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
0
20
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60% 70% 80% 90%
water content (%)
T2
re
lax
ati
on
tim
e
(ms
)
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
0
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0 1 2 3 4 5 6 7 8
proteoglycan content (%)
T2
re
lax
tio
n t
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(m
s)
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Marinelli et al, unpublished data.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
0%
10%
20%
30%
40%
50%
0% 10% 20% 30% 40% 50%
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