Time-resolved 3D MR Angiography Research Articles

Evaluation of vascular invasion in patients with musculoskeletal tumors of lower extremities: use of time-resolved 3D MR angiography at 3-T.

Background Time-resolved angiography with stochastic trajectories (TWIST) sequence makes considerable progress in temporal and spatial resolution, which presents high potential in evaluation of vascular diseases. Purpose To assess magnetic resonance imaging (MRI) using TWIST MR angiography (MRA) sequence in the assessment of vascular invasion for bone and soft-tissue tumors in comparison to computed tomography angiography (CTA) as the reference standard. Material and Methods Thirty-three patients with lower extremity musculoskeletal tumors were imaged with conventional MR and TWIST MRA. CTA was performed 48 h later. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the femoral artery were calculated. Vascular invasion as determined by MRA and CTA was separately analyzed. Vascular invasion by MRA and CTA were analyzed with kappa coefficients to determine agreement between the imaging methods. Results Seven cases of bone and 26 cases of soft tissue tumors were examined. SNR and CNR of the femoral artery were excellent for TWIST MRA (mean ± SD values of 317 ± 80 and 276 ± 76, respectively). Based on the TWIST sequence, the vessels were free of tumor in 16 cases. Vascular displacement was found in 11 cases and vascular stenosis in six cases. The MRA findings conflicted with CTA findings in only one case. The kappa value was 0.953 ( P < 0.01). In five cases, vascular malformations were found with TWIST MRA but not CTA. Conclusion TWIST MRA enables accurate delineation of anatomical structures and tumor arterial involvement, providing reliable preoperative imaging information with respect to lower extremity musculoskeletal tumors.

Quantitative Flow Measurements in the Internal Jugular Veins of Multiple Sclerosis Patients Using Magnetic Resonance Imaging

To study the blood flow through the internal jugular veins (IJVs) of the MS population. Two hundred MS patients and 14 normal volunteers were evaluated with magnetic resonance imaging (MRI) at 3T. Contrast-enhanced time-resolved 3D MR angiography and 2D time-of-flight imaging were performed to assess abnormalities in the extracranial vascular anatomy. Based on this assessment, the MS population was divided into subgroups of non-stenotic (NST), cervical 1 stenotic only (C1ST) and cervical 6 stenotic (C6ST) subjects. In this study, 2D phase contrast MR imaging was used to quantify blood flow through major veins and arteries in the neck and flow differences among the groups were analyzed. Of the 200 MS patients, 87 (43.5%) belonged to the NST group, 50 (25%) belonged to the C1ST group and 63 (31.5%) belonged to the C6ST group. The total IJV flow normalized to the total arterial flow of the NST group was 75.12 ± 12.22 %. This was significantly higher than that of the C1ST group, 63.93 ± 16.08 % (p < 0.0001), which in turn was significantly higher than that of the C6ST group, 52.13 ± 20.71 % (p = 0.001). Seventy-nine percent of the stenotic groups had a normalized subdominant IJV flow of less than 20%, a combined IJV flow of less than 5o% and/or a sub-dominant IJV flow vs. dominant IJV flow ratio of less than 1/3. Only 2% of the NST group had a combined IJV flow of less than 50%, compared to 35% of the stenotic groups. Blood flow through the IJVs was reduced in the MS population with stenoses compared to those without.

Pretreatment Evaluation of Peripheral Vascular Malformations Using Low-Dose Contrast-Enhanced Time-Resolved 3D MR Angiography: Initial Results in 22 Patients

The objective of our study was to assess the feasibility and diagnostic performance of time-resolved MR angiography (MRA) in the pretreatment evaluation of peripheral vascular malformations at 1.5 T. Twenty-two consecutive patients (15 women and seven men; mean age, 22.1 ± 12.1 years) who were known or suspected to have vascular malformations were studied using time-resolved MRA with interleaved stochastic trajectories and parallel acquisition followed by conventional MRA (n = 12). All studies were performed on a 1.5-T whole-body MR system. Image sets of time-resolved and conventional MRA were independently reviewed by two observers for image quality, level of confidence and presence, location, and classification of vascular malformations. The interobserver agreement was calculated using conventional MRA as the standard of reference. On the basis of time-resolved MRA, nine of the lesions were categorized as high-flow arteriovenous malformations (AVMs), the remaining 13 lesions were categorized as low-flow vascular malformations or hemangiomas. There was no significant difference in the image quality grading scores between the two observers for time-resolved MRA (p = 0.61) and conventional MRA (p = 0.54). The kappa coefficient revealed good agreement (κ = 0.76) between time-resolved MRA and conventional MRA. Both observers visualized fine vascular details with higher confidence in two patients on conventional MRA. The additional functional information regarding feeding artery and flow patterns provided by time-resolved MRA was confirmed by digital subtraction in all nine cases. Time-resolved MRA provided the temporal information needed for the appropriate classification of vascular malformations, enabling visualization of both the arterial feeders and draining veins. Furthermore, time-resolved MRA has the potential to be used as an initial and screening diagnostic tool obviating conventional MRA to categorize these lesions and determine their extent to correctly guide treatment.

Time-Resolved 3D MR Angiography of the Foot at 3 T in Patients with Peripheral Arterial Disease

The objective of our study was to prove the feasibility and clinical relevance of fast contrast-enhanced time-resolved 3D MR angiography (MRA) with submillimeter spatial resolution at a high magnetic field strength. Twenty-one patients (five women, 16 men; mean age +/- SD, 65 +/- 14 years) were examined on a 3-T whole-body MR system with an 8-element phasedarray coil for preoperative evaluation of the pedal arterial system and assessment of the visualized vessels to serve as a graft touch-down site in pedal bypass surgery. Time-resolved 3D MRA of the foot was performed after automatic injection of 0.2 mmol/kg of gadobenate dimeglumine using a sagittal gradient-echo T1-weighted sequence (TR/TE, 4.2/1.6; flip angle, 30 degrees ; field of view, 290 mm; matrix, 352; 120 slices; slice thickness, 0.8 mm) with a spatial resolution of 0.8 x 0.8 x 1.6 mm reconstructed to 0.6 x 0.6 x 0.8 mm and a temporal resolution of 3.9 seconds using keyhole and sensitivity-encoding (SENSE) technology (SENSE factors: 4 in anteroposterior direction and 2 in right-left direction). Dynamic subtractions and rotating maximum intensity projections were calculated. The original image data sets were transferred to a dedicated workstation for objective signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) analysis of the arteries. Subjective image analysis regarding image quality and diagnostic findings was performed by two radiologists in consensus. In all patients, images of diagnostic quality were obtained. Despite the known limitations regarding signal intensity measurements in images acquired with the use of parallel imaging technique, SNR and CNR proved to be excellent, with mean +/- SD values of 294 +/- 158 and 248 +/- 144, respectively. Although most of the patients had diabetic foot syndrome with arteriovenous shunting, the arteries and the potential vessel for bypassing could be clearly separated from the veins in each case due to the temporal information given by our study. The ability to reliably discriminate arteries from veins is of high clinical relevance in planning pedal bypass surgery. Fast contrast-enhanced time-resolved 3D MRA of the foot at 3 T is feasible and of high clinical value for the preoperative evaluation of the arterial supply of the foot.

Time-Resolved MR Angiography: A Primary Screening Examination of Patients with Suspected Pulmonary Embolism and Contraindications to Administration of Iodinated Contrast Material

The purpose of this study was to evaluate the efficiency and reproducibility of a single-breath-hold time-resolved 3D MR angiographic technique in the diagnosis of pulmonary embolism. Twenty-seven consecutively registered patients with clinically suspected pulmonary embolism and contraindication to administration of iodinated contrast agents underwent imaging by time-resolved 3D MR angiography at 1.5 T. Bolus timing was not required. Two reviewers independently analyzed MR angiograms for overall image quality and evidence of pulmonary embolism. Additional imaging techniques, including pulmonary embolism CT angiography, ventilation-perfusion (V/Q) lung scanning, venous duplex sonography for deep venous thrombosis, and echocardiography for right ventricular strain, and 30-day and 3-month clinical follow-up were used to confirm the MR angiographic findings. Image quality was sufficient for diagnosis in the cases of 98% of lobar, 92-93% of segmental, and 94-95% of all vessel parts from the main pulmonary artery though the segmental branches with excellent interobserver agreement. Findings on MR angiography were concordant with the anatomic distribution of abnormalities for all pulmonary embolism CT angiographic examinations (n = 2) and four of seven V/Q lung scans. Screening with time-resolved 3D MR angiography allowed confident exclusion or inclusion of pulmonary embolism in 96% of patients. Time-resolved 3D MR angiography provides high temporal resolution (nine phases, one phase per 3.3 seconds) and consistently yields arterial phase only images. As found with clinical follow-up, confident diagnosis of pulmonary embolism from the main pulmonary artery through the segmental branches can be incorporated into a clinical service as a screening examination of patients with contraindications to the use of iodinated contrast material.

Accelerated time-resolved 3D contrast-enhanced MR angiography at 3T: clinical experience in 31 patients

To evaluate whether time-resolved 3D MR-angiography at 3T with a net acceleration factor of eight is applicable in clinical routine and to evaluate whether good image quality and a low artifact level can be achieved with a temporal update rate that allows for additional information on pathologies. Thirty-one consecutive patients underwent time-resolved 3D contrast-enhanced MR-angiography on a 3T system. Imaging consisted of accelerated 3D gradient echo sequences combining parallel imaging with an acceleration factor of four, partial Fourier acquisition along phase and slice encoding direction, and twofold temporal acceleration using view sharing. Data volumes representing the arterial and venous contrast phases were independently evaluated by two experienced radiologists by grading of image quality and artifact level on a 0-3 scale. Time-resolved MR-angiography was successfully performed in all subjects without the need for contrast agent bolus timing. Excellent arterial (average score = 2.65 +/- 0.32) and good venous (average score = 2.56 +/- 0.28) diagnostic image quality and little image degrading due to artifacts (average score = 2.20 +/- 0.16) were confirmed by both independent readers (agreement in 65.2% of all evaluations). In 14 patients vascular pathologies were identified in the arterial phases. In eight examinations temporal resolution and depiction of contrast agent dynamics provided additional information about pathology. Without the necessity for additional bolus timing, time-resolved 3D contrast-enhanced MR-angiography with imaging acceleration along both the spatial encoding direction and temporal domain revealed excellent diagnostic image quality in neurovascular and thoracic imaging. Despite the limited spatial resolution as compared to high-resolution imaging of the carotid artery bifurcation, the results demonstrate the applicability of contrast-enhanced MR-angiography in thoracic and abdominal MRA as well as cervical imaging with a temporal update rate allowing for additional information on pathologies. Future studies may include an evaluation of optimal trade-offs between spatial and temporal resolution, different acceleration factors and a comparison to the gold-standard for accuracy.

Time-Resolved 3D MR Angiography with Parallel Imaging for Evaluation of Hemodialysis Fistulas and Grafts: Initial Experience

We optimized a time-resolved 3D contrast-enhanced MR angiography sequence with integrated parallel imaging technique that can provide a large field of view with high temporal and spatial resolution, by which the hemodialysis access and the entire course of the inflow and outflow vessels can be imaged at a single anatomic station. Our objective was to evaluate the feasibility and usefulness of this method in the evaluation of patients referred for possible abnormalities in hemodialysis access. Time-resolved contrast-enhanced 3D MR angiography with parallel imaging has the potential to provide a rapid and comprehensive evaluation for the surveillance and diagnosis of hemodialysis access malfunctions. This technique may function as an important complement to conventional digital subtraction angiography and may be able to help guide medical management. The MR angiography protocol we present is a noninvasive, versatile, and time-efficient technique, without the need of direct graft puncture or flow interruption, and can be performed using a single injection of contrast material at a single station.