Biomechanical model-based deformable registration of MRI and histopathology for clinical prostatectomy

Abstract

A biomechanical model-based deformable image registration incorporating specimen-specific changes in material properties is optimized and evaluated for correlating histology of clinical prostatectomy specimens with in vivo MRI. In this methodology, a three-step registration based on biomechanics calculates the transformations between histology and fixed, fixed and fresh, and fresh and in vivo states. A heterogeneous linear elastic material model is constructed based on magnetic resonance elastography (MRE) results. The ex vivo tissue MRE data provide specimen-specific information for the fresh and fixed tissue to account for the changes due to fixation. The accuracy of the algorithm was quantified by calculating the target registration error (TRE) by identifying naturally occurring anatomical points within the prostate in each image. TRE were improved with the deformable registration algorithm compared to rigid registration alone. The qualitative assessment also showed a good alignment between histology and MRI after the proposed deformable registration.

Keywords: Biomechanical models; correlative pathology; deformable registration; finite element model; magnetic resonance elastography.

Figure 1

Summary of the deformable registration workflow. The process starts by registering histology to fixed, and then fixed to fresh, and finally fresh to in vivo. For the last two steps MRE-derived material properties are added to the biomechanical modeling

Figure 2

Histology reconstruction. (a) 2D rigid registration between gross slices and their corresponding fixed images. (b) 2D deformable registration based on MLS between histology slides and gross slices

Figure 3

Material model construction based on MRE data. Each element of the model is assigned an E value from the MRE data. The top and the bottom left image sets are the MRE fresh and fixed scans, respectively. The top and the bottom right images display the reconstructed FEM after assigning the E values from MRE. The axes on the right side images represent the position in centimeter. Color maps show the E values in KPa. In the fresh-state E-maps variations in E were noted for diseased tissue and across normal anatomy. Fixation increases Young modulus nonuniformly and as an approximate function of distance from the tissue edge

Figure 4

Checkerboard visualization for different registration steps in the proposed workflow. Figures (a)-(d) show the corresponding slice on in vivo, fresh, fixed, and the histology, respectively, (e) is the checkerboard display of the deformed histology overlaid on the in vivo. (f) shows the deformed fresh image overlaid on the in vivo, (g) represents the fresh image overlaid on the deformed fixed, (h) is the overlay of the deformed histology on the fixed image