A three-coil comparison for MR angiography

The purpose of this work was to compare intracranial magnetic resonance angiography (MRA) image quality using three different radiofrequency coils. The three coil types included a reduced volume quadrature birdcage coil with endcap, a commercially available quadrature birdcage head coil, and a four-element phased-array coil. Signal-to-noise ratio (SNR) measurements were obtained from comparison studies performed on a uniform cylindrical phantom. MRA comparisons were performed using data acquired from 15 volunteers and applying a thick-slab three-dimensional time-of-flight sequence. Analysis was performed using the signal difference-to-noise ratio, a quantitative measure of the relative vascular signal. The reduced-volume endcap and phased-array coils, which were designed specifically for imaging the intracranial volume of the head, improved the image SNR and vascular detail considerably over that obtained using the commercially available head coil. The endcap coil configuration provided the best vascular signal overall, while the phased-array coil provided the best results for arteries close to the coil elements.     

Three-dimensional breathhold SSFP coronary MRA: a comparison between 1.5T and 3.0T

PURPOSE: To assess the feasibility of three-dimensional breathhold coronary magnetic resonance angiography (MRA) at 3.0T using the steady-state free precession (SSFP) sequence, and quantify the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) gains of coronary MRA from 1.5T to 3.0T using whole-body and phased-array cardiac coils as the signal receiver. MATERIALS AND METHODS: Eight healthy volunteers were scanned on 1.5T and 3.0T whole-body systems using the SSFP sequence. Numerical simulations were performed for the SSFP sequence to optimize the flip angle and predict signal enhancement from 1.5T to 3.0T. Coronary artery images were acquired with the whole-body coil in transmit-receive mode or transmit-only with phased-array cardiac coil receivers. RESULTS: In vivo studies of the same volunteer group at both field strengths showed increases of 87% in SNR and 83% in CNR from 1.5T to 3.0T using a whole-body coil as the signal receiver. The corresponding increases using phased-array receivers were 53% in SNR and 92% in CNR. However, image quality at 3.0T was more variable than 1.5T, with increased susceptibility artifacts and local brightening as the result of increased B(0) and B(1) inhomogeneities. CONCLUSION: Coronary MRA at 3.0T using a three-dimensional breathhold SSFP sequence is feasible. Improved SNR at 3.0T warrants the use of coronary MRA with faster acquisition and/or improved spatial resolution. Further investigations are required to improve the consistency of image quality and signal uniformity at 3.0T.     

Improved multi-station peripheral MR angiography with a dedicated vascular coil

Delineation of small branch vessels can be crucial for assessing the peripheral arterial system of patients requiring surgical grafting. Thus signal-to-noise needs to be maximized. We evaluated the performance of a dedicated peripheral vascular coil in four subjects by comparing it to the body coil using DSA as the standard of reference. SNR and CNR values of the dedicated peripheral coil exceeded those obtained with the body coil by a mean of 398%, thus permitting improved delineation of the infrapopliteal arterial morphology.     

High-resolution magnetic resonance angiography of the lower extremities with a dedicated 36-element matrix coil at 3 Tesla

INTRODUCTION: Recent developments in hard- and software help to significantly increase image quality of magnetic resonance angiography (MRA). Parallel acquisition techniques (PAT) help to increase spatial resolution and to decrease acquisition time but also suffer from a decrease in signal-to-noise ratio (SNR). The movement to higher field strength and the use of dedicated angiography coils can further increase spatial resolution while decreasing acquisition times at the same SNR as it is known from contemporary exams. The goal of our study was to compare the image quality of MRA datasets acquired with a standard matrix coil in comparison to MRA datasets acquired with a dedicated peripheral angio matrix coil and higher factors of parallel imaging. MATERIALS AND METHODS: Before the first volunteer examination, unaccelerated phantom measurements were performed with the different coils. After institutional review board approval, 15 healthy volunteers underwent MRA of the lower extremity on a 32 channel 3.0 Tesla MR System. In 5 of them MRA of the calves was performed with a PAT acceleration factor of 2 and a standard body-matrix surface coil placed at the legs. Ten volunteers underwent MRA of the calves with a dedicated 36-element angiography matrix coil: 5 with a PAT acceleration of 3 and 5 with a PAT acceleration factor of 4, respectively. The acquired volume and acquisition time was approximately the same in all examinations, only the spatial resolution was increased with the acceleration factor. The acquisition time per voxel was calculated. Image quality was rated independently by 2 readers in terms of vessel conspicuity, venous overlay, and occurrence of artifacts. The inter-reader agreement was calculated by the kappa-statistics. SNR and contrast-to-noise ratios from the different examinations were evaluated. RESULTS: All 15 volunteers completed the examination, no adverse events occurred. None of the examinations showed venous overlay; 70% of the examinations showed an excellent vessel conspicuity, whereas in 50% of the examinations artifacts occurred. All of these artifacts were judged as none disturbing. Inter-reader agreement was good with kappa values ranging between 0.65 and 0.74. SNR and contrast-to-noise ratios did not show significant differences. CONCLUSION: Implementation of a dedicated coil for peripheral MRA at 3.0 Tesla helps to increase spatial resolution and to decrease acquisition time while the image quality could be kept equal. Venous overlay can be effectively avoided despite the use of high-resolution scans.     

Whole-body MR angiography using a novel 32-receiving-channel MR system with surface coil technology: first clinical experience

PURPOSE: To demonstrate the feasibility of detecting atherosclerotic vascular disease using an innovative magnetic resonance angiography (MRA) protocol in combination with a dedicated whole-body MR scanner with new surface coil technology. MATERIALS AND METHODS: A total of 10 volunteers and eight patients with peripheral arterial occlusive disease (PAOD) were examined at 1.5 T. Conventional digital subtraction angiography (DSA) of the symptomatic region was available as a reference standard in all eight patients. Depending on subjects' size, four to five three-dimensional data sets were acquired using an adapted injection protocol. Images were assessed independently by two readers for vascular pathology. Additionally, signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) were measured. RESULTS: Whole-body MRA yielded excellent sensitivity and specificity of more than 95% for both readers with high interobserver agreement (k = 0.93). Surface coil signal reception rendered a high SNR (mean 151.28 +/- 54.04) and CNR (mean 120.75 +/- 46.47). Despite lower SNR and CNR of the cranial and cervical vessels, a two-step injection protocol exhibited less venous superposition and therefore proved to be superior compared to single-bolus injection. CONCLUSION: Our approach provides accurate noninvasive high-resolution imaging of systemic atherosclerotic disease, covering the arterial vasculature from intracranial arteries to distal runoff vessels. The recently introduced MR scanner and coil technology is feasible to significantly increase the performance of whole-body MRA.     

3D contrast-enhanced MR angiography of the run-off vessels: value of image subtraction

The diagnostic gain associated with image subtractions was assessed regarding contrast-enhanced 3D magnetic resonance angiography (MRA) image sets of the pelvic and lower extremity arteries. The MRA strategy combined a dedicated vascular coil with a single injection, two-station protocol. Voxel-by-voxel signal intensity subtraction was performed on MRA image sets obtained before and during dynamic infusion of a para-magnetic contrast agent. Non-subtracted and subtracted MRA image sets were assessed for the presence of occlusive (four grades) disease, using DSA as the standard of reference. In addition, SNR and CNR were recorded for each vascular segment on both the non-subtracted and subtracted images. While CNR values of subtracted images exceeded those of non-subtracted images (P < 0.05), there was no difference in diagnostic performance. For the detection of hemodynamically significant disease, non-subtracted and subtracted MRA provided overall sensitivity and specificity of 90.2%/90.3% and 95.1%/95.6%, respectively. Concordance between non-subtracted and subtracted MRA was excellent (Kappa = 0.86).     

3D MR angiography of the entire aorta: modified application of the body-phased array coil for a single-shot technique

OBJECTIVE: Evaluation of different contrast-enhanced MR angiography imaging protocols for visualization of the entire aorta in breath-hold technique. METHODS AND PATIENTS: Three different CE (0.15 mmol/kg) MRA protocols were evaluated by phantom and patient studies: (1) two separate MRA with conventional application of the body-phased array coil; (2) a single-shot MRA with modified application of the body-phased array coil; (3) a single-shot MRA with the body coil. Duplex sonography, CTA and DSA were used as standard of reference. RESULTS: In all examinations the entire aorta could be visualized. The best SNR was acquired with protocol (1). The SNR of protocol (2) was reduced if the sagittal body diameter of the patient was greater than 20 cm and decreased significantly with diameters over 30 cm. By the use of protocol (3) the SNR was notably poor. The quality scored for the visualization of the entire aorta was 97.5% (protocol 1); 92.5% (protocol 2); and 80.0% (protocol 3). CONCLUSION: In most cases the modified application of the body-phased array coil allows the imaging of the entire aorta as a single-shot 3D CE MRA in diagnostic quality.     

Peripheral vascular coil for peripheral MR angiography: phantom-based comparison with body coil by SNR, CNR, and visual evaluation

AIM: To evaluate the image quality of MR angiography (MRA) with a peripheral vascular coil. MATERIALS AND METHODS: A peripheral vascular coil, a technical coil used in MRA of the pelvis and lower extremities, has 12 individual coil elements arranged in six pairs. We evaluated the performance of a peripheral vascular coil for image quality, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and visual evaluation by comparing it to a body coil using a phantom. RESULTS: SNR with the peripheral vascular coil was 1.5-2.2 times higher than that with the body coil in vertical distance, and 1.6-1.8 times higher in horizontal distance. CNR with the peripheral vascular coil was 2.1-3.8 times higher than that with the body coil. Visual evaluation with the peripheral vascular coil was 1.1-1.2 times higher than with the body coil in spin echo sequences, and 1.2-1.9 times higher in 3D fast spoiled GRASS (3D-FSPGR) sequences. CONCLUSION: The peripheral vascular coil for peripheral MRA is robust and accurate in evaluating peripheral vascular diseases.     

3D time-of-flight MR angiography of the intracranial vessels: optimization of the technique with water excitation, parallel acquisition, eight-channel phased-array head coil and low-dose contrast administration

The aim of this study is three folds: to compare the eight-channel phased-array and standard circularly polarized (CP) head coils in visualiazation of the intracranial vessels, to compare the three-dimentional (3D) time-of-flight (TOF) MR angiography (MRA) techniques, and to define the effects of parallel imaging in 3D TOF MRA. Fifteen healthy volunteers underwent 3D TOF MRA of the intracranial vessels using eight-channel phased-array and CP standard head coils. The following MRA techniques were obtained on each volunteer: (1) conventional 3D TOF MRA with magnetization transfer; (2) 3D TOF MRA with water excitation for background suppression; and (3) low-dose (0.5 ml) gadolinium-enhanced 3D TOF MRA with water excitation. Results are demonstrating that water excitation is a valuable background suppression technique, especially when applied with an eight-channel phased-array head coil. For central and proximal portions of the intracranial arteries, unenhanced TOF MRA with water excitation was the best technique. Low-dose contrast enhanced TOF MRA using an eight-channel phased-array head coil is superior in the evaluation of distal branches over the standard CP head coil. Parallel imaging with an accelaration factor of two allows an important time gain without a significant decrease in vessel evaluation. Water excitation allows better background suppression, especially around the orbits and at the periphery, when compared to conventional acquisitions.     

Geometrical optimization of a phased array coil for high-resolution MR imaging of the carotid arteries.

The geometry of an RF phased-array receiving coil for high-resolution MRI of the carotid artery, particularly the bifurcation, was optimized with respect to signal-to-noise ratio (SNR). A simulation tool was developed to determine homogeneity, sensitivity, and SNR for a given imaging situation. The algorithm takes into account the coil geometry, the parameters of the measured object, and the imaging parameters of the pulse sequence. The coil with the optimum geometry was implemented as a receive-only coil for 1.5 T and comparative SNR measurements with different coils were performed. The experimental SNR measurements verified the simulations. The optimized carotid artery phased array offered the best SNR over the desired field of view. In vivo high-resolution MRI of the carotid arteries of healthy volunteers and patients with known stenosis was conducted with the optimized phased array coil. The capability of the phased array coil for resolving components within the carotid artery walls is demonstrated. Magn Reson Med 50:439-443, 2003.     

Novel RF coil geometry for lower extremity imaging.

A receive-only phased-array coil was designed to image the lower extremities. The array consists of four volume coils placed on two cylindrical formers. The coil array has the ability to image both legs simultaneously over a 40 cm longitudinal field of view (FOV). Experiments using phantoms show an increase in signal-to-noise ratio (SNR) in regions of interest through the center of the coil by an average factor of 2.8 over the body coil and 1.5 over the GE 4-channel torso array. In vivo data acquired from 10 subjects show that the X array provided similar SNR improvement in spin-echo images and more vascular details in angiographic images compared to the torso array.     

Design of a birdcage array for lower extremity angiography

PURPOSE: To investigate the application of a coil array consisting of multiple birdcages for bolus chase magnetic resonance angiography (MRA) of the lower extremities. MATERIALS AND METHODS: The prototype consisted of four birdcage coils; two adjacent birdcages for thigh imaging, and two for calf imaging. Decoupling between adjacent coils was achieved using shared capacitors. Bench measurements and MR images were used to evaluate the decoupling scheme. Image signal-to-noise ratios (SNR) were compared between the birdcage array and four commercially available coils. Contrast-enhanced imaging experiments were performed on 10 volunteers and parallel imaging was simulated. This study was approved by the local institutional review board and written informed consent was obtained from each volunteer. RESULTS: Capacitive decoupling resulted in a reduction in signal leakage. The calf birdcages provided an 84% SNR improvement over a four element array, while the thigh birdcages provided a 53% improvement. Angiographic images illustrated the utility of the coil for peripheral MRA. Parallel imaging was demonstrated with a two-fold reduction factor. CONCLUSION: Birdcage coils were demonstrated to be valuable for lower extremity imaging due to their homogenous sensitivity, good SNR, and cylindrical geometry. Coupling was controlled using shared capacitors that allowed a single birdcage to encompass each leg individually, providing a novel approach to signal reception for peripheral imaging.     

Comparison of cardiac MRI on 1.5 and 3.0 Tesla clinical whole body systems

RATIONALE AND OBJECTIVES: A cardiac imaging pilot study was performed on 1.5 and 3.0 Tesla (T) whole body magnetic resonance units equipped with identical gradient sets and geometrically equivalent body coils. The goals were to compare the signal-to-noise (SNR) and contrast-to-noise (CNR) ratios on matched studies conducted at both field strengths and demonstrate the potential for functional and morphologic cardiac evaluation at 3.0 T. METHODS: Short axis cine true fast imaging with steady precession (True FISP) was compared at 1.5 and 3.0 T using the body coil in transmit-receive mode and transmit-only with single loop and phased array receiver coils. SNR of the myocardium and CNR of the ventricular blood and myocardium were calculated from a quantitative region of interest analysis of these data. Additionally at 3.0 T, long axis and 4-chamber cine as well as "dark blood" imaging are demonstrated with sequence and parameter settings comparable to current state of the art for cardiac evaluation at 1.5 T. RESULTS: The 3.0 T data consistently demonstrates increases in SNR when all imaging conditions are closely matched but the increase has a large variability ranging from 20 to 85% depending on the radiofrequency coil configuration. Ventricular blood-myocardium CNR greater than 30 is obtained at 3.0 T, which is comparable to an optimized 1.5 T acquisition despite the specific absorption rate limitation of flip angle to nearly one half the value. The increased SNR at 3.0 T improves detection of fine anatomic detail, such as the chordae tendineae and mitral valve structure. CONCLUSIONS: Increased specific absorption rate can be a limiting fact; however, we have demonstrated that 3.0 T cardiac imaging shows gains in SNR while maintaining the CNR. The SNR gain is advantageous, and phased array coil technology is key for improving cardiac magnetic resonance imaging at 3.0 T.     

Phased-array MRI of canine prostate using endorectal and endourethral coils.

A four-channel phased array consisting of one surface coil, two endorectal coils, and one flexible endourethral loop coil was designed for MRI of the canine prostate. The endorectal coils provide high signal in the posterior region of the prostate, while the endourethral and surface coils are sensitive to the central and anterior regions of the prostate. Gel phantom experiments indicate that the proposed phased-array configuration generates 15 times more signal-to-noise ratio (SNR) than a combination of two surface coils and one endorectal coil within the posterior region of the prostate; the performance of the two configurations is comparable near the anterior prostate surface. Ultimate intrinsic SNR (UISNR) analysis was used to compare the proposed phased array's performance to the best possible SNR for external coils. This analysis showed that the proposed phased array outperforms the best-case external coil within the posterior and central regions of the prostate by up to 20 times. In canine experiments in vivo, high-resolution fast spin-echo (FSE) images of the prostate were obtained with a pixel size of 230 microm obtained in 3 min 12 s. The proposed phased-array design potentially can be used to increase the accuracy of prostate cancer staging and the feasibility of MR-guided prostate interventions.     

Gadomer-17-enhanced 3D navigator-echo MR angiography of the pulmonary arteries in pigs

The goal of this study was visualisation and quality assessment of the pulmonary arteries in pigs with modified navigator-echo magnetic resonance angiography using an intravascular contrast agent. Five sedated pigs were examined in a clinical 1.5-T system with modified three-dimensional navigator-echo magnetic resonance angiography (slice thickness 3 mm, pixel size 2.4x1.8 mm2) to evaluate the pulmonary arteries. Using a phased-array four-element thorax coil the entire thorax was scanned before and after intravenous infusion of a gadolinium-based intravascular contrast agent. Assessment of image quality, enhancement-related contrast-to-noise ratio (CNR) measurements and improvement of visibility of peripheral pulmonary vessels was performed. Improvement of quality using Gadomer-17 was found for smaller vessels; pulmonary trunks and the main pulmonary arteries were sufficiently imaged without enhancement. Mean rise of CNR measured in the pulmonary trunks was 28.64% ( P=0.0002), mean rise of CNR in the main pulmonary arteries and the segmental arteries were 79.6% and 148.2%, respectively. Mean distance between the visible peripheral end of 60 sub-segmental arteries and the inner thoracic wall was 12.2 +/- 0.4 mm, and was significantly ( P=0.00002) reduced after contrast infusion to 8.0 +/- 0.4 mm. The combination of inherent flow sensitivity of navigator-echo angiography and Gadomer-17 proved effective for imaging of the pulmonary arteries. In contrast to standard contrast-enhanced pulmonary MRA studies, breath holding is not required. Further studies and the evaluation of findings of patients suffering from pulmonary embolism are needed to evaluate the possible benefits of a higher spatial resolution which is achievable using navigator-echo techniques in contrast to the higher temporal resolution of ultra-fast pulmonary MRA.     

Moving-table MR angiography of the peripheral runoff vessels: comparison of body coil and dedicated phased array coil systems

OBJECTIVE: The aim of our study was to compare the signal-to-noise ratio and the diagnostic accuracy of moving-table MR angiography of the peripheral arteries with body coil and dedicated phased array coil systems. SUBJECTS AND METHODS: Forty patients were examined with digital subtraction angiography and moving-table MR angiography with a 1.5-T MR imaging system either with a body coil (n = 20) or with a dedicated phased array coil (n = 20). The timing of contrast material was performed with real-time MR fluoroscopy. RESULTS: For the iliac artery, upper leg, and lower leg, the mean values for signal-to-noise ratios were 56, 51, and 17, respectively, for the body coil, and 54, 74, and 64, respectively, for the dedicated phased array coil. For the body coil, sensitivity and specificity in identifying stenosis greater than 50% and occlusions were 100% and 96%, respectively, for the iliac arteries, and 100% and 96%, respectively, for the upper leg. For the dedicated phased array coil, sensitivity and specificity for stenosis greater than 50% and occlusions were 100% and 96%, respectively, for the iliac arteries, and 100% and 98%, respectively, for the upper leg. Sensitivity and specificity were inferior for the body coil (88% and 85%) compared with the dedicated phased array coil (100% and 96%) in the lower leg. A significant difference of the mean values of contrast-to-noise ratio was found before and after subtraction for the dedicated phased array coil and body-coil techniques (Student's t test, p < 0.01). CONCLUSION: In comparison with the body coil, the dedicated peripheral phased array surface coil system improves signal-to-noise ratio for the upper and lower leg and diagnostic accuracy in the lower leg.     

Dose comparison of single versus double dose in contrast-enhanced magnetic resonance angiography of the renal arteries: intra-individual cross-over blinded trial using Gd-DTPA

This study was planned as an open-label, single-centre trial with blinded evaluations by two independent radiologists, aimed at the intra-individual comparison of single-dose and double-dose Gd-DTPA-enhanced MRA in the renal arterial territory. Ten healthy volunteers were included in the study. Renal MRAs were carried out on a clinical 1.5-T MR system using a body phased-array coil. Images were acquired with three-dimensional fast spoiled gradient echo sequence. Contrast agent was injected with a power injector keeping the injection time constant for single dose and double dose. Both readers found at least 96% of vascular segments evaluable. Median overall image quality was rated excellent, and diagnostic confidence was rated confident. No statistically significant difference between the dosage groups could be demonstrated. Signal intensity, SNR and CNR were significantly higher for the double-dose group. Our results demonstrate that while a double dose of contrast agent increases SNR, it does not lead to further improvement in visual and perceptual image quality. A single dosage of approximately 0.1 mmol/kg bw Gd-DTPA may be the preferable dosage to demonstrate the renal arteries.     

Toward single breath-hold whole-heart coverage coronary MRA using highly accelerated parallel imaging with a 32-channel MR system.

Coronary MR angiography (CMRA) is generally confined to the acquisition of multiple targeted slabs with coverage dictated by the competing constraints of signal-to-noise ratio (SNR), physiological motion, and scan time. This work addresses these obstacles by demonstrating the technical feasibility of using a 32-channel coil array and receiver system for highly accelerated volumetric breath-hold CMRA. The use of the 32-element array in unaccelerated CMRA studies provided a baseline SNR increase of as much as 40% over conventional cardiac-optimized phased array coils, which resulted in substantially enhanced image quality and improved delineation of the coronary arteries. Modest accelerations were used to reduce breath-hold durations for tailored coverage of the coronary arteries using targeted multi-oblique slabs to as little as 10 s. Finally, high net accelerations were combined with the SNR advantages of a 3D steady-state free precession (SSFP) technique to achieve previously unattainable comprehensive volumetric coverage of the coronary arteries in a single breath-hold. The merits and limitations of this simplified volumetric imaging approach are discussed and its implications for coronary MRA are considered.     

Use of a three-station phased array coil to improve peripheral contrast-enhanced magnetic resonance angiography

PURPOSE: To explore the imaging capabilities of a new commercially available, three-station, 129-cm long, 12-element phased array coil for contrast-enhanced magnetic resonance angiography (CE-MRA) in patients with symptomatic peripheral arterial occlusive disease. MATERIALS AND METHODS: Nineteen patients, referred for peripheral CE-MRA, were evaluated using the new three-station coil. For each station four coil elements (two anterior and two posterior to the patient) were used. The expected improvements in signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were used to improve spatial resolution and increase anatomic coverage for the distal two stations compared to our previous protocol. Images obtained in the 19 patients imaged with the new coil were compared to those of the last 19 patients scanned without the use of the new coil. Differences in image quality before vs. after the availability of the new coil were compared in terms of SNR and CNR, subjective interpretability score (SIS), degree of venous enhancement, and anatomic coverage. Images were interpreted by two experienced observers, blinded for imaging technique and each other's results. RESULTS: Use of the coil enabled acquisition of high resolution peripheral vasculature images in all cases and allowed for substantially smaller voxel sizes (thighs: 5.3 vs. 8.4 mm(3) [-37%]; legs: 1.8 vs. 8.0 mm3 [-78%]) and much shorter acquisition durations in the aortoiliac and thigh stations (aortoiliac: 16 vs. 27 seconds [-41%]; thighs: 11 vs. 23 seconds [-52%]). Acquisition duration in the leg station was prolonged (68 vs. 29 seconds [+134%]). SNR and CNR were significantly higher only in the aortoiliac station using the three-station coil (both: P < 0.001). There were no significant differences in SIS for the aortoiliac and thigh stations (aortoiliac station: observer 1: P = 0.16, observer 2: P = 0.19; thigh station: both observers: P = 0.27). Images acquired with the new coil had significantly higher SIS for the leg station (both observers: P = 0.004). There were no significant differences in venous enhancement between the two protocols for any of the stations (all P > 0.11). In 12/12 (100%) requested cases the entire pedal arch was depicted using the new coil, whereas this was not possible with the old protocol. CONCLUSION: The new three-station dedicated peripheral vascular coil allows for much higher resolution imaging in the thigh and leg stations with greater anatomic coverage and substantially improves peripheral MRA quality of the lower leg vasculature.     

In vivo colon wall imaging using endoluminal coils: feasibility study on rabbits

PURPOSE: To assess in vivo distal colon wall magnetic resonance imaging (MRI) feasibility on rabbits using an endoluminal radio frequency (RF) coil on a 1.5-T clinical scanner. MATERIALS AND METHODS: The endoluminal coil signal-to-noise ratio (SNR) was compared to a clinical four-element phased-array body coil. High-resolution (HR) MRI of rabbit colon walls was performed on six rabbits. The imaging protocol combined T1-weighted fast low-angle-shot (FLASH) sequences with and without fat saturation (FS), T2-weighted True-Fast imaging with steady state precession (Fisp), turbo spin-echo (TSE), and T1-weighted FLASH FS after contrast media injection. Images were compared to histological sections. Catheter tracking using an endoluminal coil in addition to external coils was also evaluated on two rabbits. RESULTS: HR images allow visualization and identification of rabbit colon wall layers. Real-time tracking allows a clear visualization and a good positioning of the endoluminal coil within the rabbit. CONCLUSION: Compared to a clinical multielement array coil, a dedicated endoluminal RF coil provides an important SNR increase at the region of interest (ROI). Very HR images of in vivo rabbit colon walls were achieved providing detailed information on the different wall layers. This technique could be considered on humans for accurate tumoral and inflammatory bowel disease diagnosis.