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machine setting

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  • othman
    Hi groupe can anyone tell me the difinite role of these: power dynamic range sharpness dip density and the most important of them :grey scale and how could be
    Message 1 of 2 , Jan 2, 2011
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      Hi groupe

      can anyone tell me the difinite role of these:

      power
      dynamic range
      sharpness
      dip
      density
      and the most important of them :grey scale and how could be set to get
      optimal image quality

      as well if know a website or any book shed the light on this issue

      mny thanks
    • Andrew Horning
      Sometimes it helps to think about light photography, so you can see what happens with sound, as there are more similarities than differences. Power is
      Message 2 of 2 , Jan 3, 2011
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        Sometimes it helps to think about light photography, so you can "see" what happens with sound, as there are more similarities than differences.
         
        Power is analogous to the brightness of your light source.  For ALARA reasons, you want to keep the power as low as possible.  But for taking good pictures it makes sense as well.  Just as you can make a light source too bright and overwhelm the dynamic range of the medium/ wash out colors, you can cause unnecessary near-field "bang" and reverberation artifacts with too much sound.  Remember that sound is mechanical energy.  Too much sound, in general, can cause cavitation, heat ...bad things.  Ultrasound system presets preclude any real tissue damage, but you can make your pictures ugly with too much power.
         
        Dynamic range is the ability to discern a wide range of values between (in the case of a picture) the darkest black to the whitest white, along with every shade of color.  If you only have a black crayon and a red crayon, your picture will have very little dynamic range.  If you've got every Crayola shade, you've got a wide dynamic range.  So it is with sound.  There are many things that affect your system's ability to discern a wide range of slow-fast velocities, weak and strong echos.  But the bottom line is that your exams images can be too black/white "contrasty" with too-little dynamic range, or so high in dynamic range that human eyes cannot discern what's important.   Since your eyes can discern fewer shades of gray than shades of color, sometimes false color shows that the ultrasound system can produce much greater dynamic range than our eyes can discern.  Since our eyes are more limiting than are modern ultrasound systems (it wasn't always so!), part of your job is to expand the dynamic range around the significant findings, and reduce it where it doesn't help.  Ideally, for instance, you'd blank out bright echos from lung and bone and expand the dynamic range around that object in the apex....like darkening a background and focusing appropriate light on a photographic subject.  "Broadband" transducers have a much wider inherent dynamic range than the now-ancient single-crystal/single frequency scanners of ye olde worlde.  But effective dynamic range depends upon focal zone, power, gain, TGC, gel, technique...
         
        Sharpness is ultimately a visual phenomenon, but depends upon things like resolution, frequency, frame rate/averaging/delay/refresh, line density, tricks like edge enhancement and compound imaging, and display and brightness/contrast settings.  General ultrasound techs sacrifice sharpness for tissue differentiation, which makes a "softer" image than echocardiographers should produce.  Echo images should generally be sharp in both spatial and temporal domains (picture and motion), which means the frame rate should be high, and each frame should be distinct, with little averaging between frames.
         
        I'm not sure what you mean by dip.  That could be dipyridamole as in pharmaceutical stress echo (Usually with atropine, though I'd never done an echo with dipyridamole.  I'd done plenty with dobutamine, exercise...even mental stress), or a Doppler "dip" (as in an "A dip" on a pulmonic valve?).  Maybe I'm blanking, but I'm not aware of any imaging/ultrasound term, "dip."
         
        Density is, in one way or another, line density; the number of echo "lines" that are either fanned in a 2D sector, or more recently, criss-crossed and/or synthesized into pixel/voxels that make up the image.  The light equivalent is digital or newspaper images that, when you look real close, resolve into distinct dots of ink or pixels on a monitor.  With a typical echo sector probe, line density decreases with depth, as a finite number of lines originate from the probe, and diverge with depth.  You can increase line density by decreasing frame rate, depth, and importantly/practically, sector size.
         
        Sheesh...I'd meant a brief, quick reply.  Sorry I gushed.
         
         
         
         
        > To: echocardiography@yahoogroups.com
        > From: othmanbek2002@...
        > Date: Sun, 2 Jan 2011 16:15:18 +0000
        > Subject: [echocardiography] machine setting
        >
        > Hi groupe
        >
        > can anyone tell me the difinite role of these:
        >
        > power
        > dynamic range
        > sharpness
        > dip
        > density
        > and the most important of them :grey scale and how could be set to get
        > optimal image quality
        >
        > as well if know a website or any book shed the light on this issue
        >
        > mny thanks
        >
        >
        >
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