title: [Precision of MRI-guided needle placement--experimental results].
abstract: OBJECTIVE
  To estimate the accuracy of the determination of tip position of MR compatible biopsy needles based on signal voids and artifacts in MR guided biopsies.
  
  
  METHODS
  In a nylon grid phantom an MR compatible 18G needle (E-Z-EM) was measured in a 1.0 T imager using TSE- and FFE-sequences of 20 s and 40 s duration in 34 different orientations of needle versus B0, frequency and slice selection gradient. 4 radiologists with no experience in the evaluation of signal void artifacts estimated the needle tip positions from needle tip artifacts. The readers determined the needle tip before and after a 15 minute training session based on high resolution images with explanation of size and shape of specific artifacts of biopsy needles in 12 different orthogonal or parallel orientations to B0 and frequency encoding gradient that are possible if the needle lies parallel to the slice, i.e. orthogonal to the slice selection gradient. The values obtained before and after the training session were compared to the real position of the needle tip.
  
  
  RESULTS
  Mean distance of actual needle tip and tip position as determined from images was 1.8 +/- 2.3 mm in TSE-versus 2.5 +/- 1.2 mm in FFE-images, with the needle length overestimated. After a 15 minute training session the positioning error decreased significantly to 0.2 +/- 1.8 mm for TSE-sequences and to 1.0 +/- 1.8 mm for FFE-sequences. A higher accuracy of tip localization was obtained with TSE sequences.
  
  
  CONCLUSIONS
  In MR guided biopsies using FFE- and TSE-sequences the needle position can be more accurately determined if the reader is familiar with the 12 orthogonal or parallel positions of the needle with respect to B0 and frequency encoding gradient and the corresponding artifacts.
authors.affiliation: Röntgenabteilung der Missionsärztlichen Klinik Würzburg.
authors.forename: H J
authors.initials: HJ
authors.lastname: Langen
authors.forename: H
authors.initials: H
authors.lastname: Stützer
authors.forename: H
authors.initials: H
authors.lastname: Kugel
authors.forename: B
authors.initials: B
authors.lastname: Krug
authors.forename: V
authors.initials: V
authors.lastname: Hesselmann
authors.forename: O
authors.initials: O
authors.lastname: Schulte
authors.forename: C
authors.initials: C
authors.lastname: Walter
authors.forename: P
authors.initials: P
authors.lastname: Landwehr
mesh_terms: D016477:Artifacts; D001707:Biopsy, Needle / Q000379:methods*; D003287:Contrast Media; D019786:Gadolinium DTPA; D006801:Humans; D008279:Magnetic Resonance Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA