Quality Assurance Flashcards
Explain what is meant by holistic QA is and how this differs to that specifically for equipment.
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Describe the basic tests for a range of modalities, what these are specifically used for and what action should be taken if any technology/ equipment fails.
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Compare and contrast specific elements of the imaging chain, mechanisms used, safety measures considered, and different terminology used to with different technologies.
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Light Beam Diaphragm Alignment test
Light beam diaphragm alignment test is to test the true focal spot of the collimation/xray tube
You place the copper plate that has centimeter markers on it in a cross on the middle of the image receptor. The middle of it is a glass tube that has 2 ball bearing in it, one that it
You then open the collimation to the full size of the image receptor, and centre it on the middle of the glass tube (so the middle of the image receptor) and expose it. If the tube central ray is perfectly perpendicular to the image receptor those 2 ball bearings should be superimposed.
The circle rim of the copper circle (radiograph of the copper circle) should also be equal sharpness all the way the circle. If its not perpendicular it means the tube is off at an angle and it won’t be perfect sharpness, cause it worsens the penumbra.
At the edges it would be within the square of the image receptor (as the opened the collimation as much as it can go) if its not perfect the radiograph will show the radiation going off to side maybe. If it is off by too much this can lead to anatomy being cut off, 1cm is the remedial amount (so the amount it is allowed to go off) at 3cm you suspend using the equipment until it has been fixed as it has gone off to far and would be affecting images too much.
This means we must allow for a 1cm margin of error.
Radiation output test
Dose at various exposures measured (with known distance)
Consistency:
Remedial = +/- 20%
Suspension = +/- 50%
Measuring rad output at 1 metre.
You place a DAP on the table and place the tube 1 metre away from the DAP meter
See what the dose is and whether it is within range.
Resolution Leeds test for IR
Measures the greyscale of the image receptor. You place the equipment on the IR and expose. You should see 18 circles different scales of grey, it tells you the spatial resolution Leeds test Spatial resolution- lp/mm Greyscale Low contrast resolution High contrast resolutiont
AEC tests
Test that the AEC will switch off after enough dose of radiation has been received.
Collimate to AEC and expose and check that it cuts off
Guard timer test is to check that it kicks in when it hasn’t received dose. This is in case you chose the incorrect bulky
Image display
Monitor SMPTE phantom to test the resolution and greyscale of the monitor so that the pic is good enough for diagnosing
General condition
Greyscale
Resolution
DICOM Greyscale calibration Test patterns Uniformity Variation btw monitor Room lighting
CT phantom test
Household field units test to test that you can see all the anatomy clearly
Using phantoms or blocks to copy body parts
MRI receiver coil tests and weekly test
Circular phantom filled with water and put it on the different receiver coils
Weekly check the helium levels as the helium is used to cool the MRI machine
CT tests air calibration test why do you want a clean gantry
Air calibration test clean gantry don’t want anything attenuating radiation beam, to measure the air
RNI test?
Check the sodium iodide crystal is detecting the radiation uniformly
Check that the pulse height analyzer is detecting the energy if the gamma radiation so to check that it is detecting counts of energy at 140 keV
Flood uniformity analysis
Uniformity is checking to see that the crystal is not damaged so it’s checking for gamma radiation throughout its area.
The first way to check is to remove all the collimators of the gamma camera heads so that you can pick up what the crystal is detecting
So you might put a solid sheet of cobalt 60 on top of the gamma camera head and leave it for a while and then check if after a certain amount of counts and check that the image is uniformed across it meaning all of the gamma cameras have detected radiation across it.
You can also check it the same way with a collimator and check that the collimator is doing its job. You can compare the previous test to this one to see if the collimator has done a good job.
If it fails this test then you cant use those gamma cameras
If a crystal is cracked it would not detect any radiation
Test the centre of rotation to check that the gamma cameras are moving around the patient as they should be
In order to do this, we put cobalt buttons on a matrix in certain places so that when we recreate the different images in the axial, coronal and sagittal planes we know where the buttons should appear.
