Tissue harmonic imaging: is it useful in hepatobiliary and pancreatic ultrasonography?

The introduction of tissue harmonic imaging (THI) could solve problems related to ultrasound in technically difficult patients by providing a marked improvement in image quality. Tissue harmonics are generated by tissue vibration while the transmitted pulse propagates through tissue and are multiples of the fundamental frequency. The harmonic image is obtained by separating the fundamental and harmonic frequencies, the second harmonic, or twice the fundamental frequency, being used for imaging. Through a better spatial resolution, less artifact and an increased visualization of the deep structures, tissue harmonic sonography improves the image quality. In hepatobiliary diseases THI improves the detection and characterisation of focal liver lesions, increases the conspicuity of gallbladder polyps and stones, choledocholithiasis and intrabiliary masses. Visualization of the pancreatic duct, pancreatic calcifications or duct stones is also more accurate with THI. The results with THI are better than those with conventional ultrasonography as the body mass index increases. The limitations of THI can be overcome by the use of the new pulse inversion harmonic imaging.