New imaging strategies in Degenerative Disease of the Intervertebral Disks

Functional Spine Imaging

Introduction

Current MR imaging often fails to identify cause of pain

Surgical management of DDD changing– Biochemical targets for disk therapy– Earlier intervention

Imaging goals in transition

Functional imaging

Great potential, but limited validation– MRS, – measurement of T2 relaxation times,– measurement of T1 rho, – dynamic imaging, – fMRI of the spinal cord– measurement of CSF flow and pressure.

MRS

Lactic acid in the disk correlates with painful degenerating disksMRS noninvasively and effectively quantifies glycosaminoglycans and lactate in the diskMRS effectively distinguishes pain producing from non-pain producing disksAdditional studies are needed.

MRS peaks in disk tissue

L4/L5 Disc

Processing of raw MR spectral data

RAW SIGNAL PROCESSED

PG

PG

LA

LAL5/S1 Disc

Intervertebral disk Lactic acid/PG

T2 relaxation times and T1 rho

Clinical scanners provide the pulse sequences required to measure T2 relaxation times and T1 rhoProvide a quantitative measure that correlates with the degenerative stage of the diskT2 relaxation times a proxy measurement of disk waterMeasure changes in the disk over timePromise to distinguish early degenerative changes from age-related changesT2 relaxation times decline slowly with age and more rapidly with degenerationAcquisition T2 data requires 6 minutes; T1 rho, 30 minutes.

T2 relaxation time image

Contour map of T2 relaxation times in normal lumbar disk

Distribution of water in intervertebral disk

T1 rho

Johannessen W et al. Spine 2006

Correlation of T2 relaxation time to cadaver disk water content

T2 relaxation time correlated to disk water content

y = 407.83x - 230.72

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water content (%)

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lax

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Marinelli N et al. submitted

Correlation of relaxation time to GAG content

T2 relaxation times correlated to proteoglycan content in intervertebral disk

y = 11.307x + 19.092

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proteoglycan content (%)

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MR images, T2 maps, and water content maps

Marinelli et al, unpublished data.

Pfirrmann grade (N) II (44) III (34) IV (13) V (3)

T2-weighted image

T2 relaxation time map

H2O % Map

Calculated water content

of nucleus 81% 74% 71% 70%

Change in T2 relaxation times with degeneration

Change in T2 relaxation times with aging

Dynamic imaging

Biomedical techniques measure rotations of vertebraeMR, CT measure rotation of lumbar vertebrae “Dynamic MRI”: the application of a load or force to the spine with pre-acquisition of images Relative rotation a measure useful in selecting patients for a fusion procedureDynamic imaging without measurement: still under evaluation.

Measuring axial rotations of the lumbar spine with CT or MR

1. Table insert2. Axial images3. Application of

standardized rotation to the spine

4. Repeat axial images5. Calculation of rotation

between vertebrae from image pairs

CT measurement of vertebral rotation correlated to reference method

Rotation measurement by CT and by biomechanical methods post-instrumentation

y = 0.9438x + 0.0112

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Rotation measurement following L4/5 fusion

Rotations for lumbar motion segments

L1/L2 0.44 deg

L2/ L3 0.59 deg

L3/L4 5.37 deg

L4/L5 0.09 deg

L5/S1 1.09 deg

Axial loading of the spine

fMRI

Demonstrates activation in the spinal cord secondary to motor and sensory functions

Greater technical difficult that cerebral fMRI.

L

L4

Patrick W. Stroman, PhD, University of Manitoba

Activation in the spinal cord from thermal stimulation of R L4 dermatome

Activation of the spinal cord from tactile stimulation

Walter Backes PhD,

University Hospital Maastricht

Visualization of CSF flow and pressure

Evaluation of Chiari I patients

Measure CSF flow and pressure

Selection of patients for cranio-occipital decompression

Explanation of pathogenesis of syringomyelia

CSF flow in the Chiari I malformation

Conclusions

Future promises minimally invasive procedures that reverse intervertebral disk degeneration

Require new imaging strategies, especially for patients with early disk degeneration

“Functional imaging tools” include many different techniques including MRS, measurement of disk water, dynamic MRI