(EUS) Endoscopic ultrasound uses a small probe that is inserted in the rectum either through a proctoscope or by itself. During the test biopsies of any suspicious areas are possible. The usual necessary preparation is an enema to empty the rectum. Endoscopic ultrasound provides additional information about rectal polyps, rectal cancer, perianal infection, and sphincter muscle injuries and improves the selection of patients for local excision.
Transrectal echography using a high-frequency transducer is a well established method for preoperative rectal carcinoma assessment.
Endoscopic scanning is limited by the ultrasound physics (depth and axial resolution) of the endocavitary probe. Therefore, the combination of endoscopic and transcutaneous ultrasound is most favorable.

(HPD) Harmonic power Doppler is currently one of the most sensitive techniques for detecting ultrasound contrast agents. HPD works by transmitting multiple pulses toward the object to be imaged and detecting the pulse-to-pulse changes in the received echo signals.
Second harmonic bandbass filtering is applied to the received signals to exploit the non-linear behavior of scattering from bubbles (clutter). Harmonic power Doppler operates best at high output levels because of increased contrast destruction, and pulse amplitudes close to the maximum allowed are used much of the time.
With a high mechanical index, non-linear propagation of the sound will cause significant harmonic components from tissue, and the contrast agent to tissue ratio will decrease.
Also called Harmonic Power Angio. See also Multiple Frame Trigger.

(LVO) Ultrasound contrast agents improve the echocardiography assessment of left ventricular function and the low sensitivity of changes in left ventricular ejection fraction (LVEF). In addition, harmonic imaging techniques and automated border detection (ABD) together with contrast enhanced left ventricular opacification increase endocardial border delineation (EBD) and the results compared to native echocardiography.

(PII) Pulse inversion imaging (also called phase inversion imaging) is a non-linear imaging method specifically made for enhanced detection of microbubble ultrasound contrast agents. In PII, two pulses are sent in rapid succession into the tissue; the second pulse is a mirror image of the first. The resulting echoes are added at reception. Linear scattering of the two pulses will give two echoes which are inverted copies of each other, and these echoes will therefore cancel out when added.
Linear scattering dominates in tissues. Echoes from linear scatterers such as tissue cancel, whereas those from gas microbubbles do not. Non-linear scattering of the two pulses will give two echoes which do not cancel out completely due to different bubble response to positive and negative pressures of equal magnitude. The harmonic components add, and the signal intensity difference between non-linear and linear scatterers is therefore increased. The resulting images show high sensitivity to bubbles at the resolution of a conventional image.
In harmonic imaging, the frequency range of the transmitted pulse and the received signal should not overlap, but this restriction is less in pulse inversion imaging since the transmit frequencies are not filtered out, but rather subtracted. Broader transmit and receive bandwidths are therefore allowed, giving shorter pulses and improved axial resolution, hence the alternative term wideband harmonic imaging. Many ultrasound machines offer some form of pulse inversion imaging.

See also Pulse Inversion Doppler, Narrow Bandwidth, Dead Zone, Ultrasound Phantom.

(TOF) Time of flight is a ultrasound technique used for calculating of the distance to a target by using the timing of the returning echo from the target and the speed of sound in the medium between the target and the sensor. Time of flight is used in echo location and ultrasonic flowmeters.