Ch. 20 Screen film radiographic quality control Flashcards
Quality assurance deals with…
people
Who is mostly in control of QA?
the radiologist and the imaging services management
Quality control deals with…
instrumentation and equipment
What are the 10 steps for QA as set by the joint commission?
- Assign responsibility
- delineate scope of care
- identify aspects of care
- identify outcomes that affect the aspects of care
- establish limits of the scope of assessment
- collect and organize data
- evaluate care when outcomes are reached
- take action to improve care
- assess and document actions
- communicate information to organization-wide quality assurance programs
An acceptance QC program consists of 3 steps:
- acceptance testing
- routine performance monitoring
- maintenance
Who is principally responsible for QC?
the medical physicist
What is possible the most important patient protection characteristic of an imaging system?
filtration
What is the minimum total filtration needed in a system?
2.5 mm of Al equivalent
How is filtration measured?
by the HVL
How often are each tested and what is their tolerance?
Filtration, collimation, FSS, calibration of kVp, Exposure timer accuracy, exposure linearity, exposure reproducibility
Filtration: annually; >/=2.5mm Al Collimation: semiannually; +/- 2% SID FSS: Annually; +/- 50% kVP: Annually; +/- 10% Exp. timer: Annually; +/- 5% > 10ms Exp. linearity: Annually; +/- 10% Exp. reproducibility: Annually; +/- 5%
What type of collimators do most systems have?
PBL
What are so special about PBL collimators?
they automatically adjust to the size of the IR.
How is the spatial resolution of an imaging system determined?
Generally by the FSS of the tube.
3 tools are used for measurement of FSS…
the pinhole camera, the star pattern, and the slit camera
What is the standard of measure for FSS and why not the other 2?
The slit camera b/c it’s easy
The pinhole camera is too difficult to use and requires excessive exposure time and the star pattern is easy to use but has significant limitation s for FSS less than 0.3mm.
What is the alternative tool to FSS measurement?
the line-pair test tool….it also determines limiting spatial frequency
What is generally used to calibrate kVp?
filtered ion chambers or filtered photodiodes…less common are voltage diodes and oscilloscopes…they are more accurate but take a lot longer
What is particularly responsible for patient radiation dose and image optical density?
the exposure timer
How can the backup timer be tested?
When testing AEC, add a lead filter while doing the exposure timer test.
When should the backup timer terminate?
at 6s or 600 mA…whatever comes first
The ability of a unit to produce a constant radiation output for various combinations of mA and exposure time is called…
exposure linearity
Linearity is determined with…
a precision radiation dosimeter
Intensifying screens should be cleaned how?
with a soft, lint free cloth and a cleaning solution provided by the manufacurer and should not occur less than every other month.
What happens if blur appears during a screen film contact test?
the felt or foam pressure pad under the screen should be replaced….if it persists, replace the cassette
What does a photometer do?
tests viewbox illumination by measuring light intensity at several areas of the illuminator
What intensity should the viewbox be?
at least 1500 cd/m^2
During tomography QC, how is section uniformity evaluated?
by imaging a hole in a lead sheet. The optical density of the screen film image tracing of the hole should be uniform with no perceptible variations, gaps, or overlaps.
Processors today have how fast to drop and dry?
90 seconds..improved from 3 minutes…which was improved from 7 minutes
How many films per hour can the new processors handle ?
500/hour
How long is film immersed in a high speed processor?
22 seconds
What temperature should the developer and wash be in a high speed processor?
95 degrees F for developer and 87 degrees for the wash
How often are processors cleaned?
weekly so the rollers don’t build up with sludge and debris
