title: Accurate prostate volume estimation using multifeature active shape models on T2-weighted MRI.
abstract: OBJECTIVE
  Accurate prostate volume estimation is useful for calculating prostate-specific antigen density and in evaluating posttreatment response. In the clinic, prostate volume estimation involves modeling the prostate as an ellipsoid or a spheroid from transrectal ultrasound, or T2-weighted magnetic resonance imaging (MRI). However, this requires some degree of manual intervention, and may not always yield accurate estimates. In this article, we present a multifeature active shape model (MFA) based segmentation scheme for estimating prostate volume from in vivo T2-weighted MRI.
  
  
  METHODS
  We aim to automatically determine the location of the prostate boundary on in vivo T2-weighted MRI, and subsequently determine the area of the prostate on each slice. The resulting planimetric areas are aggregated to yield the volume of the prostate for a given patient. Using a set of training images, the MFA learns the most discriminating statistical texture descriptors of the prostate boundary via a forward feature selection algorithm. After identification of the optimal image features, the MFA is deformed to accurately fit the prostate border. An expert radiologist segmented the prostate boundary on each slice and the planimetric aggregation of the enclosed areas yielded the ground truth prostate volume estimate. The volume estimation obtained via the MFA was then compared against volume estimations obtained via the ellipsoidal, Myschetzky, and prolated spheroids models.
  
  
  RESULTS
  We evaluated our MFA volume estimation method on a total 45 T2-weighted in vivo MRI studies, corresponding to both 1.5 Tesla and 3.0 Tesla field strengths. The results revealed that the ellipsoidal, Myschetzky, and prolate spheroid models overestimated prostate volumes, with volume fractions of 1.14, 1.53, and 1.96, respectively. By comparison, the MFA yielded a mean volume fraction of 1.05, evaluated using a fivefold cross-validation scheme. A correlation with the ground truth volume estimations showed that the MFA had an r(2) value of 0.82, whereas the clinical volume estimation schemes had a maximum value of 0.70.
  
  
  CONCLUSIONS
  Our MFA scheme involves minimal user intervention, is computationally efficient and results in volume estimations more accurate than state of the art clinical models.
authors.affiliation: Department of Biomedical Engineering, Rutgers, The State University of New Jersey, Piscataway, 08854, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Toth
authors.forename: B Nicolas
authors.initials: BN
authors.lastname: Bloch
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Genega
authors.forename: Neil M
authors.initials: NM
authors.lastname: Rofsky
authors.forename: Robert E
authors.initials: RE
authors.lastname: Lenkinski
authors.forename: Mark A
authors.initials: MA
authors.lastname: Rosen
authors.forename: Arjun
authors.initials: A
authors.lastname: Kalyanpur
authors.forename: Sona
authors.initials: S
authors.lastname: Pungavkar
authors.forename: Anant
authors.initials: A
authors.lastname: Madabhushi
mesh_terms: D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010363:Pattern Recognition, Automated; D011471:Prostatic Neoplasms / Q000473:pathology*; D015203:Reproducibility of Results