8.2 Mammographer QC: Monitors, Repeat Analysis, Viewing Conditions, Compression Force, Detector Calibration

Displays are part of the mammography system

A perfect detector image is useless if the acquisition workstation (AWS) hides 5% patches or the radiologist workstation (RWS) is viewed in glare. ARRT lists acquisition and radiologist workstation monitors (cleanliness plus calibration/test pattern), viewing conditions, repeat analysis, compression force, and manufacturer detector calibration as mammographer tests. Know each one at the same depth as the phantom: purpose, frequency, how you do it, what passing looks like, how you document it, and what you do with a fail. If the facility uses manufacturer QC, rewrite the frequencies from that manual.

The 2018 ACR program treats display devices as standalone. An RWS in a reading room across the hall has its own monthly QC, even if the gantry phantom passed this morning.

Monthly AWS and RWS monitor QC

Purpose. Confirm that the display you use to check positioning (AWS) and the display used for interpretation (RWS) still render grayscale, geometry, and low-contrast detail honestly. Dirt, failed backlights, drifted calibration, and burned-in menus all change what a calcification looks like.

Frequency (ACR 2018). Monthly for both AWS and RWS. Older screen-film habits treated viewbox checks as weekly; do not import that calendar into an ACR 2018 stem. Manufacturer digital manuals may still require daily cleanliness or a daily pattern — follow that manual if it is the facility's program. Film printers and viewboxes, if the site still uses them, are also monthly in ACR 2018.

Equipment and procedure.

1. Cleanliness. Use the cleaner the display vendor allows. Ammonia and paper towels ruin coatings. Clean before you score a test pattern so you do not call fingerprints an artifact.
2. Test pattern. Display SMPTE or AAPM TG18-QC (ARRT names both). Verify that the 5% patch in the 0% (black) square and the 95% patch in the 100% (white) square are visible. Check that gray steps are distinct, lines are not bowed, and there is no obvious luminance non-uniformity or dropout.
3. Calibration. Many RWS units run a manufacturer luminance calibration (DICOM GSDF). The mammographer's job is to launch the required QC, record pass/fail, and stop using a failed primary display for interpretation.

Performance criteria. Follow the form. A classic fail is inability to see the 5% or 95% patches, which means contrast at the extremes of the gray scale is gone. Primary diagnostic displays are held to a tighter standard than the AWS used for positioning checks; that is why RWS QC is not optional just because the AWS looked fine.

Corrective action. Do not interpret mammograms on a failed RWS. Move reads to a passing workstation or wait for repair and a passing retest. A failed AWS should not be used to release images you cannot evaluate. MQSA 21 CFR 900.12(e)(8) treats digital other-modality QC as tests that can require stopping use of the failed component before further examinations — the display is a component.

Viewing conditions

Purpose. Ambient light reflecting off the monitor reduces contrast in dark breast tissue, which is exactly where subtle masses live. Viewing conditions are the room, not the phantom.

What you control as a mammographer. Dim the reading room, kill glare sources (windows, viewboxes left on, overhead floods), keep the RWS perpendicular to lights, and do not interpret from a hallway workstation. AWS rooms can be brighter for patient work, but the monitor face should still be clean and readable for QC scoring.

Relationship to physicist testing. The medical physicist measures room illuminance (8.4) with a meter. Your monthly job is to keep the conditions the physicist approved. If someone raises the lights for cleaning and leaves them up, you have changed the QC baseline even though no button on the unit failed.

Frequency. In ACR 2018, viewing conditions travel with monthly display QC and with whatever manufacturer daily viewing-condition checks still apply. Know the purpose even if the stem does not print a single magic lux number. Many digital manufacturer programs historically used about 50 lux as an upper bound for reading-room illuminance; quote the action limit on the facility's form rather than inventing a universal ACR lux value.

Repeat analysis — as needed, not automatically quarterly

Purpose. Count images that had to be repeated (motion, positioning, exposure, equipment, patient factors) so the facility can see whether technique, training, or a failing unit is wasting dose and time.

Frequency (ACR 2018). Optional / as needed. ACR training is explicit that repeat analysis is no longer a required quarterly test in the 2018 digital program. It still appears on the ARRT content list because you must know why it exists and that some facilities still run it on a schedule — especially if they remain on manufacturer QC, which may still say quarterly.

Procedure when you do it. Define a collection window, count total exposures and repeats, sort by cause, and compute a repeat rate. Older MQSA screen-film teaching often used an overall repeat rate near 2% as a quality goal and investigated higher rates. Do not recite 2% as an ACR 2018 required action limit unless the stem gives you a manufacturer or facility threshold.

Corrective action. A high repeat rate is a process signal, not a reason to hide films. It may mean EQUIP positioning problems, a detector that needs calibration, or a tech who needs coaching. Document causes; do not only file a percentage.

Semiannual compression force

Purpose. Adequate compression spreads tissue, reduces thickness and scatter, and immobilizes the breast. Too little compression costs contrast and sharpness. Uncontrolled power drive can injure.

Frequency (ACR 2018). Semiannual (twice a year). Unchanged in spirit from older ACR programs.

Equipment and procedure. Use a calibrated bathroom or compression scale (and towels to protect the receptor). Drive powered compression and record the force. Check that fine/manual adjustment still works. Document both the automatic drive and the manual mode the form asks for.

Performance criteria (MQSA equipment standard). 21 CFR 900.12 requires that the system provide at least 111 newtons (25 pounds) and that the maximum initial power drive be between 111 N (25 pounds) and 200 N (45 pounds). That is the federal window for powered compression, not the ~5 daN used on the phantom. Hands-on clinical compression is still whatever the patient can tolerate within safe technique; the QC test asks whether the machine can deliver and limit force correctly.

Worked example. Initial power drive stops at 20 pounds. That is below 25 pounds (111 N). The unit fails compression-force QC. Do not continue clinical mammography on that compression system until it is repaired and retested. A drive that slams past 45 pounds on initial power also fails the federal maximum.

Manufacturer detector calibration

Purpose. Flat-field or gain calibration maps detector element response so a uniform field looks uniform. Dust on the tube port, a drifted gain map, or a missed calibration shows up as blotches, lines, or a dirty-detector look that can mimic pathology.

Frequency. Per manufacturer — daily on some units, weekly or after service on others. ACR 2018 does not replace a vendor-required calibration with a generic monthly slot. If the stem says the manufacturer requires a calibration before the first patient each day, that is the answer.

Procedure. Follow the unit's guided calibration: clear the beam, use the required paddle or none, acquire the calibration set, and confirm the software reports completion. Do not skip a failed calibration and hope the phantom will catch it later. The phantom can miss a local bad pixel map problem that calibration is designed to fix.

Corrective action. A failed or overdue required calibration means the detector is not in the state the manufacturer certified. Stop clinical imaging on that receptor until calibration completes successfully or service intervenes.

Quarterly facility QC review

ACR 2018 added a quarterly facility QC review: a short documented meeting of the QC technologist, a facility manager, and the lead interpreting physician (LIP). The form is essentially meeting minutes: recent physicist surveys, doses, phantom scores, open corrective actions, inspections, and quality-improvement items. It is not a phantom exposure. It exists so the LIP and management actually see the QC record EQUIP expects them to oversee.

Cadence table (ACR 2018 mammographer tests in 8.2)

Exam traps for 8.2

• AWS/RWS QC is monthly in ACR 2018, not automatically weekly.
• Repeat analysis is not required quarterly in ACR 2018; it is as needed.
• Compression force is semiannual 25–45 pounds; phantom compression is ~5 daN.
• Detector calibration is not a universal ACR weekday — it is vendor-defined.
• Manufacturer QC can still demand daily monitor cleaning or quarterly repeats. Read the stem.