Motion and eddy current–induced signal dephasing in in vivo cardiac DTI

Abstract

Purpose To address motion in cardiac DWI, stimulated‐echo acquisition mode (STEAM) and second‐order motion‐compensated spin‐echo (SE) sequences have been proposed. Despite applying motion‐compensation strategies, residual motion can cause misleading signal attenuation. The purpose of this study is to estimate the motion‐induced error in both sequences by analysis of image phase. Methods Diffusion‐weighted motion‐compensated SE sequences and STEAM imaging was applied in vivo with diffusion encoding along 3 orthogonal directions. A b‐value range of 100 to 600 s/mm2 and trigger delays of 25%, 50%, and 75% of end systole and middiastole were used. Eddy‐current contributions were obtained from phantom measurements. After computation of motion‐induced phase maps, the amount of signal dephasing was computed from phase gradients, and the resulting errors in diffusion tensor parameters were calculated. Results Motion‐induced dephasing from the STEAM sequence showed less dependency on the b‐value and no dependency on the heart phase, whereas SE imaging performed best at 75% end systole followed by 50% end systole and middiastole. For a typical experimental setting, errors of 3.3%/3.0% mean diffusivity, 4.9%/4.8% fractional anisotropy, 2.9º/3.2º helix angulation, 0.8º/0.7º transverse angulation, and 9.9º/10.0º sheet angulation (SE/STEAM) were calculated. Conclusion Image phase contains valuable information regarding uncompensated motion and eddy currents in cardiac DTI. Although the trigger delay window for SE is narrower compared with the STEAM‐based approach, imaging in both systole and diastole is feasible and both sequences perform similarly if the trigger delays are selected carefully with SE.

Development of a cardiovascular magnetic resonance‐compatible large animal isolated heart model for direct comparison of beating and arrested hearts

“…As we have demonstrated, the use of an isolated perfused heart allows straightforward colocalisation of the imaging data and blocks of tissue used for histology. Future studies may include investigation of the effectiveness of motion compensation provided by the STEAM sequence by comparing the phase images between equivalent beating and arrested heart data, in a manner similar to Stoeck et al 47 Beyond the investigation of CMR methods, we believe this CMR-compatible isolated perfused beating large animal heart model has potential use in assessing myocardial tissue engineering methods, cardiac regeneration therapy and in joint imaging-electrophysiology studies. 48 There are a number of limitations to this study, in addition to the myocardial oedema and apparent failure to achieve microstructural relaxation, as discussed above.…”

“…As we have demonstrated, the use of an isolated perfused heart allows straightforward colocalisation of the imaging data and blocks of tissue used for histology. Future studies may include investigation of the effectiveness of motion compensation provided by the STEAM sequence by comparing the phase images between equivalent beating and arrested heart data, in a manner similar to Stoeck et al 47 …”

Characterization and correction of diffusion gradient‐induced eddy currents in second‐order motion‐compensated echo‐planar and spiral cardiac DTI

“…Because DW‐STEAM sequences do not require strong gradient systems, diffusion gradient‐induced eddy currents were assumed to be negligible. 54 Their approach of measuring field maps using a low‐resolution spiral for each acquisition could capture both static and variations in a convenient manner. The lower resolution of the field map, however, would not allow to correct for issues at tissue interfaces.…”

Validation of cardiac diffusion tensor imaging sequences: A multicentre test–retest phantom study

“… 23 Furthermore, DTI relies on low SNR DW images, leading to errors in measured parameters, 24 , 25 and sensitivity to image resolution and SNR. 26 The low SNR necessitates larger voxel sizes that enhance partial volume and residual motion artefacts, 27 while the rapid switching of diffusion gradient waveforms may enhance eddy current effects. 27 Additionally, early STEAM studies erroneously ascribed b‐values of 0 s/mm 2 to the non‐DW data during the reconstruction, leading to bias in MD, even within one sequence type.…”

“… 26 The low SNR necessitates larger voxel sizes that enhance partial volume and residual motion artefacts, 27 while the rapid switching of diffusion gradient waveforms may enhance eddy current effects. 27 Additionally, early STEAM studies erroneously ascribed b‐values of 0 s/mm 2 to the non‐DW data during the reconstruction, leading to bias in MD, even within one sequence type. 28 , 29 Consequently, studies in the myocardium of healthy volunteers have reported a wide range of MD (0.87 x 10 −3 to 1.72 x 10 −3 mm 2 /s) and FA (0.29 to 0.61).…”