(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.

(MRgFUS) Magnetic resonance guided focused ultrasound is a surgical procedure that uses high intensity focused ultrasound waves to destroy tissue in combination with magnetic resonance imaging (MRI), which guides the treatment.
With focused ultrasound waves uterine fibroids are heated and destroyed (ablated) inside the MRI device , allowing the physician to plan, monitor and control the treatment with temperature sensitive images while it is in progress.

See also High Intensity Focused Ultrasound, and Interventional Ultrasound.

Brachytherapy is a radiation therapy in which radioactive material (radioisotopes) sealed in needles, seeds or wires is placed directly into or near a tumor. Brachytherapy uses ultrasound imaging to visualize the needles for accurate placement of the small seeds or pellets (capsules) directly into e.g., the prostate. Ultrasound imaging allows accurate planning, placement and implantation of the radiation sources. Implantation of the seeds is a minimally invasive procedure.
Radioactive seeds are inserted through the perineum skin (the area between the scrotum and the anus) into the prostate gland. With correct planning, the surgeon can implant the radiation sources for maximum benefits to effective cancer treatment.

See also EchoSeed™, Prostate Ultrasound, Thermotherapy, High Intensity Focused Ultrasound, Urologic Ultrasound, Transurethral Sonography.

Interventional ultrasound, also known as ultrasonography, encompasses a range of invasive or surgical procedures guided by ultrasound imaging. While its widest application lies in intravascular ultrasound imaging for measuring atherosclerotic plaque, it has proven valuable in various medical fields.
In urology, ultrasound-guided interventions are employed for treatments like high intensity focused ultrasound (HIFU) in prostate conditions. The precise imaging provided by ultrasound aids in targeting the affected area and delivering therapeutic energy effectively.
In intraabdominal conditions, endoscopic ultrasound is frequently utilized. This technique combines ultrasound imaging with an endoscope to visualize and evaluate structures within the gastrointestinal tract, allowing for precise diagnoses and targeted interventions.
Ultrasound-guided procedures play a significant role in several medical specialties, including liver sonography, obstetric and gynecologic ultrasound, and thyroid ultrasound. These procedures involve interventions such as RF thermal ablation or biopsies, which are guided by real-time ultrasound imaging.
For instance, in liver sonography, ultrasound guidance is crucial for performing biopsies or RF thermal ablation, a technique used to treat liver tumors by delivering localized heat to destroy the abnormal tissue. The real-time imaging allows for precise needle placement and monitoring during the procedure.
In obstetric and gynecologic ultrasound, ultrasound-guided procedures, such as biopsies, can be performed to obtain tissue samples for diagnostic purposes. Additionally, ultrasound guidance is valuable during interventions like amniocentesis or fetal blood sampling, enabling accurate and safe procedures.
Thyroid ultrasound procedures often involve ultrasound-guided fine-needle aspiration biopsy (FNAB), which allows for the sampling of thyroid nodules for cytological examination. The ultrasound image helps guide the needle into the targeted area, ensuring accurate sampling and minimizing potential complications.
Overall, ultrasound-guided interventions provide minimally invasive and precise approaches to diagnosis and treatment. The real-time imaging capabilities of ultrasound contribute to enhanced accuracy, safety, and patient outcomes in procedures like biopsies, injections, and drainage.

See also Transurethral Sonography, Endocavitary Echography, and B-Mode Acquisition and Targeting.

(ESWL) Extracorporeal shock wave lithotripsy is a special use of kidney ultrasound, where high intensity focused ultrasound pulses are used to break up calcified stones in the kidney, bladder, or urethra. Pulses of sonic waves pulverize dense renal stones, which are then more easily passed through the ureter and out of the body in the urine. The ultrasound energy at high acoustic power levels is focused to a point exactly on the stone requiring an ultrasound scanning gel for maximum acoustic transmission.
Air bubbles in the ultrasound couplant, regardless of their size, degrade the performance of Lithotripsy and have the following effect:
Air bubbles smaller that 1/4 wavelength cause scattering of the sound waves as omni directional scatterers and less acoustic energy reaches the focal point. The result is less acoustic power at the focal point to disintegrate the kidney stone.
Air bubbles larger than 1/4 wavelength act as reflectors and deflects the acoustic energy off in a different direction. These results in less acoustic energy at the focal point.
Microbubbles dispersed throughout the ultrasound couplant layer change the average acoustic impedance of the gel layer (which reduces the total transmitted energy) and, due to refraction, change the focal point.