Advanced Imaging Techniques Flashcards
what are the 3 main advanced imaging techniques?
computed tomography (CT) scintigraphy magnetic resonance imaging (MRI)
where are most advanced imaging modalities found?
at refurral centers
where are most advanced imaging modalities found?
at refurral centers
what is seen when using CT/MRI?
slices through the animal rather than 2D projections
what can be assessed by scintigraphy?
functional remodelling activity of bone
how is CT similar to MRI and US?
uses cross-sectional imaging
how is CT similar to radiography?
makes use of ionising radiation and many of the same principles
what is used to generate the image in CT?
x rays
what constraints is CT imaging under?
same as x ray
what happens to the room while CT is running?
locked and red light outside shows no entry
how does CT gain a 360 degree image?
uses rotating x ray machine and rotating detector which pass around the patient
where is the patient positioned during CT?
on a sliding table and is advanced through the gantry as the machine rotates
what is used to construct the data gained from CT into a slice or 3D image?
complicated computer programs which analyse information from all detectors
how are different tissues represented on CT?
as with radiography (bone - white, air - black)
what is CT windowing?
choice of how to display information / tissues depending on what you would like to view
what is each tissue assigned during CT?
Hounsfield unit?
what do Hounsfield units depend on?
attenuation of beam - how much of the X-ray beam reaches the detector as it passes through each tissue
what is CT window level and width chosen to optimise?
certain tissues so that they show up more than others
what structure is assigned Hounsfield number 0?
water
how can Hounsfield units be used to optimise an image?
assigned to all tissues - area of interest (e.g. bone/brain) has range of HU and visible shades of grey are placed assigned to these values so differences in tissue density will be shown
what is a key benefit of CT windowing?
animal can be scanned once but image is reconstructed differently to show different desired tissues
what are the main uses of CT?
good bone detail
used in soft tissue particularly with contrast
scanning time is shorter than MRI so can be used for studies of thorax as respiration is not an issue
how long is CT scan time?
several seconds - longer than x ray
what restraint is needed for CT?
sedation or GA
what area of CT is particularly useful for orthopedic surgery?
can be used to create 3D models for surgical planning and custom made surgical implants
what are the disadvantages of CT?
limited availability in general practice
expensive (although cheaper than MRI)
scan time is several seconds - slower than x ray
uses ionising radiation in higher patient doses than radiography due to length of scan rime
what is CT useful for in the lung?
pathology
detection of metastatic disease
why is CT so good for detection of metastatic disease in the lungs?
detects nodules that are invisible on x-rays
what issue found with radiographs is avoided by CT?
superimposition of structures
what aspect of CT facilitates surgical planning?
3D reconstruction and rotation to view all aspects
what CT imaging can be performed in horses?
extremities and head
what is used as the source of IR during scintigraphy?
radioisotope
what is the most common radioisotope used for scintigraphy?
technetium 99
what determines where in the body the radioisotope will localise?
the substance it is bound to which will bind to a certain tissue in the body
where si increased binding of the radioisotope found?
within the target tissue where there is increased metabolism
what is the most common substance used to bind radioisotope to bone?
HDP
how does the bound isotope reach its site of binding?
IV injection into patient
how long must be allowed for the isotope to reach the tissue of interest?
~3 hours
how is scintigraphy scan performed?
gamma camera used to measure pattern of radiation emitted from the patient
what restraint is used for scintigraphy?
sedation in cats as short scan time
standing sedation in horses - must be able to stand
what are the uses of scintigraphy?
detection of skeletal injury in horses
detection of thyroid nodules (especially ectopic nodules) in cats
where is scintigraphy useful in detection of skeletal injury in horses?
areas that are difficult to radiograph
lesions not detectable radiographically
cases where it is difficult to localise lameness source
what areas of a horse may be difficult to radiograph?
pelvis/spine - due to thickness so more scatter produced and lower qualty image
what is an example of a lesion that may be undetectable radiographically but would show on scintigraphy?
stress fractures
what are the advantages of scintigraphy?
increasing availability (particularly in equine practice) functional assessment as uptake of bound isotope depends on metabolism / activity
what are the disadvantages of scintigraphy?
uses IR radiation so same risks to operator and patient as x rays
patient remains radioactive for sometime afterwards
poor anatomical detail so can be difficult to interpret images
additional legislation applies (EA) for licence to use and disposal
how long will the patient remain radioactive after tachnetium is used?
48 hours
what images are produced during MRI?
cross sectional images in different planes
what causes a nucleus to spin?
if there is an odd number of protons and/or an odd number of neutrons
what is created by the spinning electrical charge of an unbalanced atom?
a mini magnetic field
how many protons are found within 1ml of water?
6x10^22
what happens to the random proton rotation within a patient when they are placed in a strong magnetic field?
the magnetic moments of the spinning nuclei line up with the magnetic field they have been placed in
what is the strength of the magnetic field in a typical high field machine?
1.5 tesla
how is an image aquired during MRI?
patient placed in a strong magnetic field so that atoms all spin the same way
patient is then bombarded with radiowaves which cause the nuclei to become disorientated and emit a radio signal themselves
when the waves stop the nuclei realign themselves
detection and analysis of the radio signals emitted by the patient gives information about the chemical composition of the tissues
what does appearance of tissues on MRI depend on?
timing of pulses (inputs of radiowaves) and echoes (signals from tissue)
what does the timing of radiowaves depend on?
tissue environment
what does the computer reconstruction of information received from MRI machine result in?
cross sectional images through the patient
what are the advantages of MRI?
good contrast resolution - excellent anatomical detail
doesn’t use ionising radiation - non damaging long term
accurate assessment of extent of the spread of a lesion
what lesions can be assessed with MRI?
retrotubular
nasal
pelvic masses
what are the main uses of MRI?
neurology - spine and brain
soft tissue lesions
bone marrow oedema (not great with bone itself)
what are the disadvantages of MRI?
not widely available in practice
expensive (installation and maintenance)
animals must be under GA
safety hazard caused by magnet - no metallic objects around
why must all animals be under GA when having an MRI scan?
MRI sequence takes time and must remain perfectly still throughout
why must metal objects not be taken into MRI?
large permanent magnet
what equipment used in MRI must be MRI compatible?
tables
oxygen cylinders
anaesthetic machine
monitoring equipment
should animals with pacemakers have an MRI?
no
what must you take care with when the patient is having an MRI?
any implants - particularly new - as they may shift due to magnet
what artefact may be produced during MRI?
distortion of magnetic field around microchip site leading to altered image
how does MRI used during equine standing MRI differ from normal MRI?
similar technology
lower field
smaller magnet
what part of the equine limb can be imaged using standing MRI?
distal only
what is equine standing MRI useful for?
examining soft tissues within the hoof capsule
what must be placed prior to equine standing MRI?
IV catheter
what sedation level is equine standing MRI performed under?
standing
who is usually in charge of acquiring images and sedation during equine standing MRI?
nurse
