WO2012153084A2

WO2012153084A2 - Spinal navigation and spinal phantom

Info

Publication number: WO2012153084A2
Application number: PCT/GB2012/000409
Authority: WO
Inventors: Mario Ettore Giardini; Thomas CASSAR
Original assignee: University of St Andrews
Current assignee: University of St Andrews
Priority date: 2011-05-09
Filing date: 2012-05-04
Publication date: 2012-11-15
Anticipated expiration: 2013-11-09
Also published as: WO2012153084A3; GB201107691D0

Abstract

A navigational aid in epiduroscopy comprising: an insert for inserting longitudinally into the spine, the insert including means for transmitting light into patient tissue and receiving light reflected from the tissue; and means for analysing the reflected light to determine a position of an end of the insert.

Description

Spinal Navigation and Spinal Phantom

Field of the Invention

The present invention relates to an all optical method for spinal navigation. The navigation technique may use, as well as other spectroscopies, near infrared spectroscopy (NIRS), Raman spectroscopy, fluorescence detection (whether induced by a dye, nanoparticles or other tracers or dyes, or autofluorescence), or combinations thereof. The present invention also relates to a spinal phantom for use as an epiduroscopy training tool.

Background of the Invention

Epiduroscopy is a technique for visualizing the epidural space. A narrow endoscope is inserted into the epidural space, typically via the sacral hiatus, though other insertion strategies may be employed. Epiduroscopy allows the physician to view structures inside the epidural space using a camera and a light source. Many different treatments using epiduroscopy are available, ranging from the treatment of intervertebral disc hernias -to the inspection of nerve roots.

Whilst there are benefits to epiduroscopy, the technique presents risks to the patient, owing to flaws in the current navigation methods. The endoscopic view has both a poor resolution and a small screen size, which presents a very real risk that the physician may become disorientated during investigations. A current typical maximum resolution of an epiduroscope is 240X180 pixels, equating on most modern computer screens to a few square centimeters. This poor resolution makes the procedure strenuous on the clinician, especially as the low spatial resolution may lead to disorientation in even the more experienced doctors. The fundamental concern, however, is that a critical image needed for the diagnosis or treatment of a condition may be missed due to pixilation and blurring. Combined with a lack of training apparatus, the poor resolution means it is possible that entry into the wrong tissue plane may occur.

Non-imaging devices for spinal insertion (spinal catheters) are beginning to enter clinical practice. Typically, these are inserted via the sacral hiatus, though other insertion strategies are indeed possible. In the present document, the terms "epiduroscope" and "epiduroscopy" will be refer both to endoscopes and to catheters. Currently, the only navigational aid available to physicians is x-ray fluoroscopy, which provides a video feed showing the position of the epiduroscope. However, this means that the patient undergoes a high dose of ionizing radiation that can lead to damage, such as erythema and neoplasia. To compound the problems associated with epiduroscopy, no training simulators are available that can be used to train physicians in the procedure. Currently, very limited resources exist for epiduroscopic training, with 'virtual reality' simulators being the most prolific. However, these are cost prohibitive.

Recently infrared backscattering has been exploited in the field of epiduroscopy. This is described in two papers by Ting (Ting CK, Chang Y. Technique of fiber optics used to localize epidural space in piglets. Opt Express 2010 May 24; 18(11 ):11138-11147; and Ting CK, Tsou MY, Chen PT, Chang KY, Mandell MS, Chan KH, et al. A new technique to assist epidural needle placement: fiberoptic-guided insertion using two wavelengths. Anesthesiology 2010 May; 112(5): 1128-1135). These papers describe a method for epidural needle placement that involves infrared light being shone on tissue of a porcine model and reflected back onto a spectrometer. The reflected light from the epidural space and the surrounding ligamentum flavura were shown to be distinguishable. Summary of the Invention

The present invention provides a novel system and technique for a navigational aid in epiduroscopy. The system comprises an insert for inserting longitudinally into the spine (for example a catheter or endoscope), the insert including one or more optical fibres or waveguides adapted to transmit light into patient tissue and receive light reflected from the tissue.

Where only one fibre is used, the illuminating and receiving fibre is the same. Where more than one fibre is used, the illuminating fibre and the receiving fibre are different. Alternatively, light sources and/or detectors such as, for example, LEDs, laser diodes, photodiodes, can be placed on the epiduroscope tip.

Optical elements may be present on the fibre tips to improve illumination and detection efficiency or to modify detection and illumination direction. Means, for example signal processing means, are provided for analysing the reflected light to determine the position of an end of the insert thereby to provide a navigation aid. Means may be provided for generating an image of the spine, and optionally the insert or an end thereof located within the spine, based at least in part on the reflected light. A display may be provided for displaying the image.

In use, the insert is inserted longitudinally into the spinal canal (or the spinal canal of a phantom). Light is emitted by the insert tip. Backscattered light is collected through the same insert. From variations in the backscattered intensity and/or spectrum, it is possible to identify when the catheter head passes across anatomical or functional features. This gives a clear positional reference signal to locate the insert tip position without the use of x-rays.

Instead or in addition to optical backscattering, other optical spectroscopic techniques can be used to navigate along the spine. For example, near infrared spectroscopy can be used. This works by shining infrared light of a known wavelength onto a tissue, and measuring the absorption of the returning light. Because each type of tissue has different constituents, different absorption signatures are apparent.

In tests, it was possible to insert a spinal catheter into the vertebral foramen adjacent to the vertebral bodies and intervertebral discs. A significant difference (95% confidence interval) was shown between the absorption spectra of the midpoint of the vertebral body, the intervertebral disc and the edge of the vertebral body.

According to another aspect of the invention, there is provided an anatomically correct deformable phantom of a spine, of similar mechanical properties to real tissue, and with the correct infrared optical properties of real tissue (infrared scattering, absorption, fluorescence, Raman spectrum).

The phantom also presents anatomical accuracy, so that it can function, for example, as a means to test the feasibility of the new navigational technique, or as a training aid for teaching and practicing epiduroscopy. In order to emulate the presence of cerebrospinal fluid (CSF), the phantom can be immersed into a bath of transparent liquid (e.g., saline solution) with the correct refractive index. The phantom of the present invention has components that constitute the spine, i.e. vertebrae, inter-vertebral discs, spinal cord, including the spinal nerves branching out from the cord, and the cauda equina. Without loss of generality, with the same technique also finer anatomical structures, layers, details can be included, and/or tissue activity and functionality can be emulated by including active elements in the phantom.

The phantom parts are made of materials that mimic both the mechanical consistency of the anatomical tissue, and the optical properties in the infrared region. This allows not only access, but actual simulation of full optical spectroscopic investigations. In our particular embodiment of the phantom, the vertebrae are composed of styrene/polyurethane resin, and the discs and spinal cord of silicone resins, of graded hardness and elasticity. The materials are loaded with additional materials, for example powders and dyes to provide the correct optical properties (i.e. scattering and absorption.

Preferably, the phantom is reconfigurable. To allow this, a system of wires may be provided to pass through the vertebrae and discs. By applying appropriate tension to the wires, the curvature of the phantom can be altered. This allows the curvature of different sections of the spine or the curvature typical of spinal pathologies to be emulated.

The phantom can be immersed in a liquid bath to emulate the presence of cerebrospinal fluid/saline solution or other fluids. The phantom is anatomically, visually and optically correct and geometrically reconfigurable.

The phantom can be adapted to include materials with X-ray opaque loads, such as barium sulphate, nanoparticle or metallic powders, to modify the X-ray opacity of the parts, e.g. to enable the simulation of more traditional X-ray-based navigation. Dyes, including nanoparticle-based dyes, could be used to change the fluorescence, Raman signature, visual aspect or other optical properties of the parts

Flexible or otherwise reconfigurable mechanical structures may be used for parts that are normally rigid (e.g. the vertebrae), in order to enhance the reconfigurability of the phantom (e.g., by changing the angle between the two surfaces of the vertebral bodies connected to the discs, and/or by changing the vertebrae thickness and/or by changing the shape and size of the lumen that lodges the spina! cord. Channels may be included to allow fluids to be circulated in the phantom parts. This would apply the emulation of perfusion, or fluorescent liquids to allow the simulation fluoroangiography, or X-ray-opaque liquids to allow the simulation of X-ray angiography. Fixed areas of different optical/mechanical/X-ray properties may be included, again to simulate (in this case, statically) different anatomical structures or navigational targets.

LCD shutters, light sources (LEDS, OLEDS), radiation sources, chambers pressurised by fluids or gases etc., may be included to simulate reconfigurable areas of different optical/mechanical/x-ray properties, and/or tissue activity.

Heating and/or cooling elements may be included to allow temperature control of the phantom and the test of spinal temperature sensors. Actuators (for example, mechanical, electro mechanical, thermal, pneumatic) may be inserted to create moving or reconfigurable regions, and/or to simulate tissue activity.

Brief description of the drawings

Various aspects of the invention will now be described by way of example only, and with reference to the following drawings, of which:

Figure 1 is a schematic diagram of an epiduroscope;

Figure 2 is an image of a spinal phantom;

Figure 3 is a more detailed image of the spinal phantom, in which linking wires are shown to allow the shape of the phantom to be changed;

Figure 4 is a spectrum captured by the epiduroscope of Figure 1 , and Figure 5 is a plot of detected light intensity versus catheter position for the epiduroscope of Figure 1 at various positions in the phantom of Figures 2 and 3.

Detailed Description of the Drawings

Figure 1 shows a spinal navigation system. This has an elongate insert for inserting longitudinally into the spine (for example a catheter or endoscope), the insert including one or more optical fibres or waveguides adapted to transmit light from a source into patient tissue and receive light reflected from the tissue and couple it to a detector. Where only one fibre is used, the illuminating light and received light pass through the same fibre. Where more than one fibre is used, the illuminating fibre and the receiving fibre are different. The system has an image processor (not shown) for generating an image of the spine, and the insert or an end thereof located within the spine, based at least in part on the reflected light. A display may be provided for displaying the image. Near infrared spectroscopy (NIRS) is used as a navigational aid. This involves delivering light of a known intensity and wavelength to the tissue and measuring the intensity of light exiting the tissue. Light is emitted from the tip of the catheter onto different parts of the spine. Reflected / backscattered light is detected and measured. From this, is it possible to distinguish between different tissue types thereby making it possible to determine the position of the tip of the catheter in the spine. In experiments, it was possible to distinguish between three significant parts of the spine, and namely the vertebrae and the intervertebral disc faces (situated in-between the bones). In order to test the NIRS catheter navigation system of Figure 1 , a phantom emulating the lumbar vertebral region of the spine was produced. The phantom has similar mechanical and optical, in particular infrared, properties of real tissue. The phantom has regular lumbar vertebra and inter-vertebral discs repeated several times encasing the spinal cord. The spinal cord was made of a material that has the same scattering properties and infrared absorption as living tissue. A stack of identical vertebral bodies and discs was used. The vertebral body used for the phanton was the third lumbar vertebra (13), which was selected as a 'typical' lumbar vertebra.

Figure 2 shows an example of the phantom manufactured for tests. Replica of the L3 and the intervertebral discs were used to form the spine. Using the average size for a L3 intervertebral disc, and modelling the curvature of the lumbar spine itself, it was possible to create a repeating chain of L3 vertebra and manufactured intervertebral disc of the same size whilst still keeping to the shape of the original spine. The vertebrae were cast out of polyurethane fast cast resin (TOMPS, Sutton Bridge, UK). A total of seven vertebrae were manufactured. The silicone used to emulate the spinal cord and intervertebral discs was RTV 141 (Rhodorsil, Rhone-Poulenc, France), a transparent silicone that has been documented extensively in the literature for use as tissue simulation material. The silicone, once set has a consistency close to that observed with some soft tissues.

The spinal cord has the scattering and infrared absorption properties as close as possible to a real spinal cord. It also emulates the termination of the spinal cord as it transforms into the cauda equina. Several RTV silicone pigments were added to the silicone, in order to give it infrared optical absorption properties close to those of haemoglobin. Aluminium oxide powder was added to emulate the scattering, as well known in the literature.

In order to assemble the phantom four guide-wires traversing each of the vertebral bodies and intervertebral discs were used, as shown in Figure 3. This allows the user of the phantom to adjust the tension on each of the guide-wires which in turn adjusts the degree of flexion and extension of the spine. It is also be possible to simulate scoliosis by adjusting the tension of the lateral guide-wires, thus inducing a lateral deflection of the phantom.

In tests, the catheter used was a rigid probe, 0.78mm in diameter, containing two 200pm fibre-optic leads sheathed inside a gauge 18 spinal needle. One fibre lead was connected to the light source and the other, detecting the light backscattered into the needle tip, was connected to a spectrometer. The light source was an infrared light emitting diode (LED) (SFH4326, OS RAM Opto Semiconductors) that emits with a peak at 850nm. The catheter was then inserted into the phantom, between the cauda equina and the vertebral body, in much the same entry manner as would be achieved via the sacral hiatus. The catheter was then extracted, recording the spectra. Figure 4 shows a spectrum representative of a spectrum captured by the catheter. Two points were taken either side of the maximum peak and minimum peak. The difference between the two values was taken. This difference effectively represents the intensity backscattered into the catheter tip, corrected from any instrumental background, e.g. caused by the ambient light. A shown in Figure 5, such differences are directly related to the tip longitudinal position within the phantom. Therefore, from such signals, it is possible to derive the catheter tip position within the phantom.

Various modifications and variations to the described embodiments of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. For example, although the invention is described primarily with reference to NIRS, other properties of the tissues can be detected in order to distinguish the position of the catheter/epiduroscope tip, such as, for example, absoprption, backscattering, fluorescence, scattering anisotropy, fluorescence anisotropy, Raman emission. Equally, although the invention is described primarily with reference to an insert through which optical fibres and/or or waveguides are provided to guide light from a source and to a detector, this arrangement may be replaced by a light source and/or a light detector positioned at an end of the insert, so that light can be directly transmitted from and received at the insert tip Hence, although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes of carrying out the invention obvious to those skilled in the art are covered by the present invention. Work relating to the invention described in this patent application was funded within subproject 2.16 of the European Union Network of Excellence "Photonics4Life" (grant agreement FP7-ICT-224014-PHOTONICS4LIFE).

Claims

A navigational aid in epiduroscopy comprising:

an insert for inserting longitudinally into the spine, the insert including means for transmitting light into patient tissue and receiving light reflected from the tissue; and

means for analysing the reflected light to determine a position of an end of the insert.

A navigational aid as claimed in claim 1 wherein the means for analysing are operable to detect one or more characteristics of the reflected light and/or fluoresence and/or Raman emission.

A navigational aid as claimed in claim 2 wherein the one or more characteristics of the reflected light and/or fluorescence and/or Raman emission are used to identify different spinal positions, for example a midpoint of a vertebral body, an intervertebral disc or an edge of the vertebral body.

A navigational aid as claimed in any of the preceding claims wherein the means for transmitting and receiving light comprise one or more optical fibres and/or waveguides for carrying light from a source to the tissue and light reflected from the tissue to a detector.

A navigational aid as claimed in any of claims 1 to 3 wherein the means for transmitting and receiving light comprise a light source and/or a light detector positioned at an end of the insert.

A navigational aid as claimed in any of the preceding claims comprising means for generating an image of the spine based at least in part on the reflected light.

A navigational aid as claimed in any of the preceding claims comprising a display for displaying an image.

A navigational aid as claimed in any of the preceding claims wherein the light used is near infrared.

9. An epiduroscope that includes a navigational aid as claimed in any of the preceding claims.

10. An anatomically correct deformable phantom of a spine that is made of a material that has optical absorption and/or scattering and/or fluorescence and/or Raman properties that are substantially the same as a real spine.

11. An anatomically correct deformable phantom of a spine as claimed in claim 10 comprising at least one vertebrae, at least one inter-vertebral disc, and a spinal cord.

12. An anatomically correct deformable phantom of a spine as claimed in claim 11 including spinal nerves branching out from the cord, and a cauda equina.

13. An anatomically correct deformable phantom of a spine as claimed in any of claims 10 to 2 that is made of a silicone resin.

14. An anatomically correct deformable phantom of a spine as claimed in any of claims 10 to 13 that is configurable to allow the curvature of the spine to be changed.

15. An anatomically correct deformable phantom of a spine as claimed in any of claims 10 to 14 adapted to allow a catheter or insert to be inserted longitudinally into the phantom.

16. An anatomically correct deformable phantom of a spine as claimed in any of claims 10 to 15 including materials with an X-ray opaque load, such as barium sulphate, nanoparticle or metallic powders, to modify the X-ray opacity of the parts.

17. An anatomically correct deformable phantom of a spine as claimed in any of claims 10 to 16 including at least one channel to allow fluids to be circulated.

18. An anatomically correct deformable phantom of a spine as claimed in any of claims 10 to 17 comprising one or more heating and/or cooling and/or other mechanically, thermally or optically active elements.