Sonography Canada – Core Questions & Answers(rated A)

what is the I SPPA for mechanical bioeffects? -ANSWER 190W/cm^2 what is the I SPTA for thermal bioeffects? -ANSWER 720mW/cm^2 recommended MI for fetal scanning -ANSWER MI 1.9 recommended TI for fetal scanning -ANSWER TI 0.7 after what fetal age is safe to use PW doppler? -ANSWER 14 weeks what does ALARA stand for -ANSWER as low as reasonably achievable frequency -ANSWER # of cycles/second f = 1/p period -ANSWER time it takes for 1 cycle to occur (usec) P = 1/f wavelength -ANSWER length of 1 cycle (mm) wavelength = c/f inversely proportionate to frequency assumed speed of sound in soft tissue -ANSWER 1540 m/s 1.54mm/usec intensity -ANSWER I = power/area measured in Watts proportionate to amplitude squared range equation -ANSWER distance to reflector = 1/2 speed of sound x GRT go return time (GRT) -ANSWER 13usec for 1cm of depth acoustic impedance (z) -ANSWER difference between media determining % reflection and % transmission of sound (Rayls) z= density x speed of sound z = p x c % reflection equation -ANSWER larger AI difference results in ___ reflection -ANSWER greater pulse duration (PD) -ANSWER time for one pulse tx is ringing PD = period x n; n = # of cycles in pulse pulse repetition period (PRP) -ANSWER the time from the beginning of one pulse to the beginning of the next time tx is ringing and listening for 1 scan line PRP = 13usec/cm x imaging depth pulse repetition frequency (PRF) -ANSWER # of pulses in 1 second (kHz) PRF = 1/PRP duty factor -ANSWER % tx is ringing over tx ringing and listening DF = (PD/PRP) x 100% frame time -ANSWER time it takes to create a single frame (msec) FT = PRP x lines/frame frame rate -ANSWER # of frames per second (Hz) FR = 1/FT spatial pulse length (SPL) -ANSWER length of space of one pulse (mm) SPL = wavelength x n; n = # of cycles in pulse Is sound a transverse or longitudinal wave? -ANSWER longitudinal what kind of pressure wave is sound? -ANSWER mechanical infrasound range -ANSWER 20Hz audible sound range -ANSWER 20Hz - 20kHz ultrasound range -ANSWER 20kHz bulk modulus -ANSWER describing stiffness/intermolecular bond strength higher BM = more stiff relationship between speed of sound and BM -ANSWER speed is proportionate to BM which has a bigger impact on velocity: BM or density? -ANSWER BM