Thanks for an excellent video! Regarding VBM and the Jacobians: When we create the GM_mod volume and hence correct for any expansion or contraction of GM by multiplying with the jacobians, is that the same as controling for head-size? Other videos on VBM reccomend using total intercerebral volume as a covariate. Isn't that the point of using jacobians? Or is that more a "local" correction and not a "global" correction? Thanks!
Hi Robin, This is a good question! Like you said in the final sentence, I consider jacobian modulation to be a more local correction compared to dividing everything by overall intracranial volume; so I treat them as two distinct adjustments. It is also worth noting that registration would change with varying brain sizes (not head size particularly), which would in turn influence the jacobian modulations indirectly.
Thanks for an excellent video!
Regarding VBM and the Jacobians: When we create the GM_mod volume and hence correct for any expansion or contraction of GM by multiplying with the jacobians, is that the same as controling for head-size? Other videos on VBM reccomend using total intercerebral volume as a covariate. Isn't that the point of using jacobians? Or is that more a "local" correction and not a "global" correction?
Thanks!
Hi Robin, This is a good question!
Like you said in the final sentence, I consider jacobian modulation to be a more local correction compared to dividing everything by overall intracranial volume; so I treat them as two distinct adjustments. It is also worth noting that registration would change with varying brain sizes (not head size particularly), which would in turn influence the jacobian modulations indirectly.