Mammography Quality Control
Mammography quality control presented in question and answer format for radiology board review. Several mammography imaging artifacts are also discussed at the end of the episode. Remember to download the free study guide on this topic including links to other helpful mammography QC and imaging artifact articles.
Show Notes/Study Guide:
What is the name of the act that specifies quality metrics for mammography in the United States and what is the overseeing governing body of this act?
Mammography quality standards act (MQSA) as specified by the U.S. Food and Drug Administration (FDA). Basically, MQSA specifies that you must follow manufacturer recommendations for QC tests. However, the ACR has also received approval that it’s QC manual can count as an alternative and satisfy MQSA requirements for QC as well.
More info/link to ACR mammography QC manual here: https://www.acr.org/-/media/ACR/NOINDEX/QC-Manuals/Mammo_QCManual.pdf
Also, good mammography QC article in RadioGraphics here: https://pubs.rsna.org/doi/10.1148/rg.2015150036
According to the ACR, what is the purpose of routine Quality Control testing?
To detect, identify, and correct equipment related problems prior to these problems causing a deleterious effect on clinical images. QC is about prevention and is designed to preserve the integrity of clinical images.
According to the ACR, what is the definition of Quality Assurance?
QA comprises all management practices, implemented and overseen by the lead mammography radiologist (each breast imaging group has a specified lead mammography radiologist to oversee quality of the program). Goals are to ensure that every imaging procedure is necessary and appropriate, the images are of diagnostic quality, reports contain necessary information and turnaround times are acceptable, lowest possible radiation exposures, cost and inconvenience to the patient are realized.
What is repeat analysis?
Repeat analysis is the number of examinations a mammography technologist needed to repeat due to poor positioning, patient motion, or other factors that resulted in a non-diagnostic examination. Repeat analysis is performed on an “as needed” basis per ACR though I have seen some sources say quarterly.
How often is the mammography phantom test performed?
Weekly
What are the 3 components of a standard breast phantom that must be assessed?
Fibers, speck groups and masses
How many of each of these (fibers, speck groups, and mases) must be visualized in order to pass the breast phantom test?
You must be able to see at least 4/6 fibers, 3/5 speck groups, and 3/5 masses on the phantom test to pass
What additional breast imaging quality control measure is checked on a weekly basis: view box/monitor check, compression, or dark room cleanliness?
The answer is view box conditions (old film screen view box)/monitor check. This is a weekly check typically performed by a breast imaging technologist.
How often is the breast compression QC check performed?
Semi-annual basis
How many pounds of compression are you required to apply during a mammogram?
25-45 pounds of compression are required (per federal law)
What is the mammography QC visual checklist and how often must this checklist be completed?
The visual checklist is available in the ACR QC manual https://www.acr.org/-/media/ACR/NOINDEX/QC-Manuals/Mammo_QCManual.pdf and has items ensuring cleanliness of equipment, checks of indicators on equipment, cables, paddles, DBT assembly movement, monitor conditions, etc. This checklist must be completed monthly.
What is the compression thickness indicator test and how often must this be assessed?
Each month the compression thickness indicator must be checked to ensure the indicated compression thickness closely matches actual compression thickness of a phantom. This must be accurate to within +/- 5 mm of the actual compressed thickness.
How often is a medical physicist required to perform her equipment assessment?
Once per year for breast imaging a medical physicist must perform a complete equipment check to certify a mammogram machine and site. Any time equipment is installed, or otherwise modified/moved/altered the physicist is also required to perform system checks.
What are some screen film QC tests that, although largely obsolete, could show up on the ABR core exam?
Processor check, dark room cleanliness, dark room fog, screen film contrast check.
What is the difference between dark room cleanliness and dark room fog?
Dark room cleanliness refers to literally removing dust and removing debris and other unnecessary materials from the dark room. Basically, dust and loose debris could be really problematic and cause imaging artifacts on the films so you had to maintain a clean environment with daily cleaning. Note that the dark room was to be cleaned daily and the intensifying screen was to be cleaned weekly.
Dark room fog refers to how much stray light is able to enter the dark room and inadvertently expose the mammography films. This was to be tested on a semi-annual basis.
What are some components of the processor check and how frequently should this be performed?
Processor check should be performed daily. Components include ensuring processor is cleaned and chemicals are replenished, rollers are in good condition and apply proper pressure to the film, temperature and humidity levels are ok, etc. Hopefully you won’t need to get into that level of detail on the ABR Core exam as this is largely obsolete now. For those interest, more info here: https://pubs.rsna.org/doi/pdf/10.1148/radiographics.19.2.g99mr13503
How often is a screen film contrast test supposed to be performed for screen film mammography QC?
Semi-annual basis.
What is the flat field test and how often must this be performed?
The flat field test is a weekly QC test in which a thick acrylic (of different thicknesses as specified by the manufacturer of the equipment) is placed over the entire detector, without compression, and an exposure is taken. Note this is different from the ACR/MQSA phantom with specks, flecks, and masses. This is kind of more like a blank phantom test to evaluated brightness and signal to noise nonuniformities, bad pixels, high frequency modulation, etc.
Bonus questions:
What is ghosting artifact and how do you prevent this?
Ghosting artifact can occur in mammography and happens when a previously acquired image is superimposed on the current acquired image. To correct, the detector needs to be recalibrated to wipe the memory of the prior image and then a new image needs to be acquired.
What are two common interventions a technologist can do to remove motion artifact from an image?
1. Increase compression. 2. Remind patient to remain still during the image. Note that motion artifact is seen as a blurring of the image and motion artifact may be especially deleterious for evaluation of calcifications. Note that calcifications may be completely missed on an image (not shown) if motion artifact is present. Compression is key for evaluation of calcifications and other small structures, both to reduce motion blur. For example, if you are performing a stereotactic biopsy of calcifications and you know you are in the correct spot but are unable to see the calcifications on pre-biopsy scout imaging, try increasing the compression and you may suddenly be able to perceive the calcifications.
What are electrical readout errors and how do you identify these?
Electrical readout error aka vibration artifact results from electrical interference in the mammography system and are seen as vertical dark lines across an image, or sometimes alternating dark and bright lines through an image. If identified and recurrent, detector needs to be serviced.
What is grid line artifact?
Grid line artifact occurs when the bucky oscillation is too slow or stopped and you are able to see the lines from the anti-scatter grid on the image. The grid lines are often seen as repeating at a 45 degree angle over the image. If this artifact persists the mammography unit needs to be serviced.
Good mammography artifact article here: https://pubs.rsna.org/doi/pdf/10.1148/rg.287085053
Quality Control for Radiology Board Examinations:
Gamma camera:
Daily
Extrinsic flood field uniformity: Co57 or Tc-99m source, need 5-10 million counts with <5% non-uniformity.
Energy window calibration on pulse height analyzer: For Tc-99m need to be within 20% of 140 keV.
Weekly:
Phantom tests: spatial resolution and linearity
Intrinsic flood (intrinsic flood=no collimator, use point source; extrinsic flood=keep collimator in place and use flood source)
SPECT/CT:
Weekly:
Center of rotation test (look for tuning fork artifact, google for images)
Quarterly:
Flood source at every angle, look for concentric ring artifacts
Phantom test (SPECT the phantom and look for registration and attenuation correction problems)
CT from SPECT/CT:
Needs to be zeroed daily (scan air (nothing) and set all receptors to zero to make them uniform)
Dose Calibrator:
Daily:
Constancy (energy reading must stay within 5%)
Quarterly:
Linearity (use Tc-99m, need to test from 30 uCi to highest energy used, typically 200 mCi).
Annual:
Accuracy (use NIST standardized source)
Geometry is tested annually and at installation/repair (confirms that different volumes of activity and/or container shapes don’t change the reading)
PET:
Daily:
Blank scan using the system transmission source (internal radiation source on older generation scanners for attenuation correction before current PET/CT systems, used to equalize the receptor output and make sure you get an even response in the system)
Monthly:
Normalization (use use a phantom with a flood source and make sure the lines are straight and not curved/squiggly)
NaI well counter:
Daily:
Sensitivity (basically same as consistency)
Annual:
Efficiency determination (record counts per minute and compare this to the known disintegrations per minute of a standard source)
Chi squared test (make sure that actual readings over time give you a Poisson distribution/normal curve. )
Linearity (use Cs137 and make sure the 602 keV peak is detected accurately)
Geiger Muller and Ion Chambers:
Calibrate on receipt, repair and annually (typically send it out, not something done in house)
Daily
Check consistency with the calibrated source that is typically on the instrument itself
Make sure battery is charged.
Mammography:
Daily:
Check processor (obsolete and don’t know what this means but could still be asked, remnant of screen film days)
Dark room cleanliness (obsolete but who knows if they will ask this)
Weekly:
View box conditions/monitor check
Phantom test (Very high yield), need to see 4/6 fibers, 3/5 speck groups and 3/5 masses
Quarterly
Repeat analysis (this is the number of exams the techs had to repeat due to poor positioning, etc.)
Semi-annual:
Compression (ensure you get 25-45 pounds compression per federal law)
Dark room fog (this is stray light that can expose films, also obsolete so could be tested)
Screen film contrast (same as above)
Annual
Medical physicist does her equipment assessment once a year to make sure everything is working
Ultrasound:
Annual:
Uniformity (hold probe to air and check uniformity of image)
Artifact survey
System sensitivity (this is how deep probe can image)
Display
Optional but highly recommended annual tests: spatial resolution, contrast, geometric accuracy, also should make sure measurements are accurate (1 cm measurement is actually 1cm, etc.).
MRI:
Weekly:
Phantom test for contrast, geometric accuracy, artifact analysis
Center frequency (are the precessional frequencies accurate?)
Table position
Annual: like mammography, the medical physicist does all the more complicated tests each year (check RF pulses, B0 uniformity, slice thickness, etc.)
CT:
Weekly: check noise (blank scan and check HU distribution)
Monthly:
Phantom to test low contrast resolution and high contrast resolution
CT number uniformity (make sure HU numbers are same in center of image as at edge of image)
Semi-annual: physicist tests CT every 6 months unlike mammography and MRI which is every year, physicist tests radiation dose output every year
