RT Book, Section A1 Baston, Cameron M. A1 Moore, Christy A1 Krebs, Elizabeth A. A1 Dean, Anthony J. A1 Panebianco, Nova SR Print(0) ID 1161757473 T1 Physics and Knobology T2 Pocket Guide to POCUS: Point-of-Care Tips for Point-of-Care Ultrasound YR 2018 FD 2018 PB McGraw-Hill Education PP New York, NY SN 9781260441475 LK accessmedicine.mhmedical.com/content.aspx?aid=1161757473 RD 2024/03/28 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