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FundDx Final Exam Penguin Points Chapter 17: Image Artifacts -an artifact is any irregularity on an image that is not caused by the proper shadowing of tissue by the primary x-ray beam -exposure artifacts are usually easy to detect and correct -processing artifacts are eliminated w/a proper QC program and frequent cleaning -proper facility design helps to reduce handling and storage artifacts Chapter 18: Quality Control -quality assurance deals w/people -quality control deals w/instrumentation and equipment -an acceptable QC program consists of 3 steps acceptance testing, routine performance monitoring, and maintenance -misalignment must not exceed 2% of the source-to-image receptor distance (SID) -three tools are used for measurement of focal-spot size: the pinhole camera, the star pattern, and the slit camera -the measured kVp should be w/in 10% of the indicated kVp -exposure time accuracy should be w/in 5% of the indicated time for exposure times greater than 10 ms -exposure linearity must be w/in 10% for adjacent mA stations -sequential radiation exposure should be reproducible to w/in +/- 5% -an ESE of approximately 200 mR may be assumed for a cassette spot film -an ESE of approximately 100 mR may be assumed for a photofluorospot -fluoroscopic ABC should be evaluated annually Chapter 21: Fluoroscopy -a fluoroscope is used for examination of moving internal structures and fluids -the photocathode emits electrons when illuminated by the input phosphor -magnification mode results in better spatial resolution, better contrast resolution, and higher patient dose (this is because when we magnify, the image becomes dimmer. The ABC corrects for this by pumping up the mA) -vignetting at the periphery of any magnified image, there is a reduction in brightness -the center of any magnified image has better spatial resolution -video monitoring uses a rate of 30 frames per second -the higher the bandpass (bandpass is the number of times/second an electron beam can be modulated/changed), the better the horizontal resolution Chapter 23: Spiral Computed Tomography -first generation imaging system translate/rotate, pencil beam, single detector, 5 min imaging time -second generation imaging system translate/rotate, fan beam, detector array, 30 sec imaging time -third generation imaging system rotate/rotate, fan beam, detector array, subsecond imaging time, ring artifacts (better collimation is possible using a constant source to detector path length) -fourth generation imaging system rotate/stationary detector, fan beam, detector array, subsecond imaging time -reconstruction time is the time from the end of imaging to the appearance of the image -prepatient collimation determines dose profile and patient dose this collimator is located on the x ray tube housing, unlike conventional xray, 2 collimators are used… -the predetector collimator determines sensitivity profile and slice thickness -slip rings make multislice spiral CT possible by allowing the gantry to rotate without interruption -pixel size= FOV/matrix size -voxel size (mm3)= pixel size (mm2) x slice thickness (mm) -when k is 1000, the CT numbers are called Hounsfield Units and range from –1000 to +1000 - a HU is a CT number that specifies the darkness of that pixel -a low spatial frequency represents large objects and a high spatial frequency represents small objects -spatial resolution for a CT image is limited to the size of the pixel -CT image quality is determined by spatial resolution, contrast resolution, noise, linearity, and uniformity -contrast resolution is superior in CT principally b/c of x-ray beam collimation -contrast resolution is the ability to distinguish one soft tissue from another -a large variation of pixel values represents high image noise -the resolution of low-contrast objects is limited by the noise of a CT imaging system -noise is the variability of pixel values -when the CT is calibrated, there should be a straight line through 0 -uniformity is the concept that when water is imaged, all of the pixel values must be equal, even if they are not consistent from 1 hour to the next -linear interpolation at 180 degrees improves z-axis resolution -wider multislices allow imaging of greater tissue volume -smaller detector size results in better spatial resolution Chapter 32: Human Biology -at each stage in the sequence, it is possible to repair radiation damage and recover -radiobiology is the study of the effects of ionizing radiation on biologic tissue -macromolecules are very large molecules that sometimes consist of hundreds of thousands of atoms -the chief function of carbs in the body is to provide fuel for cell metabolism -DNA is the radiation-sensitive target molecule -only adenine-thymine and cytosine-guanine base bonding is possible in DNA -cell proliferation is the act of a single cell or group of cells to reproduce and multiple in number -radiation induced chromosome damage is analyzed during metaphase -meiosis is the process whereby genetic cells undergo reduction division -stem cells are more sensitive to radiation than mature cells Chapter 34: Molecular and Cellular Radiobiology -in vitro is irradiation outside of the cell or body -in vivo is irradiation w/in the body -at low radiation doses, point lesions are considered to be the cellular radiation damage that results in the late radiation effects observed at the whole-body level -metabolism consists of catabolism (the reduction of nutrient molecules for energy) and the anabolism (the production of large molecules to form and function) -DNA is the more radiosensitive molecule -half as much DNA is present in G1 as in G2 -radiation response of DNA: -main-chain scission w/only one side rail severed -main-chain scission w/both side rails severed -main-chain scission and subsequent cross-linking -rung breakage causing a separation of bases -change in or loss of a base -a free radical is an uncharged molecule that contains a single unpaired electron in the outer shell -if the initial ionizing event occurs on the target molecule, the effect of radiation is direct -the principle effect of radiation on humans is indirect -DNA is the target molecule -hits occur through both direct and indirect effects -the lethal effects of radiation are determined by observing cell survival, not cell death -radiation interacts randomly w/matter -a hit is not simply an ionizing event, but rather an ionization that inactivates the target molecule -if there were no wasted hits (uniform interaction), D37 is the dose that would be sufficient to kill 100% of the cells -a large D0 indicates radioresistant cells, and a small D0 is characteristic of radiosensitive cells -a large D0 indicates that the cell can recover from sublethal radiation damage -DQ is a measure of the capacity to accumulate sublethal damage and the ability to recover from sublethal damage -G1 is the more time variable of cell phases -human cells are most radiosensitive in phase M and most radioresistant in late S -irradiation of mammalian cells w/high-LET radiation follows the single-target, single-hit model Chapter 35: Early Effects of Radiation -diagnostic x-ray beams always result in partial-body exposure, which is less harmful than whole-body exposure -this immediate response of radiation sickness is the prodromal period -the latent period is the time after exposure during which there is no sign of radiation sickness -the hematologic syndrome is characterized by a reduction in white cells, red cells, and platelets -GI death occurs principally b/c of severe damage to the cells lining the intestines -the ultimate cause of death in CNS syndrome is elevated fluid content of the brain -the LD50/60 is the dose of radiation to the whole body that causes 50% of irradiated subjects to die w/in 60 days -acute radiation lethality follows a non-linear, threshold dose-response relationship -atrophy is the shrinkage of an organ or tissue due to cell death -damage to basal cells results in the earliest manifestation of radiation injury to the skin -ovaries and testes produce oogonia and spermatogonia, which mature into ovum and sperm -the most radiosensitive cell during female germ cell development is the oocyte in the mature follicle -under no circumstances is a periodic blood examination recommended as a feature of any current radiation protection program -the lymphocytes and spermatogonia are the most radiosensitive cells in the body -cytogenetics is the study of the genetics of cells, particularly cell chromosomes -radiation-induced chromosome aberrations follow a non-threshold dose-response relationship -a chromosome hit represents severe damage to the DNA Chapter 36: Late Effects of Radiation -our radiation protection guides are based on the late effects of radiation and on linear, nonthreshold dose-response relationships -radiation-induced cataracts occur on the posterior pole of the lens -the dose-response relationship for radiation induced cataracts in non-linear threshold -at worse, humans can expect a reduced life span of approx 10 days for every rad -radiologic technology is a safe occupation -the theory of radiation hormesis suggests that very low radiation doses are beneficial -radiation-induced leukemia follows a linear, non-threshold dose-response curve -its considered to have a latent period of 4-7 yrs and an at-risk period of approx 20 yrs -chronic lymphocytic leukemia is rare and therefore no considered to be a form of radiation-induced leukemia -radiation-induced skin cancer follows a threshold dose response relationship -the BEIR committee has further stated that b/c of the uncertainty in its analysis, less than 1 rad/yr may not be harmful -low-dose chronic irradiation does not impair fertility -all observations point to the 1st trimester during pregnancy as the most radiosensitive period -the first 2 wks of pregnancy may be of least concern b/c the response is all-or-nothing -the relative risk of childhood leukemia after irradiation in utero is 1.5 -we do not have any data that suggest that radiation-induced genetic effects occur in humans -the doubling dose of radiation that produces twice the frequency of genetic mutations as would have been observed w/out the radiation Chapter 37: Health Physics -health physics is concerned w/providing occupational radiation protection and minimizing radiation dose to the public -exposure= exposure rate x exposure time -if the distance from the source exceeds 5X the source diameter, it can be treated as a point source -during fluoroscopy, the radiologic technologist should remain as far away from the patient as practicable -one TVL is the thickness of absorber that reduces the radiation intensity to 1/10th its original value -effective dose is the equivalent whole-body dose -we assume the occupational effective dose to be 10% of the monitor dose -rescue and medical emergencies should be attended to before radiologic concerns are addressed -radiologic terrorism can be addressed safely w/an emergency responder’s equiptment kit -being exposed to radiation does not make an individual radioactive -radioactive contamination is rarely life threatening Chapter 38: Designing for Radiation Protection -leakage radiation must be less than 100 mR/hr at a distance of 1 m from the protective housing -x-ray beam on must be positively and clearly indicated to the radiologic technologist -the SID indicator must be accurate to w/in 2% of the indicated SID -the x-ray beam and light beam must coincide to w/in 2% of the SID -the PBL must be accurate to w/in 2% of the SID -the variation of the x-ray intensity should not exceed 5% -the maximum acceptable variation in linearity is 10% from one mA station to the adjacent mA station -the SSD must be not less than 38 cm on stationary fluoroscopes and not less than 30 cm on mobile fluoroscopes -primary radiation is the useful beam -the intensity of scatter radiation 1m from the patient is approx 0.1% of the intensity of the useful beam at the patient -radiologic technologists receive most of their occupational radiation exposure during fluoroscopy -design limits for a controlled area are based on the annual recommended occupational dose limit of 5000 mrem/yr (50mSv/yr) -the use factor for secondary barriers is always 1 -the ionization of gas is the basis for gas-filled radiation detectors -high sensitivity means that an instrument can detect very low radiation intensities -a photocathode is a device that emits electrons when illuminated -the dynode gain is the ratio of secondary electrons to incident electrons -the side of the electron pulse is proportional to the energy absorbed by the crystal from the incident photon -TLD is the emission of light by a thermally stimulated crystal following irradiation -lithium fluoride is a nearly tissue-equivalent radiation dosimeter Chapter 33: Fundamental Principles of Radiobiology -the LET of diagnostic x-rays is approx 3 keV/um -relative biologic effectiveness (RBE)= dose of standard radiation nec to produce a given effect dose of test radiation nec to produce the same effect -the RBE of diagnostic x-ray is 1 -dose protraction and fractionation cause less effect b/c time is allowed for intracellular repair and tissue recovery -diagnostic x-ray imaging is performed under conditions of full oxygenation -interphase death occurs when the cell dies before replicating -the combined processes of intracellular repair and repopulation contribute to recovery from radiation damage -radiation-induced cancer, leukemia, and genetic effects follow a linear-nonthreshold dose-response relationship -skin effects resulting from high-dose fluoroscopy follow a sigmoid-type dose-response relationship