Evaluation of the iliac arteries: comparison of two-dimensional time of flight magnetic resonance angiography with cardiac compensated fast gradient recalled echo and contrast-enhanced three-dimensional time of flight magnetic resonance angiography

Assessment of aortoiliac and renal arteries: MR angiography with parallel acquisition versus conventional MR angiography and digital subtraction angiography

PURPOSE

To prospectively compare the image quality, sensitivity, and specificity of three-dimensional gadolinium-enhanced magnetic resonance (MR) angiography accelerated by parallel acquisition (ie, fast MR angiography) with MR angiography not accelerated by parallel acquisition (ie, conventional MR angiography) for assessment of aortoiliac and renal arteries, with digital subtraction angiography (DSA) as the reference standard.

MATERIALS AND METHODS

The study was approved by the institutional review board; informed consent was obtained from all patients. Forty consecutive patients (33 men, seven women; mean age, 63 years) suspected of having aortoiliac and renal arterial stenoses and thus examined with DSA underwent both fast (mean imaging time, 17 seconds) and conventional (mean imaging time, 29 seconds) MR angiography. The arterial tree was divided into segments for image analysis. Two readers independently evaluated all MR angiograms for image quality, presence of arterial stenosis, and renal arterial variants. Image quality, sensitivity, and specificity were analyzed on per-patient and per-segment bases for multiple comparisons (with Bonferroni correction) and for dependencies between segments (with patient as the primary sample unit). Interobserver agreement was evaluated by using kappa statistics.

RESULTS

Overall, the image quality with fast MR angiography was significantly better (P=.001) than that with conventional MR angiography. At per-segment analysis, the image quality of fast MR angiograms of the distal renal artery tended to be better than that of conventional MR angiograms of these vessels. Differences in sensitivity for the detection of arterial stenosis between the two MR angiography techniques were not significant for either reader. Interobserver agreement in the detection of variant renal artery anatomy was excellent with both conventional and fast MR angiography (kappa=1.00).

CONCLUSION

Fast MR angiography and conventional MR angiography do not differ significantly in terms of arterial stenosis grading or renal arterial variant detection.

Magnetic resonance angiography of abdominal and lower extremity vasculature

Magnetic resonance angiography (MRA) has evolved over the past years from an experimental imaging modality to a technique that is now widely applied in clinical practice. This article reviews the fundamentals of the different magnetic resonance angiographic techniques and how they can be applied for abdominal and peripheral arterial imaging. Currently, contrast-enhanced magnetic resonance angiography (CE-MRA), whereby a luminogram is obtained during initial arterial passage of contrast material, is the most widely used technique. With current hardware and software, high-spatial resolution images of the abdominal aorta and proximal visceral branches can be obtained that are equivalent to intra-arterial digital subtraction angiography (IA-DSA). High-quality imaging of the renal arteries demands isotropic voxels and reformations orthogonal to the vessel axis for evaluation. Contrast-enhanced magnetic resonance angiography of the peripheral vascular tree is now a highly accurate technique and has replaced diagnostic intra-arterial digital subtraction angiography and duplex ultrasonography in many hospitals.

Abdominal and iliac arterial stenoses: comparative double-blinded randomized study of diagnostic accuracy of 3D MR angiography with gadodiamide or gadopentetate dimeglumine

PURPOSE

To prospectively evaluate accuracy of gadolinium-enhanced three-dimensional (3D) magnetic resonance (MR) angiography with gadodiamide and gadopentetate dimeglumine (0.1 mmol/kg), with intraarterial DSA as reference standard, for imaging abdominal and iliac arterial stenoses.

MATERIALS AND METHODS

The study was approved by all institutional review boards; informed consent was obtained from each subject before procedures. Two hundred forty-seven subjects were included; 240 received either contrast agent and were available for safety analysis; 222 were available for accuracy analysis. Enhanced 3D MR angiography and DSA were performed; image data were evaluated in a double-blinded randomized study. Stenoses were classified as not relevant (<50% stenosis) or relevant (> or =50%). For detection of main stenosis, accuracy with enhanced 3D MR angiography compared with that with DSA was determined.

RESULTS

The difference in accuracy for imaging with gadodiamide and gadopentetate was 3.6%. Noninferiority was inferred because the lower bound of the exact two-sided 95% confidence interval was -10.1 and was above the noninferiority margin (-15%). Accuracy for detection of the main stenosis was low, 56.4% for gadodiamide and 52.8% for gadopentetate group. Subgroup analysis with exclusion of inferior mesenteric artery and internal iliac arteries and the most false-positive stenosis classifications yielded better results: 76.6% and 71.6%, respectively. Sensitivity, specificity, and negative and positive predictive values did not differ substantially between study groups. In the main analysis, values were 44%, 96%, 35%, and 97% for gadodiamide and 44%, 83%, 30%, and 90% for gadopentetate, respectively. In the subgroup analysis, values were 66%, 95%, 61%, and 96% for gadodiamide and 63%, 86%, 58%, and 88% for gadopentetate, respectively.

CONCLUSION

Noninferiority of gadodiamide versus gadopentetate was verified based on the primary end point, which was accuracy for detection of the main stenosis with enhanced 3D MR angiography compared with DSA.

Magnetic resonance imaging of the vascular system: a practical approach for the radiologist

Contrast-enhanced magnetic resonance angiography (CE-MRA) has benefited from rapid technologic developments, including specific hardware and pulse sequence design. This article provides a brief practical overview of technique together with clinical examples of utility in daily application, from the view of an interventional radiologist. CE-MRA is rapidly replacing catheter-based diagnostic angiography for examination of the carotid arteries, aorta, renal arteries, and lower extremity.

MR angiography for assessment of peripheral vascular disease

Contrast-enhanced 3D MRA is emerging as a powerful noninvasive imaging modality for the assessment of patients with PVD. Its clinical utility using current technology has already been well established, and the continuous development of hard- and software will likely result in significantly improved performance. Thus, Gd-enhanced MRA is likely to emerge as the dominant noninvasive imaging modality for PVD worldwide.

Lower extremity MR angiography: universal retrofitting of high-field-strength systems with stepping kinematic imaging platforms initial experience

In 15 volunteers and 84 patients with clinically suspected peripheral vascular disease, a stepping kinematic imaging platform, a manual retrofit stepping magnetic resonance (MR) imaging table, was used with three high-field-strength MR imaging systems to perform multistation peripheral contrast material-enhanced MR angiography in the lower extremity with the existing system phased-array coil. Each examination was performed in less than 45 minutes. Mounting of the stepping kinematic imaging platform was quick and simple and allowed rapid repositioning of a patient relative to the phased-array coil and acquisition of high-spatial-resolution MR angiograms of the peripheral vasculature with use of one injection of MR imaging contrast agent.

Peripheral vascular surgery and magnetic resonance arteriography--a review

OBJECTIVES

to review the current status of lower limb MRA.

DESIGN

a literature review based predominantly on a MEDLINE database search of English-language publications from January 1991 to October 2000.

MATERIALS AND METHODS

twenty-eight articles, concerning non-enhanced MRA (13), gadolinium-enhanced MRA (14) or both (1), met the predefined requirement for quality. Results gadolinium-enhanced MRA (CE-MRA) seems to be more accurate, quicker and associated with fewer problems than non-enhanced (TOF) MRA. TOF-MRA has a sensitivity and specificity of 93% (range 64-100%) and 88% (range 57-100%) respectively, and CE-MRA presents values of 96% (range 71-100%) and 96% (63-100%), respectively, using conventional arteriography as the gold standard. Some articles report a substantial incidence of runoff vessels suitable for distal bypass visible on MRA but invisible on conventional arteriography. Gadolinium contrast is given intravenously and is generally well tolerated and has no known nephrotoxicity.

CONCLUSION

CE-MRA is accurate compared to conventional arteriography, has the potential to increase the limb salvage rate for selected patients, is non-invasive and well tolerated.

Peripheral magnetic resonance angiography

Peripheral vascular disease (PVD) is a common disorder in western society. Reflecting on the risks and costs of contrast arteriography, magnetic resonance angiography is a powerful noninvasive imaging modality for the diagnostic workup of patients with peripheral vascular disease. This article reviews the current state of the art of magnetic resonance angiography of the peripheral vasculature.

Contrast-enhanced magnetic resonance angiography of the iliac arteries: optimization by injection simulation

Protocols for contrast-enhanced magnetic resonance angiography (CE-MRA) of the iliac arteries were optimized by computer simulations based on an impulse response function (IRF) of contrast agent (CA) concentration as a function of time obtained for 20 patients. Protocols with sequential, centric, and elliptical k-space coverage, different repetition rates (5 and 10 ms), and CA doses (0.1, 0.2, and 0.3 mmol/kg b.w.) were compared in terms of signal-to-noise ratio (SNR), distortion of vessel profiles, and sensitivity to timing errors. IRF-based simulations successfully characterized CA recirculation. Slow-rate CA infusions were found to achieve relatively high enhancement. In terms of SNR, there is no advantage in increasing the repetition rate. Distortion of vessel profiles is more likely in elliptic and centric k-space coverage. Protocols based on sequential k-space coverage and relatively long CA infusions proved to be particularly suited to large-FOV iliac examinations as they are relatively insensitive to timing errors.

Contrast-enhanced magnetic resonance angiography: technical considerations for optimized clinical implementation

Contrast-enhanced magnetic resonance angiography (CE MR angiography) has benefited from advancements in MR imaging speed, pulse sequence design, and dedicated equipment and algorithms for its performance. These improvements have greatly expanded the number of options available to the operator and enabled the application of CE MR angiography to a broader range of clinical applications. In this article, the various timing options, pulse sequence innovations, and contrast administration concerns related to clinical CE MR angiography are reviewed. Pertinent issues related to multiphase and multistation bolus chase CE MR angiography also will be discussed.

MR angiography of the vascular tree from the aorta to the foot: combining two-dimensional time-of-flight and three-dimensional contrast-enhanced imaging

A composite approach for magnetic resonance (MR) angiography of the lower extremities is described. Thirty patients were studied with this approach, which combined a two-dimensional (2D) time-of-flight (TOF) technique with a 3D contrast-enhanced technique. A head/neck coil was selected for imaging mid-foot to upper calf, and the body coil was used for the remainder of the peripheral vascular tree. Acquired data were transferred to a workstation for postprocessing. The final maximum intensity projection images, which display the entire vascular anatomy from aortic bifurcation to foot, were created using a 1024 x 1024 matrix. Very small arteries can be differentiated in critical regions like the calf and foot. Compared with TOF-2D alone, the scan time was reduced. This method offers another option for MR angiography of the lower extremities. J. Magn. Reson. Imaging 2000;12:884-889.

Peripheral arterial disease: gadolinium-enhanced MR angiography versus color-guided duplex US--a meta-analysis

PURPOSE

To summarize and compare the published data on gadolinium-enhanced magnetic resonance (MR) angiography and color-guided duplex ultrasonography (US) for the work-up for peripheral arterial disease.

MATERIALS AND METHODS

Studies published between January 1984 and November 1998 were included if (a) gadolinium-enhanced MR angiography and/or color-guided duplex US were performed for evaluation of arterial stenoses and occlusions in the work-up for peripheral arterial disease of the lower extremities, (b) conventional angiography was the reference standard, and (c) absolute numbers of true-positive, false-negative, true-negative, and false-positive results were available or derivable.

RESULTS

With a random effects model, pooled sensitivity for MR angiography (97.5% [95% CI: 95.7%, 99.3%]) was higher than that for duplex US (87.6% [95% CI: 84.4%, 90.8%]). Pooled specificities were similar: 96.2% (95% CI: 94.4%, 97.9%) for MR angiography and 94.7% (95% CI: 93.2%, 96.2%) for duplex US. Summary receiver operating characteristic analysis demonstrated better discriminatory power for MR angiography than for duplex US. Regression coefficients for MR angiography versus US were 1.67 (95% CI: -0.23, 3.56) with adjustment for covariates, 2.11 (95% CI: 0.12, 4.09) without such adjustment, and 1.73 (95% CI: 0.44, 3.02) with a random effects model.

CONCLUSION

Gadolinium-enhanced MR angiography has better discriminatory power than does color-guided duplex US and is a highly sensitive and specific method, as compared with conventional angiography, for the work-up for peripheral arterial disease.

MR angiography in the evaluation of atherosclerotic peripheral vascular disease

Magnetic resonance (MR) angiography of lower extremity occlusive vascular disease has evolved into a feasible diagnostic imaging option. The previous emphasis on time-of-flight techniques was associated with lengthy acquisition times and artifactual signal losses. Those limitations presented an obstacle to widespread clinical implementation. However, the emergence of rapid imaging sequences combined with gadolinium chelate enhancement offers time-efficient alternatives that can yield a truer representation of the vascular anatomic structure. The technology is now poised to serve as a routine screening study, provided that radiologists understand all factors needed to generate clinically relevant MR angiograms. This article is intended to provide a useful resource directed toward achieving that understanding.

Ultrafast MR imaging of the pelvis

MR gradient systems with higher slew rates and gradient amplitude enable certain forms of imaging that are not practical with older gradient systems. These newer pulse sequences include single shot half-Fourier T2-weighted images and echo planar imaging. More important in MR imaging of the pelvis, these gradient systems benefit more conventional imaging methods such as gadolinium-enhanced 3D MR angiography, dynamic gradient echo contrast-enhanced images, and T2-weighted fast spin echo images, by shortening echo times. For most MR imaging of the pelvis, spatial resolution is paramount, and therefore sequences such as half-Fourier acquisition Turbo spin echo (HASTE) and 3D gadolinium-enhanced dynamic imaging play a less important role than in the upper abdomen. The potential of these techniques for diffusion or perfusion studies in the pelvis has not been explored.