Percutaneous radiofrequency ablation near large vessels in beagle livers: the impact of time and distance on the ablation zone

Figures & data

Figure 1. Evaluation of the distance between the radiofrequency ablation (RFA) electrode tip and large vessel, ablation time and specimens/images of different groups. Tissue specimens obtained after euthanizing beagles at 24 h after RFA (first column), conventional ultrasound before RFA (second column), color Doppler ultrasound before RFA (third column) and post-RFA ultrasound (fourth column) are shown. The first row represents a distance of 0.5 cm from the tip of the RFA electrode to a large vessel with the ablation time set at 3 min (3 min 0.5 cm). The second row shows the electrode tip near the large vessel with the ablation time set at 3 min (3 min 0 cm). The third row represents a distance of 0.5 cm from the tip of the RFA electrode to a large vessel with the ablation time set at 5 min (5 min 0.5 cm). The fourth row represents that the electrode tip was near the large vessel with the ablation time set at 5 min (5 min 0 cm).

Table 1. Comparison of the ablation zones among different groups.

Measurement	Group A 3 min 0.5 cm	Group B 3 min 0 cm	Group C 5 min 0.5 cm	Group D 5 min 0 cm	p
Number	16	16	13	16
Distance^a (cm)	2.98 ± 0.56	2.85 ± 0.43	3.77 ± 0.97	3.46 ± 0.83	.008
Vessel diameter (cm)	0.33 ± 0.05	0.36 ± 0.05	0.32 ± 0.03	0.34 ± 0.04	.203
Vessel wall thickness (mm)	0.71 ± 0.19	0.66 ± 0.16	0.74 ± 0.19	0.79 ± 0.29	.386
Dl (cm)	2.85 ± 0.34	2.47 ± 0.19	3.02 ± 0.21	2.89 ± 0.26	<.001
Dw (cm)	1.66 ± 0.20	1.33 ± 0.14	1.96 ± 0.23	1.67 ± 0.29	<.001
Dz (cm)	1.96 ± 0.08	1.89 ± 0.07	2.20 ± 0.21	2.23 ± 0.18	<.001
Dw/Dz	0.85 ± 0.09	0.71 ± 0.06	0.89 ± 0.03	0.75 ± 0.09	<.001
Area (cm^2)	4.14 ± 0.71	2.93 ± 0.14	5.13 ± 0.74	4.10 ± 0.77	<.001

Data are shown as mean ± standard deviation.

^a Distance between the ablation probe tip and liver surface.

D_l: distance between the proximal and distal edges of the ablation zone following the ablation needle tract on the specimens.

D_w: distance perpendicular to the D_l on the slice.

D_z: distance perpendicular to D_l and D_w in an additional plane along the electrode tracts.

The D_w/D_z ratio indicates the morphology of the ablation zone. The closer the ratio to 1, the more circular the shape.

Figure 2. Comparison of protocols with a fixed time. The graph depicts the mean (± standard deviation) distance and area of the two groups. (A) With the time fixed at 3 min, the ablation length, width, depth and area created using a distance of 0.5 cm were significantly larger than those created using a distance of 0 cm (length: p = .001; width: p < .001; depth: p = .019; area: p < .001). (B) With the time fixed at 5 min, there was no significant difference when the distances were 0 cm and 0.5 cm (length: p = .140; depth: p = .611). The ablation width and area when the distance was 0 cm were significantly smaller than when the distance was 0.5 cm (width: p = .007; area: p = .001). ***p < .001. **p < .01. *p < .05.

Figure 3. Comparison of protocols with a fixed distance. The graph depicts the mean (± standard deviation) distance and area of the two groups. (A) At a fixed distance of 0 cm, the statistically significant differences were observed when the ablation times were 3 min and 5 min (length: p < .001; width: p < .001; depth: p < .001; area: p < .001). (B) At a fixed distance of 0.5 cm, the ablation length created with an ablation time of 3 min was not statistically different from that created with an ablation time of 5 min (length: p = .112). The ablation width and ablation zone created with an ablation time of 5 min were significantly larger than those created with an ablation time of 3 min (width: p = .001; depth: p = .002; area: p = .001). ***p < .001. **p < .01. *p < .05.

Figure 4. Comparison of the ablation zones in the specimens and hematoxylin and eosin tissue taken from different areas using a light microscope (×200). (A) Normal liver. (B) Vascular wall. (C) Central ablation zone. (D) Peripheral ablation zone. All specimens were obtained 24 h after ablation.

Figure 5. Pathological staining and TUNEL immunofluorescence staining results of beagle liver vessels. Results of pathological staining with hematoxylin and eosin (HE), staining with DAPI (blue), co-stained with TUNEL (green representing apoptosis) and merging (blue and green) (from the first column to the fourth column) (×50). The vascular wall cells are still well-formed in (A–D). The vascular wall is damaged in (E–H). The thrombus is observed in (I–L).

Table 2. Pathological evaluation of the vessels.

	Number	Vascular wall injury (%)	p	Thrombus (%)	p
Time			.153		1.000
3 min	32	5 (15.6)		1 (3.1)
5 min	29	9 (31.0)		1 (3.4)
Distance^a			.003		.493
0.5 cm	29	2 (6.9)		0 (0)
0 cm	32	12 (37.5)		2 (6.3)

^a Distance between the radiofrequency ablation electrode tip and large vessels.