SE_MC sequence improves image quality of carotid arteries and atherosclerotic plaques
© Biasiolli et al; licensee BioMed Central Ltd. 2010
Published: 21 January 2010
Double-Inversion-Recovery (DIR) FSE is the standard MRI sequence used to acquire blood suppressed 2D high-resolution T1, PD and T2-weighted images for atherosclerotic plaque characterization in the carotid arteries.
FSE images suffer from blurring because of non-uniform T2-weighting of k-space [Constable, Gore.MRM.1992.28(1):9-24], which is stronger on small structures with short T2 times, such as carotid arteries. To avoid this, we propose to generate T1-PD-T2-weighted images using Spin-Echo Multi-Contrast (SE_MC) sequence. FSE and SE_MC are both CPMG multi-echo sequences; however FSE acquires different lines of the same k-space at different TEs, whereas SE_MC samples multiple k-spaces (with constant TE) at different TEs.
The image formation process for SE and FSE sequences was simulated in MATLAB (MathWorks) applying the same parameters and k-space acquisition strategy used in-vivo (TE = 14 ms, ETL = 9). An average carotid artery (lumen-diameter = 7 mm, wall-thickness = 1 mm, T2 = 40 ms) was simulated by linear combination of Bessel functions in k-space. In the in-vivo study, 6 normal volunteers (6 m, 30 ± 5 years) and 12 atherosclerotic patients (10 m, 74 ± 9 years) were imaged at 3 T (TIM Trio, Siemens Medical Solutions) using surface coils (FOV = 150 × 150 mm, matrix = 320 × 320, slice = 2 mm). The ECG-gated DIR-FSE pulse sequence (ETL = 9) was used to acquire T1w (TE = 14 ms, TR = 1RR, Tacq <60s) PDw (TE = 14 ms, TR = 2RR, Tacq <120s) and T2w (TE = 89 ms, TR = 2RR, Tacq <120s) images. The ECG-gated parallel DIR-SE_MC sequence (partial k-space = 5/8, SENSE-iPat = 2) acquired 7 contrast images (TE = 25.8-103.2 ms) for TR = 1RR (Tacq <120s) and TR = 2RR (Tacq <240s). T2 maps were estimated by non-linear regression and synthetic T1-PD-T2-weighted images were generated at TE = 14 ms (T1w-PDw) and TE = 89 ms (T2w).
This study suggests that replacing FSE with SE_MC in vascular MRI protocols could benefit the segmentation of vessel walls and atherosclerotic plaques with the only disadvantage of a slightly longer acquisition time. Phantom experiments will be soon performed to quantify the error on vessel wall measurements caused by FSE blurring.
This article is published under license to BioMed Central Ltd.