Line Scan Diffusion Imaging of the Spine
Roland Bammera,
Andreas M. Hernethb,
Stephan E. Maierc,
Kim Buttsa,
Rupert W. Prokescha,b,
Huy M. Doa,
Scott W. Atlasa and
Michael E. Moseleya
a Lucas MRS/I Center, Stanford University, Stanford, CA
b Radiological Science Laboratory, Department of Radiology, University of Vienna, Vienna, Austria
c Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA
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FIG 1. Sagittal line scan diffusion images of the spine of a 28-year-old female volunteer. Line scan diffusion image with diffusion coding (left, b = 650 s/mm2) and without diffusion coding (middle, b = 5 s/mm2) are shown together with the corresponding map of the mean diffusion coefficient (right). No ghosting artifacts or missing lines are apparent. Note the strong diffusion difference between the intervertebral disks and the vertebral bodies.
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FIG 2. Contrast changes and corresponding signal intensities over the range of b values used for representative regions of interest for different levels of diffusion weighting.
A, Three of 10 line scan diffusion images with different levels of diffusion weighting. From left to right: line scan diffusion images with a diffusion attenuation of b = 5672, and 3005 s/mm2 and corresponding map of the mean diffusion coefficients. Although the signal intensity in the intervertebral disks decays rapidly, the signal intensity in the vertebral bodies remains almost unchanged.
B, Course of diffusion-weighted signal for region of interest measurements in an intervertebral disk and a vertebral body. The plot shows the mean values for the region of interest measurements at different b levels for vertebral body (asterisks), nucleus pulposus (squares), and annulus fibrosus (triangles) and the corresponding fitted models (continuous curves). The effect of the non-Gaussian noise distribution of magnitude MR images is best seen on the fit for nucleus pulposus and annulus fibrosus. Instead of continuous signal decay, the curve levels off asymptotically. A conventional least squares fit would be strongly biased toward lower values of diffusion if the high b-value data points had been used.
C, Magnified view of the vertebral segment shown in A shows example regions that were considered for region of interest analyses of vertebral body (VB), nucleus pulposus (NP), and annulus fibrosus (AF). A, anterior; P, posterior; H, head; F, feet.
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FIG 3. Line scan diffusion images of one of the female patients with multiple acute histologically proved benign compression fractures in the thoracic spine (T8 [arrow, mean diffusivity = (1376 ± 264) x 10-6 mm2/s]; T10 [curved arrow]; and the compression fracture of the end plate of T5 [arrowhead, mean diffusivity = (829 ± 59) x 10-6 mm2/s]). Two separate imaging sessions were required to cover the entire spine of this patient because of kyphosis. To image the upper part of the spine, the imaging plane had to be rotated around the left-right axis so that the readout dimension of the line scan diffusion image aligns with the spinal column.
A, Isotropic diffusion-weighted image of the upper spine.
B, Unweighted image of the upper spine.
C, Map of the mean diffusion coefficient of the upper spine.
D, Isotropic diffusion-weighted image of the lower spine.
E, Unweighted image of the lower spine.
F, Map of the mean diffusion coefficient of the lower spine.
G, Corresponding conventional sagittal T1-weighted spin-echo image. The extent of pathologic signal alteration is consistent with that seen on the line scan diffusion images. Only faint signal intensity changes are seen in the fractured end plate of T5 (arrowhead), whereas on the map of the mean diffusion coefficient, the abnormalities in this vertebral body can be more clearly delineated. The signal intensity changes of the compression fracture in T8 (arrow) correspond with hyperintensities in the diffusion coefficient maps.
H, Corresponding conventional sagittal T1-weighted spin-echo image with fat suppression. A biopsy specimen was obtained in the center of the lesion in T10 (curved arrow). The mean diffusivity was markedly higher [(1972 ± 145) x 10-6 mm2/s] than that of the anterior aspect [(1764  287)  10-6 mm2/s]. The extent of pathologic signal intensity alteration is consistent with that seen on the line scan diffusion images.
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FIG 4. Line scan diffusion images (A–C) and fast spin-echo image (D) of an 85-year-old female patient with multiple hemangioma lesions at almost every level in the spine. The mean diffusivity measured in these lesions ranged from 1019 x 10-6 mm2/s to 1321 x 10-6 mm2/s. At the T12 level (arrows), vertebroplasty had been performed previously by injection of polymethylmethacrylate and, as expected, the diffusion coefficient was low (204 ± 123 x 10-6 mm2/s).
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FIG 5. Sets of line scan diffusion images of a 48-year-old female volunteer. The images were used for comparison of off-resonance effects.
A, Receiver bandwidth of ± 15.63 kHz.
B, Bandwidth of ± 7.8 kHz. Despite the better signal-to-noise ratio, the quality of the images with lower signal-to-noise ratios clearly suffers from strong water-fat shift artifacts. In both sets, diffusion-weighted (left column) and unweighted (middle column) images are shown with their corresponding maps of mean diffusivity (right column).
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