An intake valve includes a bladder having a face piece coupled to one end and an opening formed in the other end, a cover attached to the other end of the bladder and having a port coupled to an air reservoir and having a hub coupled to a container, which may be used for pumping air into the bladder when the air in the air reservoir has been consumed. In one embodiment, a clamped level detected signal feeds a filter with very slow response characteristics. Due to the utilization of common information at the N diffusion weighted directions, the acquisition efficiency may be enhanced and image resolution and SNR of acquired images may be improved accordingly.