Contrast Studies Flashcards
why use contrast?
changes radiolucency/opaqueness of a structure
to gain more data about the area
- creates a deeper image
helps identify structures:
- position -
- size
- shape
- internal physiology
- function over time
examples - organ shape and function, soft tissue imaging and stops superpositioning of structures (eg bladder)
ways to administer contrast material?
Intravenous
Oral
Rectal
Subarachnoid space (myelogram)
Urinary Catheter
Intraarticular
positive vs negative contrast mediums?
Positive
- makes more radioopaque
- absorbs more photons
- increases the visibility of structures
- helps identify size, shape, damage, irregularity and FBs of structures
- common in CT, X-ray and MRI
negative
- makes areas more radiolucent (darker)
- fill with fluid or air - easy to see any perforations
- no damage if leaks - maybe some oedema which will correct istelf
- cheaper
examples of positive contrast mediums?
Ionic
- highly water soluble
- eg hypaque or Conray
non-ionic
- water soluble
- eg omnipaque
barium sulphate
- water-insoluble
gadolinium
- enhances MRI images
features of ionic contrast?
Highly water soluble
Easily absorbed by tissues and excreted
- so won’t stay long
- safe to use if a potential perforation
Doesn’t taste good
High osmotic pressure
- causes more fluid into vessels
- dehydration and increased kidney function
- so give fluid therapy to support
features of non-ionic contrast?
Fairly water soluble
Slightly lower osmotic pressure
- easily absorbed but slower
- longer time to image
- can be used with perforations
Safer with renal and cardiac compromise
Expensive
Can cause seizures if enter brain
- so keep head above shoulders
features of barium sulphate?
water-insoluble
- not absorbed
- pass through without absorption
- cant use with FBs/perforation/blockages
If enters peritoneal space can cause granulomas and adhesion of tissue
Easy to use
- can be powder, paste or tablet forms
Cheaper and less effect on kidneys
features of gadolinium
Used to enhance MRI images
- changes magnetic properties of water components in the body
Reduces T1 and T2 relaxant time
- more definition between tissue types
- better details
adverse reactions of positive contrast mediums?
anaphylaxis - common with contrast
mild = v+, nausea, tremors, changes in behaviour, swelling
moderate = dyspnoea, wheezing, bronchospasm, hypotension and tachycardia
severe = convulsions, profound hypotension, arrhythmia, laryngeal oedema
use preventative drugs - eg dexamethasone
- also slow administration if IV to reduce reactions
examples of negative contrast materials?
carbon dioxide
oxygen
air
what is double contrast?
both positive and negative mediums
- air then contrast
create information on the inside of the structure and the lumen of the membrane
common with bladder
how to prep a patient for contrast studies?
administration and location-dependent
- eg if IV - use a catheter otherwise wrong placement is irritant
- eg if oral/rectal - prep GI tract first - nothing in the way and can pass through
consider the likelihood of getting any axis
- compromised functions
Standard X-rays first in case dont need contrast
- avoid use due to strain on body and organs
what is a myelography?
introduction of positive contrast medium into subarachnoid space around the spinal cord
- spinal pain, ataxia, trauma, quadriplegia
shows cord swelling/compression not seen on X-rays
gives a chance to take CSF tap
must use non-ionic media - eg omnipaque
the patient must be under GA - completely still to avoid damage of spinal cord
considerations when doing a myelography?
table tilted upward
- stop backflow of contrast to brain = seizure
- same in recovery
is water soluble - will move out of the body but at a slower rate than ionic
consider MRI first as safer
how to prep a patient for a myelography?
into spinal cord = must be sterile
- good skin prep and wide margins
- infection on the spinal cord causes pressure
- also allows for reliable lab sample
general prep for GA
- starve and catheterise
