(LIPU / LIUS) Low intensity pulsed ultrasound is a form of mechanical power that is transmitted through and into tissues as an acoustic pressure wave. Low intensity pulsed ultrasound is often used in musculoskeletal and joint ultrasound and has therapeutic benefits for healing of (fresh) fractures, those that demonstrate either a delayed union or nonunion, and soft tissue repair.

(HIFU / FUS) High intensity focused ultrasound is used in thermotherapy or thermoablation e.g., for the treatment of benign prostate hyperplasia or under study for the treatment of cancer.
An applied ultrasound probe (see transrectal sonography) focuses sound waves at one spot, elevating the tissue temperature to a point that the tissue destroys. Generally, lower frequencies (from 250 kHz to 2000 kHz) are used than for medical diagnostic ultrasound, but significantly higher time-averaged intensities.

See also Magnetic Resonance Guided Focused Ultrasound, Low Intensity Pulsed Ultrasound, and Lithotripsy.

Pressure is the force per unit area applied on a surface in a direction perpendicular to that surface.
Pressure can also be described as a form of potential energy in a fluid. The maximum pressure of the fluid medium obtained during propagation of an ultrasonic pulse.
The negative peak pressure is the peak rarefaction pressure attained during the negative portion of a propagating ultrasound pulse in a medium such as tissue.
Sound pressure can be measured using a microphone in air and a hydrophone in water. The SI unit for sound pressure is the Pascal.
Blood pressure is the pressure exerted by the blood on the walls of the blood vessels.

See also Rarefactional Pressure, Low Intensity Pulsed Ultrasound, and Projector.

Ultrasound therapy uses high energy sound waves to treat different diseases. Historically, the use of ultrasonic waves in therapy began before the wide use as a diagnostic medical imaging tool. Dependend on the intensity, ultrasound therapy reach from the thermal effect used in physical therapy to the destruction of tissue with lithotripsy.

Types of ultrasound treatment:
See also Thermal Index, History of Ultrasound, Interventional Ultrasound, and B-Mode Acquisition and Targeting.

Contrast agents improve the sensitivity of vascular Doppler ultrasound, for example in cerebrovascular sonography or examinations of deep abdominal vessels. They also enlarge the role of transcranial Doppler. Microbubbles can be used with various modes e.g., color and power Doppler imaging, as well as pulsed-wave Doppler to increase the signal intensity. However, the ultrasound system must be suitable for contrast enhanced technology.
Microbubbles usually stay within the vascular space; nevertheless, the contrast enhancement is limited to 2−6 minutes caused by physiologic clearance and bubble destruction.
Depended on the application, contrast agents can be administered with a different injection rate e.g., bolus injection, slow injection, or continuous infusion. Stable, homogeneous, and prolonged enhancement can be obtained with perfusion, lasting until the infusion is stopped.

See also Cerebrovascular Ultrasonography, Multiple Frame Trigger.