From the FS output wmparc.mgz I could select and merge the following labels to define my ROI
parsorbitalis [4019, 3019]
parstriangularis [4020, 3020]
lateralorbitofrontal [4012, 3012]
medialorbitofrontal [4014, 3014]
rostralmiddlefrontal [4027, 3027]
frontalpole [4032, 3032]
superiofrontal [4028, 3028]
caudalmiddlefrontal [4003, 3003]
paracentral [4017, 3017]
parsopercularis [4018, 3018]
postcentral [4022, 3022]
precentral [4024, 3024]
rostralantcingulate [4026, 3026]
However, a non-negligible portion of the subcortical frontal WM is classified as unsegmented WM [5001, 5002] by FS. Would you recommend any other FS output or template/atlas that I could use for the purpose of measuring MRI signal in the frontal WM?