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The principle of ultrasound: Difference between revisions
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I would like to talk about '''Duty Factor''' (DF) here. This parameter is related to ultrasound bioeffects, but since it is also related to pulsed ultrasound it is reasonable to introduce it in this section. DF is defined as a percent of time that the ultrasound system is on while transmitting a pulse. DF = pulse duration (sec) / pulse repetition period (sec) x 100. It has units of % and ranges from 0 (the system is off) to 100 (the system is on continuously). Typical valued of DF in clinical imaging are 0.1% to 1% (usually closer to 0), thus the machine is mostly listening during clinical imaging. Another interesting point to note is the fact that since the sonographer changes the PRF by changing the depth, they indirectly change the duty factor. And lastly, one must realize that an anatomic image cannot be created with a continuous wave ultrasound. Since one must listen for the return signal to make an image, a clinical echo machine must use pulsed signal with DF between 0.1 and 1%. | I would like to talk about '''Duty Factor''' (DF) here. This parameter is related to ultrasound bioeffects, but since it is also related to pulsed ultrasound it is reasonable to introduce it in this section. DF is defined as a percent of time that the ultrasound system is on while transmitting a pulse. DF = pulse duration (sec) / pulse repetition period (sec) x 100. It has units of % and ranges from 0 (the system is off) to 100 (the system is on continuously). Typical valued of DF in clinical imaging are 0.1% to 1% (usually closer to 0), thus the machine is mostly listening during clinical imaging. Another interesting point to note is the fact that since the sonographer changes the PRF by changing the depth, they indirectly change the duty factor. And lastly, one must realize that an anatomic image cannot be created with a continuous wave ultrasound. Since one must listen for the return signal to make an image, a clinical echo machine must use pulsed signal with DF between 0.1 and 1%. | ||
Back to propertied of pulsed ultrasound, we need to discuss '''spatial pulse''' length. Up to now we introduced properties that were related to timing. Spatial Pulse Length is the distance that the pulse occupies in space, from the beginning of one pulse till the end of that same pulse. It is measured in units of distance with typical values from 0.1 to 1 mm. SPL (mm) = # cycles x wavelength (mm). Axial or longitudinal resolution (image quality) is related to SPL. Axial resolution = SPL/2 = (# cycles x wavelength)/2. | Back to propertied of pulsed ultrasound, we need to discuss '''spatial pulse''' length. Up to now we introduced properties that were related to timing. Spatial Pulse Length is the distance that the pulse occupies in space, from the beginning of one pulse till the end of that same pulse. It is measured in units of distance with typical values from 0.1 to 1 mm. SPL (mm) = # cycles x wavelength (mm). Axial or longitudinal resolution (image quality) is related to SPL. Axial resolution = SPL/2 = (# cycles x wavelength)/2. | ||
[[File:PhysicsUltrasound_Fig9.svg|thumb|left|500px| Fig. 9]] | [[File:PhysicsUltrasound_Fig9.svg|thumb|left|500px| Fig. 9]] | ||