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physics 4.1
| Term | Definition |
|---|---|
| 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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