Non-contrast Enhanced MR Angiography Research Articles

Non-contrast-enhanced MR angiography of left gastric vein in patients with gastroesophageal varices: morphology and blood supply analysis.

To investigate the feasibility of non-contrast-enhanced MR angiography (NCE-MRA) in evaluating the morphology and blood supply of left gastric vein (LGV) in patients with gastroesophageal varices. Between March 2021 and October 2022, patients with gastroesophageal varices and who underwent NCE-MRA were retrospectively reviewed. In order to evaluate the blood supply of LGV, superior mesenteric vein (SMV) and splenic vein (SV) were visualized separately by using inflow-sensitive inversion recovery sequence. Two radiologists independently assessed the image quality, determined the origination and the blood supply of LGV, and measured the diameter of LGV. The origination and diameter of LGV were compared between NCE-MRA and contrast-enhanced CT. Differences in blood supply were compared between LGVs with different originations. A total of 53 patients were enrolled in this study and the image quality was categorized as good or excellent in 52 patients. No significant differences were observed in visualizing the origination and the diameter of LGV between NCE-MRA and contrast-enhanced CT (p > .05). The blood supply of LGV was related to its origination (p < .001). Most LGVs with SV origination were supplied by SV. If LGV was originated from the portal vein (PV), about 70% of them were supplied by both SV and SMV. Compared with LGVs with SV origination, LGVs with PV origination showed more chance to receive blood from SMV (p < .001). Non-contrast-enhanced MR angiography appears to be a reliable technique in evaluating the morphology and blood supply of LGV in patients with gastroesophageal varices. Non-contrast-enhanced MR angiography provides valuable information for the management of gastroesophageal varices. Especially, it benefits patients with renal insufficiency. • Non-contrast-enhanced MR angiography using inflow-sensitive inversion recovery technique can be used for evaluating not only morphology as CT but also blood supply of left gastric vein. • The blood supply of left gastric vein is related to its origination and left gastric vein with portal vein origination shows more chance to receive blood from superior mesenteric vein.

Assessment of Transplant Renal Artery Stenosis with Non-contrast-Enhanced Magnetic Resonance Angiography: Comparison with Digital Subtraction Angiography

ObjectivesEarly diagnosis of transplant renal artery stenosis (TRAS) is crucial for salvaging kidney function and improving patient prognosis. The purpose of this study was to evaluate image quality of non-contrast-enhanced MR angiography (NCE-MRA) and the value of NCE-MRA in evaluating TRAS compared to DSA. Materials and MethodsIn 60 patients with TRAS confirmed by DSA, the degree of TRAS was assessed using balanced triggered angiography non-contrast-enhanced (B-TRANCE) MR angiography and was compared with that of DSA. Image quality for NCE-MRA was assessed independently by two radiologists. The Wilcoxon signed-rank test was used to compare NCE-MRA with DSA in assessing TRAS degree. Specificity, sensitivity, accuracy, positive-predictive value (PPV), and negative-predictive value (NPV) of NCE-MRA for the detection of marked (≥ 50%) TRAS were calculated. ResultsThe image quality of NCE-MRA based on the B-TRANCE technology of transplanted renal arteries was sufficient (excellent in 81.67%, good in 8.33%, moderate in 6.67%, and non-diagnostic in 3.33%) and had a high inter-observer reproducibility (Kappa = 0.836). DSA helped identify severe, moderate, and mild stenosis in 6, 32, and 22 arteries, respectively. No significant difference in the extent of TRAS between NCE-MRA and DSA were observed (P = 0.317). The specificity, sensitivity, accuracy, PPV, and NPV of NCE-MRA in detecting marked (≥ 50%) TRAS were 90.91%, 100%, 96.55%, 94.74%, and 100%, respectively. ConclusionNCE-MRA based on B-TRANCE technology has shown promising consistency with DSA in evaluating TRAS and yielding high sensitivity, specificity, and accuracy in assessing the severity of TRAS.

Spatially and velocity-selective magnetization preparation for noncontrast-enhanced peripheral MR angiography.

The purpose of the current study was to develop spatially and velocity-selective (SVS) magnetization preparation pulses for noncontrast-enhanced peripheral MR angiography (MRA) to provide comparisons with velocity-selective (VS) MRA with comparison to velocity-selective (VS). VS preparation pulses were designed by concatenating multiple excitation steps, each of which was a combination of a hard RF pulse, VS unipolar gradient pulses, and refocusing RF pulses. SVS preparation pulses were designed by replacing the hard RF pulse with a sinc-shaped RF pulse combined with a symmetric tripolar gradient pulse (which does not perturb the velocity encoding by the VS unipolar gradient pulses). Numerical simulations were performed to verify the intended hybrid excitation selectivity of SVS pulses taking account of tissue relaxation, magnetic field errors, and eddy currents. In vivo experiments were performed in healthy subjects to verify the hybrid excitation selectivity, as well as to demonstrate the visualization of the entire peripheral arteries using six-station protocols. As demonstrated by numerical simulations, SVS preparation yielded a notch-shaped longitudinal magnetization (Mz )-velocity response within the spatial stopband (the same as VS preparation) and preserved the Mz of spins outside the stopband, regardless of its velocity. We confirmed these observations also through in vivo tests with good agreement in normalized arterial and muscle signal intensities. In six-station peripheral MRA experiments, the proposed SVS-MRA yielded significantly higher arterial signal-to-noise ratio (SNR) (51.6 ± 14.3 vs. 38.9 ± 10.9; p < 0.001) and contrast-to-noise ratio (CNR) (41.2 ± 13.0 vs. 31.3 ± 10.5; p < 0.001) compared with VS-MRA. The proposed SVS-MRA improves arterial SNR and CNR compared with VS-MRA by mitigating undesired presaturation of arterial blood upstream the imaging field of view.

MR Angiography Series: Fundamentals of Non-Contrast-enhanced MR Angiography.

Unlike CT angiography, which requires the use of contrast medium, MR angiography (MRA) can be performed without the use of contrast agents. This subfield of MRA is referred to as non-contrast-enhanced MRA (NC-MRA). While NC-MRA can be performed in many patients, it is especially useful in the imaging of pediatric and pregnant patients, as well as in patients with renal impairment. NC-MRA can also provide unique functional and hemodynamic information that is not obtainable with CT angiography or contrast-enhanced MRA. This module gives an overview of the predominant NC-MRA techniques that are currently available on modern clinical MRI systems, while also discussing some new and emerging topics in the field. This module is the second in a series created on behalf of the Society for Magnetic Resonance Angiography (SMRA), a group of researchers and clinicians who are passionate about the benefits of MRA but understand its challenges. The full digital presentation is available online. ©RSNA, 2021.

Value of non-contrast-enhanced MR angiography combined with captopril renal scintigraphy in the diagnosis of renovascular hypertension

Objective To evaluate the clinical value of non-contrast-enhanced MR angiography (NCE-MRA) combined with captopril renal scintigraphy (CRS) in the diagnosis of renovascular hypertension (RVH). Methods A total of 52 patients (33 males, 19 females; age: (54.5±16.3) years) with highly suspected RVH between January 2018 and October 2018 from Henan Provincial People′s Hospital were retrospectively analyzed. The examination data of NCE-MRA, basic renal dynamic imaging, CRS and digital subtraction angiography (DSA) were collected and reviewed. The renal artery stenosis (RAS) rate≥70% was the criterion for RVH diagnosed by DSA, which was considered as the gold standard. The diagnostic sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) of NCE-MRA, CRS and NCE-MRA+ CRS were determined. The consistency between NCE-MRA and DSA was analyzed by Kappa test. The differences of diagnostic efficiencies between CRS and NCE-MRA + CRS were compared by χ2 test or Fisher exact test. Results There was a high consistency between NCE-MRA and DSA in the diagnosis of RVH (Kappa=0.81, 95% CI: 0.62-0.96; P<0.01). The diagnostic sensitivity, specificity, accuracy, PPV and NPV of NCE-MRA were 88.89%(24/27), 92.00%(23/25), 90.38%(47/52), 92.31%(24/26), and 88.46%(23/26) respectively, those of CRS were 81.48%(22/27), 72.00%(18/25), 76.92%(40/52), 75.86%(22/29) and 78.26%(18/23) respectively, and those of NCE-MRA+ CRS were 74.07%(20/27), 100%(25/25), 86.54%(45/52), 100%(20/20) and 78.12%(25/32) respectively. Compared with CRS, the specificity (P=0.01) and PPV (P=0.03) of NCE-MRA+ CRS in the diagnosis of RVH were increased. Conclusion NCE-MRA and CRS are effective in the diagnosis of RVH, and the combination of two methods can significantly improve the diagnostic specificity and PPV than CRS alone. Key words: Hypertension, renovascular; Radionuclide imaging; Captopril; Technetium Tc 99m pentetate; Magnetic resonance imaging

Optimization of Echo Train Length in Non-contrast Enhanced MR Angiography for Clinical Examination of the Calf Arteries

Non-contrast magnetic resonanse angiography (MRA) using the three-dimensional electrocardiogram-synchronized fast spin echo method uses systolic and diastolic arterial signal differences. The method relies on the flow void signal of the arterial flow because of dephasing during systole. However, depiction of slow flow such as that in a calf artery was degraded because of insufficient dephasing during systole. In this study, we optimized echo train length (ETL) using a flow phantom and normal volunteers for clinical examination of the calf arteries. Flow phantom and normal volunteer images were obtained with various ETLs (40, 50, 60, and 70). An averaged profile across the tube in the phantom was used for detailed investigation of flow dephasing. Visual evaluation was performed and signal intensity change along vessels was measured using normal volunteer images. Comparison with peak systolic velocity (PSV) measured using ultrasound equipment was also conducted. Results of the flow phantom and normal volunteer study indicated that the overall depictability was improved with ETL 60 and 70, which was higher than the standard value. Additionally, the visualization of the peroneal artery with low PSV of ETL 70 had better depictability than ETL 60. This study suggested that ETL 70 might be better for clinical examination of the calf arteries.

Altered Ascending Aorta Hemodynamics in Patients After Arterial Switch Operation for Transposition of the Great Arteries.

Patients with transposition of the great arteries (TGA) have an altered aortic geometry after an arterial switch operation (ASO), with neo-aortic root dilatation as an important complication. Geometry-related aortic hemodynamics have been assumed to contribute to pathology of the ascending aorta (AAo). To evaluate aortic flow displacement (FD) and regional wall shear stress (WSS) in relation to ascending neo-aortic geometry in children after ASO. Prospective. Twenty-eight TGA patients after ASO and 10 healthy volunteers. 3.0T/4D flow (segmented fast-spoiled echo pulse), noncontrast-enhanced MR angiography (Dixon), and anatomic images (SSFP). Aortic diameters and body surface area-indexed aortic dimensions (Z-scores), normalized FD and planar ascending aortic WSS. Mann-Whitney and chi-square tests for differences in FD magnitude, WSS, and FD directionality between groups, respectively. Spearman rank correlation to assess the degree of association between aortic geometry, FD and WSS parameters. Shapiro-Wilk test to evaluate distribution normality on the absolute differences in octant location between FD and WSS. TGA patients showed a significantly dilated proximal AAo and relatively small mid-AAo dimensions at the level of the pulmonary arteries (Z-scores neo-aortic root: 4.38 ± 1.96 vs. 1.52 ± 0.70, P < 0.001; sinotubular junction: 3.48 ± 2.67 vs. 1.38 ± 1.30, P = 0.010; mid-AAo: 0.32 ± 3.06 vs. 1.69 ± 1.24, P = 0.001). FD magnitude was higher in TGA patients (neo-aortic root: 0.048 ± 0.027 vs. 0.021 ± 0.006, P < 0.001; sinotubular junction: 0.054 ± 0.037 vs. 0.029 ± 0.013, P < 0.05) and was related to the neo-aortic Z-score. Clear areas of higher WSS at the right and anterior aortic wall regions along the distal AAo were detected in TGA patients, most pronounced in those with relatively smaller mid-AAo diameters. TGA-specific geometry related to the ASO, evidenced by neo-aortic root dilatation and a sudden change in vessel diameter at mid-AAo level, leads to more aortic flow asymmetry in the proximal AAo and WSS distribution with higher WSS at the right and anterior aortic wall regions along the distal AAo. 1 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2020;51:1105-1116.

Free-breathing non-contrast-enhanced flow-independent MR angiography using magnetization-prepared 3D non-balanced dual-echo Dixon method: A feasibility study at 3 Tesla

In this work we aimed to investigate the feasibility of using a new pulse sequence called Relaxation-Enhanced Angiography without Contrast and Triggering (REACT) for free-breathing non-contrast-enhanced MR angiography (NCE-MRA) for multiple anatomies on 3T. Two magnetization-preparation pulses were incorporated with a three-dimensional dual-echo Dixon sequence. A T2-prep pulse, followed by a non-selective inversion pulse with a short inversion time, together suppressed tissue with short T1 and T2, while enhancing the signal of native blood with long T1 and T2. A two-point non-balanced gradient-echo Dixon method, based on dual-echo acquisition with semi-flexible echo times for water-fat separation, was used for improved fat suppression over a large field of view. General image quality, vasculature visibility, and clinical indications of the proposed method were investigated in healthy subjects and patients in both torso and extremities based on visual inspection. Preliminary results from REACT obtained in free-breathing with no cardiac triggering showed uniform suppression of background tissue over the field of view and robust blood-to-tissue contrast over multiple anatomies. Future clinical studies are warranted for further investigation of its diagnostic performance and limitations.

Non-Contrast-Enhanced MR Angiography (NCE-MRA) of the Hand Using Flow-Sensitive Dephasing (FSD)-Prepared Steady-State Free Precession (SSFP) in Patients with Rheumatoid Arthritis

To evaluate the clinical potential of a non-contrast-enhanced magnetic resonance angiography (NCE-MRA) technique using flow-sensitive dephasing (FSD)-prepared steady-state free precession (SSFP), FSD-NCE-MRA, for hand arterial angiography in patients with rheumatoid arthritis. Twenty-four patients were recruited and underwent FSD-NCE-MRA on a 1.5T MR system. For comparison, conventional dynamic CE-MRA was also conducted after the FSD-NCE-MRA scan. Images obtained by both FSD-NCE-MRA and CE-MRA were independently evaluated by two experienced radiologists using a four-point scale and the hand arteries were divided into wrist, palm and finger segments for image quality assessment. Signal-to-noise ratio (SNR), artery-to-muscle contrast-to-noise ratio (CNR), and vessel sharpness of superficial/deep palmar arch and common digital artery were also measured by a physician. Experimental results demonstrated that FSD-NCE-MRA yielded a higher percentage of diagnostic value arterial segments than CE-MRA (96 vs. 83 %, P < 0.05). Besides, average SNR, CNR, and vessel sharpness were also higher on FSD-NCE-MRA images than CE-MRA ones (SNR: 57 ± 13 vs. 15 ± 4; CNR: 54 ± 13 vs. 13 ± 4; sharpness: 1.1 ± 0.1 vs. 0.9 ± 0.1; all P < 0.05). Thus, FSD-NCE-MRA allows a higher image quality in the depiction of the hand arterial tree for the patients with rheumatoid arthritis compared to CE-MRA. The technique, FSD-NCE-MRA, may be a safe and improved clinical screening tool for the assessment of the hand arteries in rheumatoid arthritis patients without using any contrast agents.

Abstract WP120: Measuring Carotid Stenosis With a Novel Non-contrast Enhanced MR Angiography Technique (SNAP): Comparison With Contrast-enhanced MR Angiography

Introduction: Contrast-enhanced MR angiography (CE-MRA) provides highly accurate measurement of carotid stenosis. But non-contrast techniques are desired as contrast agents may lead to anaphylaxis or nephrogenic system fibrosis. Recently, an inversion-recovery gradient echo sequence with phase-sensitive reconstruction was developed for assessment of lumen and intraplaque hemorrhage in one sequence - Simultaneous Noncontrast Angiography and intraPlaque hemorrhage (SNAP). Hypothesis: We tested the hypothesis that SNAP provides an accurate and reproducible assessment of carotid stenosis compared to CE-MRA. Methods: Fifty-eight subjects with 16-79% stenosis on ultrasound were scanned using a large-coverage (16 cm), isotropic-resolution (0.8 mm) SNAP sequence. Minimum intensity projections were generated at ten degrees increments to get 3D views of carotid arteries. Carotid stenosis was measured bilaterally according to the NASCET criteria by independent readers to estimate inter-reader reproducibility. To assess agreement between SNAP and CE-MRA, 24 subjects also underwent CE-MRA with same resolution (0.8 mm isotropic) after injection of gadolinium contrast (Magnevist). Maximum intensity projections were generated for CE-MRA and analyzed while blinded to SNAP data. Results: Of 116 carotid arteries imaged by SNAP, 10 (8.6%) were excluded by at least one reader due to poor image quality or insufficient coverage. Inter-reader reproducibility was high, yielding an intra-class correlation coefficient (ICC) of 0.95 (95% CI: 0.93, 0.96). When stenosis measurements were categorized as no/mild (0-29%), moderate (30-69%) and severe (70-99%), weighted kappa was 0.77 (95% CI: 0.66, 0.88). In the 48 arteries with CE-MRA images, agreement between SNAP and CE-MRA was excellent (ICC: 0.96, 95% CI: 0.92, 0.98; weighted kappa: 0.90, 95% CI: 0.79, 1.00). Conclusions: SNAP can be used to obtain accurate and reproducible measurement of extracranial carotid artery stenosis without gadolinium contrast. The ability of SNAP to assess both traditional (stenosis) and emerging (intraplaque hemorrhage) risk factors may promote its use in clinical workup of carotid stenosis.

Ungated radial quiescent-inflow single-shot (UnQISS) magnetic resonance angiography using optimized azimuthal equidistant projections.

We hypothesized that non-contrast-enhanced MR angiography (NEMRA) could be performed without cardiac gating by using a variant of the quiescent-inflow single-shot (QISS) technique. Ungated QISS (UnQISS) MRA was evaluated in eight patients with peripheral arterial disease at 1.5T. The radial acquisition used optimized azimuthal equidistant projections, a long quiescent inflow time (1200 ms) to ensure replenishment of saturated in-plane spins irrespective of the cardiac phase, and a lengthy readout (1200 ms) so that a complete cardiac cycle was sampled for each slice. Venous and background tissue suppression was obtained using frequency-offset-corrected inversion radiofrequency pulses. Scan time for UnQISS was 15.4 min for an eight-station whole-leg acquisition. The appearance of UnQISS MRA acquired using the body coil was comparable to electrocardiographic-gated QISS MRA using phased array coils. A small radial view angle increment minimized eddy current-related artifacts, whereas image quality was inferior with a golden view angle radial increment or Cartesian trajectory. In patient studies, ≥50% stenoses were consistently detected. Using UnQISS, peripheral NEMRA can be performed without the need for cardiac gating. The use of fixed imaging parameters and body coil for signal reception further simplifies the scan procedure.

Detection of infragenual arterial disease using non–contrast‐enhanced MR angiography in patients with diabetes

To evaluate the diagnostic performance of a newly developed non-contrast-enhanced MR angiography (NCE-MRA) technique using flow-sensitive dephasing (FSD) prepared steady-state free precession (SSFP) for detecting calf arterial disease in patients with diabetes. Forty-five patients with diabetes who underwent routine contrast-enhanced MR angiography (CE-MRA) of lower extremities were recruited for NCE-MRA at the calf on a 1.5 Tesla MR system. Image quality evaluated on a 4-point scale and diagnostic performance for detecting more than 50% arterial stenosis were statistically analyzed, using CE-MRA as the standard of reference. A total of 264 calf arterial segments were obtained in the 45 patients with 88 legs. The percentage of diagnostic arterial segments was all 98% for NCE- and CE-MRA. The image quality, SNR, CNR was 3.3, 177, 138, and 3.5, 103, 99, for NCE-MRA and CE-MRA, respectively. The average sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of NCE-MRA were 97%, 96%, 90%, 99%, and 96%, respectively on a per-segment basis and 90%, 84%, 82%, 91%, and 87%, respectively, on a per-patients basis. The NCE-MRA technique demonstrates adequate image quality in the delineation of calf arteries and consistent diagnostic performance for detecting significant stenosis with CE-MRA in patients with diabetes.

Cerebral TOF angiography at 7T: Impact of B1+ shimming with a 16‐channel transceiver array

PurposeTime‐of‐flight (TOF) MR imaging is clinically among the most common cerebral noncontrast enhanced MR angiography techniques allowing for high spatial resolution. As shown by several groups TOF contrast significantly improves at ultrahigh field of B0 = 7T, however, spatially varying transmit B1 (B1+) fields at 7T reduce TOF contrast uniformity, typically resulting in suboptimal contrast and reduced vessel conspicuity in the brain periphery.MethodsUsing a 16‐channel B1+ shimming system, we compare different dynamically applied B1+ phase shimming approaches on the radiofrequency excitation to improve contrast homogeneity for a (0.5 mm)3 resolution multislab TOF acquisition. In addition, B1+ shimming applied on the venous saturation pulse was investigated to improve venous suppression, subcutaneous fat signal reduction and enhanced background suppression originating from MT effect.ResultsB1+ excitation homogeneity was improved by a factor 2.2–2.6 on average depending on the shimming approach, compared to a standard CP‐like phase setting, leading to improved vessel conspicuity particularly in the periphery. Stronger saturation, higher fat suppression and improved background suppression were observed when dynamically applying B1+ shimming on the venous saturation pulse.ConclusionB1+ shimming can significantly improve high resolution TOF vascular investigations at ultrahigh field, holding strong promise for non contrast‐enhanced clinical applications. Magn Reson Med 71:966–977, 2014. © 2013 Wiley Periodicals, Inc.

Initial clinical evaluation of a non‐contrast‐enhanced MR angiography method in the distal lower extremities

To report the initial experience and diagnostic performance applying a novel flow-dependent non-contrast-enhanced MR angiography (NCE-MRA) method, in patients with suspected peripheral vascular disease, in comparison with established contrast-enhanced MRA (CE-MRA). The lower legs of 34 patients were imaged at 1.5 T with both NCE-MRA and CE-MRA. The NCE-MRA method consisted of a cardiac-gated balanced-SSFP sequence with controllable flow-suppression preparation. Flow-suppressed and unsuppressed datasets were subtracted to obtain angiograms. Two experienced radiologists assessed both NCE-MRA and CE-MRA images, first independently and then in consensus to resolve significant disagreements. Signal loss, vessel conspicuity, vascular disease, venous contamination, artifacts, and diagnostic confidence were assessed. Using the CE-MRA as the "gold standard," the per-segment sensitivity and specificity for detection of significant disease were 81.7% and 90.9%, respectively. Mean diagnostic confidence (scale 0-4) was 3.4 for NCE-MRA and 3.9 for CE-MRA. Most vessel segments were well visualized but the popliteal arteries often suffered some technique-related signal loss. The NCE-MRA method was able to visualize most vessel segments with good or excellent confidence, few artifacts, and excellent background suppression, giving moderate agreement with CE-MRA. However, some segments were poorly visualized, probably due to flow profile distortion in these patients.

Image quality and diagnostic value of portal vein angiography in cirrhotic patients with non-contrast enhanced and contrast enhanced MR angiography

Objective To evaluate the imaging quality of the non-contrast enhanced MR angiography of sampling perfection with application optimized contrasts using different flip angle evolutions (SPACE) in showing portal system and compared it with that of the contrast enhanced MR angiography of volumetric interpolated breath-hold examination (VIBE),and study its diagnostic ability in the detection of portosystemic and portohepatic collaterals. Methods Thirty consecutively cirrhotic patients with suspected of portosystemic and portohepatic collaterals were enrolled,and underwent SPACE followed by VIBE at 1.5 T MR scanner.The diagnostic accuracy of SPACE for the portal vein disease was evaluated by two doctors and compared it with that of VIBE.The contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) of two MRA techniques were compared by using the Wilcoxon signed rank test.The quality assessment including scores of the portal vein segments and overall image quality were used the paired t test. Results Twenty-one patients were diagnosed as portal hypertension,including five types of portosystemic collaterals: esophageal varices (n=5),gastric fundic varices (n=11),splenic varices (n=5),paraumbilical varices (n=5) and cavemous transformation (n=2),and one patient was diagnosed as portal vein tumor thrombus.The diagnostic efficiency of SPACE was equivalent to that of VIBE.In SPACE,the SNR were 291±57,301±74,344±76 and the CNR were 231±59,242±73,286±76 at main portal vein,the left branch of portal vein and the right branch of portal vein,respectively.However in VIBE,the SNR were 185±56,176±52,182±52 and the CNR were 57±23,50±21,57±19 at,respectively.Both SNR and CNR of portal vein segments in the former were better than those in the latter (t values were 7.691,7.418,7.946,15.746,13.508 and 13.880,respectively,P 0.05).The scores of displaying the distal branches of left and right portal vein were 2.08±0.78,2.08±0.78 in SPACE,and 1.75±0.53,1.71±0.55 in VIBE,respectively.It was better (Z=-2.138,-2.324,P<0.05) in SPACE than that in VIBE. Conclusion The SPACE has better visualization of portal vein distal branches than VIBE,and it can be applied for the diagnosis of the portal vein disease. Key words: Portal vein; Magnetic resonance imaging; Liver cirrhosis

Four-dimensional noncontrast-enhanced MR angiography at ultrahigh field

Background Arterial spin labeled (ASL) 4D MRA has been shown to be a valuable method for simultaneously assessing anatomic structure and dynamic filling of cerebral arteries. Beyond improved SNR and parallel imaging performance, performing these studies at ultrahigh field will benefit from longer T1s resulting in more persistent labeling allowing for improved visualization of distal vessels, especially in conditions of reduced flow. Methods Studies were performed on Siemens 7T whole body MRI scanner with a 16-channel transceiver TEM stripline array head coil driven by a series of 16, 1 kW amplifiers (CPC, Pittsburgh, PA). Non-contrast enhanced 4D ASL MRA was performed using an ECG-triggered, segmented, 3D acquisition using signal targeting with alternating radiofrequency (STAR) for spin labeling. Label and control volumes were acquired with magnetization preparation immediately after the ECG R-wave and before the segmented readout used to generate the time resolved frames (Fig. 1). Background saturation over the imaging volume was applied for both label and control volumes. Data was acquired with 26 frames over 1700 ms (two R-R intervals) with a temporal resolution of ~60 ms and an acquisition time of 12:23. To address the challenges of B1+ homogeneity and efficiency at 7T, B1+ shimming was performed based on a small flip angle, calibration scan. Two B1+ shimming strategies were compared; 1) a static approach which used aC P-like mode over the entire brain for all RF pulses in the sequence, and 2) a dynamic approach which used a separate B1+ shim optimized for efficiency for the

Detailing the use of magnetohydrodynamic effects for synchronization of MRI with the cardiac cycle: A feasibility study

To investigate the feasibility of using magnetohydrodynamic (MHD) effects for synchronization of magnetic resonance imaging (MRI) with the cardiac cycle. The MHD effect was scrutinized using a pulsatile flow phantom at B(0) = 7.0 T. MHD effects were examined in vivo in healthy volunteers (n = 10) for B(0) ranging from 0.05-7.0 T. Noncontrast-enhanced MR angiography (MRA) of the carotids was performed using a gated steady-state free-precession (SSFP) imaging technique in conjunction with electrocardiogram (ECG) and MHD synchronization. The MHD potential correlates with flow velocities derived from phase contrast MRI. MHD voltages depend on the orientation between B(0) and the flow of a conductive fluid. An increase in the interelectrode spacing along the flow increases the MHD potential. In vivo measurement of the MHD effect provides peak voltages of 1.5 mV for surface areas close to the common carotid artery at B(0) = 7.0 T. Synchronization of MRI with the cardiac cycle using MHD triggering is feasible. MHD triggered MRA of the carotids at 3.0 T showed an overall image quality and richness of anatomic detail, which is comparable to ECG-triggered MRAs. This feasibility study demonstrates the use of MHD effects for synchronization of MR acquisitions with the cardiac cycle.

Modified quadruple inversion recovery prepulse for arterial spin labeling angiography without the need of subtraction

Arterial Spin Labeling (ASL) is a well-known technique that allows the non-invasive acquisition of angiograms without the need of a contrast agent [1][2]. ASL angiography is still clinically underused because of several challenges [3]: ASL requires two acquisitions (labeled and non labeled dataset) thereby doubling scan time. The need of subtraction increases the sensitivity to spatial misregistration and the need of the choice of an optimal inversion delay for best blood-to-background contrast introduces some “operator dependence”. An alternative technique not requiring image subtraction has been proposed (Figure ​(Figure1)1) [4]. This approach is based on a double inversion (DIR-ASL) prepulse and provides good background suppression if the surrounding tissues have similar T1 values (Figure ​(Figure1).1). However, DIR-ASL has only one optimal inversion delay and thus there is a trade-off between background suppression and visualized vessel extent. Our goal was to develop an ASL technique with improved background suppression and without the need of subtraction. Figure 1 Double inversion bright-blood MR angiography sequence Methods The proposed method is a modified Quadruple Inversion Recovery [5] sequence (mQIR-ASL), which provides excellent background signal suppression according to our simulations (Figure ​(Figure2).2). The first pair of RF pulses consists of a non-selective inversion RF pulse followed by a selective reinversion pulse and a navigator-restore pulse. The second pair of RF pulses consists of a non-selective inversion pulse followed by a navigator-restore pulse. With this configuration, the upstream labeled blood only “experiences” the second non-selective inversion pulse, while the static tissue “experiences” both non-selective inversion pulses. With the right choice of TI1 and TI2, signal from static tissue can be suppressed over a wide T1 range while maintaining the signal of target blood (Figure ​(Figure2).2). This pre-pulse was implemented on a 3T Achieva Gyroscan MR scanner (Philips Healthcare, Best, NL) and tested in 5 subjects. Figure 2 mQIR-ASL sequence, NS: Adiabatic Non-Selective Inversion Pulse. R: Selective Inversion Pulse, NR: Navigator Restore Pulse, N: Naviagtor, AQ: Acquisition Results Renal arteries including small branches were successfully visualized in all subjects with excellent suppression of background (Figure ​(Figure33,​,4).4). The plan scan and the maximum projection angiogram (MIP) are shown in Figure ​Figure3.3. Improved background suppression was observed with mQIR-ASL compared to DIR-ASL (Figure ​(Figure44). Figure 3 In vivo result with mQIR-ASL (TR/TI1/TI2 = 1000/480/162 ms). A- Planning procedure; B- and C- MIPs of aorta and renal arteries Figure 4 Transverse slice at the renal artery level demonstrating improved background suppression with mQIR-ASL (TW/TI1/TI2 = 480/162 ms) © compared with DIR-ASL (Inversion time (TI) of 300 ms (A) and 600 ms (B)). L=liver; M=muscle; K=kidneys. Conclusions We demonstrate a new ASL approach for non-contrast enhanced MR angiography with excellent background tissue suppression and without the need of subtraction. In comparison to DIR-ASL, mQIR-ASL yielded better background suppression and improved vessel delineation.

Vascular Abnormalities Correlate with Decreased Soft Tissue Volumes in Idiopathic Clubfoot

Lower extremity vascular anomalies have been described for patients with clubfoot but few imaging studies have investigated effects on soft tissues such as fat and muscle. To make these assessments we need noninvasive, noncontrast agents to more safely image children. We describe a novel noninvasive imaging protocol to identify vascular and soft tissue abnormalities in the lower limbs of patients with clubfoot and determine whether these abnormalities are present in patients who had recurrent clubfoot. Three-dimensional noncontrast-enhanced MR angiography was used to identify vascular, bone, and soft tissue abnormalities in patients with clubfoot. We determined whether these abnormalities were more common in patients who had experienced recurrent clubfoot. Four patients with isolated unilateral clubfoot had arterial anomalies in the clubfoot limb. All patients had less muscle volume in the affected limb, and nine of 11 patients (82%) had less subcutaneous fat, with a mean difference of 0.56 cm(3) ± 0.36 cm(3) (range, 0.08-1.12 cm(3)). Vascular anomalies and decreased fat and muscle volumes were present in all three patients with recurrent clubfoot. We found a high frequency of vascular and soft tissue anomalies in the affected limbs of patients with unilateral clubfoot that may correlate with response to treatment.

Triggered non-contrast enhanced MR angiography of peripheral arteries: Optimization of systolic and diastolic time delays for electrocardiographic triggering

The purpose of this study was to determine the optimal systolic and diastolic time delays for electrocardiographic triggering of a non-contrast media enhanced MR angiography using a 3-dimensional fast spin echo sequence in patients suffering from peripheral arterial disease. 12 patients with suspected peripheral arterial disease were examined on a 1.5 T Philips Achieva MR scanner. A cardiac-triggered Volumetric Isotropic T2-weighted fast spin echo sequence was performed using variable trigger delays for systolic and diastolic phase. The signal in the popliteal arteries and anterior tibial arteries of the systolic and diastolic images was measured and optimal delay times for systolic and diastolic phase were determined. Minimum signal to noise ratio (SNR) appears at the time difference ΔT=-21 ms on systolic images of the popliteal arteries. In the anterior tibial arteries the minimum SNR is significantly higher and appears at the time difference ΔT=-14 ms. Diastolic delay times must be chosen as long or as short as possible depending on heart rate. In peripheral vessels triggered non-contrast MR angiography can yield results which are comparable with contrast enhanced MRA techniques. It is crucial to optimize timing parameters.