Ultrasound is a very challenging imaging modality to comprehend. Sonograms are two-dimensional, grayscale images. Ultrasound waves are sent into the body in pulses. Before another pulse is sent, the time lapsed since the last pulse and the intensity of the returning sound waves (bouncing off of tissues) are used to form an image. Ultrasound waves respond differently to various mediums and artifacts play a large role in the comprehension of sonograms.
Instructions
1. Determine the image orientation. Ultrasound images are usually taken in one of two planes: longitudinal (long) and transverse (trans). In long images, the left side of the sonogram shows structures toward the patient's head. The right side shows structures toward the feet. In trans images, the left side of the sonogram shows structures on the patient's right side and vice versa. The top of the image is the skin, where the transducer, or camera, is resting.
2. Understand measurement orientation. Three measurements are taken of structures: length, height, and width. Length is measured on the long image from left to right. Height is the depth, from the top of the image towards the bottom. Width is taken in the trans image from left to right.
3. Differentiate between cystic and solid. Cysts are fluid-filled sacs. A cyst with no debris is black on the sonogram because no signal is returned to the ultrasound system. In fact, ultrasound waves get stronger when they pass through fluid and will demonstrate increased, or enhanced, through-transmission. This is evident by brighter, and sometimes clearer, structures behind the cyst. Solids are bright and white. Variations of gray are the result of varying fluid contents of structures.
4. Evaluate the fat or air content. Ultrasound does not travel well through fat and air, so images may be of poor quality and structures difficult to see when more fat or bowel is present. This is sometimes an indication of a pathology. For example, the liver is blood-rich (lots of fluid) and is used as a sonographic window to better visualize other structures. If it is difficult to see through the liver, this can be a sign of fatty-liver infiltration.
5. Asses blood flow. Doppler is used to determine the presence, direction and velocity of blood flow. Continuous Doppler demonstrates red and blue signals. Generally, red represents blood moving toward the camera, and blue represents blood moving away from the camera. Pulsed Doppler can be used to determine the resistance of blood flow. High peaks represent high resistance, and low peaks represent low resistance.
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