Registration of histopathology to magnetic resonance imaging of prostate cancer.

Background And Purpose: The diagnostic accuracy of new imaging techniques requires validation, preferably by histopathological verification. The aim of this study was to develop and present a registration procedure between histopathology and magnetic resonance imaging (MRI) of the prostate, to estimate its uncertainty and to evaluate the benefit of adding a contour-correcting registration.

Materials And Methods: For twenty-five prostate cancer patients, planned for radical prostatectomy, a 3D-printed prostate mold based on MRI was created and an MRI of the specimen, placed inside the mold, was performed. Each histopathology slice was registered to its corresponding MRI slice using a 2D-affine registration. The MRI was rigidly registered to the MRI and the resulting transform was applied to the histopathology stack. A 2D deformable registration was used to correct for specimen distortion concerning the specimen's fit inside the mold. We estimated the spatial uncertainty by comparing positions of landmarks in the MRI and the corresponding registered histopathology stack.

Results: Eighty-four landmarks were identified, located in the urethra (62%), prostatic cysts (33%), and the ejaculatory ducts (5%). The median number of landmarks was 3 per patient. We showed a median in-plane error of 1.8 mm before and 1.7 mm after the contour-correcting deformable registration. In patients with extraprostatic margins, the median in-plane error improved from 2.1 mm to 1.8 mm after the contour-correcting deformable registration.

Conclusions: Our registration procedure accurately registers histopathology to MRI, with low uncertainty. The contour-correcting registration was beneficial in patients with extraprostatic surgical margins.