2- ultrasound Flashcards
how does the ultrasound work
high frequency sound waves penetrate tissue (or don’t) and bounce back to transducer
- crystals in transducer converts sound waves to electric current and converted to image
what are the acoustic impedance of fluid, soft tissue, fibrous tissue and solids
fluid (blood): black
- waves go straight through
soft tissue (liver): grey
- a lot goes through but some bounce back
fibrous tissue (diaphragm): white
- a lot bounces back
solid (stone): ?
what does ultrasound hate
Air (all the waves bounce back)
what does anechoic mean
black color
what does hypoechoic mean
dark grey
what does hyperechoic mean
white - bright
what does isoechoic mean
light grey
what does reflective mean
explain the acoustic shadow
artifact - you cannot see below a structure that reflects back all waves
what is acoustic enhancement
artifact - brightness deep to anechoic structure
what is a reverberation artifact
sound waves reflection multiple times between 2 strong reflectors
what is a mirror image artifact
duplication of image of the opposite side of a strong reflector
- most common from thorax/abdomen interface
what is a slice thickness artifact
from imaging a 3D structure with anechoic fluid
- most common in the bladder and gall bladder = artificial sludge
what is a edge shadow artifact
when sound waves bend as they hit a curved surface tangentially
what are the different types of ultrasound transducers
linear
- large foot print and most commonly used for equine tendons
curvilinear
- either used for SA or LA abdomen and thorax
- small foot print
what does an increased frequency (mHz) mean
greater resolution but less depth
what does a decreased frequency (mHz) mean
greater depth but less resolution
what can real-time imaging (doppler mode) measure
movement
- heart movement = heart beat
can assess direction of flow
- regurgitation of blood though a leaky valve
what are the principles of computed tomography (CT scan)
X-ray tube in a circle
- intensity of x-ray allows for differentiation of structures
- computer reconstructs the data to make a “slice” image
- 2D slices to allow 3D location (way more detail and gets around superimposition of radiographs)
how are CTs applied to vet med
animals are anesthetized or very heavily sedated
- imaging in horses “generally” limited to carpus/tarsus, digit and the head
—– there are also standing CT machines for LA that can do more
what are the common imaging done with CTs
detailed evaluation of bone
- fracture repair planning
image the head
image spine
image the abdomen
- requires inj of contrast to enhance lesions (limited)
what are the principles of magnetic resonance imaging (MRI)
- all tissues have lots of hydrogen protons because they are made of H2O
- STRONG magnet is applied and protons are excited by a radiofrequency pulse
pulse removed -> protons relax -> emits signal
- protons in different tissues relax differently
what precautions must be taken with MRI machines
must remove anything metal and use non magnetic anesthesia equipment
MRI vs CT
both allow for tomography and 3D reconstruction
MRI has better contrast resolution
- superior for imaging soft tissues
CT is superior for imaging bone because it does not have a much water
– for fracture planning!!
