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Biomed Opt Express. 2019 Aug 1;10(8):4316-4328. doi: 10.1364/BOE.10.004316. eCollection 2019 Aug 1.

Validation of diffuse reflectance spectroscopy with magnetic resonance imaging for accurate vertebral bone fat fraction quantification.

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Department of Biomechanical Engineering, Delft University of Technology, Mekelweg 2, 2628 CD, Delft, the Netherlands.
Department of In-body Systems, Philips Research, Royal Philips NV, High Tech Campus 34, 5656 AE, Eindhoven, the Netherlands.
Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden and Department of Neurosurgery, Karolinska University Hospital, 17176, Stockholm, Sweden.
Department of Radiology, Klinikum rechts der Isar, Technical University of Munich, Ismaninger Straße 22, 81675 München, Germany.
Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, Ohio, USA.


Safe and accurate placement of pedicle screws remains a critical step in open and minimally invasive spine surgery. The diffuse reflectance spectroscopy (DRS) technique may offer the possibility of intra-operative guidance for pedicle screw placement. Currently, Magnetic Resonance Imaging (MRI) is one of the most accurate techniques used to measure fat concentration in tissues. Therefore, the purpose of this study is to compare the accuracy of fat content measured invasively in vertebrae using DRS and validate it against the Proton density fat fraction (PDFF) derived via MRI. Chemical shift-encoding-based water-fat imaging of the spine was first performed on six cadavers. PDFF images were computed and manually segmented. 23 insertions using a custom-made screw probe with integrated optical fibers were then performed under cone beam computer tomography (CBCT). DR spectra were recorded at several positions along the trajectory as the optical screw probe was inserted turn by turn into the vertebral body. Fat fractions determined via DRS and MRI techniques were compared by spatially correlating the optical screw probe position within the vertebrae on CBCT images with respect to the PDFF images. The fat fraction determined by DRS was found to have a high correlation with those determined by MRI, with a Pearson coefficient of 0.950 (P< 0.001) as compared with PDFF measurements calculated from the MRI technique. Additionally, the two techniques were found to be comparable for fat fraction quantification within vertebral bodies (R2 = 0.905).

Conflict of interest statement

The authors who are affiliated with Philips Research (B.H.W.H., J.W.S., D.B.) only have financial interests in the subject matter, materials, and equipment, in the sense that they are an employee of Philips. None of the other authors have any financial relationship or conflict of interests.

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