RPS 2115 - Advances in thoracoabdominal and peripheral vascular MRI

Author Block: A. Lenz, C. Riedel, F. Wright, I. Ristow, S. Zhang, B. Schönnagel, G. Adam, Y. von Kodolitsch, P. Bannas; Hamburg/DE
Purpose or Learning Objective: To determine the association of normalised aortic root diameters (Z-score) and 4D flow MRI-derived aortic haemodynamics in Marfan patients.
Methods or Background: We prospectively performed a 4D flow MRI at 3T of the thoracic aorta in 100 Marfan patients (36±14 years). Patients were divided into two groups according to Z-score of the aortic root: i) Z-score <2 (n=43), or ii) Z-score >2 (n=57). The degree of helical and vortical flow in the ascending aorta was evaluated according to a 3-point scale (0: no, 1: rotation <360º, 2: rotation >360º). In addition, we assessed wall shear stress (WSS) and flow eccentricity at the level of the sinotubular junction (STJ), mid-ascending aorta (midAAo), and proximal arch (proxAA). Results were statistically compared using unpaired t-tests or Mann-Whitney U tests.
Results or Findings: Flow eccentricity at the level of STJ was significantly higher in Marfan patients with Z-score >2 (0.15±0.07 vs 0.12±0.07; p=0.02) when compared to Marfan patients with Z-score <2. WSS at the level of STJ was significantly lower in Z-score >2 patients compared to Z-score <2 patients (0.39±0.11 N/m2 vs 0.46±0.12 N/m2; p=0.002). Aberrant vortical and helical flow patterns in the ascending aorta were more pronounced in Z-score >2 patients; however, those differences in vortical (0.5±0.7 vs 0.4±0.6; p=0.3) and helical flow (0.8±0.7 vs 0.7±0.7; p=0.4) were not statistically significant.
Conclusion: Marfan patients with pathologically increased Z-scores reveal increased flow eccentricity and reduced WSS compared to Marfan patients with physiological Z-scores.
Limitations: Visual assessment of helical and vortical flow as well as manual positioning of 2D analyses planes for assessment of WSS and flow eccentricity may introduce a subjective bias and affect both qualitative and quantitative results.
Ethics committee approval: The study was approved by the local research ethics committee.
Funding for this study: The German Heart Research Foundation funded this study.

Author Block: C. Riedel, A. Lenz, I. Ristow, F. Wright, G. Adam, B. Schönnagel, P. Bannas; Hamburg/DE
Purpose or Learning Objective: To validate 4D flow MRI-derived flow measurements in transjugular intrahepatic portosystemic shunt (TIPS) stent-grafts using a 3D-printed flow phantom.
Methods or Background: A flow phantom mimicking the portal venous vasculature was 3D-printed using Clear Resin (Formlabs). The model consisted of the superior mesenteric vein (SMV) and the splenic vein (SV) draining into the extrahepatic portal vein (PV), the intrahepatic TIPS-tract, and the liver vein. A Viatorr® stent-graft was positioned within the TIPS tract. SMV and SV served as inlets for blood-mimicking fluid and were connected over a flow regulator and a flow sensor to a pump. TIPS flow rates ranging from 0.8-2.8 L/min were preset and 4D flow MRI acquisitions were performed at 3T using a velocity encoding (venc) of both 100cm/s and 200cm/s. 4D flow MRI-derived datasets were evaluated at predefined levels including SMV, SV, PV, the uncovered part of the stent-graft as well as the covered stent-graft (distal, central, proximal). 4D flow MRI-derived flow rates were compared to preset flow rates as a standard of reference.
Results or Findings: At a venc of 200cm/s, 4D flow MRI-derived flow rates were significantly correlated with the preset flow rates at all vascular levels and within the stent-graft (all r>0.98, p<0.001). At a venc of 100cm/s, aliasing artefacts were present within the stent-graft at flow rates ≥2.0L/min. Lower preset flow rates were also significantly correlated with 4D flow MRI-derived flow rates (all r>0.99, p<0.05). In the uncovered stent-graft, 4D flow MRI underestimated the flow rate at a venc of 100cm/s by 1-6%.
Conclusion: 4D flow MRI enables valid flow evaluation within TIPS stent-grafts and warrants further in vivo validation studies to determine its clinical usefulness for monitoring TIPS function and patency.
Limitations: Not applicable.
Ethics committee approval: Not applicable.
Funding for this study: Not applicable.

Author Block: J. Liu, J. Qiu, W. LI, K. Zhao, Z. Bi; Beijing/CN
Purpose or Learning Objective: To compare the image quality of non-contrast MR pulmonary angiography (MRPA) with two different voxel sizes.
Methods or Background: This study consisted of 29 healthy volunteers (13 males, mean age: 44.1±8.0 years) who were given written informed consent. All non-contrast MRPA data were collected on a 1.5T MR scanner (MAGNETOM Aera, Siemens Healthcare, Erlangen, Germany) with an 18-channel body coil and an integrated 32-channel spine matrix coil. A free-breathing 3D turbo spin-echo (TSE) with variable-flip-angle sequence (SPACE) was used to acquire non-contrast MRPA data with the following two sequences of different parameters: 1) voxel size=1.2×1.2×4 mm3. 2) voxel size=2×2×2 mm3. The subjective image quality assessment of normal pulmonary arteries was evaluated by one experienced radiologist on primary coronary images and constructed axial images separately. The image quality of the two groups was compared by the paired t-test.
Results or Findings: The mean image quality scores of the main, left, and right pulmonary arterial trunks on primary coronary images were 3.0±0.6, 3.0±0.6, 3.0±0.6 (group 1) and 2.4±0.6, 2.5±0.6, 2.5±0.8 (group 2). The mean image quality scores of the main, left, and right pulmonary arterial trunks on constructed axial images were 2.2±0.5, 1.4±0.5, 1.6±0.5 (group 1) and 2.0±0.8, 2.1±0.7, 2.1±0.7 (group 2). The branch image quality of group 1 was better than group 2 on primary coronal images (p<0.05). However, the image quality of the left and right pulmonary artery trunk in group 2 was better than group 1 on constructed axial images (p<0.05).
Conclusion: Non-contrast MRPA images with higher resolution within a coronal plane can provide acceptable image quality but images with isotropy can acquire better constructed axial image quality.
Limitations: No limitations.
Ethics committee approval: The ethics approval was obtained.
Funding for this study: No funding was received for this study.

Author Block: J. Csőre, F. I. Suhai, M. Gyánó, A. A. Pataki, G. Juhász, M. Vecsey-Nagy, D. Pál, D. M. Fontanini, C. Csobay-Novák; Budapest/HU
Purpose or Learning Objective: Patients with lower extremity arterial disease (LEAD) often present with chronic kidney disease (CKD), in whom the use of nephroprotective imaging is of utmost importance. We compared the diagnostic performance of two such modalities: the non-contrast quiescent-interval single-shot (QISS) magnetic resonance angiography (MRA) and carbon dioxide digital subtraction angiography (CO2-DSA).
Methods or Background: CO2-DSA and QISS-MRA images of patients with chronic LEAD scheduled for elective diagnostic imaging were compared. A 19-segment lower extremity arterial model was used to assess the degree of stenosis (none, <50%, 50-70%, 70%<) and the image quality (5-point Likert scale: 1-non-diagnostic, 5-excellent) per-segment. Four radiologists evaluated the images. Intra-class correlation coefficient (ICC) was calculated for both inter-rater and intra-rater reliability. Three regions (aorto-iliac, femoro-popliteal, tibio-peroneal) were created by the segments for the final analysis. Diagnostic accuracy and interpretability were also evaluated.
Results or Findings: 523 segments were evaluated in 28 patients (mean age: 71±9 years). Subjective image quality of QISS-MRA was significantly better compared to CO2-DSA for all regions [aorto-iliac: 4(4-5) vs 3(3-4); femoro-popliteal: 4(4-5) vs 4(3-4); tibio-peroneal: 4(3-5) vs 3(2-3), all regions: 4(4-5) vs 3(3-4), p<0.001]. QISS-MRA out-performed CO2-DSA regarding interpretability (98.3% vs 86.2%, p<0.001). Diagnostic accuracy parameters of QISS-MRA for >70% luminal stenosis as compared to CO2-DSA: sensitivity 77.8%, specificity 95.2%, positive predictive value 83.2%, negative predictive value 93.3%. ICC regarding the degree of stenosis: QISS-MRA: 0.97; CO2-DSA: 0.82. Intraobserver variability for each investigator: CO2-DSA: 0.88, 0.93; QISS-MRA: 0.86, 0.91.
Conclusion: QISS-MRA had a better diagnostic value than CO2-DSA in subjective assessment of image quality in all regions studied, proved to be an excellent reproducible method for the assessment of LEAD.
Limitations: Single-centre study with a relatively small number of patients.
Ethics committee approval: Approved by the National Institute of Pharmacy and Nutrition (OGYEI/7984/2020).
Funding for this study: No funding was received for this study.

Author Block: M. Ragusi¹, C. Talei Franzesi¹, C. Maino¹, D. G. Gandola¹, T. P. Giandola¹, D. Ippolito¹, S. Sironi²; ¹Monza/IT, ²Bergamo/IT
Purpose or Learning Objective: To evaluate the diagnostic performance of a standardised MR angiography (MRA) protocol in the study of thoracic outlet syndrome (TOS).
Methods or Background: A total of 20 patients who underwent MRA study to investigate vascular TOS were retrospectively enrolled. Protocol sequences include Balanced Fast Field Echo M2D, Turbo Spin Echo T1 weighted, high-resolution TSE T1 weighted, HR TSE DIXON T2 weighted, contrast-enhanced MRA (CE- MRA), pre- and post-contrast T1-weighted high-resolution isotropic volume examination. Baseline sequences were performed with the arms in adduction, CE-MRA sequences were performed both with arms in adduction and abduction, with an injection of contrast media repeated for each arms’ position.
Results or Findings: Sixteen patients showed unilateral TOS (n=16, 80%), with the left side more frequently involved (n=10, 64.5%) than the right one (n=6, 45.5%). Thirteen patients showed venous compression (vTOS) (65%), 3 patients arterial TOS (aTOS) (15%), only in one case an overlap between vTOS-aTOS (5%) was reported. Eight patients showed compression with the arm in abduction (50%), 8 with the arm both in adduction and abduction (50%). In 5 cases TOS was caused by an osseus abnormalities both post-traumatic or post-surgical. In 6 patients (30%) vTOS was associated with thrombosis. Twenty per cent of TOS were caused by muscle hypertrophy or wrong insertion. Five out of sixteen cases involved the scalene triangle (31%), 8/16 the costoclavicular space (50%) and 3/16 patients the subacromial-pectoralis space (19%). In 4/20 patients vascular TOS was not identified (20%).
Conclusion: A standardised MRI protocol with CE-MRA sequence with arms in adduction and abduction allows identifying the presence of vascular TOS, along with the identification of the intrinsic and extrinsic abnormalities causing pathology.
Limitations: Not applicable.
Ethics committee approval: Not applicable.
Funding for this study: Not applicable.