1. A device comprising: a housing having a surface for coupling to a biological tissue; a first emitter and a second emitter coupled to the surface; a first detector and a second detector coupled to the surface, the first detector having a first output and the second detector having a second output, wherein the first emitter and the second detector are separated by a first dimension and the second emitter and the first detector are separated by approximately the first dimension, the first dimension selected to correspond with a region of interest in a first layer of the biological tissue, the first emitter and the first detector are separated by a second dimension and the second emitter and the second detector are separated by approximately the second dimension, the second dimension selected to correspond with an exclusion region in a second layer of the biological tissue, the first layer having a first depth below the surface and the second layer having a second depth below the surface, the first depth greater than the second depth; and a port coupled to the housing and configured to communicate at least one of the first output or the second output to a module.