3D Gadolinium-enhanced Magnetic Resonance Angiography Research Articles

Estudo da circulação hepatomesentérica pela angiografia por ressonância magnética com gadolínio: comparação entre doses simples e dupla no estudo de pacientes esquistossomóticos

OBJETIVO: Determinar a freqüência de visualização dos segmentos da circulação hepatomesentérica pela angiografia por ressonância magnética (angio-RM) com contraste e comparar o valor do método, utilizando-se duas diferentes dosagens de gadolínio (doses simples e dupla). MATERIAIS E MÉTODOS: Estudo prospectivo de 36 pacientes esquistossomóticos submetidos a angio-RM. Os exames foram realizados em equipamento de RM de 1,5 T, usando-se bobina de corpo e bomba injetora para a administração endovenosa do contraste. Foram utilizadas, de maneira randomizada, dose dupla do contraste paramagnético (0,2 mmol/kg de Gd-DTPA) em 21 pacientes e dose simples (0,1 mmol/kg) em outros 15 pacientes. Os exames foram interpretados por dois observadores em consenso, que classificaram o grau de visualização de 25 segmentos vasculares estabelecidos para análise, sem conhecimento da dose de gadolínio utilizada. RESULTADOS: Os segmentos vasculares proximais e de maior calibre foram as estruturas com melhor grau de visualização na maioria da amostra em estudo. O tronco celíaco, a artéria hepática comum, a artéria esplênica, a croça e terço médio da artéria mesentérica superior, a veia porta, a veia esplênica e a veia mesentérica superior apresentaram grau 2 de visualização em mais de 70% da amostra. Quanto à comparação das diferentes dosagens, não houve diferença significante (p < 0,05) no grau de visualização das diversas estruturas analisadas entre os grupos dose simples e dose dupla, com uma exceção isolada: na avaliação da artéria hepática direita (p = 0,008), o grupo dose simples apresentou maior freqüência de visualização grau 2, com valor significante. CONCLUSÃO: O grau de visualização dos segmentos vasculares hepatomesentéricos pela angio-RM com contraste é elevado, sendo maior nos segmentos proximais e de maior calibre. A comparação entre os grupos que utilizaram dose simples e dupla de contraste demonstrou resultados semelhantes.

Traumatic Pseudoaneurysm of the Descending Thoracic Aorta

A 39-year-old man presented with complaints of chest pain, dyspnea, and cough after a long-distance flight. He gave a history of having been involved in a major traffic accident 20 years ago in which he was run over by a truck, which resulted in extensive musculoskeletal injuries that necessitated several operations. He had been experiencing intermittent chest pain and dyspnea for 2 years. At the emergency department, a large upper-mediastinal mass was found on chest radiography (Figure, panel A). CT showed a large thoracic aortic aneurysm, and the patient was referred for cardiovascular MRI before surgery. This revealed a large …

Diagnostic Value of Gadolinium-Enhanced 3D Magnetic Resonance Angiography in Patients With Suspected Hepatic Arterial Complications After Liver Transplantation

To evaluate the accuracy and clinical role of gadolinium-enhanced 3D magnetic resonance angiography (MRA) in patients with suspected hepatic arterial complications after liver transplantation. Thirty-six consecutive MRA studies were performed in 33 liver transplant recipients after transplantation. MRA image quality was assessed subjectively. Thirty-two MRA studies were retrospectively reviewed and correlated with surgery (n = 2), conventional angiography (n = 18), or clinical follow-up (n = 12). MRA findings were also correlated with those of Doppler sonography in 30 of the cases. In 20 cases, concordance between MRA and surgery or conventional angiography was evaluated for each grade of hepatic artery stenosis (normal, mild [<50%], moderate [50-75%], severe [>75%], or occluded). MRA image quality was degraded 13 of 36 cases (36.1%) studies. The sensitivity, specificity, and accuracy of MRA by consensus reading for more than 50% of hepatic artery stenosis or occlusion were 67%, 90%, and 81.3%, respectively. Of the 19 cases in which Doppler sonography was abnormal, MRA correctly characterized hepatic artery stenosis in 16 (84.2%). MRA also correctly identified all 5 occurrences of celiac artery stenosis. However, MRA overestimated the severity of hepatic arterial stenosis in 3 (15%) of 20 cases and underestimated 5 (25%) of 20 cases. MRA complements Doppler ultrasound to exclude significant hepatic artery stenosis. However, a substantial number of MRA studies were technically inadequate, and MRA demonstrated limited efficacy for correctly grading the severity of hepatic artery stenosis.

Magnetic Resonance Imaging Predictors of Coarctation Severity

MRI is increasingly used for anatomic assessment of aortic coarctation (CoA), but its ability to predict the transcatheter pressure gradient, considered the reference standard for hemodynamic severity, has not been studied in detail. This study evaluated the ability of MRI to distinguish between mild versus moderate and severe CoA as determined by cardiac catheterization. The clinical, MRI, and catheterization data of 31 subjects referred for assessment of native or recurrent CoA were reviewed retrospectively. Patients were divided into 2 groups on the basis of peak coarctation gradient by catheterization: <20 mm Hg (n=12) and > or =20 mm Hg (n=19). Patients with cardiac index <2.2 L x min(-1) x m(-2) by catheterization were excluded. By logistic regression analysis, the following variables simultaneously predicted coarctation gradient > or =20 mm Hg: (1) smallest aortic cross-sectional area (adjusted for body surface area) measured by planimetry from gadolinium-enhanced 3D magnetic resonance angiography (OR 1.71 for 10 mm2/m2 decrease, P=0.005) and (2) heart rate-corrected mean flow deceleration in the descending aorta measured by phase-velocity cine MRI (OR 1.68 for 100 mL/s(1.5) increase, P=0.018). For the combination of these variables, a predicted probability >0.38 had 95% sensitivity, 82% specificity, 90% positive and negative predictive values, and an area under the receiver-operator characteristics curve of 0.938. In a subsequent validation study, the prediction model correctly classified 9 of 10 patients, with no false-negatives. The combination of anatomic and flow data obtained by MRI provides a sensitive and specific test for predicting catheterization gradient > or =20 mm Hg.

Major vascular anomalies in Turner syndrome: prevalence and magnetic resonance angiographic features.

Turner syndrome (TS) is associated with aortic coarctation and dissection; hence, echocardiographic evaluation of all patients is currently recommended. X-ray angiography in clinically symptomatic patients has suggested a range of other vascular anomalies, but the true prevalence of such lesions in TS is unknown. To better understand the prevalence and pathogenesis of cardiovascular defects in TS, we prospectively evaluated a group of asymptomatic adult volunteers with TS using magnetic resonance (MR) angiography. A total of 85 adults with TS and 27 normal female adult volunteers underwent gadolinium-enhanced 3D MR angiography. A high prevalence of aortic anomalies was seen in women with TS, including elongation of the transverse arch (49%), aortic coarctation (12%), and aberrant right subclavian artery (8%). Venous anomalies were also prominent, including persistent left superior vena cava (13%) and partial anomalous pulmonary venous return (13%). None of these anomalies were found in healthy female controls. The constellation of elongation of the transverse arch, aortic coarctation, and persistent left superior vena cava was significantly associated with women with TS. Neck webbing and increased thoracic anterior-to-posterior dimension diameters were strong predictors for arterial and venous anomalies. Thoracic vascular anomalies are common in TS, occurring in approximately 50% of a group not preselected for cardiovascular disease. The highly significant association between neck webbing, increased chest diameter, and these vascular anomalies suggests that in utero, centrally localized lymphatic obstruction may contribute to these cardiovascular deformities in TS. Improved recognition of these often-undetected vascular lesions may be important for identification of patients in need of closer cardiovascular monitoring.

High-resolution gadolinium-enhanced 3D MRA of the infrapopliteal arteries: Lessons for improving bolus-chase peripheral MRA

Peripheral magnetic resonance angiography (MRA) is growing in use. However, methods of performing peripheral MRA vary widely and continue to be optimized, especially for improvement in illustration of infrapopliteal arteries. The main purpose of this project was to identify imaging factors that can improve arterial visualization in the lower leg using bolus chase peripheral MRA. Eighteen healthy adults were imaged on a 1.5T MR scanner. The calf was imaged using conventional three-station bolus chase three-dimensional (3D) MRA, two dimensional (2D) time-of-flight (TOF) MRA and single-station Gadolinium (Gd)-enhanced 3D MRA. Observer comparisons of vessel visualization, signal to noise ratios (SNR), contrast to noise ratios (CNR) and spatial resolution comparisons were performed. Arterial SNR and CNR were similar for all three techniques. However, arterial visualization was dramatically improved on dedicated, arterial-phase Gd-enhanced 3D MRA compared with the multi-station bolus chase MRA and 2D TOF MRA. This improvement was related to optimization of Gd-enhanced 3D MRA parameters (fast injection rate of 2 mL/sec, high spatial resolution imaging, the use of dedicated phased array coils, elliptical centric k-space sampling and accurate arterial phase timing for image acquisition). The visualization of the infrapopliteal arteries can be substantially improved in bolus chase peripheral MRA if voxel size, contrast delivery, and central k-space data acquisition for arterial enhancement are optimized. Improvements in peripheral MRA should be directed at these parameters.

Gadolinium-Enhanced 3D MR Angiography of Renal Artery Stenosis: A Pilot Comparison of Maximum Intensity Projection, Multiplanar Reformatting, and 3D Volume-Rendering Postprocessing Algorithms

Rationale and Objectives The authors compared diagnostic accuracy of maximum intensity projection (MIP), multiplanar reformatting (MPR), and three-dimensional (3D) volume rendering (VR) in the evaluation of gadolinium-enhanced 3D magnetic resonance (MR) angiography of the renal arteries. They hypothesized that VR is as accurate as or more accurate than MIP and MPR at depicting renal artery stenosis. Materials and Methods The study group comprised 28 consecutive patients who underwent gadolinium-enhanced 3D MR angiography of the renal arteries. Studies were postprocessed to display images in MIP, MPR, and VR formats. Digital subtraction angiography (DSA), when performed (nine of 28 patients), was the standard for comparison. For each main renal artery, an estimate of percentage stenosis was made for any stenoses detected by three independent radiologists. For calculation of sensitivity, specificity, and accuracy, MR angiographic stenosis estimates were categorized as mild (0%–39%), moderate (40%–69%), or severe (≥70%). DSA stenosis estimates of 70% or greater were considered hemodynamically significant. Results Analysis of variance demonstrated MIP estimates of stenosis were statistically greater than VR estimates in two readers and greater than MPR estimates in all readers for all patients. MIP images also showed the largest mean difference from DSA stenosis estimates for all three readers. For both VR and MPR, mean differences between MR angiographic stenoses estimates and DSA estimates reached significance for only one reader, whereas, for MIP versus DSA, mean differences reached significance for all three readers. Although not statistically significant compared with DSA, accuracies of VR (87%) and MPR (89%) were greater than that of MIP (81%). Conclusion In this pilot study, MIP was the least accurate of the three image display algorithms tested. VR and MPR yielded similar values for each method of comparison.

Multiphase magnetic resonance angiography of the abdominal and pelvic arteries: results of a bicenter multireader analysis.

The objective is to assess the diagnostic accuracy and interobserver variability of multiphase 3D gadolinium-enhanced magnetic resonance angiography (3D-Gd-MRA) for assessment of abdominal and pelvic vascular disease. In 41 patients from two different institutions multiphase 3D-Gd-MRA of the aorta and pelvis was performed using an identical scanning protocol. In a single breath-hold three to four consecutive phases were acquired. Stenoses in the renal arteries, and aorta and pelvic arteries were independently evaluated by three readers and compared with digital subtraction angiography. Interobserver variability was compared by means of a kappa statistic. Accuracy for stenosis grading consistently ranged between 80% and 90% for all three readers in all vessel segments studied. Good interobserver agreement was found with kappa values exceeding 0.75. Vessel segments with delayed fill-in could be reliably detected on the multiple successive MRA phases. Overall, MRA was rated slightly superior to Digital Subtraction Angiography in terms of interobserver variability, diagnostic confidence and image quality. Multiphase MRA is a highly robust technique with reproducible accuracy for different observers and different institutions. It can therefore be recommended for screening of atherosclerotic abdominal and pelvic disease.

Three-dimensional gadolinium-enhanced MR angiography: applications for abdominal imaging.

Three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography is a versatile technique that combines speed, superb contrast, and relative simplicity. It has a wide range of applications, particularly in the abdomen and pelvis, where superb images of the abdominal aorta and renal arteries are routinely obtained. Aneurysms, atherosclerotic lesions, and occlusions of the major mesenteric arteries are also well depicted. In addition, 3D gadolinium-enhanced MR angiography is ideal for noninvasive evaluation of the systemic and mesenteric veins and can be used to demonstrate parenchymal lesions in the liver, pancreas, kidneys, and other organs. It is also useful in staging genitourinary neoplasms: Parenchymal lesions, venous extension, and adenopathy are all clearly depicted. Three-dimensional gadolinium-enhanced MR angiography can be useful in the preoperative evaluation of potential transplant donors and recipients and in the evaluation of vascular complications following transplantation. Delayed 3D acquisitions of the kidneys, ureters, and bladder can be performed routinely to generate gadolinium-enhanced urograms and demonstrate obstruction, delayed function, filling defects, and masses. A variety of methods for increasing the speed and improving the resolution of 3D acquisition are currently under investigation. These include novel imaging and reformatting techniques and the use of intravascular contrast agents with much longer vascular half-lives.

Peripheral arterial disease: meta-analysis of the diagnostic performance of MR angiography.

To summarize the overall diagnostic performance of magnetic resonance (MR) angiography in the evaluation of peripheral arteriosclerotic occlusive disease and to identify the most important sources of variation in diagnostic accuracy between studies. A search strategy in MEDLINE and citation tracking were used to identify relevant English-language articles published since 1991. Each article was critically appraised for examination, patient, and study design characteristics. The accuracy data from different studies were analyzed by constructing summary receiver operating characteristic curves; multiple linear regression was used to examine the variation between study results. Twenty-three studies were included. There was much heterogeneity in the study results, which could not be explained as differences in the threshold for a positive result. About half of the variation was due to the type of MR angiographic examination and the extent of image evaluation. The relative diagnostic odds ratio (DOR) for three-dimensional (3D) gadolinium-enhanced MR angiography compared with two-dimensional (2D) time-of-flight MR angiography was 7.46 (95% CI: 2.48, 22.20). The relative DOR for review of transverse source images or multiplanar reformations in addition to maximum intensity projections (MIPs) compared with the use of only MIPs for image evaluation was 4.53 (95% CI: 1.46, 13.87). The diagnostic accuracy of 3D gadolinium-enhanced MR angiography is superior to that of 2D time-of-flight MR angiography. Also, the review of transverse source images or use of additional postprocessing techniques, such as multiplanar reformation, results in significantly better diagnostic performance.

MR angiography after renal revascularization: spectrum of expected anatomic results and postintervention complications.

The use of magnetic resonance (MR) angiography in screening for renal artery stenosis has been extensively evaluated. However, the MR angiographic findings after renal artery revascularization are not as well characterized. The renal artery and parenchyma can be evaluated after revascularization with a comprehensive MR imaging protocol that includes T1- and T2-weighted spin-echo sequences, three-dimensional (3D) gadolinium-enhanced MR angiography, and 3D phase-contrast MR angiography. Because surgical techniques for revascularization vary, knowledge of the surgical procedure is necessary to ensure inclusion of the pertinent anatomy at 3D gadolinium-enhanced MR angiography and to define appropriate 3D phase-contrast MR angiography volumes. The 3D gadolinium-enhanced MR angiography volume can be manipulated to view relevant vascular anatomy at the optimal obliquity and section thickness. This protocol allows robust, noninvasive evaluation of the expected arterial anatomy after revascularization, including renal artery endarterectomy, aortorenal bypass grafts, and extraanatomic reconstructions. In cases of suspected postrevascularization complications, gadolinium-enhanced MR angiography is useful because of its lack of nephrotoxicity and radiation exposure. Immediate complications of renal revascularization include renal artery thrombosis, renal infarction, and perinephric hemorrhage. Long-term complications include aneurysms of bypass grafts and recurrent stenosis of the renal artery.

Gadolinium-enhanced 3D magnetic resonance angiography of the thoracic vessels.

MAGNETIC RESONANCE IMAGING has long been recognized as a useful tool for the non-invasive evaluation of the thoracic vasculature. Unlike computed tomography and conventional angiography, MRI is not associated with the concerns related to ionizing radiation exposure or to contrast-related nephrotoxicity. MRI is also capable of oblique image acquisition and multiplanar reformation, which aids the illustration of the thoracic vessels, inherently intertwined and complex in their arrangements. In addition, MRI using cine technique affords cardiac referenced data that enables dynamic assessment of blood flow, yielding information comparable to an echocardiogram. Gadolinium (Gd)-enhanced three-dimensional (3D) magnetic resonance angiography (MRA) is a newer technique that provides high-resolution (ie, 3D) data very quickly and is well suited for the depiction of intrathoracic vessels. Improvements in gradient technology now allow a Gd-enhanced 3D MRA to be performed during a 20–40 second breath-hold. Because it relies on T1-shortening effects of circulating Gd-chelate contrast media and not inherent flow characteristics, Gdenhanced 3D MRA can often depict pathologic vascular segments that are not adequately visualized using unenhanced flow-based MRI techniques. In addition, Gdenhanced 3D MRA provides volumetric data that can be processed for multiplanar reformation (MPR) and maximum intensity projection (MIP) viewing. In this article, the technical considerations and potential applications for Gd-enhanced 3D MRA of the systemic and pulmonary vessels within the chest will be discussed and illustrated. Traditionally, T1-weighted spin-echo and gradientecho pulse sequences have been employed for delineation of vascular pathology within the chest (1–10). The combination of T1-weighted spin-echo and gradientecho images can often provide the information necessary for the assessment of simple clinical queries such as patency of a vessel (Fig. 1) or delineation of a vascular ring (Fig. 2). These techniques, however, rely on flowing blood (ie, the movement of blood during the acquisition period) for their illustration of vascular structures. This flow dependency makes these techniques prone to flowrelated image artifacts, thereby frequently limiting their clinical utility. On spin-echo pulse sequences, vessels are characterized by their dark lumina. The black appearance of blood, also known as flow void, on spin-echo imaging occurs secondary to the wash-out of blood prior to the refocusing pulse and sampling of the echo. The washout may be incomplete if the echo time is too short, the vessel courses primarily within the imaging plane, or the blood flow is too slow. Incomplete wash-out results in the persistence of signal within the vessel lumen, which may result in the masking of underlying luminal pathology such as an intimal tear or the erroneous simulation of a vascular occlusion or thrombosis. A superior black blood effect is achieved by using preparatory pulses such as a double inversion pulse to null blood signal for more effective suppression even when the blood flow is slow. Unlike spin-echo imaging, time-of-flight (TOF) and phase contrast (PC)-MRA depict flowing blood with bright signal intensity. TOF imaging relies on the wash-in or in-flow effect of unsaturated protons; PC imaging relies, on the phase shift experienced by moving protons traveling along the gradient field (7–13). Both TOF and PC imaging provide higher intra-vascular signal-tonoise ratios than spin-echo pulse sequences. These ‘‘bright blood’’ pulse sequences (ie, TOF and PC imaging) often show intraluminal abnormalities (Fig. 1b) not clearly identified on black blood spin-echo images. However, should blood flow be slow, turbulent, or complex, vascular signal on gradient-echo images becomes unreliable. Disturbances in blood flow can often result in signal loss, which can result in the underestimation of vessel patency, overestimation of a stenosis, or even simulation of a vascular occlusion. 1Department of Radiology, University of Michigan Medical Center, Ann Arbor, Michigan 48109-0030. 2MR Research Division, Department of Radiology, Uniformed Services University, Bethesda, Maryland 20814. 3Cornell University, New York, NY 10021 Contract Grant Sponsor: Whitaker Foundation, GE. *Address reprint requests to: M.R.P., Cornell University, MRI Division, 416 East 55th Street, New York, NY 10021. Received June 29, 1999; Accepted July 13, 1999. JOURNAL OF MAGNETIC RESONANCE IMAGING 10:758–770 (1999)

Intrahepatic arterioportal fistula: gadolinium-enhanced 3D magnetic resonance angiography findings and angiographic embolization with steel coils

We describe a case of a 59-year-old patient with intrahepatic arterioportal fistula secondary to blunt trauma sustained by a motor vehicle accident 36 years earlier. The fistula was demonstrated 36 years after the accident in a clinical work-up for diarrhea of 1 month’s duration, using contrast enhanced three-dimensional breath-hold MRA. A communication between the dilated portal vein and dilated hepatic artery was shown at the level of distal branches. After subsequent demonstration by conventional angiography, the fistula was embolized using steel coils. Following the therapeutic intervention, the patient’s diarrhea ceased.

Fast magnetic resonance imaging of liver

Recent magnetic resonance (MR) units with a stronger gradient system have allowed various fast MR imaging techniques to develop. These fast scan techniques have easily realized breath-holding acquisition in the liver and the image quality has been greatly improved without sacrificing spatial resolution. The majority of the fast imaging techniques have been devoted to T2-weighted imaging to obtain useful T2-weighted images in the shortest possible time. Among the fast sequences, fast spin-echo (FSE) sequence is the most promising technique and allows high-quality T2-weighted images with reduced motion artifacts. However, FSE sequences using multiple refocused pulses may essentially realize only poor soft-tissue contrast due to magnetization transfer and T2-filtering effects, and therefore, echo-planar (EP) imaging is expected to provide high image contrast. In addition, single-shot EP imaging allows even diffusion-weighted (DW) and perfusion-weighted (PW) imaging in the liver due to its short scanning time. Recent development of fast gadolinium-enhanced 3D MR angiography has also impacted liver imaging. Combined with such gadolinium-enhanced 3D-MRA sequences and zerofilling image interpolation technique, biphasic gadolinium-enhanced 3D-MRA (whole-liver dynamic MR imaging in the arterial phase and MR portography in the portal phase) can be obtained.

Hepatic lesions: morphologic and functional characterization with multiphase breath-hold 3D gadolinium-enhanced MR angiography--initial results.

To investigate multiphase (arterial, portal venous, and late venous phases) breath-hold three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography for the detection and functional characterization of hepatic lesions. Breath-hold fast spoiled gradient-echo 3D gadolinium-enhanced MR angiography was performed in 18 patients with 35 hepatic lesions. Measurements of signal intensity were obtained for 27 seconds in each phase, with 23-second delays between the three phases. Lesion-liver visibilities at each phase on the MR angiographic, precontrast T1-weighted, T2-weighted, and postcontrast T1-weighted images were compared. The MR angiographic functional lesion characterization was based on the combined assessment of spatial variations and the evolution of contrast material enhancement in all three phases. All 35 lesions were correctly characterized on the MR angiographic images, which is significantly (P < .01) better than the precontrast T1-weighted (n = 14 [40%]), T2-weighted (n = 23 [66%]), and postcontrast T1-weighted (n = 25 [71%]) imaging results. Analysis of the spatial variations and the evolution of contrast material enhancement significantly (P < .01) improved lesion characterization in 66% (23 of 35) of all lesions. Multiphase breath-hold 3D gadolinium-enhanced MR angiography is feasible and robust and significantly improves the morphologic detection of benign or malignant lesions during the early arterial phase. It further improves the functional characterization of hepatic lesions, combining an arterial, portal-venous, and late MR angiographic phase of contrast enhancement.

Optimization of contrast dosage for gadolinium-enhanced 3D MRA of the pulmonary and renal arteries

To determine the minimal contrast dosage required for diagnostic contrast-enhanced three-dimensional (3D) magnetic resonance angiography (MRA) image quality of the pulmonary (PAs) or renal arteries (RAs). In 12 volunteers (10 females, 2 males; mean age 24 years) imaging was performed with 4 different dosages: 0.05, 0.1, 0.2 and 0.3 mmol/kg of body weight (BW) 0.5 M gadolinium (Gd) contrast agent. The PAs and RAs were evaluated separately each in groups of six volunteers. Qualitative and quantitative signal-to-noise ratio (SNR) image analysis was performed. For the PAs, the increases in signal-to-noise ratio were paralleled by increases in image quality ratings. For the PAs, with the use of 0.05 mmol/kg, only 50.3% of all segments were rated diagnostic, whereas with higher dosages the percentage rose to 89.2% for 0.1 mmol/kg, 98.2% for 0.2 mmol/kg. and 99.1% for 0.3 mmol/kg. For the RAs, 0.3 mmol/kg provided no significant increase in singal-to-noise ratio compared to 0.2 mmol/kg ( p = 0.4). Only by a dosage of 0.2 and 0.3 mmol/kg, all evaluated segments were diagnostic evaluable. A dose of 0.2 mmol/kg is required for proper assessment of the RAs or PAs.

Thoracic MR aortography: imaging techniques and strategies.

Three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography is a promising technique for thoracic aortography that complements electrocardiographically gated T1-weighted spin-echo imaging and cine MR imaging. Axial and left anterior oblique T1-weighted spin-echo images are well suited to measurement of aortic dimensions and evaluation of aortic aneurysms. Sagittal and coronal spin-echo images are helpful in evaluation of vascular rings and aortic dissection. Cine gradient-echo and cine phase-contrast imaging allow dynamic evaluation of aortic and valvular flow. Cine phase-contrast imaging also enables noninvasive quantification of blood flow. Capable of being performed during a single breath hold, 3D gadolinium-enhanced MR angiography provides high-resolution 3D data that can be readily used for projection angiography and multiplanar reformation. This technique enables further demonstration of subtle pathologic conditions. Three-dimensional gadolinium-enhanced MR angiography allows more comprehensive and efficient evaluation of the thoracic aorta.

Iliac artery MR angiography: comparison of three-dimensional gadolinium-enhanced and two-dimensional time-of-flight techniques.

To determine if a three-dimensional (3D) gadolinium-enhanced technique is useful for improving the accuracy of magnetic resonance (MR) angiography. Prospectively, two-dimensional (2D) time-of-flight (TOF) and 3D gadolinium-enhanced MR angiography was performed in 23 patients. Conventional arteriography, the reference standard, was performed in all but five patients. Images from each examination were interpreted blindly by two observers. For common and external iliac arteries, interpretations of dynamic 3D gadolinium-enhanced MR angiograms matched those of conventional arteriograms in 12 of 18 patients (67%) for both observers. Interpretations of 2D TOF images matched those of conventional arteriograms in six (33%) and seven (39%) patients for the two observers respectively. Preliminary results suggest that iliac artery MR angiography can be improved by complementing standard 2D TOF acquisitions with 3D gadolinium-enhanced acquisitions.