Comparison of flow parameters to analyse bolus kinetics of ultrasound contrast enhancement in a capillary flow model

Aim: Perfusion harmonic imaging is a new method to evaluate brain perfusion. The purpose of our study was to describe flow by analysing the kinetics of ultrasound contrast enhancement in a flow model after bolus injection of an ultrasound contrast agent (UCA). Methods: We performed an in-vitro study with an open-circuit flow model and SonoVue(R) given as bolus injection. Bolus kinetics was analysed by harmonic imaging (SONOS 5500, 1.8/3.6 MHz, MI: 1.6) at a fixed frame rate (0.67 Hz). Five different flow rates from 1.8 to 21.6 ml/min were tested. We generated time-intensity curves (TIC) from the grey scale loops. Five parameters (time-to-peak-intensity [TTP], peak-intensity [PI], area under the curve [AUC], positive gradient [PG] and full width at half maximum [FWHM]) were correlated with flow rate. Results: The analysis of both TTP and PG versus flow rate indicated a highly significant linear correlation (r = -0.96, P < .01; r = 0.91, P = .03; respectively). Neither the AUC (r = -0.67, P = .22), nor the PI (r = 0.68, P = .20) nor the FWHM (r = -0.63, P = .37) correlated significantly with flow rate. Conclusion: The relationship between TIC parameters and flow rates indicates that, in our flow model, the TTP and PG are the most robust and reliable parameters compared to the AUC, PI and FWHM.