Radiographic Quality Assurance & Processing

What does acceptance testing typically involve?

Vendors, biomedical engineers, and the PACS administrator

What are the three tests that need to be performed for acceptance testing?

1. image erasure test

2. phantom image test

3. visual check

Image Erasure Test

• ensures the photostimulable phosphor plate (PSP) is completely erased

• shouldn’t see any residual or ghost image on the PSP

• appear as a uniform, blank image

Phantom image test

• wide variety of phantoms are available (easy way to test equipment without exposing a real person)

• digital imaging processor codes/software requires phantoms have to be more anthropomorphic (true anatomic shape similar to human characteristics)

• allows for more accurate histogram and image data set

What other tests are also included in phantom image testing?

• contrast evaluation

• laser jitter (evaluates transport system)

• measurements tool evaluation

• exposure indicator calibration

• linearity

• noise

• brightness uniformity

Found within this Phantom Image test of a chest x-ray are test tools that can also evaluate and measure _____ and _____

Contrast, noise

For linearity response, why must you use properly calibrated x-ray tibe along with filtration?

Ensures consistancy of tube output and qulaity of the x-ray beam (also use the same PSP plate thought the test)

What does linearity response measure?

The pixel values produced by separate exposures

What is the equiptment needed for exposure indicator calibration?

• calibrated x-ray source and ionization chamber

• assorted types and thickness of beam filtration materials

• time

What is the best way to effectively monitor that patient dose is consistent?

By using exposure indicator calibration (PSP and readers)

Laser jitter test

• evaluates the transport system of a PSP plate reader

• caused by artifacts when PSP is pulled into the plate reader

• problem exists with the transport system

  • seen as a wavy band perpendicular to the direction of travel

Measurement tool evaluation

• evaluates how accurately the measurement tools are on either a diagnostic or technologist’s workstation

• evaluates the measurements recieved at the workstation and those of the test tool located inside the phantom

Brightness uniformity (shading test)

• ensures that the plate reader is functioning properly

• measures pixel values across the plate

  • a variation of 10% (+/ -) in pixel value is allowed

Visual check

• final check to be performed (PSP) plates

• visually inspect PSP’s for cracks, scratches, etc

Besides radiographic equiptment and PSP plates, what else might need to undergo initial acceptance testing?

• PACS

• laser printers

Besides upon initial start up, QA tests should also be performed ______ or whenever you are having problems with image quality

Yearly

Test the modality wordlist to ensure that all required patient data is being transferred from radiology information system to the ___________ (DOB, referring physician, MRN, accession #)

Hospital information system (HIS)

What does acceptance testing of laster printers require?

• initial calibration

• QC tests

For acceptance testing of laser printers initial calibration, you print the range of densities and a ______ is used to compare this printed film to the expected outcomes

Densitometer

What components of a digital imaging system require routine evaluation?

• monitor

• technologist workstation

• PACS workstation

• PSP plate

• PSP plate reading device

• flat-panel receptor/detector

What are the other QA test tools?

• light-field-radiation congruency

• timer accuracy

• beam allignment

• focal spot

• resolution

• reproducibility, reciprocity, linearity

Light-field radiation congruency

• light-localized, variable aperture rectangular collimators should be provided

• cones and diaphragms may replace the collimator for special exams

• the radiation field and the light field must coincide to within 2% of the SID

What can you test light-field radiation field congruency with?

• collimator test tool

• penny test

Timer accuracy QC

Exposure time directly affects the total quantity of radiation emitted from tube. Must have accurate exposure time

Maximum allowable variation for the exposure timer is:

• ± 5% for exposures over 10 ms

• ± 20% for exposures less than 10 ms

What is the timer accuracy QC determined by?

• manual spinning top test

• synchronous spinning top test

• digital x-ray timer (1 or 3)

Spinning top test on single-phase equipment

• dots are compared to the number that the particular time station should produce for that exposure

• half wave: exposure time (seconds) x 60

• full-wave: exposure time (seconds) x 120

Synchronous spinning top test (left), protractor to measure film (right)

What all should be evaluated for beam alignment?

1. perpendicularity

   1. must be within 1 degree of perpendicular

   2. otherwise image is distorted

2. x-ray beam Bucky tray alignment/ central ray congruency

   1. must be wishing 1% of SID

   2. risk clipping important anatomy or grid cut off

What is evaluated with a beam alignment tool?

Beam alignment

Focal spot size QC is used to measure focal spot _________

Blooming

What measures focal spot QC?

• pin hole camera

• resolution test tool (star pattern, line pairs test etc)

Pin hole camera

• plate of gold platinum alloy with a small hole in the center

• places over IRS on stand

• image of focal spot produced on film and can be measured by comparing to manufactures guidelines for machine

Focal spot test tool

• test tool places on film, radiograph taken, test tool imprint compared to manufactures guidelines for machine

Star test pattern

• used to measure resolution

• resolution measured by blur zone

  • facial spot size in mm = angle radius/ (magnification factor - 1)

Magnification may be determined using formula:

M = Di/Do (image diameter/ actual diameter)

If the stated focal spot size is 0.8 mm or less, what is the percent of blooming allowable?

50%

If the stated focal spot size is 0.8 mm to 1.5 mm, what is the percent of blooming allowable?

40%

If the stated focal spot size is 1.6 mm or greater, what is the percent of blooming allowable?

30%

Reproducibility

• the output exposure should be constant from one exposure to another

• the variation in x-ray intensity should not exceed 5%

Reciprocity

• the amount of x-ray intensity should remain constant at a specific mAs value despite the different combinations of mA and exposure time

• maximum acceptable variation is ± 10%

Linearity

• adjacent mA stations are utilized

• exposure time remains the same

• the maximum acceptable variation is 10% from one mA station to an adjacent mA station

What are the units for radiation intensity?

mR/mAs