1. Protection of Patients
Stacy Kopso, M.Ed. RT (R)(M)

2. Protection of patients
Immobilization
Beam Restriction
Beam-limiting devices
Filtration
Gonadal shielding
Exposure and technique factors
Film Screen
Electronic Imaging
Patient positioning
Grids
Pregnant patient
Repeat Radiographs
Fluoroscopic Procedures

3. Protection of patients
Immobilization
Communication
Good directions
Discomfort
Voluntary motion
Immobilization devices
Involuntary motion
heart movement/bowel peristalsis
short exposure times

4. Beam Restriction Beam limiting devices
Restrict the primary beam to the specfici area of interest
Reduce the amount of tissue exposed to the radiation beam
Small field size
Mindful of kVp
Beam limiting devices
Aperture diaphragms
Flat lead containing hole in center
Attached to tube head
angio
Cones/Cylinders
Circular metal structures
Attach to tube housing
Predetermined circular field size
Straight or flared
Longest cone, smallest diameter
Sinuses
Designed to operate most effectively at a designated SID

5. Beam limiting devices Variable aperture collimators
Manually adjustable beam restricting device
Upper and lower pair of shutters
Upper absorbs off-focus radiation inside tube
Lower located below lamp and mirror
Restrict the beam to area of interest
Right angles to each other
Each pair move independently
Square or rectangular field size
Lamp,mirror and crosshair (illuminate and deflect light)
Positive beam limitation (PBL)
Electronically interlocked with bucky tray. Automatically opens the radiation field size to the size of the image receptor
Accuracy within 2% of SID
4 sided border

6. Beam filtration Beam Filtration Primary purpose
Reduce patient exposure/reduces entrance skin exposure
Aluminum filter inserted in the path of the xray beam
Absorbs low energy photons(non diagnostic)
Improves beam quality
Increases beam energy
As filtration increases, exposure rate decreases

8. Beam filtration Inherent filtration Added filtration Total filtration
Glass window of tube and cooling oil surrounding tube housing
Increases as tube ages
Between mm Al
Added filtration
Aluminum
Located outside the glass window
Placed in the path of the primary beam to bring the total filtration amount up to the minimum standards
Total filtration
Combination of inherent and added

9. Beam filtration Operating kVp Minimum total filtration Below 50
.5 mm Al
50-70
1.5 mm Al
Above 70
2.5 mm Al
Mobile/fluoro unit
2.5mm Al

10. Beam Filtration Half value layer (HVL)
Used to determine whether a diagnostic x-ray beam is adequately filtered
The thickness of material that will reduce the x-ray intensity to half its original value
Measured by QC personnel on an annual basis or after repairs have been performed on tube housing or collimator
An increase in kVp requires an increase in HVL
Measures beam quality
Example;
Intensity of 100 mR. If one HVL is added the new intensity would be
50 mR
If inherent filtration is 1.0 how much added filtration is needed if tube is operating at above 70 kVp:
1.5mm Al

11. Gonadal shielding
Used when the gonads are in or within 5cm of primary beam
Used on anyone who is within reproductive age
Under the patient for fluoro procedures, over the patient for overheads
Types
Flat contact
Recumbent studies
Shadow
Suspended from tube housing
Cast a shadow over area
Sterile fields
Shaped
Male patients, held in place by disposable supporter
Oblique lateral and erect studies
Fluor studies
rare
Lead apron

12. Exposure factors kVp factors to reduce patient dose mAs
Increase kVp/lower entrance skin exposure
Less absorption/photoelectric effect
Decrease mAs/pt dose
Disadvantage
Poor contrast
mAs
“Rate of exposure”
Direct effect on quantity of radiation
Decrease mAs
“Patient dose”
3 phase and high frequency generators
Lower entrance skin exposure

13. Film screen considerations
High speed film and intensifying screen
Rare earth screens
More efficient than calcium tungstate
Absorb 3x more
Screens accelerate the action of xrays by converting energy into visible light

14. Electronic imaging
Computed radiography (CR) & Digital Radiography (DR)
Eliminates need for repeat due to technical factors because of the large dynamic range

15. PATIENT POSITIONING PA vs AP T-spine (PA) Scoliosis series (PA)
breast
Scoliosis series (PA)
Rib (PA)
Skull/sinuses (PA)
Lens of eye
Cervical spine (RAO and LAO)
thyroid

16. grids An increase in grid ratio, increase patient dose
Non grid to grid
70 kvp or 10cm
Air gap technique long SID/increased OID

17. Pregnant patient
Elective abdomen exams should be postponed until 10 days following the onset of menstruation
Physicist should perform calcuations to estimate the actual fetal dose

18. Repeat radiographs Positioning Pt motion
Incorrect radiographic techniques
Dirty screens
Incorrectly loaded cassettes
Light leaks
Chemical fog
Processor artifacts
Incorrect projections
Positioning errors
Grid errors
Double exposure

19. Fluoroscopic procedures
Greatest patient and personnel radiation exposure
Intermittent/pulsed fluro
Digital form of fluoroscopy
Decreases pt exposure
Stores image from last time fluoro switch was depressed
Limitation field size (collimate)
Decrease total time
Decrease image intensifier to patient distance will decrease entrance exposure
Automatically adjusts mA (exposure)
2.5mm Al
Source-tabletop/Fixed
15 inches
Mobile
12 inches
Cumulative timing device
Five minutes

20. Exposure rate no greater than 10R/min for intensified fluoro units
Cannot exceed 2.1R/minute for each mA of operation at 80 kVp
Non digital fluoro units operate within a range of 2 to 5 mA
If 4 mA is utilized at 80 kVp, what is the exposure if the fluoroscopy time is 2.5 minutes?
21R
2.1 R x 4mA=8.4
8.4 x 2.5 minutes=21R