Minimizing Exposure to the Patient Flashcards
Minimizing exposure to patient
- Exposure of the general public, patients, and radiation workers to ionizing radiation must be limited in order to minimize the risk of harmful biologic effects.
- Occupational and non-occupational effective dose (EfD) limits and equivalent dose (EqD) limits for tissues and organs such as the lens of the eye, skin, hands, and feet have been developed for radiation safety purposes.
- (EfD) -Incorporates both the effect of the type of radiation (EqD) used and the variability in radiosensitivity of the organ or body part irradiated
ALARA
As low as reasonably Achievable
- principle put forth in 1954
Radiographic apparatus and dose depends on?
- SID
- PA vs AP
- Collimation Devices
- Protective filtration
- Grids
- Protective shielding
- Optimum processing
- IR sensitivity
What is the benefit of restricting x-ray field size to include only the anatomic structures of clinical interest?
- Significant reduction in patient dose because less scatter radiation is produced
- Improves the overall quality of the radiographic image
Positive beam limitation
Automatic collimation
The radiographer must ensure that collimation is adequate by collimating the radiographic beam so that it is no larger than the IR.
What is a half value layer?
- The thickness of a designated absorber (e.g., aluminum) required to decrease the intensity of the primary beam by 50% of its initial value
- HVL is expressed in millimeters of aluminum.
- HVL is a measure of beam quality, or effective energy of the x-ray beam. A minimal HVL is required at a given kVp.
- needs to be measured yearly
Radiographic Grids
<90 kVp 8:1 satisfactory
>90 kVp >8:1 grid used
When should gonadal shielding be used?
should always be used if requested and it will not obscure necessary clinical information
- must have a lead eq. of 0.25mm
can you fold lead aprons?
no
X-ray tube housing construction
The housing enclosing the x-ray tube must be constructed so that the leakage radiation measured at a distance of 1 m from the x-ray source does not exceed 1 mGya/hr (100 mR/hr) when the tube is operated at its highest voltage at the highest current that allows continuous operation.
IR Sensitivity (DQE)
Doses are related to the sensitivity of the imaging system. Thus, an increase in the sensitivity of the imaging system reduces the dose; conversely, decreasing the sensitivity increases the dose
Safety features of Fluoroscopic Equipment
- Multifield, or magnification, image intensifier tubes
- Intermittent, or pulsed, fluoroscopy; Practice significantly decreases patient dose, especially in long procedures
- Cumulative timing device; Every 5 minutes will sound alarm, Measured in R/min
- Limiting fluoroscopic field size
- Fluoroscopic exposure control switch; Must be of the dead-man type
ESE (entrance skin exposure) equation
ESE = mR (SCD/SOD)^2
- SCD = source to chamber distance (dosimeter)
