Acoustic shadowing Definition Acoustic shadowing result from the Presence of structure of high attenuation within the field of view adjacent to the structure of normal or low attenuation. Leads to complete absence of echo from prevented ultrasound penetration into the causative structure. Mostly assumed to be caused by hard and solid object like bone gallstone or calcification. Causes of acoustic shadows: Hard solid objects Gas Soft tissue of high attenuation Anisotropic and refractive tissues investigated at acute angles Acoustic shadowing can be reduced through spatial compounding but not eliminated Assumption Violated Attenuation rate is uniform and predictable. The speed of sound in the body is constant (1540m/s) Best image for acoustic shadowing Image 1: Caustic shadowing Acoustic enhancement Definition Acoustic enhancement is an artifact produced during ultrasound imaging when a structure of low attenuation is present in the field of view of adjacent structure of low or high attenuation. structures of average propagation speed. Causes up or down replacement along the line of light. They cannot be eliminated though altered by changing the angle. Rarely observed and not useful. Assumption violated The speed of sound in the body is constant (1540m/s) Propagation speed of light is constant left8890Image 12: propagation speed artifact of the varicose veins and the subcutaneous fat. Range Ambiguity Definition Range ambiguity is quite common artifact and complex in causation. It occurs when echoes from a preceding pulse arrive at a time when other pulse-echo sequence is still active. It also occurs when the system is operating with multiple focal zones. Not diagnostically useful and can lead to bizarre appearances. Assumptions violated The arriving echo was generated by the last emitted ultrasound pulse and not another preceding pulse left2768600 Image 13: using different local zones as default machine setting o observe an intra-abdominal fluid-filled tumour. [...]
This is to be study material for my exam revision, A text will be provided, within it you will find details on the major Ultrasound artifacts. I require that each artifact be given a sub heading and very briefly defined and the mechanism/cause of artifact described. Next, if you can find in the text, information on the fundamental physical assumptions broken to cause the artifact, list those in dot points under the brief description. There is no need for referencing or advanced research.. just words to paper. I need it done within 24 hours.. the sooner the better though because I am pretty bogged down in study and work. This particular exam is coming up very soon. sorry for the short notice.