Figure 4.

Evaluation of constrained reconstruction at different sub-sampling factors using a 5 sec speech stimuli of counting numbers at a rapid pace. Constrained reconstructions at 5, 3, 2, 1 TR time resolutions are compared with the (a) 2.4 mm², and (b) 1.76 mm² single slice sequences. The spatial frame depicts the event of producing the sound /n/ in the word “one”, where the tongue hits the hard palate. The image time profile corresponds to the time evolution of the cut depicted by the horizontal dotted arrows in (a) and (b). As depicted by the white arrows in the spatial frames, the 5 TR reconstructions produce temporal blurring in capturing the formation of the /n. sound, while the 3, 2, 1 TR reconstructions depict this event well. The temporal blurring in the 5 TR reconstructions is also evident in the image time profiles (see yellow arrows). As the acceleration factor is increased, alias artifacts are predominant in the images as seen with R∼21 in the 1 TR reconstruction at 1.76 mm² spatial resolution (green arrows on the image time profiles). With R∼13, mild alias artifacts were observed in the 1 TR reconstruction at 2.4 mm² spatial resolution. Based on these observations, an acceleration factor of 6.5-7 fold is chosen for rest of the experiments in this work.