Kambiz Nael

Time-resolved contrast enhanced magnetic resonance angiography of the head and neck at 3.0 tesla: Initial results

Objectives:We sought to implement and evaluate a high-performance, extended field of view protocol for time-resolved contrast-enhanced magnetic resonance imaging (CEMRA) of the carotid circulation by using a dedicated neurovascular (NV) array coil. Materials and Methods:A total of 16 adult volunteers and 20 clinical patients with suspected cerebrovascular disease (15 male, 21 female, 25–82 years of age) were scanned with a fast 3D MRA sequence (TR/TE: 2.16/1 milliseconds, sampling BW: 1090 Hz/pixel), with echo-sharing and parallel acquisition. All studies were performed on a 3.0 T MR system using an 8-channel neurovascular array coil. After injection of 6 mL of gadodiamide at 3 mL/s, a coronal 3D data set with in-plane resolution of 1 × 1.3 was implemented for 10 consecutive measurements each 1.8 seconds apart. The subjects subsequently underwent high spatial-resolution (in-plane: 0.8 × 0.9) CEMRA for comparative analysis. The quality of segmental arterial anatomy and the presence and degree of the arterial stenosis were evaluated by 2 neuroradiologists. The interobserver variability was tested by κ statistics and comparative analysis between the TR-CEMRA and high spatial-resolution CEMRA was evaluated by mean of the Spearman rank correlation coefficient. Results:Craniocervical arteries were visualized with good image quality and definition in the diagnostic range. Occlusive disease was detected in 42 (reader A) and 44 (reader B) arterial segments with excellent interobserver agreement (κ =0.89; 95% confidence interval 0.82–0.96). There was a significant correlation between the TR-CEMRA and high spatial-resolution CEMRA (Rs = 0.91 and 0.93, for readers A and B, respectively) for the degree of stenosis. Three aneurysms, 3 AVMs, 1 AV-fistula, and 2 subclavian steals were detected by both observers and were confirmed by correlative imaging. Conclusion:Time-resolved CEMRA at 3.0 T is reliable and versatile, providing 3-dimensional time-resolved data sets with high spatial (in plane: 1.3 × 1 mm2) and temporal (1.8 seconds) resolution over a large field of view. The higher signal-to-noise ratio gain at 3.0 T can be used effectively to improve performance of fast imaging and to support aggressive parallel acquisition protocols, as in the present study. Further clinical studies are required to establish the range of applications and the accuracy of the technique.

Six-minute magnetic resonance imaging protocol for evaluation of acute ischemic stroke: Pushing the boundaries

Background and Purpose— If magnetic resonance imaging (MRI) is to compete with computed tomography for evaluation of patients with acute ischemic stroke, there is a need for further improvements in acquisition speed. Methods— Inclusion criteria for this prospective, single institutional study were symptoms of acute ischemic stroke within 24 hours onset, National Institutes of Health Stroke Scale ≥3, and absence of MRI contraindications. A combination of echo-planar imaging (EPI) and a parallel acquisition technique were used on a 3T magnetic resonance (MR) scanner to accelerate the acquisition time. Image analysis was performed independently by 2 neuroradiologists. Results— A total of 62 patients met inclusion criteria. A repeat MRI scan was performed in 22 patients resulting in a total of 84 MRIs available for analysis. Diagnostic image quality was achieved in 100% of diffusion-weighted imaging, 100% EPI-fluid attenuation inversion recovery imaging, 98% EPI-gradient recalled echo, 90% neck MR angiography and 96% of brain MR angiography, and 94% of dynamic susceptibility contrast perfusion scans with interobserver agreements (k) ranging from 0.64 to 0.84. Fifty-nine patients (95%) had acute infarction. There was good interobserver agreement for EPI-fluid attenuation inversion recovery imaging findings (k=0.78; 95% confidence interval, 0.66–0.87) and for detection of mismatch classification using dynamic susceptibility contrast-Tmax (k=0.92; 95% confidence interval, 0.87–0.94). Thirteen acute intracranial hemorrhages were detected on EPI-gradient recalled echo by both observers. A total of 68 and 72 segmental arterial stenoses were detected on contrast-enhanced MR angiography of the neck and brain with k=0.93, 95% confidence interval, 0.84 to 0.96 and 0.87, 95% confidence interval, 0.80 to 0.90, respectively. Conclusions— A 6-minute multimodal MR protocol with good diagnostic quality is feasible for the evaluation of patients with acute ischemic stroke and can result in significant reduction in scan time rivaling that of the multimodal computed tomographic protocol.

3 T contrast-enhanced magnetic resonance angiography for evaluation of the intracranial arteries: comparison with time-of-flight magnetic resonance angiography and multislice computed tomography angiography.

Purpose:We sought to prospectively evaluate the image quality and visualization of the intracranial arteries using high spatial resolution contrast-enhanced magnetic resonance angiography (CE-MRA) at 3 T and to perform intraindividual comparison with time-of-flight (TOF) MRA and multislice CT angiography (CTA). Materials and Methods:Twelve patients (5 men, 7 women, 37–71 years of age) with suspected cerebrovascular disease prospectively underwent MRA and CTA. MRA was performed on a 3 T MR system, including both 3-dimensional (3D) TOF (Voxel dimension: 0.6 × 0.5 × 0.9 mm3 in 5 minutes and 40 seconds) and 3D CE-MRA (voxel dimension: 0.7 × 0.7 × 0.8 mm3 in 20 seconds, using parallel acquisition with an acceleration factor of 4). CTA images were acquired on a 16-slice CT scanner (voxel dimension: 0.35 × 0.35 × 0.8 mm3 in 17 seconds). The image quality and visualization of up to 26 intracranial arterial segments in each study was evaluated by 2 experienced radiologists. The arterial diameter for selective intracranial arteries was measured independently on each of the 3 studies, and statistical analysis and comparative correlation was performed. Results:A total of 312 arterial segments were examined by CE-MRA, TOF-MRA, and CTA. The majority of intracranial arteries (87%) were visualized with diagnostic image quality on CE-MRA with a significant correlation to TOF (R values = 0.84; 95% confidence interval 0.79–0.86, P < 0.0001), and to CTA (R values = 0.74; 95% confidence interavl 0.68–0.78, P < 0.001). The image quality for small intracranial arteries, including the anterior-inferior cerebellar artery, the posterior communicating artery, and the M3 branch of the middle cerebral artery, was significantly lower on CE-MRA compared with TOF and CTA (P < 0.03). There was a significant correlation for the dimensional measurements of arterial diameters at CE-MRA with TOF (r = 0.88, 95% confidence interval 0.81–0.93), and CTA (r = 0.83, 95% confidence interval 0.73–0.90). Conclusion:The described 3 T CE-MRA protocol, spanning from the cervical to the intracranial vessels, visualized and characterized the majority of intracranial arteries with image quality comparable with that obtained using TOF-MRA and CTA. Further clinical studies are required to establish the accuracy of the technique in a broader clinical setting.

Functional renal imaging: nonvascular renal disease

Functional renal imaging—a fast-growing field of MR-imaging—applies different sequence types to gather information about the kidneys other than morphology and angiography. This update article presents the current status of different functional imaging approaches and presents current and potential clinical applications. Apart from conventional in-phase and opposed-phase imaging, which already yields information about the tiusse composition, BOLD (blood-oxygenation level dependent) sequences, DWI (diffusion-weighted imaging) sequences, perfusion measurements, and dedicated contrast agents are used.

Analysis of cardiac function--comparison between 1.5 Tesla and 3.0 Tesla cardiac cine magnetic resonance imaging: preliminary experience.

Purpose:We sought to assess the feasibility of magnetic resonance imaging to evaluate cardiac function at 3.0 T compared with 1.5 T. Material and Methods:In a prospective intraindividual comparative study, 12 volunteers (range, 18–54 years), and 2 patients (range, 43–53 years) underwent cardiac cine magnetic resonance at both 3.0 T and 1.5 T. Data were acquired both with a steady-state free precession sequence (SSFP) and a spoiled gradient echo (SGE) sequence. If necessary, a frequency scout was used to correct for off-resonance artifacts. For both SSFP and SGE imaging, 6-mm thick retrospectively EKG-gated short axis views were acquired with equal matrix size (192 × 163) and comparable repetition time (TR). Cardiac function parameters were determined manually by a single investigator. Cardiac function parameters, signal to noise ratio (SNR), contrast to noise ratio (CNR), and the presence of artifacts were compared between the 2 magnetic field strengths. For statistical analysis, a Pearsons correlation coefficient was calculated, and a paired Student t test was used to test statistical significance. Results:Very good correlations between cardiac function parameters at 1.5 T and 3.0 T (r > 0.84, P < 0.0011) were obtained. Compared with SGE, SSFP more frequently was prone to artifacts. With SSFP/SGE at 3.0 T, a SNR gain of 9.4/16% was achieved compared with 1.5 T. Conclusion:Functional cardiac cine magnetic resonance imaging can be regarded as equally accurate at 3.0 T compared with 1.5 T. Compared with SSFP imaging, the SGE sequence benefits more from higher field strengths and is less affected by artifacts.

High spatial-resolution CE-MRA of the carotid circulation with parallel imaging: comparison of image quality between 2 different acceleration factors at 3.0 Tesla.

Purpose:We sought to evaluate and compare the image quality and vessel delineation of the carotid arteries with high spatial-resolution contrast-enhanced MRA (CE-MRA) at 3.0 T using integrated parallel acquisition (iPAT) with acceleration factors of 2 and 4. Materials and Methods:Using an 8-channel neurovascular array coil, we performed prospective high-spatial resolution CE-MRA at 3.0 T of the head and neck on 24 patients (11 men, 13 women, ages 37–89) with suspected arterio-occlusive disease who were assigned randomly to 2 groups. Twelve patients (group A) were examined with a 3D-GRE sequence using iPAT with acceleration factor of 2. For the next 12 patients (group B) a near-identical sequence with an acceleration factor of 4 was applied. Higher iPAT factors were used to increase the spatial-resolution while keeping scan time unchanged. Two volunteers were scanned by both protocols. Phantom measurements were performed to assess the signal-to-noise ratio (SNR). The presence of artifact, noise, image quality of the arterial segments, and the presence and degree of arterial stenosis were evaluated independently by 2 radiologists. Statistical analysis of data was performed by using Wilcoxon rank sum test and 2-sample Student t test (P < 0.05 was indicative a statistically significant difference). The interobserver variability was tested by kappa coefficient. Results:SNR values were significantly lower when iPAT with acceleration factor of 4 was used (P < 0.001). There was no significant difference between 2 groups in regards to image noise (P= 0.67) and artifact (P = 0.8). Both readers visualized the majority of carotid circulation with good image quality in both groups. For smaller intracranial arteries, such as the second-division of anterior and middle cerebral artery, anterior communicating artery, and superior cerebellar artery, the image quality and vessel delineation was significantly better at an iPAT factor of 4 (P < 0.01). The overall interobserver agreement for both the vessel depiction, and detection of arterial stenoses was higher in group B compared with group A. Conclusion:Use of parallel acquisition techniques with a high acceleration factor (iPAT-4) results in superior depiction of small intracranial arterial segments. Imaging at higher magnetic field strength, in addition to the use of an optimized 8-channel array coil, provides sufficient SNR to support faster parallel acquisition protocols, leading to improved spatial-resolution. More extensive clinical studies are warranted to establish the range of applications and confirm the accuracy of the technique.

High-resolution magnetic resonance angiography of the renal arteries using parallel imaging acquisition techniques at 3.0 T: initial experience.

Objective:The purpose of this prospective study was to investigate the feasibility of high-resolution magnetic resonance angiography (MRA) of the kidneys at 3.0 T using parallel data acquisition. Material and Methods:Contrast-enhanced MRA of the renal arteries (RA) was performed in 12 volunteers and 12 consecutive patients (mean age 47.1 ± 16.3 years) on a 3.0 T MR scanner. For CEMRA, a high-resolution 3-dimensional GRE FLASH sequence was implemented. Images were assessed subjectively on a 0 to 5 scoring scale by 2 reviewers. Quantitative evaluation was done by measuring the contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR). Results:Diagnostic image quality was acquired in all individuals. In total, 62 RA were found, consisting of 48 main and 14 accessory RA. Overall visibility score for main RA was 4.82 ± 0.38. RA were identified up to the third-order branches in 88%. In 3 of 12 patients, a hemodynamic relevant stenosis was found and proven by conventional angiogram. Conclusion:CEMRA at 3.0 T is advantageous in terms of better SNR and T1 weighting; therefore, measurement time can be reduced and spatial resolution can be increased without corruption of signal yield. Consequently, high-field MRA may be preferred for the evaluation of renal vascular anatomy in potential kidney donors or for the detection of renal artery stenosis.

Multistation Whole-Body High- Spatial-Resolution MR Angiography Using a 32-Channel MR System

OBJECTIVE The objective of our study was to investigate a multistation whole-body MR angiography (MRA) protocol using a 32-channel MR system with multicoil technology in a population of patients with suspected peripheral vascular disease (PVD). SUBJECTS AND METHODS Fifty consecutive patients with suspected PVD (31 men, 19 women; age range, 46-91 years) underwent multistation whole-body contrast-enhanced MR angiography (CE-MRA) on a 32-channel 1.5-T MR system equipped with multicoil technology. A two-step contrast injection protocol was used: After the first injection, images of the most proximal station (station I, head and neck) were acquired, followed by the most distal station (station IV, calves). Images of the intermediate two stations (station II, chest and abdomen; station III, pelvis and thighs) were acquired during the second injection. Conventional catheter angiography was performed for symptomatic vascular regions in 30 patients. The image quality of the arterial segments and the presence and degree of the arterial stenosis were evaluated by two radiologists. The interobserver variability was calculated by kappa statistics, and comparative analysis between CE-MRA and catheter angiography was performed by means of the Spearmans rank correlation coefficient. RESULTS Most of the vascular segments (1,912/1,976 [97%]) were visualized on wholebody CE-MRA with diagnostic image quality. Significant arterial disease (> or = 50%) was detected in 167 (observer 1) and 177 (observer 2) segments with excellent interobserver agreement (kappa = 0.84). There was a significant correlation between CE-MRA and conventional angiography for the degree of stenosis (R = 0.92 and 0.89 for observers 1 and 2, respectively). The sensitivity and specificity of CE-MRA for the detection of arterial stenoses 50% or greater were 92% and 96% for observer 1 and 93% and 97% for observer 2, respectively, compared with those of conventional angiography. CONCLUSION Using a multichannel radiofrequency system with multicoil technology, the whole-body CE-MRA approach outlined in this article is able to provide high-spatial-resolution data sets with high diagnostic image quality for evaluation of arterial occlusive disease in most vascular territories.

Feasibility of gadofosveset-enhanced steady-state magnetic resonance angiography of the peripheral vessels at 3 Tesla with Dixon fat saturation.

Introduction:To investigate the feasibility and image quality of gadofosveset-enhanced steady-state peripheral MR-angiography using Dixon fat saturation in comparison to spectral fat saturation. Materials and Methods:After Institutional Review Board (IRB) approval, 10 healthy volunteers underwent peripheral MR-angiography at 3.0 T during the steady state 50 minutes after gadofosveset injection. A steady-state-adapted volume interpolated breathhold examination sequence with an isotropic spatial resolution of 1 mm was acquired with 2-point Dixon fat saturation (DixFS, acquisition time 52 seconds) and with conventional, spectral fat saturation (SFS, acquisition time 58 seconds). The quality of the images was rated on an ordinal 4-point scale (4, very good) by 2 radiologists in consensus. The signal-to-noise ratios (SNRs) of the vessels, the fat, and the muscles as well as the contrast-to-noise-ratio (CNR) between vessels, fat, and muscle were determined. Paired P tests were performed for statistical analysis with a significance level of P < 0.05. Results:Diagnostic image quality was achieved in all examinations. The image quality of the DixFS images was rated superior (median 4) over the SFS images (median 3; P = 0.03). The SNR of muscles and vessels was 40% higher with DixFS (P < 0.008), whereas the SNR of fat was decreased by 40.3% from 40.7 with SFS to 22.4 with DixFS (P < 0.0001). The CNR (fat/muscle) of the DixFS images of 84.1/71.7 was significantly higher than the CNR of the SFS images of 47.7/47.4 (P < 0.001). Discussion:Two-point Dixon fat suppression for MR-angiography during the steady state after the administration of gadofosveset is feasible with superior image quality and more than 50% increase in CNR (fat/muscle) compared with spectral fat saturation without an additional time penalty.

3.0 Tesla high spatial resolution contrast-enhanced magnetic resonance angiography (CE-MRA) of the pulmonary circulation: initial experience with a 32-channel phased array coil using a high relaxivity contrast agent.

Purpose:To evaluate the technical feasibility of high spatial resolution contrast-enhanced magnetic resonance angiography (CE-MRA) with highly accelerated parallel acquisition at 3.0 T using a 32-channel phased array coil, and a high relaxivity contrast agent. Materials and Methods:Ten adult healthy volunteers (5 men, 5 women, aged 21–66 years) underwent high spatial resolution CE-MRA of the pulmonary circulation. Imaging was performed at 3 T using a 32-channel phase array coil. After intravenous injection of 1 mL of gadobenate dimeglumine (Gd-BOPTA) at 1.5 mL/s, a timing bolus was used to measure the transit time from the arm vein to the main pulmonary artery. Subsequently following intravenous injection of 0.1 mmol/kg of Gd-BOPTA at the same rate, isotropic high spatial resolution data sets (1 × 1 × 1 mm3) CE-MRA of the entire pulmonary circulation were acquired using a fast gradient-recalled echo sequence (TR/TE 3/1.2 milliseconds, FA 18 degrees) and highly accelerated parallel acquisition (GRAPPA × 6) during a 20-second breath hold. The presence of artifact, noise, and image quality of the pulmonary arterial segments were evaluated independently by 2 radiologists. Phantom measurements were performed to assess the signal-to-noise ratio (SNR). Statistical analysis of data was performed by using Wilcoxon rank sum test and 2-sample Student t test. The interobserver variability was tested by kappa coefficient. Results:All studies were of diagnostic quality as determined by both observers. The pulmonary arteries were routinely identified up to fifth-order branches, with definition in the diagnostic range and excellent interobserver agreement (κ = 0.84, 95% confidence interval 0.77–0.90). Phantom measurements showed significantly lower SNR (P < 0.01) using GRAPPA (17.3 ± 18.8) compared with measurements without parallel acquisition (58 ± 49.4). Conclusion:The described 3 T CE-MRA protocol in addition to high T1 relaxivity of Gd-BOPTA provides sufficient SNR to support highly accelerated parallel acquisition (GRAPPA × 6), resulting in acquisition of isotopic (1 × 1 × 1 mm3) voxels over the entire pulmonary circulation in 20 seconds.