The axial slices of high-resolution lemon images (a, b, c) and in-vivo rat brain images (d, e, f) acquired with FLASH (a, d), GE-EPI (b, e), and RASE (c, f). In experimental setup of in-vivo rat brain imaging, the slab was chosen to include the olfactory-bulb region around which large magnetic-susceptibility effects exist. As expected, RASE showed much better image quality with much less distortion and signal loss than GE-EPI because of a high degree of tolerance to magnetic field inhomogeneity (black and white arrows). (g) illustrates the animation of the rat brain and shows the location of the short-TE slices which include the olfactory bulb.
Arterial Input Function(AIF)
Experimental results of the Gd-doped phantom imaging (a, b) and DCE imaging of mice in the kidney (c, d) obtained with RASE and 2D FLASH. a: The results obtained from RASE and FLASH were plotted with red and blue circled solid lines, respectively. By virtue of the reduced susceptibility-induced signal loss due to the quadratic-phase encoding, RASE provided higher signal enhancements than FLASH, showing a stronger positive linear correlation between signal intensity and Gd-concentration. b: The estimated Gd-concentrations from RASE agreed well with the expected Gd-concentrations (red solid line), as well as the ones estimated directly from T1 measurement as a standard reference (black solid line). In contrast, the estimated Gd-concentrations from FLASH increasingly deviated from their expected ones as the Gd-concentration increased (blue solid line). c: The arterial input functions (AIF) at the mouse kidney-feeding artery were obtained from RASE at the injection doses of 0.1, 0.2, and 0.3 mmol/kg as blue, green, and red solid lines, respectively. The subfigure shows the artery region (pointed to by a white arrow) 40 seconds after the injection. d: Peak concentrations of the AIFs were separately plotted for better representation, showing a strong positive linear correlation with the injection dose (r2 = 0.97, P < 0.001).
t-score and tSNR maps for GE-EPI (a, c) and RASE-II (b, d) on the somatosensory area of in-vivo rat brain. The top row shows t-score maps of BOLD activation in the range between 3 and 8 (a, b). The second row shows tSNR maps for the baseline volumes in the range between 0 and 40 (c, d). The table in the bottom row summarizes the number of activated voxels with t-scores in the range between 3 and 8, above 8. The maximum t-score of GE-EPI and RASE-II was 9.05 and 11.65, respectively.
Imaging of Action Potential Propagation
(ex-vivo Squid Axon)
Measurement of action potential of ex-vivo squid giant axon with an event-related electrical stimulation before MRI experiments
Experimental results performed using a giant axon dissected from squid. Experimental protocols are shown on the top row. Original and filtered time-course data were plotted as a function of time (second row) in ROI (square box) from the time-series coronal 2D-UTE images (third row) and signal increase by ~10% was observed when electrical stimulation was delivered to the axon. The corresponding 2D spatial-distribution maps in response to action potential are presented in the fourth row.
Experimental results performed using an insulated copper-wire for two different flip angles, i.e., FA = 3° (A) and FA = 20° (B). Experimental protocols are shown on the top row. Original and filtered time-course data were plotted as a function of time (second row) in ROI (square box) from the time-series coronal 2D-UTE images (third row) and signal increase occurred only at the instant of current-on and off, not during the current application. Signal change increased with FA = 20° in comparison to FA = 3°. The corresponding 2D spatial-distribution maps in response to electrical stimulation are presented in the fourth row.