Microbubble-based Ultrasound Contrast Research Articles

Hepatocellular cancer response to radiofrequency tumor ablation: contrast-enhanced ultrasound

Radiofrequency ablation (RFA) is increasingly being used as percutaneous treatment of choice for patients with early stage hepatocellular carcinoma (HCC). An accurate assessment of the RFA therapeutic response is of crucial importance, considering that a complete tumor ablation significantly increases patient survival, whereas residual unablated tumor calls for additional treatment. Imaging modalities play a pivotal role in accomplishing this task, but ultrasound (US) is not considered a reliable modality for the evaluation of the real extent of necrosis, even when color/power Doppler techniques are used. Recently, newer microbubble-based US contrast agents used in combination with grey-scale US techniques, which are very sensitive to non-linear behavior of microbubbles, have been introduced. These features have opened new prospects in liver ultrasound and may have a great impact on daily practice, including cost-effective assessment of therapeutic response of percutaneous ablative therapies. Technical evolution of CEUS focusing on findings after RFA are illustrated. These latter are detailed, cross-referenced with the literature and discussed on the basis of our personal experience. Timing of CEUS posttreatment assessment among with advantages and limitations of CEUS are also described with a perspective on further technologic refinement.

Renal cortical perfusion in rabbits: visualization with color amplitude imaging and an experimental microbubble-based US contrast agent.

To evaluate an experimental microbubble-based ultrasound (US) contrast agent (Imagent US, formulation AF0150) in the kidney to help identify focal perfusion abnormalities. Six incremental doses (0.007-0.2 mL/kg) of contrast material were injected intravenously in six New Zealand rabbits (3.1-3.5 kg), with experimental focal renal ischemia in five kidneys. Unenhanced and contrast material-enhanced color amplitude and gray-scale images of the kidney were analyzed for changes in mean pixel intensity. Kidneys were harvested and examined pathologically. On contrast-enhanced color amplitude images, mean pixel intensity increased significantly in cortex and medulla at every dose level (P < .0005) (with doses as low as 0.007 mL/kg), and differences were significant in cortical peak intensity and duration of enhancement with incremental increases in dose (P < .006). On contrast-enhanced gray-scale images, renal cortical enhancement reached statistical significance only at the highest dose (0.2 mL/kg). Duration of gray-scale tissue enhancement was not dose related. Color mean pixel intensity markedly increased in areas of normally perfused kidney (P = .002) but remained essentially unchanged in ischemic areas (P = .34). Color Doppler and gray-scale images enhanced with this microbubble-based US contrast agent depict renal cortical perfusion clearly in rabbits.

Analysis of regional cerebral blood flow in dogs, with an experimental microbubble-based US contrast agent.

To evaluate a perfluorochemical stabilized microbubble-based ultrasound (US) contrast agent (Imagent US, formulation AF0145) create regional cerebral blood flow (CBF) maps. Intravenous injections of the contrast agent (0.16-0.20 mL/kg) were performed in four anesthetized dogs (9-14 kg). Serial coronal color-Doppler-amplitude and gray-scale US scans were obtained through a cranial window during injection of contrast material. Mean pixel intensity was analyzed on digitized images. Regional CBF was varied by modifying arterial partial pressure of carbon dioxide (PaCO2). Color-Doppler-amplitude and gray-scale mean pixel intensity and percentage change in mean pixel intensity after injection of contrast material were analyzed, by means of a bolus injection curve that plotted color mean pixel intensity per unit area versus time. Contrast material injection resulted in a statistically significant difference in color-Doppler-amplitude and gray-scale enhancement of brain. Color mean pixel intensity increased from 1.4 units +/- 1 (standard error) to 122 units +/- 6 in thalamus and from 9.7 units +/- 4.0 to 107 units +/- 9 in cortex (P < .0001). Gray-scale mean pixel intensity increased from 0.55 units +/- 0.20 to 33 units +/- 11 in thalamus and from 0.42 units +/- .06 to 10.5 units +/- 2.0 in cortex (P < .005). Correlation between the area under the color-Doppler-amplitude mean-pixelintensity curve and regional CBF in thalamus and cortex was significant (r = .815, P < .0001). Color-Doppler-amplitude US can be used to create regional CBF maps and shows potential for noninvasive evaluation of CBF in the critically ill newborn.