Artan Kaso1 and Thomas Ernst1
1Diagnostic Radiology and Nuclear Medicine, University of Maryland School of Medicine, Baltimore, MD, United States
1Diagnostic Radiology and Nuclear Medicine, University of Maryland School of Medicine, Baltimore, MD, United States
Signal dropouts caused by uncorrected head movement during DWI acquisitions were recovered to a great extent by prospective motion correction using a fast optical tracking system. The residual signal shifts were larger than expected due to the asynchronous application of motion
updates.
Figure 3: k-space shifts versus rotational velocities at TE=68ms. (a,b) the same as in Fig.2. (a) Without PMC, the signal of ~75% of the
repetitions (158/216) is outside the sampling window; blue a=14.5, b=2.5, r2=0.93.
(b) less than 4% (4/216) of repetitions show signal loss. Almost all
acquisitions show 2 motion updates; blue a=-0.5, b=3.5, r2=0.1. (c)
A linear dependency of the residual echo-shift from the k-space center upon rotational
acceleration is now visible; blue a=0.5, b=-0.3, r2=0.4.
Figure 2: k-space shifts versus rotational velocities at TE=80ms. (a) Without PMC, the
signal of less than 50% of repetitions (93/216) is in the sampling window.
This occurs for rotational velocities $$$|\omega_{r}|<6^{\,\circ}/\mathrm{s}$$$,
in agreement with the simulations (grayed band). From theory:
$$$\Delta k_{x}^{max}=a\omega_{r}+b$$$; blue a=17.5, b=3.4, r2=0.97.
(b) With PMC on, less than 4% (2/216) of repetitions
are lost. Two main subpopulations are present, depending upon whether 2 (blue) or 3
(red) motion updates have been applied; blue a=1.8,
b=6.3, r2=0.3.
