Standard MRA Research Articles

Comparison of conventional MRI, MR arthrography, MR arthrography with traction, MR arthrography with pressure in the evaluation of articular distension

ObjectiveTo evaluate the performance of conventional MRI, standard MR arthrography, MR arthrography with traction and MR arthrography with pressure in articular distension in patients with ACL injury. Design and patientsThe consecutive patients (7 female, 21 male) with acute ACL injured conventional MRI, MR arthrography, MR arthrography with traction and MR arthrography with pressure were evaluated. ResultsThe amount of distension in the joint was evaluated in the posterior, femorotibial and anterior compartments. Medially, between the meniscus posterior horn and the tibial corner, MRA with pressure was found to be more effective in showing this distance than MRA with traction (p < 0,05). Laterally, in measurements made between the posterior horn of the meniscus and the capsule, MRA with traction and MRA with pressure are more effective showing this distance than conventional MRI and standard MRA (p < 0,05). In measurements made medially, between the posterior horn of the meniscus and the capsule, MRA with traction is more effective in showing this distance than standard MRA (p < 0,05). In all three different MRA modalities, the lateral femorotibial joint distance was found to be statistically higher than conventional MRI (p < 0,05). Medial femorotibial joint distance was found to be statistically higher in MRA with pressure than in conventional MRI and standard MRA (p < 0,05). The medial infrapatellar distance was found to be statistically higher in MRA with pressure than standard MRA and MRA with traction (p < 0,05). The lateral infrapatellar distance is higher in MRA with pressure than in MRA with traction, and this height is statistically significant (p < 0,05). ConclusionTraction and pressure applications added to MRA will increase the effectiveness of the method by increasing the distension in the knee joint. Although both seem to be effective in creating distension in posterior compartment and femorotibial joint distance, MRA with pressure is more effective especially in anterior compartment.

Comparison of 2D and 3D quiescent-interval slice-selective non-contrast MR angiography in patients with peripheral artery disease.

To evaluate the potential clinical benefit of the superior spatial resolution of 3D prototype thin-slab stack-of-stars (tsSOS) quiescent-interval slice-selective (QISS) MRA over standard 2D-QISS MRA for the detection peripheral artery disease (PAD), using computed tomography angiography (CTA) as reference. Twenty-three patients (70 ± 8 years, 18 men) with PAD who had previously undergone run-off CTA were prospectively enrolled. Patients underwent non-contrast MRA using 2D-QISS and tsSOS-QISS at 1.5 T. Eighteen arterial segments were evaluated for subjective and objective image quality (normalized signal-to-noise, nSNR), vessel sharpness, and area under the curve (AUC) for > 50% stenosis detection. Overall subjective image quality ratings for the entire run-off were not different between tsSOS-QISS and 2D-QISS (3 [3; 4] vs 4 [3; 4], respectively; P = 0.813). Sharpness of primary branch vessels demonstrated improved image quality using tsSOS-QISS compared with 2D-QISS (4 [3; 4] vs 3 [2; 3], P = 0.008). Objective image quality measures were not different between 2D-QISS and tsSOS-QISS (nSNR 5.0 ± 1.9 vs 4.2 ± 1.8; P = 0.132). AUCs for significant stenosis detection by tsSOS-QISS and 2D-QISS were 0.877 and 0.856, respectively (P = 0.336). The prototype 3D tsSOS-QISS technique provides similar accuracy in patients with PAD to a standard commercially available 2D-QISS technique, indicating that the use of relatively thick slices does not limit the diagnostic performance of 2D-QISS. However, subjective image quality for branch vessel depiction is improved using the 3D approach.

Abstract P344: Validation of Computational Fluid Dynamics Against PC-MRI Measurements of Blood Flow in Healthy Intracranial Arteries: On the Threshold to Clinical Utility for Stroke Prediction

Aim: Computational Fluid Dynamics (CFD) modeling of blood flow is a promising technique to obtain hemodynamic biomarkers and predict recurrent strokes. Few studies, however, have validated CFD against other methods for measuring hemodynamics, e.g. phase contrast MRI (PC-MRI). To resolve the uncertainties about the accuracy of CFD, this study validates the results of an automated software that combines deep learning and CFD for simulating blood flow given an MR angiogram against PC-MRI. Methods: Intracranial arteries in 10 healthy volunteers (60% male, mean age 38 ± 16 years) were automatically segmented from TOF MRA obtained at 3T using deep learning. Subject-specific CFD modelling was undertaken. PC-MRI flow rate for each subject was used at the inlet boundary condition, but not at the outlets. Outlet boundary condition was set to lumped parameter Windkessel model, with the resistance programmatically determined using allometric scaling laws based on the dimension and branching of vasculature. For comparison, two commonly used outlet conditions (exponent 2 &amp; 3 in Murray’s Law) were also considered. CFD results for flow rate and wall shear stress were compared against PC-MRI using Pearson’s correlation coefficient. Results: The flow rate across major intracranial arteries from CFD was in excellent agreement with the PC-MRI (MCA: r = 0.83, ACA: r = 0.81 &amp; PCA: r = 0.82). In addition, there was good correlation for both wall shear stress (WSS) and WSS Ratio (WSSR, i.e. the ratio of WSS between a branch and its parent vessel) (MCA (WSS/WSSR): r = 0.6/0.77, ACA (WSS/WSSR): r = 0.86/0.93 &amp; PCA (WSS/WSSR): r = 0.72/0.85). The inter-subject variability of the flow rate (i.e. standard deviation) obtained from CFD matched closely the variation range observed from PC-MRI and the literature. The two alternative outlet models behaved similarly but suffered from vessel truncation and high errors in some cases. Conclusion: CFD modelling of blood flow in intracranial arteries from static images has good agreement with PC-MRI measurements when allometric scaling laws are applied for setting Windkessel outflow conditions. This lays the foundation for using CFD to predict recurrent strokes as the technique uses standard MRA images already commonly acquired for stroke evaluation.

Abstract WMP64: From Static Imaging to Hemodynamic Modelling: Validation of Intracranial Blood Flow Simulations Against Population-Based PC-MRI Studies

Purpose: Modelling blood flow in cerebral arteries presents an opportunity to go beyond current luminal stenosis. These models could improve stroke prognostication by adding hemodynamic biomarkers such as translesional shear stress and pressure gradient. Such models, however, are rarely validated against real clinical data. We evaluated the accuracy of a computational fluid dynamics (CFD) model which uses allometric scaling laws against population-based Phase Contrast MRI (PC-MRI) measurements of blood flow in the brain. Methods: 3D models of the anterior circulation of 23 healthy subjects were reconstructed based on their MRA Time of Flight (TOF) images and CFD was used for modelling the blood flow. Lumped parameter Windkessel models were used as boundary conditions and allometric scaling laws were used to divide the flow and tune these boundary conditions, i.e. the resistance at each boundary was automatically adjusted based on the dimensions and branching of upstream vasculature. The results were compared against 4 PC-MRI studies from literature, covering a combined number of 417 healthy subjects. Results: The flow rate across 3 major intracranial arteries (ICA, MCA, and ACA) was obtained from the CFD simulations and was in good agreement with population-based PC-MRI studies. The agreement was 82.6% for the ICA, 85.9% for the MCA, and 80.4% for the ACA when comparing the average flow rate. The inter-patient variability of the flow rate (i.e. standard deviation) obtained from CFD simulations matched closely with the variation range measured in the literature. Allometric scaling enabled the model to accurately divide the flow at bifurcations (MCA/ICA flow ratio was 58.6% for the model vs 56.3% in the literature). We observed an average of 8 mmHg in pressure drop along the anterior circulation of healthy subjects (from ICA to MCA-M1 and ACA-A1), which agrees with the physiological range reported in the literature. Conclusion: This study shows the potential of accurately modelling blood flow based only on static images and demonstrates the validity of using allometric scaling in intracranial CFD simulations. The current modelling approach can potentially assist in stroke prognostication by obtaining hemodynamic risk factors from standard MRA TOF or CTA.

Accelerated, free-breathing, noncontrast, electrocardiograph-triggered, thoracic MR angiography with stack-of-stars k-space sampling and GRASP reconstruction.

To develop an accelerated, free-breathing, noncontrast, electrocardiograph-triggered, thoracic MR angiography (NC-MRA) pulse sequence capable of achieving high spatial resolution at clinically acceptable scan time and test whether it produces clinically acceptable image quality in patients with suspected aortic disease. We modified a "coronary" MRA pulse sequence to use a stack-of-stars k-space sampling pattern and combined it with golden-angle radial sparse parallel (GRASP reconstruction to enable self-navigation of respiratory motion and high data acceleration. The performance of the proposed NC-MRA was evaluated in 13 patients, where clinical standard contrast-enhanced MRA (CE-MRA) was used as control. For visual analysis, two readers graded the conspicuity of vessel lumen, artifacts, and noise level on a 5-point scale (overall score index = sum of three scores). The aortic diameters were measured at seven standardized locations. The mean visual scores, inter-observer variability, and vessel diameters were compared using appropriate statistical tests. The overall mean visual score index (12.1 ± 1.7 for CE-MRA versus 12.1 ± 1.0 for NC-MRA) scores were not significantly different (P > 0.16). The two readers' scores were significantly different for CE-MRA (P = 0.01) but not for NC-MRA (P = 0.21). The mean vessel diameters were not significantly different, except at the proximal aortic arch (P < 0.03). The mean diameters were strongly correlated (R2 ≥ 0.96) and in good agreement (absolute mean difference ≤ 0.01 cm and 95% confidence interval ≤ 0.62 cm). This study shows that the proposed NC-MRA produces clinically acceptable image quality in patients at high spatial resolution (1.5 mm × 1.5 mm × 1.5 mm) and clinically acceptable scan time (~6 min).

Preoperative Peroneal Perforator Mapping with Dynamic Time‐Resolved Magnetic Resonance Angiography

Objectives: Dynamic time-resolved magnetic resonance angiography (DTR MRA) is a novel imaging algorithm that allows for better visualization of small-caliber vessels when compared with standard MRA. We sought to estimate the technique sensitivity when compared with intraoperative findings. Methods: Retrospective review of 25 patients undergoing reconstruction with free fibula flap at an academic tertiary setting from 2009 to 2013. Preoperative DTR MRA was performed in all cases. Two radiologists performed blind reviews of the images and their findings were compared with surgical descriptions of the perforator anatomy. Results: Surgical exploration identified 32 perforators while DTR MRA identified 45 vessels. The technique confirmed the presence of perforators in 22 out of 23 patients with at least one perforator, and their absence in 1 out of 2 patients who had a negative exploration. There was a significant correlation in the number of perforators identified clinically and radiologically in each case ( P = .005). Twenty-seven perforators were localized to their correct anatomic location by the technique, yielding a sensitivity of 84.4% and a specificity of 16.7%. Ten out of the 18 vessels incorrectly identified by this technique were located within 30 mm of a confirmed perforator. Conclusions: DTR MRA is a highly sensitive technique for determining the presence and location of cutaneous perforators in patients undergoing reconstruction with free fibula flap. The majority of the false-positive findings corresponded to vessels located within 30 mm of a confirmed perforator; we hypothesize that they could represent distal branching patterns presenting radiologically as separate entities. These results compare favorably to perforator mapping with standard MRA techniques.

Accuracy of Abduction-External Rotation MRA Versus Standard MRA in the Diagnosis of Intra-articular Shoulder Pathology

The goal of this study was to compare the accuracy of abduction-external rotation magnetic resonance arthrography (ABERMRA) with standard MRA in the diagnosis of intra-articular shoulder pathology.One hundred three consecutive patients undergoing preoperative direct MRA and subsequent arthroscopic examination were included in the study. Seventy-eight patients underwent standard MRA and 25 underwent ABERMRA. Specialist-trained musculoskeletal radiologists reported all scans, and attending shoulder surgeons performed all arthroscopies. Arthroscopic assessment revealed 11 partial-thickness rotator cuff tears, 3 full-thickness tears, 64 labral lesions (48 soft tissue and 16 significant bony), and 17 superior labrum anterior-posterior (SLAP) tears. The sensitivity/specificity for standard MRA was 0.56/0.99 for partial-thickness rotator cuff tears, 1.00/1.00 for full-thickness rotator cuff tears, 0.75/0.91 for soft tissue labral tears, 0.58/1.00 for significant bony glenoid lesions, and 0.50/0.91 for SLAP tears. Abduction-external rotation magnetic resonance arthrography increased the sensitivity/specificity to 1.00/0.85 for soft tissue labral tears, 0.75/1.00 for significant bony glenoid lesions, and 1.00/1.00 for SLAP tears, although it missed 2 of 2 partial-thickness rotator cuff tears.This study suggests that standard MRA is a valuable investigation tool for instability, SLAP tears, and rotator cuff tears, although limitations exist. Additional ABERMRA sequences appear to improve the diagnostic accuracy of soft tissue anterior and posterior labral tears, SLAP tears, and significant bony glenoid lesions and should be routinely requested by shoulder surgeons when ordering MRAs to obtain the maximum benefit from this invasive investigation.

Nonbifurcating Cervical Carotid Artery Diagnosed by MR Angiography

A nonbifurcating cervical carotid artery is a branching anomaly in which the ECA has no proximal main trunk. We report its incidence and characteristic features on MRA. We retrospectively reviewed MRAs of 2866 patients obtained by using a standard noncontrast MRA protocol and two 1.5T MR imaging units and reviewed the English language literature to assess the occurrence and features of this nonbifurcating artery. We diagnosed 6 cases, indicating an incidence of 0.21%, and found 11 cases reported in the literature. Analysis of all 17 cases demonstrated no laterality or sex predominance. The most prevalent pattern of branching order from proximal to distal was the F-L trunk, the distal trunk of the ECA, and the OA. A nonbifurcating cervical carotid artery is rare but not as extremely rare as previously considered, and its correct diagnosis is necessary to avoid complications during interventional radiologic procedures or head and neck surgeries.

First‐pass and steady‐state magnetic resonance angiography of the thoracic vasculature using gadofosveset trisodium

To compare a high-resolution, ECG-gated, motion-compensated, steady-state magnetic resonance angiography (SS-MRA) of the thoracic vasculature to standard first-pass MRA (FP-MRA) using a blood-pool contrast agent (gadofosveset trisodium). In all, 25 patients >or=18 years with congenital or acquired disease of the thoracic vasculature, who underwent both FP-MRA and SS-MRA, were retrospectively identified. Diameters of left superior pulmonary vein (LSPV), left pulmonary artery (LPA), and aortic arch (AA) were measured. Image quality for LSPV, LPA, AA, coronary ostia, and coronary sinus were assessed. Vessel sharpness of LPA and LSPV and contrast ratio (CR) of LSPV, LPA, and AA were calculated. SS-MRA yielded significantly higher image quality for all vessels, and significantly higher vessel sharpness for LSPV and LPA compared to the FP-MRA. SS-MRA revealed lower intra- and interobserver variability for vessel diameters compared with the FP-MRA. The FP-MRA showed higher CR compared to the SS-MRA. Motion-compensated high-resolution SS-MRA of the thoracic vasculature using gadofosveset trisodium offers superior image quality compared to standard FP-MRA. Although SS-MRA delivers no dynamic information it may prove specifically helpful as an add-on to FP-MRA for imaging of small vascular structures.

Angiographie par Résonance Magnétique dans l’artériopathie distale des membres inférieurs : peut-on se passer d’une séquence multiphase (TRICKS) ?

To demonstrate the added diagnostic value of time-resolved imaging of contrast kinetics (TRICKS) in the evaluation of lower limb arteries compared to standard 3 level MRA with stepping table method. Forty patients (30% diabetics) with lower extremity peripheral arterial disease (87.5% with chronic ischemia) underwent standard contrast MRA including TRICKS of the distal arteries. Five arterial segments were defined per leg, and 395 arterial segments were compared (one patient with amputation). Two reviewers evaluated the quality of arterial imaging, presence of venous return and degree of stenosis per segment. The degree of interobserver agreement for arterial stenosis measurement was calculated. More arterial segments could be analyzed on the TRICKS sequence (good or excellent analysis in 63.03%-66.32% of arterial segments compared to 41.51%-47.08% on routine MRA). There was less venous contamination on TRICKS images (25.57% to 27.60% gain). The degree of interobserver agreement was superior with TRICKS compared to standard MRA (kappa 0.85 vs 0.69). The TRICKS sequence can be added to standard MRA for pre-therapeutic evaluation of distal arteries in patients with peripheral arterial disease, especially with chronic ischemic with rest pain and/or trophic changes.

Follow up of coiled intracranial aneurysms with standard resolution and higher resolution magnetic resonance angiography

Time-of-flight magnetic resonance angiography is a non-invasive alternative to digital subtraction angiography (DSA) for follow up of coiled intracranial aneurysms. Standard cranial MRA protocols are a compromise between spatial resolution and imaging time. This study compares a standard resolution MRA protocol with a protocol at higher spatial resolution MRA (HR-MRA) in 21 follow-up occasions in 17 coiled aneurysms in 15 patients. Images were reviewed for presence of residual or recurrent aneurysm and compared with DSA as the gold standard. Aneurysm flow signal on standard resolution MRA differed significantly from HR-MRA in 6/21 cases (P = 0.02) and DSA in 6/21 cases (P = 0.02). HR-MRA had 100% concordance with DSA (P = 1.0). In this study, three-dimensional time-of-flight magnetic resonance angiography carried out at standard resolution is inadequate for follow up of coiled intracranial aneurysms. HR-MRA is comparable to DSA for detection of aneurysm recurrence.

Time-resolved contrast-enhanced magnetic resonance angiography of the hand with parallel imaging and view sharing: initial experience

We sought to compare a three-dimensional, contrast-enhanced, magnetic resonance angiogram (3D CE MRA) sequence combining parallel-imaging (generalised autocalibrating partially parallel acquisitions (GRAPPA)) with a time-resolved echo-shared angiographic technique (TREAT) in an intraindividual comparison to a standard 3D MRA sequence. Four healthy volunteers (27-32 years), and 11 patients (11-82 years) with vascular pathologies of the hand were examined on a 1.5-Tesla (T) MR system (Magnetom Avanto, Siemens, Erlangen, Germany) using two multichannel receiver coils. Following automatic injection (flow rate 2.5 cc/s) of 0.1 mmol/kg gadoterate (Dotarem, Guerbet, Roissy, France), 32 consecutive 3D data sets were collected with the TREAT sequence (TR/TE: 4.02/1.31 ms, FA: 10 degrees, GRAPPA acceleration factor: R=2, TREAT factor: 5, voxel size: 1.0 x 0.7 x 1.3 mm(3)) and a T1-wwighted 3D gradient-echo sequence (TR/TE: 5.3/1.57 ms, FA: 30 degrees, GRAPPA acceleration factor: 2, voxel size: 0.71 x 0.71 x 0.71 mm(3,)). MR data sets were evaluated and compared for image quality and visualisation of vascular details. In the volunteer group, all MR imaging was successful while technical problems prevented acquisition of the standard protocol in two patients. For the corresponding segments, the number of visible segments was equal on both sequences. Overall image quality was significantly better on the standard protocol than on the TREAT protocol. TREAT MRA provided functional information in lesions with rapid blood flow, e.g. detection of feeding and draining vessels in an haemangioma. TREAT-MRA is a robust technique that combines morphological and functional information of the hand vasculature and deals with the very special physiological demands of vascular lesions, such as quick arteriovenous transit time.

Sensitivity encoding (SENSE) for contrast‐enhanced 3D MR angiography of the abdominal arteries

To assess sensitivity encoding (SENSE) for contrast-enhanced MR angiography (CE-MRA) of the abdominal arteries in comparison with standard MRA protocols. In 22 patients MRA of the abdominal arteries was performed twice (once using a standard protocol, and once with the additional use of SENSE). In 10 patients all examination parameters were kept constant (TR/TE/FA = 3.8 msec/1.3 msec/30 degrees ), and a reduction in scan time from 22 to 11 seconds was realized with the use of SENSE. In 12 patients, using SENSE the acquisition matrix was increased from 208 to 416, keeping the scan time constant. Image quality was scored on a five-point scale by three radiologists. Additionally, ROI-based measurements of CNR were performed. For both protocols, image quality was significantly improved using SENSE. The time-reducing SENSE protocol yielded an average score of 4.2 points vs. 3.1 for the standard protocol. Using SENSE to increase the acquisition matrix, an average score of 4.3 was reached vs. 3.2 for the standard protocol (P < 0.05). The number of depictable small vessels and their bifurcations was significantly increased by either of the two SENSE protocols as compared to the standard imaging procedure. SENSE for MRA of the abdominal arteries significantly increases image quality and permits a substantial reduction in breath-hold time or a significantly improved spatial resolution.

La perspective d’une étude dynamique des artères des membres inférieurs en IRM grâce à la séquence ECTRICKS

Purpose This article presents a new MR angiography technique, Elliptic Centric Time Resolved Imaging on Contrast KineticS (ECTRICKS), which allows dynamic evaluation of the lower limb arteries opacification when venous return prevents adequate diagnostic evaluation of calf arteries. Patient and methods Comparative examination of the calf arteries in 59 patients using a standard MRA technique and the ECTRICKS technique. Results A total of 33 examinations could be compared. Additional arteries could be evaluated in 10% of our patient population using the ECTRICKS technique, and in 20% for our diabetic population. Arterial evaluation was better with the ECTRICKS technique in patients with diabetes and venous insufficiency. Conclusion ECTRICKS is a good complementary sequence for evaluating the calf arteries in patients with diabetes or early venous return.

3D time of flight MR angiography: aquisition with small field of view and low phase encodes

The aim of the study was to evaluate and compare the image quality of the 3D TOF MRA acquired with a small FOV and low phase encodes with those MR angiographic images acquired with standard pulse sequence parameters. Twenty patients who were referred to our institution for MR imaging of the brain and strictly satisfied the selection criteria were included in this study. Apart from the routine protocol for MR imaging of the brain, 3D TOF MRA of the circle of Willis with a small FOV and a standard FOV were performed. The image quality of all MRA was evaluated by two independent observers who were blind to the pulse sequence parameters. From the standard FOV MRA, 22.5, 12.5, and 5% of the patients were graded as mild, moderate, and severe stenosis of the internal carotid artery, respectively. On the contrary, no apparent stenosis was observed from the small FOV MRA with low phase encodes. Regarding the reduction in MR artifacts and acquisition time achieved with the small FOV 3D TOF MRA with low phase encodes, this might be a useful MR angiographic technique to be used in routine clinical practice.