0.05; AC1 = 0.89 vs. 0.68 for reviewer 2, P < 0.05). DATA CONCLUSION: In this initial study, ungated radial QISS significantly outperformed 2D TOF for the evaluation of the neck arteries, with overall better image quality and more diagnostic arterial segments, and improved agreement with CEMRA for grading stenosis of the proximal internal carotid artery. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:1798-1807.

Subtraction of arterial spin-labeling magnetic resonance perfusion images acquired at dual post-labeling delay: Potential for evaluating cerebral hyperperfusion syndrome following carotid endarterectomy.

Arterial spin-labeling magnetic resonance perfusion imaging is a promising tool for the diagnosis of cerebral hyperperfusion syndrome after carotid endarterectomy. However, arterial spin-labeling with a single post-labeling delay has been reported to show a higher incidence of increased arterial spin-labeling signals in the bilateral hemisphere, probably due to a shortening of the arterial transit time or an arterial transit artifact caused by intravascular stagnant magnetically-labeled spin. To overcome these shortcomings, we used two post-labeling delay settings (1.0 and 1.5 s) in 8 patients who had undergone carotid endarterectomy. In addition, we created a subtraction image between the mean perfusion maps at post-labeling delays of 1.0 and 1.5 s. This also decreased arterial transit artifacts, as these appeared in nearly the same configuration in both post-labeling delay settings. In all eight cases examined, increased arterial spin-labeling signals were observed bilaterally on both dual post-labeling delay settings. Subtraction images revealed that these increased signals were attributable to arterial transit artifacts in seven cases. However, in one patient who developed clinical symptoms, the subtraction method demonstrated post-carotid endarterectomy hyperperfusion. This preliminary study demonstrates that the subtraction method might decrease arterial transit artifacts and yield a map that can better represent true perfusion, thus enabling the detection of post-carotid endarterectomy hyperperfusion.