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Research Papers

A Patient-Mounted, Telerobotic Tool for CT-Guided Percutaneous Interventions

[+] Author and Article Information
Conor J. Walsh, Nevan C. Hanumara, Alexander H. Slocum

Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

Jo-Anne Shepard, Rajiv Gupta

Department of Radiology, Massachusetts General Hospital, Boston, MA 02114

J. Med. Devices 2(1), 011007 (Apr 08, 2008) (10 pages) doi:10.1115/1.2902854 History: Received September 26, 2007; Revised February 07, 2008; Published April 08, 2008

This paper describes Robopsy, an economical, patient-mounted, telerobotic, needle guidance and insertion system, that enables faster, more accurate targeting during CT-guided biopsies and other percutaneous interventions. The current state of the art imaging technology facilitates precise location of sites within the body; however, there is no mechanical equivalent to then facilitate precise targeting. The lightweight, disposable actuator unit, which affixes directly to the patient, is composed primarily of inexpensive, injection molded, radiolucent, plastic parts that snap together, whereas the four micromotors and control electronics are retained and reused. By attaching to a patient, via an adhesive pad and optional strap points, the device moves passively with patient motion and is thus inherently safe. The device’s mechanism tilts the needle to a two degree-of-freedom compound angle, toward the patient’s head or feet (in and out of the scanner bore) and left or right with respect to the CT slice, via two motor-actuated concentric, crossed, and partially nested hoops. A carriage rides in the hoops and interfaces with the needle via a two degree-of-freedom friction drive that both grips the needle and inserts it. This is accomplished by two rubber rollers, one passive and one driven, that grip the needle via a rack and pinion drive. Gripping is doctor controlled; thus when not actively being manipulated, the needle is released and allowed to oscillate within a defined region so as to minimize tissue laceration due to the patient breathing. Compared to many other small robots intended for medical applications, Robopsy is an order of magnitude less costly and lighter while offering appropriate functionality to improve patient care and procedural efficiency. This demonstrates the feasibility of developing cost-effective disposable medical robots, which could enable their more widespread application.

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Copyright © 2008 by American Society of Mechanical Engineers
Topics: needles , Motion , Design , Phantoms
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References

Figures

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Figure 1

The Robopsy system. A disposable, patient-mounted telerobot is controlled by a radiologist in the radiation-shielded control room using a custom interface running on a laptop.

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Figure 2

Needle insertion experiments. The force to insert a biopsy needle into soft tissue, Finsertion, and the torque to orientate (tilt) a needle τorientation in soft tissue were measured.

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Figure 3

Beta prototype. The disposable actuator is shown strapped to a thoracic phantom. The needle is not gripped by the device and is free to move.

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Figure 4

Robopsy’s spherical mechanism. Concentric nested hoops allow for orientation of the needle in two compound angles. The hoops are actuated using microgear motors. The carriage riding in the two hoops performs the needle gripping and insertion.

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Figure 5

Section view of Robopsy. A pinion, actuated by a motor, drives a rack that applies a perpendicular gripping force to the needle. When released, the needle is free to “waggle” within a 25deg cone.

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Figure 6

Scan transparency. The motors are placed so there is a metal-free zone where the needle is gripped and scanned. This ensures that Robopsy creates minimal distorting artifacts in the CT scan image.

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Figure 7

Estimating the loads required for motors to insert and orientate a needle

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Figure 8

Robopsy prototype. The actuation module is connected to the electronics enclosure using a flexible cable and a D-sub connector. The mating D-sub then connects via four pigtails to each motor.

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Figure 9

CT Compatibility. CT scan showing that the hoops’ motors lie outside of the scan plane when the hoops are orientated at 45deg with respect to the scan plane. This ensures that Robopsy creates minimal artifacts in the CT scan.

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Figure 10

Phantom targeting experiments. (A) Robopsy placed over the metallic grid on the custom made phantom. (B) CT scan showing Robopsy being used to target a lesion. Robopsy was used to align the needle with the CT gantry so that the needle is fully visible.

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Figure 11

Porcine testing. (A) Pig in scanner with targeting grid applied. (B) Device adhesive mounted to pig. (C) Needle orientation and insertion conducted remotely inside scanner.

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Figure 12

Four CT scans from the initial in vivo porcine trial. (A) Lesion injected; (B) device affixed; (C) nearly at lesion; (D) lesion targeted.

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