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Monday, January 28, 2019

The Feasibility of Using Volumetric Phase-Contrast MR Imaging (4D Flow) to Assess for Transjugular Intrahepatic Portosystemic Shunt Dysfunction 


Summary


Doppler US evaluation of transjugular intrahepatic portosystemic shunts (TIPS) carries a high false positive rate, but there is no other currently accepted technique for assessing for TIPS dysfunction.
The authors performed a feasibility study to determine if phase-contrast magnetic resonance (MR) angiography (4D flow) could identify the absence or presence of TIPS stenosis or occlusion. They evaluated 23 patient encounters, 16 of which underwent successful segmentation and analysis of the TIPS stent and portal vein. When clinically indicated, venography was performed. In patients who did not undergo venography, clinical follow-up of at least 6 months was used to exclude stenosis. Time-resolved particle tracings were created to model flow through the stent and allow for qualitative assessment of stenosis. Velocities were also measured using 4D flow. Clinical follow-up was obtained by chart review to determine if symptoms returned, repeat intervention was required, or clinical suspicion of stenosis emerged. Lack of recurrent symptoms or need for intervention was recorded at least 6 months after the MR examination to serve as a reference standard in patients who did not undergo venography. In patient encounters with technically successful 4D flow MR imaging, the rate of dysfunction was 3 of 16 patients (19%). The 3 patients with venography-confirmed stenosis had both abnormal velocities on quantitative and qualitative 4D flow MR imaging. False-positive 4D flow MR imaging results occurred in 6 cases but only if the qualitative and quantitative results were interpreted in isolation. There were no false-positive results if criteria for dysfunction included both abnormal qualitative and quantitative results and there were no false negative cases.



Figure 2. Venography-proven TIPS dysfunction. The measured pressure gradient was 18 mmHg. (a) Still image from particle tracing cine imaging of TIPS stent showing the entire stent (double arrow), inferior vena cava(narrow arrow), portal vein (wide arrow), and elevated velocities with aliasing at the distal TIPS stent (arrowhead). (b) Spectral wave Doppler US interrogation of the distal TIPS showing normal velocities. (c)Grayscale and color Doppler US images with inadequately visualized distal TIPS. (d) Digital subtraction venography showing distal TIPS stenosis (arrowhead)

Commentary


The concordance between TIPS Doppler US and venography is relatively poor. Despite this, performing US for TIPS surveillance is the current standard. This study looks at the feasibility of performing phase-contrast MR imaging for evaluation of TIPS. The authors conclude that this technique can detect patency, stenosis, and occlusion of TIPS. Many patient and technical factors must be considered to optimize the MR imaging of TIPS and prevent failures and the authors nicely describe their imaging protocol. A small number of patients were studied and a randomized controlled trial is still required to determine if volumetric phase-contrast MR imaging will prove to be superior to Doppler US, but the results of this feasibility study suggest MR may be a promising alternative modality for TIPS surveillance.

Click here for abstract

Owen, Joseph, et al. The Feasibility of Using Volumetric Phase-Contrast MR Imaging (4D Flow) to Assess for Transjugular Intrahepatic Portosystemic Shunt Dysfunction. Journal of Vascular and Interventional Radiology. December, 2018. Volume 29, Issue 12, Pages 1717–1724.

Post Author
Zagum Bhatti, MD
Assistant Professor
Department of Radiology, Interventional Radiology Division
University of Texas Health Science Center at Houston, Houston, TX
@ZagumBhatti

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