Rationale and Objectives
Magnetic resonance angiography (MRA) is a well-established modality for the assessment of renal artery stenosis. Using dedicated quantitative analyses, MRA can become a useful tool for assessing renal artery dimensions in patients referred for renal sympathetic denervation (RDN) and for providing accurate measurements of vascular response after RDN. The purpose of this study was to test the reproducibility of a novel MRA quantitative imaging tool and to validate these measurements against intravascular ultrasound (IVUS).
Materials and Methods
In nine patients referred for renal denervation, renal artery dimensions were measured. Bland–Altman analysis was used to assess the intraobserver and interobserver reproducibility.
Results
Mean lumen diameter was 5.8 ± 0.7 mm, with a very good intraobserver and interobserver variability of 0.7% (reproducibility: bias, 0 mm; standard deviation [SD], 0.1 mm) and 1.2% (bias, 0 mm; SD, 0.1 mm), respectively. Mean total lumen volume was 1035.3 ± 403.6 mm 3 with good intraobserver and interobserver variability of 2.9% (bias, −9.7 mm 3 ; SD, 34.0 mm 3 ) and 2.8% (bias, −11.4 mm 3 ; SD, 42.4 mm 3 ). The correlation (Pearson R ) between mean lumen diameter measured with MRA and IVUS was 0.750 ( P = .002).
Conclusions
Using a novel MRA quantitative imaging tool, renal artery dimensions can be measured with good reproducibility and accuracy. MRA-derived diameters and volumes correlated well with IVUS measurements.
Percutaneous renal sympathetic denervation (RDN) is currently being studied as a potential treatment to lower sympathetic nerve activity in a broad spectrum of diseases . At present, more than 53 devices are available to disrupt renal afferent and efferent nerves traveling along the renal arterial wall. Besides the fact that initial promising, but noncontrolled studies on clinical efficacy in patients with therapy-resistant hypertension were recently challenged by a negative randomized controlled trial, data on long-term safety are mainly limited to the use of the first-generation radiofrequency devices . The currently available data on the incidence of renal artery stenosis, mostly derived from duplex ultrasound findings, are showing a low rate of adverse events, both at short and longer term follow-up . Published data from computed tomography angiography (CTA) or magnetic resonance angiography (MRA) report only binary outcomes , precluding firm conclusion on the true vascular response to RDN itself. As new renal denervation systems are being introduced, there is a need for dedicated volumetric noninvasive imaging tools to accurately assess renal artery integrity at the medium to long term . Furthermore, balloon-based RDN devices require accurate sizing to avoid complications due to oversizing . The aim of the present study was to evaluate a new software tool allowing automated vessel segmentation for quantitative renal artery lumen dimension assessment. Intraobserver and interobserver reproducibility were studied, and MRA-derived measurements were validated with intravascular ultrasound (IVUS).
Materials and methods
Patient Selection
Nine consecutive patients underwent both MRA and preprocedural IVUS at the time of the renal denervation procedure. Because of an early trifurcation in the vessel in one patient, automated segmentation with MRA was not successful in one artery. For the MRA analyses, 17 vessels were used. For the correlation analyses between MRA and IVUS, MRA vessel length was determined and manually adjusted on the basis of the length of the IVUS pullback with either the ostium or bifurcation as landmark. Because of a lack of IVUS measurement in 1 vessel and a lack of visualization of either bifurcation or ostium, a total of 16 arteries in which both MRA and IVUS data were available were used for validation of MRA against IVUS measurements. The study was approved by the hospital ethics committee and conforms to the declaration of Helsinki. All patients provided written informed consent before inclusion.
Magnetic Resonance Angiography Acquisition
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MRA Analysis
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IVUS Acquisition
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IVUS Analysis
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Statistical Analysis
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Results
Segmentation Algorithm and Renal Artery Dimensions
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Table 1
Renal Artery Dimensions After Adjustments with IVUS References
Parameter MRA, Mean ± SD; n = 14 MRA Range IVUS, Mean ± SD; n = 14 IVUS Range_P_ Value Minimum lumen diameter (mm) 5.2 ± 0.7 4.1–6.4 5.2 ± 0.7 4.2–6.7 .947 Mean lumen diameter (mm) 5.8 ± 0.7 4.6–7.1 5.9 ± 0.6 4.7–7.0 .485 Total lumen volume (mm 3 ) 861.9 ± 407.3 406.20–1687.2 902.9 ± 369.4 471.3–1527.5 .248
IVUS, intravascular ultrasound; MRA, magnetic resonance angiography; SD, standard deviation.
A paired t test is used to test differences between the mean values for MRA and IVUS.
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Intraobserver Reproducibility MRA
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Interobserver Reproducibility MRA
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Validation of MRA Dimensions Against IVUS
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Discussion
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MRA Technique
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Validation with IVUS
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Clinical Applicability
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Limitations
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Conclusions
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Acknowledgments
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Supplementary Data
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Supplementary Tables 1 and 2
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