USS Flashcards
2 categories of Medical Ultrasound
diagnostic and therapeutic
How do the probes work?
Ultrasound probes, called transducers, produce sound waves that have frequencies above the threshold of human hearing (above 20KHz), but most transducers in current use operate at much higher frequencies (in the megahertz (MHz) range).
Therapeutic USS
Uses sound waves above the range of human hearing but does not produce images. Its purpose is to interact with tissues in the body such that they are either modified or destroyed.
Where can you use therapeutic USS?
Among the modifications possible are: moving or pushing tissue, heating tissue, dissolving blood clots, or delivering drugs to specific locations in the body. These destructive, or ablative, functions are made possible by use of very high-intensity beams that can destroy diseased or abnormal tissues such as tumors.
How does USS work?
Ultrasound waves are produced by a transducer, which can both emit ultrasound waves, as well as detect the ultrasound echoes reflected back. In most cases, the active elements in ultrasound transducers are made of special ceramic crystal materials called piezoelectrics.
How are crystals used?
Materials are able to produce sound waves when an electric field is applied to them, but can also work in reverse, producing an electric field when a sound wave hits them. When used in an ultrasound scanner, the transducer sends out a beam of sound waves into the body. The sound waves are reflected back to the transducer by boundaries between tissues in the path of the beam (e.g. the boundary between fluid and soft tissue or tissue and bone). When these echoes hit the transducer, they generate electrical signals that are sent to the ultrasound scanner. Using the speed of sound and the time of each echo’s return, the scanner calculates the distance from the transducer to the tissue boundary. These distances are then used to generate two-dimensional images of tissues and organs.
Produced image
The produced image will have varying shades of grey.
White areas = hyperechoic - usually calcium containing compounds, since they will have high acoustic impedence and therefore cause more reflection of the US waves back to the detector.
Dark areas = anoechoic - usually blood, fluid, water, since they have lower acoustic impedence and therefore less reflection of the US waves back to the scanner.
What are diagnostic USS used for?
One of the most common uses of ultrasound is during pregnancy, to monitor the growth and development of the fetus, but there are many other uses, including imaging the heart, blood vessels, eyes, thyroid, brain, breast, abdominal organs, skin, and muscles
What are functional USS used for?
Doppler ultrasound is commonly used to determine whether plaque build-up inside the carotid arteries is blocking blood flow to the brain. Also can be used to test for liver fibrosis, a condition in which excessive scar tissue builds up in the liver due to inflammation.
What are therapeutic USS used for?
High Intensity Focused Ultrasound (HIFU) is currently FDA approved for the treatment of uterine fibroids, to alleviate pain from bone metastases, and most recently for the ablation of prostate tissue.
What are higher frequencies good for?
Higher frequency produce higher quality images but are also easily attenuated so better for superficial target structures
What are lower frequencies good for?
Lower frequency less attenuated so better for deeper structures
