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physics 4.1

TermDefinition
Imagining Instruments, composed of: transducer, beam former, signal processor, image processor, display
Pulse-Echo Method electrical energy is converted to acoustic energy, acoustic energy (reflection) are converted back to electrical energy
Sonographic equipment determines: echo strength, location of returning echos (by arrival time and direction), electrical, produce a visual display received echos, voltages represent received echoes
this chapter deals with how the machine puts the echoes together to produce an image
beam former the beam former sends digitized echo voltage streams to the signal processor
beam former consists of: pulser, pulse delays, transmit/receive switch, amplifiers, analog-to-digital converters, echo delays, summer
beam former functions generating voltages that drive the transducer, determine PRF, coding, frequency and intensity, compensating for attenuation, digitizing the echo voltage stream, directing, focusing and apoddizing the reception beam
Pulser where the action begins generates the voltages that drive the transducer,frequency of the voltage pulse determines the frequency of the resulting ultrasound pulse, sequencing and phasing operations of array transducers are carried out by the pulser&pulse
delays, informs the receiver and the memory when the ultrasound pulses were produced
PRF determined by the pulser, ranges from 4 to 15 kHz
the ultrasound PRF is EQUAL to the VRF
1 voltage pulse produces 1 ultrasound pulse
use of PRF must be set high enough to receive information for the display, produces a continuous image, BUT must be limited to produce an unambiguous image on the display
ambiguity overlapping information
the information (echoes) from one pulse MUST be received BEFORE the next pulse is sent out
Imagining Depth depth(cm) x PRF(khz) has to be equal to or less than 77 without getting false information
imaging depth multiplied by the PRF MUST NOT exceed 77 so ambiguity will not occur
frame rate for deeper imaging, a reduction in frame rate may be created by using a lower PRF
pulser and pulse delays the pulser and pulse delays carry out the following tasks: sequencing phase delays variations in pulse amplitudes
beam former controls the following (sequencing and phasing operations for arrays): beam scanning, beam steering, transmit focusing, dynamic aperture and apodization
amplitude and intensity the greater the voltage amplitude produced by the PULSER, the greater the amplitude (intensity) of the ultrasound pulse produced by the transducer
pulser voltages range up to 100 volts, shown as OUTPUT level on machine display, usually shown in db, 100%=0db
acoustic output amount of acoustic energy produced by machine, the higher the acoustic output, the greater the risk of bioeffects
acoustic output can be reduced by increasing the receiver gain
Created by: Sierd98765
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