SURGICAL TOOL ALIGNMENT BY LASER GUIDANCE

USING FLUOROSCOPIC-BASED NAVIGATION TECHNIQUE

A System Implementation and Validation Study

Jack T. Liang

, Shinya Onogi

and Yoshikazu Nakajima

1,2

Graduate School of Engineering, University of Tokyo, Yayoi 1-1-1, Tokyo, Japan

Intelligent Modling Laboratory, University of Tokyo, Tokyo, Japan

Keywords: Laser Guidance, Computer Aided Surgery, Fluoroscopic Surgery.

Abstract: This paper provides a novel method for intuitive and CT-less surgical navigation based on fluoroscopic-

based navigation and laser guidance technology for minimal invasive orthopaedic surgery. This method

does not require intra-operative registration of three-dimensional surface model derived from pre-operative

CT/MRI volumes and is able to project surgical path planed intra-operatively onto the patient's skin directly.

In this paper, implementation of this method and basic in vitro guidance accuracy validation were

performed. Tool insertion path planning was performed on three 2D images from a pinhole imaging source

taken at different incident angles. A 3D insertion pathway was generated and projected using two laser

beams. Our Fluorolaser system has a planning accuracy of 1.07±0.60 mm, 0.73±0.38 degrees and an overall

guidance accuracy of 1.11±0.62 mm, 0.80±0.68 degrees. These results demonstrate that the proposed

method has great potentials to ensure accurate and intuitive surgical procedures.

1 INTRODUCTION

Fluoroscopy is commonly used for real-time

viewing of patient anatomy during percutaneous or

less invasive orthopaedic surgical procedures. It

provides real-time 2D views using a fluoroscope.

However, its usage comes at the expense of

increased exposure to radiation; difficulties in

obtaining and processing multi-planar visualization;

and the mental burden for surgeons to interpret 3D

positions from 2D images.

To address the visualization problem, X-ray

computed tomography (CT)-based and magnetic

resonance (MR)-based are developed to simplify

surgical procedures. However, CT-based navigation

has large amounts of radiation exposure while MR-

based navigation does not provide high bone

intensity resolution and can only be used in non-

metal containing environments. To address radiation

exposure, X-ray fluoroscopic navigation, or virtual

fluoroscopy, has been developed to guide surgical

tool placement (Foley, 2000; Hofstetter, 1999;

Leloup, 2008). However, these systems superimpose

surgical tool location over pre-acquired x-ray images

and displays navigational plans via a secondary

display device. This unintuitive guidance method

forces surgeons to mentally calculate real-world tool

locations from a display panel during surgery.

Laser-based navigational guidance systems have

been developed for spinal pin insertion and pelvic

implant fixation surgeries (Sasama, 2002). It

generates surgical plans and uses two laser beams to

project point-of-entry and insertion orientation

directly onto the patient’s skin (Nakajima, 2004).

Thus, a direct guidance is achieved and surgeons no

longer need to mentally interpret positioning

information from a screen. However, CT or MR-

image is required for surgical planning.

This paper presents an improved system that

employs two laser sources to guide surgical tool

insertion using surgical planning from two or more

fluoroscopic X-ray images taken intro-operatively.

In particular, we elicited the virtual fluoroscopic

planning technique. As far as the authors know, this

is the first study to integrate the virtual fluoroscopic

planning technique with the dual-laser guidance

technique for practical manual execution of

surgeries. This novel combination yields an original

surgical navigation and guidance system that

displays tool insertion path directly in the surgical

field without use of any pre-surgical techniques. We

showed the feasibility of this method with a basic

system validation using a pin-hole camera.

319

T. Liang J., Onogi S. and Nakajima Y..

SURGICAL TOOL ALIGNMENT BY LASER GUIDANCE USING FLUOROSCOPIC-BASED NAVIGATION TECHNIQUE - A System Implementation and

Validation Study.

DOI: 10.5220/0003763903190323

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2012), pages 319-323

ISBN: 978-989-8425-91-1

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

2 MATERIALS

The proposed fluoroscopic-based dual-laser guided

(Fluorolaser) navigation system consists of three

major components: a Laser Guidance System

(Nakajima, 2004) with built-in tracking capabilities

using the hybrid Polaris Spectra (Northern Digital,

Waterloo, ON, Canada); active infrared markers

(AdapTrax 15 Marker, Northern Digital, Waterloo,

ON, Canada); and a web camera (P1C30 series,

Elecom, Osaka, Japan) used in place of an X-ray

fluoroscope. We implemented the fluorolaser

software using C++ (Visual Studio 2005, Microsoft

co.) with OpenCV library. It connects to the laser

guidance system over TCP/IP and to the Polaris

tracking device via RS-232c. The two functional

parts of this new system, guiding and planning, will

be discussed in this section.

2.1 Insertion Guidance Using Lasers

The intersection of two emitted laser-beams

simultaneously guides surgical tool’s entry position

and its inserting orientation as shown in Fig. 1. The

intersectional line l

made by laser planes S

and S

represents the insertion path in 3D space. The

insertion point p

is the intersection of l

and the

patient’s body surface S

. Insertion point guidance is

robust to deformations of the body surface,

represented by changes from S

to S

’ in Fig. 1.

Surface S

’ represents any deviations from S

in both

height and shape due to body surface relocation,

deformation or obstruction by soft tissues. For

proper surgical tool alignment, the tip of the surgical

tool is placed at p

and the length aligned to l

Orientation alignment can be verified using the

projections of the lasers on the side of surgical tools.

Proper alignment is indicated by two parallel lasers.

Figure 1: Left: Schematic diagram of the laser guidance

method. Right: Robust entry point displayed for surface

relocation, deformation or occulsion by soft tissue using

dual laser-beams.

2.2 Navigational Planning

Infrared markers are placed on the imaging device

and on the surgical object to create the localizer-

fluoro coordinate system (CS

) and localizer-subject

coordinate system (CS

), respectively. The surgical

planning process requires multiple sets of inputs.

Each set consists of three pieces of information

obtained from the surgical environment: an image of

the surgical object and the insertion site obtained by

the imaging device and the three-dimensional

coordinates of the two markers when the image is

taken. For each set of inputs, a two-dimensional

surgical tool insertion path is manually drawn onto

the acquired two-dimensional image. Using camera

calibration parameters, this 2D plan is projected

along the ray-lines of the imaging device to obtain a

plane in 3D space. The plane is formulated in CS

and transformed for use in CS

Following Fig. 2, two 2D plans from two sets of

inputs yields two planes in 3D space. The

intersection of two planes yields a line in 3D space

where the directional vector of the line is the cross

products of the normal of the two planes. This

intersection line represents the insertion path in 3D

space. If three sets of inputs are used, three 2D plans

are made to give three planes in 3D space. This

gives rise to three intersection lines in 3D space.

Regression of these lines is performed to obtain a

line of best fit, which represents the optimal surgical

insertion path. This optimal insertion path is stored

in CS

and thus is robust towards any slight

movements of the surgical object.

The optimal path is then transformed into the

localizer coordinate systems (CS

). Laser guidance

is realized by using two laser sources to project the

mathematical representation of this insertion path.

3 METHODS

We validated the Fluorolaser system using a pinhole

web-camera, which is mathematically similar to a

fluoroscope (Navab, 1999). We prepared a simple

validation setup using a flat surface and surgical

insertion tool, the K-wire (150 mm length, 3 mm

diameter). Guidance accuracy was validated by

tracking the position of the K-wire, which

represented the desired surgical tool insertion path

and the surgical tool itself. An active infrared marker

and a guidance sleeve were attached for position

tracking and alignment, respectively. Proper tool

orientation alignment was indicated by parallel laser

beams on the guidance sleeve, as stated previously.

3.1 Experimental Design

We created a virtual coordinate system on a flat

BIODEVICES 2012 - International Conference on Biomedical Electronics and Devices

320

Figure 2: Fluorolaser transformation

matrices: localizer to laser 1 and laser

2, localizer to subject, and localizer to

fluoroscope. Fluoroscope is positioned

at two arbitrary locations. Two 2D

plans are used to calculate insertion

path in 3D space.

Figure 3: Experimental setup includes

the laser guidance system, a flat

surface, a web camera (fluoroscope

imitation device) and a K-wire.

Location markers are used to locate

imaging device, K-wire and surface.

Flat surface represents the surgical

object.

Figure 4: Black figure represents the

initial K-wire position; white figure

represents the final K-wire position;

and green line represents the planned

surgical insertion path in 3D space.

surface (Fig. 3) and selected the z-axis as the

direction normal to the surface. We used a four

factorial Box-Behnken experimental design method

to create 28 validation trials by altering the intended

insertion path mathematically. Its factors and levels

are: x-axis (-50, 0, 50 mm), y-axis (-100, 0, 100 mm),

polar angle (-30, 0, 30 degrees), and azimuthal angle

(-30, 0, 30 degrees). Experiments were conducted

for both two-image and three-image configurations

for planning.

3.2 Experimental Protocol

First, the intended insertion path is shown by the

dual-lasers in 3D space. This ground truth path is

represented mathematically and altered according to

the experimental design. The K-wire was placed

according to the lasers. Using this initial k-wire

position, 2D images were taken for planning. The K-

wire was removed while planning was performed.

Once the 3D insertion path was generated, the laser

was turned on. The K-wire was repositioned using

guidance by laser. Once lasers became parallel, final

position of the K-wire was recorded.

3.3 Analysis

Fluorolaser accuracy validation looked at the

displacement of relative tip locations between

planed 3D insertion path, initial K-wire position and

final K-wire position. We calculated the difference

in tip positions in a plane that is perpendicular and

Figure 5: Positional and orientational error values shown

in blue and red, respectively. Results include accruies for

2-image planning, 3-image planning, and 3-image

guidance.

intersects the initial K-wire tip (Fig. 4). Planning

accuracy refers to the error between actual insertion

path and user-determined insertion path. Guidance

accuracy refers to the error of the overall system.

Transformation matrix between K-wire tip and

marker was pre-obtained.

4 RESULTS

Results of 28 validation experiments are shown in

Fig. 5. System planning accuracy using two 2D

images for planning was 2.08±1.47 mm, 0.68±0.37

deg (degrees). Planning accuracy after linear

regression of three 2D images was 1.07±0.60 mm,

0.73±0.38 deg. Positional accuracy is significantly

improved using three images (P-value: 2.00x10

-6

SURGICAL TOOL ALIGNMENT BY LASER GUIDANCE USING FLUOROSCOPIC-BASED NAVIGATION

TECHNIQUE - A System Implementation and Validation Study

321

Using three-images, max planning error was

found to be 2.22 mm, 1.85 deg. The RMS and

RMSE were 1.22 mm, 0.82 deg and 0.59 mm, 0.37

deg, respectively. The overall guidance accuracy

using three 2D images was 1.11±0.62 mm,

0.80±0.68 deg. RMS and RMSE were 1.27 mm,

1.05 deg and 0.62 mm, 0.67 deg, respectively.

Box-Behnken surface responses for planning and

guidance errors were desirable for the 28 different

four-factor three-level combinations. There was no

correlation between the system accuracies and the

positional changes of imaging device.

5 DISCUSSION

Conventional navigation systems use a secondary

viewing device to indirectly guide surgery. These

operations are often mentally challenging and

cumbersome to perform. The Fluorolaser system

guides surgeries directly using two lasers to guide

surgical tool alignment. Planning is performed using

two or more images taken intra-operatively as

oppose to complete CT or MRI registration data.

The entire surgical navigation process using the

Fluorolaser system consists of two types of errors:

planning error and guidance error. The latter has

been validated previously (Lim, 2010). The former

includes camera calibration error, and human errors

for planning and re-positioning. In this study, we

have evaluated planning and guidance errors of the

system. Planning accuracy is limited by the camera

calibration technique as well as user-based insertion

path planning. Furthermore, this validation study

was performed with the assumption of point-

accuracy, which cannot be obtained from the K-wire

tip or the crosshair created by the lasers. Generally,

navigational systems designed for precutaneous

surgeries using two-dimensional images are

considered precise and accurate when position and

orientation errors are within 2 mm and 2 deg,

respectively. However, acute accuracies may be

required for special types of surgeries such as

surgeries in the brain and neck regions.

The presented evaluation of the Fluorolaser

system may be limited. In our experiments, we could

not use fluoroscope images and instead used normal

camera images. Although different in the imaging

techniques used, the system is invariable for both

camera and x-ray images since both devices are

theoretically assumed to be pinhole devices (Navab,

1999; 2000). Validations with x-ray images are

necessary for actual surgeries.

Although this system is an improvement to

conventional systems, clinical assessment is

necessary to fully validate its robustness in actual

surgeries. We intend to further validate this system

using fluoroscopes and saw-bones or biological

specimens to better mimic the surgical environment.

We are also considering the implementation of

insertion depth guidance. The lack of the depth

guidance may result in the need to acquire additional

X-ray images or to use positioning trackers. We plan

to introduce a physical stopper attachment for the

surgical tool; however, problems may arise when

during skin deformation. Adequate implementation

of depth guidance using laser-beams may overcome

these problems as well as expand the applicability of

the system in different types of surgeries.

6 CONCLUSIONS

We have proposed a novel integration of the

fluoroscope-based navigation and the laser guidance

systems. This Fluorolaser system provides intuitive

surgical tool insertion positioning in precutaneous

surgeries without pre-operative CT/MRI volumes.

Specifically, in vitro insertion path planning was

performed using 2D images from a pinhole imaging

source and insertion guidance was directed by lasers.

The planning accuracy was 1.07±0.60 mm,

0.73±0.38 deg and overall guidance accuracy was

1.11±0.62 mm, 0.80±0.68 deg. This demonstrates

the potential of the Fluorolaser system to be used in

accurate and intuitive surgical procedures without

registration of pre-operative CT/MRI volumes.

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