Ultrasound velocity in a biological tissue, and the attenuation of the wave amplitude, vary depending on which tissue it is travelling through. If c is the wave propagation velocity, then c=f λ, where f is the wave transmission frequency and λ is its wavelength. Moving objects within the scan field can be seen, and additional information about the extent of motion along the line of a single beam can be obtained by more rapid sampling of the M (‘motion’) mode. Multiple ultrasound probe arrays and their signal processing electronics are designed to create, detect and display changing images with changes in probe position, so that the full image is created with all components at the correct distance from the probe. This pulsing allows each reflected wave to be associated with its own transmitted wave. A real-time 2-D image is produced, sometimes using multiple probes arranged in a linear fashion, each transmitting a pulsed wave of ultrasound before electronically gated switching to the receiving mode occurs. The reflected pressure changes coupled to the transducer induce electrical signals ( Fig 1B), which are processed and displayed to produce an image this is known as B (‘brightness’) mode. The same piezoelectric crystal is usually used as the receiver, with the transmission mode switched off. The reflection of the ultrasound wave at the interface between two tissues of different densities, or at tissue-fluid (air) interfaces, produces a diagnostic image. (B) Reception and detection of a reflected ultrasound pressure wave by a piezoelectric crystal, which generates an electrical signal output (Supplementary material). (A) Generation and transmission of an ultrasound pressure wave from a piezoelectric crystal using an alternating electrical signal input.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |