Objective The purpose of this study was to implement a nonmagnetic micropositioner in the MRI environment to validate displacement estimates of magnetic resonance acoustic radiation force imaging (MR-ARFI). Methods The micropositioner consisted of a stage driven by a piezoelectric stepper motor in closed-loop operation with an optical quadrature encoder. A 100-gram agar gel phantom was prepared, and three MR-ARFI pulse sequences were used to generate displacement maps. MR-ARFI measured displacements were compared to ground truth data from the optical encoder. Results The micropositioner demonstrated consistent performance with positioning times of <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$1.6 \pm 0.4$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1.6</mn> <mo>±</mo> <mn>0.4</mn> </mrow> </math></EquationSource> </InlineEquation> ms for extension and <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$2.2 \pm 0.2$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>2.2</mn> <mo>±</mo> <mn>0.2</mn> </mrow> </math></EquationSource> </InlineEquation> ms for return to baseline position. The micropositioner decreased the signal-to-noise ratio of magnitude images due to increased electronic noise. Linear regression analysis showed that displacement measurements were highly linear with <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$R^2 \ge 0.98$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>R</mi> <mn>2</mn> </msup> <mo>≥</mo> <mn>0.98</mn> </mrow> </math></EquationSource> </InlineEquation> but exhibited scaling biases that may have been due to the experimental setup. Conclusion The proposed instrument can potentially improve the accuracy and precision of MR-ARFI-based applications, including focused ultrasound dosimetry and mechanical biomarker imaging.

A nonmagnetic micropositioner for displacement measurement validation in the MRI environment

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2026年4月21日

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William Ryan Willoughby,
Mark Bolding

摘要

Objective

The purpose of this study was to implement a nonmagnetic micropositioner in the MRI environment to validate displacement estimates of magnetic resonance acoustic radiation force imaging (MR-ARFI).

Methods

The micropositioner consisted of a stage driven by a piezoelectric stepper motor in closed-loop operation with an optical quadrature encoder. A 100-gram agar gel phantom was prepared, and three MR-ARFI pulse sequences were used to generate displacement maps. MR-ARFI measured displacements were compared to ground truth data from the optical encoder.

Results

The micropositioner demonstrated consistent performance with positioning times of $1.6 \pm 0.4$ $1.6 \pm 0.4$ ms for extension and $2.2 \pm 0.2$ $2.2 \pm 0.2$ ms for return to baseline position. The micropositioner decreased the signal-to-noise ratio of magnitude images due to increased electronic noise. Linear regression analysis showed that displacement measurements were highly linear with $R^2 \ge 0.98$ $R^{2} \geq 0.98$ but exhibited scaling biases that may have been due to the experimental setup.

Conclusion

The proposed instrument can potentially improve the accuracy and precision of MR-ARFI-based applications, including focused ultrasound dosimetry and mechanical biomarker imaging.