# Ultrasound physics Flashcards

Terms Definitions
 General requirements There are 3, requirements. 1. Generation of a beam. 2. Reception of the returning echoes. 3.processing of the signal for display. All types of ultrasound scanners have these basic features The difference in various scanners is how they process, analyze, and display the returning echoes. All of the subsystems in the US machine are controlled by the? Master synchronizer Master synchronizer Electrical signal from the master synchronizer to the transducer starts, the process, a pulse of ultrasound is generated by the transducer in response to the electric stimulation. The theory of the pulse to transducer 1. The pulse travels through the body until it hits an interface and returns to the transducer. 2. The transducer then becomes a receiver and converts the ultrasound beam to an electronic signal that is processed and displayed. 3. The range equation is used to compute the depth of the returning echo. Pulse to the transducer part 2 Using the 13 u/cm of travel, round trip, the machine knows when the pulse was sent and registers the time the echo returns. Range equation or ( time of flight or go return time) The elapsed time from pulse creation to pulse reception is called the go-return time or time of flight. When a reflector is located superficially the pulse is breif, whereas trips to deeper reflectors take more time. ( TIME OF FLIGHT IS DIRECTLY RELATED TO THE DEPTH.) Range equation 13 microsecond rule For every 13 us of go return time the object creating the reflection is 1cm deeper in soft tissue. EXAMPLE: 1. When a reflector is 2 cm deep a pulse time flight is 26us. 2. When a reflector is 3 cm deep a pulse time of flight is 39 us. Frequency determination SHORTER wavelengths = better resolution. 1. The primary objective of an ultrasound scanner is to produce a unidirectional beam ( like a flashlight beam) that is of uniform intensity and has limited physical dimensions so that good spatial resolution is obtained. Axial resolution The ability to distinguish 2 objects as separate that are close together Axial resolution defined more 1. Short wavelengths better resolution the higher the frequency the the shorter the wavelength. 2. Higher frequency transducers have better axial resolution than transducers with lower frequency. 3. We need frequencies in the MHz range in order to distinguish objects 1 mm or less. Piezoelectric properties Piezoelectric effect= transducers employ the piezoelectric effect to generate sound waves and detect echo signals. Who discovered the piezoelectric effect Pierre and Jacques Curie in 1880. 1. They found that when a force is applied perpendicular to the faces of a quartz crystal, an electric charge results. Piezoelectric properties continue When a force is applied to the face of a quartz crystal an electric charge results. This charge can be detected and amplified producing a useful electrical signal. Piezoelectric properties part 3 1. Conversely if an electric signal is applied to the crystal , the crystal vibrates sending a sound wave into the medium. 2. Hence the dual action of piezoelectric transducers as detectors and transmitters of acoustic signals. Quartz and Tourmaline Natural occurring materials and are naturally piezoelectric (used in early days of medical ultrasound. 1. Quartz is commonly used today for its PZT properties, partly because of its very reliable and controllable behavior. Transducer elements Materials manufactured that exhibit the PZT effect. Examples: 1. Barium titanate, lead zircon ate titanate, barium lead zircon ate, lead meta iodate and polyvinyl ident fluoride. MOST COMMON is lead Zirconate Titanite (PZT). PZT Considered superior to other man made materials because if several elastic and piezoelectric constants. ( RESULTS in superior efficiency and higher sensitivity).
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