- Oral presentation
- Open Access
Improving the accuracy of cardiac DTI by averaging the complex data
© Scott et al; licensee BioMed Central Ltd. 2015
- Published: 3 February 2015
- Fractional Anisotropy
- Diffusion Tensor Imaging
- Mean Diffusivity
- Diffusion Weighting
- Complex Average
When performing cardiac diffusion tensor imaging (cDTI) multiple averages are typically acquired to compensate for the low signal to noise ratio of the individual images. However, the potential for reducing noise in low signal areas is not fully realized when the averaging is performed on the magnitude data. Averaging the complex cDTI data is not straightforward as the diffusion weighting introduces a different, spatially varying phase across each image. In this work we use simulations to demonstrate the benefits available when using complex averaging and then develop an algorithm for performing complex averaging of in-vivo cDTI data, which accounts for the induced phase variations.
To compare the performance of magnitude and complex averaging in the presence of noise, simulated noisy diffusion weighted images of the left ventricle were calculated with b-values from 50-3000smm-2 based on previously published in-vivo cDTI data. Magnitude or complex averaging was performed before processing the images with the software we typically use for in-vivo cDTI data.
Additionally, in-vivo cDTI was performed on a Siemens Skyra in 10 subjects using the STEAM-EPI sequence with 4 b-values, 500-2000smm-2, 12 averages, 6 directions, SENSE reconstruction (magnitude and phase images) and 2.8x2.8x8mm3 resolution. In order to remove motion-induced phase, each image (Real+Imaginary) was filtered (pyramid mask in k-space, extent: ¼ field-of-view) and the phase of the low-resolution copy was removed from the original images. The images were then processed as for the simulations.
Large b-values are required to avoid under-estimation of FA and MD in cDTI. We have demonstrated that the phase introduced by diffusion weighting in vivo can be corrected for within the reconstruction, allowing us to partially compensate for the noise-floor effects present at high b-values by using complex averaging.
This work was performed at the National Institute for Health Research Funded Cardiovascular Biomedical Research Unit at The Royal Brompton Hospital and Imperial College.
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/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.