Ultrasound QA Baseline Drift? Check the Phantom Before Repair

Why Does a Phantom-Based QA Result Drift?

A drop in penetration, a new band of uneven brightness or a shifted caliper distance can begin with the reference phantom, the acquisition setup or the scanner and transducer. Start with the baseline image and settings. Identify what changed, which phantom and probe produced the original measurement, and whether the result crossed a facility action level. Keep the first abnormal result in the record even if a repeat comes back within limits.

The American Institute of Ultrasound in Medicine (AIUM) recommends following the phantom manufacturer’s care and certification or recertification schedule, and marking the production and recommended recertification dates on the phantom. Its guidance also calls for preserving baseline and periodic test records. A QA result from a different or unverified reference object may need a controlled repeat before it can support a service decision. ¹

Escalate a suspected equipment hazard or clinical image problem through the facility’s safety process while the QA discrepancy is investigated. Under the American College of Radiology (ACR) ultrasound accreditation guidance, out-of-limit results require corrective action. Imminent danger to patients or staff requires immediate action and notification. The ACR recommends performing and documenting acceptance testing after correction. ³

For related decisions, use the ultrasound preventive maintenance checklist for program-level tasks, the probe acceptance protocol for post-repair evaluation, and the probe-versus-scanner artifact guide for a reproducible imaging fault.

What Should Be Checked Before the Scanner?

The sequence below assumes a nonpatient QA test under a facility protocol. Keep the initial images and change one variable at a time where practical. Record which change restored comparability or whether several changes were needed, since that affects how confidently you can assign the cause.

Save the actual acquisition settings alongside the preset name. A preset can keep the same label after its contents change. Record depth, overall gain, time-gain compensation, output, focus and processing, including harmonics or compounding when used. The CIRS guide bases repeat measurements on the same recorded technique. If an old baseline lacks these settings, record that uncertainty and ask the QA lead how to proceed. ²

Technique can move the reading even with the preset matched. The CIRS guide warns that pressing on the scan surface can temporarily displace the wires during vertical-distance testing. Match the original target group and caliper landmarks. The 040GSE guide measures penetration from the scanning surface to the last discernible background echoes. Wire targets may still be visible deeper in the image. ²

How Do Temperature and Storage Change the Measurement?

When a test object has just arrived from a loading dock or an unconditioned store, its interior may still be warmer or colder than the room. Temperature can change sound speed and the apparent distances on the scanner. The 040GSE guide uses a room-temperature hold to allow its core to equilibrate. Record the time and room conditions, and record phantom temperature only where the approved method provides a reading. ²

The 040GSE contains a water-based Zerdine hydrogel in a housing with a scanning membrane. The guide describes moisture loss through the membrane, possible cracking or housing damage after freeze-thaw, and faster vapor loss in extreme heat. A temperature-controlled repeat can address thermal mismatch. Evidence of surface damage or a trend in weight calls for separate review. ²

Sun Nuclear lists nominal sound speeds of 1,540 m/s for its Zerdine and HE gels and 1,450 m/s for ATS urethane. Its guide explains how target positioning can compensate for a material’s sound speed and how attenuation varies by material. For a different phantom, use its documented expected measurements and baseline. An apparent distance or penetration shift across two materials gives limited evidence about scanner drift. ⁴

For routine care of the 040GSE, CIRS specifies cleaning after each use with mild soap and water only, and room-temperature storage in the provided airtight case with the storage cover attached. If the scan surface is damaged, the guide calls for sealing the phantom in an airtight container and contacting the manufacturer immediately for return instructions. Follow the transducer’s own instructions for probe care. ²

How Do You Separate Phantom Drift From Probe or Scanner Drift?

Three comparisons can appear on the same worksheet. The first is phantom weight against its certificate. The second is an observed QA result against the historical result for that setup. The third is caliper error against the target’s known distance. Identify the comparison and reference before applying any numerical limit.

The 040GSE guide calls for weighing at least annually against the original certificate weight. It specifies manufacturer contact for a gain or loss of more than 1% together with a vertical-distance difference, or a depressed surface at any weight. For noticeable changes to the phantom, take it out of QA use and follow the manufacturer’s return instructions promptly. Sun Nuclear’s later hydrogel guidance recommends weighing every six months and identifies weight loss near 1% as one sign of advanced desiccation. Check which instructions apply to the unit and record the inspection schedule your team uses. ^{2 4}

The historical AAPM Task Group No. 1 report gives suggested B-mode caliper levels based on error relative to the expected distance. Its horizontal criterion uses the larger of the millimeter and percent values. For illustration, if a phantom has a documented horizontal reference of 120 mm, 2% is 2.4 mm. A reading of 123 mm would exceed that suggested action level. Use the facility’s current protocol and the scanner’s stated accuracy to judge the measurement. The CIRS guide assigns allowable drift from the QA baseline to the facility. ^{2 5}

Once the setup is comparable, a normal phantom uniformity image still gives only one view of probe performance. Vuorenmaa and colleagues tested 99 transducers with a FirstCall electronic tester at two Finnish tertiary hospitals. At the hospital where the authors compared all three methods, 37 of 65 probes received all three tests. Probe type or technical issues prevented the other 28 from being included. The uniformity assessment used either a CIRS 040GSE or an UltraiQ phantom. In the 37-probe subgroup, FirstCall and in-air reverberation each classified 10 as defective, and phantom uniformity classified five. ⁶

FirstCall flagged six probes that phantom uniformity classified as functional. One probe was flagged only by the in-air test, so the two tests with equal totals flagged different sets of probes. The authors found visual in-air assessment useful as a first screen on suitable probes. The comparison excluded phased-array probes because their in-air and uniformity images could not be evaluated visually. The authors also describe limits of visual in-air testing for transesophageal echocardiography (TEE) probes. Have qualified staff choose a compatible method under the applicable protocol. ⁶

If caliper error persists, Goodsitt and colleagues describe repeating the measurement with a second phantom. For that comparison, use a reference with documented condition and target spacing. Compare each reading with the expected distance for its phantom and method. If the error occurs with only one phantom, recheck its condition, temperature and coupling. If it persists across references, have qualified staff compare an approved alternate port or a compatible known-good probe under matched conditions. The result can guide probe or console evaluation. Identifying a failed board requires further testing. ⁵

For example, suppose a 040GSE still reads long on a vertical target after equilibration and weighs 1.25% less than its certificate weight. Even with an intact-looking surface, that combination meets the manufacturer’s contact criterion. Set the 040GSE aside and use a documented second phantom with the same scanner and probe. If the second phantom gives its expected reading, include both results in the manufacturer enquiry. If it also reads long, keep the phantom enquiry open and ask qualified staff to investigate the shared scanner, probe and acquisition setup. ^{2 5}

When Should the Phantom Be Replaced or Recertified?

Keep the original baseline and abnormal result while the QA lead decides whether to repeat the measurement, withdraw the reference, or establish a new baseline. A scanner adjustment or a fresh baseline can erase the evidence needed to explain an unresolved shift.

Use the manufacturer’s evaluation or reinspection route if the reference object itself is suspect. Include its model and serial number, condition photos, weight history and any saved QA images. ⁴

• Visible damage or depression. Withdraw the phantom from QA use. For a damaged 040GSE scan surface, follow the guide’s sealing and return instructions and contact the manufacturer. If the housing is breached, follow the guide’s precautions for exposed gel. A depressed surface also warrants manufacturer contact. ²
• Weight and geometry changed together. On a 040GSE, a change of more than 1% from certificate weight paired with a vertical-distance change meets the guide’s contact criterion. Check that the weight was compared on a like-for-like basis. ²
• Reference history is incomplete. If a recertification date or certificate is missing, confirm the applicable schedule and records with the manufacturer and QA lead. When another phantom is introduced, retain its serial number and record the comparison or new baseline separately. ^{1 2}

For ACR ultrasound accreditation, a qualified medical physicist or designee performs the required annual survey. The ACR allows up to 14 months between surveys. Its annual survey table lists geometric accuracy as optional and calls for uniformity evidence from a phantom or other test object. For routine quality control (QC), the ACR accepts an in-air-only uniformity assessment. It recommends routine QC generally at least semiannually and lists it as optional for accreditation. Label each record with its test method and purpose. Use the facility’s return-to-service process to verify correction and decide whether a new baseline is warranted after a repair, probe change or approved preset change. ³

What Belongs in the QA Record and the Repair Handoff?

A short record can make the follow-up test reproducible. Save the baseline image, the initial abnormal image and the repeat in the facility’s QA system. In the work order, state which inputs matched, which changed and which were unknown. Mark unavailable measurements explicitly so a blank field does not read as a passed check.

The template extends the machine settings and result fields in CIRS Appendix 1 with reference condition and disposition. Use it alongside the facility’s existing QA documentation. ²

When to involve Rongtao Medical

Rongtao Medical provides independent ultrasound probe evaluation, board repair and system diagnostics. A result that follows a probe or persists on the console with a known-good probe helps scope that work. Ask the phantom manufacturer about evaluation and recertification. The facility coordinates accreditation surveys and decides when to return equipment to clinical service. ^{7 4 3}

Send the controlled repeat and the open question. When the symptom is reproducible but still poorly localized, ask for system or probe evaluation before requesting a particular board. Share only nonpatient test images and the equipment details needed for the enquiry.

For a probe-specific finding, use the probe repair service. For a suspected console fault, review ultrasound repair services or send the test summary through the contact form for scope and a quote.

Frequently Asked Questions

What if the result returns to baseline after the phantom reaches room temperature?
Keep both runs and record the change in conditions. If the acquisition setup was held constant, the comparison supports a thermal explanation. The QA lead can decide whether further testing is needed, especially if there is a separate clinical complaint or signs of phantom damage.

How often should the 040GSE be weighed?
The model guide specifies at least once a year against the certificate weight. Sun Nuclear’s later care guide recommends every six months for hydrogel phantoms, including Zerdine. Use the instructions for the unit and record the weighing schedule in the QA plan. ^{2 4}

What if the original phantom serial number is unknown?
Record the missing link and preserve the old result. Ask the QA lead to identify the reference or establish a controlled comparison with a documented phantom. Treat the old-to-new trend as uncertain.

How do I record percentage weight change?
Subtract the certificate weight from the current weight, divide by the certificate weight, and multiply by 100. Record the direction of change and the two weights. For example, a change from 4,000 g to 3,950 g is a 1.25% loss. On a 040GSE, also document vertical-distance findings and the surface condition when evaluating the manufacturer contact criteria. ²

What if the weight is stable but the surface is visibly depressed?
For the 040GSE, a depressed scan surface is an independent reason to contact the manufacturer. Set the phantom aside and document the finding with the QA lead. ²