Registration of histopathology to magnetic resonance imaging of prostate cancer

• Main Authors: Kristina Sandgren, Erik Nilsson, Angsana Keeratijarut Lindberg, Sara Strandberg, Lennart Blomqvist, Anders Bergh, Bengt Friedrich, Jan Axelsson, Margareta Ögren, Mattias Ögren, Anders Widmark, Camilla Thellenberg Karlsson, Karin Söderkvist, Katrine Riklund, Joakim Jonsson, Tufve Nyholm
• Format: Article
• Language: English
• Published: Elsevier 2021-04-01
• Series: Physics and Imaging in Radiation Oncology
• Subjects: PET/MRI; Prostate cancer; Image registration; Histopathology correlation
• Online Access: http://www.sciencedirect.com/science/article/pii/S240563162100018X

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 in-vivo 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 in-vivo MRI was created and an ex-vivo MRI of the specimen, placed inside the mold, was performed. Each histopathology slice was registered to its corresponding ex-vivo MRI slice using a 2D-affine registration. The ex-vivo MRI was rigidly registered to the in-vivo 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 in-vivo 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 in-vivo MRI, with low uncertainty. The contour-correcting registration was beneficial in patients with extraprostatic surgical margins.