Free breathing myocardial perfusion MRI with SW-CG-HYPR using motion correction
Journal of Cardiovascular Magnetic Resonance volume 12, Article number: P205 (2010)
The diagnostic value of first-pass perfusion MRI is limited by the low spatial coverage, resolution, SNR, and motion artifacts. Sliding-Window Conjugate-Gradient HYPR  (SW-CG-HYPR) has been proposed to acquire perfusion images with increased spatial coverage, better spatial resolution, and improved SNR . However, this method is sensitive to the respiratory motion and thus limited to the breath hold. Motion correction may be useful to reduce motion artifacts and allow for free-breathing first-pass perfusion.
To develop and test a non-model-based motion correction method combined with SW-CG-HYPR to perform free-breathing myocardial MR imaging.
An ECG-triggered, multi-slice FLASH sequence with radial sampling was used. As shown in Figure 1, radial sampling was applied in a segmented interleaved fashion. Multiple slices were acquired after each saturation recovery pre-pulse. The motion correction method is illustrated in Figure 2. Both translation and rotation of the heart were detected in image domain by calculating the normalized cross-correlation coefficients. Motion correction was performed in k-space by rotating the undersampled k-space and shifting the phase by a factor of exp(-2πi(δx/Nread+δy/Npe)), where δx and δy are the number of pixels to shift in × and y direction, and Nread and Npe are the total number of pixels along readout and phase encoding direction. Sliding window was used to reconstruct the composite images, and the time-resolved images were reconstructed after CG-HYPR processing. Six healthy volunteers were scanned using a 1.5 T system, with and without breath hold, during first-pass of the contrast agent. Imaging parameters included: TR/TE/flip-angle = 3.2/1.6 ms/10º, spatial resolution = 1.3 × 1.3 × 10 mm3, and number of slices = 6. The images were qualitatively graded by a reviewer using a score of 1-4 (1: worse; 4: best), and the signal changes vs. time curves were compared.
The average image quality score of the free-breathing images with motion correction (3.09 ± 0.37) is significantly higher than those without motion correction (2.26 ± 0.40), and is comparable to the successful breath-holding images (3.10 ± 0.41) (Figure 3). The signal changes in motion corrected free-breathing images were closely related to those in the breath-holding images, with a correlation coefficient of 0.9764 for myocardial signals (Figure 4 and 5).
The image quality of myocardial perfusion MRI using SW-CG-HYPR was substantially improved after motion correction. This technique may allow myocardial perfusion MRI during free breathing.
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Ge, L., Kino, A., Griswold, M. et al. Free breathing myocardial perfusion MRI with SW-CG-HYPR using motion correction. J Cardiovasc Magn Reson 12 (Suppl 1), P205 (2010). https://doi.org/10.1186/1532-429X-12-S1-P205