Gray Surface (Under-)Expansion Failure
Using the laplace and converg figures in conjunction, one can confirm whether convergence is complete for gray surface expansion.
Below, is an example of good convergence. The laplace image is consistently green, without cool (blue/black) or warm (red/white) colors. The convergence image shows that by the final iterations, the left and right gray surfaces (blue and purple) asymptote at similarly low residuals.
In contract, below is an example of poor convergence of one hemisphere. The laplace image shows cool (blue/black) colors speckled throughout the right gray surface, suggesting it is underexpanded. The convergence image shows that by the final iterations, the right gray surface (purple) got ‘stuck’ and asymptoted at a much higher residual than the left gray surface (blue).
To be safe, all subjects showing incomplete convergence of the white and gray surfaces should be excluded from the study - even if there appears to be no subjectively detectable differences in cortical thickness.
Note: We are working actively to improve the convergence of the gray surface expansion.