Contact : Pierrick Coupé,
Pierre Hellier,
Christian Barillot
The information and the artifacts present in US and MR images being of different nature, the registration of these two modalities is a difficult task. Registration approaches based on classical similarity measure such as Sum Square Difference (SSD), Mutual Information (MI) or Correlation Ratio (CR) are known to fail [2] . Previous works have studied three options to register US and MR images : (a) the matching of homologous features extracted from both images, (b) the preprocessing of the images to make US images and MR images more similar in order to use classical similarity measures and (c) the iconic registration based on a specific similarity measure matching the US and MR image intensities [2] .
Contrary to histogram-based approaches which match all the information in both images, the proposed approach consists in matching the informative features : the hyperechogenic structures. The registration process is based on the estimation of the transformation maximizing the conjoint probability for a voxel to be included in hyperechogenic structure in both modalities. For intraoperative US image, the probability map is only a normalization. For preoperative MR image , the evaluation of f is done prior to surgery and is based both on the Mlvv operator and the manual segmentation of the pathological tissue performed by the neurosurgeon (see Schema).
Experimets on patient with hyperechogenic pathologies such as cavernoma (patient 1 and patient 2) and lowgrade glioma (patient 3) have been carried out.
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Patient1. Left : registration given by the neuronavigation
system. Right : the result after correction with our registration
approach. For this case, even if the lesion was not
entirely included in the US volume, the proposed registration
procedure converged. |
|
Patient 2. Left : registration given by the neuronavigation
system. Right : results after correction with our registration
approach. In this case, the acoustic shadow artifact was
present on the US image. The signal below the lesion was totally
dark. The proposed approach allowed to overcome these
artifacts without specic detection of the shadows. |
|
Patient 3. Left : registration given by the neuronavigation
system. Right : the result after correction with our registration
approach. |
A new framework for the 3D rigid registration of US and MR brain images is proposed. This framework is based on the probabilistic objective function of the hyperechogenic brain structures extracted from MR images. The experiments performed on 3 patients show that our approach converges robustly compared to methods such as the Mutual Information (MI), the Normalized MI on the gradient images or the Correlation Ratio on the US images and the pseudo- US created from MR images. The computational burden required for our method is compatible with intraoperative use. The visually accuracy of our methods has been shown but its quantitative accuracy needs to be futher investigated.
This new appraoch have been patented N° 07/02386
[1] P. Coupé, P. Hellier, X. Morandi and C. Barillot. A Probabilistic Objective Function for 3D Rigid Registration of Intraoperative US and Preoperative MR Brain Images. 4th IEEE International Symposium on Biomedical Imaging : From Nano to Macro, 2007, Pages 1320-1323, Washington, USA, April 2007.
[2] A. Roche, X. Pennec, G. Malandain, and N. Ayache, Rigid registration of 3D ultrasound with MR images : a new approach combining intensity and gradient information. IEEE TMI, vol. 20, no. 10, pp. 1038–1049, October 2001.
