Lecture 16 + 23 - Medical Imaging Flashcards
X-Rays
How Does it work ?
Give a Clinical Example
look at AP and PA chest X rays
AP is worse but sometimes the only option
PA is preffered
the position of scapulae / collarbone is a good indicator
X - rays are very short wavelength Electromagnetic Waves
X rays will pass through the body to an x ray receiver to produce image, Denser tissues absorb more of the radiation - so we get less X rays passing through the dense regions - this is ATTENUATION
Xrays allow us to see bones - very dense so show up white - see breaks/fractures in the bones
X rays also allow us to see density in a place where there should not be - an issue
Fluid collection in lungs shows up, lungs should be very black - just air
Infection and inflammation of the lungs will make them not as black as they should be
if we add dense contrast agents it will allow us to see narrowing or breaks in tubes
chest x rays will have a Left and Right - IDENTIFY THIS, it is th eopposite of your left or right
can also be taken AP or PA - Be aware of this
is the X ray good enough ?
what does it show - chest, thorax, arm
is it adequate ?
What are the advantages and disadvantages of X-Rays
X ray issues - Ionising radiation is bad
only 2D image
bad for soft tissue
advantages
is non inavse
cheap
short - 2 mins
Ultrasound Scanning
How Does it work ?
Give a Clinical Example
Clinical example - baby imaging
it works by sending waves via a peizoelectric crystal
the waves will detect the tissues and reflect on the changes in density of the tissue (tissue palnes), will be detected and turned into a image
a higher frequency wave will give more reflection of closer stuctures, but lower penetration
What are the advantages and disadvantages of Ultrasound
dynamic and very quick
non radiation and non invasive
bad for bones
cant view past air
2D image
MRI - Medical Resonance imaging
How Does it work ?
Give a Clinical Example
MRI - hydrogen ions have an up or down spin
Apply a magnetic field and the ions will line up with field, half up and half down
some h ions do not form an up/down spin pair,
apply a radio frequency pulse over the ions, and the unmatched ions will flip the other way, they will then return to ground state and release their energy, we detect this energy released, and the time it takes for each tissue to release its energy and its varying frequency
the time will vary for different tissues,and we use this to produce an image
T1 - water is black and T2 - water is white
What are the advantages and disadvantages of MRI
very good, as you lots of detail and good imaging of soft tissues
3D image
and cross sectional imaging
however, need specialists, its expensive, very loud and intimidating, cannot have metal inside the body, itlls rip out
non invasive and no radiation used
tests are slow - 40 mins
not great for bones
PET - positron emission technology
How Does it work ?
Give a Clinical Example
inject a radioactively labeled substance - usually glucose
Scan to show areas of high metabolic uptake - ie metabolically active
can combine with CT can to give a 3D view of the area
What are the advantages and disadvantages of PET
Very good at identifying cancer, as they are metabolically active
also can be used to image the brain
Computerised Tomography Scanning - CAT
How Does it work ?
Give a Clinical Example
how do we interpret CT cans
use of X rays in a spiral path along body,
computer uses multiple x rays to build a 3D image
Fat is low density - dark
air - lowest so black
bone high density - white
can give contrast to make organs appear brighter
CT scans are interpreted from the axial veiw - slice transverse
looking from feet to the head
What are the advantages and disadvantages of Computerised Tomography Scanning
good - 3D image, cheap , quick
Bad - uses even more ionoinsing radiation than a normal X ray
poor soft tissue detail
lots of radiation
Fluoroscopy
How Does it work ?
Give a Clinical Example
Many X rays Taken in sequence to produce a moving image / film
real time images
used with addition of contrast
shows dynamic flow through the system
What are the advantages and disadvantages of Fluoroscopy
Lots of X ray is bad, poor soft tissue bad
Moving image is good
what are nuclear scans good for ?
Use a radioactive isotope - emits detectable gamma radiation
diff isotopes will visualise diff tissues
eg sugat in pet scans for metabolically active tissues
technetium 99-n for thyroid and bone
what makes good contrast media ?
highly soluble biologically inert cheap safe stable
