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### 105 Cards in this Set

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 Nyquist Criterion f(sampling)>=2f(signal) f must be the highest freq in the signal reconstructed f = f(signal) period X frequency 1 power is proportional to amplitude**2 intensity = power/area intensity is proportional to power AND amplitude**2 speed = frequency X wavelength pulse duration = # cycles X period OR # cycles/frequency SPL = # cycles in each pulse X wavelength of each cycle PRF X PRP = 1 DUTY FACTOR (%) = (pulse duration/PRP) X 100 For Raleigh scattering Intensity is proportional to FREQUENCY**4 total attenuation = attenuation coefficient X distance attenuation coefficient = frequency/2 impedance (Rayls) = density X propagation speed OR density X (freq X wavelength) For reflection the strength of the echo received when incident angle is at or near 0 is stronger For normal or oblique incidence Incident intensity = reflected intensity + transmitted intensity For normal incidence IRC (%) = {(Z2-Z1)/(Z2+Z1)}**2 X 100 OR reflected (aka echo) intensity/incident intensity For normal incidence ITC (%) = (transmitted intensity/incident intensity) X 100 OR 1- IRC For Raleigh scattering intensity is proportional to particle radius For oblique incidence incident angle = reflected angle For reflection echo strength is inversely related to the impedance difference at the boundary For attenuation as distance increases amplitude and intensity decrease Angle of transmission = sin -1 [sin inc. angle X xmit prop speed)/inc prop speed] Refraction (only oblique incidence) if a)speed med1< speed med2 OR b)speed med1 > speed med2 OR c) speed med1 = speed med1 relate incident and transmit angles assume the propagation speeds of med1 and med2 are different a)incident angle < xmit angle b)incident angle > xmit angle c)no refract xmit angle=inc angle decreased damping (decreases ? AND increases ?) decreases pulse duration(# cycles X period) and Q AND increases bandwidth and axial resolution Snell's law sin(transmission angle)/sin(incident angle) = prop. speed in med2/prop. speed in med1 For spatial resolution increasing frequency decreases ? AND increases ? decreases penetration AND improves spatial resolution In soft tissue max imaging depth PRF(Hz) = 77,000/imaging depth(cm) In soft tissue depth of a reflector in terms of go-return time = (1.54mm/microseconds X go-return time)/2 In soft tissue max imaging depth PRP(micros) = imaging depth(cm) X 13micros/cm Quality factor = main frequency/bandwidth Relate Q-factor to bandwidth Wide bandwidth = lo Q value Narrow bandwidth = hi Q value axial resolution(mm)= (low value=better resolution) SPL/2 OR for soft tissue (.77 X #cycles in a pulse)/frequency(MHz) OR for soft tissue .77 X PD OR .77 X (# cycles in a pulse) X period OR low Q OR wide bandwidth OR reduced sensitivity focal depth = (diameter**2 X freq)/61.6 OR diameter**2/(4 X wavelength) lateral resolution = beam diameter (Time to make one frame) X (frame rate) = 1 (Time to make one frame) = # pulses X PRP ? bits are in a byte 8 ? bytes are in a word 2 ? bits are in a word 16 formula for the number of gray shades 2**# of bits Mechanical index = peak negative pressure/ square root of frequency pressure gradient = flow X resistance voltage = current X resistance Doppler shift (Hz) = reflected frequency - transmitted frequency Doppler Equation (2 X speed of blood X transducer frequency X cos(theta))/propagation speed measured velocity = true velocity X cos(theta) RI = (Vmax-Vmin)/Vmax V=velocity PI = (Vmax-Vmin)/Vmean V=velocity Nyquist Limit = PRF/2 Larger the crystal thickness the smaller the resonant frequency Near field length increases with increasing frequency and aperture thereby narrowing the focus of a focused beam Increasing frequency and aperture narrows the focus of a focused beam For spatial resolution the shorter the SPL the greater the spatial resolution For spatial resolution the shorter the PD the greater the spatial resolution axial resolution = SPL/2 lateral resolution = beam width For lateral resolution increasing the frequency increases the resolution by decreasing the focus For lateral resolution increasing the aperture (or increasing curvature) increases the resolution by decreasing the focus Elevational resolution = beam width perpendicular to the scan plane For elevational resolution increasing the delay of curvature decreases the depth of focus For elevational resolution increasing the frequency decreases the slice thickness The best overall resolution is axial Multiple transmission foci results in a long focus decreased frame rate and decreased temporal resolution Dynamic range = Largest power of system/smallest power of a system Largest power of system/smallest power of a system Largest intensity of echoes of system/smallest intensity of echoes of a system For A mode x axis and y axis units x axis depth y axis echo amplitude For M mode x axis and y axis units x axis time y axis motion For real-time, B-mode image formation Echo brightness increases with echo amplitude Frame rate is proportional to PRF Frame rate is inversely proportional to # lines per frame Time to create 1 frame = 1/frame rate Increasing the sector angle increases the number of scan lines per frame AND reduces the frame rate Greater the imaging depth reduces the PRF and frame rate Temporal resolution depends on frame rate temporal resolution is degraded by these 3 factors increased: imaging depth lines per fame number of foci Fluid viscosity causes these 2 things flow resistance energy loss Poiseuille's equation change in pressure/flow resistance = volumetric flow rate(Q) Mean velocity across a vessel = volumetric flow rate(Q)/cross-sectional area(A) Venous resistance is proportional to viscosity AND vessel length Venous resistance is inversely proportional to vessel diameter**4 Pressure = 1/volume bulk modulus = pressure change/volume change Bulk modulus = 1/compressibility The effect of stenosis on flow speed increases flow speed Doppler Equation Doppler rfequency -transmitted frequency OR Operating frequency X {(2 X volume)/propagation speed} Increasing beam angle does what to the Doppler shift decreases Doppler shift Increasing frequency does what to the Doppler shift increases Doppler shift Increasing flow velocity does what to the Doppler shift increases Doppler shift Flow direction towards the transducer causes a positive or negative Doppler shift positive Flow direction away from the transducer causes a positive or negative Doppler shift negative Sample volume width is determined by the beam width Sample volume gate is determined by how long the gate is open For color flow imaging Increasing ensemble length does what to the frame rate reduces For color flow Increasing the number of scan lines per frame does what to the frame rate decreases Sensitivity/specificity = number of + correct test results/total number of positive test results Negative predictive value = number of correct negative test results/total number of negative test results Positive predictive value = number of correct positive test results/total number of positive test results Accuracy = number of correct test results/total number of test Intensity and power values are lowest for gray-scale anatomic imaging Intensity and power values are highest for pulsed Doppler Mechanical Index = Peak rarefractional pressure amplitude/sq root(operating frequency) To correct aliasing the Nyquist Limit is (increased/decreased) AND the PRF is (increased/decreased/unchanged) Both should be increased. To sample for low blood flow use: (High/low) wall filters (High/low) PRF Low PRF with low wall filters Dynamic range calculation = Divide larger voltage by smaller, count the number of zeroes in the resultant 10 factor and multiply by 20