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Abstract
The recent introduction of tissue harmonic imaging could resolve the problems related
to ultrasound in technically difficult patients by providing a marked improvement
in image quality. Tissue harmonics are generated during the transmit phase of the
pulse-echo cycle, that is, while the transmitted pulse propagates through tissue.
Tissue harmonic images are formed by utilizing 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 harmonics allows
increased penetration without a loss of detail, by obtaining a clearer image at depth
with significantly less compromise to the image quality caused by the use of lower
frequencies. This imaging mode could be used in different organs with a heightening
of low-contrast lesions through artefact reduction, as well as by the induced greater
intrinsic contrast sensitivity of the harmonic imaging mode.