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Exposure and Effects

H H Exposure and Effects

QuestionAnswer
Dose limit for radiologic personnel 5 rem/yr
Rem = ?Rad = ?Roentgen Rad = Rem = Roentgen for x-ray radiation
3 ways to estimate patient dose 1. Entrance skin exposure 2. Gonadal dose 3. Mean marrow dose
Cardinal Principles of Radiation Protection 1. Minimize time 2. Maximize distance 3. Maximize shielding
High level radiation exposure leading to death within days or weeks Acute Radiation Syndrome
4 Period of Acute Radiation Syndrome 1. Prodromal 2. Latent 3. Manifest 4. Recovery or Death
decreased WBCs, decreased RBCs, and decreased platelets Hematologic syndrome
nausea, vomiting, diarrhea Gastrointestinal syndrome
first nausea and vomiting, then extremely nervous, confused, loss of normal senses, seizures, ataxia, lethargy CNS syndrome
the most radiosensitive macromolecule DNA
more sensitive to radiation when irradiated in an oxygenated state Tissue
the rate at which energy is transferred from ionizing radiation to soft tissue Linear Energy Transfer (LET)
RBE for x-ray 1
LET increases the biologic damage increases Relative Biological Effectiveness (RBE)
Radiosensitivity varies with maturation and metabolism Law of Bergonie and Tribondeau
high sensitivity to radiation young tissue
High metabolic rate tissues more radiosensitive
Tissue with a high proliferation rate more radiosensitive
Stem cells radiosensitive – more mature cells are less sensitive
Late effects (delayed) presents at 6 months or more Leukemia, Malignancies, Local Tissue Damage, Shortening of lifespan and Genetic Damage
concerns imaging instrumentation and equipment maintenance Quality Control
Make sure the film is not outdated Quality Control
Screens are cleaned 4x/year
concerns patient care and image quality Quality assurance
How many retakes were taken Quality assurance
Is the patient getting the right study for the problem Quality assurance
mAs controls radiation quantity, film optical density, and patient dose
A short exposure time reduces motion blur
KVp controls radiographic contrast
Increasing filtration causes a reduction of the quantity of x-ray photons but increases the quality of the radiation
Increasing the voltage ripple causes a decrease in both the quality and quantity of the x-ray radiation
Increasing the focal film distance decreases the quantity of radiation at the film but results in no change in the quality of the radiation
Increasing mAs or s causes an increase in the quantity of radiation but no change in the quality of the radiation
Increasing kVp causes an increase in both the quality and quantity of x-ray radiation
If x-ray too light need to increase mAs
unequal magnification Distortion
the ability of an image receptor to respond to a low x-ray exposure Speed
wide latitude Long gray scale
describes the amount of the shades of gray Latitude
narrow latitude Short gray scale
equal to the slope of the straight line portion of the characteristic curve Radiographic contrast
determined by the size, shape, and x-ray attenuating characteristics of the subject and the energy (kVp) of the beam Subject contrast
contrast – inherent in the film Image receptor
Latitude and contrast are inversely proportional
Use a long source to image distance (focal film distance) minimize magnification
Use a short object to image distance (object film distance) minimize magnification
image size/object size Magnification factor (MF)
optical density due to development of silver grains that contain no useful information Fog density
optical density on unexposed film – due to composition of the film and the dye that is added to the base Base density
relationship between intensity of exposure and blackness of the film after processing Sensitometry
due to the random nature of x-ray photons Quantum mottle
due to phosphor size on the screens Structure mottle
due to the distribution and size of the silver halide crystals Film Graininess
Scale of contrast # of shades of gray
known as an H and D curve characteristic curve
a graph of optical density and how it relates to exposure characteristic curve
Parts of characteristic curve toe, straight line, shoulder
If the slope is steep it will show white and black and no grayness
more horizontal the slope tells us how much grayness it has
straight line tells us about the contrast
the most important component of characteristic curve the straight line
Created by: hakrrins on 2008-08-17



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