3D Magnetic Resonance Angiography Research Articles

Collateral circulation via the circle of Willis in patients with carotid artery steno-occlusive disease: evaluation on 3-T 4D MRA using arterial spin labelling

To evaluate whether 3-T four-dimensional (4D) arterial spin-labelling (ASL) -based magnetic resonance angiography (MRA) is useful for assessing the collateral circulation via the circle of Willis in patients with carotid artery steno-occlusive disease. Institutional review board approval and prior written informed consent from all patients were obtained. The inclusion criteria were fulfilled by 13 patients with carotid artery steno-occlusive disease. All underwent 4D-ASL MRA at 3T and digital subtraction angiography (DSA). The flow-sensitive alternating inversion recovery (FAIR) preparation scheme with look-locker sampling was used for spin labeling. At 300-ms intervals seven dynamic scans were obtained with a spatial resolution of 0.5×0.5×0.6mm(3). The collateral flow via the circle of Willis was read on 4D-ASL MRA and DSA images by two sets of two independent readers each. κ statistics were used to assess interobserver and intermodality agreement. On DSA, collateral flow via the anterior communicating artery (AcomA) was observed in six patients, via the posterior communicating artery (PcomA) in four patients, and via both the AcomA and PcomA in three patients. With respect to the qualitative evaluation of 4D-ASL MRA images, interobserver agreement was excellent for all items (κ=1). 4D-ASL MRA and DSA consensus readings agreed on the type of collateral flow pattern in 10 of the 13 patients (77%). Intermodality agreement was good (κ=0.606; 95% confidence interval (CI): 0.215-0.997). 3T 4D-ASL MRA may be a useful tool for the evaluation of the collateral circulation in patients with carotid artery steno-occlusive disease.

Recent advances in 3D time-resolved contrast-enhanced MR angiography.

Contrast-enhanced magnetic resonance angiography (CE-MRA) was first introduced for clinical studies approximately 20 years ago. Early work provided 3-4 mm spatial resolution with acquisition times in the 30-second range. Since that time there has been continuing effort to provide improved spatial resolution with reduced acquisition time, allowing high resolution 3D time-resolved studies. The purpose of this work is to describe how this has been accomplished. Specific technical enablers have been: improved gradients allowing reduced repetition times, improved k-space sampling and reconstruction methods, parallel acquisition, particularly in two directions, and improved and higher count receiver coil arrays. These have collectively made high-resolution time-resolved studies readily available for many anatomic regions. Depending on the application, ∼1 mm isotropic resolution is now possible with frame times of several seconds. Clinical applications of time-resolved CE-MRA are briefly reviewed.

Comparison of great artery dimensions in 3-D dual-phase SSFP, compared with 3D CE-MRA and phase-contrast imaging (magnitude image)

Background The dimensions of great vessels are measured in different methods in different institutes. The purpose of this study was to evaluate the benefits of 3D dual phase steady-state free-precession(3D-DP SSFP)for measuring great arteries dimension, compared with 3D contrastenhanced magnetic resonance angiography (3D CEMRA) and 2D phase contrast imaging (Magnitude image) (2DPC-MI), in order to find which was the most suitable and reproducible technique for follow-up. Methods 29 patients with repaired Tetralogy of Fallot or complete transposition of the great arteries after arterial switch operation (mean age 6.5yrs; range 6m to 25yrs) were included in the study. Cross-sectional diameter and area measurements were taken of the ascending aorta (Ao), main pulmonary (MPA) and branch pulmonary arteries (BPA) by using 3D DP SSFP, 3D CE-MRA and magnitude image of 2DPC-MI. Image quality was scored by a five-point scale (0 = invisible to 4 = excellent). Statistical comparison between 3D DP SSFP and other two techniques (2DPC-MI and 3D CE-MRA) was performed by using paired-t tests and Intraclass correlation coefficient. Results All great artery cross-sectional measurements were significantly (P < 0.001) greater in systole than in diastole. Measurements (diameter and area) of great arteries were greatest for 2DPC-MI, followed by 3D SSFP in systole and 3D CE-MRA, and smallest for 3D DP SSFP in

Target volume coronary MRA revisited: usefulness of non-rigid reregistration of multi-frame 3D MRA acquisitions at 3T

Background Free-breathing whole-heart coronary MR angiography (MRA) is an established method that can visualize all coronary arteries within a single acquisition. However, a long acquisition time and suboptimal arterial signal due to thick SLAB are major limitations of 3T gradient-echo whole-heart coronary MRA without contrast. Alternatively, target-volume coronary MRA can be used to visualize coronary arteries within a predefined target volume within a shorter acquisition time. In addition, relatively small SLAB volume of this approach permits acquisitions of multi-frame 3D data without prolonging scan duration. Recently, non-rigid image registration has been emerged as a technique which can merge images and improve SNR and CNR. The purpose of this study was to develop a new technique to obtain high quality free-breathing target-volume coronary MRA with shorter acquisition time by employing multi-frame 3D acquisitions and non-rigid image registration.

The role of MRI in the evaluation of vascular malformations

Objective The aim of this study was to evaluate the role of MRI and MR angiography in the assessment of vascular malformations as compared with the usefulness of duplex sonography and digital subtraction arteriography. Participants and methods A total of 40 patients (age range, 1-35 years; 21 male and 19 female) with diagnosed vascular malformations on the basis of color duplex imaging were examined on a 1.5 T whole-body MR scanner. Using parameters based on a fast localizer sequence, we acquired axial or coronal T1-, T2-, short-time inversion recovery (STIR) and contrast-enhanced T1-weighted images. Dynamic postcontrast three-dimensional (3D) gradient-echo MRIs were used for patients with high-flow arteriovenous malformation. MR data sets were evaluated for the detection of the lesion, determination of the malformation extent, involvement of surrounding structures, and vascular details with regard to the nidus, feeding arteries, and draining veins. Results were compared with findings from the digital subtraction angiography (DSA). Results All MRIs revealed 14 low-flow venous vascular malformations, 12 high-flow arteriovenous malformations, and 14 hemangiomas. The STIR sequence was helpful for determining the extent of vascular malformation, whereas dynamic postcontrast 3D MR angiography helped in the classification of the type of the vascular malformation. MR angiography was inferior to DSA in revealing the vascular details and for interventional procedure planning. Conclusion MRI and MR angiography appear to play a significant role in the assessment of vascular malformations. The protocol for imaging such vascular malformations should include dynamic postcontrast 3D gradient-echo MRI with STIR sequences. However, DSA is still required for more vascular detail delineation and definitive treatment decisions.

Dynamic MR angiography in acute aortic dissection.

To evaluate the benefit (additional flow information), image quality, and diagnostic accuracy of a dynamic magnetic resonance angiography (MRA) combining high spatial and temporal resolution for the preinterventional assessment of acute aortic dissection. Nineteen patients (12 men, 7 women; aged 32-78 years) with acute aortic dissection underwent contrast-enhanced four-dimensional (4D) MRA and 3D conventional high-resolution MRA (3D MRA) within one examination on a 1.5 Tesla MR system. Both MRA datasets for each patient were evaluated and compared for image quality and visualization of vascular details on a 5-point scale (5 = excellent image quality, 1 = nondiagnostic image quality). In addition, presence and relevance of additional hemodynamic information (flow direction and organ perfusion delay) gained by dynamic MRA were assessed. Conventional 3D MRA provided significantly higher values for image quality of the aorta and aortic side branches compared with dynamic MRA (aorta: 4.3 versus 3.3; P = 0.006 side branches: 4.2 versus 3.3; P = 0.02). However, in 10 of the 19 patients (53%) the additionally available information on flow dynamics due to dynamic MRA (e.g., delayed perfusion of parenchymal organs) led to a change in therapy planning and realization. Dynamic MRA is a technique that combines functional flow and morphological information. Thus, the combination of 3D and dynamic MRA provides all requested information for treatment planning in patients suffering from acute aortic dissection.

Cavernous sinus meningiomas: imaging and surgical strategy.

Cavernous sinus (CS) meningiomas which are by definition those meningiomas which originate from the parasellar region are difficult skull base tumors to deal with. For deciding the most appropriate surgical strategy, surgeons need detailed preoperative neuroimaging. The vicinity of the tumor with the vital and highly functional neurovascular structures, tumor extensions into the basal cisterns and skull base structures, and the arterial vascularization and venous drainage pathways, as they shape operative strategy, are important preoperative data to take into account. Thin section CT scan with bone windows, 3D spiral CT reconstruction, MRI, MR angiography, and DSA performed with selective arteriography including late venous phases give those required detailed informations about the tumor and its relation with neurovascular and bony structures. The type of craniotomy and complementary osteotomy and the usefulness of an extradural anterior clinoidectomy with unroofing the optic canal can be decided from preoperative neuroimaging. Data collected also help in determining whether extensive exposure of the middle cranial fossa is necessary to ensure substantial devascularization of the tumor and whether proximal control of the internal carotid artery (ICA) at its intrapetrosal portion might be useful. Study of the capacity of blood supply of the Willis circle is wise for deciding the need and way of performing an extra-intracranial bypass together with tumor removal. Currently the concept of operating only the tumors with extracavernous extensions and to limit resection to only their extracavernous portions is the most accepted way of treating these tumors. It was that strategy that was adopted in the senior author's 220-patient series.Radiosurgery or stereotactic fractionated radiotherapy may complement surgery or can be only reserved for growing remnants.

100% Efficient three-dimensional coronary MR angiography with two-dimensional beat-to-beat translational and bin-to-bin affine motion correction.

To develop a flexible image navigator for 3D coronary MR angiography that allows respiratory motion of variable complexity to be compensated for on different temporal scales. A two-dimensional (2D) golden radial image navigator is proposed; translational motion is compensated for on a beat-to-beat basis, and residual affine motion is compensated for on a bin-to-bin basis in a two-step procedure. The method does not use a respiratory gating window and therefore achieves 100% scan efficiency and a predictable scan time. The proposed method was tested in 11 healthy volunteers and compared against a navigator-gated and tracked acquisition. The proposed method achieved comparable quantitative and qualitative image quality to a 6-mm navigator-gated and tracked scan while reducing the scan time by a factor of approximately 2. Combined motion correction using image navigators improved visualization of the coronary arteries in four of 11 subjects in comparison with translational correction only, and image quality was maintained in the remaining cases. In one case, visualization of the left anterior descending coronary artery was degraded using combined correction compared with translation correction only. The feasibility of correcting for 2D translational motion on a beat-to-beat basis as well as affine motion on a bin-to-bin basis has been demonstrated.

The superior ophthalmic vein: delineation with high-resolution magnetic resonance imaging.

To delineate the superior ophthalmic vein (SOV) with high-resolution magnetic resonance (MR) imaging. This retrospective study enrolled 302 consecutive outpatients, 101 patients, 51 males and 50 females, who underwent coronal T2-weighted imaging and 201 patients, 99 males and 102 females, who underwent three-dimensional (3D) phase-contrast (PC) MR angiography. Coronal T2-weighted imaging clearly delineated the intraorbital course of SOV on serial images in all 101 subjects. The SOV could be topographically divided into three segments in relation to the superior rectus muscle. The SOV crossed over the optic nerve at the level of the anterior ethmoidal foramina in 87% of right orbits and 71% of left orbits. The mean outer diameter of the SOV at the crossing point was 1.7 mm on both sides, but the SOVs were asymmetric in the same individual in 75% of the subjects. 3D PC MR angiography showed that the bilateral SOVs were symmetrical in 16% of subjects, larger in the right orbit in 18%, and larger in the left orbit in 13%, and were unidentified in 52%. The SOV showed a consistent lateral course to the ophthalmic artery. The SOV consistently courses lateral to the ophthalmic artery, but tends to show bilateral asymmetry in the outer diameter. The superior rectus muscle, anterior ethmoidal foramen, and anterior ethmoidal artery are valuable landmarks to identify the SOV during transcranial orbital surgery. Combination of high-resolution MR imaging and 3D PC MR angiography is useful for delineating the SOV.

Value of 4D MR angiography at 3T compared with DSA for the follow-up of treated brain arteriovenous malformation.

Four-dimensional, contrast-enhanced MRA is a useful technique for the diagnosis and classification of brain AVM. The purpose of this study was to evaluate its usefulness in the follow-up of treated brain AVM. Patients with treated brain AVM (embolization, radiosurgery, and/or surgery) were investigated with both DSA (the "gold standard") and 4D MRA. Four-dimensional MRA was performed at 3T using a 4D sequence, combining contrast-enhanced timing-robust angiography, keyhole, and sensitivity encoding techniques. Examinations were evaluated by 2 independent readers and disagreements were resolved by a third reader. Interobserver and intermodality agreement with respect to residual nidus, residual venous drainage, and brain AVM patency were determined. Between May 2008 and February 2013, 37 patients with a median age of 45 years (interquartile range = 26-55) were prospectively included. Examinations were acquired 36 months (IQR = 10-45.5) after the last treatment. Interobserver agreement for brain AVM patency was very good for both 4D MRA (κ 0.82, 95% CI .67-.98) and DSA (κ 0.84, 95% CI .69-.98). After consensus reading, intermodality agreement for the evaluation of brain AVM patency was good (κ 0.73, 95% CI .55-.90). Diagnostic accuracy of 4D MRA for residual brain AVM compared with DSA, reached a sensitivity of 73.7%, specificity 100%, positive predictive value 100%, and negative predictive value 78.3%. Agreements by technique of treatment are also detailed. Four-dimensional MRA is a useful radiation-free technique for the follow-up of patients with treated brain AVM, especially patients treated by radiosurgery. However, given its actual limitations it is not sufficient to assert the cure; DSA remains mandatory for this purpose.

The detection of coronary stiffness in cardiac allografts using MR imaging

ObjectiveTo test the hypothesis that biomechanical changes are quantitatively related to morphological features of coronary arteries in heart transplant (HTx) recipients. Materials and methodsWith IRB approval, three-dimensional (3D) magnetic resonance (MR) angiography and two-dimensional (2D) black-blood stead-state free precession (SSFP) MR imaging were performed to image coronary arteries of 36 HTx patients. Contours of coronary wall were manually drawn. For each coronary segment, coronary wall thickness, wall area, lumen area (in systole and diastole) were acquired. Coronary distensibility index (CDI) and the percent of the coronary wall occupying the vessel area (PWOV) were calculated. ResultsThere are totally 98 coronary segments eligible for quantitative analysis from 27 HTx patients. The CDI is 4.90±2.44mmHg−1. The mean wall thickness is 1.49±0.24mm and the PWOV is 74.6%±7.5%. CDI has moderate correlations with wall thickness (r=−0.531, P<0.001) and with PWOV (R=−0.435, P<0.001). ConclusionsDetected with coronary MR imaging, CDI is quantitatively correlated with the morphological features of the coronary artery in HTx patients. Coronary stiffness has the potential to become an alternative imaging biomarker for the quantitative assessment of the status of cardiac allografts.

Sliding time of flight: sliding time of flight MR angiography using a dynamic image reconstruction method.

To obtain three-dimensional (3D) MR angiography having high contrast between vessel and stationary background tissue, a novel technique called sliding time of flight (TOF) is proposed. The proposed method relies on the property that flow-related enhancement (FRE) is maximized at the blood-entering slice in an imaging slab. For the proposed sliding TOF, a sliding stack-of-stars sampling and a dynamic MR image reconstruction algorithm were developed. To verify the performance of the proposed method, in vivo study was performed and the results were compared with multiple overlapping thin 3D slab acquisition (MOTSA) and sliding interleaved ky (SLINKY). In MOTSA and SLINKY, the variation of FRE resulted in severe venetian blind (MOTSA) or ghost (SLINKY) artifacts, while the vessel-contrast increased as the flip angle of radiofrequency (RF) pulses increased. On the other hand, the proposed method could provide high-contrast angiograms with reduced FRE-related artifacts. The sliding TOF can provide 3D angiography without image artifacts even if high flip angle RF pulses with thick slab excitation are used. Although remains of subsampling artifacts can be present in the reconstructed images, they can be reduced by MIP operation and resolved further by regularization techniques.

Non-contrast-enhanced 4D MR angiography with STAR spin labeling and variable flip angle sampling: a feasibility study for the assessment of Dural Arteriovenous Fistula

This study aimed to evaluate the feasibility of non-contrast-enhanced 4D magnetic resonance angiography (NCE 4D MRA) with signal targeting with alternative radiofrequency (STAR) spin labeling and variable flip angle (VFA) sampling in the assessment of dural arteriovenous fistula (DAVF) in the transverse sinus. Nine patients underwent NCE 4D MRA for the evaluation of DAVF in the transverse sinus at 3T. One patient was examined twice, once before and once after the interventional treatment. All patients also underwent digital subtraction angiography (DSA) and/or contrast-enhanced magnetic resonance angiography (CEMRA). For the acquisition of NCE 4D MRA, a STAR spin tagging method was used, and a VFA sampling was applied in the data readout module instead of a constant flip angle. Two readers evaluated the NCE 4D MRA data for the diagnosis of DAVF and its type with consensus. The results were compared with those from DSA and/or CEMRA. All patients underwent NCE 4D MRA without any difficulty. Among seven patients with patent DAVFs, all cases showed an early visualization of the transverse sinus on NCE 4D MRA. Except for one case, the type of DAVF of NCE 4D MRA was agreed with that of reference standard study. Cortical venous reflux (CVR) was demonstrated in two cases out of three patients with CVR. NCE 4D MRA with STAR tagging and VFA sampling is technically and clinically feasible and represents a promising technique for assessment of DAVF in the transverse sinus. Further technical developments should aim at improvements of spatial and temporal coverage.

Comparison of native high-resolution 3D and contrast-enhanced MR angiography for assessing the thoracic aorta

To omit risks of contrast agent administration, native magnetic resonance angiography (MRA) is desired for assessing the thoracic aorta. The aim was to evaluate a native steady-state free precession (SSFP) three-dimensional (3D) MRA in comparison with contrast-enhanced MRA as the gold standard. Seventy-six prospective patients with known or suspicion of thoracic aortic disease underwent MRA at 1.5 T using (i) native 3D SSFP MRA with ECG and navigator gating and high isotropic spatial resolution (1.3 × 1.3 × 1.3 mm(3)) and (ii) conventional contrast-enhanced ECG-gated gradient-echo 3D MRA (1.3 × 0.8 × 1.8 mm(3)). Datasets were compared at nine aortic levels regarding image quality (score 0-3: 0 = poor, 3 = excellent) and aortic diameters, as well as observer dependency and final diagnosis. Statistical tests included paired t-test, correlation analysis, and Bland-Altman analysis. Native 3D MRA was acquired successfully in 70 of 76 subjects (mean acquisition time 8.6 ± 2.7 min), while irregular breathing excluded 6 of 76 subjects. Aortic diameters agreed close between both methods at all aortic levels (r = 0.99; bias ± SD -0.12 ± 1.2 mm) with low intra- and inter-observer dependency (intraclass correlation coefficient 0.99). Native MRA studies resulted in the same final diagnosis as the contrast-enhanced MRA. The mean image quality score was superior with native compared with contrast-enhanced MRA (2.4 ± 0.6 vs. 1.6 ± 0.5; P < 0.001). Accuracy of aortic size measurements, certainty in defining the diagnosis and benefits in image quality at the aortic root, underscore the use of the tested high-resolution native 3D SSFP MRA as an appropriate alternative to contrast-enhanced MRA to assess the thoracic aorta.

Numerical Simulation of the blood flow behavior in the circle of Willis.

Introduction: This paper represents the numerical simulation of blood flow in the circle of Willis (CoW). Circle of Willis is responsible for the oxygenated blood distribution into the cerebral mass. To investigate the blood behavior, two Newtonian and non-Newtonian viscosity models were considered and the results were compared under steady state conditions. Methods: Methodologically, the arterial geometry was obtained using 3D magnetic resonance angiography (MRA) data. The blood flow through the cerebral vasculature was considered to be steady and laminar, and the Galerkin’s finite element method was applied to solve the systems of non-linear Navier-Stokes equations. Results: Flow patterns including flow rates and shear rates were obtained through the simulation. The minimal magnitude of shear rates was much greater than 100 s-1 through the larger arteries; thus, the non-Newtonian blood viscosity tended to approach the constant limit of infinite shear viscosity through the CoW. So, in larger arteries the non-Newtonian nature of blood was less dominant and it would be treated as a Newtonian fluid. The only exception was the anterior communicating artery (ACoA) in which the blood flow showed different behavior for the Newtonian and non-Newtonian cases. Conclusion By comparing the results it was concluded that the Newtonian viscosity assumption of blood flow through the healthy, complete circle of Willis under the normal and steady conditions would be acceptably accurate.

Detection of acute pulmonary embolism: feasibility of diagnostic accuracy of MRI using a stepwise protocol

Multidetector computed tomography (MDCT) has become the imaging method of choice in patients suspected of having pulmonary embolism (PE) but has the inherent limitation of radiation dose and the side effects of contrast agents. The purpose of the study was to assess the feasibility of a stepwise MRI protocol in the clinical setting of acute PE. The stepwise approach should make it possible to diagnose acute PE in critically ill patients using fast MR sequences and included the option to add comprehensive sequences when patients were stable. Forty-five patients with acute PE (26 men, 19 women; 41 ± 16 years) were included in this prospective study. The diagnosis was initially confirmed by MDCT as gold standard. MRI at 1.5 T was subsequently performed without any delay in medical treatment. The MRI protocol proceeded stepwise from robust to detailed imaging techniques (i.e., from TrueFISP and single shot HASTE sequence to MR perfusion and 3D-MR angiography) if the patient was able to tolerate additional imaging time. Diagnostic accuracy was evaluated on the central (lobar) and peripheral (segmental) levels. The complete MR protocol was applied in 40 of the 45 patients (88 %). In the remaining five patients with severe dyspnea the diagnosis of acute PE was established by using fast TrueFISP sequences that were insensitive to respiratory movement. All five patients suffered from a major central PE. Highest sensitivity was achieved by MR perfusion (lobar, 98 %; segmental, 95 %). Real-time TrueFISP and MR angiography showed the highest specificity (lobar, 90-100 %; segmental, 95-97 %). The combination of all MR sequences matched closely the results of MDCT (lobar: sensitivity 98 %, specificity 100 %; segmental: sensitivity 95 %, specificity 97 %). MRI using a stepwise protocol is a promising approach for diagnosing acute PE. The protocol can be tailored for dyspneic patients with central PE using real-time MRI sequences. The diagnostic accuracy for peripheral PE can be improved by using combined MR techniques, achieving comparable results to MDCT.

Self-navigated free-breathing isotropic 3D whole heart MRI for the characterization of complex cardiac anatomy in patients with congenital heart malformations

Introduction: Cardiac anatomy of patients with congenital heart disease (CHD) is often complex and accurate evaluation mandates MR image acquisition in several non-standardized planes requiring considerable operator involvement and multiple breath-holds. The utility of self-navigated isotropic 3D-free-breathing whole-heart MRI (SN-3D) was assessed for the visualization of the heart, coronary arteries (CA) and great vessels (GV) in CHD patients. Methods: Data acquisition was performed during free breathing on a 1.5T-MRI scanner with a 3D-radial trajectory modified for respiratory self-navigation after gadobutrol injection; it was ECG-triggered, with a T2-preparation pulse and fat-saturated SSFP readout. The isotropic image data were reformatted offline. Image quality was graded and GV diameters were measured at several levels in all patients. 3D MR-angiography (MRA) was performed in a subset of patients and the GV diameters were also measured for comparison. Results: 38 patients (66% male, age 23±10y) were included. Heart rate was 71±13 bpm, scan duration 9.1±4.2 min, isotropic resolution 1.1×1.1×1.1 mm3. Image quality was good in 23, moderate in 10, mediocre in 2, and poor in 3. 3D datasets allowed the assessment of the arrangement of heart chambers and great vessels, the venous return anatomy after atrial switch for transposition of the great arteries (TGA), the morphology of cavo-pulmonary connections after Fontan operation, the morphology of the pulmonary arteries in tetralogy of Fallot or morphology of the great vessels after arterial switch for TGA. GV diameters with SN-3D were accurate using conventional MRA as the gold standard (n=25, r2=0.91, bias 0.1±2.2 mm), with a low intra- and inter-observer variability (3.7% and 5.4%). Moreover, the proximal 3 cm of the CA could be well visualized and its 3D course followed in most of the patients with moderate or good image quality (n=33: LAD 97%, LCx 73%, RCA 91%), making SN-3D useful to detect anomalous CA. Conclusion: The SN-3D methodology enables time-efficient whole-heart coverage during free breathing. The high isotropic resolution supports multi-planar offline reformatting in any plane orientation, which is particularly useful in CHD patients with complex anatomy. Self-navigation and the absence of fold-over artifacts enhance the ease of use and favor a fast acquisition planning. Reformatted images allow accurate measurement of the GV, and even small anatomical structures could be precisely identified illustrating the potential of this methodology to assess the anatomy of the proximal course of CA.

Non-contrast angiography of renal artery in 3T magnetic resonance in patients with refractory arterial hypertension before renal denervation

Introduction: Catheter-based renal sympathic denervation is a technique for treatment of resistant arterial hypertension. Planning this procedure magnetic resonance (MR) is a non-invasive method without any radiation to reliably image the anatomical conditions like diameters, possible stenosis or abnormalities of renal arteries. Impaired renal function (GFR<30 ml/min) is a known contraindication for gadolinium based contrast agent due to the risk of nephrogenic systemic fibrosis. To address the question if imaging of the anatomy of renal arteries in 3T MR may be feasible and reliable without using contrast agent the present prospective study was performed. Methods: 34 Patients with resistant hypertension (taking four antihypertensive drugs including diuretics and long term blood pressure measurement larger than 135/85mmHg) for whom renal denervation was planned were included prospectively. In 3T magnetic resonance 3D conventional contrast MR angiography (CMRA) was performed after antecubital injection of gadopentetat-dimeglumin during breath-hold. Additionally, an inflow inversion recovery steady state free precession sequence (Inhance) was used for non-contrast MR angiography (NCMRA). Diameters of renal artery were assessed 20 mm from aortic ostium. Furthermore, the aortic diameter was measured at height of renal artery orifice. Results: 34 patients (66±8 years) were included in both conventional contrast and non-contrast MR angiography and presented a total of 76 main and accessory renal arteries. In CMRA mean renal artery diameter was 6.2±1.8 mm, in NCMRA mean renal artery was determined with 6.0±2.0 mm. Mean aortic diameters were identified with 20.4±3.2 in CMRA and with 20.1±2.8 in NCMRA. Measurements of renal artery by NCMRA closely correlate to renal artery diameters assigned by CMRA (r=0.97). Furthermore, detection of aortic diameters showed also good correlation between both MRA (r=0.92). Bland-Altman-analysis did not present any signs of under- and overestimation of both measurement methods. Conclusion: At 3T CMR determination of renal artery and aortic diameter at the orifice of the renal arteries is possible by non-contrast MR angiography as well as by 3D contrast MR angiography. Both methods provide reliable estimates of the diameter of the vessel without relevant under- or overestimation. Non-contrast MR angiography should be regarded as a powerful completely non-invasive tool to image renal arteries without the need to use potentially nephrotoxic contrast media.

Contrast-enhanced time-resolved 4D MRA of congenital heart and vessel anomalies: image quality and diagnostic value compared with 3D MRA

To evaluate time-resolved interleaved stochastic trajectories (TWIST) contrast-enhanced 4D magnetic resonance angiography (MRA) and compare it with 3D FLASH MRA in patients with congenital heart and vessel anomalies. Twenty-six patients with congenital heart and vessel anomalies underwent contrast-enhanced MRA with both 3D FLASH and 4D TWIST MRA. Images were subjectively evaluated regarding total image quality, artefacts, diagnostic value and added diagnostic value of 4D dynamic imaging. Quantitative comparison included signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and vessel sharpness measurements. Three-dimensional FLASH MRA was judged to be significantly better in terms of image quality (4.0 ± 0.6 vs 3.4 ± 0.6, P < 0.05) and artefacts (3.8 ± 0.4 vs 3.3 ± 0.5, P < 0.05); no difference in diagnostic value was found (4.2 ± 0.4 vs 4.0 ± 0.4); important additional functional information was found in 21/26 patients. SNR and CNR were higher in the pulmonary trunk in 4D TWIST, but slightly higher in the systemic arteries in 3D FLASH. No difference in vessel sharpness delineation was found. Although image quality was inferior compared with 3D FLASH MRA, 4D TWIST MRA yields robust images and added diagnostic value through dynamic acquisition was found. Thus, 4D TWIST MRA is an attractive alternative to 3D FLASH MRA. • New magnetic resonance angiography (MRA) techniques are increasingly introduced for congenital cardiovascular problems. • Time-resolved angiography with interleaved stochastic trajectories (TWIST) is an example. • Four-dimensional TWIST MRA provided inferior image quality compared to 3D FLASH MRA but without significant difference in vessel sharpness. • Four-dimensional TWIST MRA gave added diagnostic value.

Direct coronary motion extraction from a 2D fat image navigator for prospectively gated coronary MR angiography

Direct 2D tracking of cardiac motion may provide superior respiratory navigator gating for coronary magnetic resonance angiography compared to conventional liver-diaphragm navigators. However, additional 2D processing for motion extraction is unsuitable for real-time prospective gating. In this work, a 2D fat-selective image navigator, which delineates the epicardial fat surrounding coronary arteries, is developed to directly monitor epicardial fat motion at every heartbeat in real-time for prospective gating. The proposed navigator is incorporated into a real-time interactive software that allows rapid setup and efficient motion extraction, and runs on standard clinical hardware without any additional dedicated components for processing. The proposed 2D cardiac fat image navigator was compared with the conventional 1D diaphragm navigator in free-breathing b-SSFP coronary MRAs in 12 healthy volunteers at 1.5T. Real-time motion extraction from 2D cardiac fat navigator images was feasible within 20 ms, enabling successful prospectively gated coronary magnetic resonance angiographies in all subjects. Compared to 1D diaphragmatic navigator, 2D fat image navigator reduced scan time by 38% (P < 0.0005), and significantly improved vessel sharpness, myocardial suppression, and image quality (P < 0.05). This demonstrates the feasibility of a 3D SSFP coronary magnetic resonance angiography sequence using a 2D epicardial fat image as a navigator for real-time prospective motion tracking.