Fig. 6.

Pixel to background ${\mu }_a$ contrast ratio shown without spatial interpolation measured using 808 nm with the probe at ${\rho }_8$. (a) The dashed squares enclose high-contrast datapoints from the two pinholes seen in the high-density dataset. (b) For the left pinhole, high-contrast datapoints fell between the 1-cm spaced grid points, resulting in only the right pinhole appearing in the sparse sampled image. The dashed circle denotes a high-contrast datapoint from the right pinhole which was successfully captured by sparse sampling. However, only a single point at the far edge of the pinhole contrast region was captured. This resulted in an apparent translation of the pinhole position in the sparse sampled data, with the actual position of the pinhole more closely represented by the higher density data. (c) The sampling grid points can be shifted ($-0.3\mathrm{cm}$, $-0.3\mathrm{cm}$) to capture the left pinhole. However, doing so results in suboptimal sampling of the right pinhole as well as the inclusion edges. This further emphasizes that the placement of a sparse sampling grid can return highly variable images.