1. Conducting the Fluoroscopic Examination & Basic Operational Procedures
Based on:
Syllabus on Fluoroscopy Radiation Protection, 6th Rev.
By: Radiologic Health Branch – Certification Unit
PPT created by: Jed Miles, BSRS, RT(R), CRT-CA

2. Direct Influence by Technical Factors
Technical factors that directly influence radiation dose rate at panel or tabletop and consequently dose rate to both patient and operator:
Milliamperage (mA)
Kilovoltage (kVp)
Collimation
Filtration
Exposure time
Target-panel distance
The last four factors listed above will be reviewed on the following slides.

3. Collimation
Radiation dose rate at input phosphor is almost independent of beam size
Image will not become brighter with increasingly open x-ray field, due to ABC
However, total volume of patient exposed will increase and subsequently exposure to operator by scatter radiation
During fluoroscopy, restrict field size to smallest size practicable for the given exam

4. Integral Dose
Defined as total energy absorbed from the beam by the patient
The unit of integral dose is the “gram rad”
1 gm rad = 100 ergs
Good collimation will both:
Decrease patient’s absorbed dose and
Increase image quality by limiting scatter to the image receptor

5. Filtration
Main purpose is to reduce number/amount of lower energy photons reaching the patient
Appropriate filtration in terms of aluminum equivalency are:
Up to 125 kVp // 2.5 mm Al (equivalency)
Over 125 kVp // 3.0 mm Al (equivalency)
Total filtration = inherent and added filtration
Regulations require total filtration permanently in path of beam at normal operating voltages to not be less than 2.5 mm Al equivalency
Intensity of x-ray beam measured at tabletop “should not exceed 2.2 rads/min for each mA of operating tube current at 80 kVp”

6. Half-Value Layer (HVL)
HVL defined as thickness of absorbing material necessary to reduce x-ray intensity to half its original value
This concept is also used in shielding were lead is used as the material of choice
Example:
In order to reduce 200 millirads/min radiation dose rate to 50 millirads/min, enough attenuating material to create two HVL’s would be used

7. Exposure Time Series of short “looks” can be sufficient
Example - assuming a beam intensity of 5 rads/min
5 “looks” at 12 seconds each = 60 seconds or 1 minute of exposure = 5 rads
Each 12 sec “look” = roughly 400 millirad dose to patient (500 millirad / 12)
Fluoroscopy system’s cumulative timer must be manually reset after 5 minutes of beam “on” time
Timer may either
Produce an audible signal or
Temporarily interrupt the x-ray beam
Designed to protect patient by making fluoroscopist aware of “on” time during each procedure

8. Allowable Exposure Rates
For routine fluoroscopy, dose rate measured at panel or tabletop shall be as low a practicable and may not exceed 5 rads/min
Fluoroscopic equipment manufactured after August 1, 1974 equipped with automatic exposure rate controls:
May operate up to but not over 10 rads/min unless recording or when using the optional “boost” position
If “boost” or high level output control is provided, the fluoroscope may not operate over 5 rads/min unless boost is manually activated
Boost or high level must be activated manually and produce an audible signal during operation

9. After August 1, 1974
Fluoroscope equipped without automatic exposure rate controls
May operate up to but not over 5 rads/min unless recording or using when using the optional “boost” position
If a “boost” or high level output control is provided, then the fluoroscope may not operate over 5 rads/min unless the boost is manually activated

10. Allowable Exposure Rates, Cont.
Devices which display operating tube potential (kVp) and tube current (mA) must be located where operator can see them
CA law requires x-ray tube current and potential for fluoroscopes with ABC be monitored at least once each week and logs must be kept of monitored readings.
Dose rate measurement must also be done by a health or medical physicist
Check any fluoroscope that has had alteration or replacement of a major component, such as a new x-ray tube, exposure controls, or image intensifier tube
For cineradiography fluorographic equipment, physicist must check dose rate every year due to increased cumulative dose rates received by the patient

11. Target-to-Panel Distance (TPD)
Target-to-panel distance is only an over the table tube or portable C-arm concern as under-the-table tubes are fixed in position
Cross referencing to page 6 of the syllabus states TPD is a concern for both under and over table tubes – bottom line is the tube to skin distance is the real issue
Shorter TPD distances results in greater skin doses to the patient and greater image distortion (pincushion and magnification)
Assuming the same x-ray beam intensify is used for two exposures, increasing the TPD from 12 to 18 inches will reduce the entrance skin dose by 30%

12. Target-to-Panel Distance (TPD)
CA Regulations: Target-to-panel or target-to-tabletop distance should not be less than 18 inches and shall not be less than 12 inches
While the target (tube) distance can be varied when using a c-arm, the image intensifier should be positioned as close as possible to patient to reduce entrance skin dose
Moving tube closer will not increase image brightness as automatic brightness control (ABC) will compensate to maintain brightness at all times

13. Indirect Influence by Technical Factors
Technical factors that indirectly influence radiation dose rate by affecting the use of the direct factors include:
Lighting in the fluoroscopy room
Poor image receptor quality
Low absorption tabletop

14. Human Eye: Rods and Cones
Two types of light receptors in the human retina
Cones:
Function in daylight or photopic levels of brightness
Rods:
Function in night or scotopic level of brightness
Visual acuity of photopic vision about 10 times better than scotopic
Image intensifiers were created to intensify the image and bring brightness levels into the photopic visual range

15. Viewing Distance and Time
Normal viewing distance for human binocular vision is inches for inch TV monitor
Move monitor closer to observer to perceive details in image
Too close if you can see the raster lines of the monitor
Eye requires 0.2 seconds to recognize an image
Light burst is shorter than this may not be perceived
Light blinking faster that 0.2 seconds perceived as solid light

16. Lighting in the Fluoroscopy Room
For fluoroscopy examination, room lighting should be dim to enhance visualization of black and white TV image
Excessive room light will decrease visual acuity and cause the image to appear dim
This may cause the operator to change the technical factors to increase image brightness – this then is considered an indirect influence affecting patient dose

17. Image Receptor Quality
Inadequate image receptor system (i.e. the image intensifier in this case)
Old: poor conversion gain
Not finely tuned to produce the best image
May cause operator to increase kVp or mA, thus increasing exposure to patient and operator
Indirect technical factors that will increase dose rate to the patient and operator

18. Low Absorption Tabletop
The Aluminum equivalence of tabletop may not be more than 1.0 mm
This is true when a cassette tray is used under-the-tabletop and for the front panel of a vertical cassette holder
Carbon fiber tabletops, which are very radiolucent, serve well to reduce patient radiation dose rates
Less overall exposure required to properly expose image receptor be it a film/screen, imaging plate, or image intensifier
Again, this is an indirect influence on the technical factors used to conduct a fluoroscopy examination

19. Gonadal Shielding
Radiation safety issue (ALARA) and the law in the State of California
Suitable devices must be provided to shield gonads in potentially procreative patients when gonads cannot be excluded from x-ray beam and shielding does not interfere with diagnosis
Male patients:
Most effective type of shield is shaped contact shield
Female patients:
Gonads are situated in the pelvis at varying depths so shielding will more frequently interfere with diagnosis
However, whenever possible, shielding should be utilized

20. Bucky Slot Cover and Generator
Opening created by parking of Bucky slot cover must be automatically covered by at least 0.25 mm lead equivalent material
Look inside Bucky tray opening when moving the tray to see a shield automatically slide into place
Technical advantages of three-phase and high frequency generators
Near constant tube potential
High mA available for very short exposure times
Higher effective kVp
Due to not having to ramp up the kVp from zero in each phrase. kVp potential is held or kept near the peak value

21. Basic Operating Procedures
Operators of fluoroscopy equipment must reduce unnecessary radiation dose to the patient, themselves and others by observing and following these operational procedures
Carefully read and understand Chapter V in the syllabus – questions will be asked regarding these procedures and provisions…
This includes both stationary and mobile fluoroscopy equipment

22. What’s Next?
Please close this PowerPoint presentation, and then click Topic 2 to continue.