MRI IMAGING OF THE LUMBAR SPINE USING A LOW-FIELD DEDICATED TILTING SCANNER: COMPUTED ASSISTED MORPHOMETRIC EVALUATION OF POSITIONAL CHANGES (1) Institute of Biostructure and Bioimages (IBB), CNR and IRCCS SDN, Naples, Italy; (2) Neuroradiology – Diagnostic Imaging University Federico II, Naples, Italy; (3) Esaote SpA, Genova, Italy C. Mollica ¹ ², F. Ferrando ³, R. Spagnuolo ², L. Satragno ³, Marco Salvatore ², A. Brunetti ¹ ²

BACKGROUND MRI is the essential imaging method for diagnostic evaluation in patients with Low Back Pain The imaging protocol of a lumbar spine MRI study requires the patient to rest in supine position during the exam Patients with LBP often feel pain only in specific dynamic postural positions MRI study in supine position does not show the “real” morphometric condition of lumbar spine

To report the results obtained in the evaluation of the lumbar spine with a dedicated low-field open-bore tilting MR scanner, showing representative comparative findings in the supine and upright standing position in patients with Low Back Pain and sciatica. AIMS The quantitative assessment was performed with an original applicative software for segmentation, calculation and computed quantitative analysis of lumbar spine morphometric data with a radiologist supervised automated procedure.

MATERIALS AND METHODS MR studies of lumbar spine in upright standing and recumbent position were successfully carried out in 75 subjects (41 M; mean age 47 y/o; range: ) The MR scanner (G-Scan, ESAOTE, Genova, Italy) used in this study is a low field (0.24 T) fully tilting open MR scanner device (0-90°; 2 steps). Unlike other similar equipment the entire system including the magnet can tilt.

MATERIALS AND METHODS The coil used for lumbar spine examination is a DPA coil made up of a rigid section and a flexible section designed to morphologically adapt to lumbo-sacral region ensuring optimal Signal/Noise ratio. Standing scanning is performed 5-10° off the vertical line to improve patient stability. The standard scanning protocol includes Fast Spin-echo sequences in axial and sagittal planes (slice thickness 3-5 mm, slice gap 0,5mm; Nex: 3-4). The quantitative and computed assessment of lumbar spine morphometric data with dedicated software was performed in 22 patients (13M; mean age 44.4 y/o; range 24-72) whose MRI examinations were free from motion artifacts.

Applicative software Sagittal FSE T2 Level set Segmentation Algorithm 3D Model

For each image set in both upright and recumbent position the following parameters were calculated and measured: Morphometric parameters (1) Spinal canal volume: defined for L1- S1 tract and for each level from L1-L2 to L5-S1 Lordosis angle defined on the basis of top and bottom endplates of L1 to S1 Sacral angle defined as the angle between the upper endplate of S1 and the horizon

Morphometric parameters (2) Intervertebral angle defined as the angle between the opposing endplates of two adjacent vertebrae from L1-L2 to L5-S1 Spinal canal cross area defined for each level from L1-L2 to L5-S1 is the sectional cross area defined by the intersection of a plane orthogonal to the major axis of the canalar volume’s 3D model Foraminal cross area calculated from L1-L2 (F1) to L5-S1 (F5) on both sides

Morphometric parameters (3) Wedging or index of vertebral wedge deformation is the angle between the two endplates each vertebra from L1 to L5. Listhesis index calculates the distance between the line through the posterior somatic wall of a superior vertebra and the line through superior endplate of the vertebra below.

Morphometric parameters (4) Intervertebral Translation defined as the shift between the centroid of the vertebra below and the centroid of the vertebra above Vertebral collapse or Index of collapse evaluated by calculating for each vertebra from L1 to L5 the three heights front, middle and rear of the vertebra according to the morphometric parameters for the diagnosis of vertebral fractures by standardized "footnote 79" of the Ministry of Health

Statistical analysis Statistical analysis for comparison of MRI-supine and standing positions was performed using the SPSS software vers. 16 using the Wilcoxon test (nonparametric test for paired data) The limit of significance for all tests was set at p <0.05.

Results Statistically significant changes were found for the following morphometric parameters:  Lordosis angle  Spinal canal volume  Spinal canal cross-area  Foraminal cross-area

Results: Lordosis Angle RecumbentUp-right In our study we observed an increase in the angle of lordosis in the up-right position compared to recumbent position in the 86.7% (19/22) of examined patients. The comparative statistical analysis showed a statistically significant difference for the angle of lordosis (p = 0.002).

Results: Spinal canal volume recumbentUp-right In our study we observed a reduction of the volume of the spinal canal in the up- right position compared to the recumbent position in 80% (17/22) of the examined subjects. The comparative analysis showed a statistically significant difference for the volume of the spinal canal (p = 0.041)

Results: Spinal canal cross-area recumbent Up-right In our study we observed a reduction of the spinal canal cross-area in the up-right position compared to the recumbent position in 70% (77/110) of the examined spinal segments. The comparative analysis show a statistically significant difference for the spinal canal cross-area for L2-L3 and L3-L4 levels (p : range from to 0,004)

Results: Foraminal cross-area recumbentUp-right Our results show a reduction of the foraminal cross-area in the up-right position compared to the recumbent position in the 77.3% (193/220) of patients The comparative statistical analysis showed a statistically significant difference for all the foramina examined (p: range from to 0.031)

Conclusions Dynamic MRI imaging of the lumbar spine allows to evaluate and study the physiological and pathological changes that occur in the transition from recumbent to the upright standing position. Compared to other qualitative studies published so far in the literature, our study was aimed to a quantitative analysis of dynamic changes in lumbar spine morphometric parameters in the supine vs. upright position using an original dedicated software. Large cohorts of patients will have to be studied to verify the potential value of a quantitative morphometric approach in a clinical context.

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