11C-4 Fast Blood Vector Velocity Imaging: Simulations and Preliminary In Vivo Results

Conventional ultrasound methods for acquiring color flow images of the blood velocity are limited by a relatively low frame rate and are restricted to only give velocity estimates along the ultrasound beam direction. To circumvent these limitations, we propose a method where the frame rate can be significantly increased, and the full 2-D vector velocity of the blood can be estimated. The method presented in this paper uses three techniques: 1) The ultrasound is not focused during the transmit of the ultrasound signals, and a full speckle image of the blood can be acquired for each pulse emission. 2) The transmitted pulse consists of a 13 bit Barker code which is transmitted simultaneously from each transducer element. 3) The 2-D vector velocity of the blood is found using 2- D speckle tracking between segments in consecutive speckle images. The method was tested with a 5.5 MHz linear array transducer scanning a flow phantom. This was done first with the Field II ultrasound simulation program. Standard deviation and bias of the velocity estimates were evaluated when six parameters were changed around an initial point. The conclusions drawn from the simulations were then used in a scanning with our experimental RASMUS scanner. The same setup as in the simulations was used, and the standard deviation and bias were found. Finally, the common carotid artery of a healthy 36 year old male was scanned for 1.29 sec. with the RASMUS scanner, and 129 independent vector velocity images were acquired with a frame rate of 100 Hz. The derived volume flow estimates were compared with MR angiography, and a deviation of 9 % was found.