Understanding the Nuances of Microwave Ablation for More Accurate Post-Treatment Assessment

Figures & data

Figure 1. Underlying mechanism of action and heat transfer for microwave ablation and radiofrequency ablation.

microwave ablation A & C; radiofrequency ablation B & D.

Table 1. Parameters that affect ablation volumes using microwave ablation and radiofrequency ablation technologies.

Parameter	MWA	RFA	Ref.
Tissue properties	+	++	[4,9,10]
Perfusion/heat sink	+	++	[1,6–8,11–13]
Ablation assessment	+	+	[8,14–16]
Imaging accuracy	++	+	[17–19]
Tissue contraction	++	+	[20–22]

+ Sensitive; ++ More sensitive.

MWA: Microwave ablation; RFA: Radiofrequency ablation.

Table 2. Summary of average percent differences of in vivo short and long axis diameters relative to ex vivo references for the AMICA and Certus PR Microwave Ablation Systems at various power and time settings.

Settings		Short axis diameter				Long axis diameter
Power (W)	Time (min)	In vivo (mm)	Ex vivo (mm)	% Diff. (rel. to ex vivo)	Avg % diff.	In vivo (mm)	Ex vivo (mm)	% Diff. (rel. to ex vivo)	Avg % diff.
AMICA
40	5	16.3	29	-43.8	-22.9 ± 17.4	36.3	36	0.8	-2.7 ± 16.9
40	15	32.6	42	-22.4		51.9	50	3.8
60	3	22.8	26	-12.3		33.6	35	-4.0
60	5	28.95	34	-14.9		45.4	48	-5.4
60	10	33.1^†	40	-17.3		56.35^†	54	4.4
60	15	48.6	48	1.3		75	61	23.0
80	10	21.7	46	-52.8		41.2	66	-37.6
80	15	43.5	55	-20.9		68.5	73	-6.2
Certus PR
65	5	20.05	26.4	-24.1	-23.2 ± 1.2	32.65	41.4	-21.1	-17.7 ± 4.8
65	10	23.75	30.6	-22.4		39.85	46.5	-14.3

† Taken as an average of 2 data points instead of 3 due to an outlier.

AMICA in vivo versus ex vivo: short axis diameter p = 0.105; long axis diameter p = 0.799 (α =0.05; two-tailed unpaired Student’s t-test).

Certus PR in vivo vesus ex vivo: short axis diameter p = 0.142; long axis diameter p = 0.223 (α =0.05; two-tailed unpaired Student’s t-test).

Figure 2. Comparison of in vivo and ex vivo reference ablation diameters for the AMICA and Certus PR applicators at a specified wattage with respect to time.

Figure 3. Ex vivo versus in vivo parameters that inherently make accurate comparisons a challenge with the use of MWA technology.

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