Non-contrast enhanced 3D SSFP MRA of the renal allograft vasculature: a comparison between radial linear combination and Cartesian inflow-weighted acquisitions

Assessment of Transplant Renal Artery Stenosis with Non-contrast-Enhanced Magnetic Resonance Angiography: Comparison with Digital Subtraction Angiography

RATIONALE AND OBJECTIVES

Early diagnosis of transplant renal artery stenosis (TRAS) is crucial for salvaging kidney function and improving patient prognosis. The purpose of this study was to evaluate image quality of non-contrast-enhanced MR angiography (NCE-MRA) and the value of NCE-MRA in evaluating TRAS compared to DSA.

MATERIALS AND METHODS

In 60 patients with TRAS confirmed by DSA, the degree of TRAS was assessed using balanced triggered angiography non-contrast-enhanced (B-TRANCE) MR angiography and was compared to that of DSA. Image quality for NCE-MRA was assessed independently by two radiologists. The Wilcoxon signed-rank test was used to compare NCE-MRA with DSA in assessing TRAS degree. Specificity, sensitivity, accuracy, positive-predictive value (PPV), and negative-predictive value (NPV) of NCE-MRA for the detection of marked (≥50%) TRAS were calculated.

RESULTS

The image quality of NCE-MRA based on the B-TRANCE technology of transplanted renal arteries was sufficient (excellent in 81.67%, good in 8.33%, moderate in 6.67%, and non-diagnostic in 3.33%) and had a high inter-observer reproducibility (Kappa=0.836). DSA helped identify severe, moderate, and mild stenosis in 6, 32, and 22 arteries, respectively. No significant difference in the extent of TRAS between NCE-MRA and DSA were observed (P = 0.317). The specificity, sensitivity, accuracy, PPV, and NPV of NCE-MRA in detecting marked (≥50%) TRAS were 90.91%, 100%, 96.55%, 94.74%, and 100%, respectively.

CONCLUSION

NCE-MRA based on B-TRANCE technology has shown promising consistency with DSA in evaluating TRAS and yielding high sensitivity, specificity, and accuracy in assessing the severity of TRAS.

Non-contrast magnetic resonance angiography/venography techniques: what are my options?

Non-contrast magnetic resonance (MR) angiography and MR venography techniques are gaining popularity for vascular imaging because they are faster, more forgiving and less costly compared with contrast-enhanced MR angiography. Non-contrast MR angiography also avoids gadolinium deposition, which is especially important in imaging children. Non-contrast MR angiography has an array of specific applications for numerous clinical indications. This review summarizes the non-contrast MR angiography methods and their relative advantages and disadvantages. The paper also guides the reader on which technique to consider when determining the optimal imaging modality for each individual patient.

Evaluation of Renal Allograft Vasculature Using Non-contrast 3D Inversion Recovery Balanced Steady-state Free Precession MRA and 2D Quiescent-interval Slice-selective MRA

BACKGROUND AND OBJECTIVES

Renal transplant patients often require periodic imaging to evaluate the transplant vessel anastomosis for potential vascular complications. The use of non-contrast enhanced magnetic resonance angiography (NCE-MRA) techniques is encouraged in these patients because they are at increased risk of nephrogenic systemic fibrosis (NSF) due to their renal insufficiency. This study aimed to evaluate the performance of two NCE-MRA techniques (three-dimensional [3D] balanced steady-state free precession [bSSFP] with inversion recovery and quiescent-interval slice-selective [QISS]) for the evaluation of renal allograft vasculature in patients with clinical suspicion, or Doppler ultrasound, or both of arterial anastomotic stenosis.

METHODS

A total of 43 patients were included in this retrospective study. Two radiologists independently scored the images from 3D bSSFP and QISS MRA sequences for image quality and confidence in anastomosis interpretation, and the degree of stenosis at the arterial anastomosis. Correlations with digital subtraction angiography (DSA) were carried out when available. In addition, inter-rater agreement was calculated.

RESULTS

In total, 43 patients underwent QISS and 3D bSSFP MRA. For QISS, all cases were adequate for evaluation. For 3D SSFP, 86% of cases were adequate for evaluation. There was a good-to-excellent inter-rater agreement for all scores and an excellent correlation between NCE-MRA and DSA results when available (12 patients).

CONCLUSIONS

QISS and 3D SSFP showed good inter-rater agreement for image quality and stenosis grade, with more cases being of adequate image quality that used QISS. Further study is required; however, NCE-MRA shows potential as a risk-free alternative to CTA and contrast-enhanced MRA (CE-MRA) for the evaluation of arterial anastomoses in renal transplant patients.

Interleaved, undersampled radial multiple-acquisition steady-state free precession for improved left atrial cine imaging

PURPOSE

Balanced steady-state free precession (bSSFP) left atrial (LA) cine suffers from off-resonance artifacts, particularly in the pulmonary veins (PVs). Linear combination or multiple-acquisition SSFP (MA-SSFP) effectively removes banding but greatly increases scan time. We hypothesized that MA-SSFP with interleaved radial undersampling, where each phase-cycling is acquired with an interleaved set of radial projections, would improve image quality of LA cine with a small increase of scan time and streak artefacts.

METHODS

Undersampled radial MA-SSFP with and without interleaving was compared with fully sampled radial bSSFP by means of simulations, phantoms, and in vivo imaging. Ten healthy subjects were imaged on a 3T scanner, with bSSFP and MA-SSFP cine of the left atrium, and B0-mapping. Images were assessed (1 = worst, 5 = best) by 2 independent readers, with respect to 5 qualitative criteria and apparent signal-to-noise ratio.

RESULTS

In healthy subjects, off-resonance differed from the right inferior PVs to the LA cavity by 163 Hz ± 73 Hz at 3T. Compared with fully sampled radial bSSFP, interleaved radial MA-SSFP significantly improved image quality with respect to off-resonance artifacts (3.8 ± 0.6 versus 2.3 ± 1.0; P = 0.005), PV conspicuity (2.8 ± 1.0 versus 4.3 ± 0.5; P = 0.005), and the number of visualized PVs (1.7 ± 0.4 versus 0.9 ± 0.7; P = 0.008), although with greater streak artifacts (3.4 ± 0.4 versus 4.9 ± 0.2; P = 0.004) and lower measured apparent signal-to-noise ratio (24 ± 9 versus 69 ± 36; P = 0.002). Flow artifacts were similar. Interleaved radial MA-SSFP reduced streaking artifacts and increased apparent signal-to-noise ratio versus noninterleaved radial.

CONCLUSIONS

Interleaved radial MA-SSFP cine reduces banding artifacts with an acceptable increase of scan time and streak artifacts. The proposed technique improves the LA and PV visualization in bSSFP cine imaging.

Congenital anomalies of the aortic arch

Congenital anomalies of the aortic arch include diverse subgroups of malformations that may be clinically silent or may present with severe respiratory or esophageal symptoms especially when associated with complete vascular rings. These anomalies may be isolated or may be associated with other congenital heart diseases. Volume rendered computed tomography (CT) and magnetic resonance angiography (MRA) help in preoperative surgical planning by providing information about the complex relationship of aortic arch and its branches to the trachea and esophagus. Three dimensional capabilities of both computed tomography angiography (CTA) and MRA are helpful in determining evidence of tracheal or esophageal compression or other high-risk features in patients with a complete vascular ring.

MR Angiography of Renal Transplant Vasculature with Ferumoxytol:: Comparison of High-Resolution Steady-State and First-Pass Acquisitions

RATIONALE AND OBJECTIVES

This work aimed to quantify the differences in signal-to-noise ratio (SNR) and vessel sharpness between steady-state and first-pass magnetic resonance angiography (MRA) with ferumoxytol in renal transplant recipients.

MATERIALS AND METHODS

We performed a retrospective study of adult patients who underwent steady-state and first-pass MRA with ferumoxytol to evaluate renal transplant vasculature. SNR was calculated in the external iliac artery, and vessel sharpness was calculated in the external iliac and renal transplant arteries for both acquisitions. Data were compared using Student's t test.

RESULTS

Fifteen patients were included (mean age 56.9 years, 10 males). The mean SNR of the external iliac artery was 42.2 (SD, 11.9) for the first-pass MRA and 41.8 (SD, 9.7) for the steady-state MRA (p = 0.92). The mean vessel sharpness was significantly higher for the steady-state MRA compared to first-pass MRA for both external iliac (1.24 vs. 0.80 mm(-1), p < 0.01) and renal transplant arteries (1.26 vs. 0.79 mm(-1), p < 0.01).

CONCLUSION

Steady-state MRA using ferumoxytol improves vessel sharpness while maintaining equivalent SNR compared to conventional first-pass MRA in renal transplant patients.