Quantitative evaluation of frequency domain measurements in high density diffuse optical tomography

High Density Diffuse Optical Tomography (HD-DOT) as applied in fNIRS is largely limited to continuous wave (CW) data. Using a single modulation frequency, frequency domain (FD) HD-DOT has recently demonstrated better localisation of focal activation as compared to CW data. This study shows that combining CW and FD measurements and multiple modulation frequencies increases imaging performance in fNIRS. This work evaluates the benefits of multiple modulation frequencies, combining different frequencies as well as CW data in fNIRS HD-DOT. A slab geometry model was used, with activation occurring within a cortex layer. CW and FD measurements were simulated at 78, 141 and 203 MHz. The localization error, full width half maximum and effective resolution were evaluated. Across the average of the three metrics, at 141 MHz, FD performed 8.4% better than CW and the combination of CW and FD was 21.7% better than CW. FD measurements at 203 MHz performed 5% better than 78 MHz. Moreover, the three combined modulation frequencies of CW and FD performed up to 3.92% better than 141 MHz alone. This work shows that combining CW&FD measurements offer better performance than FD alone, with higher modulation frequencies increasing accuracy. Combining CW&FD measurements at multiple modulation frequencies yields the best overall performance.