Excellent - I now have everything needed to write a comprehensive, well-referenced protocol. Let me compile it.---
Full Research Protocol
CT-Based Opportunistic Bone Mineral Density Screening for Undiagnosed Osteoporosis in Patients Undergoing Routine Contrast-Enhanced Abdominal CT
1. TITLE PAGE
Full Title: Prevalence of Undiagnosed Osteoporosis Detected by Opportunistic L1 Trabecular Bone Attenuation Measurement on Routine Contrast-Enhanced Abdominal CT: A Retrospective Cross-Sectional Study
Short Title: Opportunistic CT Osteoporosis Screening on Abdominal CT
Study Design: Retrospective, cross-sectional observational study
Target Journal: Osteoporosis International / American Journal of Roentgenology (AJR) / European Radiology
2. BACKGROUND AND RATIONALE
Osteoporosis affects an estimated 200 million people worldwide and is a leading cause of fragility fractures, morbidity, and mortality, particularly in post-menopausal women and elderly men. Despite being preventable and treatable, the condition remains substantially underdiagnosed - fewer than 20% of patients who sustain a fragility fracture are evaluated or treated for underlying osteoporosis.
The gold standard for osteoporosis diagnosis is dual-energy X-ray absorptiometry (DXA), which measures bone mineral density (BMD) at the lumbar spine and hip. However, DXA is underutilized due to limited access, cost, lack of patient awareness, and absence of referral pathways.
Routine CT scans of the abdomen and pelvis - performed in millions of patients annually for unrelated indications such as renal colic, abdominal pain, malignancy staging, and surveillance - invariably include the lumbar vertebrae. The trabecular bone of the L1 vertebral body is consistently visualized on all abdominal CTs, and its attenuation value in Hounsfield units (HU) correlates significantly with DXA-measured BMD.
Multiple studies have validated CT-based opportunistic screening:
- A meta-analysis (Zhu et al., Clinical Imaging, 2021, PMID 34530357) of 10 studies reported pooled sensitivity 0.83 and specificity 0.74 for CT-based detection of osteoporosis using HU thresholds, with AUC 0.84.
- Pickhardt et al. (Radiology, 2013) established normative L1 trabecular HU values across >20,000 adults, with thresholds of 110 HU (>90% specific) and 135 HU (optimal ROC) for osteoporosis.
- A recent Thai study (Chaisen et al., Diagnostics, 2024, PMID 39767207) found HU ≤142 at L1 had 91.9% sensitivity and 48.4% specificity vs DXA in a predominantly female population (mean age 66.3 years).
- Sobecki et al. (Osteoporosis International, 2025, PMID 40493237) confirmed that a 200 mm² circular ROI at the L1 vertebral body centroid on axial imaging is the optimal, reproducible measurement technique, with excellent intra- and inter-observer reliability (ICC >0.95).
Despite this evidence base, the practice of opportunistic CT-based BMD screening has not been systematically implemented in most radiology departments, and prevalence data from specific high-risk populations (e.g., post-menopausal women, steroid users, oncology patients) in [your region/country] remain lacking.
3. RESEARCH GAP
While normative data and diagnostic thresholds are established primarily in Western and East Asian populations, local/regional prevalence data are limited. Additionally, most published studies use non-contrast CT; this protocol addresses the gap regarding contrast-enhanced CT (the most common abdominal CT type in clinical practice) and validates whether HU thresholds require adjustment for contrast phase.
4. OBJECTIVES
4.1 Primary Objective
To determine the prevalence of undiagnosed osteoporosis (L1 trabecular HU ≤110) and osteopenia (HU 111-135) in patients undergoing routine contrast-enhanced abdominal CT.
4.2 Secondary Objectives
- To compare mean L1 HU values across age groups and sex.
- To identify clinical and demographic predictors of low L1 HU on CT.
- To determine the proportion of patients with low HU who had no prior DXA or osteoporosis diagnosis documented in medical records.
- To assess whether HU values differ between non-contrast and contrast-enhanced CT phases (in patients where both are available).
- To identify the prevalence of incidental vertebral compression fractures in the same cohort.
5. RESEARCH QUESTION (PICO Format)
| Element | Detail |
|---|
| P - Population | Adults ≥50 years (with sub-analysis in post-menopausal women ≥45 years and patients on chronic steroids) undergoing routine contrast-enhanced abdominal CT |
| I - Index test | L1 trabecular HU measurement on CT (200 mm² ROI at vertebral body centroid, axial plane) |
| C - Comparator | Published DXA-validated HU thresholds (Pickhardt et al.; Chaisen et al.) |
| O - Outcome | Prevalence of undiagnosed osteoporosis/osteopenia; proportion with no prior diagnosis or DXA referral |
6. STUDY DESIGN
- Type: Retrospective cross-sectional study
- Setting: Radiology department, [Hospital Name], [Institution]
- Duration: CT scans performed over a 2-year period (e.g., January 2022 - December 2023)
- Ethics: Retrospective use of anonymized imaging and medical record data; minimal risk. Waiver of informed consent to be sought from institutional ethics committee (IEC/IRB).
7. STUDY POPULATION
7.1 Inclusion Criteria
- Adults aged ≥50 years
- Underwent contrast-enhanced abdominal CT (portal venous phase) for any clinical indication other than known osteoporosis or metabolic bone disease
- L1 vertebra adequately visualized on axial images without significant artifact
- Medical records accessible for clinical data extraction
7.2 Exclusion Criteria
- Known pre-existing diagnosis of osteoporosis or metabolic bone disease documented before the CT date
- Presence of metal implants, vertebral augmentation (kyphoplasty/vertebroplasty), or extensive degenerative changes at L1 affecting HU measurement
- Active osseous metastatic disease or primary bone tumor involving the L1 vertebra
- Vertebral fracture at L1 (as this alters trabecular HU)
- Scans with significant motion or streak artifact at L1 level
- Patients who underwent the same CT scan >once (only most recent scan included)
- Severe scoliosis precluding reliable L1 measurement
7.3 Sub-Group of Interest (for secondary analysis)
- Post-menopausal women (aged ≥45 years, documented amenorrhea ≥12 months)
- Patients on chronic corticosteroids (≥5 mg prednisolone equivalent for ≥3 months)
- Oncology patients on aromatase inhibitors or androgen deprivation therapy
- Patients with CKD (eGFR <30 mL/min)
8. SAMPLE SIZE CALCULATION
Basis: Prevalence estimation study.
Using the formula:
n = Z² × p(1-p) / d²
Where:
- Z = 1.96 (95% confidence level)
- p = expected prevalence of osteoporosis in target population ≈ 0.25 (25%, based on published estimates in adults >50 years; conservative estimate)
- d = acceptable margin of error = 0.05 (±5%)
n = (1.96)² × 0.25 × 0.75 / (0.05)²
n = 3.84 × 0.1875 / 0.0025 = 288
Adding 15% for exclusions and data loss: minimum sample size = ~332 patients
For a robust study, target n = 400-500 patients to allow subgroup analyses.
9. METHODOLOGY
9.1 CT Data Retrieval
- Identify all patients ≥50 years who underwent contrast-enhanced abdominal/abdominopelvic CT during the study period from the PACS/RIS database.
- Anonymize all retrieved CT datasets before analysis.
9.2 L1 HU Measurement - Standardized Protocol
Step-by-step measurement (following Sobecki et al., 2025 and Pickhardt et al.):
- Open the CT scan in standard DICOM viewer (e.g., OsiriX, RadiAnt, or PACS workstation).
- Identify the L1 vertebra as the first non-rib-bearing lumbar vertebra on sagittal scout or reformatted images.
- Navigate to the axial (transverse) plane at the mid-body level of L1.
- Place a circular ROI of 200 mm² at the vertebral body centroid, in the anterior trabecular region, avoiding cortical bone, basivertebral vein, osteophytes, and any sclerotic/lytic areas.
- Record the mean HU value within the ROI.
- If the axial plane is unsatisfactory, a sagittal anterior ROI placement is acceptable as a secondary option.
- All measurements performed on soft tissue window settings (W:400, L:40 or W:350, L:35).
Threshold Classification (based on validated literature):
| Category | L1 HU Value |
|---|
| Normal BMD | >135 HU |
| Osteopenia (low bone mass) | 111-135 HU |
| Osteoporosis (likely) | ≤110 HU |
| High-specificity osteoporosis | ≤90 HU |
(Reference: Pickhardt et al., Radiology 2013; Zhu et al., Clinical Imaging 2021)
Note on contrast effect: Contrast enhancement may increase HU by approximately 10-30 HU. A sensitivity analysis will be performed comparing HU in portal venous phase vs. non-contrast scans (in patients where both are available, e.g., triphasic CT). Where only contrast-enhanced scans are available, a conservative threshold adjustment (+20 HU buffer) will be applied, or measurements will be interpreted using the upper thresholds (≤130 HU instead of ≤110 HU for osteoporosis screening).
9.3 Data Collection Form (per patient)
Demographic:
- Age, sex, BMI, menopausal status (women)
- Ethnicity
Clinical:
- CT indication
- Presence of known diabetes, CKD, liver disease, malignancy
- Current medications: corticosteroids, bisphosphonates, aromatase inhibitors, androgen deprivation therapy, PPIs, anticonvulsants
- Prior DXA scan documented in records (yes/no; result if available)
- Prior osteoporosis or fracture diagnosis (yes/no)
- Referral to endocrinology/rheumatology for bone health (yes/no)
Imaging:
- CT scanner make and model, kVp, mAs
- Contrast phase (non-contrast, arterial, portal venous, delayed)
- L1 HU value
- Presence of vertebral compression fracture at any level (yes/no; level if yes)
- Quality of measurement (adequate/suboptimal/excluded)
9.4 Inter-Observer Reliability
- L1 HU measurements performed independently by two observers (one radiologist with ≥3 years experience; one radiology resident).
- A randomly selected subset of 50 scans (10-15%) measured by both observers.
- Inter-observer agreement assessed using Intraclass Correlation Coefficient (ICC).
- Discordant readings (>15 HU difference) adjudicated by a third senior radiologist.
10. STATISTICAL ANALYSIS PLAN
10.1 Descriptive Statistics
- Continuous variables: mean ± SD or median (IQR) based on normality (Shapiro-Wilk test)
- Categorical variables: frequencies and percentages
- L1 HU distribution plotted as histogram
10.2 Primary Outcome
- Prevalence of low bone mass (HU ≤135) and osteoporosis (HU ≤110) reported as percentage with 95% confidence intervals (Wilson score method)
10.3 Secondary Analyses
- Independent t-test or Mann-Whitney U for HU comparison between sexes
- One-way ANOVA or Kruskal-Wallis for HU comparison across age groups (50-59, 60-69, 70-79, ≥80 years)
- Pearson or Spearman correlation between L1 HU and age, BMI
- Logistic regression (univariate then multivariate) to identify independent predictors of HU ≤110: age, sex, BMI, steroid use, CKD, malignancy, menopausal status
- Sensitivity analysis comparing HU on contrast vs. non-contrast phases (paired t-test in subgroup with both phases available)
- Chi-square test to compare prevalence across subgroups (post-menopausal women vs. men, steroid users vs. non-users)
- ICC with 95% CI for inter-observer agreement (≥0.90 = excellent)
10.4 Reporting Rate Analysis
- What proportion of patients with HU ≤110 had:
- A prior DXA documented
- A prior osteoporosis diagnosis
- An existing referral for bone health assessment
This "treatment gap" analysis forms the key public health contribution of the study.
10.5 Software
- SPSS v25 or higher / R version ≥4.2 / MedCalc
- p <0.05 considered statistically significant
- No correction for multiple comparisons in secondary exploratory analyses (reported as hypothesis-generating)
11. ETHICAL CONSIDERATIONS
| Issue | Plan |
|---|
| Ethics approval | Submit to Institutional Ethics Committee (IEC) / IRB before data collection |
| Informed consent | Waiver of consent to be requested (retrospective, anonymized data, minimal risk) |
| Data anonymization | All CT data de-identified before analysis; patient IDs replaced with study codes |
| Data storage | Stored on password-protected institutional server; accessible only to study investigators |
| Incidental findings | If a patient is found to have osteoporosis (HU ≤110) and has no prior diagnosis, a reporting pathway to the referring clinician will be recommended to the ethics committee for prospective implementation |
| Conflict of interest | All authors to declare no financial conflict of interest |
12. EXPECTED OUTCOMES AND SIGNIFICANCE
Expected findings:
- Prevalence of osteoporosis (HU ≤110) expected in ~20-30% of patients aged >50 years based on published data, with higher rates in post-menopausal women and steroid users.
- A substantial proportion (estimated 50-70%) will have had no prior DXA or osteoporosis diagnosis - the "treatment gap."
Significance:
- Provides local/regional prevalence data for opportunistic screening
- Demonstrates the scale of underdiagnosis using an already-performed, no-additional-cost investigation
- Supports the case for implementing a systematic reporting protocol for low L1 HU in radiology departments
- Directly actionable: could prompt referral for DXA, initiation of bisphosphonate therapy, and fracture prevention
13. LIMITATIONS
- Contrast enhancement effect: Portal venous phase contrast may elevate HU by ~10-30 HU, potentially underestimating the true prevalence. Addressed via sensitivity analysis and conservative threshold adjustments.
- Single-center retrospective design: Limits generalizability; selection bias possible.
- No DXA correlation in all patients: Most patients will not have a DXA for direct correlation, so DXA-validated thresholds are used as proxies.
- Scanner variability: HU values can vary between CT scanners; scanner model and parameters will be recorded as covariates.
- L1-only measurement: Lumbar spine DXA typically averages L1-L4; single vertebra measurement may not reflect overall spinal BMD equally well in all patients.
- Medical record completeness: Underreporting of prior DXA or medications possible in retrospective records.
14. TIMELINE
| Phase | Activity | Duration |
|---|
| Month 1 | Protocol finalization, IEC/IRB submission | 4 weeks |
| Month 2-3 | Ethics approval and data retrieval setup | 4-8 weeks |
| Month 3-5 | CT data collection, HU measurements, clinical data extraction | 8 weeks |
| Month 5-6 | Data cleaning, statistical analysis | 4 weeks |
| Month 6-7 | Manuscript writing and internal review | 4 weeks |
| Month 7-8 | Submission and revision | 4-8 weeks |
Total estimated duration: 8-10 months
15. PUBLICATION TARGETS
| Journal | Impact Factor (approx.) | Notes |
|---|
| Osteoporosis International | ~4.5 | Primary target; directly relevant |
| American Journal of Roentgenology | ~4.3 | Radiology readership; practical focus |
| European Radiology | ~5.2 | High visibility; strong fit |
| Skeletal Radiology | ~2.8 | Backup; subspecialty journal |
| Clinical Radiology | ~3.0 | Good fit for diagnostic accuracy studies |
16. KEY REFERENCES
-
Pickhardt PJ, et al. CT-based screening for osteoporosis at routine abdominal and thoracic CT. Radiology. 2013;268(1):120-127.
-
Zhu Y, Triphuridet N, Yip R, et al. Opportunistic CT screening of osteoporosis on thoracic and lumbar spine: a meta-analysis. Clin Imaging. 2021;80:111-122. [PMID: 34530357]
-
Chaisen M, Sritara C, Chitrapazt N, et al. Opportunistic Screening for Osteoporosis by CT as Compared with DXA. Diagnostics (Basel). 2024;14(24):2846. [PMID: 39767207]
-
Sobecki JN, Krueger D, Pickhardt PJ, et al. Optimizing region of interest size and placement for clinical opportunistic CT trabecular bone Hounsfield unit measurements. Osteoporos Int. 2025. [PMID: 40493237]
-
Guenoun D, Champsaur P. Opportunistic Computed Tomography Screening for Osteoporosis and Fracture. Semin Musculoskelet Radiol. 2023;27(4). [PMID: 37748468]
-
Deshpande N, Hadi MS, Lillard JC, et al. Alternatives to DEXA for the assessment of bone density: a systematic review. J Neurosurg Spine. 2023;38(4). [PMID: 36609369]
-
Reschke P, Koch V, Sommer CM, et al. The Association between opportunistic DECT-derived bone values and vertebral fracture status. Eur J Radiol. 2025. [PMID: 40373671]
17. TEAM ROLES (Suggested)
| Role | Responsibility |
|---|
| Principal Investigator | Protocol design, final manuscript, corresponding author |
| Co-Investigator (Radiologist) | CT measurement, image quality assessment, inter-observer analysis |
| Co-Investigator (Radiology Resident) | Data collection, HU measurements, data entry |
| Statistician / Co-Author | Statistical analysis plan execution |
| Clinical Co-Author (Endocrinology/Rheumatology) | Interpretation of clinical data, treatment gap analysis |
This protocol is ready to submit to your IEC/IRB. The most distinctive element is the treatment gap analysis - showing what proportion of patients with CT-detected low BMD had zero prior workup. That angle is what makes it publishable in a mid-tier journal above simple prevalence reports. Let me know if you need a synopsis/synopsis form, sample data collection sheet in Excel format, or a manuscript draft outline.