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Intervertebral foramen to caudal and rostral rootlets to update spinal levels: limitations #12

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@sandrinebedard

Description

@sandrinebedard

Description

We want to update the spinal levels in teh PAM50 using the measures from the Mendez 2021 paper. We discussed the potential limitations in #10 of placing direclty the segment length using linear scaling. Instead, we propose to use a surrogate measure for each level to find the center of each segment.

The following distance were provided from the Mendez 2021 paper:

  • Intervertebral foramen -> caudal rootlet at dorsal entry
  • Intervertebral foramen -> rostral rootlet at dorsal entry

The intervertevral foramen was measured the following way:

This parameter was obtained by measuring the distance between the most caudal point of each intervertebral foramen to the rostral rootlet of its corresponding dorsal root at the point of dorsal column entry using a slide caliper (Mendez, 2021)

Identifying the intervertebral foramen in the PAM50

Images from Mendez 2021

image

image

MRI Labels

image

How to label caudal point of the foramen (awaiting validation by a specialist):

  • Get the level of the first frame (rostral) with spine segmentation (in the foramen region) for each spine level , take the most lateral point and go up 1 slice. (so the frame over the frame on the image)
    image
    File with labeled foramen

Distances in the PAM50

Without standard deviation
With standard deviation

  1. Compute the distance from the spinal cord centerline shifted to adjust in xy plane using the half width across dorsal
    columns

image

  1. Find the closest distance corresponding to the measures from Mendez 2021 for rostral and caudal rootlet

RESULTS

image
We see that level 4, the caudal rootlet is at the same z than the intervertebral foramen.

The caudal distances are too small to be placed in the PAM50 space: the caudal entry is placed at the same slice as the intervertebral foramen.

Expected behaviour:

image

**Current behaviour: **
image

Bellow are some potential causes to explain this behaviour.

Potential limitations

1. Label in MRI differs than in ex vivo measurements

The ex vivo were measured on the dorsal rootlets, but the intervertebral foramen is more anterior. We might not be labeling the right location of the foramen in MRI images compared to the ex vivo measures.

2. Shrinking of ex vivo spinal cords (fixed)

  • Fixed spinal cord experience some shrinking, resulting in smaller measures

3. Mean age is 90 y.o.

4. Height of subjects: 162 cm

5. Mean and std only on n=9

6. Straightening adds variablity and inacuracy in the PAM50 template

  • Adds variability to the interverterbral foramen location in the PAM50 template.

Other

  • Other approaches using fMRI (see Nawal Kinany at EPFL)

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