Free‐breathing cine DENSE MRI using phase cycling with matchmaking and stimulated‐echo image‐based navigators

Abstract

For free-breathing cine DENSE, the proposed method addresses both types of breathing-induced artifacts and provides better quality images than conventional dNAV and iNAV methods.

Compensation for respiratory motion–induced signal loss and phase corruption in free‐breathing self‐navigated cine DENSE using deep learning

“…where the first and the second terms describe the stimulated echo and the T 1 echo, respectively; M is the displacement-encoded longitudinal magnetization; M 0 is the longitudinal magnetization at thermal equilibrium; k e denotes the combination of the displacement encoding frequency and the through-plane dephasing frequency 11 ; 𝛼 is the flip angle of the RF excitation pulse; ⟨, ⟩ denotes the inner product; r denotes the position of the tissue at the time of signal readout; and Δr is the displacement of the tissue during the time between application of the displacement-encoding pulses and the readout. As the match-making method 8 has previously been shown to effectively perform phase-cycling suppression of the T 1 echo during free breathing, for the remainder of this section we neglect the second term of Equation (1). Diagrams of a short-axis view of the heart and motion and deformation of a small element of myocardium are illustrated in Figure 1A,B, respectively, and show that, without respiratory motion, the stimulated-echo phase is proportional to Δr = Δr C , where Δr C represents displacement due to cardiac motion.…”

“…8 The second type is blurring due to motion-induced position shifts of the tissue, which correspond to (approximately) linear phase errors in k-space of the stimulated echo. 8 The third artifact type comes from an image-domain phase shift (not a position shift) of the stimulated echo due to breathing (i.e., the breathing-induced tissue displacement that is encoded into the phase of the stimulated echo). This image domain phase shift corresponds to a constant phase error in k-space of the stimulated-echo signal and manifests as signal loss (as demonstrated later in this paper).…”

“…The first type is image striping due to imperfect suppression of the T 1 ‐relaxation echo 8 . The second type is blurring due to motion‐induced position shifts of the tissue, which correspond to (approximately) linear phase errors in k‐space of the stimulated echo 8 . The third artifact type comes from an image‐domain phase shift (not a position shift) of the stimulated echo due to breathing (i.e., the breathing‐induced tissue displacement that is encoded into the phase of the stimulated echo).…”

“…The second type is common among most MRI methods and is predicted and accounted for using conventional models that describe the effects of breathing in MRI. 12 Prior work developing self-navigated DENSE introduced the match-making method, 8 which effectively deals with suppression of the T 1 echo in free-breathing phase-cycled DENSE and uses stimulated echo-based image navigators (ste-iNAVs) to estimate and correct for in-plane position shifts due to breathing (i.e., the first and second types of artifacts, respectively, as discussed previously). However, the encoding of respiratory motion into the phase of the stimulated echo (the third type of artifact) has yet to be well described and corrected.…”

Suppression of artifact‐generating echoes in cine DENSE using deep learning

“…These methods include using a relatively high displacement-encoding frequency, 1 acquiring complementary phase-cycled acquisitions, [9][10][11] applying inversion recovery, 12 using through-plane dephasing, 8 and combinations of the aforementioned methods. However, these methods have limitations such as partial loss of the STE signal due to intravoxel dephasing, 8 imperfect suppression of the artifact-generating echoes due to motion between complementary acquisitions, 13 decreasing the signal amplitude and altering the contrast, and increasing the scan time. An ideal method would suppress the artifact-generating echoes without these limitations.…”