TY  - CHAP
M1  - Book, Section
TI  - Physics and Knobology
A1  - Baston, Cameron M.
A1  - Moore, Christy
A1  - Krebs, Elizabeth A.
A1  - Dean, Anthony J.
A1  - Panebianco, Nova
PY  - 2018
T2  - Pocket Guide to POCUS: Point-of-Care Tips for Point-of-Care Ultrasound
AB  - Table  Graphic  Jump  Location|Download  (.pdf)|PrintConceptDetailsWhy  It  MattersFrequency#  of  cycles/second—measured  in  Hertz.  A  megahertz  (MHz)  =  106  Hz.  Human  hearing  is  in  the  range  20-20,000  Hz.Probe  Selection:  low  frequency/long  wavelength,  provide  better  penetration  with  less  resolution,  good  for  deep  structures.  High  frequency/short  wavelength,  provide  better  resolution,  less  penetration.ResolutionSchematic  showing  ultrasound  beam  edge-onLateral  resolution  is  the  smallest  distance  that  can  be  distinguished  with  a  given  probe  and  machine  at  any  given  depth.  This  explains  why  focal  depth  and  the  number  of  crystals  in  the  transducer  are  important.  Axial  resolution  allows  differentiation  parallel  to  the  beam,  and  is  dependent  on  frequency:  higher  frequencies  give  higher  axial  resolution.Pulse  Echo  PrincipleUltrasound  waves  leave  the  probe,  strike  an  object,  and  are  reflected  back.  Depth  on  the  screen  is  measured  by  the  time  for  this  echo  to  return  to  the  transducer.Basics  of  machine  function.  Also  important  to  understand  several  artifacts,  including  reverberation  and  shadowing.Impedance  or  Density/StiffnessWhen  ultrasound  encounters  material  of  different  impedance  (from  liquid  to  gas,  or  a  change  in  tissue  stiffness),  it  reflects.Explains  reflection  of  ultrasound  by  gas  and  solids,  and  the  artifact  of  posterior  acoustic  enhancement.EchogenicityHyperechoic:  brighter  echoes  than  surrounding  structuresIsoechoic:  equal  in  echoes  to  surrounding  structuresHypoechoic:  darker  echoes  than  surrounding  structuresAnechoic:  completely  blackHeterogeneous:  nonuniform  textureHomogeneous:  uniform  texture  
SN  - 
PB  - McGraw-Hill Education
CY  - New York, NY
Y2  - 2024/04/19
UR  - accessmedicine.mhmedical.com/content.aspx?aid=1161757473
ER  -