Skip to content

Advertisement

Journal of Cardiovascular Magnetic Resonance

Open Access

SE_MC sequence improves image quality of carotid arteries and atherosclerotic plaques

  • Luca Biasiolli1,
  • Alistair C Lindsay1,
  • Robin P Choudhury1 and
  • Matthew D Robson1
Journal of Cardiovascular Magnetic Resonance201012(Suppl 1):P138

https://doi.org/10.1186/1532-429X-12-S1-P138

Published: 21 January 2010

Introduction

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.

Purpose

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.

Methods

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).

Results

In normal volunteers, FSE images show a significant blurring along the phase-encoding direction, consistent with the simulated images. T1w and PDw are more affected by blurring than T2w images because low spatial frequencies (along the phase-encoding direction) are sampled at short TEs. Horizontal and vertical image profiles highlight the difference between the phase-encoding and the frequency-encoding directions for both FSE and simulated images. SE_MC images do not suffer from blurring, thus arterial wall boundaries are sharper and better contrasted. Details of plaque morphology and composition are more clearly visible in SE_MC images, Figure 1.
Figure 1

Comparison between FSE and SE_MC dark-blood carotid images in computer simulations, normal volunteers and atherosclerotic patients.

Conclusion

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.

Authors’ Affiliations

(1)
University of Oxford, Oxford, UK

Copyright

© Biasiolli et al; licensee BioMed Central Ltd. 2010

This article is published under license to BioMed Central Ltd.

Advertisement