A MnCl2-based phantom for IVD hydration status determination using MRI: Pre-clinical reliability analyses

Introduction

Non-biological, yet signal-responsive, MR phantom materials are becoming increasingly commonplace. One such novel agent, semi-solid manganese chloride (MnCl₂), has recently been described as a potential calibration standard for direct assessment of in vivo cartilage fluid content. Given the established correlation between intervertebral disc (IVD) hydration state and physiologic spinal functioning, such a tool, allowing calibration for ‘quantitative’ appraisal of disc fluid content, has many potential applications. The purpose of this study was to demonstrate MR signal-to-noise ratio (SNR) measurement reliability of a novel MnCl₂-based signal calibration phantom for in vivo disc hydration analysis, using a 10 × 10 inter- and intra-observer reliability analysis in the pre-clinical setting.

Materials and methods

A series of novel MnCl₂ calibration phantoms were imaged to assess intra-/inter-observer reliability during measurement of signal intensity. The phantoms were imaged under ten different MR sequences, generating 75 signal regions from which SNR values were measured. Inter-observer reliability was tested by inviting ten individuals to obtain signal measurements from each image, on a single occasion. To test intra-observer reliability, a single participant was asked to record measurements of the same features on ten separate occasions.

Results

1425 Discrete measurement points were available for combined reliability analyses. Single-measure intraclass correlation coefficients showed high measurement agreement, with both intra- and inter-observer values approaching 1.00.

Conclusion

This study demonstrates that signal measurements can be obtained using MnCl₂ disc phantoms, with a high degree of observer reliability, supporting their use as a signal calibration standard during orthopaedic MR-based cartilage imaging.