title: Realization of a biomechanical model-assisted image guidance system for breast cancer surgery using supine MRI.
abstract: OBJECTIVE
  Unfortunately, the current re-excision rates for breast conserving surgeries due to positive margins average 20-40 %. The high re-excision rates arise from difficulty in localizing tumor boundaries intraoperatively and lack of real-time information on the presence of residual disease. The work presented here introduces the use of supine magnetic resonance (MR) images, digitization technology, and biomechanical models to investigate the capability of using an image guidance system to localize tumors intraoperatively.
  
  
  METHODS
  Preoperative supine MR images were used to create patient-specific biomechanical models of the breast tissue, chest wall, and tumor. In a mock intraoperative setup, a laser range scanner was used to digitize the breast surface and tracked ultrasound was used to digitize the chest wall and tumor. Rigid registration combined with a novel nonrigid registration routine was used to align the preoperative and intraoperative patient breast and tumor. The registration framework is driven by breast surface data (laser range scan of visible surface), ultrasound chest wall surface, and MR-visible fiducials. Tumor localizations by tracked ultrasound were only used to evaluate the fidelity of aligning preoperative MR tumor contours to physical patient space. The use of tracked ultrasound to digitize subsurface features to constrain our nonrigid registration approach and to assess the fidelity of our framework makes this work unique. Two patient subjects were analyzed as a preliminary investigation toward the realization of this supine image-guided approach.
  
  
  RESULTS
  An initial rigid registration was performed using adhesive MR-visible fiducial markers for two patients scheduled for a lumpectomy. For patient 1, the rigid registration resulted in a root-mean-square fiducial registration error (FRE) of 7.5 mm and the difference between the intraoperative tumor centroid as visualized with tracked ultrasound imaging and the registered preoperative MR counterpart was 6.5 mm. Nonrigid correction resulted in a decrease in FRE to 2.9 mm and tumor centroid difference to 5.5 mm. For patient 2, rigid registration resulted in a FRE of 8.8 mm and a 3D tumor centroid difference of 12.5 mm. Following nonrigid correction for patient 2, the FRE was reduced to 7.4 mm and the 3D tumor centroid difference was reduced to 5.3 mm.
  
  
  CONCLUSIONS
  Using our prototype image-guided surgery platform, we were able to align intraoperative data with preoperative patient-specific models with clinically relevant accuracy; i.e., tumor centroid localizations of approximately 5.3-5.5 mm.
authors.affiliation: Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA. rebekah.h.conley@vanderbilt.edu.
authors.forename: Rebekah H
authors.identifier: http://orcid.org/0000-0002-9352-9813
authors.initials: RH
authors.lastname: Conley
authors.affiliation: Department of Surgical Oncology, Vanderbilt University Medical Center, Nashville, TN, USA.
authors.forename: Ingrid M
authors.initials: IM
authors.lastname: Meszoely
authors.affiliation: Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA.
authors.forename: Jared A
authors.initials: JA
authors.lastname: Weis
authors.affiliation: Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA.
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Pheiffer
authors.affiliation: Vanderbilt University Institute of Imaging Science, Nashville, TN, USA.
authors.forename: Lori R
authors.initials: LR
authors.lastname: Arlinghaus
authors.affiliation: Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA.|Vanderbilt University Institute of Imaging Science, Nashville, TN, USA.|Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, USA.|Departments of Physics and Cancer Biology, Vanderbilt University, Nashville, TN, USA.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Yankeelov
authors.affiliation: Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA.|Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, USA.|Department of Neurological Surgery, Vanderbilt University, Nashville, TN, USA.
authors.forename: Michael I
authors.initials: MI
authors.lastname: Miga
mesh_terms: D001696:Biomechanical Phenomena; D001943:Breast Neoplasms / Q000601:surgery*; D005260:Female; D057918:Fiducial Markers; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D053783:Magnetic Resonance Imaging, Interventional / Q000379:methods; D015412:Mastectomy, Segmental / Q000379:methods*; D008954:Models, Biological; D008962:Models, Theoretical; D012086:Reoperation; D016683:Supine Position; D025321:Surgery, Computer-Assisted / Q000379:methods*; D018084:Ultrasonography, Interventional
keywords: Biomechanical models; Breast conserving therapy; Image-guided surgery; Lumpectomy; Nonrigid registration; Tracked ultrasound