Download comprehensive quality control of nmr tomography using 3d printed

COMPREHENSIVE QUALITY CONTROL
OF NMR TOMOGRAPHY USING
3D PRINTED PHANTOM
Mažena MACIUSOVIČ*, Marius BURKANAS*,
Jonas VENIUS*, **
*Medical
**Laboratory
Physics Department, National Cancer Institute, Vilnius, Lithuania
of Biomedical Physics, National Cancer Institute, Vilnius, Lithuania
12TH INTERNATIONAL CONFERENCE “MEDICAL PHYSICS IN THE
BALTIC STATES 2015” 5-7th of November
Kaunas
What is MRI?
A non-invasive imaging technique for studying soft tissue
structures and characteristics.
The MRI technique has been used for imaging the brain,
heart, muscles and joints, for early diagnosing and staging
of the diseases, monitoring the effects of therapies.
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In short
The patient is placed into a magnetic field.
A radio frequency wave is sent in.
The radio frequency wave is turned off.
The patient emits a signal.
The signal is received and used for reconstruction
of the picture.
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Bayer, 2010.
Purpose
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To achieve the full potential of MRI and optimal images in a
hospital there is a need for testing instrument performance
and evaluating the system stability.
Protocols for quality assurance (QA) and quality control (QC)
of MRI system are required.
A simple 3D printer compatible “all in one” phantom design
was presented to fulfil the basic requirements for the
assessment of stable MRI scanner operation.
Daily/weekly/monthly measurements were performed and the
suitability of the proposes system for the stability evaluation
was confirmed.
Methods and materials
Spherical phantom (20 cm Ø) has been made using a
SOLIDWORKS software program.
The phantom has been printed using a Dimension 1200es 3D
Printer.
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Image and the view of the modelled phantom design rendered on SOLIDWORKS
software.
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Methods and materials
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The phantom has been printed in four different parts – two
hemispheres, the grid plate and the rest inner structures printed
in one object (low contrast plate, spatial resolution plate, four
side structures with crossing grooves).
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The structures were fixed together and filled with aqueous
nickel chloride and sodium chloride solution.
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Methods and materials
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Experiments were performed on a clinical 1.5 T MR-system Achieva
XR at National Cancer Institute using Philips SENSE Head coil.
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All measurements were performed in one procedure – no removing
or repositioning of the phantom has been done.
Measurements for every parameter have been performed five times,
to acquire reliable data.
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Results: Image uniformity
The variation of percentage image uniformity over measurement period.
PIU obtained for the properly functioning scanner should be more than 90%.
Calculated PIU is 94.93% ± 1.54.
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Results: SNR
The variation of SNR values in the MRI images over measurement period.
The observed SNR stability is 73.99 ± 6.05 (the allowed limits over
measurement time ± 10 %).
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Results: Geometrical distortion
The variation of calculated maximum percent geometric distortion (PGD) over
measurement period.
The allowed value of maximum PGDs should not exceed 2%. The average
maximum PGDs over the whole measurement period was 1.04 % ± 0.20.
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Results: High contrast spatial resolution
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The plate consists of a line shape holes that form a high
resolution test pattern of 1 – 16 line pair/cm.
Spatial resolution is evaluated by visually estimating the amount
of line pairs in centimetre that are still possible to distinguish as
different lines.
During the whole measurement
period 6 lp/cm has been clearly
visible.
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Results: Low contrast resolution
The variation of different contrast levels over measurement period.
The average values of different contrast levels (from 1 to 6) are: 0.5 ± 0.01, 0.39 ±
0.01, 0.26 ± 0.01, 0.17 ± 0.01, 0.14 ± 0.01, 0.07 ± 0.004. The observed different
contrast levels vary less than 10 % .
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Results: Slice thickness
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Slice thickness is evaluated by measuring the width of the
groove G seen in the images and multiplied by the factor of
0.5.
The width of the groove is calculated as FWHM of pixel
intensity profile (Line P) of the groove.
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Results: Slice thickness
The calculated slice thicknesses over measurement period.
The calculated average slice thickness is 5.3 mm ± 0.15. The values are
randomly distributed and no tendency can be identified.
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Results: Slice position
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Verification is performed by measuring distances between
crossing grooves seen in Slice 1 (distance d1) and Slice 6
(distance d2).
The distance between slices is 25 mm.
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Results: Slice position
Deviations of the measured slice position from the set position over measurement
period.
The average difference from the set position is 0.72 mm ± 0.39 when the positioning
distance is 25 mm.
The deviations are distributed randomly and there is no tendency to lower or increase.
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Conclusion
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The 3D printed phantom allowed to measure and
calculate all required parameters to evaluate image
uniformity, geometric accuracy, SNR, high contrast and
low contrast spatial resolution, slice thickness and slice
position.
The deviation of the measured/calculated parameters has
been insignificant therefore the observed constancy of
these parameters is sufficient to declare the stable
operation of the MRI scanner.
To expand the abilities of the printable system further
developments and investigations are planned to be
performed.
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