# Evaluation of magnetic resonance imaging and deep learning-based synthetic computed tomography for calcified intradural tumors – importance of domain-specific training and validation of synthetic imaging methods for clinical application

## TL;DR

This study evaluates synthetic CT from MRI for spinal tumors and finds it misses calcified intradural tumors, showing the need for careful application.

## Contribution

Demonstrates limitations of synthetic CT in detecting calcified intradural tumors, emphasizing domain-specific validation.

## Key findings

- Synthetic CT images failed to visualize intradural tumors visible on conventional CT.
- Tumor dimensions and density were significantly different between conventional and synthetic CT.
- The study highlights the importance of validating synthetic imaging methods for specific clinical domains.

## Abstract

For intradural spinal tumors, information on the degree of calcification is helpful to plan the surgery. Novel deep-learning algorithms allow to generate synthetic computed tomography (CT) images from magnetic resonance imaging (MRI).

We conducted a prospective observational cohort study, including n = 105 patients with spinal pathologies between 07/2022 – 09/2023, to validate the accuracy of BoneMRI (MRIGuidance BV©, Utrecht, the Netherlands). Patients underwent both conventional CT and MRI; synthetic CT images were generated from MRI source data with artificial intelligence (AI). For the scope of this post-hoc analysis, only patients with intradural tumors were selected.

Five patients with intradural tumors of the spine were included (mean age 67.8 years; 4 (80%) female). The tumors were visible on 5/5 conventional CT images (100%), on average 19.6 × 11.6 mm in size and 4/5 (80%) were densely calcified (mean Hounsfield units (HU) 463.6). Although well-visible on the T1w/T2w/BoneMRI source data, none of the tumors showed up (0%) on synthetic CT. Visible tumor dimensions were 0 mm in both axial (p < 0.001) and sagittal planes (p = 0.017), with an average density of 20.9 HUs (p = 0.034).

BoneMRI generated synthetic CT is a promising, radiation-free alternative to conventional CT. Intradural tumors – even those with dense calcifications – were not visualized by synthetic CT images, highlighting that this novel technology is currently not able to capture lesions outside its main scope. Our analysis demonstrates powerfully that synthetic imaging must be cautiously applied to populations for which it was developed and validated, and that any extrapolation can be clinically misleading.

The online version contains supplementary material available at 10.1007/s00701-025-06731-0.