Guiding Medical Needles Using Single-Point Tissue ManipulationMeysam Torabi1, Kris Hauser2, Ron Alterovitz3, Vincent Duindam2, and Ken Goldberg4Abstract— This paper addresses the use of robotic tissuemanipulation in medical needle insertion procedures to improvetargeting accuracy and to help avoid damaging sensitive tissues.To control these multiple, potentially competing objectives, wepresent a phased controller that operates one manipulatorat a time using closed-loop imaging feedback. We presentan automated procedure planning technique that uses tissuegeometry to select the needle insertion location, manipulationlocations, and controller parameters. The planner uses astochastic optimization of a cost function that includes tissuestress and robustness to disturbances. We demonstrate thesystem on 2D tissues simulated with a mass-spring model,including a simulation of a prostate brachytherapy procedure.It can reduce targeting errors from more than 2cm to less than1mm, and can also shift obstacles by over 1cm to clear themaway from the needle path.I. INTRODUCTIONNeedle insertion is a widely-used minimally invasive med-ical procedure with applications in tissue sample removal andtherapy delivery. Its success depends largely on the physi-cian’s skill and (often) luck. Procedures that require preciseneedle-tip positioning can fail due to improper positioningof the needle insertion point or by needle deflection as ittravels through tissue. Furthermore, the target may shift dueto tissue deformation from friction along the needle shaft, thepatient’s breathing, or the patient’s involuntary movements.Procedures can be difficult even under imaging guidance.Breast and abdominal biopsies fail to sample malignanciesin approximately 10% of insertions [8], [12]. Furthermore,straight-line needle paths may pass through sensitive tissues,such as arteries, nerves, or certain organs, to reach the target.Damaging these tissues may cause undesirable side effects.In this paper, we investigate the use of robot-controlledtissue manipulation during needle insertion procedures. Tis-sue manipulators may be used to shift the target’s location inthe tissue to improve accuracy. They could also be used toimprove target accessibility by pushing obstacles and sensi-tive tissues away from the needle path. Tissue manipulationcan be used alongside other promising techniques, such asmodel-based optimization of needle insertion parameters [3],This work is supported in part by the National Institute of Health underNIH grant R01 EB006435 and NIH grant F32 CA124138, and by theNetherlands Organization for Scientific Research1School of Electrical Engineering, Sharif University of Technology,Tehran, Iran. [email protected] of Electrical Engineering and Computer Science,University of California at Berkeley. {[email protected],[email protected]}3Department of Computer Science, University of North Carolina atChapel Hill. [email protected] of Electrical Engineering and Computer Science and theDepartment of Industrial Engineering and Operations Research, Universityof California at Berkeley. [email protected]. 1. Sagittal slice of a needle insertion procedure with tissue manip-ulation in a prostate cancer brachytherapy application. A cross depicts theseed’s target location. Image from The Visible Human Project.applying external forces on the shafts of flexible needles [7],[9], and steering flexible bevel-tip needles [15], [17]. Specif-ically, we consider image-guided, straight line, rigid-needleinsertions using one or more manipulators.Our primary motivation is an application to prostate can-cer brachytherapy (see Fig. 1). In low dose rate (LDR)brachytherapy, dozens of needle insertions are used to in-sert radioactive seeds into the prostate. Seed locations arecarefully preplanned to deliver a sufficient radioactive doseto cancerous regions, and minimize the dose absorbed bysurrounding tissues. With manual insertions under ultrasoundguidance, the average seed placement error is approximately0.63cm [16], which is about 15% of the width of the prostate.This placement error may cause excess radiation to be ab-sorbed by the urethra and reproductive organs, contributing tothe risks of incontinence and sexual dysfunction. We considerusing a single manipulator within the rectum (depicted ingray in Fig. 1) to help guide the needle insertion in orderto reduce targeting errors. Furthermore, the manipulator mayalso be used to guide the needle around sensitive structureswithin the prostate, which could further diminish side effects.We consider a single-manipulator, closed-loop controllerthat uses 2D imaging feedback (typically ultrasound, flu-oroscopy, or magnetic resonance imaging) to position asingle point in the tissue. Even though only one point ismoved at a time, the system uses a phased operation thatsequentially pushes sensitive tissues away from the needlepath, and finally corrects for residual needle targeting errors.The method could be applied to prostate and other cancertreatments as well as biopsies of the breast [13] or abdominalorgans. We analyze several design choices in terms oftheir clinical applicability, such as whether compression,shearing, or tension manipulation forces are preferable. Ourtechnical contributions include an approximation of the setof attainable displacements of points in the tissue. Thisapproximation is valid for small, quasistatic deformationsand linearly elastic tissues. We also present a preoperativeprocedure planner that optimizes the placement of the needleand manipulators, given a geometric and physical model ofthe tissue and manipulator.We evaluate our controller in simulation using 2Dmass-spring models, including a simulation of a prostatebrachytherapy procedure. These experiments suggest thatsingle-point tissue manipulation can reduce targeting errorto the order of one millimeter and helps the needle avoidsensitive tissue while reaching relatively inaccessible targets.II. RELATED WORKSeveral researchers are studying methods for improvingneedle insertion accuracy using robotics technology. Mostsimilar to our work, Mallapragada et. al. applied tissuemanipulation to improve targeting accuracy for a breastbiopsy procedure [13]. Their technique was based on thecontrol of multiple frictionless contact points; we use asimilar feedback control strategy, but consider moving onlyone manipulator at a time, in phases. We also considermanipulation via friction