Improved imaging of liver metastases with stimulated acoustic emission in the late phase of enhancement with the US contrast agent SH U 508A: Early experience

PURPOSE: To see whether stimulated acoustic emission (SAE) in the liver par enchyma in the late phase of enhancement with SH U 508A increases the consp icuity of occult metastases at ultrasonography (US). MATERIALS AND METHODS: Eighteen patients with known hypo- or hypervascular hepatic metastases underwent US after SH U 508A administration, after a del ay of at least 5 minutes, to ensure decay of blood pool enhancement. In 16 patients with visible metastases, conspicuity was compared on registered SA E and gray-scale scans by two blinded readers and by using computerized ana lysis of relative gray-scale and color Doppler conspicuity scores inside an d outside the lesion. In nine patients, areas suspected of being involved b ut without definite gray-scale masses were imaged in the same way. Paired s ections were analyzed by two blinded readers looking for parenchymal color deflects without corresponding gray-scale masses; nine control images from three healthy volunteers were also included. RESULTS: Intense, transient parenchymal SAE was seen in all subjects. All m etastases appeared as areas of reduced or absent signal. The conspicuity sc ore was 80% for SAE versus 9% for gray-scale US (P < .001,Wilcoxon signed r ank test). SAE-specific II defects were seen in all patients but in none of the volunteers. Metastases seen on SAE but undetectable on gray-scale imag es were proved in three patients. CONCLUSION: SAE with SH U 508A improves the conspicuity of metastases. SAE- specific defects may reveal isoechoic or subtle metastases.