Assessment of Reproducibility of Geometric Distortion in MRI using Phantom Measurements

Authors

1 M.Sc. in Nuclear Engineering Dept., Islamic Azad University, Tehran, Iran.

2 Associate Professor, Physics and Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran. Research Center for Science & Technology in Medicine, Imam Khomeini Hospital, Tehran. Iran.

3 M. Sc. in Research Center for Science & Technology in Medicine, Imam Khomeini Hospital, Tehran. Iran.

4 Associate Professor, Radiology Dept., Medical Imaging Center, Imam Khomeini Hospital, Tehran University of Medical Sciences , Tehran, Iran.

5 Assistant Professor, Radiology Dept., Medical Imaging Center, Imam Khomeini Hospital, Tehran University of Medical Sciences , Tehran, Iran.

6 B. Sc. in Medical Imaging Center, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran, Iran.

Abstract

Introduction:  Image  distortion  is  one  of  the  major  problems  of  magnetic  resonance  imaging 
(MRI) for use in 3DMRI, velocity MRI, FMRI and radiotherapy treatment planning (RTTP). It is 
widely known that the most obvious effect of the inhomogenity of the magnetic fields and the 
nonlinearity  of  the  gradient  is  the  Geometric  Distortion  of  MR  tomograms.  In  this  study,  the 
accuracy of MR images was considered by the phantom study and the reproducibility of images 
was evaluated by repeating the phantom measurements. 
Materials and Methods: MRI scans of the phantom with grid pattern inside it were performed 
using head coil in two 1.5 Tesla MRI systems (Picker VISTA TM HPQ, USA & GE Signa Echo 
Speed, USA). For the Geometric Distortion reproducibility evaluation the T1W, T2W and PDW 
SE  protocols  were  repeated  three  times.  The  Geometric  Distortion  was  measured  by  an  edge 
detection program in MATLAB.  
Results: The geometric distortion in the peripheral area of the images tends to be generally larger 
than it in the central area in all images. The average displacement in Picker MRI was 3 pixels in 
the y and 1 pixel in the x direction and in GE MRI it was 1 pixel in both x and y direction for 24 
cm FOV (pixel = 0.9 mm). 
Discussion and Conclusions: Since the positional variation was within 1 to 3 pixels for the head 
coil, it will be possible to use this MR system in 3DMRI, velocity MRI, FMRI and RTTP. To 
decrease the geometric distortion the use of suitable coil and protocol are expected.  

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Iranian Journal of Medical Physics
Volume 2, Issue 3 - Serial Number 3
September and October 2005
Pages 1-8

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History

  • Receive Date: 07 June 2005
  • Revise Date: 11 July 2005
  • Accept Date: 10 August 2005

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