RDTC 119 – Class 8: Ultrasound, Nuclear Medicine & Radiation Therapy – Flashcards
41 test answers
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what produces the image in sonography?
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the reflected sound waves
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why are there different frequency ultrasound transducers?
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used for different body parts
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describe the advantage and disadvantage of high frequency ultrasound transducers
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- adv: better resolution - disadv: less penetration
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why do higher frequency ultrasound transducers produce less penetration?
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higher frequency sound waves don't travel as far through the body (won't go as deep)
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for body parts close to the transducer (carotids, trans-vaginal, prostate/trans-rectal), what frequency ultrasound transducers are used?
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5-12 MHz (or 12-15 MHz??)
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abdomen studies that must see deeper into the body use what frequency ultrasound transducers?
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3-5 MHz
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how is ultrasound today similar to fluoroscopy?
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- it is in "real time" - image is dynamic and continuous
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at how many frames per second is ultrasound produced?
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20-30 frames per second
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type of ultrasound that occurs when frequency of sound waves change as the sound is reflected off of moving tissue (blood)
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doppler
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in doppler ultrasound, how much the frequency changes determines what?
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velocity (or speed) of the motion
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what does color doppler do?
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assigns different colors to different directions and velocities of flow
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describe color doppler
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- red: flowing toward transducer (higher frequency) - blue: flowing away from transducer (lower frequency) - white: swirling (indicates blockage, clot, etc.)
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tagged radionuclides injected in a pt in nuclear medicine
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tracers
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how is an image produced in nuclear medicine?
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- radionuclide collects in various organs - radiation is emitted from pt - imaging equipment detects radiation emitted from organs where radionuclide is collected - image is produced
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what types of conditions can be detected by nuclear medicine studies?
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- vascular/avascular tumors - stress fx
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differentiate between static studies and dynamic studies in nuclear medicine
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- static studies collect data once - dynamic studies collect data over time
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what detects radioactivity in nuclear medicine?
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scintillation camera
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when radiated, what type of crystals emit light during nuclear medicine procedures?
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sodium iodide
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describe what happens during a nuclear medicine procedure
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- radioactivity detected by scintillation camera - sodium iodide crystals emit light when radiated - light rcvd by photomultiplier tube - pmt amplifies and converts light into electric signal
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what does SPECT stand for?
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single photon emission computed tomography
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how does SPECT work?
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- uses same principles as CT to create images - scintillation detectors rotate around pt or are positioned 360º around pt
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what does PET stand for?
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positron emission tomography
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what is a positron?
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- positively charged electron - antimatter - very unstable - immediately finds e-
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how does PET work?
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- uses positron emitters - two 511 keV photons given off in opposite directions during annihilation reaction
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how have recent combination scanners like PET-CT and SPECT-CT improved imaging?
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merge structural information (CT) with physiological information (PET or SPECT)
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name common radionuclides and what each is used for
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- technicium-99: most imaging - iodine-123: thyroid (imaging & treatment) - thallium-201: some cardiac imaging - xenon-133 gas: pulmonary studies - fluorine-18: most common positron emitter for PET scans
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what half-life range do the common radionuclides have and why?
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- half-life of hours to days - mostly urinated out of pt
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what is the basis for radiation therapy?
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healthy tissue is better able to recover from radiation than cancerous tissue
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about how much radiation is delivered to a tumor during radiation therapy?
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6000 rad
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radiation therapy procedure involving insertion of radioactive nuclides (i.e. seeds) into pt's body near tumor to deliver highest amount of radiation directly to tumor (less common)
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brachytherapy (internal)
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give examples of brachytherapy
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- prostate seeds (permanent) - breast or uterus seeds (temporary after surgery, usually 3-4 days)
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radiation therapy procedure that uses linear accelerators to produce 6-35 MeV x-rays or high-energy e- that kill cancer cells (more common)
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teletherapy (external beam)
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radiation therapy procedure that uses a highly sophisticated c-arm to simulate therapy machine so that treatment area plan can be as accurate as possible; uses variable distances to match variety of linear accelerators; becoming more common
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simulation
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what is the therapy technologist's role in radiation therapy?
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- apply radiation plan to pt - assist w/ simulations - work w/ materials used to ensure radiation goes only where intended
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what is the dosimetrist's role in radiation therapy?
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assist physicist and oncologist w/ design or treatment plan
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radiation therapy procedure that delivers radiation from multiple angles to spare more healthy tissue while delivering high dose to tumor
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intensity modulated radiation therapy (IMRT)
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radiation therapy procedure in which radiation dose is delivered from multiple directions, reducing dose to healthy tissue, with entire dose delivered in one procedure (i.e. 6,000 rad in 20 min.); uses 4-5" thick lead molded to shape of tumor to provide additional collimation to prevent/reduce radiation to healthy tissue.
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- stereotactic - brands: radiosurgery, gamma knife
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