Intro to Ultrasound Flashcards
What is ultrasound
High frequency sound waves beyond the range of human hearing (20Hz-20 kilohertz)
What is the diagnostic ultrasound frequency?
1-30megaHz
What are the physics of ultrasound?
Mechanical energy as sound waves are transmitted through a patient and returning echoes are detected
What is the propagation velocity of ultrsound waves?
1540m/sec
What is the equation for ultrasound physics?
Acoustic impedance (z) = velocity (v) X tissue density (p)
What is the equation for velocity?
velocity= frequency (f) x wavelength
Wavelength
Distance between one peak or trough and the next peak or trough (mm)
Frequency
cycles per second (hertz, Hz)
Why are wavelength and frequency important?
Higher frequency gives higher resolution but lower penetration
Lower frequency gives lower resolution but deeper penetration
Attenuation
loss of ultrasound
What increases attenuation?
Increased distance from the transducer
Less homogenous medium to traverse due to increased acoustic impedance
Higher frequency (shorter wavelength) transducers
What has a low acoustic impedance?
Air
What has a high acoustic impedance?
Bone
Acoustic Impedance
characteristic of the propagation medium
a reflected sound wave is generated at the interface of an impedance mismatch
no reflections occur in a homogenous medium
What are the artifacts of ultrasound?
Acoustic shadowing Acoustic enhancement Edge shadowing Reverberation artifact Slice thickness artifact Mirror image artifact
Acoustic Shadowing
Distal to highly reflective objects
Interface absorbs or reflects entire sound
Results in an anechoic area
Clean Acoustic Shadowing
at the tissue-bone interface
complete absence of reverberation artifacts
homogenous anechoic shadow produced
Dirty Acoustic Shadowing
99% of the sound wave gets reflected
Acoustic shadow is dirty (inhomogenous/reverberation artifact)
What causes Clean Acoustic Shadowing?
Bone
Plastic
What causes Dirty Acoustic Shadowing?
Air
Acoustic Enhancement
Fluid of homogenous acoustic impedance attenuates less sound than the surrounding tissue
Edge Shadowing
Small shadow at the edge of round structures
Slice Thickness Artifact
at curved surfaces the machine averages
Mirror Image Artifact
At highly reflective air/fluid interfaces a false image is produced on the other side of the reflector
What are the three types of transducers?
Liner
Sector
Convex
What is in the transducer that emits and receives?
Peizoelectric-crystals
How do you prepare a patient for an ultrasound?
12 hour fasting Free access to water Avoid stress --> Aerophagia Shave fur Dorsal recumbency
Where do you place the ultrasound machine and examiner?
on the left side of the table
Where is the direction of the dog’s head?
in the direction of the machine
What are the two planes of scanning?
Sagittal or dorsal plane
Transverse plane
Anechoic
homogenous black
Ex: Fluid
Hypoechoic
Less echoic than other structures
“Darker” than other structures
Isoechoic
“Same” echogenicity as another structure
Hyperechoic
Higher echogenicity than other structures
“Brighter”
Normoechoic
Returning signal as expected for this organ
Compressible
Does it disappear with pressure
Invaded
Tumor that is infiltrating the surrounding tissue
What is the pneumonic for increasing echogenicity?
My Cat Loves Sunny Places
Anechoic
Transudate
Speckled/more echogenic
exudate, blood, chyle
