Time-resolved contrast-enhanced MR angiography of renal artery stenosis: diagnostic accuracy and interobserver variability

Optimal Blood Suppression Inversion Time Based on Breathing Rates and Heart Rates to Improve Renal Artery Visibility in Spatial Labeling with Multiple Inversion Pulses: A Preliminary Study

OBJECTIVE

To determine whether an optimal blood suppression inversion time (BSP TI) can boost arterial visibility and whether the optimal BSP TI is related to breathing rate (BR) and heart rate (HR) for hypertension subjects in spatial labeling with multiple inversion pulses (SLEEK).

MATERIALS AND METHODS

This prospective study included 10 volunteers and 93 consecutive hypertension patients who had undergone SLEEK at 1.5T MRI system. Firstly, suitable BSP TIs for displaying clearly renal artery were determined in 10 volunteers. Secondly, non-contrast enhanced magnetic resonance angiography with the suitable BSP TIs were performed on those hypertension patients. Then, renal artery was evaluated and an optimal BSP TI to increase arterial visibility was determined for each patient. Patients' BRs and HRs were recorded and their relationships with the optimal BSP TI were analyzed.

RESULTS

The optimal BSP TI was negatively correlated with BR (r1 = -0.536, P1 < 0.001; and r2 = -0.535, P2 < 0.001) and HR (r1 = -0.432, P1 = 0.001; and r2 = -0.419, P2 = 0.001) for 2 readers (κ = 0.93). For improving renal arterial visibility, BSP TI = 800 ms could be applied as the optimal BSP TI when the 95% confidence interval were 17-19/min (BR1) and 74-82 bpm (HR1) for reader#1 and 17-19/min (BR2) and 74-83 bpm (HR2) for reader#2; BSP TI = 1100 ms while 14-15/min (BR1, 2) and 71-76 bpm (HR1, 2) for both readers; and BSP TI = 1400 ms when 13-16/min (BR1) and 63-68 bpm (HR1) for reader#1 and 14-15/min (BR2) and 64-70 bpm (HR2) for reader#2.

CONCLUSION

In SLEEK, BSP TI is affected by patients' BRs and HRs. Adopting the optimal BSP TI based on BR and HR can improve the renal arterial visibility and consequently the working efficiency.

Low-dose, time-resolved, contrast-enhanced 3D MR angiography in the assessment of the abdominal aorta and its major branches at 3 Tesla

RATIONALE AND OBJECTIVES

The aims of this study were to evaluate the effectiveness of low-dose, contrast-enhanced (CE), time-resolved, three-dimensional magnetic resonance angiography (MRA) in the assessment of the abdominal aorta and its major branches at 3 T and to compare the results with those of high-spatial resolution CE MRA.

MATERIALS AND METHODS

Twenty-two consecutive patients (eight men, 14 women; mean age, 43.9 +/- 17.9 years) underwent CE time-resolved three-dimensional MRA and high-spatial resolution three-dimensional MRA. Studies were performed using a 3-T magnetic resonance system; gadolinium-based contrast medium was administered at a dose of 3 to 5 mL for time-resolved MRA, followed by 0.1 mmol/kg gadopentetate dimeglumine for single-phase CE MRA. For analysis purposes, the abdominal arterial system was divided into 11 arterial segments, and image quality as well as the presence and degree of vascular pathology were evaluated by two independent magnetic resonance radiologists.

RESULTS

A total of 242 arterial segments were visualized with good image quality. Time-resolved MRA was able to visualize the majority of arterial segments with good definition in the diagnostic range. Vascular pathologies (stenosis, occlusion) or abnormal vascular anatomy was detected in 19 arterial segments, with good interobserver agreement (kappa = 0.78). All image findings were detected with time-resolved CE MRA by both observers and were confirmed by correlative imaging.

CONCLUSION

Low-dose, time-resolved MRA at 3 T yields rapid and important anatomic and functional information in the evaluation of the abdominal vasculature. Because of its limited spatial resolution, time-resolved MRA is inferior to CE MRA in demonstrating fine vascular details.

Ultra-low-dose, time-resolved contrast-enhanced magnetic resonance angiography of the carotid arteries at 3.0 tesla

PURPOSE

To determine whether time-resolved magnetic resonance angiography (TR-MRA) with ultra-low-dose gadolinium chelate (1.5-3.0 mL) can reliably detect or rule out hemodynamically significant disease in the carotid-vertebral artery territory.

MATERIALS AND METHODS

Hundred consecutive patients (62 women, 38 men, mean age = 56.6 years) underwent both TR-MRA and standard high-resolution contrast-enhanced magnetic resonance angiography (CE-MRA), having been randomized to 1 of 2 groups; group A receiving a contrast dose of 1.5 mL for TR-MRA and group B receiving 3.0 mL. For scoring purposes the arterial system was divided into 21 segments. All TR-MRA and CE-MRA studies were blindly assessed by 2 radiologists for overall image quality, segmental arterial visualization, grading of arterial stenosis/occlusion, and incidence and severity of artifact. TR-MRA findings were directly compared with those of the corresponding CE-MRA examinations.

RESULTS

Group A TR-MRA studies were of significantly inferior overall image quality compared with those of the corresponding CE-MRA examinations (P = 0.01 for both observers). In group B, overall image quality was similar for TR-MRA and single-phase CE-MRA examinations. On a segmental basis, a higher number of "insufficient quality" segments were identified in group A TR-MRA studies than in group B. A similar reduction in the incidence of artifacts was observed for group B relative to group A TR-MRA studies. Both groups A and B TR-MRA studies were of high specificity, negative predictive values, and accuracy (>97%).

CONCLUSION

Ultra-low dose TR-MRA may be performed with 3 mL of gadolinium chelate with preservation of overall image quality and arterial segmental visualization relative to single phase CE-MRA, whereas a 1.5 mL contrast dose is associated with more suboptimal studies. Nonetheless, even at doses as low as 1.5 mL, TR-MRA can exclude arterial stenosis or occlusion.

Renal artery stenosis evaluation: diagnostic performance of gadobenate dimeglumine-enhanced MR angiography--comparison with DSA

PURPOSE

To prospectively determine diagnostic performance and safety of contrast material-enhanced (CE) magnetic resonance (MR) angiography with 0.1 mmol per kilogram of body weight gadobenate dimeglumine for depiction of significant steno-occlusive disease (> or =51% stenosis) of renal arteries, with digital subtraction angiography (DSA) as reference standard.

MATERIALS AND METHODS

This multicenter study was approved by local institutional review boards; all patients provided written informed consent. Patient enrollment and examination at centers in the United States complied with HIPAA. Two hundred ninety-three patients (154 men, 139 women; mean age, 61.0 years) with severe hypertension (82.2%), progressive renal failure (11.3%), and suspected renal artery stenosis (6.5%) underwent CE MR angiography with three-dimensional spoiled gradient-echo sequences after administration of 0.1 mmol/kg gadobenate dimeglumine at 2 mL/sec. Anteroposterior and oblique DSA was performed in 268 (91.5%) patients. Three independent blinded reviewers evaluated CE MR angiographic images. Sensitivity, specificity, and accuracy of CE MR angiography for detection of significant steno-occlusive disease (> or =51% vessel lumen narrowing) were determined at segment (main renal artery) and patient levels. Positive and negative predictive values and positive and negative likelihood ratios were determined. Interobserver agreement was analyzed with generalized kappa statistics. A safety evaluation (clinical examination, electrocardiogram, blood and urine analysis, monitoring for adverse events) was performed.

RESULTS

Of 268 patients, 178 who were evaluated with MR angiography and DSA had significant steno-occlusive disease of renal arteries at DSA. Sensitivity, specificity, and accuracy of CE MR angiography for detection of 51% or greater stenosis or occlusion were 60.1%-84.1%, 89.4%-94.7%, and 80.4%-86.9%, respectively, at segment level. Similar values were obtained for predictive values and for patient-level analyses. Few CE MR angiographic examinations (1.9%-2.8%) were technically inadequate. Interobserver agreement for detection of significant steno-occlusive disease was good (79.9% agreement; kappa = 0.69). No safety concerns were noted.

CONCLUSION

CE MR angiography performed with 0.1 mmol/kg gadobenate dimeglumine, compared with DSA, is safe and provides good sensitivity, specificity, and accuracy for detection of significant renal artery steno-occlusive disease.

Fibromuscular dysplasia in an accessory renal artery causing renovascular hypertension: a case report

Background

Renovascular hypertension is defined as hypertension caused by renal artery stenosis. The two main etiologies are atherosclerosis and fibromuscular dysplasia. Fibromuscular dysplasia in an accessory renal artery as a cause of renovascular hypertension is uncommon.

Case presentation

In this report, we present a relatively uncommon case of renovascular hypertension in a 35-year-old female with a history of intractable hypertension as a result of fibromuscular dysplasia involving an accessory renal artery. Selective renal angiography was performed and revealed a single renal artery on the right and two renal arteries supplying the left kidney, upper and lower poles. Selective renal angiography showed the typical fibromuscular dysplasia lesion characterized by its classic "string of beads" appearance, consisting of alternating areas of narrowing and dilatation, located in the middle portion of the lower left renal artery (accessory artery) associated with moderate stenosis. Percutaneous balloon dilatation of the stenotic lesion was successfully performed. Following angioplasty, her blood pressure normalized over a period of several months using a single antihypertensive medication (rather than 3 medications).

Conclusion

Fibromuscular dysplasia in an accessory renal artery can, even though rarely, be responsible for renovascular hypertension. Selective renal angiography is the 'gold standard' test and should be performed when renovascular intervention is contemplated.

Efficacy and safety of gadodiamide (Gd-DTPA-BMA) in renal 3D-magnetic resonance angiography (MRA): a phase II study

PURPOSE

To determine the most efficacious dose of gadodiamide for three-dimensional (3D) contrast-enhanced (CE) magnetic resonance angiography (MRA) of the renal arteries on a patient level based on the sensitivity in detecting the main hemodynamically relevant (> or =50% or occlusion) renal artery stenosis (RAS) using intra-arterial digital subtraction angiography (IA DSA) as the gold standard.

MATERIALS AND METHODS

This prospective, randomized, double-blind, parallel-group, multicenter study included 273 patients referred to IA DSA for suspected RAS. Patients underwent 3D CE MRA after injection of 0.01, 0.05, 0.1, or 0.2mmol/kg of body weight gadodiamide (0.5mmol/ml). The images were assessed for location and degree of RAS by independent blinded readers (MRA: three readers, IA DSA: one reader). Hypothesis testing for a significant trend in sensitivity across dose groups was based on the one-sided Cochran-Armitage style trend test for each independent MRA reader.

RESULTS

The lowest dose group (0.01mmol/kg) proved non-efficacious in detecting hemodynamically relevant (i.e., > or =50% or occlusion) RAS. A statistically significant dose trend (p<0.001) was shown for each of the three independent readers. Depending on reader, the sensitivity obtained with 0.05, 0.1, and 0.2mmol/kg was 63.9-86.1%, 75.8-91.4% and 80.6-90.6%, the specificity was 66.7-73.9%, 59.3-75.0%, and 59.3-75.0% and accuracy was 67.8-78.9%, 75.4-77.4%, and 76.3-81.0%, for the three dose groups, respectively. There were eight non-severe adverse events (AEs). Three serious AEs occurring in one patient were judged not related to gadodiamide by the on-site investigator.

CONCLUSION

A significant dose trend between the four doses examined was observed. The lowest dose (0.01mmol/kg) differed significantly from those of the other three doses. Based on the analysis of the primary and secondary endpoints, 0.1mmol/kg gadodiamide appears to be the most suitable dose in diagnosing hemodynamically relevant RAS. The present study also demonstrated gadodiamide to be safe and well tolerated.

3D contrast-enhanced MR angiography

Safe, fast, accurate contrast arteriography can be obtained utilizing gadolinium (Gd) and 3D MR data acquisition for diagnosing vascular diseases. Optimizing contrast enhanced MRA (CE MRA), however, requires understanding the complex interplay between Gd injection timing, the Fourier mapping of 3D MR data acquisition and a multitude of parameters determining resolution, anatomic coverage, and sensitivity to motion artifacts. It is critical to time the bolus peak to coincide with central k-space data acquisition, which dominates image contrast. Oversampling the center of k-space allows reconstruction of multiple 3D acquisitions in rapid succession to time-resolve the passage of the contrast bolus. Parallel imaging increases resolution, shortens scan time and compresses the center of k-space into a shorter period of time, thereby minimizing motion and timing artifacts. Absence of ionizing radiation allows MRA to be repeated and combined with additional sequences to more fully characterize anatomy, flow, and physiology. Utilizing stepping table technology and thigh compression, whole body MRA is possible with a single contrast injection. As MR technology continues to advance, CE MRA becomes better and simpler to perform, increasing its efficacy in the diagnosis and management of vascular diseases.

Renovascular disease imaging: Today more than ever the invasive cardiologist may make the difference

Doppler ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI) are gaining wide acceptance as gold standard for diagnosing peripheral artery disease at thoracic and abdominal aorta level and infrainguinal arteries. A different case is that of renal artery stenosis (RAS): noninvasive techniques, CT and MRI in particular, failed to become the new gold standard. Image interpretation and artifacts seems to invalidate MRI and CT sensitivity and specificity that remain quite low. The debacle of noninvasive imaging of renal arteries may have important reflexes on the invasive cardiology practice. In the light of the results of noninvasive tests for renal artery stenosis, the angiography of renal vessels performed at the time of coronary artery angiography may became a new tool for invasive professional to optimize the diagnosis of renal artery stenosis at least in patients scheduled for coronary angiography. The invasive cardiologist, today more than ever, has the chance to really impact the diagnosis and therapy of patients with renovascular disease and the prognosis of patients with both coronary artery and renal artery disease.

Estimation of the Ratio of Renal Artery Stenosis with Magnetic Resonance Angiography Using Parallel Imaging Technique in Suspected Renovascular Hypertension

BACKGROUND

Renovascular hypertension, which may lead to end-stage renal failure, necessitates prompt diagnosis and medication. Although various diagnostic tools exist for evaluation of renal arteries, magnetic resonance angiography (MRA), with the improvement of hardware and software systems, has become a very promising technique in screening patients with suspected renal hypertension. In this study, we aimed to assess renal artery stenosis on MRA in patients with suspected renovascular disease using a parallel imaging technique which allows faster scanning with higher resolution.

METHODS

Eighty-four patients with hypertension underwent MRA and digital angiography.

RESULTS

MRA detected renal artery stenosis with a sensitivity rate ranging from 69.3 to 100% and specificity rate ranging from 85.7 to 96%.

CONCLUSION

Contrast-enhanced MRA of renal arteries is very effective in the demonstration of renal artery stenoses and assessment of stenosis ratio. Furthermore, parallel imaging technology has improved this procedure by reducing the scan time. Renal MRA, as a diagnostic tool, can accurately direct patients with renovascular disease to intravascular treatment.

Comparison of intraarterial MR angiography at 3.0 T with X-ray digital subtraction angiography for detection of renal artery stenosis in swine

PURPOSE

To compare the accuracy of catheter-directed intraarterial (IA) magnetic resonance (MR) angiography at 3.0 T with that of x-ray digital subtraction angiography (DSA) for the measurement of renal artery stenosis (RAS) in swine.

MATERIALS AND METHODS

Unilateral hemodynamically significant RAS (>50%) was induced surgically in six pigs with use of reverse cable ties. One to two weeks after surgery, each pig underwent x-ray DSA and MR angiography before and after percutaneous transluminal balloon angioplasty (PTA). X-ray DSA was performed before and after PTA of RAS by injection of iodinated contrast agent through a 5-F multiple-side hole angiographic catheter placed in the abdominal aorta under fluoroscopic guidance. MR angiography of RAS was performed before and after PTA of RAS on a 3.0-T clinical MR imager with use of gadolinium-based contrast agent. MR angiography and DSA images were analyzed with the full width at half maximum method. Percent stenosis measurements between x-ray DSA and MR angiography were compared with a paired t test and were correlated with linear regression and Bland Altman analysis (alpha = 0.05).

RESULTS

Six cases of RAS were induced and imaged successfully with DSA and MR angiography techniques before and after PTA. On x-ray DSA, median stenoses was 64% (95% CI 57%-80%) before PTA and 20% (95% CI 5%-32%) after PTA. Corresponding MR angiography median stenosis measurement was 69% (95% CI 58%-80%) before PTA and 26% (95% CI 16%-36%) after PTA. A paired t test comparison did not show a difference between DSA and MR angiography (P = .16). RAS measurements on MR angiography correlated closely (P < .01) with DSA measurements (r(2) = 0.92).

CONCLUSION

In swine, the accuracy of catheter-directed IA MR angiography with use of a clinical 3.0-T MR imaging unit for the measurement of RAS was similar to that of conventional x-ray DSA.

Renal MR and CT angiography: current concepts

During the past decade, noninvasive CTA and MRA imaging techniques have replaced catheter angiography for evaluation of the renal arteries. This article reviews techniques for optimizing renal MRA and CTA, assesses the advantages and limitations of MRA and CTA, and provides the current indications for renal vascular imaging including renal artery stenosis screening. New and future developments in these rapidly evolving techniques are also discussed.

Angiografia por ressonância magnética na avaliação das artérias renais: achados de imagem

OBJETIVO: Descrever as indicações, os principais diagnósticos e os achados de imagem nas angiografias por ressonância magnética das artérias renais. MATERIAIS E MÉTODOS: Estudo retrospectivo, no período de 6/12/2001 a 11/3/2004, num total de 56 exames, totalizando 111 artérias renais estudadas. Os exames foram realizados em um equipamento de 1,5 tesla, segundo o protocolo do Serviço. RESULTADOS: Foi demonstrado que 55,4% (n = 31) pacientes eram masculinos e 44,6% (n = 25), femininos. O paciente mais novo tinha 12 anos e o mais velho, 88 anos. De um total de 25 diferentes indicações, a hipertensão arterial sistêmica com 26,7% (n = 15) foi a principal, seguida de dor abdominal e/ou lombar com 12,5% (n = 7), aneurisma da aorta abdominal com 10,7% (n = 6), estenose da artéria renal com 8,9% (n = 5), e outros. No que se refere às imagens, 43 (76,7%) exames tiveram algum tipo de alteração e 13 (23,2%) foram normais. Dentre os que tinham alterações, a maioria se deu no calibre, e dentre elas, as irregularidades parietais, aneurismas e estenoses foram as mais comuns. Na artéria renal direita as alterações mais comuns foram as irregularidades parietais com 17,87% (n = 10), e na artéria renal esquerda foram as estenoses com 25,45% (n = 14). CONCLUSÃO: A angio-RM mostrou-se excelente método no estudo das artérias renais, devido à sua sensibilidade e capacidade multiplanar para avaliar as estruturas vasculares.

Update of renal imaging

Significant technical improvements have allowed the use of radiological techniques to play a growing role in the imaging of renal diseases. Noninvasive ultrasound methods (ie, sonography and Doppler) are now positioned as first-line methods for the evaluation of renovascular diseases. Multidetector computed tomography is able to provide high spatial resolution images of the kidneys and renal arterial vessels. Magnetic resonance imaging, which provides higher signal-to-noise ratio and higher spatial and/or temporal resolution, can display both morphological information about renal parenchyma and vessels and functional data, including perfusion, filtration, diffusion, or oxygenation. In renovascular diseases, these techniques have the potential to drive new strategies, including Doppler sonography as a first-line method, followed by computed tomography angiography or magnetic resonance angiography, depending mainly on renal function. Imaging of parenchymal renal diseases is developing toward more quantitative (volumetric and functional measurements) and more specific (through in vivo cell targeting) acquisitions for obtaining the adequate information on tissue characteristics relevant either for diagnosis or for prognosis or treatment follow-up.

Intraindividual comparison of 1.0 M gadobutrol and 0.5 M gadopentetate dimeglumine for time-resolved contrast-enhanced three-dimensional magnetic resonance angiography of the upper torso

PURPOSE

To compare the signal characteristics and bolus dynamics of 1.0 M gadobutrol and 0.5 M Gd-DTPA for time-resolved, three-dimensional, contrast-enhanced (CE) MRA of the upper torso.

MATERIALS AND METHODS

Ten healthy volunteers were examined with time-resolved three-dimensional CE-MRA (scan time per three-dimensional data set: 0.86 second; voxel size: 3.6 x 2 x 6.3 mm(3)). Each volunteer underwent eight individual examinations after intravenous injection of 0.05 and 0.1 mmol/kg body weight (b.w.) of 1.0 M gadobutrol and 0.5 M Gd-DTPA using two injection rates (2.5 and 5 mL/second). The data analysis included quantitative measurements of the peak signal-to-noise ratio (SNR) and bolus dispersion (full width at half maximum (FWHM)) in the pulmonary artery, left atrium, and thoracic and abdominal aortas.

RESULTS

No significant differences in the peak SNR and bolus dispersion were observed between gadobutrol and Gd-DTPA for all dose levels and injection rates in any of the vascular segments. For both contrast agents a dose of 0.1 mmol/kg b.w. injected with 5 mL/second achieved the highest SNR in all vascular segments.

CONCLUSION

For the imaging parameters used in this study, higher-concentrated gadolinium chelates offer no relevant advantages for time-resolved three-dimensional CE-MRA of the upper torso.

In Vivo Evaluation of the Carotid Wallstent on Three-dimensional Contrast Material–enhanced MR Angiography: Influence of Artifacts on the Visibility of Stent Lumina

PURPOSE

Contrast material-enhanced magnetic resonance (MR) angiography is increasingly used in postinterventional imaging after implantation of endovascular stents. The main limitations are stent-related artifacts compromising the visibility of the stent lumen. The aim of this in vivo study is the evaluation of contrast-enhanced MR angiography imaging characteristics of the carotid Wallstent.

MATERIALS AND METHODS

The carotid arteries of 29 patients were examined with contrast-enhanced MR angiography 3-6 days and/or 7-23 months after implantation of a carotid Wallstent into the internal carotid artery. Images were evaluated with regard to the diameter and signal intensity (SI) of the visible stent lumen. Digital subtraction angiography (DSA) was used as the standard of reference.

RESULTS

Stent-related artifacts on contrast-enhanced MR angiography caused an artificial lumen narrowing and a reduction of the SI within the stent. Artifacts were pronounced on imaging 3-6 days after stent implantation, but 68% of stents imaged 7-23 months after stent implantation presented with a significantly decreased artificial signal reduction and an improved visibility of the stent lumen.

CONCLUSIONS

The results of this study indicate that a reliable evaluation of the stent lumen is limited as a result of an artificial decrease of the SI inside the stent. However, in follow-up examinations 7-23 months after stent implantation, visibility of the stent lumen was improved and diagnostic reliability of contrast-enhanced MR angiography was markedly increased. A probable explanation for this phenomenon might be the formation of a neointimal layer covering the stent struts and thereby reducing stent-related artifacts.

The limitations of magnetic resonance angiography in the diagnosis of renal artery stenosis: Comparative analysis with conventional arteriography

PURPOSE

Gadolinium-enhanced magnetic resonance angiography (MRA) is commonly used as a screening modality for the detection of renal artery stenosis. However, evidence supporting its utility in clinical practice is lacking; few rigorous studies have compared MRA with contrast arteriography (CA). After making anecdotal clinical observations that MRA sometimes overestimated the degree of renal artery stenosis, we decided to determine the interobserver variability, sensitivity, specificity, and diagnostic accuracy of MRA compared with CA.

METHODS

From September 1999 to April 2003, we evaluated 68 renal arteries in 34 patients with clinically suspected renal artery stenosis using both MRA and CA. All studies were independently reviewed by four blinded observers. Renal arteries were categorized by MRA as normal, <50%, and >50% stenosis/occlusion. The sensitivity, specificity, and accuracy of MRA detection of renal artery stenosis were compared to CA as the gold standard. Interobserver variability (kappa) was also calculated.

RESULTS

MRA demonstrated 87% sensitivity, 69% specificity, 85% accuracy, 95% negative predictive value, and 51% positive predictive value for the diagnosis of renal artery stenosis. Interobserver agreement was moderate for MRA (kappa = 0.53) and good for CA (kappa = 0.76). In 21 arteries (31%), MRA was falsely positive.

CONCLUSIONS

In patients with a high clinical suspicion of renal artery stenosis, MRA is 87% sensitive in the detection of >50% stenosis. However, MRA is relatively nonspecific compared with CA and results in significant overestimation of renal artery stenosis in nearly one third of patients. To reduce unnecessary CA, clinicians should consider supplemental studies.

Contrast-enhanced MR Angiography of the renal arteries: blinded multicenter crossover comparison of gadobenate dimeglumine and gadopentetate dimeglumine

PURPOSE

To prospectively and intraindividually compare 0.1 mmol/kg gadobenate dimeglumine with 0.2 mmol/kg gadopentetate dimeglumine for contrast material-enhanced magnetic resonance (MR) angiography of the renal arteries.

MATERIALS AND METHODS

Institutional review board approval was granted by each of three participating centers. The study accorded with international standards for good clinical practice and Declaration of Helsinki and subsequent amendments. Patients gave written informed consent before enrollment. Patients (n = 34) underwent two MR angiographic examinations more than 48 hours but less than 12 days apart. Gadobenate dimeglumine followed by gadopentetate dimeglumine was administered in 18 patients; the order of administration was reversed in 16 patients. A 1.5-T MR imager was used with a phase-encoded three-dimensional spoiled breath-hold pulse sequence. Two blinded independent readers qualitatively assessed randomized subtracted maximum intensity projection images. A three-point scale for diagnostic quality (0, poor; 1a or 1p, moderate; and 2a or 2p, adequate [a and p refer, respectively, to absence and presence of vascular lesions]) was used to score each of nine segments of the abdominal aorta and both renal arteries (possible overall score, 18). Quantitative assessment (vessel signal-to-noise ratio [SNR], vessel-muscle contrast-to-noise ratio [CNR]) of source images was performed for regions of interest in supra-, juxta-, and infrarenal aorta segments and psoas muscle. Data were tested with analysis of variance for two-period crossover design. Interreader agreement was evaluated with Cohen kappa statistics.

RESULTS

No difference in mean image quality between the two contrast agents was observed; scores for gadobenate dimeglumine and gadopentetate dimeglumine were 15.15 and 15.23 for reader 1 and 16.77 and 17.01 for reader 2. The order of contrast material administration likewise produced no quality differences: readers 1 and 2 reported scores of 14.4 +/- 4.2 (standard deviation) and 16.7 +/- 2.3, respectively, when gadobenate dimeglumine was given first, and 15.2 +/- 1.8 and 16.6 +/- 1.6, respectively, when gadopentetate dimeglumine was given first. Results of quantitative evaluation showed increasing SNR and CNR with gadobenate dimeglumine in segments at progressively lower levels of the aorta, but increases in SNR and CNR at the infrarenal aorta (48.3 vs 40.6 and 44.2 vs 36.4, respectively) were not significant (P = .05 for both).

CONCLUSION

Gadobenate dimeglumine at a dose of 0.1 mmol/kg is comparable to gadopentetate dimeglumine at 0.2 mmol/kg for contrast-enhanced renal MR angiography.

Renal MR angiography

The high accuracy of renal MR angiography makes it well suited for diagnosing renal vascular disease. A comprehensive examination includes three-dimensional gadolinium MR angiography to assess lumenal anatomy and functional techniques to assess the hemodynamic significance of any stenosis identified. Postprocessing is critical to provide reformations, maximum intensity projections, and optional volume-rendered images to display arteries in an angiographic format for optimal demonstration of any vascular lesions. It is important to review source images to avoid missing pathologic findings. As MR imaging continues to develop, the renal MR angiography examination will likely expand to include extensive functional information about creatinine clearance, flow, and response to pharmacologic agents as well as spectroscopy, diffusion, perfusion, phase contrast, and other techniques.

Gadopentetate dimeglumine-enhanced three-dimensional MR-angiography: dosing, safety, and efficacy

Noninvasiveness, inherent three-dimensionality allowing reformations in any desired plane, and safe contrast agents, coupled with high diagnostic accuracy have driven the rise in popularity of contrast-enhanced MR angiography (CE-MRA) within the medical community. Reflecting its dominant market share as a paramagnetic contrast agent, gadopentetate dimeglumine (Gd-DTPA) has been used for the majority of clinically-performed MRA exams. Over the period January 1994 to February 2002, a total of 172 original studies describing the use of gadolinium-enhanced MRA in more than three human subjects were identified. Of these, 117 described the use of Gd-DTPA as the contrast agent for MRA. A total of 4046 subjects who received Gd-DTPA for MRA are described in these studies. Analysis of these data demonstrate Gd-DTPA to be a safe contrast agent for MRA when applied in a dose ranging from 0.1 to 0.3 mmol/kg of bodyweight. The documented clinical results show Gd-DTPA to be efficacious in the assessment of the arterial system. The effectiveness of Gd-DTPA-enhanced MRA extends beyond the detection, localization, and characterization of arterial disease, and encompasses choice and planning of appropriate therapy, as well as evaluation of therapeutic effectiveness.

Accessory Renal Arteries Are Not Related to Hypertension Risk:A Review of MR Angiography Data

OBJECTIVE

It has been hypothesized that accessory renal arteries are related to the risk of hypertension. Our goal was to determine the prevalence of accessory renal arteries in hypertensive patients using MR angiography and to assess the relationship between accessory renal arteries and hypertension risk.

MATERIALS AND METHODS

From 1996 to 2002, 185 hypertensive patients underwent MR angiography of the renal arteries at our institution for assessment of renal artery stenosis. MR angiograms were obtained using a 1.5-T magnet, IV gadolinium, and 3D gradient-echo sequences. Interpretations of the MR angiograms were retrospectively reviewed.

RESULTS

Of 185 hypertensive patients, 45 (24%) showed accessory renal arteries. Of these 45 patients, nine (20%) showed renal artery stenosis and 36 (80%) showed no significant stenosis. Of the 140 patients with a single renal artery, 42 (30%) showed renal artery stenosis and 98 (70%) showed no stenosis. The odds ratio of renal artery stenosis in the accessory renal artery group versus the single renal artery group was 0.58 (95% confidence interval, 0.26-1.3%), which is not statistically significant at a power of 0.85 (chi(2) = 1.705; p = 1.0).

CONCLUSION

We found no statistically significant difference in the prevalence of renal artery stenosis between patients with accessory renal arteries and those without accessory renal arteries. Assuming that the presence of two separate causes of hypertension in the same patient would be unlikely, this finding implies that accessory renal arteries are a vascular anomaly and not a direct cause of hypertension. The findings are potentially relevant in refuting the theory of accessory renal arteries as an anatomically treatable cause of hypertension.

Contrast-Enhanced Magnetic Resonance Angiography of the Carotid Arteries:

RATIONALE AND OBJECTIVES

To assess the influence of injection rates and volumes on the arrival time of contrast material (CM) in the common carotid artery, the jugular vein and the resulting arterial-venous transit time. Additionally the relationship between injection parameters and the extent of a CM plateau was evaluated.

MATERIALS AND METHODS

In 60 patients a CM injection was necessary to investigate suspected cranial disease. All patients were prospectively assigned to 6 protocol groups with varying volumes of gadolinium dimeglumine (2, 10, 20 mL) and injection rates (0.5, 1, 2, 4 mL/s). Simultaneously to the CM injection, 50 repetitive transverse measurements (1/s) were acquired at the level of the common carotid artery. Based on the resulting signal-time curves, the arrival time of the contrast material in the common carotid artery and the jugular vein, the resulting arterial-venous transit time, the peak enhancement and the extent of a CM-plateau were calculated as a function of the injection parameters.

RESULTS

Smaller flow rates (0.5 mL/s) resulted in a longer arrival time in the common carotid artery (mean value 22,6 seconds +/- 2.3) and the jugular vein (mean value 32.6 seconds +/- 2.6) and resulted in longer arterial-venous transit time (mean value 10.1 second +/- 1.9). The volume showed no effect on these parameters. The peak arterial and venous signal intensity and a consistent CM-plateau after 50 seconds were dependent on the volume, but not on the injection rate.

CONCLUSION

The injection rate showed an influence to the arrival time in the common carotid artery and the jugular vein and also to the arterial-venous transit time. The injected volume only affected the extent of the contrast plateau. A flow rate of 1 to 2 mL/s and a minimum of 20 mL gadolinium dimeglumine are recommended to achieve optimal image quality without venous overlay.

MR techniques for renal imaging

This article describes the principles, attributes, and pitfalls of the many MR imaging approaches available for assessment of renal-related disorders. Tables 1 and 2 summarize the specific approach and rationale.

Utility of a 0.014" pressure-sensing guidewire to assess renal artery translesional systolic pressure gradients

Renal ischemia due to renal artery stenosis (RAS) is an important cause of secondary hypertension and renal insufficiency. Several methods are available to diagnose RAS; however, the identification of clinically significant lesions remains problematic. We measured the translesional systolic pressure gradient (TSPG) with a 4 Fr catheter and a 0.014" pressure-sensing guidewire and compared these data to angiographic findings. The TSPG obtained by pressure-sensing guidewire correlated more strongly with angiographic minimal lumen diameter (r(2) = 0.801) than those obtained by 4 Fr catheter (r(2) = 0.360). The relationship of TSPG with percent stenosis was not strong, regardless of the method used (r(2) = 0.228 with pressure-sensing guidewire, 0.358 with 4 Fr catheter). Using a 0.014" pressure-sensing guidewire is effective for assessing TSPG and provides a more reliable indication of stenosis significance than use of a 4 Fr catheter.

Percutaneous stenting of incidental unilateral renal artery stenosis: decision analysis of costs and benefits

PURPOSE

To determine the incremental cost-effectiveness of prophylactic percutaneous transluminal angioplasty with stent placement (PTA-S) in patients with incidentally discovered, asymptomatic renal artery stenosis (RAS) compared to delaying PTA-S until patients develop refractory hypertension or renal insufficiency (therapeutic PTA-S).

METHODS

The Markov decision analysis model was used to determine the incremental cost per quality adjusted life year (QALY) saved for prophylactic PTA-S as compared to therapeutic PTA-S in a hypothetical cohort of patients with 50% unilateral atherosclerotic RAS followed from age 61 to death.

RESULTS

Prophylactic PTA-S compared to therapeutic PTA-S results in more QALYs/patient (10.9 versus 10.3) at higher lifetime costs ($23,664 versus $16,558). The incremental cost effectiveness of prophylactic PTA-S was estimated to be $12,466/QALY. Prophylactic stenting was not cost effective (>$50,000/QALY) if the modeled incidence of stent restenosis exceeded 15%/year and the incidence of progression in the contralateral renal artery was <2% of arteries/year.

CONCLUSIONS

PTA-S of incidental, asymptomatic unilateral RAS may improve patients' quality of life at an acceptable incremental cost. However, this technology should be used hesitantly until a randomized comparison confirms its effectiveness.

Is it necessary to study accessory arteries when screening the renal arteries for renovascular hypertension?

PURPOSE

To determine the prevalence of isolated hemodynamically significant stenoses of accessory renal arteries when the main renal arteries are patent.

MATERIALS AND METHODS

In 68 adults (24 men, mean age, 67 years +/- 10; 44 women, mean age, 67 years +/- 12), angiograms that fulfilled the following criteria were studied: (a) technically adequate renal angiograms obtained to evaluate suspected renovascular hypertension and (b) angiographically documented hemodynamically significant stenosis of any renal artery. The percentage of kidneys and the percentage of patients with hemodynamically significant isolated stenoses of accessory renal arteries were calculated.

RESULTS

Eighty-seven kidneys in 68 patients had hemodynamically significant renal artery stenoses. Fifteen kidneys had 16 accessory renal arteries. Four accessory arteries in three patients had hemodynamically significant stenoses. Only one of 68 patients (1.5%) had an accessory artery stenosis unaccompanied by a main renal artery stenosis in either kidney; this patient had bilateral hemodynamically significant accessory artery stenoses. Two patients had coexistent hemodynamically significant stenoses of accessory and main renal arteries.

CONCLUSION

The prevalence of a hemodynamically significant stenosis isolated to an accessory renal artery was 1.5% in our study. Thus, failure to detect accessory renal arteries should not unduly affect the utility of a noninvasive test for detecting renovascular hypertension.

Gadobenate dimeglumine-enhanced MR angiography of the abdominal aorta and renal arteries

OBJECTIVE

This study was conducted to determine the efficacy and safety of four different doses of gadobenate dimeglumine for contrast-enhanced three-dimensional MR angiography of the abdominal aorta and renal arteries.

SUBJECTS AND METHODS

Ninety-four patients with suspected abnormality of the abdominal aorta or renal arteries underwent unenhanced three-dimensional gradient-recalled echo time-of-flight MR angiography and contrast-enhanced MR angiography after the IV injection of one of four doses of gadobenate dimeglumine (0.025, 0.05, 0.1, and 0.2 mmol/kg of body weight). Efficacy was assessed on-site and by two blinded off-site reviewers in terms of change in total diagnostic quality score and diagnostic quality score per vessel segment from baseline unenhanced time-of-flight MR angiography to contrast-enhanced MR angiography. Secondary efficacy end points included lesion count and level of confidence in lesion characterization. Safety assessments comprised adverse event monitoring, physical evaluation, vital signs, ECG, and laboratory investigations.

RESULTS

A significant change in the total diagnostic quality score from unenhanced to contrast-enhanced MR angiography was observed at all doses. The change increased with increased dose, plateauing at the 0.1 mmol/kg dose level. More patients with lesions detected and increased reviewer confidence for lesion characterization were noted on contrast-enhanced MR angiography compared with unenhanced MR angiography, although no dose-related trends were observed. All doses were well tolerated, and no significant changes in safety parameters were observed.

CONCLUSION

Gadobenate dimeglumine is an effective and safe agent for contrast-enhanced MR angiography of the abdominal aorta and renal arteries. A dose of 0.1 mmol/kg of body weight appears to be the most suitable.

MR-velocity mapping in vascular stents to assess peak systolic velocity. In vitro comparison of various stent designs made of Stainless Steel and Nitinol

INTRODUCTION

Peak systolic velocity (PSV) measurements of blood flow inside vascular stents allow reliable detection of in-stent re-stenosis. The purpose of this in vitro study was to evaluate the feasibility of obtaining PSV measurements inside vascular stents made of Stainless Steel and Nitinol, using a velocity encoded MR technique.

MATERIALS/METHODS

In a flow phantom, stents of Stainless Steel and Nitinol were studied. The phantom was integrated into a closed-tubing circuit driven by a MR dedicated pulsatile flow pump. MR imaging was performed on a 1.5 T system. The PSV in the tube without stent was used as the gold standard to determine the accuracy and the variability (paired t-test and Pittman's test) of the PSV measurements inside the stents.

RESULTS

PSV values inside the stents showed percentual difference in mean of -15 to 21% (P < 0.05) at a pump setting of 10 and 20 ml/s.

CONCLUSION

PSV measurements can be accurately obtained inside stents made of Stainless Steel and Nitinol. MR-velocity measurements may be used in patients to non-invasively evaluate stent patency and in-stent re-stenosis.

Time-resolved contrast-enhanced magnetic resonance angiography of the carotid arteries: diagnostic accuracy and inter-observer variability compared with selective catheter angiography

RATIONALE AND OBJECTIVES

To assess the diagnostic accuracy and interobserver variability of contrast-enhanced magnetic resonance angiography (CE-MRA) in a time-resolved technique compared with digital subtraction angiography (x-ray DSA) in patients with suspected stenoses of the internal carotid artery.

MATERIALS AND METHODS

A total of 43 patients were enrolled in this prospective study. All patients underwent selective x-ray DSA involving a total of 84 carotid arteries. CE-MRA was performed in a time-resolved technique with a fast gradient-echo sequence on a 1.5 T MR scanner: TR 3.8 milliseconds, TE 1.49 milliseconds. Four consecutive measurements, each a duration of 10 seconds, were performed with omission of measuring bolus transit time. Four independent radiologists scored the degree of stenosis. The interobserver variability was calculated for CE-MRA and x-ray DSA.

RESULTS

In the 43 cases, at least one MRA measurement showed arterial contrast without venous degradation. Compared with x-ray DSA the mean sensitivity and specificity for grading stenosis > or = 70% were 98% and 86%, respectively. The interobserver agreement was substantial with no significant difference between CE-MRA (kappa value 0.794) and x-ray DSA (kappa value 0.786).

CONCLUSIONS

The short acquisition time of a fast CE-MRA sequence allows a selective visualization of the internal carotid arteries without degradation from venous enhancement. It is a reliable method with a good interobserver agreement.

Value of MR angiography before percutaneous transluminal renal artery angioplasty and stent placement

PURPOSE

To determine the benefit of preprocedural three-dimensional gadolinium (Gd)-enhanced magnetic resonance (MR) angiography before percutaneous transluminal renal artery angioplasty and stent placement (PTRA/S) in terms of procedural success, iodinated contrast material load, and procedure duration.

MATERIALS AND METHODS

Over an 18-month period, 39 patients underwent attempted percutaneous renal angioplasty with or without stent placement. A total of 48 renal arteries were treated (40 cases of atherosclerosis, one of stent restenosis, five of fibromuscular dysplasia, and two of transplant stenosis). Preprocedural Gd-enhanced MR angiography was available in 16 procedures (41%). Procedural outcome, complications, iodinated contrast material load, number of diagnostic angiographic runs, and total procedure duration were each compared between two subgroups: patients who had preprocedural Gd-enhanced MR angiography ("prior MR angiography group") and those who did not ("no MR angiography" group).

RESULTS

All procedures were technically successful. The two groups were equivalent in terms of age and disease pattern. However, technical complexity of the procedure was judged to be high in five of 16 procedures in the prior MR angiography group compared to three of 23 procedures in the no MR angiography group (P =.16). Bilateral or dual interventions were performed in six of 16 procedures in the prior MR angiography group compared to three of 23 in the no MR angiography group (P =.075). Iodinated contrast material load was significantly lower in the prior MR angiography group than in the no MR angiography group (68.7 mL +/- 28.4 vs 119.1 mL +/- 49.2 mL;P <.0008). The number of diagnostic angiographic runs before interventions were also significantly lower in the prior MR angiography group (1.2 +/- 0.4 vs 2.6 +/- 0.7; P <.0001). Overall procedure duration was comparable between the two groups (91.9 +/- 47.8 vs 112.2 +/- 49.4;P =.2).

CONCLUSION

Preprocedural planning with use of Gd-enhanced MR angiography significantly reduces the iodinated contrast material requirement during percutaneous renal artery interventions. It can also significantly shorten procedure duration.

Magnetic resonance angiography for the diagnosis of renal artery stenosis: a meta-analysis

AIM

To review the published literature comparing the diagnostic accuracy of magnetic resonance angiography (MRA) with and without gadolinium in diagnosing renal artery stenosis, using catheter angiography as reference.

MATERIALS AND METHODS

A meta-analysis was performed of English language articles identified by computer search using PubMed/MEDLINE, followed by extensive bibliography review from 1985 to May 2001. Inclusion criteria were: (1) blinded comparison with catheter angiography; (2)indication for MRA stated; (3) clear descriptions of imaging techniques; and (4) interval between MRA and catheter angiography < 3 months and only the largest of all studies from one centre was selected in the analysis.

RESULTS

A total of 39 studies were identified, of which 25 met the inclusion criteria. The number of patients included in the meta-analysis was 998: 499 with non-enhanced MRA and 499 with gadolinium-enhanced MRA. The sensitivity and specificity of non-enhanced MRA were 94% (95% CI: 90-97%) and 85% (95% CI: 82-87%), respectively. For gadolinium-enhanced MRA sensitivity was 97% (95% CI: 93-98%) and specificity was 93% (95% CI: 91-95%). Thus, specificity and positive predictive value were significantly better for gadolinium-enhanced MRA (P < 0.001). Accessory renal arteries were depicted better by gadolinium-enhanced MRA (82%; 95% CI: 75-87%) than non-gadolinium MRA (49%; 95% CI: 42-60%) (P < 0.001).

CONCLUSIONS

Gadolinium-enhanced MRA may replace arteriography in most patients with suspected renal artery stenosis, and has major advantages in that it is non-invasive, avoids ionizing radiation and uses a non-nephrotoxic contrast agent.

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

RATIONALE AND OBJECTIVES

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

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 (> or = 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.

Renal artery stenosis and ischemic nephropathy

Renal artery stenosis (RAS), in its most severe form, can result in diminished renal function and loss of kidney mass. The prevalence of ischemic nephropathy is greatly under-appreciated in the elderly population and is the source of substantial morbidity and mortality. Diagnostic tests for RAS in patients with renal insufficiency are problematic, and medical therapy does little to slow the natural progression of the disease. Renal artery stenting can achieve long-term vessel patency and has been shown to preserve renal function. Proper technique and careful case selection are critical to the success of such procedures. Large-scale trials are needed to clearly identify groups of patients who will benefit most from percutaneous revascularization.

Renal time-resolved MR angiography: quantitative comparison of gadobenate dimeglumine and gadopentetate dimeglumine with different doses

PURPOSE

Results with different doses of gadobenate dimeglumine and gadopentetate dimeglumine were compared at magnetic resonance (MR) angiography of the renal arteries. The signal-to-noise ratio (SNR) was evaluated as a quantitative measure of image quality.

MATERIALS AND METHODS

Sixty consecutive patients (age range, 24-81 years; mean age, 65 years) underwent intraarterial digital subtraction angiography (DSA) and contrast material-enhanced time-resolved MR angiography. DSA was the standard of reference. Fifteen patients received gadopentetate dimeglumine at doses of 0.2 or 0.1 mmol per kilogram of body weight. Fifteen patients received gadobenate dimeglumine at doses of 0.05 or 0.1 mmol/kg. The SNR was calculated in the aorta and both main renal arteries. The number and degree of stenoses of the renal arteries and accessory vessels were evaluated by four observers.

RESULTS

SNRs with gadobenate dimeglumine at a dose of 0.1 mmol/kg were significantly superior to those with gadopentetate dimeglumine at a dose of 0.1 mmol/kg. Differences were not statistically significant between the SNRs in the other groups. Eleven (85%) of 13 hemodynamically significant renal artery stenoses were detected correctly with MR angiography as were 22 (85%) of 26 accessory renal arteries.

CONCLUSION

SNRs with gadobenate dimeglumine were higher than those with gadopentetate dimeglumine, but in most cases the differences in SNRs were not statistically significant.

Evaluation and treatment of renal artery stenosis: impact on blood pressure and renal function

The conventional non-invasive tests to diagnose renal artery stenosis in a general hypertensive population are not accurate enough for screening purposes. Magnetic resonance angiography might become the new gold standard, with the advantages of the absence of contrast toxicity, good accuracy, and information on flow characteristics. With regard to the treatment of hypertension in patients with renal artery stenosis, intervention is advised only when blood pressure cannot be controlled by at least three antihypertensive drugs. Patency after stenting is superior to angioplasty, although its clinical benefit has not been proved. As for renal function, evidence - although from uncontrolled studies - for the preservation of renal function by intervention is accumulating, especially in those patients with bilateral stenosis or stenosis in a single functioning kidney.