Manifold‐based respiratory phase estimation enables motion and distortion correction of free‐breathing cardiac diffusion tensor MRI

Abstract

Purpose: For in vivo cardiac DTI, breathing motion and B 0 field inhomogeneities produce misalignment and geometric distortion in diffusion-weighted (DW) images acquired with conventional single-shot EPI. We propose using a dimensionality reduction method to retrospectively estimate the respiratory phase of DW images and facilitate both distortion correction (DisCo) and motion compensation. Methods: Free-breathing electrocardiogram-triggered whole left-ventricular cardiac DTI using a second-order motion-compensated spin echo EPI sequence and alternating directionality of phase encoding blips was performed on 11 healthy volunteers.The respiratory phase of each DW image was estimated after projecting the DW images into a 2D space with Laplacian eigenmaps. DisCo and motion compensation were applied to the respiratory sorted DW images. The results were compared against conventional breath-held T 2 half-Fourier single shot turbo spin echo. Cardiac DTI parameters including fractional anisotropy, mean diffusivity, and helix angle transmurality were compared with and without DisCo. Results: The left-ventricular geometries after DisCo and motion compensation resulted in significantly improved alignment of DW images with T 2 reference. DisCo reduced the distance between the left-ventricular contours by 13.2% ± 19.2%, P < .05 (2.0 ± 0.4 for DisCo and 2.4 ± 0.5 mm for uncorrected). DisCo DTI parameter maps yielded no significant differences (mean diffusivity: 1.55 ± 0.13 × 10 −3 mm 2 /s and 1.53 ± 0.13 × 10 −3 mm 2 /s, P = .09; fractional anisotropy: 0.375 ± 0.041 and 0.379 ± 0.045, P = .11; helix angle transmurality: 1.00% ± 0.10°/% and 0.99% ± 0.12°/%, P = .44), although the orientation of individual tensors differed.

Cardiac q‐space trajectory imaging by motion‐compensated tensor‐valued diffusion encoding in human heart in vivo

“…First, we observed potential bias in parameters (higher MD and lower FA, μFA, and MK) in the inferior wall due to susceptibility artifacts near the posterior vein. This may be ameliorated by acquiring additional data with reversed phase encoding 69,70 . Second, the slice‐selection gradients were neglected in the experimental design and analysis but are known to contribute to motion encoding 71 .…”

“…This may be ameliorated by acquiring additional data with reversed phase encoding. 69 , 70 Second, the slice‐selection gradients were neglected in the experimental design and analysis but are known to contribute to motion encoding. 71 Third, the sample size was small and consisted of young healthy volunteers with relatively steady heart rates.…”

Cardiac DTI using short‐axis PROPELLER: A feasibility study

“…M2‐ssEPI offers rapid data acquisition and reduced susceptibility to subject motion, making it the preferred sequence for cDTI in many cases 22–24 . However, M2‐ssEPI does have certain drawbacks, including the Nyquist ghost artifact (specific to EPI), geometric distortion, and misalignment due to B0 field inhomogeneities, as well as reduced resolution resulting from the extended readout time and $$$ {\mathrm{T}}_2^{\ast } $$$ decay.…”

“…It offers enhanced acquisition efficiency, reduced geometric distortion, decreased motion-induced phase errors resulting from bulk motion in the presence of diffusion gradients, and the capability to image rapid physiological processes within the human body. [22][23][24] However, M2-ssEPI still exhibits susceptibility to B 0 inhomogeneities and gradient eddy current effects, which can result in moderate to severe geometric distortion, especially near air-tissue interfaces, and lead to Nyquist ghost artifacts. Additionally, the long echo train length (ETL) in ssEPI, along with significant T * 2 decay, contributes to reduced resolution and SNR in the acquired DW images.…”

“…The combination of M2 and 2D spatially selective RF single‐shot spin‐echo EPI (M2‐ssEPI) 22 has proven to be a valuable acquisition method for clinical cDTI scans, particularly excelling in FB conditions and robustness against cardiac motion. It offers enhanced acquisition efficiency, reduced geometric distortion, decreased motion‐induced phase errors resulting from bulk motion in the presence of diffusion gradients, and the capability to image rapid physiological processes within the human body 22–24 . However, M2‐ssEPI still exhibits susceptibility to B 0 inhomogeneities and gradient eddy current effects, which can result in moderate to severe geometric distortion, especially near air‐tissue interfaces, and lead to Nyquist ghost artifacts.…”