Published online before print May 10, 2007, 10.1148/radiol.2433060184
(Radiology 2007;244:144-150.)
© RSNA, 2007
Renal Artery Stenosis in Swine: Feasibility of MR Assessment of Renal Function during Percutaneous Transluminal Angioplasty1
Jonathan K. Park, BA,
Thomas K. Rhee, MD,
Ty A. Cashen, BS,
Wanyong Shin, MS,
Brian E. Schirf, MD,
James A. Gehl, BS,
Andrew C. Larson, PhD,
Pottumarthi V. Prasad, PhD,
Debiao Li, PhD,
Timothy J. Carroll, PhD, and
Reed A. Omary, MD, MS
1 From the Departments of Radiology (J.K.P., T.K.R., T.A.C., W.S., B.E.S., J.A.G., A.C.L., P.V.P., D.L., T.J.C., R.A.O.) and Biomedical Engineering (T.A.C., W.S., D.L., T.J.C., R.A.O.), Northwestern University Feinberg School of Medicine, 448 E Ontario St, Suite 700, Chicago, IL 60611. Received January 30, 2006; revision requested March 29; revision received June 16; accepted June 23; final version accepted October 25. R.A.O. supported in part by National Institutes of Health grant K08 DK60020. J.K.P. supported in part by Northwestern University Feinberg School of Medicine Summer Student Research Grant.
Address correspondence to R.A.O. (e-mail: reed{at}northwestern.edu).
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ABSTRACT
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Purpose: To prospectively test—in a swine model of renal artery stenosis (RAS)—the hypothesis that magnetic resonance (MR) imaging can reveal changes in renal function at the time of percutaneous transluminal angioplasty (PTA).
Materials and Methods: In this animal care and use committee–approved study, high-grade unilateral RAS was surgically induced in six pigs. MR imaging at 3.0 T was used for intraprocedural assessment of the anatomic and physiologic changes induced by x-ray–guided PTA. With use of MR imaging, changes in single-kidney glomerular filtration rate, extraction fraction, and renal blood flow were assessed during PTA. The arterial diameter of stenosis before and after PTA was assessed by using conventional digital subtraction angiography. Mean changes in functional and anatomic parameters were compared by using the Wilcoxon signed rank test (
= .05).
Results: At digital subtraction angiography, the mean percentage of stenosis was 69% ± 10 (standard deviation) before PTA and 26% ± 10 after PTA (P < .03). Mean pre- and post-PTA extraction fraction values were 0.11 ± 0.03 and 0.19 ± 0.06, respectively (P < .03). The mean single-kidney glomerular filtration rate before PTA, 19 mL/min ± 13, increased to 41 mL/min ± 33 after PTA (P < .03). There was no significant change in mean renal blood flow after PTA (P = .44).
Conclusion: In swine, MR imaging can reveal changes in renal function after x-ray–guided PTA for unilateral RAS.
© RSNA, 2007
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INTRODUCTION
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Renal vascular disease, an important cause of hypertension and kidney disease (1,2), is usually caused by atherosclerotic stenosis of the main renal artery (3). Conventional (x-ray) digital subtraction angiography (DSA) can be used to detect and quantify the anatomic severity of atherosclerotic stenosis. However, an anatomic diagnosis of renal artery stenosis (RAS) does not always correlate with the functional significance of the stenosis (4). Knowledge of the functional significance of an RAS can guide the selection of candidates for therapy and help predict treatment outcomes. Currently, functional significance can be assessed at the time of angiography by measuring the hemodynamic pressure gradients across the stenosis. This technique is limited because it can yield overestimates of the true resting gradient (5) and depends heavily on renal blood flow (RBF) rates (6). Thus, an alternative method of quantifying the effect of RAS would enable accurate selection of patients who would benefit the most from accepted therapies, including percutaneous transluminal angioplasty (PTA) (7).
The glomerular filtration rate (GFR) is an established measure of renal function. Techniques to measure GFR include nuclear medicine imaging and measurements of serum creatinine level and inulin clearance (8). The disadvantages of these techniques include (a) the ability to estimate global kidney function only as opposed to the single-kidney GFR (skGFR), (b) prolonged time requirements that preclude the use of these approaches at the time of therapy, and (c) the inability to depict the renal artery anatomy (9–11).
In contrast to previous methods of evaluating GFR, magnetic resonance (MR) imaging (12) (a) enables noninvasive measurement of renal function (13–15), (b) depicts the blood vessel anatomy, and (c) spares patients from exposure to the ionizing radiation typical of conventional (x-ray) angiography. MR imaging also rapidly yields skGFR values that are within 11% of reference-standard inulin measurements (12). MR imaging has been used successfully to estimate RBF in humans (16) and to measure the GFR in pigs with normal (12) and stenotic (17) kidneys and in humans with normal kidneys (13,18).
Although MR imaging has been used to measure GFR in a swine ischemia model of RAS (17), the feasibility of intraprocedural MR imaging to assess changes in renal function during renal PTA remains unknown. If MR imaging can be demonstrated to depict changes in renal function at the time of PTA, then it might help determine the functional end point of therapy when it is used in the setting of hybrid conventional DSA and MR interventional examinations (19). Thus, the purpose of our study was to prospectively test—in a swine model of RAS—the hypothesis that MR imaging can reveal changes in renal function at the time of PTA.
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MATERIALS AND METHODS
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Animal Model
Our institutional animal care and use committee approved these experiments. We chose male domestic pigs younger than 6 months as the animal model because their size facilitates percutaneous vascular catheterization and their renal anatomy and physiologic characteristics closely resemble those of humans (20). All pigs weighed 21–26 kg and had no anatomic vascular irregularities, as assessed with conventional DSA. Before surgery, the pigs were tranquilized intramuscularly with 10–15 mg of ketamine per kilogram of body weight (Ketaset; Fort Dodge Laboratories, Fort Dodge, Iowa), 1–2 mg/kg xylazine (Xyla-ject; Phoenix Pharmaceuticals, St Joseph, Mo), and 0.05 mg/kg atropine (Atroject; Phoenix Pharmaceuticals). The animals were then intubated for general anesthesia and were administered isoflurane (Iso-Flo; Abbott Laboratories, North Chicago, Ill). In six pigs, we surgically induced four left RAS and two right RAS by using reverse cable ties (bundle diameter, 1.5–20.6 mm) (Gardner Bender, Milwaukee, Wis) sterilized in ethylene oxide (21). We asymmetrically induced four stenoses rather than three on the left because surgery could be executed more rapidly on the left, reducing the risk of surgical complications. A small cohort size was selected for this initial feasibility study.
In a sterile surgical environment, the pigs were placed in a prone position and the flank area was prepared sterilely with betadine. An incision was made in the flank, and blunt dissection was performed through the subcutaneous tissue and muscle layers until the kidney and renal artery were isolated. Two investigators (B.E.S., T.K.R.) and two animal technicians aimed to produce a hemodynamically significant (>50% of vessel diameter) stenosis by constricting one cable tie around one renal artery in each pig. The surgical incisions were then closed by using standard three-layer suture techniques, and each pig was monitored until it recovered from anesthesia.
DSA Examination
With use of the time interval reported in previous studies (22,23), the animals were transferred to the conventional angiography suite 1–2 weeks after surgery and were tranquilized and intubated for anesthesia before PTA. The following protocol was then performed in each pig: (a) Baseline DSA was performed to reveal the RAS; this took an average of 20 minutes; (b) 10 minutes later the animals were transferred to the MR unit for pre-PTA baseline renal anatomic and functional measurements, which took 45 minutes; (c) 10 minutes later the animals were transferred to the angiography suite for PTA, which took 30 minutes; and (d) 10 minutes later the animals were transferred back to the MR unit for post-PTA imaging, which took 10 minutes. The average total procedural time was 2 hours 15 minutes.
After sterile preparation, we accessed each pig's femoral artery by using a micropuncture introducer set (Cook, Bloomington, Ind) and inserted a 7-F sheath over a .035-inch guidewire. With x-ray fluoroscopic guidance (PowerMobil; Siemens Medical Solutions, Erlangen, Germany), we advanced a 5-F multiple–side hole angiographic catheter (Royal Flush II; Cook) into a suprarenal position in the abdominal aorta. We then performed baseline DSA by using 20 mL of iodinated contrast agent (iohexol, Omnipaque 350; Amersham Health, Princeton, NJ) to visualize the stenosis and obtain a reference standard for stenosis measurements (B.E.S., R.A.O.). We initially administered 5000 U of heparin intravenously for anticoagulation during catheterization and subsequently administered 1000-U doses of heparin hourly. Transdermal nitroglycerine (200 µg) was administered to reduce vasospasm. Forty-five minutes before MR imaging, 2.5 mg of enalapril (Enalaprilat; Abbott Laboratories) was administered intravenously, as described previously (24). To determine the hematocrit level for subsequent GFR measurements, a 2–4-mL sample of arterial blood was taken from the arterial catheter before the animal was transferred to the MR unit.
Pre-PTA MR Imaging
MR examinations were performed with a whole-body 3.0-T MR unit (Trio; Siemens Medical Solutions) by using an eight-channel cardiac-array coil. Contrast material–enhanced MR angiography, T1-weighted MR examination of arterial and venous blood for extraction fraction (EF) measurement, and phase-contrast flow-quantification MR imaging were performed (T.A.C., W.S.). After localization of the kidneys and renal arteries, coronal time-resolved three-dimensional contrast-enhanced MR angiograms (25) were acquired with a time-resolved echo-sharing angiographic pulse sequence (3.61/1.11 [repetition time msec/echo time msec], 1.1 x 1.1 x 4.2-mm voxels, 280 x 280 x 50-mm field of view, 256 x 256 x 20 matrix, 3 seconds per frame, 25° flip angle, 560 Hz/pixel bandwidth, in-plane and through-plane phase-encoding partial Fourier factor of 6/8) to define the renal artery anatomy, an in-plane generalized autocalibrating partially parallel acquisition factor of two (26) with 24 reference lines, and a three-region time-resolved imaging of contrast kinetics, or TRICKS, acquisition (25).
Unlike in some previous studies, in which intravenous gadolinium-based contrast agent injections were used to measure the GFR (17), we used intraarterial injections. On the basis of the results of a previous intraarterial renal MR angiographic study (23), we injected 40 mL of an 8% gadolinium-based contrast agent solution (gadopentetate dimeglumine, Magnevist; Berlex, Wayne, NJ) through the abdominal aorta catheter at 6 mL/sec by using a power injector (Spectris Solaris; Medrad, Indianola, Pa) during the contrast-enhanced MR angiographic acquisition. Each animal was administered 0.05 mmol/kg gadopentetate dimeglumine, which is below the Food and Drug Administration dose limit (0.3 mmol/kg per day). Three-dimensional TRICKS imaging, which can serve as a fluoroscopic examination, does not require synchronization with contrast agent administration.
Three-plane (coronal, sagittal, and transverse) three-dimensional maximum intensity projection MR angiograms were used to localize the renal artery as on the two-dimensional phase-contrast and T1-weighted images. Image section positions that (a) were perpendicular to the renal artery, (b) were proximal to the stenosis, and (c) included a segment of ipsilateral renal vein (for EF analysis) were chosen. Flow quantification and T1 mapping were performed and yielded images for RBF and EF calculations, respectively. A two-dimensional phase-contrast sequence (95/3.2, 2.5 x 3.1 x 5.0-mm voxels, 320 x 160-mm field of view, 128 x 51 matrix, 30° flip angle, 400 Hz/pixel bandwidth, six acquired signals, 25 phases, seven segments, 80 cm/sec velocity encoding) was used to quantify blood flow. To calculate EF, an inversion-recovery Look-Locker echo-planar imaging sequence (23/11, 2.5 x 2.5 x 5.0-mm voxels, 320 x 160-mm field of view, 128 x 64 matrix, 20° flip angle, 1220 Hz/pixel bandwidth, 0.98-msec echo spacing, 120 phases after inversion pulse) (10) was used to determine the T1 of arterial and venous blood. Arterial blood and venous blood T1 values were determined by using a null point measurement.
X-ray Fluoroscopy–guided PTA
A guide catheter (Lieberman B; Cook) was inserted through the 7-F femoral sheath and advanced to the level of the renal artery in the abdominal aorta. A 0.035-inch-diameter guidewire (TAD II; Mallinckrodt, St Louis, Mo) tapered to 0.018 inch distally was used to cross the stenosis. A 5–6-mm-diameter noncompliant balloon catheter (Cordis Endovascular, Warren, NJ) was introduced through the sheath to the level of the RAS; then PTA to 8 atm of pressure was performed with conventional methods by two interventionalists (B.E.S., R.A.O.) who had 13 years combined experience performing this procedure. Once PTA was completed, the balloon catheter was removed and a standard multipurpose angled, shaped angiographic catheter (Royal Flush Plus; Cook) was placed suprarenally for post-PTA conventional DSA. After completion of DSA, the pigs were transferred back to the MR unit for post-PTA renal functional measurements, which were performed by using the same MR sequences and parameters used to perform the pre-PTA measurements in each animal.
Necropsy
After all imaging examinations were completed, the pigs were sacrificed by using sodium pentobarbital (1 mL per 22 kg) (Beauthanasia-D; Schering-Plough Animal Health, Kenilworth, NJ). The kidneys were examined at necropsy to confirm successful PTA results, as determined on the basis of the complete opening of the cable ties. The renal arteries were inspected (T.K.R.) to verify the absence of injury, such as that due to puncturing.
Data Analyses
All functional data were analyzed off-line by using a computer workstation (Leonardo; Siemens Medical Solutions). Parameter values related to kidney function were calculated by using pre- and post-PTA image findings (J.K.P., J.A.G.). To measure RBF, the phase-contrast MR images were analyzed by using an approach similar to the technique described by Bax et al (16). The phase-contrast images were used to select a circular region of interest 4–5 mm in diameter that encompassed the renal artery (J.K.P.). The analysis software automatically propagated these regions of interest throughout the cardiac cycle. Each region of interest on each image was refined manually to account for arterial pulsatility. Mean blood flow rates for an entire cycle were used to calculate the GFR. Clinically, the flow quantification performed by using phase-contrast MR imaging has been estimated to be more than 75% accurate (16).
The EF was calculated from arterial blood and venous blood T1 measurements, which were based on gadopentetate dimeglumine concentrations in the blood (10,12–14,17,27), by using the equation EF = [(T1V – T1A) · T1B]/[(T1B – T1A) · T1V], where T1A and T1V are the T1 values of arterial blood and venous blood, respectively, determined from the signal null point and T1B is the T1 of blood in the absence of gadopentetate dimeglumine. With use of contrast-enhanced MR angiograms and phase-contrast MR images to aid in localization, regions of interest encompassing the renal artery and the renal vein were drawn. The skGFR was calculated as the product of EF and RBF (28): skGFR = EF · RBF · (1 – H), where H is the hematocrit level. In addition, renal measurements were performed on the contralateral side in three animals to serve as additional internal control values.
To assess changes in vessel diameter after PTA, pre- and postprocedural DSA images were analyzed on the computer workstation (J.K.P., J.A.G.) by using the full width at half maximum (FWHM) method (29) and the ImageJ 1.32j computer program (National Institutes of Health, Bethesda, Md). Percentage of stenosis was measured by using the equation [1 – (FWHMs/FWHMpa)] · 100, where FWHMs and FWHMpa are the FWHM values at the stenosis and at the proximal artery, respectively.
Statistical Analyses
Mean pre- and post-PTA values and standard deviations were calculated and compared for all anatomic (stenosis degree) and functional (RBF, EF, and skGFR) parameters (J.K.P.). Functional parameters were assessed on the stenotic side in all pigs and on the contralateral side in three animals; thus, statistical analysis data for only functional changes in the stenotic kidneys were available. Percentage changes in luminal area and skGFR values were also compared. Statistical differences were determined for anatomic changes, stenotic kidney functional changes, and correlation between changes in skGFR and arterial lumen by using a two-tailed Wilcoxon signed rank test (P = .05) (J.K.P.). We used GraphPad InStat, version 3.0, software (GraphPad Software, San Diego, Calif) to perform the statistical analyses.
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RESULTS
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Stenosis Data
Unilateral stenosis was induced successfully in all six animals without renal function deterioration. Conventional DSA findings verified that the baseline diameter stenosis for each RAS was more than 50%. Each stenosis was successfully reduced with PTA (Fig 1). In all pigs, we confirmed the presence of each unilateral RAS and observed anatomic improvement in the RAS after the procedure by using MR imaging (Fig 2). DSA stenosis percentage measurements ranged from 60% to 85% before PTA and from 4% to 35% after PTA. The mean percentage of stenosis at DSA before PTA was 69% ± 10, which decreased significantly to 26% ± 10 after the procedure (P < .03).
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Figure 1a: Coronal conventional intraprocedural DSA images of PTA in a unilateral model of RAS in a pig. (a) Pre-PTA DSA image shows hemodynamically significant RAS (arrow) in right renal artery. (b) Post-PTA DSA image shows dilatation (arrow) of the stenotic artery achieved with a balloon catheter.
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Figure 1b: Coronal conventional intraprocedural DSA images of PTA in a unilateral model of RAS in a pig. (a) Pre-PTA DSA image shows hemodynamically significant RAS (arrow) in right renal artery. (b) Post-PTA DSA image shows dilatation (arrow) of the stenotic artery achieved with a balloon catheter.
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Figure 2a: Coronal maximum intensity projection dynamic T1-weighted contrast-enhanced MR angiograms (3.61/1.11) of right unilateral RAS (arrow) (a) before and (b) after PTA in a pig.
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Figure 2b: Coronal maximum intensity projection dynamic T1-weighted contrast-enhanced MR angiograms (3.61/1.11) of right unilateral RAS (arrow) (a) before and (b) after PTA in a pig.
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Renal Function
In addition to the anatomic changes in RAS identified with conventional DSA, changes in renal function after PTA were detected with MR imaging (Fig 3). Functional (GFR, EF, and RBF) measurements obtained before and after PTA (Fig 4) revealed mean skGFR values of 19 mL/min ± 13 before PTA and 41 mL/min ± 33 after PTA. Increases in skGFR after PTA were significant (P < .03). In addition, the mean EF was 0.11 ± 0.03 before PTA and 0.19 ± 0.06 after PTA; this change was also significant (P < .03). The mean pre-PTA RBF, 266 mL/min ± 182, increased to 311 mL/min ± 253 after PTA; this change was not significant (P = .44). Overall, percentage improvements in luminal area were accompanied by significant improvements in skGFR (P < .04).
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Figure 3a: Sagittal MR images used to measure renal function in unilateral model of left RAS in a pig. (a) On two-dimensional phase-contrast MR image (95/3.2, 80 cm/sec velocity encoding), the renal artery (R1) is located inferiorly, whereas the renal vein (R2) is located above the renal artery. (b) On Look-Locker echo-planar MR image (23/11), the renal artery (region of interest 1) again is located inferiorly, whereas the renal vein (region of interest 2) is located above the renal artery.
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Figure 3b: Sagittal MR images used to measure renal function in unilateral model of left RAS in a pig. (a) On two-dimensional phase-contrast MR image (95/3.2, 80 cm/sec velocity encoding), the renal artery (R1) is located inferiorly, whereas the renal vein (R2) is located above the renal artery. (b) On Look-Locker echo-planar MR image (23/11), the renal artery (region of interest 1) again is located inferiorly, whereas the renal vein (region of interest 2) is located above the renal artery.
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Figure 4a: Graphs illustrate MR measurements of renal function before and after PTA in pigs. Pigs 1–4 had left RAS, whereas pigs 5 and 6 had right RAS. (a) Comparison of pre- and post-PTA GFR measurements in unilateral RAS model. (b) Comparison of pre- and post-PTA EF measurements in unilateral RAS model; all values measured after PTA were greater than those measured before PTA. (c) Comparison of pre- and post-PTA RBF measurements in unilateral RAS model.
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Figure 4b: Graphs illustrate MR measurements of renal function before and after PTA in pigs. Pigs 1–4 had left RAS, whereas pigs 5 and 6 had right RAS. (a) Comparison of pre- and post-PTA GFR measurements in unilateral RAS model. (b) Comparison of pre- and post-PTA EF measurements in unilateral RAS model; all values measured after PTA were greater than those measured before PTA. (c) Comparison of pre- and post-PTA RBF measurements in unilateral RAS model.
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Figure 4c: Graphs illustrate MR measurements of renal function before and after PTA in pigs. Pigs 1–4 had left RAS, whereas pigs 5 and 6 had right RAS. (a) Comparison of pre- and post-PTA GFR measurements in unilateral RAS model. (b) Comparison of pre- and post-PTA EF measurements in unilateral RAS model; all values measured after PTA were greater than those measured before PTA. (c) Comparison of pre- and post-PTA RBF measurements in unilateral RAS model.
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In addition to measurements performed in the kidney with RAS, renal function measurements were also performed contralaterally (on the right) in three pigs. Minor changes in function after PTA were recorded in this small subset of normal kidneys; however, this small sample size prevented us from performing statistical analysis. In the normal kidneys, mean pre- and post-PTA skGFR values were 11 mL/min ± 4.5 and 13 mL/min ± 8.3, respectively. Mean pre- and post-PTA EF values were 0.09 ± 0.03 and 0.09 ± 0.02, respectively. Mean pre- and post-PTA RBF values were 186 mL/min ± 88 and 196 mL/min ± 115, respectively.
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DISCUSSION
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Our study results demonstrate the feasibility of MR imaging to document intraprocedural changes in renal function at the time of renal PTA. In an acute model of RAS in swine, we successfully dilated six unilateral stenotic renal arteries with x-ray fluoroscopic guidance, as verified by using conventional DSA. We observed a significant improvement in the mean percentage of stenosis, from 69% ± 10 before PTA to 26% ± 10 after PTA. These anatomic changes resulted in prompt improvement in renal function (EF and skGFR) at the time of the procedure. After PTA, the mean EF increased from 0.11 to 0.19 (P < .03) and the mean skGFR increased from 19 mL/min ± 13 to 41 mL/min ± 33 (P < .03).
Our study results suggest that functional changes can be observed at the time of PTA. In all animals, we recorded significant increases in EF and GFR after PTA. Unlike the changes in EF and GFR measurements, significant changes in RBF were not seen after PTA. Prasad et al (30) proposed that the lack of correlation between RBF and anatomic stenosis could be due to the varying capacity of kidneys to regulate blood flow in the presence of a stenosis. Also, the stenosis in the swine model described herein may not represent all the types of RAS encountered clinically (29). The absence of significant changes in RBF may also suggest some insensitivity in flow measurements. Last, the ischemic kidney was used primarily as its own control because significant differences in GFR and EF between stenotic and normal kidneys have been demonstrated (17).
In our study, we used a 3.0-T MR unit, whereas 1.5-T units have been used in previous comparable studies (12,17). With cardiac MR imaging, use of a 3.0-T unit facilitates improved image quality, with a 53% increase in the blood signal-to-noise ratio compared with the signal-to-noise ratio achieved at 1.5 T (31). Thus, use of the 3.0-T unit may have enabled us to locate vessels more accurately than we would have with a lower-field-strength unit. This advantage is particularly important when analyzing images in a swine model, where renal vessels are smaller than those in humans and thus more difficult to localize. Thus, a higher spatial resolution and a higher signal-to-noise ratio are desirable.
In our study, we also used the renal artery for EF measurements, whereas the inferior vena cava was used in previous studies (28). Buonocore and Katzberg (32) questioned the validity of substituting the inferior vena cava with the renal artery. By using a 3.0-T MR unit and the specific T1-weighted imaging parameters described, we were able to successfully locate the renal artery on T1-weighted images.
Our study had several important limitations. Although we surveyed acute RAS in our preclinical experimental model, it is still unclear whether our results can be extrapolated to patients with chronic RAS. Given our promising results, however, translation of our protocol into early clinical studies involving the use of hybrid DSA and MR units (33) holds promise. Also, in addition to PTA, intraarterial stent placement is frequently used in RAS therapy, so future experiments of GFR measurements after stent placement seem warranted. Before our study results are applied to the clinical arena, however, the effectiveness of MR imaging in measuring the GFR at the time of PTA needs to be validated with clinical 1.5-T MR units.
Another study limitation was that the right-kidney GFR measurements—in both affected and normal kidneys—were consistently lower than the left-kidney measurements (normal right vs normal left and stenotic right vs stenotic left). Possible explanations for this finding include variable autoregulatory responses, delayed systemic responses to enalapril administration, or a combination of these mechanisms. Alternatively, the sample size may not have reflected the true normal range of right-kidney GFR measurements. Future studies with larger sample sizes are needed to assess the functional parameters for the right kidney and the applicability of the proposed renal function MR techniques to all stenoses.
Finally, systemic measurements of kidney function with use of inulin clearance were not performed, as the goal of our study was to assess skGFR changes rather than the systemic values obtained by using inulin clearance. Furthermore, the prolonged sampling time (6–24 hours) required for accurate inulin clearance precluded the use of inulin during the PTA procedures.
Practical applications: Our study results demonstrate the feasibility of MR imaging for monitoring improvement in kidney function after PTA in a swine model of RAS. The encouraging results of MR imaging–guided PTA achieved in other studies (22) suggest that MR imaging may serve as the sole method of guiding PTA and monitoring functional effect. Given that MR imaging represents a potentially effective method of real-time kidney function assessment, we postulate that in the future, MR imaging might be helpful in selecting candidates for therapy and in predicting the success of endovascular therapy.
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ADVANCES IN KNOWLEDGE
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- MR assessment of renal function before and after therapeutic percutaneous transluminal angioplasty (PTA) for renal artery stenosis is feasible.
- Use of a 3.0-T MR unit enables measurement of significantly (P < .04) increased renal function in swine after PTA.
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ACKNOWLEDGMENTS
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The authors thank Kathleen R. Harris, BS, and Richard Tang, MD, of the Department of Radiology, Northwestern University Feinberg School of Medicine, for their expert assistance with the animals.
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FOOTNOTES
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Abbreviations: DSA = digital subtraction angiography • EF = extraction fraction • GFR = glomerular filtration rate • PTA = percutaneous transluminal angioplasty • RAS = renal artery stenosis • RBF = renal blood flow • skGRF = single-kidney GFR
Authors stated no financial relationship to disclose.
Author contributions: Guarantors of integrity of entire study, J.K.P., R.A.O.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, J.K.P., T.K.R., T.A.C., W.S., J.A.G., P.V.P., D.L., T.J.C., R.A.O.; experimental studies, all authors; statistical analysis, J.K.P., T.K.R., R.A.O.; and manuscript editing, all authors
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ABSTRACT
INTRODUCTION
