Measuring the Axial Rotation of Lumbar Vertebrae in Vivo with MR Imaging
Victor M. Haughtona,
Baxter Rogersb,
M. Elizabeth Meyerandb and
Daniel K. Resnickc
a Department of Radiology, University of Wisconsin, Madison
b Department of Medical Physics, University of Wisconsin, Madison
c Department of Neurosurgery, University of Wisconsin, Madison
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FIG 1. Table insert that provides clockwise and counterclockwise rotation at the lumbar spine. The insert is placed on the MR gantry. The patient is positioned on the insert with head and thorax on the longer segment and hips on the shorter segment. The segments are on rollers that permit them to rotate 8° in a clockwise and a counterclockwise direction, with the axis of rotation centered at a point 10 cm above the segment, so that the spine is at the isocenter of rotation.
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FIG 2. A–G, Images illustrate the application of the pixel shift program to measure rotation. The first step is to choose a vertebral level from each of the image sets with the thorax rotated clockwise (A) and counterclockwise (B). Note the vertical reference line to the left of each image. The next step is to choose the pivot point and region of interest for the pixel shift analysis (crosshairs and circular cursor in A and B). All voxels outside the cursor are excluded from analysis of motion (C and D). Alignment of the one image with the other before pixel shifting is illustrated by a subtraction image (E), which reveals a mismatch. When the one image is rotated with respect to the other to maximize the correlation, the angle of rotation (illustrated by the reference lines in F) is recorded. Alignment of the images after rotation is illustrated by a subtraction image (G), which shows no mismatch for the vertebral bodies.
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FIG 3. Sagittal T2-weighted image in a 29-year-old woman with chronic back pain. Intervertebral disks at L4–L5 and L5–S1 have diminished height, diminished signal intensity, and bulging of the posterior anulus fibrosus. No herniations are evident. Diskography subsequently showed concordant pain at the L4–L5 level only. The rotations were 0.3° at L1–L2, 1.3° at L2–L3, -0.1° at L3–L4, 2.2° at L4–L5, and 1.9° at L5–S1.
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FIG 4. Average rotation occurring at the five lumbar levels in the five control subjects as the gantry table is rotated left and right.
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FIG 5. Average rotation at the two lower lumbar levels with normal disks (gray line) and those with concordant pain (black line) elicited at diskography in group 3 patients.
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