Reviews

Vijayaraghavan Rajagopal

Friday 4 July 2008

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

Originality 2

Methodological originality 2

Biologic originality 2

Completeness of discussion 3

Appropriate references 3

Organisation 3

Clarity 3

Is the technical treatment plausible and free from technical errors? No

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

(C) Accept with major revisions

(D) Reject

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)?

Comments to the manuscript:

At first glance I thought that the paper would present a novel contact-mechanics implementation (or modifications to existing implementations of this difficult problem). But, as I read on I realised that the paper explains, in a complicated way, that displacements can be applied to nodes of the brain that appear to penetrate the skull so that they touch the surface of the skull. A simulation using an explicit scheme is then run to obtain total brain deformation. Although the search algorithm may be novel, I do not believe this to be immediately relevant to the workshop community. More relevant results would include patient validation studies and comparison of performance of the presented simulation studies with true contact-mechanics simulations. It is unclear to me how accurate this technique is and how accurate it needs to be. I would therefore argue to reject this paper.

Poul Nielsen

Friday 4 July 2008

Please, rank the following on the scale from 1 (worst) to 5 (best)
Originality             3
Methodological originality    4
Biologic originality         2
Completeness of discussion     3
Appropriate references         4
Organisation             4
Clarity             3


Is the technical treatment plausible and free from technical errors?    yes
Have you checked the equations                        yes
Are you aware of prior publication or presentation of this work        no
Is the paper too long                            yes


Recommendation:    C
(A)    Accept
(B)     Accept subject to minor revisions
(C)    Accept with major 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 or podium


Comments to the manuscript:
The authors present a computationally efficient method for determining whether two surfaces, represented by C0 bilinear simplex meshes, have regions of penetration. The work is motivated by the desire to solve the contact problem between the soft brain and rigid skull. The description in section 3 is thorough, if somewhat verbose. I believe that this section could be shortened, without loss of completeness, with a careful rewrite. The modelling assumptions appear to be rather simplistic, especially the claim that “contact force is not specifically of interest”. How does this approach account for separation of the brain from the skull when/if air or fluid is allowed to enter into the cavity? Is this not an issue relevant to the brain-skull contact mechanics problem? A more considered discussion of the assumptions is required. Some discussion is also required regarding the assumptions associated with surface representations. It appears to me that the algorithm is limited to surface representation using bilinear C0 simplex elements. If so, this needs to be stated explicitly. It would be of interest to know if the approach could be generalised to other representations (e.g. higher order bases and/or smoother interelement continuity).

The text needs to be proof-read. For example, it took several readings to understand what the following sentence in section 1 means: “A registration method that leads to physically plausible deformation estimates is the computation of the intra-operative brain deformations using a biomechanical model, therefore treating the brain shift as a solid mechanics problem”.

Jae-hoon Chung

Thursday 3 July 2008

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

Originality                                                             3

Methodological originality                                 4

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                                                                     yes

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

Is the paper too long                                                                                           yes

 

 

Recommendation:              (C)

(A)    Accept

(B) Accept subject to minor revisions

(C)    Accept with major 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:

 

This paper describes a contact mechanics problem between the brain tissue and the surrounding skull during surgical procedures. A lot of emphasis has been put on the detecting the penetration of slave nodes defined on the brain tissue into the master body. Yet the treatment of the penetration itself is rather simple (explicit displacement boundary conditions). I wonder if this is appropriate to be called a contact problem, since it does not involve any computation on contact forces. Authors claim that the computation speed is almost independent of the mesh density for the skull surface, which seems trivial since the degrees of freedom for the master body are removed due to the fact that the skull is much stiffer than the brain tissue. Also, the algorithm requires no configuration parameters because contact forces are not computed. It seems that this method is more closely related to the approach of applying explicit boundary conditions over the entire surface of the brain, than contact mechanics approach.

 

I think Section 3can be substantially shortened, and it would be good to have some preliminary results on actual brain and skull geometries. Also, I wonder if any numerical issues were observed for not having continuous normal vector field defined on the master surface (due to C­₀-continuity).