Pulmonary arteriovenous malformation: Characterization with time-resolved ultrafast 3D MR angiography

To avoid potentially deadly consequences from paradoxical emboli, early detection and accurate characterization of pulmonary arteriovenous malformations (AVMs) is highly desirable. We report on a patient with a suspected pulmonary AVM who underwent ultrafast time-resolved 3D MR angiography of the pulmonary arteries. The case documents the suitability of the MRA technique as a noninvasive alternative to computed tomographic angiography and digital subtraction angiography for accurate pre-therapeutic characterization of pulmonary AVMs.     

New approach to 3D time-resolved angiography.

TRICKS is an acquisition and reconstruction method capable of generating 3D time-resolved angiograms. Arguably, the main problem with TRICKS is the way it handles the outer regions of the k-space matrix, leading to artifacts at the edges of blood vessels. An alternative to the data- processing stage of TRICKS, designed to better represent edges and small vessels, is presented here. A weakness of the new approach is an increased sensitivity to motion compared to TRICKS. Since this method can use the same data as TRICKS, a hybrid reconstruction method could conceivably be developed where the advantages of both approaches are combined. Magn Reson Med 47:1022-1025, 2002.     

Blood velocity assessment using 3D bright-blood time-resolved magnetic resonance angiography.

Blood velocity is a functional parameter that is not easily assessed noninvasively, especially in small animals. A new noninvasive method that uses magnetic resonance angiography (MRA) to measure blood flows is proposed. This method is based on the time-of-flight (TOF) phenomenon. By initially suppressing the signal from the stationary spins in the area of interest, it is possible to sequentially visualize only the signal from the moving spins entering a given volume. With this method, 3D cine images of the blood flow can be generated by positive contrast, with unparalleled spatial (<200 microm) and temporal resolutions (<10 ms/image). As a result, it is possible to measure flow in sinuous paths. The present method was applied in vivo to measure the blood velocity in mouse carotid arteries. Because of its robustness and simplicity of implementation, this method has numerous potential applications for fundamental studies in small animal models.     

Three-dimensional dynamic magnetic resonance angiography for the evaluation of radiosurgically treated cerebral arteriovenous malformations

We assessed the value of three-dimensional (3D) dynamic magnetic resonance angiography (MRA) for the follow-up of patients with radiosurgically treated cerebral arteriovenous malformations (AVMs). Fifty-four patients with cerebral AVMs treated by radiosurgery (RS) were monitored using conventional catheter angiography (CCA) and 3D dynamic MRA with sensitivity encoding based on the parallel imaging. Cerebral AVM was qualitatively classified by two radiologists into one of five categories in terms of residual nidus size and persistence of early draining vein (I, >6 cm; II, 3–6 cm; III, <3 cm; IV, isolated early draining vein; V, complete obliteration). 3D MRA findings showed a good agreement with CCA in 40 cases (κ=0.62). Of 23 nidus detected on CCA, 3D dynamic MRA showed 14 residual nidus. Of 28 occluded nidus on 3D dynamic MRA, 22 nidus were occluded on CCA. The sensitivity and specificity of 3D dynamic MRA for the detection of residual AVM were 81% and 100%. 3D dynamic MRA after RS may therefore be useful in association with MRI and can be repeated as long as opacification of the nidus or early venous drainage persists, one CCA remaining indispensable to affirm the complete occlusion at the end of follow-up.     

Differentiation of spinal cord arteries and veins by time-resolved MR angiography

PURPOSE: To dynamically resolve the inlet arteries and outlet veins of the spinal cord, particularly the Adamkiewicz artery (AKA) and great anterior radiculomedullary vein (GARV), using MR angiography (MRA). MATERIALS AND METHODS: First, conventional two-phase angiography (acquisition time = 38-55 seconds) utilizing elliptic centric k-space ordering was applied to aortic-aneurysm patients. Changes of vessel intensity were compared between two subsequent dynamic phases. Computer modeling of bolus enhancement and k-space sampling was performed to demonstrate the relation between vessel enhancement, acquisition time, and vessel diameter. Second, time-resolved (TR, or "keyhole") angiography using a reduced number of phase-encoding steps was explored in healthy volunteers and aortic-aneurysm patients using acquisition times (range = 6-8.5 seconds) shorter than the spinal cord circulation time. RESULTS: Using two-phase angiography the AKA and GARV were covisualized in the early phase, and contrast decreased for the AKA and increased for the GARV in most (70%) but not all cases. Computer modeling showed that the arteriovenous contrast strongly depended on vessel diameter, and complete separation was only obtained with short acquisition times. Using TR MR angiography (TR-MRA), complete temporal separation of the AKA and GARV was realized in all cases (100%). CONCLUSION: The AKA and GARV can be completely separated by TR-MRA.     

Time-resolved magnetic resonance angiography: evaluation of intrapulmonary circulation parameters in pulmonary arterial hypertension

Purpose

To determine whether pulmonary arterial and venous transit times measured by time‐resolved magnetic resonance angiography (MRA) can be used as a diagnostic tool for pulmonary arterial hypertension (PAH).

Materials and Methods

Twelve patients with confirmed PAH and 10 healthy volunteers were scanned with Institutional Review Board (IRB) approval. Time‐resolved MRA and 2D phase contrast flow images of the pulmonary vasculature were acquired. Pulmonary arterial and venous transit times (PaTT and PvTT) and pulmonary valve flow (PVF) were obtained. Pulmonary arterial and pulmonary venous blood volumes (PaBV and PvBV) were calculated as the product of flow and transit time.

Results

Patients with PAH showed statistically significant increases in PaTT and PvTT (P < 0.0004, P < 0.05, respectively) compared to controls. PaBV (165.2 ± 92.0 mL) was significantly higher in PAH subjects than controls (97.0 ± 47.1 mL) (P < 0.04), whereas PvBV (127.9 ± 148.9 mL) of PAH subjects had no significant increase from those of healthy controls (142.5 ± 104.1 mL) (P < 0.38).

Conclusion

Pulmonary arterial transit times measured using time‐resolved MRA can be used as a simple, noninvasive metric for detection of altered hemodynamics in PAH. J. Magn. Reson. Imaging 2011;33:225–231. © 2010 Wiley‐Liss, Inc.     

Contrast-enhanced MRA in pre-embolization assessment of a pulmonary arteriovenous malformation

We describe a case of a single pulmonary vascular malformation studied with a new contrast-enhanced three-dimensional MRA technique. Images provided the interventional radiologist with a pre-embolization road map from which information regarding the number and size of feeding and draining vessels was obtained accurately and noninvasively.     

The role of time-resolved 3D contrast-enhanced MR angiography in the assessment and grading of cerebral arteriovenous malformations

Purpose

To assess the role of three-dimensional (3D) contrast-enhanced, time-resolved MR angiography (CE TR MRA) in patients with intracranial arteriovenous malformations (AVMs).

Methods

We studied 12 patient with intracranial AVMs on a 3.0 T MR imaging system (Magentom TIM Trio, Siemens Medical Solutions, Erlangen, Germany) using 3D CE TR MRA with autocalibrating partially parallel acquisitions and echo sharing schemes, which provided temporal resolution of 0.58 or 1.7 s and near isotropic voxels. We qualitatively assessed image quality of the 3D CE TR MRA and compared the grading of the AVMs based on modified Spetzler-Martin system for 3D CE TR MRA and catheter digital subtraction angiography (DSA).

Results

CE TR MRA provided good quality images in the 3 standard orthogonal planes, and good arterial-venous separation in all cases. All AVMs were correctly graded by CE TR MRA when compared with DSA.3D CE TR MRA provides a non-invasive alternative to DSA for the evaluation of cerebral AVMs.     

Dural arteriovenous fistula involving the transverse sigmoid sinus after treatment: assessment with magnetic resonance digital subtraction angiography

Introduction The purpose of this study was to evaluate the utility of magnetic resonance digital subtraction angiography (MRDSA) in showing the presence or absence of retrograde venous drainage (RVD) in patients with intracranial dural arteriovenous fistula (DAVF) involving the transverse sigmoid sinus (TSS) after treatment. Methods Of 16 patients with DAVF involving the TSS, 13 underwent digital subtraction angiography (DSA) and MRDSA before and after treatment, and 3 underwent DSA before treatment and DSA and MRDSA after treatment. Five patients underwent these procedures twice after treatment. A total of 21 examinations after treatment were evaluated retrospectively. The presence or absence of DAVF and RVD was decided on the basis of the DSA findings. Two neuroradiologists reviewed the MRDSA findings concerning the presence or absence of DAVF and RVD. Results DSA showed residual DAVF in 9 and residual RVD in 5 of 21 examinations. MRDSA revealed residual DAVF in 8 of 21 examinations. MRDSA did not show residual DAVF in one examination because of a very small (low-flow) residual DAVF without RVD. MRDSA identified residual RVD in 5 of 21 examinations. MRDSA was completely consistent with DSA concerning the presence or absence of residual RVD. Conclusion MRDSA could evaluate the presence or absence of RVD in patients with DAVF involving TSS after treatment. MRDSA may give reliable information as to whether patients with DAVF involving the TSS should undergo additional DSA after treatment.     

Noncontrast‐enhanced four‐dimensional MR angiography for the evaluation of cerebral arteriovenous malformation: A preliminary trial

Purpose:

To prospectively evaluate noncontrast‐enhanced (NCE), time resolved, four‐dimensional (4D) magnetic resonance angiography (MRA) for assessment of cerebral arteriovenous malformation (AVM), with intraarterial digital subtraction angiography (DSA) performed as the reference standard.

Materials and Methods:

Fifteen patients (ten men, five women; age range 2–59 years, mean 29.4 years) with 15 untreated cerebral AVMs comprised the study population. NCE 4D MRA was performed on a 3.0 T MR scanner. MR images were reviewed by two independent readers and compared with DSA with respect to arterial feeders, nidus size, and venous drainage. Kappa coefficients of concordance were computed to determine the interobserver and intermodality agreements for the depiction of arterial feeders, nidus, and venous drainage between the two techniques.

Results:

Fifteen AVMs detected in DSA were visualized in NCE 4D MRA. Intermodality agreements were excellent for the arterial feeders (K = 0.918, P = 0.000), good for the nidus size (K = 0.692, P = 0.000), and moderate for the venous drainage (K = 0.495, P = 0.001).

Conclusion:

NCE 4D MRA is a promising and potentially valuable method for noninvasive assessment of angioarchitecture and hemodynamics of cerebral AVMs. Further improvement of labeling persistence is desirable in order to enhance the depiction of draining veins for AVMs. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Rapid time‐resolved magnetic resonance angiography via a multiecho radial trajectory and GraDeS reconstruction

Contrast‐enhanced magnetic resonance angiography is challenging due to the need for both high spatial and temporal resolution. A multishot trajectory composed of pseudo‐random rotations of a single multiecho radial readout was developed. The trajectory is designed to give incoherent aliasing artifacts and a relatively uniform distribution of projections over all time scales. A field map (computed from the same data set) is used to avoid signal dropout in regions of substantial field inhomogeneity. A compressed sensing reconstruction using the GraDeS algorithm was used. Whole brain angiograms were reconstructed at 1‐mm isotropic resolution and a 1.1‐s frame rate (corresponding to an acceleration factor > 100). The only parameter which must be chosen is the number of iterations of the GraDeS algorithm. A larger number of iterations improves the temporal behavior at cost of decreased image signal‐to‐noise ratio. The resulting images provide a good depiction of the cerebral vasculature and have excellent arterial/venous separation. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Three‐dimensional dynamic time‐resolved contrast‐enhanced MRA using parallel imaging and a variable rate k‐space sampling strategy in intracranial arteriovenous malformations

Purpose

To evaluate the effectiveness of three‐dimensional (3D) dynamic time‐resolved contrast‐enhanced MRA (TR‐CE‐MRA) using a combination of a parallel imaging technique (ASSET: array spatial sensitivity encoding technique) and a time‐resolved method (TRICKS: time‐resolved imaging of contrast kinetics) and to compare it with 3D dynamic TR‐CE‐MRA using ASSET alone in the assessment of intracranial arteriovenous malformations (AVMs).

Materials and Methods

Twenty consecutive patients with angiographically confirmed AVMs were investigated using both 3D dynamic TR‐CE‐MRA techniques. Examinations were compared with respect to image quality, spatial resolution, number and type of feeders and drainers, nidus size, presence of early venous filling and temporal resolution. Digital subtraction angiography was used as standard of reference.

Results

The higher temporal and spatial resolution of 3D dynamic TR‐CE‐MRA TRICKS ASSET allowed a better assessment of intracranial vascular malformations, namely better depiction of feeders, drainers and better detection of early venous drainage. There was no significant difference between them in terms of nidus size.

Conclusion

3D dynamic TR‐CE‐MRA combining parallel imaging and a time‐resolved method with subsecond and submillimeter resolution could become the first‐line investigation technique in both diagnosis and follow‐up of intracranial AVMs. J. Magn. Reson. Imaging 2009;29:7–12. © 2008 Wiley‐Liss, Inc.     

High temporal and spatial resolution 3D time-resolved contrast-enhanced magnetic resonance angiography of the hands and feet

Methods are described for generating 3D time-resolved contrast-enhanced magnetic resonance (MR) angiograms of the hands and feet. Given targeted spatial resolution and frame times, it is shown that acceleration of about one order of magnitude or more is necessary. This is obtained by a combination of 2D sensitivity encoding (SENSE) and homodyne (HD) acceleration methods. Image update times from 3.4-6.8 seconds are provided in conjunction with view sharing. Modular receiver coil arrays are described which can be designed to the targeted vascular region. Images representative of the technique are generated in the vasculature of the hands and feet in volunteers and in patient studies.     

4D time-resolved MR angiography with keyhole (4D-TRAK): more than 60 times accelerated MRA using a combination of CENTRA, keyhole, and SENSE at 3.0T

PURPOSE: To present a new 4D method that is designed to provide high spatial resolution MR angiograms at subsecond temporal resolution by combining different techniques of view sharing with parallel imaging at 3.0T. MATERIALS AND METHODS: In the keyhole-based method, a central elliptical cylinder in k-space is repeated n times (keyhole) with a random acquisition (CENTRA), and followed by the readout of the periphery of k-space. 4D-MR angiography with CENTRA keyhole (4D-TRAK) was combined with parallel imaging (SENSE) and partial Fourier imaging. In total, a speed-up factor of 66.5 (6.25 [CENTRA keyhole] x 8 [SENSE] x 1.33 [partial Fourier imaging]) was achieved yielding a temporal resolution of 608 ms and a spatial resolution of (1.1 x 1.4 x 1.1) mm(3) with whole-brain coverage 4D-TRAK was applied to five patients and compared with digital subtraction angiography (DSA). RESULTS: 4D-TRAK was successfully completed with an acceleration factor of 66.5 in all five patients. Sharp images were acquired without any artifacts possibly created by the transition of the central cylinder and the reference dataset. MRA findings were concordant with DSA. CONCLUSION: 4D time-resolved MRA with keyhole (4D-TRAK) is feasible using a combination of CENTRA, keyhole, and SENSE at 3.0T and allows for more than 60 times accelerated MRA with high spatial resolution.     

Optimization of 3D contrast-enhanced pulmonary magnetic resonance angiography in pediatric patients with congenital heart disease.

Contrast kinetics were studied in the main pulmonary artery (MPA) and ascending aorta (AAo) of 12 children with congenital heart disease. This information was used to optimize the timing of data acquisition for contrast-enhanced MR angiography in these vessels. To reduce contrast-agent dosage in these fragile patients, contrast enhancement was measured during routine diagnostic 3D magnetic resonance (MR) angiography instead of using test-bolus methods. This was possible by acquiring 2D cross-sectional images of the MPA and AAo during the 3D scan. Time-to-peak in the MPA and AAo was 4.9 +/- 2.2 and 6.1 +/- 2.2 s, respectively, while the transit time between the two vessels was 4.5 +/- 0.6 s. A point-spread-function analysis showed that intravascular signal strength was maximized if data acquisition began 4.7 +/- 2.3 s after the first arrival of contrast in the MPA and 5.6 +/- 2.3 s in the AAo. Little signal loss and artifact resulted when longer acquisition delays were used because contrast-agent clearance was slow. Based on these results, MR angiography of both the MPA and the AAo in children with congenital heart disease can be performed using elliptic-centric k-space sampling and a trigger delay of 7.9 s after contrast arrival in the AAo (i.e., time-to-peak signal strength in the AAo plus one SD to account for intersubject variability).     

Time‐resolved MR venography of the pulmonary veins precatheter‐based ablation for atrial fibrillation

Purpose:

To evaluate time‐resolved magnetic resonance angiography (TR‐MRA) of the pulmonary venous circulation using the time‐resolved angiography with interleaved stochastic trajectories (TWIST) method and compare it with the more commonly used conventional contrast‐enhanced magnetic resonance angiography (CE‐MRA) approach in atrial fibrillation patients referred for preablation pulmonary vein mapping.

Materials and Methods:

This study was approved by the Institutional Review Board. Twenty‐six patients (15 males; age 59.6 ± 12.7 years) referred for preablation pulmonary vein mapping underwent both conventional CE‐MRA and TR‐MRA with TWIST. Imaging was performed on a 1.5 T (Magnetom Avanto, Siemens Healthcare, Erlangen, Germany) MRI scanner. Source partition and maximum intensity projection (MIP) images were evaluated retrospectively. For quantitative analysis, pulmonary vein ostium orthogonal dimensions were measured using double oblique multiplanar reformatting. The results were analyzed using paired t‐tests, Lin's concordance correlation coefficient, and Bland–Altman plots. For qualitative analysis, both source partition images and MIP images were assessed by two observers (A.P. and M.G.). The presence of common ostiums or accessory veins was recorded and analyzed using unweighted Cohen's kappa. Pulmonary vein conspicuity was scored on a scale of 1–4 (1 = poor, 2 = fair, 3 = good, 4 = excellent) and analyzed using paired t‐tests, intraclass correlation coefficients, and quadratic weighted kappa statistics.

Results:

Orthogonal venous diameters were comparable for both TR‐MRA and conventional CE‐MRA (1.34 ± 0.37 vs. 1.38 cm ± 0.36, respectively). Results of paired t‐tests, Lin's concordance correlation coefficient, and Bland–Altman analysis revealed relatively close comparison between methods. The magnitude of the mean difference for any of the statistical comparisons did not exceed 0.10 cm. The visualization of variant pulmonary vein anatomy was very similar for both techniques. Agreement between techniques was determined to be “good” to “very good” (κ = 0.78–0.85). Conspicuity scores for each pulmonary vein were also very close. Paired t‐tests, intraclass correlation coefficients, and quadratic weighted kappa statistics all revealed strong agreement between methods.

Conclusion:

TR‐MRA using TWIST produces comparable anatomic images and pulmonary venous dimensions to the more widely used CE‐MRA technique. Additionally, the TWIST technique improves arterio‐venous separation, does not need exact bolus timing, requires less gadolinium, and gives additional information on vein perfusion. J. Magn. Reson. Imaging 2013;37:127–137. © 2012 Wiley Periodicals, Inc.     

Radial sliding‐window magnetic resonance angiography (MRA) with highly‐constrained projection reconstruction (HYPR)

Sufficient temporal resolution is required to image the dynamics of blood flow, which may be critical for accurate diagnosis and treatment of various intracranial vascular diseases, such as arteriovenous malformations (AVMs) and aneurysms. Highly‐constrained projection reconstruction (HYPR) has recently become a technique of interest for high‐speed contrast‐enhanced magnetic resonance angiography (CE‐MRA). HYPR provides high frame rates by preferential weighting of radial projections while maintaining signal‐to‐noise ratio (SNR) by using a high SNR composite. An analysis was done to quantify the effects of HYPR on SNR, contrast‐to‐noise ratio (CNR), and temporal blur compared to the previously developed radial sliding‐window technique using standard filtered backprojection or regridding methods. Computer simulations were performed to study the effects of HYPR processing on image error and the temporal information. Additionally, in vivo imaging was done on patients with angiographically confirmed AVMs to measure the effects of alteration of various HYPR parameters on SNR as well as the fidelity of the temporal information. The images were scored by an interventional radiologist in a blinded read and were compared with X‐ray digital subtraction angiography (DSA). It was found that with the right choice of parameters, modest improvements in both SNR and dynamic information can be achieved as compared to radial sliding‐window MRA. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Contrast-enhanced peripheral magnetic resonance angiography using time-resolved vastly undersampled isotropic projection reconstruction

PURPOSE: To investigate the application of time-resolved vastly undersampled isotropic projection reconstruction (VIPR) in contrast-enhanced magnetic resonance angiography of the distal extremity (single station), and peripheral run-off vasculature in the abdomen, thigh, and calf (three stations). MATERIALS AND METHODS: Time-resolved distal extremity imaging was performed using VIPR sequence through the comparison of two acquisition matrix sizes: 256 with TR/TE=3.7/1.4 msec and 320 with TR/TE=4.5/1.8 msec under the same scan time of two minutes. VIPR acquisition was combined with a bolus-chase technique to image the peripheral run-off vasculature. The time-resolved images were reconstructed using a revised sliding window reconstruction filter whose temporal aperture remained narrow for low spatial frequencies and increased quadratically to include all the projection data for high spatial frequencies. RESULTS: The new temporal filter significantly suppressed the undersampling streak artifacts and venous contamination, while maintaining a high temporal resolution. Both high spatial resolution (ranging from 1.56 x 1.56 x 1.56 mm to 1.25 x 1.25 x 1.25 mm) and high temporal resolution (three seconds per frame) distal extremity images and peripheral run-off images were generated using time-resolved VIPR acquisition, which provides isotropic spatial resolution and isotropic coverage. CONCLUSION: Time-resolved VIPR acquisition was demonstrated to be well suited for distal extremity imaging by providing isotropic spatial resolution, isotropic coverage, and high temporal resolution. The combination of time-resolved VIPR and bolus chase technique provided a novel approach for peripheral run-off examinations.