Diagnostic Ultrasound Imaging

Question 1

Piezoelectric crystal sound wave principle

Answer 1

used for generating ultrasound
- voltage off → contraction of material
- voltage on → expansion of material
→ switching on/off in given frequency → sound wave

Question 2

piezoelectric crystal sensitivity

Answer 2

• sensitivity to mechanical perturbation
• variation in air pressure deform crystal and produce voltage
• can detect reflected waves

Question 3

transducers

Answer 3

Ultrasound probes

- large number of individual piezoelectric crystals

Question 4

Reflection, Refraction, Absorption

Answer 4

Reflection: soundwave on surface btw two media with different acoustic properties
Refraction: remainder of beam continues to the tissue (transmission) but under different angle
Absorption: sound wave penetrates tissue → part of energy converted into heat

Question 5

acoustic impedance

Answer 5

unique properties of tissues determined by

• density & speed of sound in substance
• proportion of wave reflected & refracted

Question 6

ultrasound wave travel properties

Answer 6

• waves cross form one tissue to next, each with different acostic impedance and different proportions of reflection
• multiple reflected waves return to probe → display an image representing different tissues

Question 7

Absorption

Answer 7

• Energy lost to medium of propagation → weak local heating
• measured in dB
• high frequency for good resolution → but the higher the frequency, the higher the absorption

Question 8

Reflection factor

Answer 8

Z = pc

Reflection factor RF = (Z1-Z2)/(Z1+Z2)

Question 9

transmission factor

Answer 9

TF= 1 + RF= 2* Z2/(Z2+Z1)

Question 10

Absorption equation

Answer 10

Absorption = alpha * f^gamma * z

alpha: absorption coeff
gamma: exponent of power law
z: depth of penetration

Question 11

doppler effect

Answer 11

• transmitted wave with certain frequency, returned wave with same frequency
• object moving toward probe → higher frequency
• object moving away from probe → lower frequency
• the faster the object moves away, the greater the frequency difference will be

Question 12

Doppler frequency

Answer 12

shift in frequency of transmitted wave → wave bounced back from moving object
fD= f0 [2(v/c0) cos(phi)]

Question 13

Ultrasound frequency

Answer 13

in clinical assessments btw 2-15 MHz
- higher frequency can provide higher resolution, but are attenuated by tissue more quickly
FWHM=1.206lamdaz/ L
lamda=c/f

Question 14

highest to lowest impedance of different tissues

Answer 14

bone > blood > muscle > water > fat > air