title: The use of magnetic resonance imaging to evaluate the accuracy of a handheld ultrasound machine in localizing the sciatic nerve in the popliteal fossa.
abstract: OBJECTIVE
  Ultrasound has become an increasingly popular modality in facilitating the performance of peripheral nerve blocks. There is a paucity of data describing techniques of ultrasound-guided sciatic nerve blocks. By using magnetic resonance imaging (MRI) as a gold standard, the objective of this study was to describe the ability of a handheld ultrasound machine to accurately locate the sciatic nerve.
  
  
  METHODS
  Ten patients were prospectively enrolled and placed in the prone position. By using a 4- to 7-MHz ultrasound transducer, the sciatic nerve was visualized in short axis between 5 to 10 cm above the popliteal crease. The distance from the skin to the nerve was measured by ultrasound, and a MRI lucent marker was placed at this site. This process was repeated in one additional location. The patient was then placed supine in the MRI scanner and short-axis T1-weighted images were obtained. On the MRI image, we recreated the 2 lines extending down from the markers using the distances previously measured by ultrasound. The point of intersection of these 2 lines represents the ultrasound-determined location of the sciatic nerve, which was then compared with the midpoint of the nerve complex on MRI.
  
  
  RESULTS
  The sciatic nerve was easily visualized by ultrasound in all 10 patients. MRI showed the division of the sciatic nerve in 9 out of 10 patients. Ultrasound was able to confirm this division in 7 patients. The mean distance between the MRI and ultrasound midpoint location of the sciatic nerve was 2.9 +/- 1.3 mm.
  
  
  CONCLUSIONS
  The data presented here suggest that the specific ultrasound machine evaluated in this study can accurately localize the sciatic nerve in the popliteal fossa.
authors.affiliation: Department of Anesthesiology, Dartmouth Medical School, Dartmouth Hitchcock Medical Center, Lebanon, NH 03756, USA. brian.sites@hitchcock.org
authors.forename: Brian D
authors.initials: BD
authors.lastname: Sites
authors.forename: John D
authors.initials: JD
authors.lastname: Gallagher
authors.forename: Ivan
authors.initials: I
authors.lastname: Tomek
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Cheung
authors.forename: Michael L
authors.initials: ML
authors.lastname: Beach
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007717:Knee / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000294:innervation*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D016684:Prone Position / Q000502:physiology; D011446:Prospective Studies; D015203:Reproducibility of Results; D012584:Sciatic Nerve / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D012680:Sensitivity and Specificity; D016683:Supine Position / Q000502:physiology; D014463:Ultrasonography / Q000295:instrumentation* / Q000379:methods*