title: Multiscale bilateral filtering for improving image quality in digital breast tomosynthesis.
abstract: OBJECTIVE
  Detection of subtle microcalcifications in digital breast tomosynthesis (DBT) is a challenging task because of the large, noisy DBT volume. It is important to enhance the contrast-to-noise ratio (CNR) of microcalcifications in DBT reconstruction. Most regularization methods depend on local gradient and may treat the ill-defined margins or subtle spiculations of masses and subtle microcalcifications as noise because of their small gradient. The authors developed a new multiscale bilateral filtering (MSBF) regularization method for the simultaneous algebraic reconstruction technique (SART) to improve the CNR of microcalcifications without compromising the quality of masses.
  
  
  METHODS
  The MSBF exploits a multiscale structure of DBT images to suppress noise and selectively enhance high frequency structures. At the end of each SART iteration, every DBT slice is decomposed into several frequency bands via Laplacian pyramid decomposition. No regularization is applied to the low frequency bands so that subtle edges of masses and structured background are preserved. Bilateral filtering is applied to the high frequency bands to enhance microcalcifications while suppressing noise. The regularized DBT images are used for updating in the next SART iteration. The new MSBF method was compared with the nonconvex total p-variation (TpV) method for noise regularization with SART. A GE GEN2 prototype DBT system was used for acquisition of projections at 21 angles in 3° increments over a ± 30° range. The reconstruction image quality with no regularization (NR) and that with the two regularization methods were compared using the DBT scans of a heterogeneous breast phantom and several human subjects with masses and microcalcifications. The CNR and the full width at half maximum (FWHM) of the line profiles of microcalcifications and across the spiculations within their in-focus DBT slices were used as image quality measures.
  
  
  RESULTS
  The MSBF method reduced contouring artifacts and enhanced the CNR of microcalcifications compared to the TpV method, thus preserving the image quality of the structured background. The MSBF method achieved the highest CNR of microcalcifications among the three methods. The FWHM of the microcalcifications and mass spiculations resulting from the MSBF method was comparable to that without regularization, and superior to that of the TpV method.
  
  
  CONCLUSIONS
  The SART regularized by the multiscale bilateral filtering method enhanced the CNR of microcalcifications and preserved the sharpness of microcalcifications and spiculated masses. The MSBF method provided better image quality of the structured background and was superior to TpV and NR for enhancing microcalcifications while preserving the appearance of mass margins.
authors.affiliation: Department of Radiology, University of Michigan, Ann Arbor, Michigan 48109.
authors.forename: Yao
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Department of Radiology, University of Michigan, Ann Arbor, Michigan 48109.
authors.forename: Heang-Ping
authors.initials: HP
authors.lastname: Chan
authors.affiliation: Department of Radiology, University of Michigan, Ann Arbor, Michigan 48109.
authors.forename: Jun
authors.initials: J
authors.lastname: Wei
authors.affiliation: Department of Radiology, University of Michigan, Ann Arbor, Michigan 48109.
authors.forename: Lubomir M
authors.initials: LM
authors.lastname: Hadjiiski
authors.affiliation: Department of Radiology, University of Michigan, Ann Arbor, Michigan 48109.
authors.forename: Ravi K
authors.initials: RK
authors.lastname: Samala
mesh_terms: D001940:Breast / Q000378:metabolism; D002114:Calcinosis / Q000000981:diagnostic imaging; D006801:Humans; D008327:Mammography / Q000379:methods*; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement / Q000379:methods*; D059629:Signal-To-Noise Ratio