Information Technology Reference
In-Depth Information
Fig. 8 Example of virtual templating and volume render representation at one vertebral segment.
a Templating of pre-operative CT scan; b
“
reverse templating
”
of post-operative CT (high
intensity metal implants are visible in the image)
counterpart in the pre-operative image (Fig.
9
), as knowledge of the voxel intensity
of the displaced bone segment is required. Given the rigid nature of individual
vertebrae, an intensity-based rigid registration was used, followed by minimal
manual adjustment. Following registration, the intensity
area product was com-
puted for each pedicle bone segment displaced by the post-operative implant.
Table
1
summarizes the implant dimension (diameter and length), the Fastening
Strength, computed displaced bone volume, as well as the mean voxel intensity
across the displaced bone volume, for both the pre-operative planned and post-
operative procedure. Since the assessment consist of the comparison of homologous
implants in both the retrospective plans and procedures with respect to different
parameters (implant dimensions, displaced bone volume, mean voxel intensity of
—
Fig. 9 Registration of post-operative
“
reverse plan
”
(c) to the pre-operative plan (a) for
assessment of displaced bone volume to estimate Fastening Strength. The planned and post-
operatively inserted pedicle screws can be seen in the fused image (b)
Table 1 Summary of planned versus post-operative measurements for implant diameter and
length, as well as Fastening Strength, displaced bone volume, and mean voxel intensity of
displaced bone volume
Measure (units)
Pre-operative plan
Post-procedure assessment
Screw diameter (mm)
5.5
±
1.2
6.9
±
0.8
Screw length (mm)
40.0
±
2.0
47.1
±
5.0
Fastening strength (mm
3
10
7
10
7
10
7
10
7
·
HU)
3.6
×
±
0.7
×
4.7
×
±
0.8
×
Displaced bone volume (mm
3
)
2.5
×
10
3
±
0.4
×
10
3
3.3
×
10
3
±
0.5
×
10
3
Mean bone intensity (HU)
164
±
65
167
±
59
