Lecture 1 Notes

Attenuation 1 db cm mhz 60mhz attenuation 60 dbcm

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: uation leads to a decrease in amplitude of the ultrasound signal: Ultrasound radiated away from transducer Attenuation ~ 1 dB / cm / MHz Attenuation: An Example What relative amplitude of a 60 MHz ultrasound signal do you expect to receive from a depth of 5 mm? Attenuation ~ 1 dB / cm / MHz @ 60MHz: Attenuation ~ 60 dB/cm Attenuation: Consequences   Consequences of frequency dependent attenuation for imaging: –  Penetration of ultrasound is limited by frequency –  Frequency of ultrasound decreases with increasing depth of imaging Depth = 5 mm: Ultrasound propagates through 1 cm Attenuation ~ 60 x 1 = 60 dB 1/1000 of the transmitted signal is received! Resolution in Ultrasound Imaging   Axial Axial Resolution: –  Resolution in propagation direction –  Determined by length of pulse propagating in tissue   Lateral Resolution: Lateral Axial Resolution   Axial Resolution: Axial Resolution = pulse width (s) x speed of sound (m/s) /2 = N λ/2 –  Resolution orthogonal to propagation direction –  Determined by focusing properties of transducer Nλ Resolution vs Penetration Lateral Resolution   Lateral 2a Resolution: f-number = focal length/aperture = f/2a Lateral Resolution = wavelength x f-number = λf/2a     Resolution (axial and lateral) with frequency Penetration with frequency f Compromise between resolution and penetration Doppler Ultrasound: Basic Concepts   Ultrasound wave reflected from moving targets (Blood cells)   Frequency shift in received ultrasound wave compared to transmitted wave: Doppler Shift Fre...
View Full Document

Ask a homework question - tutors are online