Ultrasonic characterization of tissues via backscatter frequency dependence

Phantom and patient studies were performed to assess the potential of backscatter frequency dependence as a useful parameter for tissue characterization. A commercial phased-array ultrasonic scanner was adapted to allow digitization of the intermediate-frequency ultrasonic data. Studies of agar phantoms containing polystyrene microspheres with 3.5 and 5 MHz transducers indicated the ability for robust differentiation of phantoms having different scatterer size and frequency dependence, based on calculated differences in mean frequencies of backscattered spectra. Using a 3.5-MHz probe, significantly lower mean frequency of ultrasound backscattered from cirrhotic, compared to normal, liver tissue was noted. Studies of benign and malignant liver tumors (hemangiomas and metastases, respectively) indicated differences in frequency content of these tumors, compared to the adjacent normal liver, that were statistically significant for 3.5-MHz data.