Final Physics review Flashcards
When wave intensity doubles what is the change in decibel
3db incfrdase
Wehn intensity increases 10 fold what is change in db
10
What 3 processes contribute to wave attenuation?
Reflection, scattering absorption
What ar e2 forms of reflection?
Specular - mirror reflections that don’t return to transducer. Diffuse reflection - backscatter
Diffuse reflection vs scattering
scattering reflects in many directions. Diffuse reflection is bounced back at different angles.
What are typical units of attenuation?
It summarizes reflection, scattering and absorption ad 2Db/cm
What is attenuation coefficient in soft tissue
1/2 dB/cm/MHz
Order of attenuation of different medium
water, blood/urine, fat, soft, muscle, bone/lung, air
What is half value layer thickness
Term referring to attenuation. Distance to reduce attenuation by half.
What is acoustic impedance definition
Density of medium x speed of sound in medium
Unit of acoustic impedance
Rayls
What does acoustic impedance relate to?
Relates to the amount of reflection at a tissue boundary layer
How does the attenuation coefficient relate to the ultrasound frequency in soft tissue?
In soft tissue attenuation coefficient (in dB/CM) is 1/2 the frequency
Definition of incident intensity
Sound wave’s intensity before striking boundry
What is the intensity reflection and transmission coefficients and what are units?
Percentages reflecting how much is reflected vs transmitted
At soft tissue boundary how much is reflected vs transmitted
99% transmitted
When a sound wave hits a tissue boundary at 90 degree angle what determines whether reflection occurs?
Only the impedance difference between the two
What is equation intensity transmission coefficient with normal incidence?
ITC (%) - transmitted intensity/incident intensity x 100
Is it easy to determine how much transmission occurs with oblique incidence?
No - there is no predictable way to make determination
If US signal hits interface at oblique angle, what happens?
Part reflected at incident angle, the other bit transmitted and refracted based on the speed of sound difference between the two media
If you know attenuation coefficient what is ultrasound frequency?
F = attenuation coefficiente x 2
What is range equation
1.54 mm/us x (go return time (us))/2
What is the 13 us rule?
For every 13us that sound travels in soft it is 1 cm deeper into body
What is PRP (us) in soft tissue
imaging depth (cm) x 13 us/cm
