Volume 13 Supplement 1
Flip angle optimization for quantitative phase contrast MR imaging
© Ennis et al; licensee BioMed Central Ltd. 2011
Published: 2 February 2011
The overall objective of the work proposed herein is to optimize the flip angle in gradient-echo based PC-MRI methods for decreased measurement variability in quantitative blood velocity measurements of the common femoral arteries.
PC-MRI is a noninvasive imaging technique used to measure the velocity of flowing blood in a particular blood vessel with flexible spatial and temporal resolution [1, 2]. It is considered the clinical “gold standard” for quantification of blood flow. PC-MRI boasts a variety of established applications in quantifying cardiovascular function and hemodynamics. In particular, this technique offers clinicians with a means of measuring peak velocity, mean velocity, flow rate, and total flow throughout the vasculature of the human body. One of the challenges in PC-MRI is the wide range of variables that make up a given protocol requiring careful optimization of each imaging parameter in an effort to accomplish the goals of a given scan. Surprisingly, the current PC-MRI utilizes a default flip angle, which has not been optimized. A theoretical description of the signal acquired from flowing spins in spoiled gradient-echo pulse sequences has been previously developed . These efforts indicate that there exists a flip angle that provides an optimized SNR for a given tissue, echo time, repetition time, slice thickness and velocity, which leads to increased reproducibility of quantitative PC-MRI measurements. This optimization cannot be performed empirically because of the number of parameters involved, hence mathematical and computation work is required.
All measurements were performed on a 1.5 Tesla system (Avanto; Siemens Medical Solutions, Erlangen, Germany) using a 16-channel surface coil. Blood velocity data in the common femoral arteries were obtained in 5 healthy consenting volunteers (4 male, 1 female, age __ ± __ years). PC-MRI was performed without breath-hold using retrospective ECG triggering. Imaging parameters included 340 x 212.5 mm field of view, 256 x 160 matrix, 1.3 mm isotropic resolution, 8 mm slice thickness, 5.4/3.2 msec TR/TE, 32.4 msec temporal resolution, a range of flip angles for optimization (5,10,15,20,30,40,60,75 and 90°), 888 Hz/pixel acquisition bandwidth, three views per segment and a velocity encoding strength of 75 cm/sec (53 second scan time). The imaging was repeated 5 times in each volunteer.
This article is published under license to BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.