Measurement system of optical properties of vertebra
bones on near-infrared spectrum
Weitao Li, Zhiyu Qian, Hui Gao, Lidong Xing,
Xiaofeng Song
Department of Biomedical Engineering
Nanjing University of Aeronautics and Astronautics
Nanjing, China
liweitao@nuaa.edu.cn
Xinzhi Cao
Medical Imaging Department
Nanjing General Hospital
Nanjing, China
to_cxz@163.com
Abstract— Near-infrared spectrum scattered from biological
tissue can be used to characterize the optical properties of the
tissues. If the optical properties of different parts of vertebra
bones are different, a new navigation method in pedicle screw
insertion surgery can be proposed. The goal of this study is to
develop an optical measurement method which can detect the
optical properties of vertebra bones on near-infrared spectrum.
A 2.0-mmdiameter steel probe containing two 200-micron
diameter optic fibers was used to deliver light and collect light
spectrum from the surface of vertebra bones. In experiment,
the integrated pig vertebra bones were split. The steel probe
was put on the different position of the anatomical section and
the spectrum was detected at each point. The optical properties
deduced from the spectrum were distinguished between the
cortical bones and cancellous bones in the trajectory of pedicle
screw placement.
Keywords—optical properties; near-infrared spectrum;
reduced scattering coefficient; verbra bones
I.
I
NTRODUCTION
Pedicle screw (PS) fixation is significant popular in
spinal surgeries. The accuracy of placement of PS is the most
important thing during the operation. Many methods have
been utilized to increase the accuracy of pedicle screw
placement. All of them have varying degrees of advantages
and limitations [1].
The X-ray C-arm, computer tomography (CT) and
magnetic resonance images (MRI) are most recently used in
navigation of PS fixation surgery [2]. Nowadays, computer-
assisted image-guide surgery has been proved to
significantly improve the accuracy of pedicle screw
placement. However, this method is too complex to use and
is very expensive in developing country. Comparing with the
complex instruments, a simple, portable and new electrical
conductivity-measuring device was described [3]. The device
was a free hand drilling probe which measured electrical
conductivity at its tip. If the probe passed into the boundary
between two different media, variation of conductivity
would occur. In fact, this electrical conductivity device could
only detect the presence of pedicle cortical breaches. It could
not give the electrical conductivity properties along the
trajectory of pedicle screw placement and it’s hard for us to
know the position of pedicle screw by this method.
The anatomical structure of pig’s vertebra bones and the
trajectory of pedicle screw are shown in Figure 1. The
integrated vertebra bones can be divided into cortical bones
in pedicle, cortical bones in body, cancellous bones in
pedicle, cancellous bones in body, bones in arch and pedicle
inside wall. If the pedicle screw is placed along the proper
trajectory, it will go through cortical bones in pedicle,
cancellous bones in pedicle, bones in arch and cancellous
bones in body and the pedicle screw’s tip will stop in the
cortical bones in body. During this process, the pedicle screw
has been implanted successfully.
Figure 1. Schematic diagram of correct implant path of PS
and the components of vertebra
If the pedicle screw is misplaced to the spinal cord
(inside misplacement) or to the outside direction, the bones
tissues, which the pedicle screw passes, are different to
which the pedicle screw in the proper trajectory passes.
Recent studies carried out the integrated vertebra bones
could be divided into many parts according to physical
properties, such as density, mineral content, etc. Light in the
wavelength region of 650-950 nm has relatively low
attenuation in the biological tissues. The scattered light
spectrum has some information on the inner tissue. It can be
proved the vertebra bone is not a uniform tissue, so the
optical properties of the vertebra bone are also not uniform.
Some papers have developed a needle-like, near-infrared
(NIR) probe to measure the optical properties of some soft
tissues [4]. They proved the optical reflectance spectra
exhibited significant differences between different soft
Fundamental Research Funds for the Central Universities,NO.2013035
ational Natural Science Foundation o
China (Grant No. 61275199)
978-1-4673-5936-8/13/$31.00 ©2013 IEEE 111