*Equation lists:* Wave relationships: C = λ f; λ = c/f , f= c/λ; C= speed of sound, λ= wavelength, f= frequency; C = ⱱ 1/kρ with compressibility k = 1/stiffness T = 1 /f, frequency is inversely proportional to period T. I = A2 / 2ρ C; I = intensity, A = amplitude, ρ = density, C = speed of sound. Power = 1 x Area Decibels: d = 10 log10 (I2/ I1) 3 dB ≈ 2 (note that this implies also that -3dB ~1/2 Reflection from planer interface, orthogonal incidence: Z = ρ c , Z = acoustic impedance, ρ = density , c = speed of sound. RA = (Z2 – Z1) / (Z2 + Z1), RA = Amplitude reflection coefficient RINT = (RA)2 , RINT = intensity reflection coefficient, RA = Amplitude reflection coefficient RINT + TINT = 1 (conversion of energy), TINT = 1- RINT , TINT = Intensity transmission coefficient; Refraction (snell’s law): C1 sin θ = C2 sin θ, sin θi /sin θt= C1/C2 ; Pulse echo range equation: T = 2d/c , d = ct/2 Doppler equation: FD = fr –ft = (2ft v cos θ) / c, FD = Doppler frequency shift, fr = received frequency, ft = transmitted frequency, v = velocity of the blood, cos θ = angle of insonation, c = speed of sound; cosθ 00 = 1 , cosθ 900 = 0, cosθ 600 = 0.5, cosθ 450 = 0.7; Remember to determine the sign (positive or negative) of the frequency shift from the motion of the reflector relative to the source (transducer). Frequency of echo moving towards transducer is positive. Doppler shift + Transducer frequency; Frequency of echo moving away from transducer is negative. Thermal index: TI = W/Wdeg ; W = power exposing the tissue during use, Wdeg = power required to cause a maximum temperature increase of 10 C, anywhere in the beam; If any maths given, then calculate power from equation Power = 1 x Area. A Thermal Index (TI) of 2.0 means that you can expect a temperature rise of about 20C. Mechanical index: MI = pr / ⱱf ; where pr is the derated peak rarefaction pressure. Remember that the pressure should be expressed in megapascals (MPa) and the frequiency in megahertz (MHz). Frame rate limitation: FR = c/ 2dNn Where d is depth, n is number of scan lines, and n is number of focal zones.
Posted on: Thu, 13 Nov 2014 21:13:17 +0000
Trending Topics
Recently Viewed Topics
© 2015