title: Use of an automatic exposure control mechanism for dose optimization in multi-detector row CT examinations: clinical evaluation.
abstract: OBJECTIVE
  To prospectively compare dose reduction and image quality achieved with an automatic exposure control system that is based on both angular (x-y axis) and z-axis tube current modulation with dose reduction and image quality achieved with an angular modulation system for multi-detector row computed tomography (CT).
  
  
  METHODS
  The study protocol was approved by the institutional review board, and oral informed consent was obtained. In two groups of 200 patients, five anatomic regions (ie, the thorax, abdomen-pelvis, abdomen-liver, lumbar spine, and cervical spine) were examined with this modulation system and a six-section multi-detector row CT scanner. Data from these patients were compared with data from 200 patients who were examined with an angular modulation system. Dose reduction by means of reduction of the mean effective tube current in 600 examinations, image noise in 200 examinations performed with each modulation system, and subjective image quality scores in 100 examinations per-formed with each modulation system were compared with Wilcoxon signed rank tests.
  
  
  RESULTS
  Mean dose reduction for the angular and z-axis tube current modulation system and for the angular modulation system was as follows: thorax, 20% and 14%, respectively; abdomen-liver, 38% and 18%, respectively; abdomen-pelvis, 32% and 26%, respectively; lumbar spine, 37% and 10%, respectively; and cervical spine, 68% and 16%, respectively. These differences were statistically significant (P < .05). There was no significant difference in image noise and mean image quality scores between modulation systems, with the exception of cervical spinal examinations (P < .001 for both), where the examinations with angular modulation resulted in better scores. There is good correlation between the mean effective tube current level and the body mass index of patients with the new modulation system. Correlation was as follows: thorax, 0.77; abdomen-pelvis, 0.83; abdomen-liver, 0.84; lumbar spine, 0.8; and cervical spine, 0.6. This correlation was not observed with the angular modulation system.
  
  
  CONCLUSIONS
  An automatic exposure control mechanism that is based on real-time anatomy-dependent tube current modulation delivers good image quality with a significantly reduced radiation dose.
authors.affiliation: Department of Radiology, Heilig Hart Hospital, Kolveniersvest 20, B-2500 Lier, Belgium. tom.mulkens@hhzhlier.be
authors.forename: Tom H
authors.initials: TH
authors.lastname: Mulkens
authors.forename: Patrick
authors.initials: P
authors.lastname: Bellinck
authors.forename: Michel
authors.initials: M
authors.lastname: Baeyaert
authors.forename: Dirk
authors.initials: D
authors.lastname: Ghysen
authors.forename: Xavier
authors.initials: X
authors.lastname: Van Dijck
authors.forename: Elvier
authors.initials: E
authors.lastname: Mussen
authors.forename: Caroline
authors.initials: C
authors.lastname: Venstermans
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Termote
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011829:Radiation Dosage; D011860:Radiography, Abdominal; D013902:Radiography, Thoracic; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*