title: A comparison between acoustic output indices in 2D and 3D/4D ultrasound in obstetrics.
abstract: OBJECTIVE
  Three-dimensional (3D) ultrasound is gaining popularity in prenatal diagnosis. While there are no studies regarding the safety of 3D ultrasound, it is now widely performed in non-medical facilities, for non-diagnostic purposes. The present study was aimed at comparing the acoustic output, as expressed by thermal index (TI) and mechanical index (MI), of conventional two-dimensional (2D) and 3D/4D ultrasound during pregnancy.
  
  
  METHODS
  A prospective, observational study was conducted, using three different commercially available machines (iU22, Philips Medical Systems; Prosound Alfa-10, Aloka; and Voluson 730 Expert, General Electric). Patients undergoing additional 3D/4D ultrasound examinations were recruited from those scheduled for fetal anatomy and follow-up exams. Fetuses with anomalies were excluded from the analysis. Data were collected regarding duration of the exam, and each MI and TI during 2D and 3D/4D ultrasound exams.
  
  
  RESULTS
  A total of 40 ultrasound examinations were evaluated. Mean gestational age was 31.1 +/- 5.8 weeks, and mean duration of the exam was 20.1 +/- 9.9 min. Mean TIs during the 3D (0.27 +/- 0.1) and 4D examinations (0.24 +/- 0.1) were comparable with the TI during B-mode scanning (0.28 +/- 0.1, P = 0.343). The MIs during the 3D volume acquisitions were significantly lower than those in the 2D B-mode ultrasound studies (0.89 +/- 0.2 vs. 1.12 +/- 0.1, P = 0.018). The 3D volume acquisitions added 2.0 +/- 1.8 min of actual ultrasound scanning time (i.e. not including data processing and manipulation, or 3D displays, which are all post-processing steps). The 4D added 2.2 +/- 1.2 min.
  
  
  CONCLUSIONS
  Acoustic exposure levels during 3D/4D ultrasound examination, as expressed by TI, are comparable with those of 2D B-mode ultrasound. However, it is very difficult to evaluate the additional scanning time needed to choose an adequate scanning plane and to acquire a diagnostic 3D volume.
authors.affiliation: Department of Obstetrics and Gynecology, Rush University Medical Center, Chicago, IL 60612, USA. sheiner@bgu.ac.il
authors.forename: E
authors.initials: E
authors.lastname: Sheiner
authors.forename: R
authors.initials: R
authors.lastname: Hackmon
authors.forename: I
authors.initials: I
authors.lastname: Shoham-Vardi
authors.forename: X
authors.initials: X
authors.lastname: Pombar
authors.forename: M J
authors.initials: MJ
authors.lastname: Hussey
authors.forename: H T
authors.initials: HT
authors.lastname: Strassner
authors.forename: J S
authors.initials: JS
authors.lastname: Abramowicz
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D005260:Female; D005865:Gestational Age; D006801:Humans; D009622:Noise; D009774:Obstetrics / Q000379:methods*; D011247:Pregnancy; D011446:Prospective Studies; D012016:Reference Values; D016037:Single-Blind Method; D013995:Time; D016216:Ultrasonography, Prenatal / Q000009:adverse effects / Q000379:methods / Q000592:standards*