Linear scaling : potentially inaccurate positioning of individual spinal levels

[sandrinebedard]

Description

We are currently working to update the spinal levels files in the PAM50 (see #3 ).

Philips Lab created updated spinal levels files : Philips Lab spinal level files from the Mendez (2021).

The measures used from Mendez: Segment length at dorsal column entry

To bring the spinal level positioning in the PAM50 space, linear scaling between length of Mendez and the length of pixels between C2 and L5 in the PAM50 was done.

However, the spinal segments length doesn't vary linearly along the spinal cord. Using the length between C2-L5 won't necessarly be accurate for all levels to get the position in the PAM50 space.

New spinal segment positions vs before on PAM50

Here are the different positions of the center of each segment with the updated spinal levels vs before:

Level	Mendez (Slices in I-->S)	Old (Slices in I-->S)	Difference
C2	954	945	9
C3	927	927	0
C4	899	891	8
C5	868	857	11
C6	839	826	13
C7	812	794	18
C8	787	757	30
T1	760	713	47
T2	729	668	61
T3	695	622	73
T4	655	572	83
T5	608	522	86
T6	558	471	87
T7	507	417	90
T8	454	365	89
T9	403	310	93
T10	351	251	100
T11	301	194	107
T12	259	169	90
L1	221
L2	188
L3	162
L4	137
L5	114

Examples

Here are some examples:
Mendez --> yellow; Old --> blue

Segment C3

The center position is the same. We see the rootlet in the axial view.

Segment C4

Axial view at the center of the segment for the new and old spinal segment


--> Not much difference of the appearance of the spinal rootlet

Segment C5

Axial view at the center of the segment for the new and old spinal segment


--> We can better see the spinal rootlet in the old spinal segment file

Segment T6

Segment T10

Suggestion

We need a surrogate measure to get the position of each spinal segment that we can relate to the PAM50.

Measures that relate the vertebrae to the spinal rootlets could be relevant here since we can position it for each level in the PAM50.

• Intervertebral foramen to rostral rootlet
  

• Intervertebral foramen to caudal rootlet
  
  This would require identifying the intervertebral foramen on the PAM50 template