Week #7 Review Flashcards
An xray tube and image intensifier attached in a C configuration
C-arm/base
Offers both static and dynamic imaging during the procedure
Display monitors
What power source do mobile xray units most commonly have?
Capacitor discharge generators or battery powered
-Operates by charging a series of silicon-controlled rectifiers from the DC voltage of a nickel-cadmium battery or a wall
-by electrically stacking the SCRs the charge is stored at a very high voltage
-during exposure the charge is released
Capacitor Discharge models
What is a disadvantage to the capacitor discharge models?
The capacitor may continue to discharge after the usable exposure, which can create radiation leakage
Generators in these units produce output that is essentially high frequency
Battery powered cordless models
-Powered by 10 to 16 rechargeable, sealed, lead acid type 12-volt batteries connected in series
-equipped with circuitry to monitor battery strength
Battery powered cordless models
According to SC35, how far from the mobile xray unit must the tech be if not wearing ppe?
3 metres
-consists of two perpendicular sets of ceiling mounted rails
-attached to the xray tube by a telescoping column
-detents
Ceiling support system
-has a single column with rollers at each end
-the xray tube slides up and down the column as the column rotates
Floor to ceiling support system
-has a single column positioned on one or two floor mounted rails
Floor support system
-one end of the c arm is connected to an xray tube
-the other end is connected to the image receptor
-may be ceiling or floor mounted
C-arm support system
What is the radiation limit for a controlled area?
20 mSv per year
What is the radiation limit for an uncontrolled area?
1 mSv per year
The immediate area where xray equipment is used such as the procedure room and xray control booths
Controlled area
Areas occupied by individuals such as patients, visitors to the facility, and employees who do not work routinely with or around radiation sources
Uncontrolled area
What is the radiation limit in a controlled area with a radiation sensitive population?
0.30mSv per year
What is the standard for control booth shielding?
No operator is occupationally exposed to more than 0.4mSv/week
Provides shielding from the direct xray beam and therefore must be placed in such an orientation as to intersect the xray beam
Ex. Wall behind vertical IR
Primary protective barrier
Provide shielding from scattered and leaked X-rays
Ex. Ceiling
Secondary protective barriers
The xray tube should never be directed towards the control booth
(These walls are considered secondary barriers)
True
A measure of the operational time or the amount of use of the xray equipment over a set period of time
Maximum workload (W)
The fraction of time that the area under consideration is occupied by the individual who spends the most time at that location while the xray equipment is operating
Occupancy factor (T)
Admin offices, attended waiting rooms, adjacent xray rooms, image viewing areas, xray control rooms…
T=1
Rooms used for patient exam and treatment
T=1/2
Corridors, patient rooms, staff lounges…
T=1/5
Corridors doors
T=1/8
Public toilets, unattended waiting areas…
T=1/20
Outdoor areas, stairways, janitors closets….
T=1/40
The fraction of the workload during which the xray beam is pointed in the direction under consideration
Use factor (U)
Floors of radiation rooms, walls routinely exposed to direct radiation….
Primary barrier
U=1
Doors, walls of radiation room not routinely exposed to direct radiation…
Primary barrier
U=1/4
Ceiling area of radiation rooms not routinely exposed to direct radiation
Primary barrier
U=1/16
Use factor for secondary protective barriers (ex. Control booth)
U=1
*always taken to be 1
Threshold of feeling, tingling sensation
1ma
Accepted as maximum harmless current
5ma
Beginning of sustained muscular contraction
10-20ma
Ventricular fibrillation, fatal if continued. Respiratory function continues
100-300ma
Sustained ventricular contraction followed by normal heart rhythm. Temporary respiration paralysis and possibly burns
6 A
What do product standards seem to be these upper limit for children and adults?
4-6ma
What happens as the resistance of the skin is broken down by electrical current?
Resistance drops and current levels increase
What currents are considered less dangerous at lower voltage?
DC Currents
What are the 3 current pathways through the body?
-Touch potential
-step potential
-touch/step potential
The smaller the area of contact the greater the heat produced
True
Devices used in electrical systems to prevent against excess current
Fuse
Open a circuit as current climbs to an unsafe level
Circuit breakers
What are Ground Fault Circuit Interrupters designed for?
(GFCI)
To protect people from electric shock rather than prevent damage to a buildings wiring
What is the minimum depth of a conductive pipe or rod for an earth ground?
8 feet
(Water pipes are commonly used)
