title: Detection of Focal Longitudinal Changes in the Brain by Subtraction of MR Images.
abstract: OBJECTIVE
  The detection of new subtle brain pathology on MR imaging is a time-consuming and error-prone task for the radiologist. This article introduces and evaluates an image-registration and subtraction method for highlighting small changes in the brain with a view to minimizing the risk of missed pathology and reducing fatigue.
  
  
  METHODS
  We present a fully automated algorithm for highlighting subtle changes between multiple serially acquired brain MR images with a novel approach to registration and MR imaging bias field correction. The method was evaluated for the detection of new lesions in 77 patients undergoing cardiac surgery, by using pairs of fluid-attenuated inversion recovery MR images acquired 1-2 weeks before the operation and 6-8 weeks postoperatively. Three radiologists reviewed the images.
  
  
  RESULTS
  On the basis of qualitative comparison of pre- and postsurgery FLAIR images, radiologists identified 37 new ischemic lesions in 22 patients. When these images were accompanied by a subtraction image, 46 new ischemic lesions were identified in 26 patients. After we accounted for interpatient and interradiologist variability using a multilevel statistical model, the likelihood of detecting a lesion was 2.59 (95% CI, 1.18-5.67) times greater when aided by the subtraction algorithm (P= .017). Radiologists also reviewed the images significantly faster (P< .001) by using the subtraction image (mean, 42 seconds; 95% CI, 29-60 seconds) than through qualitative assessment alone (mean, 66 seconds; 95% CI, 46-96 seconds).
  
  
  CONCLUSIONS
  Use of this new subtraction algorithm would result in considerable savings in the time required to review images and in improved sensitivity to subtle focal pathology.
authors.affiliation: From the Department of Cardiovascular Sciences (N.P., M.A.H., M.N., J.N., E.M.L.C.), University of Leicester, Leicester Royal Infirmary, Leicester, UK.|Leicester National Institute of Health Research Cardiovascular Biomedical Research Unit (N.P., E.M.L.C.), Glenfield Hospital, Leicester, UK.
authors.forename: N
authors.identifier: http://orcid.org/0000-0002-1400-1456
authors.initials: N
authors.lastname: Patel
authors.affiliation: From the Department of Cardiovascular Sciences (N.P., M.A.H., M.N., J.N., E.M.L.C.), University of Leicester, Leicester Royal Infirmary, Leicester, UK.
authors.forename: M A
authors.identifier: http://orcid.org/0000-0002-0815-6697
authors.initials: MA
authors.lastname: Horsfield
authors.affiliation: Medical Physics (C.B., E.M.L.C.), University Hospitals of Leicester National Health Service Trust, Leicester, UK.
authors.forename: C
authors.identifier: http://orcid.org/0000-0002-4941-949X
authors.initials: C
authors.lastname: Banahan
authors.affiliation: Departments of Radiology (A.G.T., P.B.A.).
authors.forename: A G
authors.identifier: http://orcid.org/0000-0003-2393-4191
authors.initials: AG
authors.lastname: Thomas
authors.affiliation: From the Department of Cardiovascular Sciences (N.P., M.A.H., M.N., J.N., E.M.L.C.), University of Leicester, Leicester Royal Infirmary, Leicester, UK.
authors.forename: M
authors.identifier: http://orcid.org/0000-0002-0753-0464
authors.initials: M
authors.lastname: Nath
authors.affiliation: From the Department of Cardiovascular Sciences (N.P., M.A.H., M.N., J.N., E.M.L.C.), University of Leicester, Leicester Royal Infirmary, Leicester, UK.
authors.forename: J
authors.identifier: http://orcid.org/0000-0002-6578-0963
authors.initials: J
authors.lastname: Nath
authors.affiliation: Departments of Radiology (A.G.T., P.B.A.).|Neuri Beaujon (P.B.A.), University Paris Diderot, Paris, France.
authors.forename: P B
authors.identifier: http://orcid.org/0000-0001-7042-5598
authors.initials: PB
authors.lastname: Ambrosi
authors.affiliation: From the Department of Cardiovascular Sciences (N.P., M.A.H., M.N., J.N., E.M.L.C.), University of Leicester, Leicester Royal Infirmary, Leicester, UK emlc1@leicester.ac.uk.|Leicester National Institute of Health Research Cardiovascular Biomedical Research Unit (N.P., E.M.L.C.), Glenfield Hospital, Leicester, UK.|Medical Physics (C.B., E.M.L.C.), University Hospitals of Leicester National Health Service Trust, Leicester, UK.
authors.forename: E M L
authors.identifier: http://orcid.org/0000-0003-3723-9085
authors.initials: EML
authors.lastname: Chung
mesh_terms: D000368:Aged; D000465:Algorithms; D001927:Brain Diseases / Q000000981:diagnostic imaging* / Q000473:pathology; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D013382:Subtraction Technique