Echo boards Flashcards
What is the frequency of US waves?
20,000 Hz
Return of US signal to transducer when it encounters a strong reflector
Reflection
Radiation of US beams in multiple directs from a small structure i.e. blood cell
Scattering
Deflection of US beams from straight line caused by difference in acoustic impedance of tissues
Deflection
Loss of signal strength as US energy is absorbed in tissue
Attenuation
Wavelength formula
Wavelength (mm) = 1.54/frequency (MHz)
Speed of US waves in soft tissue
1,540 m/s
CSA formula
Area = πr² = 0.785D²
SV formula
SV = VTI x CSA
CO formula
CO = SV x HR
AVA by continuity formula
AVA = [(0.785 LVOT-D²) x LVOT-VTI]/AV-VTI
EROA formula
EROA = (2πr² x Alias-V)/MR-V
Regurgitant volume formula
R Vol = EROA x MR-V
PHT from DT
PHT = 0.29 x DT
MVA from PHT
MVA = 220/PHT
MVA from DT
MVA = 759/PHT
MVA by PISA
MVA = [(2πr² x Alias-V)/MR-V] (Θ/180)
RIMP formula
Normal cut offs
RIMP = (IVCT + IVRT)/ET - abnormal > 0.43
OR
RIMP = (TCO - ET)/ET - abnormal > 0.56
LAP in MR
LAP = SBP - 4MR-V²
LVEDP in AR
LVEDP = DBP - 4AR-V²
RVSP/PASP in TR
RVSP/PASP = 4TR-V² + RAP
PVR formula
PVR = (TR-V/RVOT-VTI) x 10 + 0.16
Nyquist limit formula
Nyquist limit = PRF/2
Qp:Qs formula
Significance cut off
Qp:Qs = RV SV/LV SV = [(0.785 RVOT-D²) x RVOT VTI]/[(0.785 LVOT-D²) x LVOT VTI]
Significant if > 1.5
Pulse repetition period
TIME from the start of one pulse to the start of the next pulse - includes when pulse is “on” and listening period
Affected by depth of view
Pulse repetition frequency
Definition
Formula
Number of pulses that occur in 1 second
PRF = 77,000 cm/s / depth of view cm
Affected by depth of view
Duty factor
Definition
Formula
Percentage of time that the system transmits a pulse
Duty factor (%) = pulse duration/PRP x 100
Temporal resolution
Ability to distinguish two events close in time
Accurate locate moving structures in a particular instant of time
Higher frame rate, better temporal resolution
M-MODE
Axial resolution
Type of spatial resolution. ability to differentiate 2 objects PARALLEL to US beam
Higher frequency, higher axial resolution
axial resolution (mm) = (0.77 x # cycles in pulse)/frequency
Lateral resolution
Ability to differentiate 2 objects PERPENDICULAR to US beam
Dependent on width of beam
“Go-return time”/”Time of flight” formula
distance to boundary (mm) = time (microsec) x 0.77 mm/microsec
13 microsec rule
- total distance traveled = 2 times reflector depth
- 1 cm reflector = 13 microsec
- 2 cm reflector = 26 microsec
- 3 cm reflector = 39 microsec
- 4 cm reflector = 52 microsec
Doppler shift formula
Doppler shift = (2 x reflector speed x incident frequency x cos (angle))/propagation speed
0 degree –> 1 cosine
60 degree –> 0.5 cos
90 degree –> 0
