# Opportunistic assessment of bone mineral density using computed tomography in pediatric liver transplant recipients

## TL;DR

This study explores using CT scans to assess bone health in children who had liver transplants, finding that CT measurements can provide useful supplementary information when traditional DXA scans are not available.

## Contribution

The study demonstrates that CT-derived sagittal vertebral Hounsfield unit values can moderately correlate with DXA z-scores in pediatric liver transplant recipients.

## Key findings

- Sagittal Hounsfield unit values showed a moderate correlation with DXA z-scores (r = 0.429).
- A threshold of 188 HU had 83% sensitivity and 68% specificity for identifying low bone mineral density.
- Axial HU values showed weaker correlation compared to sagittal measurements.

## Abstract

Pediatric liver transplant (LT) recipients are at increased risk of impaired bone mineral accrual due to chronic liver disease, growth disturbances, and post-transplant metabolic factors. Although dual-energy X-ray absorptiometry (DXA) remains the reference method for evaluating bone mineral density (BMD), opportunistic assessment using routine abdominal computed tomography (CT) has emerged as a potential adjunct tool. This study aimed to evaluate the potential of using routine abdominal CT scans to assess bone health in pediatric LT recipients by comparing lumbar vertebral Hounsfield unit (HU) values with those obtained using DXA. This retrospective study included 62 pediatric LT recipients who underwent both abdominal CT and lumbar spine DXA within a 3-month period. HU values were measured at vertebral levels L1–L4 in both the sagittal and axial planes. DXA z-scores were classified according to International Society for Clinical Densitometry pediatric guidelines. Correlation and receiver operating characteristic (ROC) analyses were performed to determine the diagnostic performance of HU values. Patients with low bone mineral density had significantly lower sagittal HU values (p < 0.05). Moderate correlation was found between sagittal mean HU and DXA z-scores (r = 0.429, p = 0.003), whereas weaker correlation was observed for axial HU values (r = 0.266, p = 0.037). ROC analysis demonstrated a moderate discriminative ability for sagittal HU (AUC = 0.713, p = 0.016), with an optimal cut-off value of 188 HU yielding 83% sensitivity and 68% specificity.

Conclusion: CT-derived HU values from routine abdominal imaging may provide valuable supplementary information on bone health in pediatric LT recipients. However, CT-based bone assessment should be considered a complementary approach, enhancing clinical decision-making by providing supportive quantitative information in scenarios where DXA is unavailable or impractical.

What is Known:• Pediatric liver transplant recipients are at increased risk of impaired bone mineral accrual, and DXA remains the reference standard for pediatric bone mineral density assessment.• In adults, vertebral HU values from routine CT correlate with bone mineral density, but evidence in pediatric populations remains limited.What is New:• CT-derived sagittal vertebral HU values showed a moderate correlation with DXA lumbar z-scores in pediatric liver transplant recipients, whereas axial measurements were weaker.• A sagittal mean threshold of ~188 HU demonstrated a moderate diagnostic performance for identifying low bone mineral density, supporting opportunistic contrast-enhanced CT as a complementary—not replacement—tool to DXA.

What is Known:

• Pediatric liver transplant recipients are at increased risk of impaired bone mineral accrual, and DXA remains the reference standard for pediatric bone mineral density assessment.

• In adults, vertebral HU values from routine CT correlate with bone mineral density, but evidence in pediatric populations remains limited.

What is New:

• CT-derived sagittal vertebral HU values showed a moderate correlation with DXA lumbar z-scores in pediatric liver transplant recipients, whereas axial measurements were weaker.

• A sagittal mean threshold of ~188 HU demonstrated a moderate diagnostic performance for identifying low bone mineral density, supporting opportunistic contrast-enhanced CT as a complementary—not replacement—tool to DXA.