title: Comparison of image quality between conventional and low-dose nonenhanced head CT.
abstract: OBJECTIVE
  Increasing use of CT for evaluating neurologic disease may expose patients to considerable levels of ionizing radiation. We compared the image quality of low-mAs head CT scans with that of conventional nonenhanced scans.
  
  
  METHODS
  Conventional head CT scans were obtained in 20 patients (all >65 years with history of non-CNS malignancy) by using a multidetector technique: 170 mA and 1-second scanning time (ie, 170 mAs), 140 kVp, table speed of 7.5 mm per rotation, pitch of 0.75, section thickness of 5 mm, and field of view of 25 mm. A limited volume helical data acquisition covering four 5-mm-thick images was obtained by using 90 mAs but otherwise the same parameters. Three neuroradiologists visually rated the resulting images for quality in a blinded comparison. Representative 1- to 4-mm(2) regions of interest were chosen in gray matter and white matter locations. Conspicuity and the contrast-to-noise ratio were analyzed. Statistical comparisons were done by using the Student t test.
  
  
  RESULTS
  Mean gray matter conspicuity was not significantly different between the 170- and 90-mAs groups (0.39 +/- 0.19 vs 0.41 +/- 0.03, P =.32). Mean gray matter contrast-to-noise ratio was approximately 22% higher with 170 mAs than with 90 mAs (1.77 +/- 0.52 vs 1.39 +/- 0.38, P =.005). All 90-mAs images were rated as having slightly greater image noise than the 170-mAs scans but with sufficient perceived resolution.
  
  
  CONCLUSIONS
  Although 90-mAs head CT images were moderately noisier than 170-mAs images, they were rated as having acceptable diagnostic quality.
authors.affiliation: Neuroradiology Division, Massachusetts General Hospital and the Harvard Medical School, Boston, MA, USA.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Mullins
authors.forename: Michael H
authors.initials: MH
authors.lastname: Lev
authors.forename: Peter
authors.initials: P
authors.lastname: Bove
authors.forename: Cara E
authors.initials: CE
authors.lastname: O'Reilly
authors.forename: Sanjay
authors.initials: S
authors.lastname: Saini
authors.forename: James T
authors.initials: JT
authors.lastname: Rhea
authors.forename: James H
authors.initials: JH
authors.lastname: Thrall
authors.forename: George J
authors.initials: GJ
authors.lastname: Hunter
authors.forename: Leena M
authors.initials: LM
authors.lastname: Hamberg
authors.forename: R Gilberto
authors.initials: RG
authors.lastname: Gonzalez
mesh_terms: D000368:Aged; D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging* / Q000528:radiation effects; D005260:Female; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D011786:Quality Control; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement; D011858:Radiographic Magnification / Q000592:standards; D011874:Radiometry / Q000592:standards*; D012680:Sensitivity and Specificity; D036542:Tomography, Spiral Computed / Q000592:standards*; D014057:Tomography, X-Ray Computed / Q000592:standards*