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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