Surgical Simulation - Needle Insertion 
Motivation: There are multiple procedures in surgery, where accurate placement of needles is vital to the success of the procedure. One such procedure is prostate brachytherapy during which the surgeon inserts a needle through the perineum, fatty tissue, muscle and then prostate to place radioactive seeds. The goal for seed placement is to maximize the radiation dose to the tumor while minimizing radiation doses to the surrounding tissue such as the rectum, bladder and urethra. Accurate seed positioning inside the prostate is very important for the success of the procedure. Minor deviations in seed placement caused by gland and tissue compression and needle retraction, gland edema, and needle deflections, can lead to significant areas of over dosage or under dosage to the gland. For various needle insertion procedures such as prostate brachytherapy, lumbar puncture and liver biopsy the success rate of the procedure is directly related to the clinician’s level of expertise. Therefore, improvement in the complication rates will be dependent on improving the training tools used by clinicians. Obtaining real world parameters for characterizing needle and soft-tissue interaction is the first step towards developing a model to provide accurate haptic feedback in a training simulator for needle insertion tasks.
Approach: The table below demonstrates the approach for modeling needle insertion.
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Dual C-arm fluoroscopes for fiducial tracking: The figure below shows the dual C-arm experimental setup for tracking the motion of beads inside the soft-tissue. To view the internal tissue movement during needle insertion and withdrawal, forty 1mm diameter stainless steel beads were inserted into the soft tissue to measure the internal movement of the soft-tissue. These beads were chosen because of their radiopacity (ability to block x-ray transmission) and their size, which was small enough to not affect the properties of the soft tissue or impede the needle insertion path. The beads were placed in a grid pattern spaced approximately 10mm apart from one another and in such a way to minimize occlusion between beads during imaging. In general, the orientation of the tissue can also be changed to minimize occlusion in C-arm experiments. The OEC 7700 (side view) and OEC 9600 fluoroscopes (top view) were used to image the needle and implanted markers inside of the tissue during experiments. The OEC 9600 by OEC Medical Systems Inc. has a 12” tri-mode image intensifier with 44lp/cm central resolution and 42 lp/cm peripheral resolution at 70% radius. The OEC 7700 by OEC Medical Systems Inc. has a 9” tri-mode image intensifier. The video from each C-arm was captured onto a hard disk using a video capture device (Pinnacle Systems – Dazzle Digital Video Creator 150) at 30fps and at a resolution of 720 x 480 pixels. We performed the calibration of the distortion and magnification correction in the C-arm images.
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| Dual C-arm setup for measuring internal tissue movement during needle insertion. |
Findings:
1) Needle deflection and Marker movement: The figure shows the trajectory of the needle through the soft tissue during needle insertion and withdrawal. Deflection of the needle tip from the straight line trajectory was observed during every needle experiment. Although within one standard deviation of each other, deflection was found to increase slightly with an increased needle velocity. The maximum deflection from the straight line needle trajectory seen in our experiments was found to be 7.84mm. Furthermore the movement of the markers during a typical needle insertion and withdrawal in soft tissue was also observed. For clarity, we have only shown a small subset of beads actually used in the experiment. For this sample data set, the needle was inserted at 12.7mm/sec to a depth of approximately 95mm. Each bead has a corresponding blue color for its position during insertion and red color for its position during withdrawal. As seen from the figure, there is significant movement of the bead during insertion and withdrawal of the needle from the tissue. Beads closest to the needle path showed the largest range of movement while the movement of beads farther away from the needle path was less. The estimated movement of the beads is used to validate a finite element model to predict soft tissue deformation during needle insertion and withdrawal task. The tracking algorithm is shown to be accurate to within 2.09% ± 1.61% of the actual movement.
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| Motion of the needle and the fiducials during a typical needle insertion and withdrawal event. |
2) Soft-tissue Property: Forces- The figure shows the force data during an experimental needle insertion and withdrawal task broken into 4 sections, puncture, insertion, relaxation, and withdrawal. The adjoining figure illustrates the mean force at the moment of puncture for each liver at various insertion speeds. As seen from the figure, the mean puncture force for each liver sample is within one standard deviation of each other. As the speed increases, the mean puncture force decreases, however the values are still within one standard deviation of each other.
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| Total needle forces during insertion and withdrawal. Each phase of the experiment is segmented by a horizontal line through the plot. The data plotted are the needle forces during an insertion and withdrawal in soft tissue at 1.016 mm/sec. |
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| Mean puncture force for each soft tissue sample at various insertion speeds. |
The figure below highlights ten major puncture events occurring inside of a soft tissue sample during an insertion at a speed of 1.016mm/sec. Finally, it is observed that the approximate cutting force varies around a single force value throughout the insertion, illustrating that the force required to cut through the tissue is fairly constant throughout the specimen (across all the 45 trials).
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| Major puncture events within a sample of soft tissue during one experimental insertion at 1.016mm/sec. A major puncture event occurs when the needle encounters some obstacles inside the tissue during insertion. A puncture event is comprised of a rise in the force and then a sudden drop in force representing the moment of puncture. During a puncture event, the tissue is no longer being cut and is assumed to be deforming at the same rate as the needle tip velocity. |
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| Plot of the approximate cutting force during needle insertion for an insertion speed of 12.7 mm/sec. The withdrawal force is subtracted from the total insertion force to obtain the approximate cutting force. |
3) Soft-Tissue property: Tissue Relaxation- The figures below show the typical tissue relaxation profile during a needle insertion and withdrawal event.
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| Top view of the bead movement during relaxation of the tissue after needle insertion and withdrawal. The max position during insertion shows the location of the bead before relaxation of the compression of the tissue and the max position during withdrawal shows the location of the bead before relaxation of the tension in the tissue. |
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| Averaged force plots during tissue relaxation at various needle insertion speeds. |
4) Modeling and Validation - The bead displacements due to puncture estimated by the 3D realistic geometry in the ABAQUS finite element model compared well with the observed experimental displacement.
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| Error between the ABAQUS model and the actual observed motion of the bead during needle insertion experiment. | Realistic 3D ABAQUS model generated from x-ray and physical measurement. The mesh is refined in the needle puncture site and the bead locations. |
Relevant archival publications:
- James T. Hing, Ari D. Brooks, and Jaydev P. Desai, “A Biplanar Fluoroscopic Approach for the Measurement, Modeling, and Simulation of Needle and Soft tissue Interaction”, Medical Image Analysis, pp. 62-78, Volume 11, Issue 1, February 2007.
For further information, please contact:
Prof. Jaydev P. Desai
Director, RAMS Laboratory
Department of Mechanical Engineering
Room 0160, Building 088
Glenn L. Martin Hall
University of Maryland
College Park, MD, 20742
Email: jaydev (at) umd.edu
Phone: 301-405-4427
Fax: 301-314-9477