Breath-hold 3D gadolinium-enhanced subtraction MRA in the detection of transplant renal artery stenosis

Diagnostic Performance of Magnetic Resonance Angiography for Artery Stenosis After Kidney Transplant: A Systematic Review and Meta-Analysis

RATIONALE AND OBJECTIVES

Magnetic resonance angiography (MRA) is used to diagnose artery stenosis after kidney transplant. However, there is a lack of applicable consensus guidelines, and the diagnostic value of this technique is unclear. Therefore, the aim of the present study was to evaluate the diagnostic performance of MRA for the detection of artery stenosis after kidney transplant.

MATERIALS AND METHODS

We searched PubMed, Web of Science, Cochrane Library, and Embase from database inception to September 1, 2022. Two independent reviewers assessed the methodological quality of eligible studies using the quality assessment of diagnostic accuracy studies-2 tool. The diagnostic odds ratio, pooled sensitivity, and specificity values, positive likelihood ratios, and negative likelihood ratios were calculated to synthesize data with a bivariate random-effects model. Meta-regression analysis was performed in cases of high among-study heterogeneity.

RESULTS

Eleven studies were included in the meta-analysis. The area under the summary receiver operating characteristic curve was 0.96 (95% confidence interval [CI]: 0.94-0.98). The pooled sensitivity and specificity values for MRA in diagnosing artery stenosis after kidney transplant were 0.96 (95% CI: 0.76-0.99) and 0.93 (95% CI: 0.86-0.96), respectively.

CONCLUSION

MRA demonstrated high sensitivity and specificity for diagnosing artery stenosis after kidney transplant, suggesting that it may be used reliably in clinical practice. However, further large-scale studies are required to validate the present findings.

Visualization of the renal artery in kidney transplant patients using time-resolved computed tomography angiography

Background

Transplant renal artery stenosis (TRAS) is a post-operative complication which most often occurs between 3 months and 2 years after transplantation. TRAS is associated with kidney failure and hypertension and, thereby, with an increased risk of cardiovascular events.

Purpose

The purpose of this retrospective study was to report our experience of perfusion computed tomography angiography (P-CTA) to identify a 50% lumen reduction (as compared to digital subtraction angiography, DSA), assess its subjective image quality and evaluate if contrast-induced acute kidney injury (CI-AKI) occurred.

Material and Methods

All 13 patients who had undergone P-CTA for suspected TRAS at our institution were retrospectively evaluated. At P-CTA, eight or 12 g of iodine were administered intravenously, and five to seven scan sequences were merged into time-resolved images after motion correction. Eight patients underwent subsequent DSA.

Results

The average patient weight was 76 kg (range 55-97 kg). Image quality was rated as good or excellent for all patients, and pathological changes were shown in 10 of 13 patients undergoing P-CTA. Two patients had a serum creatinine increase of >26 μmol/L during the first 3 days, but serum creatinine was significantly lower in all patients 1 month after P-CTA (165+/-69 μmol/L versus 232+/-66 μmol/L, P < .01). The diagnosis at P-CTA was verified in all eight patients who underwent DSA. However, in two cases with suspected stenosis, renal function was restored without angioplasty.

Conclusion

Anatomy and blood flow of the transplant renal artery can be visualized using less than a third of the standard contrast media dose by using P-CTA technique.

Comparing the diagnostic accuracy of contrast-enhanced computed tomographic angiography and gadolinium-enhanced magnetic resonance angiography for the assessment of hemodynamically significant transplant renal artery stenosis

To compare diagnostic accuracy of contrast-enhanced computed tomographic angiography (CTA) and gadolinium-enhanced magnetic resonance angiography (MRA) for the assessment of hemodynamically significant transplant renal artery stenosis (TRAS). After institutional review board approval, records of 27 patients with TRAS confirmed on digital subtraction angiography (DSA) were retrospectively reviewed. A total of 13 patients had MRA and 14 had CTA before DSA. Two board-certified fellowship-trained radiologists, one each from interventional radiology and body imaging blindly reviewed the DSA and CTA or MRA data, respectively. Sensitivity (SN), specificity (SP), positive predictive value, and negative predictive value of MRA and CTA were estimated using 50% stenosis as the detection threshold for significant TRAS. These parameters were compared between modalities using the Fisher exact test. Bias between MRA or CTA imaging and DSA was tested using the Wilcoxon signed-rank test. Two patients were excluded from the MRA group owing to susceptibility artifacts obscuring the TRAS. The correlation between MRA and DSA measurements of stenosis was r = 0.57 (95% CI:-0.02, 0.87; P = 0.052) and between CTA and DSA measurements was r = 0.63 (95% CI: 0.14, 0.87; P = 0.015); the difference between the 2 techniques was not significant (P = 0.7). Both imaging modalities tended to underestimate the degree of stenosis when compared with DSA. MRA group (SN and SP: 56% and 100%, respectively) and CTA group (SN and SP: 81% and 67%, respectively). There were no significant differences in detection performance between modalities (P>0.3 for all measures). We did not find that either modality had any advantage over the other in terms of measuring or detecting significant stenosis. Accordingly, MRA may be preferred over CTA after positive color Doppler ultrasound screening when not contraindicated owing to lack of ionizing radiation or nephrotoxic iodinated contrast. However, susceptibility of artifacts owing to surgical clips at the anastomosis may limit diagnostic utility of MRA as found in 2 of 13 patients. Trend towards no significant difference between the CTA and enhanced MRA in the detection of hemodynamically significant TRAS.

Renal transplant imaging using magnetic resonance angiography with a nonnephrotoxic contrast agent

BACKGROUND

In renal allograft recipients presenting with graft dysfunction, it is critical to determine the patency of the transplant vasculature to guide clinical management. Conventional modalities such as Doppler ultrasound, contrast-enhanced computed tomography, magnetic resonance angiography (MRA), and noncontrast MRA are each of limited use because of technical factors and toxicity of standard contrast agents. The purpose of this study was to retrospectively review our institutional experience with renal transplant MRA using ferumoxytol (a nonnephrotoxic medication) as a contrast agent and evaluate its use in the assessment of allograft vascular patency in patients with graft dysfunction, either delayed or slow graft function within hours to days after kidney transplantation or acute kidney injury weeks to months after kidney transplantation.

METHODS

Sixteen kidney transplant recipients were retrospectively identified who underwent ferumoxytol-enhanced MRA after a nondiagnostic ultrasound for kidney dysfunction after transplantation. Image evaluation was performed by two radiologists, and clinical follow-up data were collected.

RESULTS

In 1 of 16 subjects, MRA with ferumoxytol demonstrated complete arterial occlusion of an allograft. In 2 of 16 subjects, MRA detected moderate to severe anastomotic stenoses, which were confirmed at catheter angiography and successfully treated, resulting in the improvement of graft function. In 13 of 16 subjects, MRA demonstrated normal graft vasculature, and an alternative cause of allograft dysfunction was ultimately confirmed.

CONCLUSIONS

Our study suggests that ferumoxytol-enhanced MRA may be a novel, safe method to accurately detect graft artery abnormalities in renal transplant recipients without the risk of nephrotoxicity, when transplant ultrasound is nondiagnostic.

Detection and treatment of transplant renal artery stenosis

Purpose:

To assess the effects of transplant renal artery stenosis (TRAS) on blood pressure, renal function, and graft survival. To assess the usefulness of Doppler in predicting the clinical significance of TRAS and also to identify the predictive factors in Doppler that correlated with clinical features of TRAS.

Materials and Methods:

A prospective study was done on consecutive renal allograft recipients at Christian Medical College, over a period of 66 months from January 2002. All recipients underwent Doppler ultrasound (DUS) evaluation on the fifth post-operative day. Subsequent evaluation was done if the patients had any clinical or biochemical suspicion of TRAS. Angiogram was done in case of a high index of suspicion of significant stenosis or before angioplasty and stenting. The clinical and radiological outcomes of the patients with symptomatic or asymptomatic TRAS were analyzed.

Results:

Five hundred and forty three consecutive renal allograft recipients were analyzed, of whom, 43 were found to have TRAS. Nine recipients (21%) were detected to have TRAS on first evaluation. All had a high peak systolic velocities (PSV) recorded while 25 of them had other associated features. Patients with only high PSV required no further intervention and were followed up. They had a pretransplant mean arterial pressure (MAP) of 107.83 mmHg (SD = 13.32), ranging from 90 to 133 mm Hg and a posttransplant MAP of 106.56 mmHg (SD =16.51), ranging from 83 to 150 mm Hg. Their mean nadir serum creatinine was 1.16 mg% (SD = 0.24), at detection was 1.6 mg% (SD = 1.84) and at 6 months follow-up was 1.26 mg% (SD=0.52). Of the remaining 25 patients with other associated Doppler abnormalities, 11 required further intervention in the form of re-exploration in 2, angioplasty in 3 and stenting in 6 patients. One patient in the group of patients intervened, expired in the immediate post-operative period due to overwhelming urosepsis and consumption coagulopathy. The mean creatinine clearance (Cockroft-Gault method) in this group of remaining 10 patients, before and after intervention was 44.75 ml/min (SD=17.85) and 68.96 ml/min (SD = 10.56), respectively, with a mean increase by 24.21 ml/min (P=0.000). The mean arterial pressure before and after intervention in this group were 132.80 mm Hg (SD = 13.22) and 102 mm Hg (SD = 10.55), with a decline in the MAP by 30.80 mmHg (P=0.017). The haemoglobin levels also increased from 11.72 (SD=2.13) to 12.48 gm% (SD = 1.75), with a mean increase by 0.76 gm% (P=0.05).

Conclusions:

Patients with isolated high PSV do not have a significant alteration of blood pressure or allograft function and required no intervention. Although high PSV with associated Doppler anomalies are more suggestive of significant TRAS, the decision regarding surgical intervention is largely based on clinical assessment.

Management of transplant renal artery stenosis

Transplant renal artery stenosis is the most frequent vascular complication of transplantation. Early detection and correction reduce patients' morbidity and allograft dysfunction. Although noninvasive imaging can detect an underlying stenosis, angiography with subsequent angioplasty or stenting, or both, provides definitive diagnosis and treatment. With the introduction of alternative contrast agents and newer catheter and stent technology, these procedures can be performed safely with little risk of contrast-induced nephropathy or allograft loss.

Restoration of failed renal graft function after successful angioplasty of pressure-resistant renal artery stenosis using a cutting balloon: a case report

This study is the report of a 37-year-old male with a transplanted kidney from a 3.5-year-old donor: the graft had two arteries transplanted with an aortic patch to an external iliac artery. Four months after transplantation, the graft function deteriorated, together with the development of hypertension. Stenosis of both graft arteries was detected and the patient was referred for angioplasty. The angiographic result was suboptimal, nevertheless, the graft function improved and was more or less stable (serum creatinine, 160-200 micromol/l) for 4 years, along with persistently difficult-to-control hypertension. Five years after transplantation, the graft function deteriorated again and severe graft artery restenosis was detected. The restenosis did not respond to dilatation, graft function failed, hypertension decompensated, and left ventricular failure developed. The patient required dialysis. A cutting balloon angioplasty opened the artery, and kidney function was restored after a few days: the serum creatinine level dropped to 140-160 micromol/l, and the glomerular filtration rate (creatinine clearance) to 0.65 ml/min/1.73 m(2). The graft function has now been stable for more than 2 years, however, the hypertension is still difficult to control.

Long-term follow-up of renal transplant patients with renal artery stenosis treated by percutaneous angioplasty

PURPOSE OF THE STUDY

To evaluate if renal angioplasty (PTRA) in patients with transplanted kidney and renal artery stenosis (TRAS) can have long-term effect on hypertension and renal function.

MATERIALS AND METHODS

Within a 24-year time period, 58 PTRAs in 55 adults (three times Re-PTRA) with transplanted kidney were performed. The group included 34 males and 21 females, average age 41+/-10.6 (18-72) years. After exclusion of 7 technical failures, 51 PTRAs were followed at 1 week, 6 months and 1-3 years after PTRA. Hypertension improvement was defined as mean arterial pressure (MAP) decrease of at least 15% from the pre-PTRA value. Graft function was evaluated by serum creatinine (Scr) and creatinine clearance (Ccr) levels, and the improvement was defined as a 20% change. Clinical FU was 3 years.

RESULTS

PTRA technical success was 88.4%. In 51 kidney recipients at the end of FU, blood pressure improved in 65.2% of patients (MAP decreased from 123+/-13.1 to 107+/-12.1 mmHg), but no patient remained normotensive medication free. Graft function improved in 44.8% of patients and was stabilized in 20.7% of them (average Ccr before PTRA: 0.48+/-0.29, after PTRA: 0.78+/-47 ml/s). PTRA complications were observed in 25.5% of procedures, most often with no clinical sequel. Thirty days mortality was 1.8% (one patient).

CONCLUSIONS

PTRA results in kidney recipients are valuable mainly in preserving graft function.

Supramolecular aggregates of amphiphilic gadolinium complexes as blood pool MRI/MRA contrast agents: physicochemical characterization

In this paper, we present the development of a new potential blood pool contrast agent for magnetic resonance imaging applications (MRA/MRI) based on gadolinium complexes containing amphiphilic supramolecular aggregates. A novel amphiphilic unimer, containing the DTPAGlu chelating agent covalently bound to two C18 alkylic chains, has been synthesized. DTPAGlu is a well-known chelating agent for a wide number of ions such as the paramagnetic metal ion Gd3+ used as contrast agent in MRA/MRI. The wide aggregation behavior of this surfactant, as free base or as gadolinium complex, has been studied and compared by means of dynamic light scattering, small-angle neutron scattering and cryogenic transmission electron microscopy techniques. Near neutral pH in both cases, the dominant aggregates are micelles. The high negative actual charge of the surfactant headgroup causes a strong headgroups repulsion, promoting the formation of large and high curvature aggregates. By decreasing pH and less markedly increasing the ionic strength, we observe a micelle-to-vesicle transition driven by a decreased electrostatic repulsion. A straightforward switch between different aggregation states can be particularly useful in the development of pH-responsive MRA/MRI contrast agents.

An MRA study of vascular stenosis in a pig model using CH3-DTPA-Gd (NMS60) and Gd-DTPA

PURPOSE

This study used an experimental arterial stenosis model in pigs to evaluate the utility of a new medium-weight MRI contrast agent, NMS60 (a synthetic oligomeric Gd complex containing three Gd(3+) atoms, molecular weight of 2158 Da) compared to Gd-DTPA for contrast-enhanced MRA.

MATERIALS AND METHODS

We used six male white hybrid pigs. Under anesthesia, one femoral artery was exposed and an inflatable cuff placed around it. The cuff was tightened around the vessel until 80-90% stenosis was achieved using digital subtraction angiography as a guide. Animals were then immediately transferred to the MRI scanner and images acquired pre- and postcontrast injection (0.1 or 0.2 mmol Gd/kg Gd-DTPA or NMS60, as a rapid bolus) using high-resolution and dynamic MRA.

RESULTS

The dynamic MRA scans acquired during contrast bolus injection clearly showed the stenosed femoral artery as a segment of close to zero enhancement during the arterial phase of the bolus transit, while on the high-resolution scans the stenosis was difficult to detect due to venous signal contamination. The signal-to-noise at peak enhancement on the dynamic scans was significantly greater with 0.1 mmol Gd/kg NMS60 compared to 0.1 mmol Gd/kg Gd-DTPA (14.6 vs. 9.9, P < .05) and not significantly greater than 0.2 mmol Gd/kg (14.6 vs. 12.8).

DISCUSSION AND CONCLUSION

This new medium-weight contrast agent demonstrated significantly greater enhancement than Gd-DTPA and may be valuable to aid detection of vascular stenosis in humans.

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.

Duplex Doppler sonography of transplant renal artery stenosis

PURPOSE

The aim of this study was to evaluate the accuracy of duplex Doppler sonography in diagnosing transplant renal artery stenosis (TRAS) and to determine which parameter is the most reliable for making that diagnosis.

METHODS

Over a 3-year period, we sonographically evaluated patients who were referred for investigation of possible TRAS. We investigated the following parameters: peak systolic velocity (PSV) in the external iliac and renal arteries, acceleration time and acceleration in the intrarenal arteries, acceleration time in the renal artery, resistance index, and the ratio of the PSVs in the renal and external iliac arteries. We also used MR angiography and digital subtraction arteriography to verify the degree of stenosis. After the evaluations, the patients were classified into 2 groups, 1 with and the other without significant stenosis (> 50% narrowing of the lumen) on digital subtraction arteriography. We also included a control group of patients who had undergone renal transplantation at least 6 months before, had had a good course after transplantation, had a diastolic blood pressure of 90 mm Hg or less, and were taking a maximum of 1 antihypertensive drug.

RESULTS

Our study population consisted of 22 patients suspected to have TRAS (10 without and 12 with confirmed significant stenosis) and 19 control patients. We found statistically significant differences between the mean values of these 3 groups except for the PSV in the iliac artery and the resistance index in the intrarenal arteries. The most accurate parameters to use in diagnosing TRAS were an acceleration time of 0.1 second or higher in the renal and intrarenal arteries, a PSV of greater than 200 cm/second in the renal artery, and a ratio of PSVs in the renal and external iliac arteries of greater than 1.8.

CONCLUSIONS

Duplex Doppler sonography is an excellent method for screening patients suspected to have TRAS and can help select which of those patients should undergo digital subtraction arteriography.

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.

Renal Arterial Stenosis in Renal Allografts: Retrospective Study of Predisposing Factors and Outcome after Percutaneous Transluminal Angioplasty

PURPOSE

To determine the predisposing factors to transplant renal arterial stenosis (TRAS) and assess the outcome of percutaneous transluminal angioplasty (PTA) as the primary treatment.

MATERIALS AND METHODS

Of 831 renal allograft recipients (584 cadaveric, 247 living related) between January 1991 and December 1998, 72 had hypertension and/or renal dysfunction. All 72 underwent arteriography, and their medical charts were retrospectively reviewed.

RESULTS

Prevalence of TRAS was 3.1% (26 of 831). Technical success rate of PTA was 94% (16 of 17), and clinical success rate was 82% (14 of 17). Those with renal dysfunction had a mean pre-PTA creatinine value of 2.6 mg/dL (230 micromol/L) +/- 0.5 (SD) versus a 1-week post-PTA value of 1.7 mg/dL (150 micromol/L) +/- 0.3 (P <.001). Of those with hypertension, all but one had substantial improvement in mean diastolic blood pressure. At 26.9 months mean follow-up in 16 patients with successful PTA, two stenoses reoccurred, and two grafts were lost to chronic rejection. TRAS was present in 14 of 45 end-to-side anastomoses and 12 of 27 end-to-end anastomoses (P =.31), and TRAS was more prevalent in cadaveric grafts (24 of 584) than in living related grafts (two of 247). In cadaveric grafts, the mean cold ischemia time was 29.0 hours +/- 6.9 in those with TRAS (n = 24), as compared with 25.5 hours +/- 8.1 in those with no TRAS (n = 39; P = .35). Seven of 17 patients with acute rejection and six of 35 with chronic rejection had TRAS.

CONCLUSION

Primary treatment of TRAS with PTA has good intermediate-term results. TRAS is more prevalent in cadaveric allografts with long cold ischemia time.

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

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

Comparison of non-breath-hold high resolution gadolinium-enhanced MRA with digital subtraction angiography in the evaluation on allograft renal artery stenosis

AIM

The study objective was to compare the diagnostic accuracy of non-breath-hold high resolution gadolinium-enhanced magnetic resonance angiography (Gd-MRA) with intra-arterial digital subtraction angiography (DSA) in the evaluation of allograft renal artery stenosis (ARAS).

MATERIALS AND METHODS

We studied 17 renal transplant recipients (six men, 11 women, age 34-64 years) with a systolic bruit in the transplant region beyond the early post-operative period. Gadolinium-enhanced magnetic resonance angiography was performed by non-breath-hold high resolution 3D acquisition in the oblique coronal plane using a 256 x 512 matrix.Digital subtraction angiography was performed with AP and oblique views and ARAS was graded as < or =50% or >50% diameter stenosis on the view that displayed the maximal narrowing.

RESULTS

Digital subtraction angiography showed >50% stenosis in seven patients, all of whom were diagnosed correctly on Gd-MRA. Gadolinium-enhanced magnetic resonance angiography diagnosed two patients with >50% stenosis which were not confirmed on DSA. Eight patients had no or < or =50% stenosis on both Gd-MRA and DSA. The sensitivity and specificity of Gd-MRA in revealing >50% stenosis were 100% and 75%, respectively, using DSA as the gold standard.

CONCLUSION

High resolution Gd-MRA employing a non-breath-hold technique is highly sensitive in the diagnosis of ARAS greater than 50%. It is preferred as a non-invasive screening technique to DSA in suspected ARAS.