In a diabetic patient with a septic foot ulcer, a positive probe‑to‑bone test, and wound cultures growing methicillin‑resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli), what is the initial imaging study of choice?

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Last updated: September 6, 2026 • View editorial policy

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Initial Imaging Study of Choice

Plain radiographs (X-rays) of the foot are the initial imaging study of choice in this diabetic patient with a septic foot ulcer and positive probe-to-bone test. 1

Rationale for Plain Radiographs First

Despite the high clinical suspicion for osteomyelitis (positive probe-to-bone test has 89% positive predictive value 2), plain radiographs should always be obtained first because they:

  • Provide essential anatomic detail and detect alternative diagnoses (fracture, foreign body, soft tissue gas, neuropathic arthropathy) 1
  • Combined with the positive probe-to-bone test, may provide sufficient diagnostic accuracy to initiate treatment without further imaging 1, 3
  • Are readily available, low-cost, and guide subsequent imaging decisions 1

When Advanced Imaging is Needed

If plain radiographs are negative or indeterminate, MRI without IV contrast is the next imaging study of choice 1. The 2025 ACR Appropriateness Criteria specifically recommend MRI without IV contrast for initial advanced imaging evaluation 1.

Alternative Advanced Imaging Options

When MRI is contraindicated or unavailable, consider:

  • WBC scintigraphy with SPECT/CT 3
  • [18F]FDG PET/CT 3

The 2024 EANM guidance notes there is no definitive evidence to prefer one advanced modality over another, though MRI is generally performed first 3. If MRI results are equivocal, radiolabeled WBC imaging or FDG PET/CT should be used 3.

Critical Timing Consideration

Plain radiographs may be falsely negative in early osteomyelitis (first 10-14 days) or when bone involvement is limited (<1 cm extension or <30-50% mineral content loss) 1. Given your patient's positive probe-to-bone test, if radiographs are negative, proceed directly to MRI rather than waiting for radiographic changes to develop 1, 3.

Microbiological Considerations

The wound cultures showing MRSA and E. coli do not change the imaging algorithm but should guide antibiotic selection after imaging confirms the extent of infection 3, 4. Whenever possible, obtain bone biopsy for microbiological confirmation if osteomyelitis is identified on imaging 3.

References

3
Guideline

diagnostic imaging of the diabetic foot: an eanm evidence-based guidance.

European Journal of Nuclear Medicine and Molecular Imaging, 2024

4
Research

Diabetic foot infection.

American family physician, 2008

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