PHYSICS - US Flashcards
PACS (acronym)
Picture Archiving and Communication System
DICOM (acronym)
Digital Imaging and COmmunications in Medicine
Speed of sound in soft tissue
1540 m/s
Terms for areas of high and low pressure created by sound waves
compression and rarefaction, respectively
Bone - higher or lower speed of sound
higher speed of sound (dense, less compressible)
Air - higher or lower speed of sound
lower speed of sound (less dense, more compressible)
Change in decibels equivalent to a 50% loss in sound intensity
-3 dB
Half value thickness definition
thickness of tissue that attenuates sound intensity by 3 dB (50%)
Strength of returning echoes is influenced by…
magnitude of impedence difference and angle of incidence
Distance traveled in US
twice the depth of the reflector (lesion)
No refraction occurs if…
incident waves are perpendicular to tissue boundary or no impedence difference between tissues
Snell’s Law
angle of refraction increases with increasing speed difference between tissues and increasing angle of incidence
“Edge shadowing”
refraction artifact (distal to curvilinear surface); computer assumes linear progression of sound waves
Specular scatter
a.k.a. smooth scatter (not really scatter, just reflection); occurs when reflector dimensions are larger than wavelength
Non-specular scatter
a.k.a. diffuse scatter; occurs when reflector dimensions are smaller than wavelength
Non-specular scatter increases with…
decreasing wavelength (smaller waves “see” more small irregular surfaces which cause scatter)
Relationship between scatter and frequency
directly proportional; increased TF => decreased wavelength => increased scatter
Attenuation increases with…
TF and tissue depth
Attenuation coefficient for soft tissue
0.5 (dB/cm)/MHz
Effect of increasing frequency on HVT
decreased HVT (less tissue required to attenuate a higher frequency beam by 50%)
Components of transducer
piezoelectric crystals, dampening block, matching layer
Frequency at which maximum intensity waves are produced
center (resonance) frequency
Transducer crystal thickness is equal to…
half of the wavelength (or wavelength is equal to 2x crystal thickness)
Effect of thinner crystal on frequency
thinner crystal => smaller wavelength => higher transducer frequency