Opportunistic CT Biomarkers

What it does

Opportunistic CT Biomarkers turns a chest or abdomen CT that was ordered for another reason into a screening panel, with no extra scan and no extra radiation. Upload the study as it was acquired; the run finds the vertebral levels, checks which of them the scan covers and measures what that coverage allows.

The panel has five parts: muscle and fat at the third lumbar vertebra, trabecular bone attenuation at the first lumbar vertebra, liver attenuation against the spleen, calcification of the thoracic and abdominal aorta, and osteoporotic compression fractures from T4 to L5. Each value comes with its reference range and a flag when it falls outside it, so a single page tells the clinician which follow-up test to consider. Aortic calcium is quantified without a reference threshold.

Intended use

Population-health decision support: a routine CT gains a biomarker panel, and the general practitioner or internist decides whether a bone densitometry scan, a liver work-up, a nutrition review or a cardiovascular risk assessment is due.

Who it is for

General practitioners, internists, endocrinologists, geriatricians, hepatologists and oncologists following body composition, and radiology departments running opportunistic screening. Developers run the panel in the background on CTs already in the archive and feed the flags into a population-health or care-gap system.

Accepted input

• Any chest or abdomen CT, contrast-enhanced or not, as DICOM CT series.
• One axial series is enough; when several reconstructions exist, the run picks a soft-tissue series for muscle and fat and the one best suited to bone measurement.
• Typical sources: staging, emergency, follow-up and screening CTs of the chest or abdomen.

Requirements

Requirement	Why
Coverage of L3, or of T12 to L5	The sarcopenia cut-offs are defined at L3; neighbouring levels are measured when L3 is outside the scan
Coverage of L1	Trabecular attenuation for bone density is read at L1, with T12 to L5 as fallback
Liver and spleen in the field of view	Steatosis is judged from both attenuations
Detected contrast phase and tube voltage (KVP)	Contrast and kVp change HU, so bone and liver values are phase-corrected
Sagittal reformat possible from thin slices	Vertebral height loss is measured on sagittal images

A vertebra with a fracture or hardware is excluded from the bone-density measurement and the next level is used.

Optional context

Sex goes in clinical_context: the sarcopenia cut-offs differ by sex. The indication of the original CT is kept with the result.

The result

One JSON panel with one section per biomarker, each with its value, threshold where one exists, flag and the vertebral level it was measured at.

Section	Content
Body composition	Skeletal-muscle area and index, muscle attenuation (myosteatosis), visceral, subcutaneous and intermuscular fat, sarcopenia flag
Bone density	Trabecular attenuation at L1 (or T12–L5) with a BMD estimate and an osteoporosis or osteopenia flag
Liver fat	Liver and spleen attenuation and their difference, with a hepatic steatosis flag
Aortic calcium	Quantified calcification of the abdominal and thoracic aorta
Vertebral compression fractures	Fractured vertebrae from T4 to L5 with height loss and Genant grade 1–3
Draft report	Opt-in (options.report): an English narrative that interprets the result for the reader (findings, impression, limitations); every number is checked against the findings

Standards

• DICOM: SR TID 1500 Measurement Report with one measurement group per biomarker; Encapsulated PDF; FHIR DiagnosticReport with one Observation per biomarker.
• Reference thresholds: L3 skeletal-muscle index cut-offs for sarcopenia (Prado 2008); L1 trabecular attenuation thresholds for osteoporosis (Pickhardt 2013); Genant semiquantitative grading of vertebral fractures (1993).

Interpretation notes

Contrast phase and tube voltage change attenuation, so bone and liver values from enhanced scans are phase-corrected before they are compared with the thresholds. Calibration also differs between scanners, and the result records the series, phase and kVp behind every value.