Comparison of pulse subtraction Doppler and pulse inversion Doppler.

In this paper, a new Doppler technique based on pulse subtraction imaging (PSD) is described and compared with pulse inversion Doppler (PID). Combining a nonlinear contrast agent imaging technique with a Doppler process provides a tool for detecting motion of both contrast agents and tissues. This has potential in targeted imaging in which attached microbubbles need to be separated from moving ones and surrounding tissues. The results from both simulation and experiment show that PSD is able to differentiate bubble motion from tissue motion. For Doppler processing conducted at the fundamental frequency, the contrast-to-tissue ratio (CTR) in PSD was 3.3 (±0.4) times higher on average than PID at a mechanical index (MI) of 0.1. At the harmonic frequency, PID was shown to have a 3.1 (±0.4) times higher CTR than PSD. Overall, taken in their optimum processing conditions, PID has a CTR up to 1.9 (±0.4) times higher than PSD. The CTRs for both techniques have also been shown to increase with increasing MI. However, for the same axial Doppler resolution. PSD also allows less energy to be transmitted into the medium, which makes it less disruptive. The relative performances of PSD and PID in terms of the bandwidth of the imaging system are also discussed.

On sizing and counting of microbubbles using optical microscopy.

Intra- and interobserver (n = 3) variability of sizing and counting microbubbles using optical microscopy (OM) was assessed. The system was calibrated using standardised mono-disperse and poly-disperse microspheres. Results of the calibration show intraobserver variations of number count (C) = 13.0% and arithmetic mean size (MS) = 0.2%, and interobserver variations of C = 18.4% and MS = 0.6%, for the mono-disperse microspheres. For the poly-disperse microspheres, intraobserver variations were: C = 6.9% and MS = 0.8%, and interobserver: C = 10.5% and MS = 0.3%. For SonoVue™ the intraobserver variations were: C = 23.3% and MS = 8.0%, and interobserver C = 6.8% and MS = 3.8%. The results suggest that the higher values of the intraobserver variation for SonoVue™ arise from the natural decay of microbubbles over time. This article presents a detailed protocol and outlines potential pitfalls in our approach. These results are in general agreement with those previously reported and compare well with known size distributions.