Renal artery stenosis: comparative assessment by unenhanced renal artery mra versus contrast-enhanced MRA

Noncontrast Magnetic Resonance Angiography in the Era of Nephrogenic Systemic Fibrosis and Gadolinium Deposition

ABSTRACT

Gadolinium-based contrast agents for clinical magnetic resonance imaging are overall safe. However, the discovery of nephrogenic systemic fibrosis in patients with severe renal impairment and gadolinium deposition in patients receiving contrast have generated developments in contrast-free imaging of the vasculature, that is, noncontrast magnetic resonance angiography. This article presents an update on noncontrast magnetic resonance angiography techniques, with comparison to other imaging alternatives. Potential benefits and challenges to implementation, and evidence to date for various clinical applications are discussed.

Non-contrast renal MRA using multi-shot gradient echo EPI at 3-T MRI

OBJECTIVES

The purpose of this study was to investigate the feasibility of non-contrast renal MRA using multi-shot gradient echo planar imaging (MSG-EPI) with a 3-T MRI system.

METHODS

Seventeen healthy volunteers underwent non-contrast renal MRA using MSG-EPI and balanced steady-state free precession (b-SSFP) sequences on a 3-T MRI system. Two radiologists independently recorded the images' contrast, noise, sharpness, artifacts, and overall quality on 4-point scales. The signal-to-noise ratio (SNR) for the renal artery, the contrast ratio (CR) between the renal artery and erector spinae, and acquisition time were compared between the two sequences.

RESULTS

The SNR and CR were significantly higher with MSG-EPI than with the b-SSFP sequence (17.80 ± 3.67 vs. 10.84 ± 2.86 and 0.77 ± 0.05 and 0.66 ± 0.09, respectively; p < 0.05), and the acquisition time was significantly lower (164.5 ± 34.0 vs. 261.5 ± 39.3 s, respectively; p < 0.05). There were significant differences in image contrast, noise, sharpness, artifacts, and overall image quality between the two sequences (p < 0.01).

CONCLUSIONS

The MSG-EPI sequence is a promising technique that can shorten the scan time and improve the image quality of non-contrast renal MRA with a 3-T MRI system.

KEY POINTS

• The multi-shot gradient echo planar imaging with an inversion pulse is a brand-new fast scan technique for an unenhanced renal MRA. • The image quality of multi-shot gradient echo planar imaging is better than that of b-SSFP for an unenhanced renal MRA.

Noncontrast MR angiography: An update

Both computed tomography (CT) angiography (CTA) and contrast-enhanced MR angiography (CEMRA) have proven to be useful and accurate cross-sectional imaging modalities over a wide range of vascular territories and vascular disorders. A key advantage of MRA is that, unlike CTA, it can be performed without the administration of a contrast agent. In this review article we consider the motivations for using noncontrast MRA, potential contrast mechanisms, imaging techniques, advantages, and drawbacks with respect to CTA and CEMRA, and the level of evidence for using the various MRA techniques. In addition, we explore new developments that promise to expand the reliability and range of clinical applications for noncontrast MRA, along with functional MRA capabilities not available with CTA or CEMRA. Level of Evidence: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:355-373.

The Prevalence of Japanese Outpatients with Hypertension Who Meet the Definition of Treatment Resistant Hypertension and Are Eligible for Enrolment in Clinical Trials of Endovascular Ultrasound Renal Denervation

Objective A clinical trial (REQUIRE) was started to investigate the use of an ultrasound renal denervation system in the treatment of resistant hypertension (RHT). We analyzed the prevalence of patients who were eligible for inclusion in this cross-sectional study at the time of screening. Methods Nine-hundred ninety-nine consecutive hypertension (HT) patients who were treated in our hospital as outpatients were classified into the following categories: patients treated with at least 3 types of antihypertensive drugs including diuretic agents who were eligible for enrolment in SYMPLICITY HTN-Japan (SH-J) with an office systolic blood pressure (SBP) of ≥160 mmHg, who were ≤80 years of age, and an estimated glomerular filtration rate (eGFR) of ≥45 mL/min/1.73 m² (RHT-S); and patients who were treated similar medications and who were eligible for enrolment in REQUIRE, with an SBP of ≥150 mmHg, ≤75 years of age, and an eGFR of ≥40 mL/min/1.73 m² (RHT-R). We investigated the proportion of patients in each category. We also investigated HT patients (1,423 cases) who were enrolled in the Chikushi Anti-Hypertension Trial (CHAT), a research network that includes general practitioners. Results Eleven patients (1.1%) with RHT-S and 18 patients (1.8%) with RHT-R were identified. After the exclusion of patients with secondary HT and a diastolic blood pressure (DBP) of <90 mmHg (applied in REQUIRE), 5 patients (0.5%) with RHT-S and 4 patients (0.4%) with RHT-R remained. In the analysis of the CHAT study, only 2 (0.1%) patients with RHT-R remained. Conclusion The number of eligible patients in the REQUIRE trial was decreased, largely due to the strict age restriction and the new DBP limitation. The prevalence of eligible patients in REQUIRE was estimated to be approximately 0.5 to 0.8 times that in SH-J. Since patient enrollment will be difficult, drastic measures may be required to recruit eligible patients.

The capability of inflow inversion recovery magnetic resonance compared to contrast-enhanced magnetic resonance in renal artery angiography

PURPOSE

To assess the capability of inflow inversion recovery (IFIR) magnetic resonance angiography (MRA), compared with contrast-enhanced MRA (CE-MRA) as reference standard, in evaluating renal artery stenosis (RAS).

METHODS

Seventy-two subjects were examined by IFIR MRA with respiratory-gated, prior to CE-MRA with a 1.5-T scanner. Two readers evaluated the quality of IFIR MRA images and renal artery depiction on artery-by-artery basis. The agreement of two methods to assess RAS was analyzed using the Kappa test. The relationship between image quality of IFIR MRA and respiratory rate was analyzed by ANOVA test.

RESULTS

The visibility of renal artery branch vessels was significantly higher using IFIR MRA than CE-MRA (p < 0.05). A good agreement of two methods in evaluating stenosis grade, and a near-perfect inter-observer agreement for IFIR MRA (Kappa value 0.98) and CE-MRA (Kappa value 0.93), were demonstrated. As RAS ≥50%, the sensitivity and specificity of IFIR MRA were 92 and 98% in reader 1, 93 and 98% in reader 2, respectively. The image quality was significantly better in patients with stable respiration (p < 0.01).

CONCLUSIONS

IFIR MRA in patients with stable respiration has higher visibility of renal artery branch vessels than CE-MRA, and a good agreement with CE-MRA in evaluating stenosis grade. It could be used to evaluate RAS for screening, and monitoring treatment.

The Performance of Noncontrast Magnetic Resonance Angiography in Detecting Renal Artery Stenosis as Compared With Contrast Enhanced Magnetic Resonance Angiography Using Conventional Angiography as a Reference

OBJECTIVE

The aims of this study were to evaluate the performance of noncontrast magnetic resonance angiography (NC MRA) for detecting renal artery stenosis (RAS) as compared with contrast-enhanced magnetic resonance angiography (CE MRA) and to evaluate the clinical feasibility, technical success rate, and performance of NC MRA for detecting RAS as compared with CE MRA.

METHODS

Thirty-six subjects who underwent NC MRA and/or CE MRA were enrolled. Feasibility, technical success rate, and image quality scores were compared. Diagnostic ability was calculated using conventional angiography as a reference.

RESULTS

Noncontrast MRA had higher feasibility and technical success rates than CE MRA did (100% and 97.2% vs 83.3% and 90%, respectively). Noncontrast MRA yielded significantly better image quality in motion artifact (P = 0.016). The diagnostic ability for detecting RAS is without significant difference between NC MRA and CE MRA.

CONCLUSION

Although NC MRA and CE MRA demonstrated comparable ability in diagnosing RAS, NC MRA achieved better technical success rates, feasibility, and image quality in motion artifacts than CE MRA did.

Efficacy and safety of gadobutrol-enhanced MRA of the renal arteries: Results from GRAMS (Gadobutrol-enhanced renal artery MRA study), a prospective, intraindividual multicenter phase 3 blinded study

PURPOSE

To compare the performance of magnetic resonance angiography (MRA) with 1M gadobutrol, a high relaxivity macrocyclic contrast agent, to 2D time-of-flight MRA (ToF-MRA) using computed tomographic angiography (CTA) as the standard of reference. Primary objectives were evaluation for superiority of structural delineation and noninferiority for detection and exclusion of clinically significant disease.

MATERIALS AND METHODS

In all, 315 subjects underwent unenhanced and contrast-enhanced MRA with 1M gadobutrol (CE-MRA) and were scanned with 1.5T MRI equipped with an at least 6-element body coil. Evaluations were based on both centralized blinded read (BR) performed by six readers as well as investigator site interpretations for the 292 subjects who completed the study. Quantitative evaluations including percent stenosis and normal vessel measurements were also performed. Secondary endpoints included identification of accessory renal arteries, diagnosis of fibromuscular dysplasia (FMD), diagnostic confidence, and need for additional imaging.

RESULTS

A total of 292 patients suspected of renal artery disease completed the study. CE-MRA demonstrated statistically significant improvement in assessability of vascular segments compared to ToF: 95.9% vs. 77.6% (P < 0.0001). In the BR, the sensitivity and specificity of CE-MRA were noninferior to ToF-MRA (53.4% vs. 46.6% and 95.1% vs. 85.7%, respectively). There was less error in the CE-MRA stenosis measurements (0.15 mm gadobutrol vs. 0.41 mm ToF, P < 0.05). FMD was correctly diagnosed more frequently, 10% more accessory renal arteries were identified (P < 0.01), diagnostic confidence increased (P < 0.01), and fewer additional imaging studies were recommended (P < 0.01).

CONCLUSION

Gadobutrol-enhanced MRA of the renal arteries has superior visualization, more accurate vessel measurements, and may serve as a CTA alternative without any ionizing radiation.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:572-581.

Unenhanced respiratory-navigated NATIVE® TrueFISP magnetic resonance angiography in the evaluation of renal arteries: Comparison with contrast-enhanced magnetic resonance angiography

PURPOSE

To compare unenhanced three-dimensional (3D) NATIVE^® true fast imaging with steady-state precession (TrueFISP) magnetic resonance (MR) angiography with the more conventional MR angiography technique obtained after intravenous administration of a gadolinium chelate in the evaluation of renal arteries and their branches in patients with suspected renal artery stenosis.

MATERIALS AND METHODS

A total of 39 patients (25 men, 14 women) with a mean age of 51.4±17.5years (SD) (range: 10-82years) were included in the study. All patients with suspected renal artery stenosis underwent unenhanced 3D NATIVE^® TrueFISP MR angiography and contrast-enhanced MR angiography. The two MR angiography methods were compared by two independent readers for image quality using a four-point scale, diagnostic performance and grading of renal artery stenosis on a total of 78 renal arteries.

RESULTS

For both readers image quality of unenhanced 3D NATIVE^® TrueFISP MR angiography (3.12 to 3.63) was greater than that of contrast-enhanced MR angiography (1.94 to 2.71) for renal artery ostium-trunk and the left renal artery segmental branches. The sensitivity of 3D NATIVE^® TrueFISP MR angiography for the diagnosis of renal artery stenosis was 100% for both readers for the right renal artery and 66% and 80% for the left renal artery for reader 1 and reader 2, respectively. Agreement between 3D NATIVE^® TrueFISP MR angiography and CE-MR angiography was 95% (74/78) for reader 1 and 92% (72/78) for reader 2.

CONCLUSION

Unenhanced NATIVE^® TrueFISP magnetic resonance angiography can play an additional role in the evaluation of renal arteries in patients with hypertension, especially in subjects at risk of nephrogenic systemic fibrosis.

Accuracy of unenhanced magnetic resonance angiography for the assessment of renal artery stenosis

Purpose

To evaluate the accuracy of unenhanced magnetic resonance angiography (U-MRA) using balanced steady-state free precession (SSFP) sequences with inversion recovery (IR) pulses for the evaluation of renal artery stenosis.

Materials and methods

U-MRA was performed in 24 patients with suspected main renal artery stenosis. Two radiologists evaluated the quality of the imaging studies and the ability of U-MRA to identify hemodynamically significant main renal artery stenosis (RAS) defined as a stenosis ≥50% when compared to gold standard tests: contrast-enhanced magnetic resonance angiography (CE-MRA) (18 patients) or digital subtraction arteriography (DSA) (6 patients).

Results

A total of 44 main renal arteries were evaluated. Of them, 32 renal arteries could be assessed with U-MRA. When CE-MRA or DSA was used as the reference standard, nine renal arteries had hemodynamically significant RAS. U-MRA correctly identified eight out of nine arteries as having ≥50% RAS, and correctly identified 22 out of 23 arteries as not having significant RAS, with a sensitivity of 88.8%, a specificity of 95.65%, positive and negative predictive value of 88.8% and 95.65%, respectively, and an accuracy of 93.75%. Renal artery fibromuscular dysplasia (FMD) was observed in the two misclassified arteries.

Conclusion

U-MRA is a reliable diagnostic method to depict normal and stenotic main renal arteries. U-MRA can be used as an alternative to contrast-enhanced magnetic resonance angiography or computer tomography angiography in patients with renal insufficiency unless FMD is suspected.

Optimization of non-contrast-enhanced MR angiography of the renal artery with three-dimensional balanced steady-state free-precession and time-spatial labeling inversion pulse (time-SLIP) at 3T MRI, in relation to age and blood velocity

PURPOSE

To determine the optimal inversion time (TI) value of three-dimensional (3D) balanced steady-state free-precession time-spatial labeling inversion pulse (time-SLIP) technique for visualization of the renal artery at 3T MRI, and to assess whether the optimal TI is affected by the subject's age and blood velocity.

MATERIALS AND METHODS

Forty-two healthy volunteers (range 20-67 years) were enrolled in the study and subjected to non-contrast-enhanced renal MR angiography. Five different TI values (1200, 1400, 1600, 1800, and 2000 ms) were selected for evaluation. For quantitative evaluation, the relative signal intensity (SI) of the main renal artery was compared with that of the renal medulla (Vessel-to-Kidney ratio; VKR). Blood velocity of the abdominal aorta was measured using 2D phase contrast technique. For qualitative evaluation, two radiologists scored the depiction of the renal pelvis and the quality of visualization of the renal artery.

RESULTS

VKR is the highest at TI = 1600 ms. A strong negative correlation between age and blood velocity was demonstrated. Regarding the qualitative evaluation, the overall image scores of renal arteries were the highest at a TI = 1800 ms for both readers. The optimal TI values in subjects below 50 years of age were 1600 and 1800 ms, whereas in subjects above 50 years of age, the optimal TI value was 1800 ms.

CONCLUSION

The optimal TI value for the visualization of renal arteries using time-SLIP technique at 3T MRI was 1800 ms. Subjects' age affected optimal TI and this is likely due to differences in the blood velocity of the abdominal aorta.

Computed tomography angiography and magnetic resonance angiography imaging of the mesenteric vasculature

Computed tomography angiography (CTA) and magnetic resonance angiography (MRA) are highly accurate cross-sectional vascular imaging modalities that have almost completely replaced diagnostic catheter angiography for the evaluation of the mesenteric vasculature. CTA is the technique of choice when evaluating patients with suspected mesenteric ischemia; it permits to differentiate between occlusive and nonocclusive etiologies, to evaluate indirect signs of bowel ischemia, and in some instances, to provide alternative diagnoses. MRA has the advantage of not using ionizing radiation and iodinated contrast agents and can be appropriate in the nonacute setting. Both CTA and MRA are suitable for the assessment of patients with suspected chronic mesenteric ischemia, allowing to evaluate the degree of atherosclerotic steno-occlusive disease and the existence of collateral circulation, as well as other nonatherosclerotic vascular pathologies such as fibromuscular dysplasia and median arcuate ligament syndrome. CTA provides excellent depiction of visceral aneurysms and has an important role to plan therapy for both occlusive and aneurysmal diseases and in the follow-up of patients after open or endovascular mesenteric revascularization procedures. This article provides an introduction to the CTA and MRA imaging protocol to study the mesenteric vasculature, the imaging findings in patients presenting with acute and chronic mesenteric ischemia and visceral aneurysms, and the value of these imaging techniques for therapy planning and follow-up.

Non-enhanced MR angiography of renal arteries: comparison with contrast-enhanced MR angiography

BACKGROUND

The main causes of renal artery stenosis (RAS) are atherosclerosis and fibromuscular dysplasia. Despite contrast-enhanced magnetic resonance angiography (CE-MRA) being a safe and reliable method for diagnosis of RAS especially in young individuals, recently it has been possible to adopt innovative technologies that do not require paramagnetic contrast agents.

PURPOSE

To assess the accuracy of steady-state free-precession (SSFP) non-contrast-enhanced magnetic resonance angiography (NC-MRA) by using a 1.5 T MR scanner for the detection of renal artery stenosis, in comparison with breath-hold CE-MRA as the reference standard.

MATERIAL AND METHODS

Sixty-three patients (33 men, 30 women) with suspected renovascular hypertension (RVHT) were examined by a 1.5T MR scanner; NC-MRA with an electrocardiography (ECG)-gated SSFP sequence was performed in 58.7% (37/63) of patients; in 41.3% (26/63) of patients a respiratory trigger was used in addition to cardiac gating. CE-MRA, with a three-dimensional gradient echo (3D-GRE) T1-weighted sequence, was performed in all patients within the same session. Maximum intensity projection (MIP) image quality, number of renal arteries, and the presence of stenosis were assessed by two observers (independently for NC-MRA and together for CE-MRA). The agreement between NC-MRA and CE-MRA as well as the inter-observer reproducibility were calculated with Bland-Altman plots.

RESULTS

MIP image quality was considered better for NC-MRA. NC-MRA identified 143 of 144 (99.3%) arteries detected by CE-MRA (an accessory artery was not identified). Fourteen stenoses were detected by CE-MRA (11 atherosclerotic, 3 dysplastic) with four of 14 (28.5%) significant stenosis. Bland-Altman plot demonstrated an excellent concordance between NC-MRA and CE-MRA; particularly, the reader A evaluated correctly all investigated arteries, while over-estimation of two stenoses occurred for reader B. Regarding NC-MRA, inter-observer agreement was excellent.

CONCLUSION

NC-MRA is a valid alternative to CE-MRA for the assessment of renal arteries.

Comparison of diagnostic accuracy of Doppler USG and contrast-enhanced magnetic resonance angiography and selective renal arteriography in patients with atherosclerotic renal artery stenosis

Background

There are many systemic complications of conventional selective renal arteriography (SRA), such as contrast-mediated nephropathy. Contrast-enhanced magnetic resonance angiography (CE-MRA) and renal artery Doppler ultrasonography (DUSG) have been used increasingly for renal artery stenosis (RAS). The aim of this study was to evaluate the accuracy of CE-MRA and DUSG as used for diagnosis of RAS.

Material/Methods

We divided 130 consecutive patients investigated for resistant hypertension into 2 groups based on age: group 1 was patients <60 years old and group 2 was patients >60 year. DUSG, CE-MRA, and SRA were performed in group 1 and group 2 patients.

Results

Seventy-two patients (24 males [M], 48 females [F]) in group 1, and 58 patients (26 M, 32 F) in group 2 were included in the study. In the evaluation of clinically significant renal artery stenosis with DUSG, in group 1 the overall sensitivity was 83.33% and overall specificity was 81.82%, and in group 2 they were 69.23% and 0%, respectively, when compared with SRA. In the evaluation of clinically significant renal artery stenosis with CE-MRA, the overall sensitivity and specificity were 92.31% and 36.36%, respectively, in group 1 and 100.00% and 73.33%, respectively in group 2, when compared with SRA.

Conclusions

CE-MRA is an accurate, non-invasive method for the diagnosis of RAS in patients above 60 years of age and DUSG may be the choice of diagnostic method for RAS in patients under 60 years of age.

Non-contrast-enhanced renal and abdominal MR angiography using velocity-selective inversion preparation

Non-contrast-enhanced MR angiography is a promising alternative to the established contrast-enhanced approach as it reduces patient discomfort and examination costs and avoids the risk of nephrogenic systemic fibrosis. Inflow-sensitive slab-selective inversion recovery imaging has been used with great promise, particularly for abdominal applications, but has limited craniocaudal coverage due to inflow time constraints. In this work, a new non-contrast-enhanced MR angiography method using velocity-selective inversion preparation is developed and applied to renal and abdominal angiography. Based on the excitation k-space formalism and Shinnar-Le-Roux transform, a velocity-selective excitation pulse is designed that inverts stationary tissues and venous blood while preserving inferiorly flowing arterial blood. As the magnetization of the arterial blood in the abdominal aorta and iliac arteries is well preserved during the magnetization preparation, artery visualization over a large abdominal field of view is achievable with an inversion delay time that is chosen for optimal background suppression. Healthy volunteer tests demonstrate that the proposed method significantly increases the extent of visible arteries compared with the slab-selective approach, covering renal arteries through iliac arteries over a craniocaudal field of view of 340 mm.

Diagnostic performance of a non-contrast-enhanced magnetic resonance imaging protocol for potential living related kidney donors

RATIONALE AND OBJECTIVES

The objective of the study was to evaluate the performance of a non-contrast-enhanced magnetic resonance (MR) imaging protocol for preoperative screening of living related kidney donors.

MATERIALS AND METHODS

Forty consecutive subjects (mean age 52.2 ± 11.3 years, range 29-73 years) underwent MR imaging with T2-weighted sequences (coronal and axial plane), with a non-contrast-enhanced respiratory-gated three-dimensional steady state free precession MR angiography (NCE-MRA) sequence and with contrast-enhanced magnetic resonance MR angiography (CE-MRA) sequences in the arterial and venous phases. Two blinded readers independently assessed arterial and venous anatomy and potential kidney lesions. Results of non-contrast-enhanced images were compared to CE-MRA and in a subgroup of 21 subjects to surgery as standard of reference.

RESULTS

Regarding arterial anatomy, NCE-MRA yielded sensitivity, specificity, and accuracy of 100%, 89%, and 91% compared to CE-MRA. Three kidneys were found to have more accessory renal arteries at NCE-MRA than at CE-MRA. In the subgroup of 21 subjects, 1 surgically proven accessory artery was depicted with NCE-MRA but not with CE-MRA. Accuracy of T2-weighted images regarding accessory veins or variant venous course was 99%, with one missed circumaortic vein on T2-weighted images. Two simple cysts were missed on T2-weighted and NCE-MRA but not on CE-MRA images.

CONCLUSION

A non-contrast-enhanced MR imaging protocol including NCE-MRA and T2-weighted images allows for the accurate screening of living related kidney donors and may serve as an alternative to CE-MRA.