Image Registration for Prostate MR Spectroscopy Using Biomechanical Modeling and Optimization of Force and Stiffness Parameters

Ron Alterovitz1, Ken Goldberg1,2, John Kurhanewicz3, Jean Pouliot4, I-Chow Hsu4

1Department of Industrial Engineering & Operations Research, University of California, Berkeley, CA, USA
2Department of Electrical Engineering & Computer Science, University of California, Berkeley, CA, USA
3Magnetic Resonance Science Center, University of California, San Francisco, CA, USA
4Department of Radiation Oncology, University of California, San Francisco, CA, USA

We develop an image registration system based on biomechanical modeling of the prostate and surrounding tissues to register cancerous tumor locations for targeted prostate brachytherapy treatment planning. Cancerous tumors can be identified using magnetic resonance spectroscopy (MRS) imaging, which is acquired with an endorectal probe that causes significant nonlinear deformation of the prostate. The probe is removed during magnetic resonance (MR) imaging for brachytherapy planning and therapy.

Given 2-dimensional segmented probe-in and probe-out images, our finite element based model defines a mapping between the images by estimating the deformation of the prostate and surrounding tissues due to endorectal probe insertion and balloon inflation. Treating uncertain patient-specific model parameters for tissue stiffness and external forces as variables, we compute a locally optimal solution to maximize image registration quality.

We visualize results by applying the computed mapping to the probe-out image to generate a predicted probe-in image. We compare the predicted probe-in images to the given probe-in images for 5 patients and obtain an average Dice Similarity Coefficient (DSC) of 95.6% for the prostate. Using the mapping, we warp a regular MRS grid from the given probe-in image to the given probe-out image for use during treatment planning.



(a) Given probe-in image with MRS grid
(b) Given probe-out image

(c) Predicted probe-in image with MRS grid
(d) Given probe-out image with predicted MRS grid

Figure 1: MR Spectroscopy data, obtained within the yellow MRS grid, requires insertion of an endorectal probe (a). HDR brachytherapy treatment for prostate cancer is performed with the probe removed (b). Using a finite element-based biomechanical simulation, the rectum of the given probe-out image (b) is inflated to the shape of the probe in the given probe-in image with MRS grid (a) to produce a predicted probe-in image with MRS grid (c). The predicted probe-in image can then be easily undeformed to predict the MRS grid warping for the given probe-out image (d).

Publications/Presentations

  1. Ron Alterovitz, Ken Goldberg, John Kurhanewicz, Jean Pouliot, I-Chow Hsu, "Image Registration for Prostate MR Spectroscopy Using Biomechanical Modeling and Optimization of Force and Stiffness Parameters," to appear in the 26th Annual Int. Conf. of the IEEE Engineering in Medicine and Biology Society (EMBS), San Francisco, CA, 2004.
  2. Ron Alterovitz, Ken Goldberg, John Kurhanewicz, Jean Pouliot, I-Chow Hsu, "Registering MR with MRS images for HDR prostate treatment using finite element modeling," to appear in the 46th American Association of Physicists in Medicine (AAPM) Annual Meeting, Pittsburgh, PA, July 25-29, 2004.