Table 3.

mTREs and range, in mm, of initial alignment between landmarks (obtained by rigidly registering ultrasound images using tracking information) and after SIFT-Rank-based affine and SIFT-Rank-based thin-plate spline

Patient	Data	SIFT feature correspondences	Initial	After SIFT-based Affine	After SIFT-based TPS
1	Pre-dura/post-dura	124	3.38 (2.44–4.38)	1.16 (0.34–3.29)	1.12 (0.07–3.00)
	Pre-dura/pre-iMR	123	5.33 (4.08–7.35)	1.77 (0.36–3.40)	1.43 (0.18–3.22)
	Post-dura/pre-iMR	81	3.08 (1.04–4.79)	1.40 (0.51–3.10)	1.23 (0.29–2.81)
2	Pre-dura/post-dura	57	2.11 (1.37–3.41)	1.39 (0.42–2.63)	1.20 (0.30–2.21)
	Pre-dura/pre-iMR	71	3.88 (2.11–8.23)	2.36 (0.69–7.61)	1.95 (0.58–7.58)
	Post-dura/pre-iMR	22	3.71 (1.66–8.18)	2.87 (0.94–6.96)	2.48 (0.56–6.17)
3	Pre-dura/post-dura	84	2.62 (1.11–3.55)	1.49 (0.89–2.67)	1.43 (0.73–2.56)
4	Pre-dura/post-dura	14	2.50 (0.17–4.28)	2.40 (0.12–4.10)	2.12 (0.10–3.33)
5	Pre-dura/pre-iMR	49	2.36 (0.60–4.00)	2.20 (0.56–3.75)	2.19 (0.35–2.34)
6	Post-dura/pre-iMR	98	3.32 (1.28–4.74)	1.66 (0.41–3.39)	1.13 (0.33–3.16)
7	Pre-dura/post-dura	30	3.11 (1.82–4.85)	1.68 (0.62–2.95)	1.49 (0.31–2.04)
	Pre-dura/pre-iMR	12	3.70 (2.43–5.16)	1.71 (0.56–3.92)	1.69 (0.54–3.63)
	Post-dura/pre-iMR	46	2.00 (0.79–3.14)	1.25 (0.36–2.54)	1.19 (0.22–2.13)
8	Pre-dura/post-dura	37	4.31 (1.09–5.81)	1.67 (0.62–3.36)	1.06 (0.54–3.12)
9	Pre-dura/post-dura	151	3.01 (0.83–4.12)	1.54 (0.75–2.31)	1.32 (0.39–2.22)
	Pre-dura/pre-iMR	64	3.56 (1.80–5.84)	1.52 (0.56–2.77)	1.42 (0.48–2.51)
	Post-dura/pre-iMR	123	3.22 (1.55–6.22)	1.76 (0.76–3.21)	1.74 (0.62–3.19)
Grand mean			3.25 (1.54–5.18)	1.75 (0.56–3.54)	1.54 (0.39–3.25)

Each cell contains the mean Euclidean distance (mm) between the 10 tag sets and the range