Phase-contrast MRI evaluation of haemodynamic changes induces by a coeliac axis stenosis in the gastroduodenal artery

Contemporary Management of Median Arcuate Ligament in Liver Transplantation

Median arcuate ligament (MAL) can impair arterial inflow during orthotopic liver transplantation (OLT). Furthermore, approaches to ensure optimal vascular inflow in the presence of MAL is not standardized.

Methods

We undertook a systematic review according to the Cochrane systematic review protocol and Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We analyzed the incidence of MAL, investigations, treatment options, and potential complications associated with MAL intervention in patients undergoing OLT. After the exclusion criteria were implemented, the dataset from the final 21 manuscripts yielded 117 patients who underwent a liver transplant in the presence of MAL.

Results

The incidence of MAL in patients undergoing OLT is between 1.6% and 12%. In 63.2% of cases, an open approach for MAL intervention was undertaken. Hepatic artery thrombosis developed in 17% (7) patients without MAL intervention versus 2.6% (2) after MAL intervention. Seven grafts (5.9%) were lost after OLT in patients with MAL. Three (3.9%) patients developed arterial stenosis post-MAL intervention.

Conclusions

We propose an algorithm for intraoperative assessment and management of liver transplant arterial inflow in the presence of MAL based on the hepatic artery flow changes with respiration, following clamping of the recipient gastroduodenal artery. In the presence of a 30%-50% flow variation on respiration, the arterial inflow should be established preserving additional inflow from the recipient gastroduodenal artery. Consider an open MAL release if the flow remains insufficient. A poor arterial flow with no variation with respiration and lack of evidence of aortoiliac atherosclerosis indicates the need for arterial jump graft.

Assessment of hepatic arterial hemodynamics with 4D flow MRI: in vitro analysis of motion and spatial resolution related error and in vivo feasibility study in 20 volunteers

OBJECTIVES

To assess the ability of four-dimensional (4D) flow MRI to measure hepatic arterial hemodynamics by determining the effects of spatial resolution and respiratory motion suppression in vitro and its applicability in vivo with comparison to two-dimensional (2D) phase-contrast MRI.

METHODS

A dynamic hepatic artery phantom and 20 consecutive volunteers were scanned. The accuracies of Cartesian 4D flow sequences with k-space reordering and navigator gating at four spatial resolutions (0.5- to 1-mm isotropic) and navigator acceptance windows (± 8 to ± 2 mm) and one 2D phase-contrast sequence (0.5-mm in -plane) were assessed in vitro at 3 T. Two sequences centered on gastroduodenal and hepatic artery branches were assessed in vivo for intra - and interobserver agreement and compared to 2D phase-contrast.

RESULTS

In vitro, higher spatial resolution led to a greater decrease in error than narrower navigator window (30.5 to -4.67% vs -6.64 to -4.67% for flow). In vivo, hepatic and gastroduodenal arteries were more often visualized with the higher resolution sequence (90 vs 71%). Despite similar interobserver agreement (κ = 0.660 and 0.704), the higher resolution sequence had lower variability for area (CV = 20.04 vs 30.67%), flow (CV = 34.92 vs 51.99%), and average velocity (CV = 26.47 vs 44.76%). 4D flow had lower differences between inflow and outflow at the hepatic artery bifurcation (11.03 ± 5.05% and 15.69 ± 6.14%) than 2D phase-contrast (28.77 ± 21.01%).

CONCLUSION

High-resolution 4D flow can assess hepatic artery anatomy and hemodynamics with improved accuracy, greater vessel visibility, better interobserver reliability, and internal consistency.

KEY POINTS

• Motion-suppressed Cartesian four-dimensional (4D) flow MRI with higher spatial resolution provides more accurate measurements even when accepted respiratory motion exceeds voxel size. • 4D flow MRI with higher spatial resolution provides substantial interobserver agreement for visualization of hepatic artery branches. • Lower peak and average velocities and a trend toward better internal consistency were observed with 4D flow MRI as compared to 2D phase-contrast.

Hemodynamic Changes Before and After Endovascular Treatment of Type B Aortic Dissection by 4D Flow MRI

Objective:

The standard treatment for complicated Stanford type B aortic dissection (TBAD) is thoracic endovascular aortic repair (TEVAR). Functional parameters, specifically blood flow, are not measured in the clinical assessment of TEVAR, yet they are of outmost importance in patient outcome. Consequently, we investigated the impact of TEVAR on the flows in the aorta and its branches in TBAD using 4D Phase-Contrast Magnetic Resonance Imaging (4D Flow MRI).

Methods

Seven patients with TBAD scheduled for TEVAR underwent pre and post-operative 4D Flow MRI. An experienced reader assessed the presence of helical flow in the false lumen (FL) using streamlines and measured net flow at specific locations. In addition, forward and reverse flows, stasis, helicity, and absolute helicity were computed automatically along the aorta centerline. Average values were then computed in the segmented vessels. Impact of TEVAR on these parameters was assessed with a Wilcoxon signed rank test. Impact of the metallic stent on the velocity quantification was assessed using intra-class correlation coefficient (ICC) between velocities measured intra-stent and in adjacent stent-free regions.

Results

FL helical flow was observed proximally in 6 cases and distally in 2 cases pre-operatively. Helical flow disappeared post-TEVAR proximally, but developed distally for 2 patients. Intra-stent measures were similar to stent-free with a median difference of 0.1 L/min and an ICC equal to 0.967 (p < 0.01). Forward flow increased from 59.9 to 81.6% in the TL and significantly decreased in the FL from 15.9 to 3.3%. Similarly, reverse flow increased in the TL from 4.36 to 10.8% and decreased in the FL from 10.3 to 4.6%. No significant changes were observed in net flow for aortic branches (p > 0.05). A significant increase in FL stasis was observed (p = 0.04).

Discussion

TEVAR significantly increased forward flow in the TL and significantly decreased both forward and reverse flows in the FL. Interestingly, reverse flow in the TL increased post-TEVAR, which could be due to increased rigidity of the wall, due to the metallic stent. User independent helicity quantification enabled detection of elevated helicity at the level of secondary entry tears which had been missed by streamline visualization.

Celiac axis stenosis and digestive disease: Diagnosis, consequences and management

Arterial blood flow to the organs of the upper abdomen is provided by the celiac axis (CA) and the superior mesenteric artery (SMA) that communicate between each other via the gastro-duodenal artery, the anterior and posterior pancreatico-duodenal arcades, the branches of the dorsal pancreatic artery and inconsistently, though a supplementary arcade that connects the CA and the SMA (arcade of Bühler). Celiac axis stenosis may or may not have a hemodynamic impact on the splanchnic circulation. Hemodynamically significant CA stenosis can be asymptomatic, or symptomatic with variables clinical consequences. Management depends on whether the mechanism of stenosis is extrinsic or intrinsic. When upper gastrointestinal interventional radiology or surgery is indicated, stenosis can pose technical difficulties or create severe ischemia requiring good understanding of this entity in the planning of operative steps and adapted management. Management of CA stenosis is therefore multidisciplinary and may involve interventional radiologists, gastrointestinal surgeons, vascular surgeons as well as medical physicians. Even though the prevalence of CA stenosis is relatively low (between 5 and 10%) and irrespective of its etiology, surgeons, radiologists and physicians must be aware of it because it can intervene in the management of upper gastrointestinal disease. It must be sought, and treatment must be adapted to each particular situation to avoid potentially severe complications.

CT and MRI assessment of intestinal blood flow

The accuracy of multi-slice computed tomography (CT) in the diagnosis of acute mesenteric ischemia is very high, however, it cannot demonstrate the small embolus of blood vessels and abnormal intestinal blood flow. The intestinal blood flow in chronic mesenteric ischemia decreases whereas there are few morphology changes, which leads to a high misdiagnosis rate of CT and CT angiography. In addition, inflammatory bowel disease, intestinal tumors, and portal hypertension can be diagnosed definitely by conventional CT, but the hemodynamics and microcirculation in these conditions cannot be assessed, which affects the accuracy of clinical staging and the assessment of therapeutic effect. For intestinal diseases, especially mesenteric ischemia, therefore, it is needed not only to make CT morphologic diagnosis but also to further assess the abnormal intestinal blood flow. In recent years, more and more CT and magnetic resonance imaging (MRI)-related new techniques for assessing blood flow have emerged, including CT perfusion, spectral CT imaging, magnetic resonance perfusion imaging, and phase contrast MRI. This paper reviews the clinical application and progress of these techniques for assessing intestinal blood flow.

Computational simulation of flow-induced arterial remodeling of the pancreaticoduodenal arcade associated with celiac artery stenosis

Arterial remodeling of the pancreaticoduodenal arcade, which enables collateral flow to the liver, spleen, and stomach, is a well-recognized clinical sign of celiac artery (CA) stenosis. However, the hemodynamic changes due to remodeling are poorly understood, despite their importance in surgical procedures such as pancreaticoduodenectomy. In this study, a framework to simulate remodeling of the arterial network following pathological flow alterations was developed and applied to investigate the hemodynamic characteristics of patients with CA stenosis. A one-dimensional-zero-dimensional cardiovascular model was used for blood flow simulation. After introducing CA stenosis into the normal network, arterial remodeling was simulated by iteratively changing the diameter of each artery until time-averaged wall shear stress reached its value under normal conditions. A representative case was simulated to validate the present framework, followed by simulation cases to investigate the impact of stenosis severity on remodeling outcome. A markedly dilated arcade was observed whose diameter agreed well with the corresponding values measured in subjects with CA stenosis, confirming the ability of the framework to predict arterial remodeling. A series of simulations clarified how the geometry and hemodynamics after remodeling change with stenosis severity. In particular, the arterial remodeling and resulting blood flow redistribution were found to maintain adequate organ blood supply regardless of stenosis severity. Furthermore, it was suggested that flow conditions in patients with CA stenosis could be estimated from geometric factors, namely, stenosis severity and arcade diameter, which can be preoperatively and non-invasively measured using diagnostic medical images.