Inter-observer reliability in ultrasound measurement of benign thyroid nodules in the follow-up of radiofrequency ablation: a retrospective study

Figures & data

Table 1. Clinical characteristics of patients before RFA.

Characteristics	Data
No. of patients	76
Age (years)	46.53 ± 10.21 (18–73)
Sex (F/M)	67/9 (88.16/11.84)
No. of nodules	88
No. of patients with number of treated nodules
One nodule	66 (86.84)
Two nodules	8 (10.53)
Three nodules	2 (2.63)
Mean diameter (cm)	2.90 ± 1.46 (1.10–6.40)
Initial volume (ml)	10.49 ± 14.87 (0.40–71.31)
<10 ml (N = 59)	2.81 ± 2.63 (0.40–9.41)
≥10 ml (N = 29)	26.11 ± 17.18 (10.13–71.31)

Values are presented as mean ± SD (range) or number of tumors (%).

Figure 1. US image of a 48-year-old female with a benign thyroid nodule. (a) Before RFA, US image showed a solid benign thyroid nodule located in the left thyroid lobe with an initial volume of 1.78 ml. (b) At 1 month after RFA, the volume of nodule was 0.98 ml and the VRR was 44.65%. (c) At 36 months after RFA, nodule shrunk to 0.21 ml and the VRR was 88.05%.

Figure 2. The Bland–Altman plots of volume by the observers during the follow-up period. The Bland–Altman plots of volume measured by the two observers at 1, 3, 6, 12, 24 and 36 months after RFA are shown from (a) to (f). Logarithmic transformation was used to show the data. The x-axes showed the log means of volume measurements by the observers. The y-axes showed the log differences between the observers. Solid lines were the mean difference (bias). Top and bottom dashed lines correspond to upper and lower margins of 95% limits-of-agreement (LOA).

Figure 3. The Bland–Altman plots of VRR by the observers during the follow-up period. The Bland–Altman plots of VRR measured by the two observers at 1, 3, 6, 12, 24 and 36 months after RFA are shown from (a) to (f). Logarithmic transformation was used to show the data. The x-axes showed the log means of VRR measured by the observers. The y-axes showed the log differences between the observers. Solid lines were the mean difference (bias). Top and bottom dashed lines correspond to upper and lower margins of 95% limits-of-agreement (LOA).

Table 2. Volume and VRR measured by two observers at each follow-up period of RFA.

Time (months)	Volume (ml)			VRR (%)
	Observer A	Observer B	p Value	Observer A	Observer B	p Value
1	4.76 ± 6.66	4.78 ± 6.72	.170	52.66 ± 18.30	52.64 ± 18.06	.757
3	2.30 ± 3.73	2.30 ± 3.70	.156	73.13 ± 17.46	73.14 ± 17.30	.250
6	2.82 ± 5.50	2.83 ± 5.55	.107	82.53 ± 12.51	82.58 ± 12.52	.423
12	2.70 ± 6.37	2.71 ± 6.40	.306	84.86 ± 18.58	84.86 ± 18.58	.796
24	2.55 ± 7.07	2.55 ± 7.04	.236	88.36 ± 15.60	88.25 ± 15.66	.079
36	0.33 ± 0.68	0.33 ± 0.67	.959	94.30 ± 8.85	94.28 ± 8.80	.569

Values are presented as mean ± SD.

Table 3. Inter-observer reliability of volume and VRR during the follow-up by the Bland–Altman analysis.

	Log volume		Antilogarithms		Log VRR		Antilogarithms
	Mean difference	LOA	Mean difference	LOA (width)	Mean difference	LOA	Mean difference	LOA (width)
Total
1 month	–0.0039	–0.0738 to 0.0661	0.9961	0.9288–1.0683 (0.1395)	–0.0006	–0.0470 to 0.0459	0.9994	0.9541–1.0469 (0.0929)
3 months	–0.0013	–0.0896 to 0.0869	0.9987	0.9143–1.0908 (0.1765)	–0.0008	–0.0336 to 0.0320	0.9992	0.9670–1.0325 (0.0655)
6 months	0.0016	–0.1257 to 0.1289	1.0016	0.8819–1.1376 (0.2557)	–0.0006	–0.0219 to 0.0207	0.9994	0.9783–1.0209 (0.0426)
12 months	–0.0028	–0.1394 to 0.1338	0.9972	0.8699–1.1432 (0.2733)	0.0002	–0.0179 to 0.0183	1.0002	0.9823–1.0184 (0.0362)
24 months	–0.0023	–0.1441 to 0.1395	0.9977	0.8658–1.1497 (0.2839)	0.0019	–0.0119 to 0.0156	1.0019	0.9882–1.0157 (0.0276)
36 months	–0.0031	–0.1659 to 0.1598	0.9969	0.8471–1.1733 (0.3261)	0.0002	–0.0091 to 0.0096	1.0002	0.9909–1.0096 (0.0187)
<10 ml
1 month	–0.0022	–0.0832 to 0.0789	0.9978	0.9201–1.0821 (0.1620)	–0.0032	–0.0568 to 0.0503	0.9968	0.9448–1.0516 (0.1068)
3 months	0.0014	–0.1006 to 0.1033	1.0001	0.9043–1.1088 (0.2045)	–0.0019	–0.0390 to 0.0352	0.9981	0.9618–1.0358 (0.0740)
6 months	0.0028	–0.1449 to 0.1505	1.0028	0.8651–1.1624 (0.2973)	–0.0013	–0.0255 to 0.0228	0.9987	0.9748–1.0231 (0.0482)
12 months	–0.0015	–0.1646 to 0.1616	0.9985	0.8482–1.1754 (0.3272)	–0.0010	–0.0208 to 0.0188	0.9990	0.9794–1.0190 (0.0396)
24 months	0.0019	–0.1673 to 0.1711	1.0019	0.8459–1.1866 (0.3470)	0.0036	–0.0117 to 0.0190	1.0036	0.9883–1.0192 (0.0308)
36 months	–0.0062	–0.1855 to 0.1732	0.9939	0.8307–1.1891 (0.3584)	0.0004	–0.0099 to 0.0106	1.0004	0.9902–1.0106 (0.0205)
≥10 ml
1 month	–0.0079	–0.0401 to 0.0244	0.9921	0.9607–1.0246 (0.0640)	0.0057	–0.0127 to 0.0241	1.0057	0.9874–1.0244 (0.0369)
3 months	–0.0077	–0.0468 to 0.0314	0.9923	0.9542–1.0319 (0.0777)	0.0019	–0.0167 to 0.0205	1.0019	0.9834–1.0207 (0.0373)
6 months	0.0012	–0.0641 to 0.0617	0.9988	0.9379–1.0637 (0.1257)	0.0007	–0.0146 to 0.0159	1.0007	0.9855–1.0160 (0.0305)
12 months	–0.0047	–0.0875 to 0.0780	0.9953	0.9162–1.0811 (0.1649)	0.0020	–0.0127 to 0.0167	1.0002	0.9874–1.0169 (0.0295)
24 months	–0.0075	–0.1102 to 0.0953	0.9926	0.8957–1.1000 (0.2043)	–0.0003	–0.0107 to 0.0101	0.9997	0.9894–1.0102 (0.0208)
36 months	0.0069	–0.1029 to 0.1168	1.0069	0.9022–1.1239 (0.2217)	–0.0002	–0.0071 to 0.0067	0.9998	0.9929–1.0067 (0.0138)

Figure 4. The Bland–Altman plots of volume in the regrowth group by the observers during the follow-up period. The Bland–Altman plots of volume in the regrowth group measured by the two observers at 1, 3, 6, 12, 24 and 36 months after RFA are shown from (a) to (f). Logarithmic transformation was used to show the data. The x-axes showed the log means of volume measurements by the observers. The y-axes showed the log differences between the observers. Solid lines were the mean difference (bias). Top and bottom dashed lines correspond to upper and lower margins of 95% limits-of-agreement (LOA).

Table 4. Inter-observer reliability of volume in the non-regrowth group and regrowth group during the follow-up by the Bland–Altman analysis.

	Log volume		Antilogarithms
	Mean difference	LOA	Mean difference	LOA (width)
Non-regrowth group
1 month	–0.0050	–0.0803 to 0.0703	0.9950	0.9228–1.0728 (0.1500)
3 months	0.0018	–0.0959 to 0.0994	1.0018	0.9085–1.1046 (0.1960)
6 months	0.0041	–0.1410 to 0.1492	1.0041	0.8685–1.1609 (0.2924)
12 months	–0.0076	–0.1530 to 0.1378	0.9924	0.8581–1.1477 (0.2896)
24 months	0.0026	–0.1497 to 0.1549	1.0026	0.8610–1.1675 (0.3066)
36 months	0.0061	–0.1907 to 0.2028	1.0061	0.8264–1.2248 (0.3984)
Regrowth group
1 month	–0.0012	–0.0378 to 0.0402	1.0012	0.9629–1.0410 (0.0781)
3 months	–0.0121	–0.0467 to 0.0225	0.9880	0.9544–1.0227 (0.0684)
6 months	–0.0058	–0.0562 to 0.0447	0.9942	0.9453–1.0457 (0.1004)
12 months	0.0098	–0.1012 to 0.1208	1.0099	0.9038–1.1284 (0.2246)
24 months	–0.0192	–0.1163 to 0.0779	0.9810	0.8902–1.0810 (0.1908)
36 months	–0.0198	–0.0938 to 0.0542	0.9804	0.9105–1.0557 (0.1452)