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Ready, Aim, Ablate: Liver Ablation Procedure Techniques

Author Taylor J. Robinson covers Ready, Aim, Ablate: Liver Ablation Procedure Techniques on BackTable VI

Taylor J. Robinson • Jan 28, 2022 • 137 hits

The treatment of liver lesions has advanced significantly in recent years with the development of microwave ablation. However, with innovation comes resistance to change and obstacles to enact that change. To build a successful microwave ablation program, interventional radiologists must garner the trust of their referring colleagues and adopt new liver ablation procedure techniques to optimize outcomes with microwave devices.

As an operator, two key challenges of the microwave liver ablation procedure are navigating the background liver parenchyma and determining the extent of lesion ablation possible without compromising liver function. Dr. Driss Raissi, an Interventional Radiologist at the University of Kentucky discusses how to navigate these challenges and shares his approach on the BackTable Podcast. We’ve provided the highlight reel in this article, and you can listen to the full podcast below.

The BackTable Brief

• A recent systematic review of microwave vs radiofrequency ablation devices for lesions over 3 cm showed no significant difference.

• Microwave ablation is most efficient in cirrhotic livers due to the high percentage of water molecules.

• When advantageous, Dr. Raissi divides up the procedure into two sessions, allowing him to achieve up to six ablations without liver failure.

• New ablation probes are based on ex-vivo data from healthy livers. Your ablation zones will vary in practice.

Image-guided microwave liver ablation procedure

Image provided by Dr. Christopher Beck.

Table of Contents

(1) Microwave vs Radiofrequency Ablation Outcomes for Liver Tumors

(2) The Influence of Liver Physiology on Liver Tumor Ablation Success

(3) Maximizing the Number of Liver Tumor Ablations: Beyond the Milan Criteria

Microwave vs Radiofrequency Ablation Outcomes for Liver Tumors

Referring physicians are generally less aware of microwave ablation than they are of radiofrequency ablation, as radiofrequency ablation has garnered more recognition as a comparable alternative to surgical resection up to 3.5-centimeter lesions. To establish trust from referring colleagues as a microwave operator, it’s important to be well-versed in the literature comparing microwave ablation to radiofrequency ablation outcomes. Recent studies have demonstrated that microwave ablation is non-inferior to radiofrequency ablation, as discussed in detail by Dr. Raissi and Dr. Beck in detail below.

[Dr. Christopher Beck]
Got it. And how about resources for some interventional radiologists out there? Are there any papers or sites that you've looked at that, as you were kind of getting your ablation practice off the ground that you thought these were good foundational papers that either help you participate in tumor boards or help educate referring docs?

[Dr. Driss Raissi]
I think one of the things that I've tried to do when dealing with through my referring colleagues is radiofrequency ablation is rather what's trusted out there. And people now know that radiofrequency ablation works so when you talk to surgeons and hepatologists, radiofrequency ablation is something that instills trust in them like, "Oh, okay. Yeah, we know about it. We know it's being compared to surgical resection. We know it's rather comparable up to 3.5 centimeter lesions." It's something that they now feel comfortable with. So your first step is to know the literature that compares microwave ablation to radiofrequency ablation. So you can sell microwave ablation as equivalent or non-inferior to radiofrequency ablation.

[Dr. Christopher Beck]

[Dr. Driss Raissi]
So there is a paper that I like which is in the International Journal of Hyperthermia and it's a rather recent one from 2019, which compares micro ablation to radiofrequency ablation in hepatocellular carcinoma. It's a systematic review and meta-analysis comparing both modalities. I think they looked at 14 studies, a combination of retrospective studies and control cohort studies for lesions specifically larger than three centimeters and it found no significant difference. You're not going to find papers out there comparing five centimeter radiofrequency ablation because it would inherently have its limitations and the local control starts to drop after 3.5.

Also, one of my favorite articles actually, recently actually, was in 2019 by de Jong et al, which was a systematic review of microwave ablation itself published in 2019 European Journal of Radiology. I think it was called, microwave ablation systematic review of various FDA approved devices. Why do I like that article and I use it in a lot of my presentations? Because you would learn a lot of the physical properties of microwave ablation. You'll learn that not all microwave ablation devices are made the same. Some have different properties than others. Some may be better than others.

And you will also see something very important. You will see how the performance in ex vivo models has nothing to do with in vivo models, which if you're a fellow, you're going to see all these excited numbers in ex vivo model so I'm like, "Oh gee, I can ablate at six centimeter lesion with one probe and be done." No, you won't.

Listen to the Full Podcast

Microwave Ablation for Liver Lesions with Dr. Driss Raissi on the BackTable VI Podcast)
Ep 158 Microwave Ablation for Liver Lesions with Dr. Driss Raissi
00:00 / 01:04

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The Influence of Liver Physiology on Liver Tumor Ablation Success

When performing a liver tumor ablation, it is important to consider the native tissue types. Microwave liver ablation works most efficiently when there are sufficient water molecules upon which energy can transfer through. When comparing patients with a cirrhotic, steatotic, and healthy liver tissue at baseline, the variability in ablation effect is significant. The current data for estimated ablation efficiency in probes is based on ex vivo data, often from healthy livers.

[Dr. Christopher Beck]
The topic that I want to go back to before I forget is, ablations in a cirrhotic liver versus ablations in a steatotic liver, how do they differ and how do you approach them?

[Dr. Driss Raissi]
Do I approach them any differently? I actually don't. I don't really do anything different for them, I'm just cognizant of it. We wrote a paper about ablation. We wanted to see, are there any predictors for the success of your ablation. And we found that different tumor environments basically, background liver might actually affect the likelihood that you have early recurrence or not. And it kind of makes sense, right? I mean, a fatty liver, if you just go by the physics of microwave ablation, less water molecules, probably you will have less microwave energy delivery efficiency. That's just how it works.

Microwave ablation energy is more effective, the more watermark molecules, it'll be more effective, the less water molecules it'll be less effective. Same thing for fibrotic livers. And if you look at most of the microwave ablation devices, the data you receive is based on ex vivo healthy livers. So that made me think well, I get this company that shows me, basically, I'm in the Society of Interventional Radiology annual conference and I'm in an ablation workshop and I'm trying, I go there and try one of the operation probes and I'm like, "Oh wow, I just ablated five by five, this is beautiful, but hold on a second, this is a totally healthy liver. This is not a cirrhotic liver full of fat or full of fibrotic nodules. It's not going to be five by five."

And that got me thinking, what factors in the underlying liver might affect my microwave ablation efficiency. And obviously, there are several. The fact that it's a live liver, the fact that it is a diseased liver, the fact that it is a fatty liver. What if it's an iron overloaded liver? We haven't really considered how these underlying liver pathologies might actually affect your final ablation zone.

[Dr. Christopher Beck]
So anecdotally, do you find that... I mean, excluding healthy livers, which virtually or infrequently happen, but comparing fatty liver to cirrhotic liver, which one do you get better ablation zones in, just anecdotally?

[Dr. Driss Raissi]
Cirrhotic livers, not fatty livers.

Maximizing the Number of Liver Tumor Ablations: Beyond the Milan Criteria

When ablating hepatocellular carcinoma, many reference the Milan criteria of up to three lesions. However, with this standard many patients that do not qualify for surgery but who could potentially benefit from ablation are excluded from treatment. This then begs the question, what is the limit in total liver ablation surface area before liver failure is a pressing concern? Below, Dr. Raissi discusses his method for achieving up to six ablations.

[Dr. Christopher Beck]
I know we've been talking a lot about HCC, and this could still be HCC, it can be multifocal HCC. Do you have a limit as to the number of lesions that you want to ablate before you start thinking about another treatment modality?

[Dr. Driss Raissi]
That's a good question, right Chris? Because it doesn't seem like there is anything written in the letters where people just kind of mention things here and there. You want to go by Milan criteria and say, "No more than three." I mean, we're going to lose a lot of patients.

[Dr. Christopher Beck]
Yeah. Seems conservative, right?

[Dr. Driss Raissi]
Yeah, we're going to lose a lot of patients. Then somebody told me once, "Oh, four." And I'm like, "Based on what? Why four? Because it's one more than three?"

[Dr. Driss Raissi]
Yeah. I mean obviously, you can do more. My surgical colleagues, when they start doing their burns, they're like, "Oh yeah, I burned eight lesions." Yeah. I mean, you have the benefit of doing an intraop. So they don't seem to have a limit of how many lesions they Zap intraoperatively. So should we have a limit? Well, maybe. I mean, sometimes it's very tedious and if you ablate eight lesions in the same session knowing that you are ablating let's say, I don't know, 30, 40, CC's of liver, that adds up to potentially sending the patient into liver failure. So we have to be smart about it.

So I usually take up to six lesions. But what do I do? I try to do what I think makes sense. Why do they have the same sessions? So if I have them in the right maybe, and if I feel like, you know what? The left will take care of the patient so I can freely maneuver in his right lobe now when he has a healthy left, okay. And vice versa, but if I'm going to try to target left and right, a total of three lesions, three lesions here, especially in a patient with HCC, it could be dicey.

So what I do is, I actually divide my sessions. I'm like, "Come to me. Right lobe will give you three or four lesions in that right lobe and then we'll take care of the other one, two, three lesions, whatever you have in the left lobe." The test of time, within two to three weeks. And look at his life, it seems like he has tolerated it. There's no reason to rush. Why are we rushing? We might be dealing with dire consequences.

Podcast Contributors

Dr. Driss Raissi discusses Microwave Ablation for Liver Lesions on the BackTable 158 Podcast

Dr. Driss Raissi

Dr. Driss Raissi is the Chief of the Division of Vascular and Interventional Radiology with UK Healthcare in Kentucky.

Dr. Christopher Beck discusses Microwave Ablation for Liver Lesions on the BackTable 158 Podcast

Dr. Christopher Beck

Dr. Chris Beck is a practicing interventional radiologist with Regional Radiology Group in New Orleans.

Cite This Podcast

BackTable, LLC (Producer). (2021, October 3). Ep. 158 – Microwave Ablation for Liver Lesions [Audio podcast]. Retrieved from

Disclaimer: The Materials available on are for informational and educational purposes only and are not a substitute for the professional judgment of a healthcare professional in diagnosing and treating patients. The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.



Microwave Ablation for Liver Lesions with Dr. Driss Raissi on the BackTable VI Podcast)
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