title: Emergency CT head and neck imaging: effects of swimmer's position on dose and image quality.
abstract: OBJECTIVE
  To compare the effects of different arm positions on dose exposure and image quality (IQ) in cervical spine CT after trauma in different patient groups.
  
  
  METHODS
  Patients in standard (STD = 126) and in swimmer's position (SWIM = 254) were included. Body mass index (BMI subgroup 1 = underweight to subgroup 4 = obese), anterior-posterior diameter (AP), left-right diameter (LR), area of an ellipse (AoE) and angle between the humeral heads (optimal STD < 3°, optimal SWIM > 10°) were used as grouping criteria. Computed tomography dose index (CTDI) was documented. Two radiologists rated the IQ at three levels (CV1/2, CV4/5, CV7/T1) using a semi-quantitative scale (0 = not diagnostic, 1 = diagnostic with limitations, 2 = diagnostic without limitations). The Mann-Whitney U test correlations of grouping criteria with dose effects and intra-class correlation (ICC) were calculated.
  
  
  RESULTS
  ICC was 0.87. BMI grouping showed the strongest correlation with dose effects: CTDI of optimal STD versus optimal SWIM positioning was 3.17 mGy versus 2.46 mGy (subgroup 1), 5.47 mGy versus 3.97 mGy (subgroup 2), 7.35 mGy versus 5.96 mGy (subgroup 3) and 8.71 mGy versus 8.18 mGy (subgroup 4). Mean IQ at CV7/T1 was 1.65 versus 1.23 (subgroup 1), 1.27 versus 1.46 (subgroup 2), 1.06 versus 1.46 (subgroup 3), 0.79 versus 1.5 (subgroup 4).
  
  
  CONCLUSIONS
  Patients with a BMI > 20 kg/m(2) benefited from both potential dose reduction and improved image quality at the critical cervicothoracic junction when swimmer's position was used.
  
  
  CONCLUSIONS
  • BMI is a useful metric for personalized optimization in CT for the c-spine. • Using swimmer's position, patients can benefit from dose reduction. • In some patients a superior image quality can be achieved with swimmer's position. • For swimmer's positioning an angle of more than 10° is optimal.
authors: Institut für Klinische Radiologie, LMU Klinikum der Universität München - Innenstadt, Department of Clinical Radiology, LMU Hospital of the University of Munich - Downtown Campus, Nußbaumstr. 20, 80336, Munich, Germany, fabian.mueck@med.uni-muenchen.de.
authors: Fabian G
authors: FG
authors: Mueck
authors: Sebastian
authors: S
authors: Roesch
authors: Lucas
authors: L
authors: Geyer
authors: Michael
authors: M
authors: Scherr
authors: Michael
authors: M
authors: Seidenbusch
authors: Robert
authors: R
authors: Stahl
authors: Zsuzsanna
authors: Z
authors: Deak
authors: Stefan
authors: S
authors: Wirth
mesh_terms: D000328:Adult; D000368:Aged; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging*; D004307:Dose-Response Relationship, Radiation; D004632:Emergency Medical Services / Q000379:methods; D005260:Female; D006257:Head / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D009333:Neck / Q000000981:diagnostic imaging; D011187:Posture; D011829:Radiation Dosage; D013550:Swimming / Q000502:physiology*; D014057:Tomography, X-Ray Computed / Q000379:methods* / Q000592:standards