Tissue Harmonic Imaging

without THI

with THI

Tissue Harmonic Imaging (THI) is a procedure in medical ultrasound imaging that primarily increases contrast resolution , but also increases spatial resolution . Basically, ultrasound is sent into the tissue at one frequency (" fundamental wave " or "1st  harmonic ") and the signals at twice the frequency, ie (" harmonic wave " or "2nd harmonic") are used for the imaging, which is caused by the non-linear propagation in the tissue . ${\displaystyle f_{0}}$ ${\displaystyle 2f_{0}}$

The manufacturers of ultrasonic systems offer various methods for separating the harmonics from the fundamental waves. Simpler systems work with high-pass filter technology, while more sophisticated systems are equipped with subtraction filters.

Tissue Harmonic Imaging is a by-product of contrast-enhanced ultrasound : The principle of displaying only the harmonics was developed to suppress tissue signals and only display contrast-medium signals. It was discovered that harmonics are also caused by tissue.

Mode of action

The fatty tissue on the body surface is often the cause of bothersome artifacts . Since the harmonics only increase with the propagation in the tissue, images that are created from these frequencies are free of these artifacts. In addition, the spatial resolution is higher because the frequency is higher.

See also

• Frequency doubling
• Fourier series

literature

• JD Thomas et al. In: J Am Soc Echocardiogr. , 1998 Aug, 11 (8), pp. 803-808.