14. Role of magnetisation transfer in MS

Question 1

why use MTR in MS

Answer 1

• more quantitative measure that relates to tissue macromolecular structure
• sensitive to early disease abnormalities
• available on most scanners

Question 2

why is MTR reduced in MS lesion

Answer 2

loss of macromolecular proteins

Question 3

methods of analysis for MTR data

Answer 3

ROI
analysis of average MTR
histogram (looks at whole brain at all voxels can separate into regions)
voxel-based statistical analysis

Question 4

ROI analysis - why

Answer 4

used to study individual lesions or regions in the NAWM or GM to obtain info of regional changes in MTR

Question 5

what is MTR dependent on

Answer 5

macromolecular density of cell membranes and phospholipids

Question 6

what does low MTR show

Answer 6

reduced capacity to exchange magnetisation,

• GM MTR reductions are likely to reflect decreases in the size and no. of neurons and dendritic density
• WM MTR reductions are likely to reflect myelin changes/reduced axonal density

Question 7

what is MT sensitive to

Answer 7

myelin

Question 8

how can MT be used to probe myelin

Answer 8

• can access macromolecular protons indirectly by making measurements related to the amount of exchange taking place between the free and restricted pools
• can be used to monitor progression of disease and effects of treatment as it is sensitive to demyelination and remyelination

Question 9

what does the degree of signal loss in the presence of MT saturation depend on

Answer 9

density of macromolecules

Question 10

where are high MTR values found in WM and GM and overall which values are higher

Answer 10

WM - corpus callosum
GM - thalamus
MTR higher in WM

Question 11

what does reduced MTR mean

Answer 11

reduced capacity of free protons to exchange magnetization with the bound proton pool
MTR as low as 0 in CSF (no macromolecules)
low MTR reflects tissue damage

Question 12

what is MTR related with

Answer 12

loss axonal density within and outside lesions

and damage to myelin

Question 13

evidence of MTR sensitive to cortical demyelination in MS at 3T

Answer 13

use PLP staining on demyelinated and myelinated tissue

demyelinated cortical tissue has lower normalised MTR value

Question 14

MTR abnormalities in low MTR lesions

Answer 14

homogeneous enhancing lesions
enhancing lesions only onbserved with triple dose of Gd,
small

Question 15

very low MTR in lesions

Answer 15

ring lesions (old)
lesions enhance for 2/more months

Question 16

MTR abnornmal on T1

Answer 16

hypointense and isointense

Question 17

MTR abnormal on T2

Answer 17

hyperintense

Question 18

findings of periventricular gradient in MTR NAWM in CIS

Answer 18

gradient occurs early, independent of WM lesions, associated with subsequent risk of developing MS by 2 years, associated with subsequent risk of developing disability by 5 years

Question 19

what is MTR in inner/outer cortex

Answer 19

reduced

most in sp-ms

Question 20

challenges of MTR in spinal cord and optic nerve

Answer 20

motion
size of cord/nerve
fat/CSF contamination (coptic)

Question 21

in ppms, what is localised reduced GM MTR linked to

Answer 21

motor and cognitive disability