SU‐F‐I‐15: Evaluation of a New MR‐Compatible Respiratory Motion Device at 3T

Abstract

Purpose:Recent advances in MRI‐guided radiotherapy has inspired the development of MRI‐compatible motion devices that simulate patient periodic motion in the scanner, particularly respiratory motion. Most commercial devices rely on non MR‐safe ferromagnetic stepper motors which are not practical for regular QA testing. This work evaluates the motion performance of a new fully MRI compatible respiratory motion device at 3T.Methods:The QUASAR™ MRI‐compatible respiratory motion phantom has been recently developed by Modus QA Inc., London, ON, Canada. The prototype is constructed from diamagnetic materials with linear motion generated using MRI‐compatible piezoelectric motors that can be safely inserted in the scanner bore. The tumor was represented by a fillable sphere and is attached to the linear motion generator. The spherical tumor‐representative and its surroundings were filled with different concentrations of MnCl2 to produce realistic relaxation times. The motion was generated along the longitudinal (H/F) axis of the bore using sinusoidal reference waveform (amplitude = 15 mm, frequency 0.25 Hz). Imaging was then performed on 3T Philips Achieva using a 32‐channel cardiac coil. Fast 2D spoiled gradient‐echo was used with a spatial resolution of 1.8 × 1.8 mm2 and slice thickness of 4 mm. The motion waveform was then measured on the resultant image series by tracking the centroid of the sphere through the time series. This image‐derived measured motion was compared to the software‐generated reference waveform.Results:No visible distortions from the device were observed on the images. Excellent agreement between the measured and the reference waveforms were obtained. Negligible motion was observed in the lateral (R/L) direction.Conclusion:Our investigation demonstrates that this piezo‐electric motor design is effective at simulating periodic motion and is a potential candidate for MRI‐radiotherapy respiratory motion simulation. Future work should focus on evaluating non‐sinusoidal waveforms, fast 3D pulse sequences, and perform dosimetric QA.