# Assessment of fNIRS Signal Processing Pipelines: Towards Clinical Applications
## 3 Results
### Step and Overall ERD Assessment  
Table 2 shows the percentage of ERD relevant to each method and each step: Table 2a) displays the percentage of ERD referred to in the specific step related to its input value; Table 2b) provides the cumulative percentage of the ERD effect shown as the rest energy compared to the unprocessed \(\Delta OD\) signal (i.e., raw signal = 100%). The HYA group statistics, as the mean (std) across subjects and measurement channels, is reported. Table 2a clearly demonstrates the large differences in signal cleaning through single steps among the different methods. The highest impact in the MA reduction step was found in the global approaches of TDRR and Wavelet. A lower, yet large impact was found in Hybrid-MARA, with the lowest values in MARA. As for the last method, less impact was found in MC variants compared to the SC original algorithms. This result is counterintuitive, since the MC MA correction spanned larger time windows. However, this can be attributed to some baseline drift amplification due to local MARA corrections, which is less critical when longer windows are corrected after the MC MA detection logic. A significantly larger final power decrease was shown by both global methods: maximal and significant in TDRR; lesser yet noticeable in the wavelet method. Most likely, global methods, fixing a data-driven normal range, are also compelled to cut out the tails (i.e., out of the fixed 90 or 95 central percentiles) of standard components while canceling out the truly artifactual outliers. This eventually reduces the output signal power. However, it does not appear to negatively affect the final SNR.  
Considering the last column of the cumulative percentage of ERD effects shown in Table 2b as the output of the whole preprocessing pipeline, two aspects are impressive: (i) the huge decrease of power finally obtained, which saves only about 5% of the raw signal; (ii) the modest differences found in the final outcomes of the eight pipelines, which further reassure us that essentially different MA approaches converge to similar outcomes, if followed by proper BPF and PCA steps. Conversely, large differences are found in  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & \multicolumn{4}{c}{**(a) Single Step ERD [\%]**} & \multicolumn{4}{c}{**(b) Cumulative ERD [\%]**} \\ \cline{2-7}  & \(\Delta OD_{raw}\) to \(\Delta OD_{MA}\) & \(\Delta OD_{MA}\) to \(\Delta OD_{BPF}\) & \(\Delta OD_{BPF}\) to \(\Delta OD_{PCA}\) & \(\Delta OD_{MA}\) & \(\Delta OD_{BPF}\) & \(\Delta OD_{PCA}\) \\ \hline SC-MARA-spline & \(-27.76\) (17.12) & \(-73.91\) (10.84) & \(-73.68\) (18.44) & 72.23 (17.12) & 18.84 (8.92) & 5.79 (8.22) \\ MC-MARA-spline & \(-11.09\) (26.09) & \(-80.30\) (10.26) & \(-73.61\) (18.39) & 88.90 (26.09) & 17.37 (9.64) & 5.37 (7.79) \\ SC-MARA+PCA & \(-15.13\) (23.40) & \(-76.64\) (11.02) & \(-73.55\) (18.40) & 84.86 (23.40) & 19.26 (8.85) & 5.91 (8.19) \\ MC-MARA+PCA & \(-5.04\) (31.95) & \(-79.14\) (9.88) & \(-73.71\) (18.46) & 94.95 (31.95) & 19.24 (8.31) & 5.79 (7.72) \\ HybridMARA- & \(-30.96\) (23.67) & \(-73.01\) (12.73) & \(-73.95\) (18.49) & 69.03 (23.67) & 17.93 (9.29) & 5.58 (8.26) \\ HybridMARA- & \(-29.42\) (18.06) & \(-72.83\) (11.94) & \(-74.10\) (18.52) & 70.57 (18.06) & 18.87 (9.12) & 5.77 the partial ERD% outcomes described by Table 2a, which trivially reflects the different single-step impacts.