Simple methods to test the accuracy of MRgFUS robotic systems

Abstract

Background: Robotic-assisted diagnostic and therapeutic modalities require a highly accurate performance to be certified for clinical application. In this paper, three simple methods for assessing the accuracy of motion of magnetic resonance-guided focused ultrasound (MRgFUS) robotic systems are presented.

Methods: The accuracy of motion of a 4 degrees of freedom robotic system intended for preclinical use of MRgFUS was evaluated by calliper-based and magnetic resonance imaging (MRI) methods, as well as visually by performing multiple ablations on a plastic film.

Results: The benchtop results confirmed a highly accurate motion in all axes of operation. The spatial positioning errors estimated by MRI evaluation were defined by the size of the imaging pixels. Lesions arrangement in discrete and overlapping patterns confirmed satisfactory alignment of motion trajectories.

Conclusions: We believe the methods presented here should serve as a standard for evaluating the accuracy of motion of MRgFUS robotic systems.

Keywords: MRgFUS robotic devices; motion accuracy; simple evaluation methods.

FIGURE 1

Computer‐aided design drawing of the 4 degrees of freedom robotic system (A) without the cover (components are visualized) and (B) with the cover

FIGURE 2

(A) Stationary (1, 2, 4) and moveable (3) 3D‐printed structures that were used for the X and Y axes distance measurements and (B) computer‐aided design drawing of the setup that was used for the X axis motion accuracy estimation

FIGURE 3

Experimental setup used for estimating the angular motion accuracy using the digital angle calliper; (A) computer‐aided design drawing and (B) photo

FIGURE 4

(A) The robotic device (i) as placed on the magnetic resonance imaging table, showing the location of the plastic marker (ii) and the flex surface coil (iii), and (B) computer‐aided design drawing of the plastic marker used for accuracy measurements

FIGURE 5

Distance measurements for 20 repetitions in the X‐axis with step movement of 5 mm in bidirectional movements. The black straight line indicates the commanded distance

FIGURE 6

Minimum intensity projection from a combination of fast spin echo coronal images that shows a (A) reverse step movement of 3 mm in the X direction and (B) right step movement of 3 mm in the Y direction

FIGURE 7

Effect of varying sonication time on lesion formation on the plastic film, using low power and a spatial step of 10 mm (transducer specifications: 1.1 MHz frequency, 50 mm diameter and 70 mm focal length)

FIGURE 8

Discrete lesions as formed on the plastic film for sonications in a 6 × 5 grid pattern, with acoustical power of 10 W for 1 s and a step distance of 5 mm

FIGURE 9

Overlapping lesions as formed on the plastic film for sonications in a 15 × 15 grid pattern, with acoustical power of 10 W for 3 s and a step distance of 2 mm