OP23.05: Influence of pulse repetition frequency adjustment on three-dimensional power Doppler indices and STIC volumetric pulsatility index using an in vivo model

Recently, the “volumetric pulsatility index” (vPI) based on a technique known as spatio-temporal imaging correlation (STIC) has been proposed as one technique to reduce the liability of 3D-PD to machine settings, attenuation and sampling volume by generating indices of vascular impedance across the cardiac cycle. The objective of this study was to determine the influence of PRF upon 3D-PD indices and vPI from STIC datasets acquired from a common carotid of a healthy subject. Additionally, we sought to investigate the influence of wall motion filter (WMF) upon 3D-PD quantification. Eleven STIC datasets were acquired, one for each PRF value ranging from 0.6 to 9.0 KHz. VFI and vPI values were determined from the 440 static 3D datasets contained in these STIC datasets. Three sets of radiofrequency (RF) data were acquired, for off-line processing of different WMF values for PRF values of 0.6, 3.3 and 10 KHz. VFI curves were constructed and two patterns were observed: a flat pattern with low PRF and a triphasic pattern with high PRF correlating with the known pulsed-wave Doppler profile of this vessel. vPI values were around zero for low PRF settings and increased with increasing PRF, becoming relatively stable at PRF 3.2 and 4.0 KHz. Analysis of the RF data demonstrated that increasing WMF values gradually filters out the low intensity PD signals whilst retaining the higher intensity ones, allowing the distinction of integrated PD signals intensity throughout the cardiac cycle. We conclude that PRF and WMF dramatically influence 3D-PD indices and vPI, and that use of PRF values in which minimum VFI values are measured in the diastolic phase in the spectral Doppler wave may validate the use of vPI.