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Assessment of myocardial strain using strain-encoding (SENC) MRI: comparison of acquisition strategies
Journal of Cardiovascular Magnetic Resonance volume 13, Article number: P15 (2011)
Strain-encoding (SENC) MRI was recently introduced for measuring strain with high-resolution and simple post-processing(1). Figure-1 shows SENC pulse sequence. In typical SENC sequence, k-space data is acquired line-by-line in rectilinear fashion, which results in long scan-time and renders the technique impractical for many applications. Nevertheless, fast imaging techniques, e.g. Radial or Spiral acquisition, allow for reducing scan time while maintaining adequate image quality. In this work, Radial and Spiral acquisitions were implemented in SENC for improved performance. The developed sequences were tested on volunteers and the results were evaluated and compared to standard Cartesian acquisition.
Radial and Spiral acquisitions(2) were implemented in SENC, and the different sequences were tested on three volunteers on Siemens Tim-Trio 3.0-Tesla scanner. The imaging parameters were: FOV=350mm, slice-thickness =10mm, flip-angle=15°, # heart-phases=25, and scan time=17 s. The three sequences were optimized for the fixed scan-time. Maximum resolution obtained was 160x160 for Cartesian (80% phase-encoding coverage) and Radial (128 Radial spokes), and 256x256 for Spiral (10 spiralsx2 averages). The low-tuning and high-tuning images were combined together as described in(1) to construct the strain images. Strain values were measured at five different points along the lateral left-ventricular wall on all volunteers. Bland-Altman analysis was conducted to compare measurements from different sequences.
Figure-2 shows example of the acquired SENC images. The strain values measured at the same position were similar in different images, as shown in the strain curves in Figure-3. The Bland-Altman analysis showed no bias between strain measurements from different acquisitions (Figure-4). The mean±SD of the (circumferential) strain differences were 0.42±2.46 and -0.25±1.76 % for the Radial-Cartesian and Spiral-Cartesian differences, respectively. All the differences lied within the ±2SD limit.
Discussion and conclusions
Data acquisition strategy (k-space trajectory) affects scan-time and the resulting image-quality in SENC. Image quality was similar in Cartesian and Radial. Less radial spokes can be acquired to reduce scan-time without much affecting image-quality. Due to its acquisition nature, spatial-resolution is compromised in Radial acquisition. For the same scan time, Spiral acquisition allowed for improving resolution by more than 60% and doubling # averages, compared to Cartesian or Radial, despite longer reconstruction time. High spatial-resolution would allow for accurate measurements in small structures, e.g. thinning myocardial wall, or it can be traded for faster or real-time imaging. The choice of the acquisition-technique depends on patient condition, available scan-time, and imaging features of importance.
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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.
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Ibrahim, ES.H., Rehwald, W., Sutton, B.P. et al. Assessment of myocardial strain using strain-encoding (SENC) MRI: comparison of acquisition strategies. J Cardiovasc Magn Reson 13 (Suppl 1), P15 (2011). https://doi.org/10.1186/1532-429X-13-S1-P15
- Acquisition Strategy
- Typical SENC
- Myocardial Strain
- Strain Image
- Spiral Acquisition