Imaging Flashcards
barium examinations
not very commonly used today because there is better tech.
barium sulphate is swallowing, travels through the oesophagus, stomach, duodenum. Because it has higher atomic number, it can swallow more protons from the X-ray than the surrounding tissues and will appear on the radio graph.
- is not absorbed by the body.
barium meal VS. enema
MEAL:
- 1.5 mSv
- goes to the stomach
ENEMA:
- 7.0 mSv (stronger radiation)
- goes to the large bowel. is no swallowed but inserted through the rectum and pushed forward by inflating the bowel with air.
Types of cross sectional imaging
CT, MRI, PET
the type of gas used in CT colonography?
CO2
- you drag the tool around the colon and image will be displayed on the screen.
CT scan is useful for?
- initial diagnosis of disease (if nothing shows on CT, most likely not serious)
- monitoring response to treatment and post treatment.
colors in CT scan
depends on how much photon of light passes through. Lighter means less got through, darker means lots got through:
bone - white
air - black
fat - dark grey, will be darker than water.
contrast agents used in CT
dilute iodine based gastrografin - oral route, for GI tract
iondine based omnique - IV route, gets excreted by the kidneys
organs you should no use PET on
brain and spinal cord , liver- PET targets highly metabolic organs, therefore, there will be bad effects on these
kidney - all the agents used for contrast will be excreted in the kidneys.
the reproductive organs
organs you should not use MRI on
lungs - too little soft tissue, is made of mostly air
stomach, colon - MRI is not good with things that move
organs you should not use CT on
spinal cord - the structure is too small, and is also made of soft tissue.
what should pancreas, upper urinary tract, and testis be scanned by
CT
what should spinal cord by scanned by
MRI
MRI vs CT
MRI - 45-60 mins
unlike CT, it does not use rays but instead magnet and therefore completely harmless unless the patient has pacemakers or metal implants.
- MRIs can’t be turned off if there is a problem, but CT you can turn on and off whenever
how MRI works
use of magnet to reorientate molecules in the body, and the different amount of time it takes for them to rotate back to their original orientation is what produces the images.
light weight molecules like water will take longer to return than fat.
screening
done in population, not one person - useful for diseases with a latent stage that does not manifest too quickly. - common condition - must be treatment or else ppl won't be interested
radionuclide imaging
use unstable radioactive molecule called radionuclide that will emit nuclear radiation.
PET vs CT
PET uses gamma rays
- the rays are emitted in 2 180 degree directions
- the patient will be injected with gamma radiating radionuclide and they will emit radiations that are detected by the scan
- harmful
- ideally half life of 6 hrs. But if we use it for treatment, it can be weeks or months
- shows metabolic changes while CT or MRI don’t
- functional imaging
- sensitive
CT uses x-rays
- single photon emission, only in 1 direction
- anatomical imaging
- high resolution, specific location.
- both have rotating cameras
- both are 3D?
radioactive element vs pharmaceutical element
RE are radionuclides that emit radiation while PE is the stuff attached to RE to lead it to the target organ.
common pharmaceutical elements
Hydroxy diphosphonate: bone
Dimercaptosuccinic acid (DMSA): kidney
Hexamethyl propine amine oxime (HMPAO): brain, WBCs
Macroaggregated albumin: lung
what is a SPECT collimator
sheet that restricts the number of oncoming rays detected by the screen to only perpendicular ones for high resolution image
- made of tungsten
radiography vs radionuclide imgaing
RI uses gamma rays emission
radiography uses x-rays
how does X- ray work
electrons emitted from a source and deflected so that it goes through the body
some of the rays will pass through, pass through or reduced, deflected back, or scattered. we will only focus on the rays that passed through.
different types of particles
alpha: slow moving but easily stopped by paper, basically a moving electron
beta: fast moving, high energy, short wavelengths, basically a moving electron
gamma: high energy wave/particle. formed from radioactive decay of particle’s nuclei
x- ray: high energy photon
ventilation vs perfusion
ventilation: radioactive isotopes inhaled
perfusion: injected
you can have normal perfusion of the lungs but abnormal ventilation and vice versa
angiography define
imaging used to visualise the lumen of blood vessels especially in the heart chamber for obstruction
radionuclide imaging pros and cons
PROS: useful in scans of structures that are disease specific - Ex. WBC scan for ulcerative colitis
CONS: not specific, the elements can target a location, and that could be both and tumor or inflammation.
- we know where, but not what.
give one commonly used example of pharmaceutical element in radionuclide imaging
technetium 99
what disease is 123 iondine dopamine transporter spect specifically used for
Parkinson’s disease
- normal appearance should be like 2 commas.
SPECT
like PET, it uses gamma emissions, but is different by the type of radionuclide used, which have different mechanisms of emission.
- rays only in 1 direction
PET
- very similar to SPECT, but uses positron (electron with + charge) emission. this will combine with e- and annihilate one another, which produces 2 photons that travel in opposite directions.
- used in cancer mostly, but also in inflammation and infection.
- reveals metabolism of the structure as well
- often combined with CT so you get both anatomical and functional information.
- not high resolution, not very specific, but very sensitive.
ideal energy of gamma rays used in imaging
50-300 keV
common PET radionuclides
18F - half life 110 mins (most ideal)
11C choline- 20 mins
13N - 10 mins
15O - 2 mins
18F (fluorodeoxy glucose) - aka FDG
attached to pharma element glucose.
- will go to any cell in the body where there is infection, inflammation, tumor
- also go to brain and spinal cord due to high metabolism
- shown in black
cyclotron
11 MeV
particle accelerator that produces radioactive isotopes that is carried out under computer control
radiation pros and cons
PRO:
- good for diagnosis , management, treatment
CON:
- radiation –> cancer later in life
- make sure benefits > damage
ultrasound
effective for looking at soft tissues
- pregnancy
- gallstones
