Surgical Planning Interface for Image-Guided Pediatric Bone Biopsies Akiv Jhirad1, Thomas Looi2, James Drake2 Main email contact:
[email protected] 1McMaster School of Biomedical Engineering, Hamilton, Ontario, Canada; 2Neuroscience and Mental Health, The Hospital for Sick Children, Toronto, Ontario, Canada
Methods (cont’d)
Objective: • To develop a surgical planning interface to integrate an MRIcompatible, tele-operated Pediatric Surgical Robot (PSR) • Allow clinicians to simultaneously image and biopsy bone while Figure 2 – PSR configuration patients remain in the MRI, with in the bore of an MRI minimal impact to workflow
Methods Intra-operative MR images
HOPE-PSR
Surgeon
MRI Image Viewer 3D Visualization Jointspace Control
PSR Control System Coregistration Robot Kinematics
MRI Control Room
Figure 3 – Overall System Level Diagram
PSR Controller
Low MR Field
PSR Inside MRI
High MR Field
System Description: • An existing system named HIFU Operations for Pediatrics (HOPE) was adapted to develop the HOPE-PSR interface (Fig. 4) • The HOPE system has DICOM file retrieval and viewing capabilities, while the PSR interface provides the method for controlling the robot in the MRI • Both systems are based on the Qt Python platform
Communication Latency: • The mean communication latency between the PSR encoders and HOPE-PSR was 78 milliseconds Packet Communication Latency 0.09 0.085
Time Delay (s)
Clinical Problem • Bone tumours occur in almost 1 in 15 pediatric patients (between the ages of 10-20 years old) • MRI has been used as a guidance method to biopsy patients for tumour diagnosis due to its non-ionizing nature, and ability to avoid critical Figure 1 – MRI-compatible structures due to detailed images bone biopsy needle (In-vivo) • Bone biopsies require high forces, precision, and patient accessibility, which are all unavailable while the patient is in the MRI
Results
0.08 0.075 0.07 0.065
Joint Control Accuracy: • Joint angle accuracy varied with angle input from HOPE-PSR • The maximum variance between input angle and measured angle was 10 degrees • The maximum error in joint angle precision was 3.74 degrees PSR Joint Angle Accuracy 70
Figure 4 – HOPE-PSR Interface
Communication Protocol: • Communication between HOPE-PSR and the low level PSR code written in C++ is performed using sockets and threads • Parallel processing using threads allows for reduced delay in communication, making real-time control of the PSR possible • Sending structured commands over a socket enable future modifications to the interface to maintain the communication protocol
3D Visualization: • A 3D model of the PSR (Fig. 5) was developed from CAD files using the Mayavi Python toolbox • Threading enables real-time updating to be possible, which allows the surgeon to visualize the actions of the PSR while it is in the MRI
Figure 5 – 3D Mayavi PSR Model
Coregistration: • The position of the fiducial markers in the PSR frame is transformed to that of the MRI image frame by applying a transformation matrix
Measured Joint Angle (Degreed)
Introduction
60 50 40
15
30
30
Joint Standard Angle Mean Deviation 15 19 2.00 30 36 3.74 45 55 3.16
45 20 10 0 Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
Discussion • The surgical planning interface has been shown to allow clinicians to image, plan, and execute bone biopsy procedures with minimal impact to workflow • Further development is underway to make the interface modular so It can be used to control any tele-operated, MRI-compatible robot • Finer control of robot joints is required to more closely emulate the behaviour of a physician’s hand • Fiducial holder design needs to be optimized to increase the accuracy of the coregistration • Joint angle precision and accuracy was poor due to slippage of gears, resulting in improper PSR movement
References Figure 6 – Fiducial Marker Holder
[1] Su H, Iordachita I, Yan X, Cole GA, Fischer GS. Reconfigurable MRI-Guided Robotic Surgical Manipulator: Prostate Brachytherapy and Neurosurgery Applications. Proc. of 33rd Int. Conf. IEEE Engineering in Medicine and Biology, Boston, USA, August 2011. [2] IGAR Breast System: MRI Breast Biopsy and Ablation [Online]. http://csii.ca/robotic_development/igar [3] Bone cancer stats (http://www.ped-onc.org/diseases/SOCC.html#bone cancer)
