4.4 Scan Preparation: Patient Data Entry, Artifact Removal, and Infection Control
Key Takeaways
- Demographic entry is not clerical: date of birth, sex, and ethnicity select the reference database used to compute T-scores and Z-scores, so an error changes the reported diagnosis without changing the measured BMD.
- Height and weight must be measured at the visit rather than reported, because height loss is a clinical finding and weight drives both scan mode selection and FRAX.
- Artifact-producing objects include zippers, snaps, buttons, underwire, belts, coins, jewelry, navel piercings, and metallic thread over the lower back, abdomen, and hips.
- Non-removable artifacts such as surgical hardware, pacemakers, and umbilical piercings that cannot be removed must be documented rather than ignored, so the interpreting physician and future technologists know.
- Table pads, leg blocks, hip positioners, and straps are disinfected between every patient with an EPA-registered product used for its full wet contact time.
4.4 Scan Preparation: Patient Data Entry, Artifact Removal, and Infection Control
Quick Answer: Three preparation tasks each have the power to invalidate an otherwise perfect acquisition. Data entry selects the reference database that converts BMD into a T-score and Z-score. Artifact removal determines whether the edge-detection algorithm sees bone or metal. Infection control protects a population that is old, often immunosuppressed by glucocorticoids, and frequently moving between healthcare facilities.
Patient Identification
Before anything else, confirm identity using two patient identifiers — typically full name and date of birth — against the requisition and the scanner worklist. Bone densitometry has an unusual exposure here: studies are compared across years, so a misidentified scan does not merely produce one wrong report. It contaminates a longitudinal record, and the error may not surface until a follow-up comparison produces an impossible change.
Verify that the order matches the patient and the sites. An order for an axial study does not authorize a forearm substitute; that requires contacting the ordering provider.
Entry of Patient Data
Every field entered before acquisition has a downstream consequence.
| Field | Why it matters |
|---|---|
| Date of birth | Determines age, which selects the Z-score age-matched reference. An error shifts the Z-score without changing BMD |
| Sex | Selects the reference database. ISCD recommends a uniform Caucasian (non-race-adjusted) female NHANES III reference for femoral neck and total hip T-scores in both sexes in the United States |
| Ethnicity | Affects reference selection on some systems and some sites; enter what the facility protocol and the manufacturer's database require, consistently across serial studies |
| Height | Measure it at the visit. Historical height loss is itself a clinical indicator of vertebral fracture and may trigger VFA |
| Weight | Drives acquisition mode selection, affects soft-tissue baseline, and is a FRAX input |
| Referring provider, indication, prior study date | Support coverage, reporting, and valid serial comparison |
Two data-entry habits prevent most reference-database errors. First, measure height and weight rather than accepting reported values — patients systematically report their younger height, and the difference is diagnostically interesting. Second, check the demographics carried forward on a follow-up study; an incorrect date of birth entered years ago silently propagates.
A demographic error is uniquely dangerous because the scan looks fine. BMD in g/cm² is a physical measurement and is unaffected. Only the derived scores move — and those are what the report says.
Removal of Artifact-Producing Objects
The scanner cannot distinguish a snap from a bone edge; it sees attenuation. Anything dense in the beam path is either included in the bone map or excluded as an artifact, and either way the measurement is wrong.
Change the patient into a gown unless clothing is verifiably free of metal over the scan field. It is faster than debating whether a particular garment qualifies.
| Category | Examples |
|---|---|
| Clothing hardware | Zippers, snaps, buttons, rivets, grommets, hooks, metallic thread, sequins, reflective prints |
| Undergarments | Underwire bras, hook-and-eye closures, bodyshapers with metal or dense elastic panels |
| Accessories | Belts, belt buckles, keys, coins, phones, wallets in back pockets |
| Jewelry | Long necklaces that fall over the spine field, navel and abdominal piercings, body chains |
| Medical and personal | Ostomy appliances with metal clips, incontinence products with metallic-backed liners, transdermal patches with metallic backing, some compression garment closures |
| Ingested or injected | Recently taken calcium tablets, barium, iodinated contrast, radiopharmaceuticals |
The scan field is wider than patients assume. For the lumbar spine it extends from roughly the iliac crest to above T12; for the femur it includes the pelvis and proximal shaft. A necklace resting on the sternum is out of field; the same necklace on a supine patient often is not.
Non-Removable Artifacts
Some artifacts cannot be removed, and the correct response is documentation, not silence:
- Surgical hardware: spinal fusion rods, pedicle screws, interbody cages, hip arthroplasty components, plates and screws
- Implanted devices: pacemakers and defibrillators, intrathecal pumps, spinal cord stimulators, IVC filters, aortic stents and endografts
- Radiopaque contraceptive devices in the pelvis
- Piercings that cannot be removed by the patient
- Vascular calcification and osteophytes — pathologic rather than foreign, but equally non-removable
For these, the responses are: exclude the affected vertebra or region where exclusion rules permit; select an alternative site where the order and protocol allow; record precisely what was present and where, so the interpreting physician can judge validity and the next technologist can reproduce the same analysis; and photograph or annotate the scan if the system supports it.
Documenting an artifact that was accommodated is what makes a follow-up study comparable. An unrecorded excluded vertebra is a future serial-comparison error.
Contraindication Confirmation
Before acquisition, confirm the screening answers obtained during history-taking: no recent barium study, no recent iodinated contrast, no recent nuclear medicine radiopharmaceutical, no oral calcium within the facility's specified interval, and pregnancy status resolved for patients of childbearing potential. These are pre-scan checks precisely because performing the study and discovering the contradiction afterwards wastes the appointment and the dose.
Infection Control
The DXA population skews old, and many patients are on glucocorticoids, biologic therapy, or chemotherapy. The scan table is a large shared horizontal surface that every patient contacts directly.
- Between every patient, disinfect the table pad, leg elevation block, hip positioners and foot braces, forearm positioning tray, restraining straps, and any handrails or grab points.
- Use an EPA-registered hospital disinfectant compatible with the manufacturer's materials — some products degrade table upholstery and radiolucent foam — and observe the full wet contact time stated on the label, commonly 1 to 3 minutes. A surface wiped and immediately dried has not been disinfected.
- Perform hand hygiene before and after every patient contact, after glove removal, and after handling positioning accessories. Alcohol-based hand rub is appropriate unless hands are visibly soiled or the patient has a spore-forming organism such as C. difficile, in which case soap and water is required.
- Change table paper or linens between patients.
- Follow transmission-based precautions communicated by the referring unit. Patients on contact precautions may require dedicated equipment handling, gowning, and terminal cleaning after the study.
- Handle sharps and body fluids per facility policy, and clean spills immediately using the facility's spill protocol rather than a routine wipe.
- Keep the workstation clean too. Keyboard, mouse, and trackball are touched with the same hands that positioned the patient and are frequently the least-cleaned surfaces in the room.
A follow-up study shows the patient's date of birth was entered incorrectly at the original visit, recording her as five years younger. What is affected?
A patient has an L4 to S1 posterior fusion with pedicle screws. What is the correct technologist action?
A disinfectant label specifies a 2-minute wet contact time. A technologist wipes the table pad and immediately dries it with a towel before the next patient. What is the problem?