On the ability of ultrasound parametric perfusion imaging to predict the area of infarction in acute ischemic stroke.

PURPOSE: Cerebral perfusion deficits in acute ischemic stroke can be detected by means of transcranial harmonic imaging after ultrasound contrast agent bolus injection. We evaluated five different parameters of the bolus kinetics as parametric images and correlated areas of disturbed perfusion with the area of definite infarction. MATERIALS AND METHODS: Perfusion harmonic imaging after SonoVue bolus injection (BHI) was used to investigate 22 patients suffering from acute internal carotid artery infarction. For each subject, we calculated five different images based on the following parameters from the time-intensity curve in each pixel: pixelwise peak intensity (PPI), area under the curve (AUC), positive gradient (PG), time to peak (TTP), and a three factor image from the factor analysis of medical image sequences (FAMIS). The findings in the diencephalic imaging plane were compared with the definite area of infarction, as diagnosed by cranial CT. RESULTS: In predicting the definite area of infarction in follow-up CT, we found the following sensitivities and positive predictive values (PPV): PPI (100 %/95 %), AUC (100 %/90 %), FAMIS (89 %/89 %), PG (84 %/94 %) and TTP (47 %/100 %). The areas of disturbed perfusion in all five types of parametric images correlated significantly with the area of infarction in CT. Images from the FAMIS algorithm and PPI images showed the highest Spearman rank correlation with the area of definite infarction as displayed in CT (both r = 0.76, p < 0.001). Images from the other parameters correlated as follows: PG: r = 0.62 (p = 0.003), AUC: r = 0.53 (p = 0.014), TTP: r = 0.50 (p = 0.021). CONCLUSION: BHI can detect disturbed perfusion in acute hemispheric stroke. In their ability to predict the development of an infarction, intensity-based parameters and FAMIS were determined to have a high sensitivity, and TTP was found to have a high PPV and specificity.

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.