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.
Keywords
Main Subjects
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