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Noise in polymer gel measurements using MRI
D A Low1, J Markman, J F Dempsey
1Mallinckrodt Institute of Radiology, Division of Radiation Oncology, St. Louis, Missouri 63110, USA. low@castor.wustl.edu
Medical Physics
|September 13, 2000
Summary
BANG-2 gel shows potential as a multidimensional dosimeter for radiation therapy. However, voxel-to-voxel variations and magnetic resonance imaging artifacts limit its accuracy, necessitating improved readout sequences.
Area of Science:
- Medical Physics
- Radiotherapy Dosimetry
- Polymer Chemistry
Background:
- Advancements in conformal radiotherapy, like intensity-modulated radiation therapy (IMRT), demand sophisticated multidimensional dosimeters.
- BANG-2 gel is a novel polymerizing gel with potential for 3D radiation dose measurement.
Purpose of the Study:
- To investigate and characterize noise and magnetic resonance (MR) imaging artifacts in BANG-2 gels.
- To assess the accuracy of BANG-2 gel as a multidimensional dosimeter for radiotherapy.
Main Methods:
- Irradiating BANG-2 gel samples in vials using a water bath.
- Reading irradiated gels using magnetic resonance imaging (MRI) with specific parameters (B0=1.5 T, TE=20 ms/100 ms, TR=3000 ms).
- Calibrating the gel by comparing measured depth-dose distributions with changes in solvent-proton R2 relaxivity.
Main Results:
- The calibration curve demonstrated high accuracy (within 1.3%) for depth dose measurements.
- Voxel-to-voxel variations were identified as the primary source of dose measurement uncertainty, ranging from 0.2 Gy to 0.7 Gy.
- Slice-to-slice R2 magnitude deviations, equivalent to 0.2 Gy, were also observed, impacting overall accuracy.
Conclusions:
- BANG-2 gel shows promise as a multidimensional dosimeter but requires further optimization.
- Noise and MR artifacts, particularly voxel-to-voxel variations, currently limit the precision of dose measurements.
- Further research into advanced MR readout sequences is recommended to enhance the accuracy of BANG-2 gel dosimetry.