Assessment of geometric distortion of eleven clinical MRI scanners across the UK
Alzahrani, M. Broadbent, D. Chuter, Robert Al-Qaisieh, B. Jackson, Stephen J Hutton, M Johnstone, R. Shah, S. Wetscherek, A. Chick, J.
Alzahrani, M.
Broadbent, D.
Chuter, Robert
Al-Qaisieh, B.
Jackson, Stephen J
Hutton, M
Johnstone, R.
Shah, S.
Wetscherek, A.
Chick, J.
Citations
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Abstract
Purpose or Objective
MRI is increasingly being used in radiotherapy (RT) in the
UK for delineation, MRI-only planning and image guidance
on an MR-linac. Geometric distortions are a known challenge of using MRI in RT. The aim of this work was to
assess large FOV MRI distortions in a number of scanners
used for RT throughout the UK.
Material and Methods
MRI scans of a GRADE phantom (Spectronic Medical AB,
Helsingborg, Sweden) were acquired using a protocol
recommended by the manufacturer (3D gradient echo, FoV
50x50x50 cm, voxel size 1x1x2 mm and Bandwidth 490
Hz/pixel) on the following 11 MRI scanners that are used
for RT in the UK: Siemens Aera (Leeds, Guy’s and St
Thomas’, Royal Marsden and Christie); Siemens Prisma
(Leeds); Siemens Sola (Leeds); Siemens Skyra (Christie);
Siemens Espree (Newcastle); Elekta Unity (Christie);
Philips Ingenia 1.5T (Christie); GE Signa PET/MR
(Newcastle). Scanners are referred to as 1-11 in a
randomised order (for anonymity). Analysis was performed
using MriPlanner (Spectronic Medical AB, Helsingborg,
Sweden), the mean and max distortions and variance (δ2)
between scanners were reported at <100, 100-150, 150-
200, 200-250 and ≥250 mm from the isocentre.
Results
The range of the mean and max distortions for all scanners
at 100-150 mm (representing the typical size of a brain)
were 0.28-0.62 mm and 0.69-2.81 mm respectively. The
range of the mean and max distortions for all scanners at
200-250 mm (representing the typical size of a pelvis) were
0.67-2.52 mm and 2.0-10.75 mm respectively. The mean
and maximum distortions are shown in figure 1 and at
<100, 100-150, 150-200, 200-250 and ≥250 mm from the
isocentre, δ2 was 0.004, 0.009, 0.045, 0.232 and 0.779
mm2 respectively. The greatest mean geometric distortion
(5.04 mm) observed was scanner 9 at ≥250 mm from the
isocentre. For uses requiring a small FOV (less than 150
mm from the isocentre) such as brain imaging, both mean
and maximum distortions would be < 2 mm except for the
maximum distortion of one scanner. For uses requiring a
large FOV (up to 250 mm from the isocentre) such as the
head and neck and the entire pelvis, the mean distortions
would be < 2 mm except for those from one scanner. Conclusion
Geometric distortion was assessed on 11 scanners used for
RT across the UK and for all scanners distortion increased
with distance to isocentre. Variance of geometric
distortions between scanners was found to be low (<0.8)
and increased with distance to isocentre. The vast
majority of scanners showed mean distortions of > 2 mm
at a distance ≥ 250 mm from the isocentre, but these
values have limited clinical relevance. This assessment
demonstrates feasibility of the technique to be repeated
in a UK wide audit of all MRI scanners used clinically for
RT.
Description
Date
2020
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Alzahrani M, Broadbent D, Chuter R, Al-Qaisieh B, Jackson S, Hutton M, et al. PH-0531: Assessment of geometric distortion of eleven clinical MRI scanners across the UK. Radiotherapy and Oncology . 2020 Nov;152:S293–4.