RPS 1815 - MR in vascular imaging

Purpose:

To assess the benefits of TRI in patients with clinical suspicion of MTS. The main objective is to correlate the presence of a collateral venous pattern in the left inferior limb with the compression degree in the left common iliac vein (LCIV). We also aim to asses the inter and intraobserver variability in the degree of LCIV compression using different techniques.

Methods and materials:

This retrospective study included 112 patients submitted to MRI-angiography with TRI sequences using intravenous contrast infusion on the left foot, between October 2014-May 2019. We selected 97 patients who did not undergo any interventional procedures and with an appropriated exam. One senior radiologist reviewed the images looking for collateral venous drainage and measured the maximal degree of LCIV compression. One fellow with 1 year of vascular training measured the maximal degree of venous compression in different sequences, without knowledge of the results from the senior radiologist. The readings took place at different times with each sequence to mitigate memory bias.

Results:

We found a statistically significant difference between the presence of collateral venous drainage and the degree of compression with a median LCIV of 0.4 (0.3-0.7) cm in patients without collaterals (67) and a median LCIV of 0.3 (0.2-0.3) cm in patients with collaterals (30), with a p<0.001.

The intraclass correlation (ICC) between techniques by the fellow was 0.81 (IC95%: 0.73-0.87), with a mean variation of 0.11 cm. The ICC between the fellow and senior radiologist was worse, reaching 0.57-0.77 between techniques.

Conclusion:

Time-resolved imaging allows a dynamic assessment of collaterals in MTS patients that correlates with the degree of LCIV compression in patients with MTS, but there is relevant variation between readers and techniques.

Limitations:

A small sample and single institution.

Ethics committee approval

n/a

Funding:

No funding was received for this work.

Purpose:

In Marfan patients, accurate aortic diameter measurements are crucial for life-long monitoring. We compared the influence of overall image quality, amount of image artefacts, contrast-to-noise-ratio (CNR), and aortic root surgery on the reliability of aortic measurements of non-contrast MRA in Marfan patients at 1.5T and 3T.

Methods and materials:

40 Marfan patients were prospectively evaluated by non-contrast 2D-bSSFP MRA of the aorta at 1.5T and after 12 months at 3T before (n=24) and after aortic surgery (n=16). Two readers independently rated the image quality and the presence/amount of artefacts on Likert scales at 9 (8) aortic levels before (after) aortic surgery. The CNR of the delineated aortic wall was separately calculated for each aortic level.

Results:

Aortic imaging at 3T provided significantly superior CNR and more reproducible aortic diameters compared to 1.5T. Interobserver variances of aortic measurements were significantly smaller at the sinuses of the valsalva, sinotubular junction, mid-ascending aorta, and proximal descending aorta in pre-surgical patients (p<0.05). After aortic surgery, the majority of the advantages of 3T were mitigated by a significantly impaired image appearance due to the higher number of susceptibility/flow artefacts at 3T compared with 1.5T. This resulted in significantly higher aortic diameter variances at the mid-graft and distal anastomosis.

Conclusion:

Non-contrast aortic imaging at 3T results in a higher CNR and more reproducible aortic measurement in pre-surgical Marfan patients compared to 1.5T. Most of these advantages are mitigated in post-surgical Marfan patients due to increased susceptibility/flow artefacts at 3T.

Limitations:

The time delay between measurements at 1.5T/3T, differences of exact technical parameters at 1.5T/3T, and the measurements only in para-sagittal planes.

Ethics committee approval

Written informed consent was assessed. IRB approved this work.

Funding:

No funding was received for this work.

Purpose:

4D flow is an emerging imaging technique. Beside traditional flow parameters, 4D flow enables the calculation of advanced parameters like wall shear stress or the loss of kinetic energy. The aim of this prospective study was to evaluate differences in the loss of kinetic energy over the aortic arch between healthy volunteers and aortic dissection patients after surgical repair with implantation of an antegrade stent-graft (“frozen elephant trunk"; FET).

Methods and materials:

In 17 healthy volunteers (HV) and 11 patients, 4D flow imaging was performed using a 4D flow prototype on a 3-Tesla MRI scanner. All patients had undergone aortic surgery for treatment of acute aortic dissection (type A) with supracoronary aortic replacement and “frozen elephant trunk” antegrade stent-graft implantation. 4D flow measurements and a calculation of the loss of kinetic energy (LoE) were performed with a dedicated 4D flow software tool (cvi42, Circle, Calgary, Canada) from the aortic annulus to the descending aorta.

Results:

The mean maximum and average LoE was 2-3 times higher over the aortic arch in FET patients compared to healthy volunteers (mean maximum LoE FETvsHV: 9.0± 6.1 vs 3.7±1.3 mW; p=0.016 and mean average LoE FETvsHV: 2.4±1.3 vs 0.9±0.3 mW; p=0.003).

Conclusion:

FET repair of acute aortic dissection leads to a significant increase in the loss of kinetic energy measured by 4D flow MR imaging. The prognostic implications of these changes on end-organ perfusion and cardiac remodelling have to be determined in prospective studies.

Limitations:

A single-centre study without invasive correlation.

Ethics committee approval

All patients provided written informed consent. The study was approved by the local ethics committee (2018-13520).

Funding:

No funding was received for this work.

Purpose:

To investigate the influence of the frequency of pulses and the flip angle on the quality of the non-enhanced renal arterial MRA.

Methods and materials:

We prospectively recruited 14 volunteers [19 men, 6 women; age=23.8±2.61].Each volunteer was scanned 6 times with different flip angles (45°, 90°, and 135°) and frequency of pulses (1 or 3 times) with 1.5T MR NATIVE True-FISP sequences. The quality of the images and renal arterials presentation were graded ranging from 0-3 and 1-3, respectively. The average value of the bilateral renal arterials score was used for analysis. ICC was used to test the agreement between the two observers. Factorial analysis was used to compare image quality scores and renal artery scores between different scanning groups.

Results:

The interobserver agreement of image quality and renal artery scores were good (ICC =0.77-0.88, 0.80-0.98). There was no difference in image quality and renal artery scores between different pulse groups (p=0.191, 0.177). There was a significant overall difference of image quality and renal artery scores between different flip angle groups (p=0.01, 0.00). There were no statistical significant differences for the interaction of pulse and flip angel in image quality and renal artery scores (p=0.87, 0.52). The image quality and renal artery scores were highest in 135° group.

Conclusion:

Different pulse times have no significant effect on the image quality and renal artery display of NATIVE True-FISP sequences. For the flip angel, 135° is the better choice.

Limitations:

A lack of objective quantitative parameters. The effect of blood flow velocity on image quality was not considered.

Ethics committee approval

Approved by the hospital ethics review committee.

Funding:

No funding was received for this work.

Purpose:

To evaluate the image quality and diagnostic accuracy in the pelvis and abdomen of free-breathing fast low-angle shot (FLASH)-based quiescent interval slice-selective (QISS) techniques in comparison to standard QISS in patients with peripheral artery disease (PAD), using CTA as the reference.

Methods and materials:

27 patients (69±10y) with PAD underwent non-contrast MRA using standard bSSFP-based QISS and prototype free-breathing radial-FLASH and Cartesian-FLASH-based QISS at 3T. A subset of patients (n=22) also underwent CTA as the reference standard. 9 arterial segments per patient were evaluated spanning the abdomen, pelvis, and upper thigh regions. Objective (signal intensity ratio (SIR) and relative standard deviation (SD)) and subjective image quality (4-point scale) and stenosis (>50%) were evaluated by two readers and compared using a one-way analysis of variance, Wilcoxon, and McNemar tests, respectively.

Results:

A total of 179 vascular segments were available for analysis by all QISS techniques. No significant difference was observed among bSSFP, radial-FLASH, and Cartesian-FLASH-based techniques in SIR (p=0.428) and relative SD (p=0.220). Radial-FLASH-based QISS demonstrated the best image quality (p<0.0001) and the highest inter-reader agreement (κ=0.721). The sensitivity values of bSSFP, radial-FLASH, and Cartesian-FLASH-based QISS for the detection of >50% stenosis were 76.0%, 84.0%, and 80.0%, respectively, while specificity values were 97.6%, 94.0%, and 92.8%, respectively. Moreover, FLASH-based QISS consistently reduced off-resonance artefacts compared to the bSSFP-based approach.

Conclusion:

Free-breathing FLASH-based QISS MRA techniques provide improved image quality and sensitivity, high specificity, and reduced off-resonance artefacts for vascular stenosis detection in the abdomen and pelvis.

Limitations:

The limited sample size and lack of a control group.

Ethics committee approval

IRB-approved with written informed consent obtained.

Funding:

NIH-NHLBI.

Purpose:

To investigate whether magnetic particle imaging (MPI) can visualise and quantify the lumen of endovascular stents.

Methods and materials:

We investigated 21 commercially available stents (diameter: 3-10 mm, material: stainless steel, nitinol, platinum-chromium, cobalt-chromium) which were implanted in silicone vessel phantoms. All phantoms (stented phantoms and reference phantoms without stents) were filled with tracer dilution (1:100, Resovist, I’rom Pharmaceuticals, Tokio, Japan) and visualised with a preclinical commercially available MPI scanner (Bruker Biospin, Ettlingen, Germany). The quantification of the lumina was performed on the xz-planes of the images based on a calibrated signal intensity threshold.

Results:

The visualisation of the stent lumen is feasible without any material induced artefacts. Between the stented phantoms and the reference phantoms there was no visual or quantitative difference observed (stented phantoms/reference phantoms vs nominal diameter r=0.98). The root mean square inaccuracy of stent lumen quantification was below half the spatial resolution.

Conclusion:

In principle, MPI is able to depict and quantify the lumina of endovascular stents accurately without material induced effects.

Limitations:

The in vitro study design and that we only used a single tracer concentration.

Ethics committee approval

n/a

Funding:

This study was partially funded by the Federal Ministry of Education and Research BMBF grant numbers 13GW0071D, 13GW0069A, 13GW0230B, and 01DL17010A.

Purpose:

To compare the performance of time-of-flight with sparse undersampling MRA and TOF-MRA in the image quality and evaluation of size parameters of intracranial aneurysms with DSA as the reference standard.

Methods and materials:

54 aneurysms from 46 patients who underwent TOF-MRA, TOFu-MRA, and DSA were included. For objective image quality, the contrast-to-noise ratio (CNR) and signal-to-noise (SNR) of two MRA images were compared. The subjective image quality was assessed using a 5-point score scale by two experienced observers and the interobserver agreement was determined. With DSA as the reference, the neck, height, and width of aneurysms in two MRAs were measured and compared on maximum intensity projection (MIP) image datasets, respectively.

Results:

The SNRs and CNRs in TOFu-MRA (SNR=24.21±8.06; CNR=17.08±7.44) were significantly higher than those in TOF-MRA (SNR=18.94±6.44; CNR=13.27±6.00) (P<0.001). With an excellent interobserver agreement (к values=0.94), the subjective image quality was significantly improved when the sparse TOF was used (P＜0.05). For measurement of size parameter, there were significant differences between TOF-MRA and TOFu-MRA among the three groups (neck, 3.63±2.22 vs 3.52±2.16; width, 4.62±4.59 vs 4.64±4.71; height, 4.62±4.59 vs 4.64±4.71, all P<0.05). Moreover, in the Bland-Altman plot analysis, TOFu-MRA showed no significant differences between DSA.

Conclusion:

Compared with conventional TOF, sparse TOF could assess intracranial aneurysms more accurately with a better image quality and the same acquisition time.

Limitations:

Further optimisation of the image quality with regard to NO settled protocol parameters would be needed.

Ethics committee approval

The study has been approved by the West China Hospital ethics committee.

Funding:

1.3.5 project for disciplines of excellence, West China Hospital, Sichuan University (ZYGD18019).