Author : Mr. Md Irwan and Mr. Wu Ruoyun
Last Updated : 1 October 2004

AR Assisted Breast Cancer Biopsy / Treatment

Introduction

Breast cancer is currently the 3^rd most common cancer in Singapore of which 99% are female. It can be treated successfully and even cured if diagnosed at an early stage. There are basically four types of breast cancer where those confined within the duct and lobules are at the early stages.

Figure 1.   Types of breast cancer.

When a patient is diagnosed with breast cancer, the next step is to remove the tumor. There are two surgical procedures for the treatment of breast cancer:

Lumpectomy  -  removal of the tumor plus 1 cm margin of healthy breast tissue                            surrounding the tumor

Mastectomy   -  removal of the entire affected breast

Factors influencing the decision of either a lumpectomy or mastectomy procedure are; number and size of tumor, degree of the tumor spread, prepared to undergo radiation therapy and personal preference. About 80-90% of the patient diagnose with breast cancer requires lumpectomy procedure and most female patient prefers this procedure as it would still give them that psychological feeling of being a complete women. 

Figure 2.   Lumpectomy procedure via open surgery.

Figure 2 illustrates a lumpectomy surgery procedure via open surgery. Initially, the surgeon identified the tumor from the ultrasound scan and visualizes an imaginary margin about 1cm around the tumor. An incision is made which enable the surgeon to further cuts into the breast tissue and removes the tumor plus the margin. The breast is then closed. Open surgery procedure would disturb the healthy breast tissue as the surgeon cuts its way into the breast to reach the tumor. It will take a considerably amount of time for the breast to heal and also risk of infection during this period. 

Figure 3.   An ultrasound scan image: (a) normal and (b) segmented.

Typically, the patient is required to undergo a routine breast biopsy procedure where samples of the breast tissue are to extract to determine the existence of cancer cells. The common practice in Singapore is to use a commercial vacuum-assisted breast biopsy probe, like the Mammotome^® Breast Biopsy System developed by Johnson & Johnson, USA. The procedure begins by positioning the probe beneath the tumor. The cutting process is then initiated which sucks the tissue into the cavity followed by the cutter tool advancing and simultaneously rotating. The tissue is removed, giving strips of breast tissue. This entire process it done under direct vision, example from ultrasound scan, Figure 3. From the scan image, the tumor can be easily distinguished, as the contrast between the tumor and healthy breast tissue is very prominent. Surgeon uses the image as a guide to locate the breast tumor.

Objective

The motivation of the project is to remove a uniform margin around a tumor that is found via ultrasound by minimally invasive therapy method without the need of open surgery. Our research project aims to use the vacuum-assisted breast biopsy probe and turn it into a treatment device to perform a lumpectomy procedure.

The objective is to develop a tracked semi-automated arm manipulator system to position a 3D-ultrasound probe and the vacuum-assisted breast biopsy probe to enable a lumpectomy procedure to be carried out via a small opening with full confidence that the tumor plus the margin is extracted. Augmented Reality (AR) and Virtual Reality (VR) are introduced to provide intuitive visual guidance for the surgeon.

System Overview

In order to turn the biopsy device into a treatment device, the procedure of the tissue cutting and position of the biopsy probe must be well controlled. The cutting protocol is to remove the tumor first followed by the margin, which is actually healthy tissue and can only be delineate imaginary, Figure 3(b). When the tumor is being removed, the size reduction of the tumor can be observed via the ultrasound scan. However, concurrently, the margin collapses as well which is difficult to delineate. It is almost impossible to trace the margin when the entire tumor is removed. Therefore, the collapse of the margin is also tracked at all time especially when the entire tumor is removed. Soft tissue deformation study is part of the project deliverable.

In December 2003, the first prototype system was completed that comprises of two sub-arm called ultrasound arm and surgical arm, which tracks the ultrasound probe and surgical tool, respectively. The position information is conveys to the surgeon via AR and VR visualization. There are also motors to control the surgical tool. Figure 4 illustrates how the system would be used in the operating theater and the system in its Alpha version.

Figure 4.   (a) Conceptual drawing of the system in the operating theater and (b) The Alpha version of the system as at December 2003. The VR visualization on the touch screen shows the posture of the arm system in real time

Tracking Method

A commercial stereo camera – Digiclops is used to track a three-dot marker, Figure 5. According to our experiments, the accuracy in tracking the three-dot marker is about 1 ~ 2mm (X/Y) at a distance of about 1meter, and about 2 ~ 3mm in Z direction (the camera’s view direction). There are 4 encoders in the ultrasound arm, and 7 encoders in the surgical arm. Each encoder track one degree of freedom of the arm. Their resolution is 0.044 degree/count, with a size compact enough to fit into the arm joints, Figure 6. 

Figure 5.   (a) The marker for camera tracking is mounted on the holder of 3D ultrasound probe. (b) A sample augmented reality displays a virtual tumor within the box representing the 3D ultrasound image.

Figure 6.   (a) The VR visualization showing the whole arm system based on encoder tracking alone. (b) A close view of the 3D ultrasound volume with tumor surface model inside. The biopsy needle interactively slices the ultrasound volume when its virtual rectangle plane intersects the volume.

Figure 7 shows the overall tracking configuration of the Alpha version when using both camera tracking and encoder tracking. Based on a common main arm, two sub-arms links to the Ultrasound probe and the surgical tool, and the encoders track vector V_US and V_tool. The camera tracks vector V_AR. Vector V_camera can be computed from V_US and V_AR. Encoder tracking provides high accuracy in V_US and V_tool for AR/VR visualization, and the accuracy of V_camera would be lower because of camera tracking, but it is sufficient for AR visualization. Camera, ultrasound probe, and surgical tool are referenced in a single coordinate system. 

Figure 7.   Tracking configuration using the combined tracking method. Encoders track V_US and V_tool, while the camera tracks V_AR. Vector V_camera can be computed from V_US and V_AR.

The protocol of tracking is the following:

The protocol above uses camera tracking only in the beginning. This avoids the camera-tracking problems, such as line-of-sight (LOS) requirement and sensitive to environment changes such as illumination.

Status

The project is funded by National Medical Research Council (NMRC) and started in August 2002. The participants include Tan Tock Seng Hospital and Nanyang Technological University. A team consisting of surgeons and researchers has been formed gradually. We are targeting to release the first version at the end of 2003 for clinical trial purpose.

Publications related to Mammotome.

We would be glad if you could sign our guest book.

For more information, please contact the co-principal investigator:

A/P Ng Wan Sing
School of Mechanical & Aerospace Engineering
Nanyang Technological University
Nanyang Avenue, Singapore 639798
Fax:(65) 6791 1859

Hospital Partner

Dr. Wee Siew Bock
Wee Breast & General, Surgery Mount Elizabeth Hospital

Dr. Mona Tan
Associate Consultant, Department of General Surgery
Tan Tock Seng Hospital

Dr. Jaideepraj Rao  
Registrar, Department of General Surgery
Tan Tock Seng Hospital