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Authors
Callum Little, Shaoyan Zhang, Richard Colchester, Sacha Noimark, Sunish Mathews, Edward Zhang, Paul Beard, Malcolm Finlay, Tara Mastracci, Roby Rakhit, Adrien Desjardins
Abstract
An abdominal aortic aneurysm (AAA) is a persistent localized dilatation of the aorta to more than 1.5 times the expected diameter, which may lead to rupture with resultant high mortality. Endovascular repair (EVAR) of AAAs is a mini-mally invasive procedure that involves the peripheral delivery of one or more covered endografts to the aneurysmal segment, via a catheter-based system. A particularly challenging group of patients to treat are those in which the aneurys-mal sac extends proximally to include the origin of the renal arteries (15% of all AAAs). To maintain the patency of renal side branches in these “complex” cases, in situ fenestration (ISF) of endografts during AAA procedures has been pro-posed. The challenges addressed in this study were a) to develop an endovascular imaging system for visualizing side branches beyond deployed endografts and thereby to determine the locations for ISF; b) to obtain an initial assessment of the clinical utility of this system. Here, all-optical ultrasound (OpUS) imaging with a fiber optic transducer was used for real-time guidance, wherein ultrasonic pulses are generated in nanocomposite coatings via the photoacoustic effect and received optically using a Fabry-Perot cavity. These custom OpUS transducer components were integrated into a steerable sheath (6 Fr) that also included a separate optical fiber for delivering laser pulses for fenestrating the endograft. In an ex-vivo mod-el, it was shown that OpUS imaging extended through the endograft and underly-ing aortic tissue, and permitted aortic side-branch visualization. During an EVAR procedure in a porcine model in vivo, an aortic side branch was visualized with OpUS imaging after the endograft was deployed and optical fenestration of the stent graft was successfully performed. This study showed that OpUS is a prom-ising modality for guiding EVAR and could find particularly utility with identify-ing aortic side branches for ISF during treatment of complex AAAs.
Link to paper
DOI: https://doi.org/10.1007/978-3-031-43996-4_67
SharedIt: https://rdcu.be/dnwQe
Link to the code repository
N/A
Link to the dataset(s)
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Reviews
Review #4
- Please describe the contribution of the paper
The paper describes a design of optical ultrasound (OpUS) through a catheter for AAA applications, aiming at custom fenestration of EVAR stents. The prototype OpUS catheter was tested on swine aortas in a benchtop and in-vivo setting.
- Please list the main strengths of the paper; you should write about a novel formulation, an original way to use data, demonstration of clinical feasibility, a novel application, a particularly strong evaluation, or anything else that is a strong aspect of this work. Please provide details, for instance, if a method is novel, explain what aspect is novel and why this is interesting.
The paper presents a clear description of the proposed system, and evaluates it on swine-aortas in a benchtop and in-vivo setting, examining different power and pulse settings. As such the translation to a clinical setting has been maximally approached, and findings are clinically relevant and convincing.
- Please list the main weaknesses of the paper. Please provide details, for instance, if you think a method is not novel, explain why and provide a reference to prior work.
Apart from some minor remarks presenred below, this reviewer did not have any major concern with the paper, nor the research setup, nor the presented results.
- Please rate the clarity and organization of this paper
Excellent
- Please comment on the reproducibility of the paper. Note, that authors have filled out a reproducibility checklist upon submission. Please be aware that authors are not required to meet all criteria on the checklist - for instance, providing code and data is a plus, but not a requirement for acceptance
Since the paper is very clear, the only aspects that complicate reproducibility are the effort involved in creating such an OpUS catheter, benchtop experimental setup and animal experimental setup. All of these are simply intinsic to the presented work.
- Please provide detailed and constructive comments for the authors. Please also refer to our Reviewer’s guide on what makes a good review: https://conferences.miccai.org/2023/en/REVIEWER-GUIDELINES.html
I have only a few comments and recommendations:
- section 2.2: “if tissue was visible from above” -> could you better descrive what you exactly mean
- section 3 is called “Results and Discusison”, while section 4 is called “Discussion”. You might consider calling section 3 simply “Results”
- Figure 3: there seem to be wires in both renal arteries which are not labeled. Maybe add labels for these and explain why they are there.
- Section 4: “depths of 20 mm from the device tip”: please explain where the 20 mm comes from. Was this an observation? Or is it simply known from literature?
- Rate the paper on a scale of 1-8, 8 being the strongest (8-5: accept; 4-1: reject). Spreading the score helps create a distribution for decision-making
8
- Please justify your recommendation. What were the major factors that led you to your overall score for this paper?
The presented research is clinically relevant, innovative, and the validation in the benchtop and in-vivo setting is comprehensive and convincing.
- Reviewer confidence
Very confident
- [Post rebuttal] After reading the author’s rebuttal, state your overall opinion of the paper if it has been changed
N/A
- [Post rebuttal] Please justify your decision
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Review #1
- Please describe the contribution of the paper
This paper describes an optical ultrasound (OpUS) for guiding endovascular repair of AAA (abdominal aortic aneurysms). The author clearly state the problem and proposed solution as follows: (1) AAA repair involves one or more covered endografts to the aneurysmal segment via a catheter-based treatment system (2) in situ fenestration of the endographs are needed (3) a challenge is to visualize the aortic side branches in situ (3b) [listed in the Discussion] the cost difference of using a non-fenestrated graph is GPB$6K versus GPB$15-22K, (4) OpUS has the potential to provide image guidance due to catheter-sized transducer (5) this study answers the question of whether OpUS allows visualization of side branches through endograft material with OpUS integrated into a steerable sheath by (6) demonstrating it experimentally and (7) assessing the pros/cons and next steps.
- Please list the main strengths of the paper; you should write about a novel formulation, an original way to use data, demonstration of clinical feasibility, a novel application, a particularly strong evaluation, or anything else that is a strong aspect of this work. Please provide details, for instance, if a method is novel, explain what aspect is novel and why this is interesting.
The major strengths are a clear problem definition with a novel and clinically feasible solution that is demonstrated here. There is a real potential benefit to both surgeon and patient. The paper is clearly written and easy to follow with sufficient detail for others to replicate the OpUS system and experiments. It is well-aligned to the MICCAI conference and is one of the few papers with a hardware focus. In particular, a strength is the practical implementation of OpUS in a 7 French Tourguide steerable sheath. Another strength of the paper is the demonstration on a porcine model in vivo. This has not been shown before and highlights a clinical application where OpUS is useful and practical. OpUS is novel itself (by converting optical energy into ultrasound and vice versa it opens up the ability to create a transducer at the end of an optical fibre – suitable for a catheter-based treatment system.
- Please list the main weaknesses of the paper. Please provide details, for instance, if you think a method is not novel, explain why and provide a reference to prior work.
Weaknesses are the limited number of experiments (just one animal) and therefore lack of statistical analysis of metrics of success. The authors provide an image and label the side-branch but that is it. No repeated tests, no numerical evaluation against gold standard. The authors also admit that the small size of the porcine vessel gave additional problems compared to human vessels. Despite bend-induced losses in the optical fibre (which lowers SNR), OpUS could see the hyperechoic side branch region to a depth of 3mm and post-mortem dissection confirmed a successful fenestration. Yet, given these early results, it is too soon to be confident that surgeons would actually trust these images for guidance.
- Please rate the clarity and organization of this paper
Excellent
- Please comment on the reproducibility of the paper. Note, that authors have filled out a reproducibility checklist upon submission. Please be aware that authors are not required to meet all criteria on the checklist - for instance, providing code and data is a plus, but not a requirement for acceptance
As mentioned, this paper is clearly presented with a good problem definition, literature review and assessment of results plus suggestions for next steps. The experiments appear reproduceable.
- Please provide detailed and constructive comments for the authors. Please also refer to our Reviewer’s guide on what makes a good review: https://conferences.miccai.org/2023/en/REVIEWER-GUIDELINES.html
This paper checks all the boxes of clearly describing a real clinical problem, proposing a feasible and novel solution and then demonstrating it in vivo.
Suggested revisions: Figure 1 is a clear description of how to incorporate OpUS into the catheter-based treatement system but the authors could make it clearer whether the 7 French Tourguide is the current standard or whether a further reduction in diameter is needed for clinical acceptance.
Ethical review board review of the animal study is mentioned in section 2.3 but no mention in section 2.2 that describes animal tissue too. And where is the detailed analysis of the five different fenestration pulse-energy/duration combinations? Section 3.1 only mentions the 1.8W/0.5s combination and the rest “size of the fenestration increased”? How much? What is learned here (i.e. quantified)?
Section 2.3 describe the use of iodine-based contrast agents but does iodine affect the OpUS?
- Rate the paper on a scale of 1-8, 8 being the strongest (8-5: accept; 4-1: reject). Spreading the score helps create a distribution for decision-making
7
- Please justify your recommendation. What were the major factors that led you to your overall score for this paper?
The novelty of optical ultrasound is high- being able to convert from light to ultrasound and back opens up new possibilities such as this optical-fibre based guidance system for life-saving treatment. There are many other possible applications that are also worth exploring, so this should be of wide interest to MICCAI attendees.
- Reviewer confidence
Very confident
- [Post rebuttal] After reading the author’s rebuttal, state your overall opinion of the paper if it has been changed
N/A
- [Post rebuttal] Please justify your decision
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Review #6
- Please describe the contribution of the paper
For some challenging AAA cases, where the aneurysmal sac extends to include the origin of the renal arteries, this paper presents an interesting device design. The design comprises an optical ultrasound for imaging guidance and an ISF fiber for optical fenestration. Preliminary experiments have demonstrated that this design shows promise for visualizing the side branches behind the endograft and achieving in-situ optical fenestration.
- Please list the main strengths of the paper; you should write about a novel formulation, an original way to use data, demonstration of clinical feasibility, a novel application, a particularly strong evaluation, or anything else that is a strong aspect of this work. Please provide details, for instance, if a method is novel, explain what aspect is novel and why this is interesting.
This paper presented a novel design that shows good clinical potential value. The compact design, integrated into the current catheter, not only helps physicians localize and visualize where the side branch is, but also achieves in-situ fenestration. This paper is well-organized and easy to follow. The topic fits well with the MICCAI community
- Please list the main weaknesses of the paper. Please provide details, for instance, if you think a method is not novel, explain why and provide a reference to prior work.
The visibility of the side-branch under optic ultrasound needs to be demonstrated more strongly. In Figure 3(a), it is difficult to differentiate between the stent and the aorta. Since clinical scenarios are typically more complex, this paper should demonstrate whether this device can still provide good visibility to assist with side-branch identification.
- Please rate the clarity and organization of this paper
Good
- Please comment on the reproducibility of the paper. Note, that authors have filled out a reproducibility checklist upon submission. Please be aware that authors are not required to meet all criteria on the checklist - for instance, providing code and data is a plus, but not a requirement for acceptance
Re-implementing this design may not be easy for individuals. However, if this design is ready for wide-scale manufacturing in the future, it would have a high clinical impact.
- Please provide detailed and constructive comments for the authors. Please also refer to our Reviewer’s guide on what makes a good review: https://conferences.miccai.org/2023/en/REVIEWER-GUIDELINES.html
(1) In benchtop imaging, this work conducted fenestrating experiments using different sets of parameters in different sections of the aorta. Please clarify how this experiment was performed, including the selection of fenestration sites. Additionally, the associated results were not well presented. What are the performance differences in using different sets of fenestration parameters? (2) To better describe the use of this design, this paper should include a system overview figure that shows the workflow and the order of using different sensors (3) Please clarify why the figure 3(a) cannot easily identify the stent and aorta, and whether this problem will affect actual clinical applications. (4) Please add relevant references to support your point “distortion of the aorta due to deployment of the endograft limits the accuracy of this technique.”
- Rate the paper on a scale of 1-8, 8 being the strongest (8-5: accept; 4-1: reject). Spreading the score helps create a distribution for decision-making
5
- Please justify your recommendation. What were the major factors that led you to your overall score for this paper?
This CAI work showed a novel clincial application and has a high clinical potential impact.
- Reviewer confidence
Somewhat confident
- [Post rebuttal] After reading the author’s rebuttal, state your overall opinion of the paper if it has been changed
N/A
- [Post rebuttal] Please justify your decision
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Primary Meta-Review
- Please provide your assessment of this work, taking into account all reviews. Summarize the key strengths and weaknesses of the paper and justify your recommendation. In case you deviate from the reviewers’ recommendations, explain in detail the reasons why. In case of an invitation for rebuttal, clarify which points are important to address in the rebuttal.
The paper presents a first study of using optical ultrasound imaging for real-time visualization and guidance of endovascular repair of AAAs. The proposed system is validated in an ex-vivo model as well as in-vivo in a porcine model. The topic is well-motivated from a clinical perspective, the solution is novel, the in-vivo validation demonstrates the clinical application and practicality, and the paper is well-written. The topic is of interest to the MICCAI community.
Feedback from reviewers, including additional details and clarification regarding the experiments and improvements to figures (Fig 3), should be incorporated in the final manuscript.
Author Feedback
We are grateful to the reviewers for their constructive and insightful comments. Overall, we were struck by the positive feedback, including:
- ‘There is a real potential benefit to both surgeon and patient. … It is well-aligned to the MICCAI conference’ (Reviewer #1)
- ‘award-worthy paper … the translation to a clinical setting has been maximally approached, and findings are clinically relevant and convincing’ (Reviewer #4)
- ‘This CAI work showed a novel clinical application and has a high clinical potential impact’ (Reviewer #6)
All reviewers who indicated their confidence as “Very confident” ranked this paper first in their stack.
We address specific feedback below.
== Reviewer #1
- Weaknesses are the limited number of experiments … given these early results, it is too soon to be confident that surgeons would actually trust these images for guidance
Response: the limited size of this dataset reflected the nature of this development: a pilot study providing the first demonstration that optical ultrasound imaging, as an emerging modality, is promising for endovascular aneurysm repair.
- the authors could make it clearer whether the 7 French Tourguide is the current standard
Response: the 7 French Tourguide is the current standard; this will be made clear.
- Ethical review board review of the animal study is mentioned in section 2.3 but no mention in section 2.2 that describes animal tissue too.
Response: this will be included.
- And where is the detailed analysis of the five different fenestration pulse-energy/duration combinations?
Response: it will be mentioned that the 1.8W/0.5s combination was chosen as having the smallest energy that yielded fenestration.
== Reviewer #4
- section 2.2: “if tissue was visible from above” -> could you better describe what you exactly mean
Response: it will be clarified: “if tissue was visible through a fenestration in the endograft material”.
- section 3 is called “Results and Discussion”, while section 4 is called “Discussion”. You might consider calling section 3 simply “Results”
Response: this will be corrected.
- Figure 3: there seem to be wires in both renal arteries which are not labeled.
Response: labels will be added: J-tip 0.035” wires passed into both renal arteries to provide radiological landmarks.
- Section 4: “depths of 20 mm from the device tip”: please explain where the 20 mm comes from. Was this an observation? Or is it simply known from literature?
Response: this depth was obtained from in vivo images in this study, but as those imaging data were not included in this manuscript, the phrase “20 mm from the device tip” will be left out.
== Reviewer #6
- In benchtop imaging, this work conducted fenestrating experiments using different sets of parameters in different sections of the aorta. Please clarify how this experiment was performed, including the selection of fenestration sites. What are the performance differences in using different sets of fenestration parameters?
Response: it will be mentioned that these were benchtop experiments; 1.8W/0.5s combination was chosen as having the smallest energy that yielded fenestration.
- To better describe the use of this design, this paper should include a system overview figure
Response: thank you; however, there is not sufficient room to add this to the paper.
- Please clarify why the figure 3(a) cannot easily identify the stent and aorta, and whether this problem will affect actual clinical applications.
Response: the aorta presented as a region that was hypoechoic relative to the overlying stent. Going forward, it will be important to determine the consistency of this appearance for clinical training and segmentation algorithms.
- Please add relevant references to support your point “distortion of the aorta due to deployment of the endograft limits the accuracy of this technique.”
Response: A reference will be added: Koutouzi, et al. DOI:10.1016/j.ejvs.2016.07.024