Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Positron emission tomography wikipedia , lookup
Nuclear medicine wikipedia , lookup
Center for Radiological Research wikipedia , lookup
Neutron capture therapy of cancer wikipedia , lookup
Proton therapy wikipedia , lookup
Backscatter X-ray wikipedia , lookup
Image-guided radiation therapy wikipedia , lookup
Radiosurgery wikipedia , lookup
Industrial radiography wikipedia , lookup
effective dose for -chest radiograph -skull radiograph -abdomen radiograph -Lower extremity CT -head ct -abdomen CT -chest Ct Chest radiograph- 0.05 mSv Skull radiograph- 0.1 mSv Abdominal radiograph- 0.5 mSv Lower extremity CT- < 1 mSv Head CT- 1- 2 mSv Abdomen CT- 4 mSv (book says 5-10 for Abd/Pelvis) Chest CT- 6 mSv (book says 5-10) entrance skin exposure (ese) for-chest -skull -abdomen -l spine -Fluoro (1 min) -body ct -head ct chest 0.2 mGy skull 1.5 mGy abdomen 3 mGy L spine 10 mGy Fluoro 20 mGy body ct 30 mGy head ct 60 mGy receptor exposures -Fluoro -Cine -photospot -film screen (200 speed) -detail film screen -mammo Fluoro- 0.01- 0.02 μGy Cine- 0.15- 0.30 μGy Photospot- 1 μGy Film screen (200 speed)- 5 μGy Detail screen film- 20 μGy Mammo- 100-200 μGy what is the typical equivalent dose for a body ct midway through the body? 5-10 mSv What is linear energy transfer? (LET) • Energy absorbed by medium per unit length of travel (kEv/um) - Proportional to particle charge squared. - Inversely proportional to particle kinetic energy what is 10th value layer (tvl)? It is the thickness of material that attenuates the beam by 90% what is the quality factor? Linked to relative biologic effectiveness (RBE) -orThe radiation weighing factor -It compares the ability of different radiation to cause biologic change. WHAT IS THE BIOLOGICAL HALF LIFE (Tb)? It measures the clearance of the radionuclide from the organ, tissue, or body. 7th hvl 1% transmitting (1/2)^7 compton interactions are proportional to _______? The # of outer shell electrons (electron density) -Inversely proportional to photon energy (1/E) Lateral resolution on ultrasound is dependent on _________? The width of the beam and the line density. what is vignetting? - Image intensifier artifact - Fall off in brightness at the peripheral of II field - Decreases 25% - Caused by curvature of II faceplate What is pincushion distortion? - Image intensifier artifact - Straight lines appear curved - 3% for 23 cm II - Caused by curvature of II faceplate ct is advantageous because...? - Low contrast detectability - Increased dynamic range What is the typical percent conversion of a photon into light? 10% What is beta plus decay? - Proton converted into a neutron - Excess energy released as a positron and a neutrino - C 11, O 15, F 18, and Ga 68 - Z decreases by 1, A stays the same what is Beta minus decay? - A neutron is converted to a proton. - Excess energy released as a Beta particle and an antineutrino. - P 32, H 3, C 14 - Z increases by 1, A stays the same what is the tr and te for T1 weighted sequences? -Short TR (less than 500 msec) - Short TE (less than 8 msec) what is the tr and te for T2 weighted sequences? -Long TR (more than 1500 msec) - Long TE (more than 60 msec) what causes ghost signal in mr? - Caused by mismapped signal - in the phase encoding direction (duration of RF pulse) spin echo Multiphase encoding steps - 1st, 90 degrees - then, multiple 180 degree what percent of an x-ray is characteristic? approximately 10% what exposure is needed to blacken film? -0.5 mRad (film), results in OD of 1.5 -5-20 mRad (mammo) -0.5 mRad/5mGy produces satisfactory image what is the ct attenuation coefficient? Attenuation coefficients are expressed in Hounsfield units. Air -1000 Lung -300 Fat -90 Water 0 White matter +30 Gray +40 Muscle +50 Bone +1000 Metal +3000 What is electron capture? -A proton is converted to a neutron by capturing an electron from another shell. -Vacancy is filled by an outer shell electron. -Excess energy is emitted as characteristic x-ray or an Auger electron. -Z decreases by 1, A stays the same. What is exposure and in what unit is it measured? The ability to ionize air measured in Roentgens (R). what is dose and in what unit is it measured? Dose is the absorbed energy -Given in rad or Gy what is dose equivalent and what unit is it in? The measure of biologic damage likely to occur from dose. -Given in rem or Sv limiting fields close to magnets 0.5 mT= pacemakers, cathode x-ray tubes 1 mT= credit cards, watches 2 mT= floppy disks 5 mT= power supplies what is dqe? Detected Quantum Efficiency SNR^2(out)/ SNR^2 (in) -SNR performance of the imaging system QUANTITY e^Mx REPRESENTS? -Fraction of primary photons transmitted by x cm of attenuation. -Linear attenuation coefficient (μ =cm^-1) -Formula N=No^(e^(μ t)) production of radiation slowing down and changes direction? Brehmstralung increases withaccelerating voltage (kV) & Z (atomic #) quench MR wire heats up too much and loses superconductivity & the magnetic field is converted to heat. physical half-life (t1/2) Time required for a radionuclide to decay to half it’s original activity. F18 2 x 511 KeV photons produced in cyclotron Beta + decay t1/2 = 110 minutes noise level of mr systems? 65- 120 dB 1 curie= 3.7 x 10^10 Bq 1 mCI= 37 kBq proton density tr/te long TR, short TE film temperature, speed & fog are inversey related to ____? Exposure, Dose & Contrast what improves pin-cushion & vignetting artifacts? Smaller field size (less minification) Technesium 99m -140 KeV photons -produced in generator -decays by isomeric transition -T1/2 = 6 hrs imaging system with resolving power of 10 lp/mm represents system mtf response of? 10 lp/mm = 10% or 0.1 30 lp/mm = 30% or 0.3 lambda decay constant 0.693/ T(1/2) dose limit for the general public? 2 mRem/hour average 100 mRem/year For radiologists- 5000 mRem/year in nm, as resolution decreases, distance ____ increases in nm, as sensitivity decreases, distance ____ increases in nm, as sensitivity increases, resolution ____ increases focal spot size on ct? 0.7- 1 mm hvl calculation 0.693/ μ why is a1 filtration done? To decrease entrance dose to skin. what is the inverse square law? If you double the distance, you decrease the exposure by 25%. 1/distance^2 Double distance= 1/(2^2)= 1/4= 25% what is zipper artifact with mri? Dotted line across an image caused by hardware or software problem such as radiofrequency entering the scanning room when the door is open during acquisition. what is a slow screen? Thinner, increased resolution, used in extremity imaging, higher patient dose, absorbs less photons. -10 lp/mm what is a fast screen? Thicker, decreased resolution (have more blur), used in abdominal imaging, absorbs more photons (increased absorption efficiency). -5 lp/mm what is the focal spot size for angio? 0.3- 1.2 mm fwhm for nm? 3- 5 mm higher resolution gamma camera fwhm? 7.5 mm storage for single ct image? 0.5 MB male sterility occurs at? 5-6 Gy 500-600 rad dose that results in mammalian cell death? -deterministic More than 0.5 Gy or 50 rad dose limit for workers extremities (hands)? 500 mSv/year 50,000 mrem/year annihilation pair production -Proton energy threshold= 1.02 meV -Makes 2- 511 keV photons at 180 degrees. ct artifacts 1. streak 2. beam hardening 3. ring 4. partial volume average 1. Random motion produces it and it’s in the direction of motion 2. Low energy photons absorbed- causes underestimation of HU usually at higher contrast interfaces such as bone/brain. 3. 3rd generation CT scanners- detector failure 4. averaging linear attenuation coefficient in a voxel. bandwidth Horizontal resolution TV systems intensity is directly proportional to ____? mAs ADC Analog to digital converter Changes varying voltages to closest binary equivalent order of beam traveling in fluoro? Grid input phosphor (converts xray to electron) photocathode focusing lenses (electrostatic lenses) anode output phosphor (converts to visible light) camera quantum mottle -Noise -Random variation of photon incident based on poisson stats. types of us transducers? 1. Linear 2. Curvilinear (sector scanner) 3. Endocavitary 4. Phase array 5. Annular federal law requires ____ in an x-ray unit? Filtration 256 shades of gray = how many bits? 8 bits (1 byte) n bits codes for 2^n gray levels what is the largest contributor to background radiation? Radon what modality does not use filtered back projection? MRI dose response curve for radiation and cancer risk is _____? Linear which of the following is not directly ionizinga. proton b. electron c. neutron d. alpha particle Neutron power is measured in _____? Watts (W) W= Amp x Volt MC grid used 12:1 lead equivalent for shielding apron? 0.5 mm units of dose equivalent? Sv Rem best detector for gamma radiation? Geiger- Mueller counter speed or velocity of us is inversely proportional to _____? Compressibility Velocity = 1/compressibility example- bone is non-compressible so velocity increases. maximum allowable nonuniformities in nm? Less than 10% why is csf bright on t2? Long T2 most to least radiosensitive a. skin b. breast c. lung d. gi GI- most radiosensitive Skin Lung Breast- least radiosensitive how can you increase mean photon energy without affecting max photon energy? Filtration stir T1 weighted saturates fat Atomic #? Z= # of protons Electron interacts with a positron to produce _____? 2- 511 keV photons difference between3rd generation ct & 4th generation ct 3rd Generation CT- Fan beam and Detectors rotate 4th Generation CT- Fan beam rotates, Detectors are fixed US can cause what at increased power levels? Cavitation= creation and collapse of microbubbles functional mri uses changes in oxygenation 5 mm lead shield blocks ___% of tc99 ___% of x-rays 70% of Tc99 >90% of X-rays most radiosensitive part of the cell cycle? Mitosis- metaphase ratio of heat to x-ray production 99-1 do you need a grid with 10cm air gap to decrease scatter? No how do you decrease scatter? - Collimation - Air gaps - Grids what is not associated with digital radiology screens? Silver halide grains If hu changes by 3, it represents what % of attenuation change? 0.3 % units of exposure? Roentgen (R) Coulombs/ kg (C/ kg) units of radioactivity? Ci Bq units of absorbed dose? Gy rad Threshold dose for cataract formation for chronic radiation dose, & acute radiation dose. Chronic radiation dose threshold- 5 Gy or 500 rad Acute radiation dose threshold- 2 Gy or 200 rad Focal spot size for mag mammo? 0.1 - 0.15 mm greatest amount of scatter occurs where? At the skin entrance Coulomb is a measure of what? Charge are there different mutations seen in hiroshima survivors? No result of major radiation exposure prior to implantation? Intrauterine death radionucleus with excess neutrons decays by _____? Beta minus decay increase scatter by _____? Increasing field size, or, Increasing patient thickness what changes when us passes from one medium to another? Velocity and wavelength (frequency doesn’t change) frequency= velocity x wavelength put the following in order of increasing wavelengthuv, ir, visible, gamma Gamma, Xray, UV, Visible, IR, Microwave, Radiowave. what are the units for the sfactor? H-157 S-factor= absorbed energy/ target organ mass mGy/Bq S (SI) rad/μGi hv (common) increase noise in film by _____? Increasing conversion efficiency -ability of intensifying screen phosphors to emit a large amount of light per x-ray absorption. phase contrast mr Background is taken out and flow enhancement is noted