- Definition
Ultrasound (US, U/S) is an imaging technique that uses sounds waves to visualize internal structure in real time. The sound waves have frequency that is too high for us to hear (3-10MHx). There are different types of U/S as well:
Doppler U/S: Using the principle of the Doppler effect, this ultrasound imaging also allows real-time visualization of blood flow velocity.
CEUS: Contrast-enhanced ultrasound. When encountering air, the sound waves scatters in countless reflection artifacts. Using this principle, a contrast is injected into the patient that contains microbubbles (the job of the contrast is to keep the bubbles at a micro-scale). This enhances the view of the target organ or the vessel.
- Discovery
The origin of medical ultrasound cannot seem to be pinpointed to a single person. Dr. Donald applied the technology in the field of obstetrics. Biologist John Wild used the ultrasound to image the tissues in breasts. Other pioneers in the U.S., Japan, and Europe also did their work around the same time to develop the ultrasound in the health care system. Physicists played a large role in understanding the piezoelectric effect, a core technology for the U/S.
Fun Fact: Karl Dussik first used the U/S to find brain tumors in 1942.
- Mechanism
Unlike other imaging methods (like x-ray, CT), ultrasound is a portable machine with a screen, attached transducer, and gel. A gel is first applied to the transducer, then placed on the appropriate part of the body.
- A transducer produces ultrasound waves by employing the piezoelectric effect (converting electrical energy into sound energy). High-frequency U/S provides higher resolution, low-frequency U/S provides deeper view in tissues.
- The sound waves then travel through the gel, and into the soft tissues.
- Why Gel?: The gel effectively prevents air from getting in the way of the sound waves and distorting the images. When sound waves travel between two media with large differences in density (as speed of sound differs according to the medium they travel through), the waves get reflected (Snell’s law). Gel, with higher density than air, minimizes these reflections.
- The echoes of the ultrasound are reflected to the transducer, to be processed by the portable computer. Digital images are then created for analysis.
- Indications
There are numerous circumstances to use the ultrasound. Some examples include:
- Abdominal organ diseases: cholecystitis (gallbladder inflammation), choledocholithiasis (bile duct stones), appendicitis (appendix inflammation)
- Pelvic organ etiology: uterine leiomyomas, ovarian torsion (twisting of the ovary that cuts off the ovarian artery supply), ectopic pregnancy, endometriosis, prostate cancer, testicular torsion
- The thyroid: thyroid nodules, parathyroid masses
- Joints: rotator cuff tears
Pros: No ionizing radiation, readily available, affordable, quick
Cons: limited resolution and view. Conductor-dependent.