Clinical use of ultrasound tissue harmonic imaging

The recent introduction of tissue harmonic imaging could resolve the proble ms related to ultrasound in technically difficult patients by providing a m arked improvement in image quality. Tissue harmonics are generated during t he transmit phase of the pulse-echo cycle, that is, while the transmitted p ulse propagates through tissue. Tissue harmonic images are formed by utiliz ing the harmonic signals that are generated by tissue and by filtering out the fundamental echo signals that are generated by the transmitted acoustic energy. To achieve this, two processes could be used; one by using filters for fundamental and harmonic imaging and the second using two simultaneous pulses with a 180 degrees difference in phase, The introduction of harmoni cs allows increased penetration without a loss of detail, by obtaining a cl earer image at depth with significantly less compromise to the image qualit y caused by the use of lower frequencies. This imaging mode could be used i n different organs with a heightening of low-contrast lesions through artef act reduction, as well as by the induced greater intrinsic contrast sensiti vity of the harmonic imaging mode. (C) 1999 World Federation for Ultrasound in Medicine & Biology.