Vessel-wall imaging and quantification of flow-mediated dilation using water-selective 3D SSFP-echo
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RESEARCH
Open Access
Vessel-wall imaging and quantification of flow-mediated dilation using water-selective 3D SSFP-echo Michael C Langham1, Cheng Li1, Erin K Englund1, Erica N Chirico1, Emile R Mohler III2, Thomas F Floyd3 and Felix W Wehrli1,4*
Abstract Background: To introduce a new, efficient method for vessel-wall imaging of carotid and peripheral arteries by means of a flow-sensitive 3D water-selective SSFP-echo pulse sequence. Methods: Periodic applications of RF pulses will generate two transverse steady states, immediately after and before an RF pulse; the latter being referred to as the SSFP-echo. The SSFP-echo signal for water protons in blood is spoiled as a result of moving spins losing phase coherence in the presence of a gradient pulse along the flow direction. Bloch equation simulations were performed over a wide range of velocities to evaluate the flow sensitivity of the SSFP-echo signal. Vessel walls of carotid and femoral and popliteal arteries were imaged at 3 T. In two patients with peripheral artery disease the femoral arteries were imaged bilaterally to demonstrate method’s potential to visualize atherosclerotic plaques. The method was also evaluated as a means to measure femoral artery flow-mediated dilation (FMD) in response to cuff-induced ischemia in four subjects. Results: The SSFP-echo pulse sequence, which does not have a dedicated blood signal suppression preparation, achieved low blood signal permitting discrimination of the carotid and peripheral arterial walls with in-plane spatial resolution ranging from 0.5 to 0.69 mm and slice thickness of 2 to 3 mm, i.e. comparable to conventional 2D vessel-wall imaging techniques. The results of the simulations were in good agreement with analytical solution and observations for both vascular territories examined. Scan time ranged from 2.5 to 5 s per slice yielding a contrast-to-noise ratio between the vessel wall and lumen from 3.5 to 17. Mean femoral FMD in the four subjects was 9%, in good qualitative agreement with literature values. Conclusions: Water-selective 3D SSFP-echo pulse sequence is a potential alternative to 2D vessel-wall imaging. The proposed method is fast, robust, applicable to a wide range of flow velocities, and straightforward to implement.
Background The most common site of cerebrovascular atherosclerotic disease is the outer wall of the carotid sinus proximal to the bifurcation. At arterial bifurcations or regions of high curvature the unidirectional flow gives way to complex hemodynamics including reversing flow patterns leading to low wall shear stress, a condition promoting atherogenesis * Correspondence: [email protected] 1 Department of Radiology, School of Medicine, University of Pennsylvania, Philadelphia, USA 4 Radiologic Science, Biochemistry and Biophysics, Medical Center, University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, USA Full list of author information is available at the end of the article
[1,2]. Much of the work on the high-resolution vessel-wall, black-blood cardiovas
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