Flashcards
medical imaging
Cards in this deck (29)
- 1how does an x ray machine produce a photographx ray machine above the patient contains an d ray tube that produces x ray photoms that pass through the patient to the detection plate below
- 2what is an x ray tube & how does it workan evacuated tube containing 2 electrodes, a large pd is produced between the 2 electrodes the cathode is a heater which produces electrons by thermionic emmision, which are then accelerated to the anode which is made of the target metal
- 3why is an x ray tube evacuatedso that electrons pass through the tube without intercting with gas atoms
- 4how are x ray photons producedthey are produced when the electrons are decelerated by hitting the anode
- 5how is the energy from the KE incident electrons in an x ray distributedless than 1% is the energy output of x rays, the rest is tranformed into thermal energy of the anode
- 6how is the anode cooled in an x ray machineoil is circulated, or the anode is rotated to distripute the heat over a large SA
- 7what shields the radiographer from x rays emmitted in other directionsthe lead lining of the x ray tube
- 8what is the value of the KE an electron gains when it is accelerated through a pd of VeV
- 9what is the mac energy of a photon of an x ray tube and whysince conservation of energy, it must equal the max KE of a single electron
- 10guve an equation for wavelength involving hlambda = hc / eV
- 11name the 4 attenuation mechanismssimple scatter, photoelectric effect, compton scattering, & pair production
- 12describe simple scatterimportant for x ray photons with energy in the rand 1-20 keV, x ray photon interacts with an electron in the atom that has less energy than the energy required than the energy required to remove the electton, so the photon bounces without any energy change
- 13dezxibe the photoelectric effectsignificant for energy less than 100 keV, photon is absorbed by an electron int he atom the electron uses this energy to escape from the atom. this is significant for hispital x ray machines
- 14compton svcatteringsig for energy of 0.5 - 5 MeV, incoming phton interacts with electron which is then ejected from the atom, but the photon doesnt dissapear, instrad its scattered with reduced energy
- 15pair productionsig for energy equal to or greater than 1.02 MeV. photon interacts with nucleau of atom, it dissapeares and the EM energy of the photon is used to create an electron and its anitparticle (positron)
- 16what does the transmitted intensity of x-rays depend onenergy of the photons and the thickness and type of substance
- 17give the equation of the transmitted intensityI = initial intensity x e^-attenuation coefficient x thickness
- 18when is a contrast medium used in an x-rayto see soft tissues that have low absorption coefficience
- 19how are x-rays used to kill of cancerous cellslinaces (linear accelerators) are used to create high energy x-ray photons using the mechanism of Compton scattering and pair production
- 20describe how a CAT scanner workspatient lies on their back on a table that can slide in and out of a large vertical gantry which houses a x-ray tube on one side and a ray of x-ray detectors opposite which rotate
- 21how are the images produced in a CAT scannerthe x-ray tube produces a beam of x-rays that irradiate a thin slice of the patient. x-rays are attenuated by different amounts by different tissues, the intensity of the transmitted x-rays is recorded by the detector s which send electrical signals to the computer which forms the image
- 22give 2 advantages of a CAT scanner1 - can create 3-D image that can assess a shape, size, and position of disorders - e.g. tumours
2 - can distinguish between soft tissues of similar attenuation coefficients - 23give the four disadvantages of CAT scanners1 - expensive
2 - takes a while
3 - higher radiation exposure
4 - patients have to remain very still for a prolonged time - 24why are gamma emmiting sources used as radioisotopesbecause gamma photons are the least ionising and they can penetrate through the body to be detected externally
- 25describe a characteristics of a radioisotope used in the human bodyshort half life to ensure high activity from the source sp that only a small amount is required to form the image, and to minimise the radiation exposure
- 26what is a radiopharmesitical comprised ofa radioisotope chemically combined with elements that will target the desired tissues
- 27describe the path of the gamma photons through a gamma camerathey travel to the collimator, then some photons reach the scintilator, the the photons of visible light travel through the light guide into the photomultiplier tubes which then form an image
- 28what do PET scans use to produce images of the bodygamma radiation
- 29—
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- physics A level (M6 Chapter 27 Medical imaging - unfinished) Flashcards on medical imaging, created by lizabeth rawson on 09/06/2022.
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- lizabeth rawson
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