MIDAS Journal - Fast image-based model of mitral valve closure for surgical planning

Fast image-based model of mitral valve closure for surgical planning

Hammer P., Vasilyev N., Perrin D., Del Nido P., Howe R.

Department of Cardiac Surgery, Children's Hospital, Boston, MA, USA

Please use this identifier to cite or link to this publication: http://hdl.handle.net/10380/1379

Published in The MIDAS Journal - Computational Biomechanics for Medicine (MICCAI 2008 Workshop).

Submitted by Peter Hammer on 05-30-2008.

Surgical repair of the mitral valve results in better
outcomes than valve replacement, yet diseased valves
are often replaced due to the technical difficulty of the
repair process. A surgical planning system based on
patient-specific medical images that allows surgeons to
simulate and compare potential repair strategies could
greatly improve surgical outcomes. The system must
simulate valve closure quickly and handle the complex
boundary conditions imposed by the chords that tether
the valve leaflets. We have developed a process for
generating a triangulated mesh of the valve surface
from volumetric image data of the opened valve. The
closed position of the mesh is then computed using a
mass-spring model of dynamics. In the mass-spring
model, triangle sides are treated as linear springs
supporting only tension. Chords are also treated as
linear springs, and self-collisions are detected and
handled inelastically. The equations of motion are
solved using implicit numerical integration. The
simulated closed state is compared with an image of the
same valve taken in the closed state to assess accuracy
of the model. The model exhibits rapid valve closure
and is able to predict the closed state of the valve with
reasonable accuracy.

Reviews

Review of a fast image-based model of mitral valve closure for surgical planning by Anonymous on 07-04-2008 for revision #2

expertise: 3 sensitivity: 4.5

Please, rank the following on the scale from 1 (worst) to 5 (best)

Originality 3

Methodological originality 3

Biologic originality 3

Completeness of discussion 5

Appropriate references 4

Organisation 4

Clarity 4

Is the technical treatment plausible and free from technical errors?

Have you checked the equations no.

Are you aware of prior publication or presentation of this work no.

Is the paper too long no.

Recommendation:

(A) Accept

(B) Accept subject to minor revisions

(D) Reject

B, accept subject to minor revisions.

Should this paper be presented as poster or as podium presentation (this recommendation does not reflect upon the relative quality of the paper)? Presentation.

Comments to the manuscript:

The paper is well written, providing a clear idea of the methods used to model mitral valve closure. The authors’ aim of providing quick computations of valve closure justifies the use of mass-spring models.

However, I am not able to understand the reasoning for why the authors desire low sensitivity of valve closure to leaflet properties. Doesn’t the indication of large variance in these properties (from ref [14]) indicate that subject-specific material properties are necessary? Indeed, biological tissue properties are individual-specific and time-specific (properties change over time as well). Change in material properties affect mechanical stress and deformation. Therefore, more clarification is needed on this part. What range of material properties should we expect physiologically in normal and diseased hearts?

Fig. 5 is a bit confusing. Do the authors refer to the top and bottom rows or the left most and right most columns? More clarification in the caption for Fig. 5 would suffice.

Fast Image-based Model of Mitral Valve Closure for Surgical Planning by Anonymous on 07-03-2008 for revision #2

expertise: 3 sensitivity: 4.5

Please, rank the following on the scale from 1 (worst) to 5 (best)

Originality 3

Methodological originality 3

Biologic originality 3

Completeness of discussion 4

Appropriate references 4

Organisation 4

Clarity 4

Is the technical treatment plausible and free from technical errors? YES

Have you checked the equations NO

Are you aware of prior publication or presentation of this work NO

Is the paper too long NO

Recommendation: (B)

(A) Accept

(B) Accept subject to minor revisions

(D) Reject

Should this paper be presented as poster or as podium presentation (this recommendation does not reflect upon the relative quality of the paper)?

Poster

Comments to the manuscript:

Couple of mistakes:

On page 3, 5^th paragraph, 4^th line, know -> known
On page 7, 2^nd paragraph, 1^st line, as well-> as well as

As authors have suggested, stress levels in the leaflets might also be desired for the repair process, in which case a FE modelling is a better choice. If model’s robustness and speed is more desirable than the accuracy (which is a fair argument), one might consider explicit time scheme for FE method (Karol Miller, Total Lagrangian explicit dynamics finite element algorithm for computing soft tissue deformation, MICCAI 2007). It will be an interesting comparison between mass-spring approach and FE modelling on speed, and also modelling accuracy.

On page 7, paragraph 2, authors mention “homogeneous/nonhomogeneous boundary conditions”. Please clarify.

If the model is stable and does not take long time to run, then a more detailed sensitivity analysis such as a factorial analysis will be more adequate.

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Paper Id:	564
Keywords:	mitral valve, surgical planning, mass-spring model, simulation,
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