title: Improved CT Detection of Acute Herpes Simplex Virus Type 1 Encephalitis Based on a Frequency-Selective Nonlinear Blending: Comparison With MRI.
abstract: OBJECTIVE
  The purpose of this study is to compare the diagnostic efficacy of a new CT postprocessing tool based on frequency-selective nonlinear blending (best-contrast CT) with that of standard linear blending of unenhanced head CT in patients with herpes simplex virus type 1 and herpes simplex virus encephalitis (HSE), using FLAIR MRI sequences as the standard of reference.
  
  
  METHODS
  Fifteen consecutive patients (six women and nine men; mean [± SD] age, 60 ± 19 years) with proven HSE (positive polymerase chain reaction results from CSF analysis and the presence of neurologic deficits) were retrospectively enrolled. All patients had undergone head CT and MRI (mean time interval, 2 ± 2 days). After standardized unenhanced head CT scans were read, presets of the best-contrast algorithm were determined (center, 30 HU; delta, 5 HU; slope, 5 nondimensional), and resulting images were analyzed. Contrast enhancement was objectively measured by ROI analysis, comparing contrast-to-noise ratios (CNRs) of unenhanced CT and best-contrast CT. FLAIR and DWI MRI sequences were analyzed, and FLAIR was considered as the standard of reference. For assessment of disease extent, a previously reported 50-point score (HSE score) was used.
  
  
  RESULTS
  CNR values for unenhanced head CT (CNR, 5.42 ± 2.77) could be statistically significantly increased using best-contrast CT (CNR, 9.62 ± 4.28) (p = 0.003). FLAIR sequences yielded a median HSE score of 9.0 (range, 6-17) and DWI sequences yielded HSE scores of 6.0 (range, 5-17). By comparison, unenhanced head CT resulted in a median HSE score of 3.5 (range, 1-6). The median best-contrast CT HSE score was 7.5 (range, 6-10). Agreement between FLAIR and unenhanced CT was 54.44%, that between DWI and best-contrast CT was 95.36%, and that between FLAIR and best-contrast CT was 85.21%. The most frequently overseen findings were located at the level of the upper part of the mesencephalon and at the subthalamic or insular level.
  
  
  CONCLUSIONS
  Frequency-selective nonlinear blending significantly increases contrast and detects brain parenchymal involvement in HSE more sensitively compared with unenhanced CT. The sensitivity of best-contrast CT seems to be equal to that of DWI and almost as good as that of FLAIR.
authors.affiliation: 1 Department of Diagnostic and Interventional Radiology, University Hospital of Tübingen, Hoppe-Seyler-Strasse 3, Tübingen 72076, Germany.
authors.forename: Malte Niklas
authors.initials: MN
authors.lastname: Bongers
authors.affiliation: 1 Department of Diagnostic and Interventional Radiology, University Hospital of Tübingen, Hoppe-Seyler-Strasse 3, Tübingen 72076, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: Bier
authors.affiliation: 2 Healthcare Sector, Siemens AG, Forchheim, Germany.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Ditt
authors.affiliation: 3 Institute of Medical Virology and Epidemiology of Viral Diseases, University Hospital of Tübingen, Tübingen, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Beck
authors.affiliation: 4 Department of Diagnostic and Interventional Neuroradiology, University Hospital of Tübingen, Tübingen, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Ernemann
authors.affiliation: 1 Department of Diagnostic and Interventional Radiology, University Hospital of Tübingen, Hoppe-Seyler-Strasse 3, Tübingen 72076, Germany.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Nikolaou
authors.affiliation: 1 Department of Diagnostic and Interventional Radiology, University Hospital of Tübingen, Hoppe-Seyler-Strasse 3, Tübingen 72076, Germany.
authors.forename: Marius
authors.initials: M
authors.lastname: Horger
mesh_terms: D020803:Encephalitis, Herpes Simplex / Q000000981:diagnostic imaging* / Q000821:virology*; D005260:Female; D018259:Herpesvirus 1, Human; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed
keywords: CT; MR tomography; contrast enhancement; herpes simplex virus type 1 encephalitis; nonlinear blending