Patent Publication Number: US-2021174706-A1

Title: Injection site training system

Description:
This application is a continuation of U.S. patent application Ser. No. 15/886,363, filed Feb. 1, 2018, which is a continuation of U.S. patent application Ser. No. 14/598,614, filed Jan. 16, 2015, which claims the benefit of U.S. Provisional Application No 61/928,915, filed on Jan. 17, 2014, U.S. Provisional Application No 61/939,093, filed on Feb. 12, 2014, and U.S. Provisional Application No. 62/066,792, filed on Oct. 21, 2014, the entirety of each of which is hereby incorporated herein by reference. 
    
    
     Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. 
     BACKGROUND 
     A variety of medical injection procedures are often performed in prophylactic, curative, therapeutic, or cosmetic treatments. Injections may be administered in various locations on the body, such as under the conjunctiva, into arteries, bone marrow, the spine, the sternum, the pleural space of the chest region, the peritoneal cavity, joint spaces, and internal organs. Injections can also be helpful in administering medication directly into anatomic locations that are generating pain. These injections may be administered intravenously (through the vein), intramuscularly (into the muscle), intradermally (beneath the skin), subcutaneously (into the fatty layer of skin), or intraperitoneally (into the body cavity). Injections can be performed on humans as well as on animals. The methods of administering injections typically vary for different procedures and may depend on the substance being injected, needle size, or area of injection. 
     Injections are not limited to treating medical conditions, but may be expanded to treating aesthetic imperfections or restorative cosmetic procedures. Many of these procedures are performed through injections of various products into different parts of the body. The aesthetics and therapeutic industry comprises two main categories of injectable products: neuromodulators and dermal fillers. The neuromodulator industry commonly uses nerve-inhibiting products such as Botox®, Dysport®, and Xeomin®. The dermal filler industry uses products administered by providers to patients for both cosmetic and therapeutic reasons, such as, for example, Juvederm®, Restylane®, Belotero®, Sculptra®, Artefill®, and others. These providers or injectors may include plastic surgeons, facial plastic surgeons, oculoplastic surgeons, dermatologists, nurse practitioners, dentists and nurses. 
     A problem in the administration of injections is that there is no official certification or training process. Anyone with a minimal medically-related license may inject a patient. These “injectors” may include primary care physicians, dentists, veterinarians, nurse practitioners, nurses, physician&#39;s assistants, or aesthetic spa physicians. However, the qualifications and training requirements for injectors vary by country, state, and county. For example, in most states in the United States, the only requirement to be permitted to inject patients with neuromodulators and/or fillers is to have a nursing degree or medical degree. Accordingly, there is a lack of uniformity and expertise in administering such injections. The drawbacks with this lack of uniformity in training and expertise are widespread throughout the medical industry. Doctors and practitioners often are not well-trained in administering injections of diagnostic, therapeutic, and cosmetic chemical substances. This lack of training has led to instances of chronic pain, headaches, bruising, swelling, or bleeding in patients. 
     Current injection training options are classroom-based, with hands-on training performed on live models. The availability of models is limited. Moreover, even when available, live models are limited in the number and types of injections they may receive. The need for live models is restrictive because injectors are unable to be exposed to a wide and diverse range of situations and anatomies in which to practice. For example, it may be difficult to find live models with different skin tones or densities. This makes the training process less effective because patients have diverse anatomical features as well as varying prophylactic, curative, therapeutic, or cosmetic needs. Live models are also restrictive because injectors are unable to practice injection methods on the internal organs of a live model due to safety and health considerations. 
     As a result of these limited training scenarios, individuals seeking treatments involving injections have a much higher risk of being treated by an inexperienced injector. This may result in low patient satisfaction with the results, or in failed procedures. In many instances, patients have experienced lumpiness from incorrect dermal filler injections. Some failed procedures may result in irreversible problems and permanent damage to a patient&#39;s body. For example, patients have experienced vision loss, direct injury to the globe of the eye, and brain infarctions where injectors have incorrectly performed dermal filler procedures. Additional examples of side effects include inflammatory granuloma, skin necrosis, endophthalmitis, injectable-related vascular compromise, cellulitis, biofilm formation, subcutaneous nodules, fibrotic nodules, and other infections. 
     As a result of the varying qualifications and training requirements for injectors, there is currently no standard to train, educate, and certify providers on the proper and accurate process of various injection techniques. Patients seeking injections also have few resources for determining the qualifications or experience of a care practitioner. 
     SUMMARY 
     The present disclosure generally relates to an injection apparatus and training system for prophylactic, curative, therapeutic, acupuncture, or cosmetic injection training and certification. The training system eliminates the need to find live models for hands-on training sessions. The training system provides feedback on trainees and the accuracy of injection procedures performed. In an embodiment, feedback is provided in real time. The training system can be used as a measurement on how the “trainee” is doing prior to receiving actual product by the manufacturing company as a measure of qualification. The training system reduces the risks associated with inexperienced and uncertified medical personnel performing injection procedures. 
     The training system can be used to educate, train, and certify medical personnel for injection procedures. It can also be utilized as a testing program for certifying medical personnel. The system will enable users to practice a variety of injections, ranging from on label to off label product injections. In some embodiments, the system may allow users to train for therapeutic treatments. In other embodiments, the system may allow users to train for injections into arteries, bone marrow, the spine, the sternum, the pleural space of the chest region, the peritoneal cavity, joint spaces, internal organs, or any other injection sites. The system may be used for any type of injection, including, but not limited to those involving prophylactic, curative, therapeutic, or cosmetic treatments in both humans and animals. Illustratively, by way of non-limiting example, the disclosed system may be used to simulate a cosmetic application of filling of a wrinkle with a dermal filler. In other applications, the systems disclosed herein can be used for dental application and training for dental procedures. 
     In an aspect of the present disclosure, an injection training system is described that includes a testing tool having a needle and a position sensor, where the position sensor is configured to obtain position information of the testing tool. The system also includes an injection apparatus configured to receive a simulated injection by the testing tool. The system includes a display device configured to receive the position information and to display position data reflective of the position information, wherein the display device includes a processor and a memory device. 
     In an embodiment of the disclosed injection training system, a method of tracking the position of a testing tool used in an injection training system is described. The method includes obtaining position information of the testing tool from one or more sensors; determining an estimate of the position of the testing tool; transmitting, to a display device, data reflective of the estimate of the position of the testing tool; and displaying, on the display device, the data reflective of the estimate of the position of the testing tool. 
     In an embodiment, an injection training system is disclosed. The injection training system includes a testing tool having a needle, a plunger, and a marker configured to reflect electromagnetic waves. The system also includes an injection apparatus configured to receive a simulated injection by the testing tool. The injection apparatus also has a marker configured to reflect electromagnetic waves. The system includes an optical tracking system having a field of view, where the optical tracking system is positioned such that the injection apparatus is in the field of view. The optical tracking system is configured to obtain position information of the testing tool and the injection apparatus and to transmit the position information to a display device. The display device is configured to receive the position information and to display position data reflective of the position information. 
     In one embodiment, there are three main components of the training system: (1) a training apparatus (also referred to interchangeably as an injection apparatus throughout the present disclosure) which features an anatomically accurate model of a human or human body part necessary for injection training, (2) a light detection device, such as, for example, a camera, associated with the training apparatus, and (3) a testing tool with light emitting capabilities. In an embodiment, a fourth component of the training system can include an output device that can run an application which receives communications from the training apparatus or light detection device and generates information regarding injection parameters based on the communications from the injection apparatus or light detection device. In an embodiment, the images captured by the camera are processed by a processor included either in the injection apparatus or in the light detection device before being communicated to the output device. This processing can include, for example, determining an indication of one or more injection parameters. In an embodiment, the anatomical model can include various injection conditions, such as, for example, layered skin, available in multiple tones and textures to mimic a diverse span of age, race, and skin texture. In an embodiment, the layered skin can be removable and/or replaceable. The injection apparatus can simulate any human or animal part, such as, for example, the face, head, brain, neck, back, chest, spine, torso, arms, legs, hands, feet, mouth, or any other body part or portion of the body of interest. In an embodiment, the testing tool can be, for example a syringe or hypodermic needle. In an embodiment, the injection apparatus is reusable. In an embodiment, the injection apparatus is disposable. 
     In an embodiment a syringe for simulating injection is disclosed. The syringe can include a barrel having a portal at a distal end, and an electronics assembly having a light source at a distal end of the electronics assembly. The electronics assembly can be configured to fit inside the barrel with the light source positioned at the portal of the barrel. A needle can be attached to the barrel. The needle can have a fiber bundle extending axially through it such that the fiber bundle is in close-fitting relation with the light source. 
     In some embodiments a testing tool for use in an injection training system includes a barrel having a fitting at a distal end of the barrel. The fitting can have a portal, and the barrel can have an opening and a finger grip at a proximal end of the barrel. A plunger can be configured to fit in the opening of the barrel to apply a force directed axially toward the distal end of the barrel. The testing tool can include an electronics assembly that has a light source at its distal end and a force sensor at its proximal end. The electronics assembly can be configured to fit inside the barrel with the light source positioned at the portal of the fitting, and the force sensor positioned near the proximal end of the barrel. The force sensor can be configured to sense the force applied by the plunger. The testing tool can include a needle assembly attached to the fitting of the barrel. The needle assembly can have a hollow needle, a fiber bundle extending axially through the hollow needle, and a hub configured to secure the hollow needle and to attach the needle assembly to the fitting of the barrel. The needle assembly can be attached to the barrel such that the fiber bundle within the hollow needle is in close-fitting relation with the light source of the electronics assembly. 
     In an embodiment, a method of simulating an injection into a synthetic anatomical structure is disclosed. The synthetic anatomical structure can be configured to attenuate light emitted into it and to detect the attenuated light. The method can include providing a testing tool to simulate a syringe. The testing tool can be configured to emit light through a needle at a distal end of the testing tool. The method can also include inserting the needle into the synthetic anatomical structure such that the light emitted through the needle is attenuated and detected by the synthetic anatomical structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an injection training system comprising an injection apparatus, a testing tool and an output device in accordance with an embodiment of the present disclosure. 
         FIG. 2A  is a perspective view of an embodiment of an assembled testing tool. 
         FIG. 2B  is an exploded perspective view of an embodiment of a testing tool. 
         FIG. 2C  is a perspective view of an embodiment of a barrel of a testing tool. 
         FIG. 2D  is a perspective view of an embodiment of a label of a testing tool. 
         FIG. 2E  is a perspective view of an embodiment of a needle assembly of a testing tool. 
         FIG. 2F  is an exploded perspective view of an embodiment of a needle assembly of a testing tool. 
         FIG. 2G  is a top view of the distal end of an embodiment of the needle assembly of a testing tool. 
         FIG. 3A  is a simplified block diagram of an embodiment of an electronics assembly of a testing tool. 
         FIG. 3B  is a perspective view of an embodiment of an electronics assembly of a testing tool. 
         FIG. 3C  is an exploded perspective view of an embodiment of a force sensor sub-assembly of an electronics assembly of a testing tool. 
         FIG. 4A  is a perspective view of an embodiment of a testing tool docked in an embodiment of a docking station. 
         FIG. 4B  is a perspective view of an embodiment of a docking station. 
         FIG. 4C  is a perspective view of an embodiment of a docking station with its cover removed. 
         FIG. 5  illustrates an embodiment of the injection training system. 
         FIGS. 6A and 6B  are two perspective views of an example trajectory for an injection. 
         FIG. 7  illustrates an example embodiment of a three-dimensional (3D) injection detection sensor. 
         FIG. 8  illustrates an example embodiment of a 3D injection detection sensor. 
         FIG. 9  illustrates a side view of one embodiment of the injection apparatus including a 3D injection detection sensor. 
         FIG. 10  is a process flow diagram of a method of manufacturing an anatomically shaped injection apparatus including a 3D tracking system. 
         FIG. 11  is a process flow diagram for a method of 3D injection training. 
         FIG. 12  illustrates an embodiment of an injection training system comprising an injection apparatus, a testing tool, and a resting cradle in which the testing tool follows a sequence of motion (A through D) from the resting cradle to an injection site of the injection apparatus. 
         FIG. 13A  illustrates a process flow diagram of a process to determine the position and orientation of a testing tool according to an embodiment of the disclosed injection training system. 
         FIGS. 13B ,  13 B 1 , and  13 B 2 , collectively, illustrate a process flow diagram of a process to determine the position and orientation of a testing tool according to an embodiment of the disclosed injection training system. 
         FIG. 14A  is simplified perspective view of an exemplary optical tracking system illuminating a testing tool according to an embodiment of the disclosed injection training system. 
         FIG. 14B  is simplified perspective view of an exemplary optical tracking system sensing reflected light from testing tool according to an embodiment of the disclosed injection training system. 
         FIG. 14C  illustrates a testing tool configured with multiple markers according to an embodiment of the disclosed injection training system. 
         FIG. 14D  illustrates aspects of the user interface/display device according to an embodiment of the disclosed injection training system. 
         FIG. 15A  illustrates an embodiment of an injection training system comprising an injection apparatus, a testing tool, an output device and an optical tracking system, in accordance with an embodiment of the present disclosure. 
         FIG. 15B  illustrates an embodiment of an injection training system comprising an injection apparatus, a testing tool, an output device and a plurality of optical tracking systems, in accordance with an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will now be described with reference to the accompanying figures. The following description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or its uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. The terminology used in the description presented herein is not intended to be interpreted in any limited or restrictive manner, simply because it is being used in conjunction with a detailed description of certain specific embodiments of the disclosure. Furthermore, embodiments of the disclosure may include several novel features, no single one of which is solely responsible for its desirable attributes or which is essential to practicing the present disclosure. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
       FIG. 1  depicts an embodiment of an injection training system  100 . An injection apparatus  105 , comprising a synthetic anatomical structure, can be used for any type of injection training involved with administering diagnostic and therapeutic chemical substances. For example, injection training can be provided for epidural techniques and for intra-cardiac injections. In one embodiment, the injection apparatus  105  can anatomically model the face, neck, and head of a human or animal. Although not shown in the accompanying drawings, the injection apparatus  105  can model other injection sites including the chest, arms, mouth, back, buttocks, etc. The injection apparatus  105  may also represent any body part of a human or animal, including internal organs. In some embodiments, the injection apparatus  105  may include a simulated skull and layers of muscle and skin. The injection apparatus  105  can be positioned on a base  108  to facilitate use on flat surfaces, such as a table or desk. 
     A testing tool  110  is also illustrated which can be used with the injection apparatus  105  and in conjunction with a camera/light detector  120  located within the injection apparatus  105 . The testing tool  110  may simulate any type of equipment used in connection with an injection or minimally invasive procedure, such as a needle, catheter or cannula. As described in further detail below, the camera/light detector  120  can capture visual indications of the user&#39;s injection using the testing tool  110 . The visual indications provide an operator or user with information regarding the location, depth, pressure, or angle of the injection. In an embodiment, the testing tool  110  contains a light source that emits light through the needle portion of the testing tool  110  which is used to aid in obtaining the visual indications detectable by a camera/light detector  120 . The light source can emit visible light. In an embodiment, a gradient of white light is emitted through the needle portion of the testing tool. Other colors of visible light can also be used, such as green, blue, red, yellow or any combination of those colors. In an alternative embodiment, the light source may emit light along a spectrum of visible or non-visible light, such as fluorescent, ultraviolet, or infrared light. In some embodiments, the light emitted from the light source is attenuated differently depending on which layer of simulated skin, muscle, or tissue the injection apparatus  105  is penetrated. Different colors, directions, graph lines, visual patterns, polarization, fluorescence, or intensities of light can be captured by the camera/light detector  120  as the testing tool  110  is inserted through the different layers of material surrounding the injection apparatus  105 . The resulting light detected by the camera/light detector  120  can be used to determine the location of the injection, the pressure exerted by the user, the angle of injection, and/or the depth of the injection. This information can be detected, for example by a camera/light detector  120 , and communicated to a user interface/display device  140  for training, testing, and/or certification purposes. In some embodiments, information used to determine the location of the injection, the pressure exerted by the user, the angle of injection, and/or the depth of the injection can be collected by the testing tool  110  and communicated to a user interface/display device  140  and/or a camera/light detector  120  for training, testing and certification purposes. 
     The camera/light detector  120  within the simulated skull of the injection apparatus  105  captures the attenuated light emitted by the testing tool  110 , simulating an injection, through video recording and/or photographic images. The camera/light detector  120  can include a processor and can communicate output from the camera/light detector  120  to a user interface/display device  140 . The information gathered from the camera/light detector  120  and testing tool  110  may be communicated to a user interface/display device  140  for data collection, testing or certification purposes. Output from the camera/light detector  120  can be raw or processed video or images obtained from the camera/light detector  120 . The processor of the camera/light detector  120  can include software configured to interpret the visual indications for testing purposes or can merely pass images to the user interface/display device  140  for further processing. In an embodiment, the user interface/display device  140  can also communicate instructions to the camera/light detector  120  and/or to the testing tool  110 . 
     Attention is now directed to embodiments of the testing tool  110 . Although disclosed with reference to particular embodiments of the testing tool  110 , an artisan will recognize from the disclosure herein that there is a large number and wide variety of embodiments and configurations that may be used to perform the functions of a testing tool  110  as described herein. 
       FIGS. 2A and 2B  illustrate (in assembled and exploded views, respectively) an embodiment of the testing tool  110  adapted for use to train individuals to inject materials with a syringe. In an embodiment the testing tool  110  includes a plunger  210 , a barrel  220 , a needle assembly  230 , and an electronics assembly  240 . Also illustrated are fasteners  221 , such as screws, to secure portions of the electronics assembly  240  to the barrel  220 . 
     For purposes of this description, the end of the test tool  110  toward the needle assembly  230  is referred to as the “distal end,” and motion or direction toward the distal end is described as being “distal.” The end of the test tool  110  longitudinally opposite the distal end is referred to as “the proximal end,” and motion or direction toward the proximal end is described as being “proximal.” 
     The plunger  210  can be manufactured by using many types of materials including polypropylene, glass, and other materials known to skilled artisans. The plunger  210  includes a top portion  212  at the proximal end of the plunger  210 . The plunger  210  also includes a shaft  214  which, in an embodiment, is x-shaped. In some embodiments the plunger shaft  214  can be cylindrical or any other shape suitable to perform the function of a plunger  210 . In some embodiments, the plunger  210  is collapsible to simulate the process of injecting material into a patient. In some embodiments the plunger  210  is configured to house the electronics assembly  240 . In some embodiments the plunger  210  is collapsible and configured to measure the plunger&#39;s  210  motion of contraction to determine a volume of material that would have been injected under the simulated circumstances and conditions of use of the testing tool  110 . The collapsible plunger  210  can be reset by pulling it back to its original, un-collapsed (or extended) position. In some embodiments data reflecting the position of the plunger  210  is collected and communicated to, for example, the user interface/display device  140  and/or to the camera/light detector  120 . In an embodiment the testing tool  110  includes a hydraulic and/or a friction-based device, acting against the plunger  210 , to simulate the force of resistance that a liquid material with certain properties of viscosity, would exert against the plunger  210  as it is injected into a patient. 
     At the distal end of the plunger  210  is a seal  216 , which is made of rubber in an embodiment. A skilled artisan will appreciate that in some embodiments the plunger seal  216  may be made from any material suitable for creating a seal between the plunger  210  and the inside walls of the barrel  220 , such as various types of elastomers and/or polymers. In some embodiments the plunger  210  lacks a seal  216  because the testing tool  110  is not used to deliver liquid, chemical substances, thereby lacking a need to form a seal. 
       FIG. 2C  is a perspective view of an embodiment of a barrel  220  of a testing tool  110 . The barrel  220  can be made from many types of materials including polypropylene, glass, and other materials known to skilled artisans. The barrel  220  includes a grip  222  and an opening  223  at the barrel&#39;s proximal end. The grip  222  provides finger support for reciprocation of the plunger  210  relative to the barrel  220  during use for training. At the distal end of the barrel  220  is a threaded portion  224  configured to receive a fitting  226 . The fitting has a portal  225  through which light passes from a light source (on the electronics assembly  240 ) to a fiber bundle housed within a hollow needle (in the needle assembly  230 ). In some embodiments the fitting  226  can be a Luer fitting, a standardized set of fittings used to make leak-free mechanical connections between a male-taper fitting and a mating female part on medical and laboratory instruments, including hypodermic syringe tips and needles. In some embodiments the fitting  226  is not tapered. Advantageously, in some embodiments, the fitting  226  can accommodate numerous configurations of needle assemblies  230  corresponding to various injection indications and applications. In some embodiments a customized fitting  226  includes a thread with no taper component to facilitate intimate contact between a light source and a fiber bundle that transmits the emitted light into the injection apparatus  105 . In an embodiment the barrel  220  includes bores  228  configured to receive connector pins attached to the electronics assembly  240  to enable charging of a battery when, for example, the testing tool  110  is housed in a docking station. The barrel  220  also includes holes  229  through which fasteners, such as screws, can be used to secure the electronics assembly  240  to the barrel  220 . 
       FIG. 2D  is a perspective view of an embodiment of a label  250  of a testing tool  110 . In an embodiment, the label  250  is configured to fit inside the barrel  220  in close-fitting relation with an inner wall of the barrel  220 . In an embodiment the label  250  is configured to fit outside the barrel  220  in close-fitting relation with an outer wall of the barrel  220 . The label  250  can be configured to present any type of information including, among other things, branding and/or instructional information. 
       FIGS. 2E-2F  are perspective views (assembled and exploded, respectively) of an embodiment of a needle assembly  230  of a testing tool  110 , including a hollow needle  232 , a needle hub  234 , an adapter  236 , and a fiber bundle  238  positioned centrally along the longitudinal axis of the needle assembly  230  and configured to transmit light at the distal end of the testing tool  110 . In some embodiments a needle hub  234  is configured to connect directly to the fitting  226  of the barrel  220 , thereby eliminating the need for an adapter  236 . The fiber bundle  238  is housed within the hollow needle  232 . In an embodiment the hollow needle  232  is made from hypodermic tubing. A wide variety of hollow needles  232  used for, among other things, hypodermic applications, have outer diameters described by gauge numbers ranging from 7 to 34. Hollow needles  232  within this gauge range can be used in various embodiments of the disclosed needle assembly  230 . Smaller gauge numbers indicate larger outer diameters. The inner diameters of such hollow needles  232  depend on both gauge and wall thickness. Thin-wall needles have identical outer diameters, but larger inner diameters, for a given gauge. Thin-wall needles can also be used in various embodiments of the needle assembly  230 . In an embodiment the hollow needle  232  is made of stainless steel and has a gauge size of 23RW. A skilled artisan will appreciate that the hollow needle  232  can be of many different gauge sizes without departing from the scope of the disclosure herein. Free space between the fiber bundle  238  and the inner wall of the hollow needle  232  can be potted with optical epoxy. The proximal and distal ends of the hollow needle  232 , having the fiber bundle  238  secured inside it, can be polished flat. The hollow needle  232  can be epoxy-bonded to the needle hub  234 , which attaches to the fitting  226  on the barrel  220 .  FIG. 2G  is a top view of the distal end of the needle assembly  230  illustrating the fiber bundle  238  housed and secured with optical epoxy within the hollow needle  232 . 
       FIG. 3A  is a simplified block diagram of an embodiment of the electronics assembly  240  of the testing tool  110 . Functionally, among other things, the electronics assembly  240  emits light from a light source  320 , measures the electronic assembly&#39;s  240  physical position and/or orientation with a position sensor  308 , and measures force applied to the plunger  210  by a force sensor  312 . The electronics assembly  240  communicates the measured position information and the measured force information to, for example, an external user interface/display device  140 , and/or to a camera/light detector  120 , by way of a communications protocol. In some embodiments the electronics assembly  240  communicates data by way of a USB port  322  using a cable that has a minimal diameter and is highly compliant. In some embodiments the electronics assembly  240  communicates data by way of a radio  310  employing, for example, a Bluetooth wireless communications protocol. 
     As illustrated in  FIG. 3A , an embodiment of the electronics assembly  240  includes a battery  302 , a power management controller  304 , a voltage regulator  306 , a position sensor  308 , a radio  310 , a force sensor  312 , a data acquisition system  314 , one or more processors  316 , a light source driver  318 , a light source  320  and one or more power/communication ports  322 . In some embodiments the battery  302  is rechargeable, and the power management controller  304  is configured to communicate with an external battery-charging power/communication port  322 , such as, for example, a universal serial bus (USB) port. The battery  302  can supply power to the components and circuitry of the electronics assembly  240 . In an embodiment the battery  302  is an ultrathin, rechargeable, lithium polymer cell. A skilled artisan will appreciate that numerous other batteries can be used in the disclosed electronics assembly  240 . 
     According to an embodiment, the electronics assembly  240  comprises a battery  302  and a light source  320 , where the electronics assembly  240  is configured to emit light through the hollow needle  232  to achieve basic functionality of the disclosed testing tool  110 . In an embodiment, the electronics assembly  240  comprises a light source  320  and a port  322  through which an external power source may be electrically connected to energize the light source  320  to achieve basic functionality of the testing tool  110 . One skilled in the art will appreciate that various functional capabilities described in connection with embodiments of the electronics assembly  240  can be implemented in numerous ways. To illustrate this point, illustrative components, blocks, modules, and circuits have been described generally in terms of their functionality. The manner by which such functionality is implemented can depend upon the particular application and design constraints imposed on the overall system. The described functionality can be implemented in varying ways for each particular application, but such embodiment decisions should not be interpreted as causing a departure from the scope of the present disclosure. 
     To operate effectively in the injection training system  100 , the light source  320  must be sensed by the camera/light detector  120 . In an embodiment the camera/light detector  120  is configured to sense visible light and infrared light. In an embodiment the light source is a light emitting diode (LED) that emits low, infrared light at a wavelength of 810 nanometers (nm). In an embodiment the light source  320  is a laser that emits low infrared light at a wavelength of 850 nm. In an embodiment the light source  320  has a narrow emission angle of twenty degrees or less. In an embodiment, the light source  320  is an LED that has its dome removed and is polished flat to facilitate intimate contact with the proximal end of the fiber bundle  238  and the light source  320  when the testing tool  110  is assembled. In some embodiments lenses, reflectors, and/or fiber optic tapers are coupled to the light source  320  to focus and/or to intensify the emitted light in the direction of the fiber bundle  238 . In some embodiments the intensity of the light emitted by the testing tool  110  is proportional to the amount of pressure applied to a plunger  210  of the testing tool  110 , thereby simulating a process by which liquid material is injected through the testing tool  110 . A skilled artisan will appreciate that many other light sources  320  and light ranges of various wavelengths can be used in the disclosed training system  100  without departing from the scope of the disclosure herein. 
     In an embodiment the force sensor  312  is configured to sense up to twenty pounds (20 lbs.) of force with a 2 percent accuracy factor. In an embodiment the position sensor  308  is a three-axis digital gyroscope with angle resolution of two degrees and with a sensor drift adjustment capability (pitch, yaw and roll) of one degree. A skilled artisan will appreciate that numerous other position sensors  308  and force sensors  312  can be used in the disclosed electronics assembly  240  without departing from the scope of the disclosure herein. In an embodiment the electronics assembly includes a power conditioning component, such as a voltage regulator  306 , to enable operation of the position sensor  308  and the force sensor  312 . In an embodiment the position sensor  308  senses the position of the testing tool  110  in three-dimensional space, and the sensed position information is communicated to the user interface/display device  140  and/or to the camera/light detector  120 . 
       FIG. 3B  is a perspective view of an embodiment of the electronics assembly  240 . Advantageously, the electronics assembly  240  is configured to fit within the barrel  220  of the testing tool  110 . A rectangular circuit board  324  comprises a substrate onto which several components of the assembly  240  are attached. In an embodiment the electronics assembly includes the battery  302 , the power management controller  304 , the voltage regulator  306 , the light source driver  318  and the light source  320 . When the electronics assembly  240  is configured in the testing tool  110 , it is positioned such that the light source  320  is located at the distal end of the testing tool  110 , within the fitting  226  so as to make intimate contact with the proximal end of the fiber bundle  238 , which is secured to the needle assembly  230 . 
     In an embodiment the electronics assembly  240  also includes a force sensor sub-assembly  360  illustrated in  FIG. 3B  and in  FIG. 3C , in assembled and exploded views, respectively. The force sensor sub-assembly  360  has a circular printed circuit board  326  comprising a substrate to which several components of the force sensor sub-assembly  360  are attached, including a force sensor  312 , backstops  328 , and connector pins  330 . The backstops  328  provide structural support for the force sensor sub-assembly  360  and serve as a mechanism by which to secure the force sensor sub-assembly  360  to the barrel  220 . The circular printed circuit board  326  is attached to the two backstops  328  with fasteners  329 . The connector pins  330  are used to couple to an external power source to charge the battery  302 . In an embodiment, the connector pins  330  are spring-loaded contacts that are soldered to the circular printed circuit board  326  and configured to fit through the bores  228  in the barrel  220 . By protruding through the bores  228  the connector pins  330  are able to make electrical connection with an external power source to enable charging of the battery  302 . 
     When positioned within the testing tool  110 , the force sensor sub-assembly  360  is oriented substantially perpendicular to the rectangular printed circuit board  324  such that the force sensor  312  is configured to sense axial force applied in the distal direction by the plunger  210 . The force sensor sub-assembly  360  is secured to the barrel  220  by fasteners  221  (shown in  FIG. 2B ), such as flat head screws, that are inserted through the holes  229  of the barrel  220  and secured into threaded screw holes  362  located centrally on the backstops  328 . In this manner the force sensor sub-assembly  360  resists being deflected in response to force applied to the force sensor  312  by the plunger  210 . 
     In an embodiment the circular printed circuit board  326  is electrically coupled to the proximal end of the rectangular printed circuit board  324  to enable electrical communication between the force sensor  312  and the processor  316 , and between the connector pins  330  and the power management controller  304 . 
     An artisan will recognize from the disclosure herein that the functionality of the electronics assembly  240  may be accomplished in many different ways, using many different electronic components and organized in a large number of ways without departing from the scope of the disclosure herein. 
     Referring back to  FIGS. 2A-2B , assembly of the testing tool  110 , for some embodiments, is accomplished by securing the needle assembly  230  to the fitting  226 , and by securing the electronics assembly  240  into the barrel  220 . Spring-loaded connector pins  330  retract inward to permit the electronics assembly  240  to move to the distal end of the inside of the barrel  220 , such that the light source  320  is in close intimate relation with the proximal end of the fiber bundle  238  of the needle assembly  230 . The electronics assembly  240  may be rotated axially such that the spring-loaded connector pins  330  are aligned with bore holes  228 , at which point the spring-loaded connector pins will expand to lock into position. Fasteners  221  are then used to secure the electronics assembly  240  to the barrel  220 . The plunger  210  is inserted into the proximal end of the barrel  220 . 
     In some embodiments the plunger  210  is configured to move distally through the barrel  220  when force is applied to the plunger  210 , thereby simulating the plunger motion associated with injecting material into a patient. In an embodiment, the plunger shaft  214  is cylindrical, having an outer diameter slightly less than the inner diameter of the barrel  220 . As the cylindrical plunger shaft  214  moves through the barrel  220  in the distal direction, the plunger shaft  214  slides around and envelops the electronics assembly  240 . In an embodiment, a resistance device offers a resistive force in response to the force applied to the plunger  210 , corresponding to a resistive force experienced when injecting liquid materials into a patient. In an embodiment the resistive device is a friction-based device. In an embodiment the resistive device is a fluid-based device. In an embodiment the resistive device includes a spring configured to apply a resistive force to the plunger  210 . One skilled in the art will readily appreciate that there are many ways by which to achieve the functionality of the resistive device. In an embodiment, the force applied by the plunger  210  and the force applied by the resistive device are sensed and communicated to a user interface/display device  140  and/or to a camera/light detector  120 . 
     In some embodiments the plunger shaft  214  is configured to collapse telescopically to simulate plunger motion associated with injecting material into a patient. In some embodiments, the collapsible plunger shaft  214  is configured to sense positional displacement of the plunger shaft  214  and to communicate the plunger shaft  214  displacement coordinates to a user interface/display device  140  and/or to a camera/light detector  120 . In some embodiments measurements of the position of a movable, collapsible or telescoping plunger  210  are communicated to a user interface/display device  140  and/or to a camera/light detector  120  and used to determine whether proper doses are being delivered. 
     In some embodiments, the electronics assembly  240  is positioned within the plunger shaft  214 , and is configured to move distally and proximally through the barrel  220 , along with the plunger  210 . Placing the electronics assembly  240  in a hollowed shaft  214  of the plunger  210  makes the barrel  220  available to hold a therapeutic agent that can be injected during the training into the injection apparatus  105 . The position sensor  308  is configured to obtain position and orientation information of the testing tool  110  and of the plunger  210 , and to wirelessly transmit the information to the user interface/display device  140 . In an embodiment, the force sensor sub-assembly  360  can be positioned within the shaft  214  of the plunger  210  to measure the resistive force of the therapeutic agent in the barrel  220 , as the injection is applied. The measured force information can be wirelessly transmitted to the user interface/display device  140 . Illustratively, in such an embodiment the testing tool  110  operates in a manner similar to a syringe in that the testing tool  110  is configured to deliver a therapeutic agent through the needle  232  into the injection apparatus  105 . In some embodiments the electronics assembly  240  is positioned within the plunger shaft  214  and is configured to move distally and proximally through the barrel  220 , along with the plunger  210 . The light source  320  is positioned at the distal end of the barrel  220 , and a flexible connector connects the light source  320  to the electronics assembly  240 . In some embodiments the flexible connector connecting the light source  320  to the electronics assembly is extendable and retractable. Accordingly, the plunger  210  is able to move axially into and out of the barrel  220 , while the light source is configured to emit light through the tip  233  of the hollow needle  232 . 
       FIG. 4A  illustrates an embodiment of a testing tool  110  docked in a docking station  400 . The docking station  400  includes a dock cover  402 , a USB port  404 , and two indicator lights  406 . The docking station  400  is contoured to accommodate the testing tool  110  such that the connector pins  330  of the testing tool  110  are in contact with contact pins  408  to facilitate charging of the battery  302 .  FIG. 4B  provides a view of a contact pin  408  of the docking station  400 .  FIG. 4C  illustrates the docking station  400  with its cover  402  removed revealing a dock circuit board  410  electrically coupled to the USB port  404  and to the indicator lights  406 . The dock circuit board  410  is also electrically coupled to contact pins  408  such that when a connection is made from, for example, a standard power outlet to the USB port  404 , the contact pins are configured to support charging of the battery  302  of the testing tool  110  when the testing tool is docked in the docking station  400 . Standoff elements  412  are employed to provide appropriate spacing within the structure of the docking station  400 . 
     In some embodiments of the injection training system  100 , an injection training apparatus  105  or method can use one or more three-dimensional (3D) position sensors to determine a position of a testing tool  110 , such as a syringe and/or needle, in an artificial patient injection site (such as, for example, an artificial face). One or more 3D position sensors can also be used for training caregivers on performing injections where accurate positioning is important, such as in facial injections (e.g., Botox®), spinal injections, and/or the additional injections described above. 
     By integrating one or more 3D sensors, the injection training apparatus and method may provide enhanced accuracy when tracking the trainee&#39;s injection technique. Increased training accuracy can facilitate increased detail on the feedback provided to the trainee. The features discussed below with reference to  FIGS. 5-11  may be included, in whole or part, with the training systems, methods, and devices described herein. 
       FIG. 5  illustrates an embodiment of the injection apparatus  105 , testing tool  110  and user interface/display device  140 . The injection apparatus  105  shown forms a head bust with realistic look and feel of human flesh. The external surface of the injection apparatus  105  may be a substantially synthetic or simulated skin. The synthetic or simulated skin can be an opaque rubber or other material which simulates skin and facial features of real patients. Underlying the skin may be a layer of substantially clear rubber (and/or any suitable elastomer) which simulates the viscosity, elasticity, and feel of skin, muscle, nerve, and bone tissue of a patient. The opaque skin and clear underlay may be capable of being pierced by a needle. It should be noted that the injection apparatus  105  need not include colored underlying skin to attenuate light. 
     The injection apparatus  105  is hollow and includes, within the cavity, a three-dimensional (3D) sensor  502 . The 3D sensor  502  may include a camera, an array of light detectors or other sensor(s) capable of detecting a location of an object in three dimensions. The 3D sensor  502  is configured to detect a position of a needle and/or to view the interior surface of the injection apparatus  105 . A field of view  504  is established in front of the 3D sensor  502 . The field of view  504  represents an area in which the 3D sensor  502  may detect light. 
     A testing tool  110  is also shown. The testing tool  110  may be implemented as a syringe equipped with a light emitting needle, for example, as described in greater detail above. The light emitted by the testing tool  110  may be detected by the 3D sensor  502 . 
     As shown in  FIG. 5 , the 3D sensor  502  and the testing tool  110  are coupled with a signal processing and display interface  555  via cables  560  and  570 . The signal processing and display interface  555  can include one or more processors configured to receive and process information, provided from the 3D sensor  502  and/or from the testing tool  110  that corresponds to the position of the testing tool  110  relative to the injection apparatus  105 . Illustratively, the processing and display interface  555  processes the received information from the 3D sensor  502  and from the testing tool  110  to determine the testing tool&#39;s  110  position relative to the injection apparatus  105 . Although illustrated in  FIG. 5  as being coupled by wires, coupling between the 3D sensor  502 , the testing tool  110 , and the user interface/display  140  can be accomplished via wired, wireless, or a combination of wired and wireless configurations. Moreover, the processing and interface  555  can be incorporated into the user interface/display  140 . The method of coupling the 3D sensor  502  need not be identical to the method of coupling used for the testing tool  110 . 
     In use, as illustrated in  FIG. 5 , a trainee punctures the face of the injection apparatus  105  with the testing tool  110  which is emitting light from a tip  233  of the hollow needle  232 . When the tip  233  passes through the opaque skin layer of the injection apparatus  105 , the 3D sensor  502  is configured to detect the light emitted from the tip  233  and to determine the three-dimensional position, in space, of the tip  233 . The three-dimensional position information is transmitted to the signal processing and display interface  555 , which is configured to communicate the three-dimensional position information to the user interface/display device  140 . The user interface/display device  140  integrates the communicated position information into a digital model of the head bust injection apparatus  105 . The user interface/display device  140  may be configured to present a visual representation of the position of the needle tip  233  relative to the injection site on the injection apparatus  105 . The user interface/display device  140  allows the trainee to evaluate the actual needle position, as represented on the user interface/display device  140 , in comparison to the ideal position, which is also represented on the user interface/display device  140 . The user interface/display device  140 , shown in  FIG. 5 , is coupled with the signal processing and display interface  555  by a cable  580 . The coupling may be via wired, wireless, or a combination of wired and wireless configurations. 
     The three-dimensional position information relative to the 3D sensor  502  is mapped in software to a graphical representation of the injection site on the user interface/display device  140 . This mapping is performed by determining accurate three-dimensional coordinates corresponding to the position of the injection apparatus  105  in the world. The position of the 3D sensor  502  relative to the injection apparatus  105  is also determined with a high degree of precision. This precision allows a very accurate mapping of the detected three-dimensional position information of the hollow needle  232  and its tip  233  to be accurately detected by the 3D sensor  502  and accurately mapped in software to recreate the position of the needle  232  and the needle tip  233  of the testing tool  110 . This information is then used to determine both the accuracy of the injection relative to a predetermined injection site accuracy goal, as well as to provide a graphical illustration of the injection, again relative to the injection site goal. This mapping and display can be provided substantially in real time so that a user can adjust the trajectory of injection during the training. 
       FIGS. 6A and 6B  illustrate two views of a trajectory for an injection.  FIG. 6A  illustrates a view from the perspective of the 3D sensor  502 , positioned inside the injection apparatus  105  and directed at the inner surface of the injection apparatus  105 . To orient the reader, an eye  602  and a nose  604  have been labeled. An injection starting point  610  is detected by the 3D sensor  502 . As the needle tip  233  proceeds into the injection apparatus  105 , the changing positions of the light emitted from the needle tip  233  are measured by the 3D sensor  502 . In some implementations, the measurement may be a video capture of the injection. In some implementations, the measurement may be a sampled capture at, for example, predetermined intervals. A trajectory path  630 , from the starting point  610  to an ending point  620 , is thus obtained. As shown in  FIG. 6A , the trajectory path  630  takes the form of an irregular injection path, which may, in some circumstances, indicate the need for additional training. 
     The trajectory path  630  may be presented via the user interface/display device  140 . The presentation may include providing a line tracking the injection path. The presentation may include providing an animated depiction of the injection. In some implementations, the presentation may be augmented with additional information such as identifying and showing which muscles, skin, body parts, etc. the injection is coming in contact with or is penetrating. The augmentation of the presentation may retrieve one or more models of the desired physiological information from a data store. The models include three-dimensional information indicating the location(s) of certain anatomical or physiological features. The feature information, along with the three-dimensional injection location information, is mapped onto the presentation of the injection apparatus  105 . 
     Because three-dimensions of information are being obtained, multiple views of the injection trajectory may be provided.  FIG. 6B  provides a second view of the injection trajectory shown in  FIG. 6A .  FIG. 6B  illustrates a view taken from an overhead perspective of a horizontal cross-section of the injection apparatus  105 . The cross-section is taken at a point on the injection apparatus  105  which allows the viewer to see a horizontal injection trajectory path  660  of the needle. As in  FIG. 6A , to orient the reader, the eye  602  and the nose  604  have been labeled. 
     The horizontal injection trajectory path  660  begins at the starting point  610  and ends at the ending point  620 . However, because the perspective has changed, the shape of the path  660  is different than that shown in  FIG. 6A . This provides another view of the injection result. It will be understood that the presentation model may be arbitrarily rotated, and a representation of the trajectory path for the representational model, as rotated, may be generated. The rotation may be provided to the system as a display point of view identifying the location in space from which to view the trajectory path. Because the injection apparatus digital model is combined with the three-dimensional injection information and, in some instances, anatomical or physiological information, the injection training may provide a wide variety of views, depending on the technique needed for the injection. The views may be provided as animated depictions, such as video or reconstructed animations. For example, in some embodiments, historical trajectories for the same type of injection can be shown in a 3D overlap view which illustrates historical injection trajectories to a current injection trajectory. In this way, a care provider can visually compare trajectory information for improvement progression analysis and general accuracy analysis. Different historical trajectories can be shown in different colors, shades, and/or highlights in order to illustrate age and/or accuracy of the trajectories. 
     The aspects shown in  FIG. 5  allow a trainee to adjust his or her technique and monitor his or her progress toward the ideal injection technique. For example, the user interface/display device  140  may provide a view selector (not shown) to allow the trainee to see the injection site from a variety of views, such as rotated, zoomed in, zoomed out, cross-sectional, time-lapsed, and the like, both in real time and after the injection has occurred. As shown in  FIG. 5 , a cross-sectional view is displayed on the user interface/display device  140  whereby the trainee can see how far through an opaque skin layer  590  into a clear material layer  592  the testing tool has passed. 
     In some implementations, the three-dimensional position information received from the 3D sensor  502  may be converted before integration into the digital model of the injection apparatus  105 . In such implementations, the received three-dimensional position information may be calibrated, adjusted, or otherwise converted such that the position information of the testing tool  110  may be correlated with a position on the digital model of the injection apparatus  105 . 
     As discussed, one or more sensors may be provided within the training apparatus  105  which provide three-dimensional position information for the testing tool  110 .  FIG. 7  illustrates an example embodiment of a 3D sensor  502 . A dimensional legend  799  is provided to indicate the three axes (e.g., X, Y and Z) of detection. This dimensional legend  799  is logical and may not physically be included in an embodiment of the injection training systems described. The names attributed to each axis may differ, but each axis should represent one unique dimension. 
     The 3D sensor  502  is shown receiving light from a testing tool  110  at a first position  702 , and then at a second position  704 . These positions are not simultaneous, but rather represent the sequential movement of the testing tool  110  over time. The light emitted from the testing tool  110  is received by the 3D sensor  502 . The light is emitted from the tip  233  of the testing tool  110  and disperses on its way to the 3D sensor  502 . As shown in  FIG. 7 , a first area of light  710  is generated when the testing tool is located at the first position  702 . A second area of light  712  is generated at a second time when the testing tool  110  is located at the second position  704 . The 3D sensor  502  may be configured to measure one or more characteristics of the received light and generate information corresponding to the three-dimensional position of the testing tool  110  based on the characteristics detected. Illustratively, the characteristics may include angle, intensity, brightness, color, dispersion, and/or duration of the light. 
     In one implementation, the 3D sensor  502  may include an array of light sensors. As light is emitted from the needle tip  233 , one or more of the sensors in the array may receive light. By aggregating the information about which sensors received light and characteristics of the light received at each sensor, three-dimensional information about the position of the light source may be determined. Some 3D sensors  502  may be housed in a recess and, based on the light pattern cast on the sensor, determine the location of the light source. In generating the 3D location information, the 3D sensor  502  may also obtain calibration information for the needle tip  233  of the testing tool  110  to account for variability, such as in manufacturing, wear-and-tear, and power. Further calibration information may be used to specify the field of view  504  for the 3D sensor  502 . The calibration information may be received, for example, through an initialization sequence whereby the testing tool  110  is placed at a predetermined location on the injection apparatus. 
     Because the 3D sensor  502  knows the light source and its particular location vis-à-vis the light source, the 3D sensor  502  can generate accurate and, in some implementations, real-time 3D location information for the testing tool  110 . 
       FIG. 8  illustrates another embodiment of a 3D sensor  502 . It may be desirable to implement the 3D sensor  502  as a stereoscopic sensor pair. A dimensional legend  899  is provided indicate the three axes (e.g., X, Y and Z) of detection. This dimensional legend  899  is logical and may not physically be included in an embodiment of the injection training systems described. The names attributed to each axis may differ, but each axis should represent one unique dimension. 
     The 3D sensor pair includes a first 3D sensor  502 A and a second 3D sensor  502 B. The first 3D sensor  502 A and the second 3D sensor  502 B are configured to receive, at substantially the same time, light from a testing tool  110 . The testing tool  110  may be located at different positions at different times.  FIG. 8  shows a first position  810  at a first time, and a second position  812  at a second time, for the testing tool  110 . 
     Each 3D sensor  502 A and  502 B is configured to measure one or more characteristics of the light transmitted from the testing tool&#39;s  110  position and to generate three-dimensional location information corresponding to the position of the testing tool  110 , based in the detected characteristics. The characteristics may include angle, intensity, dispersion, brightness, color, or duration of the sensed light. Combining the characteristic data received from the first 3D sensor  502 A and the second 3D sensor  502 B, three-dimensional information for the testing tool  110  may be generated. The combination may be performed by one of the 3D sensors  502 A and  502 B, or by the signal processing and display interface  555 . In an embodiment the combination can be performed in the user interface/display device  140 . 
     In generating the 3D location information, the generation of the three-dimensional information may also include obtaining calibration information for the needle tip  233  to account for variability such as in manufacturing, wear-and-tear, and power. The calibration information may be received, for example, through an initialization sequence whereby the testing tool  110  is placed at a predetermined location on the injection apparatus  105 . 
       FIG. 9  depicts a side view of one embodiment of the injection apparatus  105 , including a 3D sensor  502 . The injection apparatus  105  is formed as a human head. A testing tool  110  is shown inserted into the injection apparatus  105 . The testing tool  110  may be implemented as described above, such as in reference to  FIGS. 2A-G ,  3 A-C and  4 A-C. To minimize diffraction of the light emitted from the testing tool  110 , a surface of clear elastomer  910  may be made substantially perpendicular to the direction of light travel. Accordingly, in an embodiment the inner surface of the clear elastomer  910  is formed as a spherical surface with the center facing a 3D sensor  502 . The 3D sensor  502  may be implemented as described above such as in reference to  FIGS. 5, 7 and 8 . The 3D sensor  502  is configured to detect light emitted by the testing tool  110  within a field of view  504 . 
     Rather than utilize a light emitting testing tool  110  in combination with a single two-dimensional (2D) camera that detects a two-dimensional position of the light emitting needle tip  233 , the injection training system  100  may include one or more 3D sensors  502  and/or tracking equipment. With a single 2D camera, a position with respect to a third dimension may be determined, for example, by tinting the clear elastomer surface  910 , causing a color of the light to change as the needle tip  233  transitions through the tinted layer. Illustratively, the color may trend toward white light as the needle tip  233  moves closer to the inner surface of the clear elastomer surface  910 . 
     It may be desirable to avoid tinting the clear elastomer surface  910  and allow the use of 3D tracking equipment, such as 3D sensors  502  (which may be cameras or other types of sensors), examples of which are shown in  FIGS. 7 and 8  above. Further examples of 3D tracking equipment include equipment sold by Personal Space Technologies B.V. (available at http://ps-tech.com/). An additional example of 3D tracking equipment is described in a Centre Suisse d&#39;Electronique et Microtechnique SA (CSEM) Scientific &amp; Technical Report entitled “spaceCoder: a Nanometric 3D Position Sensing Device,” which is incorporated by reference herein in its entirety. 
     As the testing tool  110  penetrates an opaque skin layer  590  and enters the internal clear elastomer layer  592 , the 3D sensor  502  detects characteristics of the light which can be used to generate a three-dimensional location of the testing tool  110 . For example, it may be desirable to track a desired range  912  of needle penetration. In some implementations, the depth information is displayed on a display, such as the user interface/display device  140 , as the testing tool  110  is inserted. This allows a trainee to visualize the location of the injection in near real-time. The signal processing and display interface  555  may provide the location information to facilitate such displays. In some implementations, the feedback may be provided in audio form such as a beep or an alert. 
       FIG. 10  shows a process flow diagram of a method of manufacturing an anatomically shaped injection apparatus  105  including a 3D sensor  502 , such as that shown in  FIG. 9 . The method includes, at block  1002 , forming an at least partially hollow base configured to provide structural support for a target injection test area. The method includes, at block  1004 , coating at least a portion of the base with a clear layer of elastomer. The method also includes, at block  1006 , coating at least a portion of the clear layer with an opaque layer. The base, clear layer, and opaque layer form an anatomical shape such as a skull. The method further includes, at block  1008 , affixing a three-dimensional (3D) tracking system (which can include one or more 3D sensors  502 ) within the hollowed portion of the base, wherein the three-dimensional tracking system provides a field of view of the clear layer covering the target injection test area. The three-dimensional tracking system may be a 3D camera such as that shown in  FIG. 7  or a stereoscopic camera pair such as those shown in  FIG. 8 . In some implementations, the method may also include coupling the 3D tracking system with a location processor configured to provide location information for a light source inserted into the clear layer. The location information identifies a three-dimensional location of the light source relative to the injection apparatus  105 . The location processor may be implemented in the signal processing and display interface  555  shown in  FIG. 5 . 
       FIG. 11  illustrates a process flow diagram for a method of three-dimensional (3D) injection training. The method may be performed in whole or in part by one or more of the devices described herein such as the training apparatuses described above. 
     The method includes, at block  1102 , calibrating at least one of a light source and a three-dimensional tracking system. The light source may be a light emitter located at the tip  233  of a testing tool  110 . The three-dimensional tracking system may include a 3D camera, a stereoscopic camera pair, or other sensor configured to provide three-dimensional location information for the light source. The method also includes, at block  1104 , detecting, by the three-dimensional tracking system, a characteristic of light emitted from the light source for an injection. The characteristic may include intensity, angle, dispersion, brightness, color, or duration of the light. In some implementations, an array of sensors may be used to detect light. In such implementations, the characteristic may include which sensors in the array of sensors received light. The method further includes, at block  1106 , generating three-dimensional location information of the light source based on the detected characteristics and said calibrating. 
     In some embodiments, the testing tool  110  is configured to determine its position and orientation in three-dimensional space relative to the injection apparatus  105 . The testing tool  110  is also configured to communicate its position and orientation information to other components of the injection training system  100 , such as, for example, the user interface/display device  140 . The user interface/display device  140  can display, in near real time, the testing tool&#39;s  110  position relative to the injection apparatus  105 , as injection training is performed. The testing tool  110  can also communicate its position and orientation information to the 3D sensor  502  and/or to the signal processing and display interface  555 . 
     In an embodiment, the position sensor  308  collects nine dimensions of sensed information to determine the 3D position and orientation of the testing tool  110  in space with adequate accuracy. This is because processing sensed three-dimensional angular velocity provided by a 3D gyroscope leads to an accumulating error in the calculated position and orientation of the testing tool  110 . To compensate for this error accumulation, measurements from a 3D accelerometer and from a 3D magnetometer can be used. The 3D accelerometer measures the earth&#39;s gravitational field, and the 3D magnetometer measures the earth&#39;s magnetic field. Together, the sensed information from the 3D accelerometer and 3D magnetometer can provide an absolute reference of orientation that can be used to compensate for the progressively accumulating error of the sensed and processed angular velocity data provided by the 3D gyroscope. A method for sensor fusion includes processing the measured nine dimensions of sensed information (from the 3D gyroscope, the 3D accelerometer, and the 3D magnetometer) to determine a single estimate of position and orientation of the testing tool  110 , in three-dimensional world coordinates. 
     In an embodiment, the position sensor  308  of the testing tool  110  comprises a inertial measurement unit (IMU) that includes one or more accelerometers, one or more gyroscopes, one or more magnetometers to provide, in near real time, information describing the 3D position and orientation of the testing tool  110 . In some embodiments, the position sensor  308  can also include an embedded processor that handles, among other things, signal sampling, buffering, sensor calibration, and sensor fusion processing of the sensed inertial data. The position sensor  308  can also include a wireless network protocol for data transmission to external components, such as, for example, the user interface/display device  140 , the 3D sensor  502 , and the signal processing and display interface  555 . Illustratively, the position sensor  308  senses, processes and transmits sensed position and orientation data of the testing tool  110  to a sensor fusion processing component that can be configured to operate on, for example, the user interface/display device  140 . In an embodiment, the position sensor  308  transmits already-processed position and orientation information, delivered in three-dimensional, world coordinates, to the user interface/display device  140  which graphically displays the position of the testing tool  110  relative to the injection apparatus  105  in near real time as the injecting training occurs. The position sensor  308  can provide calibrated 3D linear acceleration, 3D angular velocity, 3D magnetic field, and optionally, atmospheric pressure data, to the sensor fusion processing component which processes the data to deliver precise position and orientation information of the testing tool  110 . In an embodiment, the sensor fusion processing component employs a Kalman filter to provide three degrees-of-freedom position and orientation information of the testing tool  110  relative to the injection apparatus  105 . The sensor fusion processing component uses data collected from the gyroscopes, accelerometers and magnetometers to compute a statistical, optimal 3D position and orientation estimate, of high accuracy and with no drift, for movements of the testing tool  110 . 
     Illustratively, the sensor fusion processing component comprises an algorithm in which the measurement of gravity (by the 3D accelerometers) and the earth&#39;s magnetic north (by the 3D magnetometers) compensate for otherwise slowly, but steadily increasing drift errors from the processing (using mathematical integration) of rate-of-turn data (angular velocity) measured from the rate gyroscopes. The described approach for compensating for drift can be referred to as attitude and heading referenced, and a system that employs this approach can be referred to as an Attitude and Heading Reference System (AHRS). 
       FIG. 12  illustrates an embodiment of an injection training system  100  comprising an injection apparatus  105 , a testing tool  110 , and a resting cradle  1202  in which the testing tool  110  follows a sequence of motion (A through D) from the resting cradle  1202  to an injection site of the injection apparatus  105 . In  FIG. 12 , the injector&#39;s hand is not shown to better illustrate the motion of the testing tool  110 . At position A, the testing tool  110  sits in the resting cradle  1202 . The resting cradle  1202  is in a known, fixed position relative to the injection apparatus  105 . This can serve to calibrate the injection training system  100  to know where the testing tool  110  is located relative to the injection apparatus  105  at the initiation of the injection training. In an embodiment, the resting cradle  1202  is attached to the base  108  of the injection apparatus  105 . In an embodiment, the injection apparatus  105  has calibration points  1204  that can be used to establish an initial position of the testing tool  110  relative to the injection apparatus  105 . 
     Starting from the known position relative to the injection apparatus  105 , such as from the resting cradle  1202 , the movement of the testing tool  110  can be determined, even as the needle tip  233  penetrates the material of the artificial face. By way of non-limiting illustration, the testing tool is lifted from the resting cradle  1202  to position B. The testing tool  110  is rotated to position C, where the needle tip  233  is directed toward the injection apparatus  105 . At position D, the needle tip  233  of the testing tool  110  is inserted into the injection apparatus  105 . Position information corresponding to the testing tool  110 , including the needle tip  233 , can be conveyed to a digital model of the injection apparatus  105 . The digital model includes target tissue (individual muscles) and details of vital structures (VS, which is also referred to as vital tissue, VT), such as, for example, arteries, veins, nerves, and skeletal portions, that are to be avoided or accommodated. By comparing the position of the needle tip  233 , based on the determined position of the testing tool  110 , to the target tissues and the vital structures illustrated on the user interface/display device  140 , proximity to a desired injection target can be established. This proximity to target and to vital structures can serve as the basis for evaluating the skill of the injection trainee. 
     Various manufacturers offer for sale inertial measurement systems, devices, and methods, including sensor fusion processing components, for incorporation into products and systems. Such manufacturers include Xsens Technologies, B.V., of Enschede, the Netherlands; InvenSense, Inc. of Sunnyvale, California, USA; and Synopsys, Inc., of Mountain View, California, USA. Examples of systems, devices and/or methods for inertial measurement of objects in three-dimensional space are disclosed in U.S. Pat. No. 7,725,279B2, issued on May 25, 2010; U.S. Pat. No. 8,165,844B2, issued on Apr. 24, 2012; U.S. Pat. No. 8,203,487B2; issued on Jun. 19, 2012; U.S. Pat. No. 8,250,921B2, issued on Aug. 28, 2012; U.S. Pat. No. 8,351,773B2, issued on Jan. 8, 2013; and in U.S. Patent Application Publication Numbers 2009/0278791A1, published on Nov. 12, 2009; and 2009/0265671A1, published on Oct. 22, 2009, each of which is incorporated by reference herein in its entirety. 
     Computation of the position and orientation of an object in three-dimensional space is a task that can process inputs from several sensors to achieve accurate estimates of the position and orientation of the object. The method can be referred to generally as a fusion of sensor inputs. A sensor fusion process can reduce the impact of, and/or compensate for, inaccuracies of senor measurements and/or processing approximations. Disclosed herein is a system and method to implement a fusion process that is computationally efficient and that includes nine dimensions of sensor input. In an embodiment, the system includes a processor that can be supplemented with hardware accelerators to help reduce power consumption. An example of a system, device and method to compute the 3D orientation of an object by processing nine dimensions of data using a sensor fusion process is described in a paper entitled “Ultra Low-Power 9D Fusion Implementation: A Case Study,” by Pieter Struik, which is incorporated by reference herein in its entirety. 
     The disclosed system and method to fuse sensor information is one among many possible sensor fusion approaches. One skilled in the art will appreciate that there are numerous systems and methods for fusing sensor input to derive accurate position and orientation information of an object in three-dimensional space without departing from the spirit of the present disclosure. The disclosed system and method offers effective tracking performance while executing computations that are similar to those used by other sensor fusion processes. Performance optimization for this embodiment is based on an analysis of processing-intensive activities. One approach to optimization is to employ a fixed point processing implementation. Another approach to optimization can include the use of one or more hardware accelerators to execute certain computations efficiently. Such optimization approaches are directed at reducing the number of processing cycles required to determine accurate estimates of the position and orientation of an object in three-dimensional space. 
     Described herein is a system and method to calculate three-dimensional (3D) position and orientation of an object derived from inputs from three motion sensors attached to the object: an accelerometer configured to measure linear acceleration along three axes; a gyroscope configured to measure angular velocity around three axes; and a magnetometer configured to measure the strength of a magnetic field (such as the earth&#39;s magnetic field) along three axes. In an embodiment, the three motion sensors are attached to the testing tool  110 . In an embodiment the three motion sensors are integrated into a single position sensor  308 , as reflected in  FIG. 3A . In an embodiment, the sensors are sampled at a rate of 50 Hz; however, one skilled in the art will appreciate that the sensors can be sampled at different rates without deviating from the scope of the present disclosure. The sampled data from the three motion sensors, which provide nine sensor inputs, are processed to describe the testing tool&#39;s  110  position and orientation in three-dimensional space. The testing tool&#39;s position and orientation are described in terms of Euler angles as a set of rotations around a set of X-Y-Z axes of the testing tool  110 . 
     Theoretically, the method to determine orientation angles around the three axes of the testing tool  110  is a straightforward process that includes mathematically integrating the three angular velocity measurements provided by the 3D gyroscope sensor. However, when implemented, sensor drift and/or processing approximations can lead to a steadily increasing set of errors that affect the accuracy of such determinations. A method to compensate for the inaccuracy of the processed angular velocity measurements includes processing accelerometer data and magnetometer (or compass) data, in a sensor fusion process. The disclosed system and method to fuse sensor input applies principles that are comparable in accuracy to systems and methods that employ techniques of linear quadratic estimation, such as Kalman filtering, which may also be used to fuse sensor input data in some embodiments. 
     The disclosed system and method to fuse sensor input uses quaternion algebra to determine a present position and orientation of the testing tool  110 . In practical application, quaternions can be used in conjunction with other processing methods, such as Euler angles and rotation matrices, to calculate rotations of objects in three-dimensional space. Illustratively, a quaternion, where Q=[q0 q1 q2 q3], can define a three-by-three rotation matrix “R” that translates each coordinate  x =(x,y,z) of the initial testing tool&#39;s  110  orientation into its current position, R x . A product (known as the Hamilton product in quaternion algebra, which is represented by the symbol “⊗”) of two quaternions, such as Q0⊗Q1, delivers another quaternion that describes a compound rotation performed by a first rotation, described by Q0, which is followed by a second rotation, described by Q1. Use of quaternion algebra can reduce computational processing requirements because most of the computations used to perform quaternion algebra do not employ computationally-intensive trigonometric functions. 
       FIG. 13A  illustrates a process flow diagram of a process  1300  to determine the position and orientation of a testing tool  110  according to an embodiment of the disclosed injection training system  100 . One skilled in the art will appreciate that there are numerous ways by which the position and orientation of the testing tool  110  can be determined without departing from the scope of the present disclosure. At block  1302 , the process begins by collecting measured data from the 3D gyroscope, the 3D accelerometer, and the 3D magnetometer. The sampling rate can vary, depending on the components used to implement the process. 
     At block  1304 , the present orientation of the testing tool  110  is represented by a quaternion “Q” which represents the currently measured angular acceleration data from the 3D gyroscope. This quaternion is an initial estimate of the position and orientation of the testing tool  110 . The present orientation can be updated with information provided by the gyroscope sensor which may be represented as (gx, gy, gz). Additional rotation of the testing tool  110  that occurred since the most recent measurement can be represented by a quaternion [1 (gx/f) (gy/f) (gz/f)], where f is defined as a sampling frequency used to execute the sensor fusion process. This representation may be expressed as quaternion [C gx gy gz ], with “C” being a constant that is proportional to the sampling frequency, f. 
     At block  1306 , information provided by an accelerometer sensor is used to help compensate for accuracy errors in the angular velocity data provided by the gyroscope sensor. An acceleration vector (ax, ay, az), measured by the accelerometer, will equal the acceleration of gravity when the testing tool  110  is not in motion. When the testing tool  110  is in motion, its rotation can be characterized by rotation R, and the vector corresponding to gravity is directed towards the earth&#39;s center. When viewed relative to the motion of the sensors attached to the testing tool  110 , the gravity vector will have been rotated by the same rotation R. Accordingly, the initial gravity vector  v  becomes R v , relative to the testing tool  110 , after rotation has taken place. If the testing tool  110  is not moving, the computed gravity vector, R v , will be aligned with the measured accelerometer information (ax, ay, az). When R v  and (ax, ay, az) are pointing in different directions, we determine that rotation R is inaccurate and, therefore, the coordinates representing the present orientation, Q, must be adjusted based on the vector cross product R v ×(ax, ay, az). 
     At block  1308 , fusion with information sensed by the magnetometer can also be applied. It is assumed that the testing tool  110  is subject to the earth&#39;s magnetic field. It is also assumed that the testing tool  110  is not subject to interference from a separate magnetic field, such as, for example, the field of a permanent magnet. Under these assumed conditions, the magnetic field measured by the 3D magnetometer (mx, my, mz) can be related to the initial orientation of the testing tool  110  by applying a reverse rotation R*, where the vector  w =R*(mx, my, mz). It is also assumed that the earth&#39;s magnetic north is aligned in the direction of the X axis. Accordingly, an alignment error can be determined by comparing the vector  w  to a vector  w ′, which is obtained by rotating the vector  w  onto the plane of the testing tool  110 . An alignment error vector  c  can be calculated. The alignment error vector,  c , is proportional to the vector cross product  c = w × w ′. As  c  is related to the initial orientation of the testing tool  110 , R c  corresponds to the adjustment that can be applied to the testing tool&#39;s  110  present position and orientation, represented by quaternion Q. 
     At block  1310 , the adjusted quaternion Q is converted into three Euler angles. Euler angles are a way of representing the spatial orientation of a coordinate system as a composition of three elemental rotations, starting from a known, standard orientation. The relation between the quaternion Q and the converted Euler angles includes calculations that use inverse sine and inverse tangent functions. Illustratively, the rotation angle around the Y axis is determined with the following conversion equation: Y=−asin(2*q1*q3+2*q0*q2), where the quaternion Q=[q0 q1 q2 q3]. 
     In an embodiment, the method  1300  to determine the position and orientation of a testing tool  110  updates the position and orientation of the testing tool  110  at the sampling rate of the sensors. Accordingly, at block  1312 , the process  1300  determines whether the present injection training is continuing or whether it has ended. When the present injection training is continuing, the method  1300  returns to block  1302  to update the position and orientation information of the testing tool  110 . When the present injection training is completed, the process  1300  terminates at block  1314 . 
       FIGS. 13B ,  13 B 1 , and  13 B 2 , collectively, illustrates a process flow diagram of a process  1340  to determine the position and orientation of a testing tool  110  according to an embodiment of the disclosed injection training system  100 . Illustratively, process  1340  discloses one approach to implementing process  1300 , described above. One skilled in the art will appreciate that there are numerous ways by which process  1300  can be implemented without departing from the scope of the present disclosure. 
     At block  1350 , the process begins by collecting measured data from the 3D gyroscope (providing angular momentum information), the 3D accelerometer (providing linear accelerations information), and the 3D magnetometer (providing magnetic field information). The present position and orientation of the testing tool  110  is represented by a quaternion, based on the measured angular acceleration data from the 3D gyroscope. Blocks  1352  through  1358  illustrate computation actions implemented to compensate for inaccuracies in the angular velocity data, provided by the 3D gyroscope, based on the linear acceleration information provided by the 3D accelerometer. This methodology uses the earth&#39;s gravitational field to identify inaccuracies in the measured angular momentum data and to compensate for those inaccuracies. At block  1352 , the measured 3D accelerometer data is compared with a rotated initial gravity vector. At block  1354 , the accelerator data is inverted and normalized. At block  1356 , a vector cross product of the normalized accelerator data and the rotated gravity vector is computed. And at block  1358 , a compensation for gyroscope data inaccuracies is made, using a constant acceleration compensation factor. 
     Blocks  1360  through  1368  illustrate actions implemented to compensate for inaccuracies in the angular velocity data, provided by the 3D gyroscope, based on the magnetic field information provided by the 3D magnetometer. This methodology uses the earth&#39;s magnetic field to identify inaccuracies in the measured angular momentum data and to compensate for those inaccuracies. At block  1360 , the measured 3D magnetometer data is normalized and inverted. At block  1362 , an inverse rotation of the normalized magnetometer data is computed. At block  1364 , the computed rotation is aligned in orientation with the testing tool  110 , based on earth&#39;s magnetic north. At block  1366 , the computed rotation is rotated back to the original orientation, and an alignment error vector is computed by computing a cross product of rotation vector with the measured magnetometer data. At block  1370 , a compensation for gyroscope data inaccuracies is made, using a constant magnetic compensation factor. At block  1370 , the testing tool&#39;s position and orientation, represented in a quaternion, is updated based on the adjusted gyroscope data, and it is normalize at block  1372 . At block  1374 , the updated position and orientation information of the testing tool  110  is converted into Euler angles which can be used by, for example, the user interface/display device  140  to graphically display the position of the testing tool  110 . At block  1376 , the process  1340  returns to block  1350 , to begin another iteration when the injection training is continuing. Alternatively, the process terminates at block  1378  when the injection training is finished. 
     Advantageously, the disclosed method for determining the position and orientation of a testing tool  110  is robust, even when assumptions are not held. For example, when the testing tool  110  is moving, the measured accelerometer data (ax, ay, az) represents a non-zero linear acceleration relative to gravity; however the sensor fusion processing method nevertheless delivers accurate position data. Moreover, fusion of magnetometer data proves to be accurate in the presence of distortion in the gravitational magnetic field. 
     In an embodiment, the disclosed method can be implemented in a system of integrated hardware and software (or firmware) that can be optimized to process data from digital and analog sensors and to engage in power-efficient processing of the sensor data. The system can include a processor (such as the ARC EM4 32-bit processor core offered by Synopsys Inc.), a user-configurable set of serial digital interfaces, analog-to-digital converter interfaces, hardware accelerators, and a software library of digital signal processor (DSP) functions and input/output (I/O) software drivers. The system can take advantage of capabilities to implement tightly coupled I/O peripherals and tightly coupled hardware accelerators, which may be accessed directly from the processor pipeline without the overhead of additional hardware infrastructure, such as, for example, busses, bridges, and/or adapters. 
     In an embodiment, the system configuration contains one or more Inter-Integrated Circuit (I2C) master peripheral ports, a Serial Peripheral Interface (SPI) master peripheral port, and a general purpose input/output (GPIO) port. The processor can be configured to have a single-cycle 32-bit integer multiplier. The system can be configured to include one or more fixed-point hardware accelerators to perform computationally-intensive operations, such as, for example, multiply-accumulate (MAC) operations, trigonometric operations, and the square root operation. Illustratively, use of hardware accelerators can reduce processor cycle time with respect to computationally-intensive operations such as the square root operation. A hardware accelerator accepts a 32-bit fixed point number as input and computes the square root in 31 cycles, evaluating one bit at a time which is substantially faster than calculating a square root by use of software delivered as part of a compiler&#39;s standard library. 
     Many of the required computations used in the disclosed method are computationally-intensive when implemented using standard software routines. For example, rotation and inverse rotation operations are matrix-vector multiplications where the (inverse) rotation matrix has coefficients that are based on the quaternion Q. Illustratively, inverse rotation operations involve many multiplications and additions. Similarly computing the inverse norm of a vector or a quaternion requires the following operations: multiplication, addition, square root, and division. Likewise, computing a vector cross product requires multiplication operations and addition operations. Computing the Hamilton product of two quaternions takes many multiplications and additions. Computing Euler angles involves trigonometric functions (atan 2 and asin), where the arguments are expressions that are based on quaternion Q. These expressions include multiplication operations and addition operations. Use of one or more hardware accelerators to implement such operations can reduce overall processing time and power consumption. 
     To further improve performance and to reduce power consumption the disclosed system, device and method can be configured to be implemented using fixed point arithmetic as opposed to using floating point arithmetic. Conversion of numerical processing using floating point arithmetic to fixed point arithmetic requires care with respect to overflow and underflow in computations. However, after such conversion is performed successfully, the processing workload can be reduced by replacing floating point multiplication operations with single-cycle, 32-bit multiplications, and floating point addition operations with simple, 32-bit additions (or subtractions). Evaluation of the resulting fixed-point version of the disclosed method shows that the square root function, which is executed four times in each cycle of the disclosed method, consumes many processing cycles. Using a standard square root function call, which is typically included in a library of digital signal processing (DSP) functions, to apply the square root hardware accelerator can further reduce processing cycle count. Another optimization can be to reduce the cycle count of the Euler angles computation by applying a hardware accelerator for the inverse sine function. Because the inverse tangent function can be expressed in terms of the inverse sine and square root operations, using the hardware accelerators for thee computations reduces computational workload, power consumption, and processing time per iteration. Thus the processing cycle count of the disclosed nine-dimensional sensor fusion method can be reduced by implementing a fixed point version of the process that takes advantage of available hardware accelerators. Reduction of cycle count leads to lower energy, as the energy that is used for executing the algorithm is proportional to the required performance. 
     In an embodiment, position sensors  308  are used in both the barrel  220  of the testing tool  110  and in the plunger  210  of the testing tool  110  to determine the position of the plunger  210  relative to the barrel  220  of the testing tool  110 . This information can be used to indicate distal travel movement of the plunger  210  in the testing tool  110  during simulated injection. The distal travel movement can represent a volume of fluid that would be injected, and therefore the distal travel movement can be used to determine a measure of the injection trainee&#39;s performance. 
     An embodiment of the disclosed system, device and method to determine the position and orientation of the testing tool  110 , relative to the injection apparatus  105 , during injection training includes the use of one or more retro-reflectors attached to the testing tool  110  in association with an optical tracking system. A retro-reflector (sometimes called a retroflector or cataphote) is a device or surface that reflects light back to its source with a minimum of scattering. In a retro-reflector, an electromagnetic wave front is reflected back along a vector that is parallel to, but opposite in direction from, the wave&#39;s source. The angle of incidence at which the device or surface reflects light in this way is greater than zero, unlike a planar mirror, which reflects an electromagnetic wave (such as light) only if the mirror is exactly perpendicular to the wave front, having a zero angle of incidence. The retro-reflectors are locatable by an optical tracking system that can operate in, for example, the infrared (IR) range. The retro-reflectors can be positioned on the external surface of the testing tool  110  for use with optical tracking systems that operate by use of infrared illumination. This type of optical tracking allows for the triangulation of energy reflected from the retro-reflectors to determine the testing tool&#39;s  110  position in three-dimensional space. In an embodiment, alignment of the needle tip  233  with the injection apparatus  105  can be accomplished by touching the needle tip  233  to a known location on the injection apparatus  105 , such as calibration points  1204 . 
       FIGS. 14A and 14B  are perspective views of an exemplary optical tracking system  1400 . Optical tracking is a 3D localization technology that monitors a defined measurement space using two or more light sensors  1402 , such as, by way of non-limiting example, cameras. In an embodiment, each light sensor  1402  is equipped with an infrared (IR) pass filter (not shown) in front of the lens, and a ring of IR light emitting diodes (not shown) around the lens to periodically illuminate the measurement space of the optical tracking system  1400  with IR light, as illustrated in  FIG. 14A . Reflections from markers  1404  on the testing tool  110  are sensed by the light sensors  1402 , and the sensed information is processed by the optical tracking system  1400  to determine the position and orientation of the testing tool  110  in three-dimensional space. Examples of optical tracking systems  1400  are described in a paper entitled “PST iris: Instruction Manual,” published by Personal Space Technologies B.V, and in International Patent Application Number PCT/NL2009/050607, having International Publication Number WO 2011/043645A1, published on Apr. 14, 2011, which are incorporated by reference herein in their entirety. 
     Computer stereo vision is the extraction of 3D information from digital images, such as obtained by a charge-coupled device camera. By comparing information about a scene from two vantage points, 3D information can be extracted by examination of the relative positions of objects in the two panels. In traditional stereo vision, two cameras, displaced horizontally from one another are used to obtain two differing views on a scene, in a manner similar to human binocular vision. By comparing these two images, the relative depth information can be obtained, in the form of disparities, which are inversely proportional to the differences in distance to the objects. To compare the images, the two views are superimposed in a stereoscopic device. In camera systems, several pre-processing steps are required. The image is removed of distortions, such as barrel distortion to ensure that the observed image is a pure projection. The image is projected back to a common plane to allow comparison of the image pairs, known as image rectification. An information measure which compares the two images is minimized. This gives the best estimate of the position of features in the two images, and creates a disparity map. Optionally, the disparity as observed by the common projection, is converted back to a height map by inversion. Using a correct proportionality constant, the height map can be calibrated to provide precise distances. Active stereo vision is a form of stereo vision which actively employs a light, such as an infrared light source, to simplify the stereo matching problem. An examples of a stereo vision system and processing method is disclosed in U.S. Pat. No. 8,208,716B2, issued on Jun. 26, 2012, which is incorporated by reference herein in its entirety. 
     Objects to be tracked, such as the testing tool  110 , can be equipped with retro-reflective markers  1404  that reflect the incoming IR light back to the light sensors  1402 . The IR reflections are detected by the light sensors  1402  and then internally processed by the optical tracking system  1400 . The optical tracking system  1400  calculates the 2D marker position, in image coordinates, with high precision. Using at least two light sensors  1402 , the 3D position of each marker  1404  can be derived, as described above. The 3D position can be measured by using a single marker  1404  in the measurement space; however, to be able to also measure the orientation of an object (or to track multiple objects simultaneously), multiple markers  1404  must be placed on each object. Such a configuration can be created by affixing markers  1404  randomly onto the object, making sure at least two markers  1404  can be seen from each angle of the object that the user desires to be detected. By establishing a model of the configuration of each object, the optical tracking system  1400  can distinguish between objects and can determine the 3D position and orientation of each object. 
     Optical tracking systems  1400  offer some advantages over other approaches to measure and determine the 3D position and orientation of an object in three-dimensional space. For example, optical tracking is less susceptible to noise from the environment, such as, for instance, ferromagnetic metal in the environment which can influence the accuracy of the measurements of magnetic tracking systems. Additionally, optical tracking does not suffer from drift problems experienced in, for instance, inertial sensors, which cause measurements to slowly deviate from actual values, for which compensation techniques must be applied. Optical tracking also allows for many objects to be tracked simultaneously. Optically tracked devices can be lightweight and they do not require wires or power. As such, users are neither hampered by wires nor limited in their manipulation of the object. 
       FIG. 14C  illustrates a testing tool  110  configured with multiple markers  1404 , in accordance with an embodiment of the present disclosure. In an embodiment, an optical tracking system  1400  measures the 3D positions of markers  1404 , such as, for example, retro-reflectors, affixed to the testing tool  110 . The markers  1404  can be active or passive. Using this information, the optical tracking system  1400  can determine the position and orientation of the marked testing tool  110  within a specific field of view defined by the optical tracking system. The optical tracking system  1400  can be a self-contained, integrated system that does not require external processing or calibration components. The optical tracking system  1400  can be connected to the user interface/display device  140  via a wired or by a wireless communication scheme. The optical tracking system  1400  can deliver 3D position and orientation measurement of the testing tool  110  to the interface unit/display device  140 . Advantageously, the disclosed optical tracking system  1400  delivers fully-processed position and orientation data to the user interface/display device  140 , thereby freeing up the processing capability of the user interface/display device  140  for other computationally-intensive activities, such as, for example, processing and rendering of a digital model representative of the injection apparatus  105  and the testing tool  110  during injection training. 
       FIG. 14D  illustrates, among other things, aspects of the user interface/display device  140  according to an embodiment of the disclosed injection training system  100 . Shown in magnified perspective are examples of how the user interface/display device  140  can graphically display, either during the injection training or afterwards, the location of the needle tip  233  as it penetrates the injection apparatus  105 . The user interface/display device  140  illustrates portions of the anatomy in the vicinity of the injection site. In particular, vital tissue (VT), and muscle are represented digitally on the user interface/display device  140 . Advantageously, the user can view a target site, a proximity to the target site, and nearby vital tissues or structures. In some embodiments, visual and/or aural signals are delivered to the trainee as indications of the needle tip&#39;s  233  proximity to the target site. During an injection, for example, the display can graphically illustrate the different skin and tissue layers as the needle tip  233  penetrates each layer. For example, this can be done by graphically peeling back the layers as a new layer is penetrated. For training purposes, the different layers can be labeled or provided with different textures or colors to indicate a new layer is shown. 
     In an embodiment, a single optical tacking system  1400  can track the testing tool  110  in an injection training environment, as illustrated in  FIG. 15A . In an embodiment, multiple optical tracking systems  1400  can be coupled together to extend the workspace environment or to reduce issues due to the line-of-sight requirement of the optical tracking system  1400 , as illustrated in  FIG. 15B . In an embodiment, the optical tracking system  1400  can be configured with different optics configurations to adapt the field of view and the performance characteristics of the optical tracking system  1400  to the intended environment and application. Illustratively, optics with a higher field of view result in a wider tracking area closer to the system, whereas optics with a lower field of view provide a narrower, but longer, tracking area. 
     The optical tracking system  1400  can use tangible, wireless devices for 3D interaction and 3D measurement, such as the testing tool  110 . In an embodiment, the position and orientation (sometimes referred to as the “pose”) of the testing tool  110  can be reconstructed with millimeter accuracy. Advantageously, the optical tracking system  1400  can be based on infrared lighting, which can reduce the interference of visible light sources from the environment. This allows the optical tracking system  1400  to be used under normal, ambient working conditions without requiring controlled lighting. The testing tool  110 , and the injection apparatus  105 , can be tracked by applying retro-reflective markers  1404  to their external surfaces. The optical tracking system  1400  employs these markers to recognize different objects and to reconstruct their poses. In an embodiment, and by way of non-limiting illustration, the optical tracking system  1400  reconstructs the pose of the testing tool  110 , and optionally, of the injection apparatus  105 , at an adjustable sampling frequency with a maximum of 120 times per second. One skilled in the art will appreciate that other sampling frequencies can be used without departing from the scope of the present disclosure. The optical tracking system  1400  can be triggered externally, such that it can be synchronized to external clock sources. This can, for instance, be used to prevent interference between the internal infrared flash and shutter glasses that are synchronized to a 3D monitor, such as the user interface/display device  140 , using an infrared signal. 
     In an embodiment, tracking devices comprise physical objects, such as the testing tool  110  and the injection apparatus  105 , that can be recognized by the optical tracking system  1400  and of which the 3D position and orientation can be measured. In an embodiment, such devices can be used to measure the spatial coordinates of objects, or for instance, to interact with virtual 3D objects in an application. Illustratively, just as a mouse can be used to position a pointer in two-dimensional space, so too can a tracking device be used to position an object in three-dimensional space, with six degrees of freedom. The 3D position and orientation (pose) of a tracking device, such as the testing tool  110 , is optically tracked, ensuring wireless operation. Retro-reflective markers  1404  can be applied to objects, such as the testing tool  110  and the injection apparatus  105 , to transform them into tracking devices. The tracking system uses these markers  1404  to recognize devices and to reconstruct each pose. In order for the optical tracking system  1400  to be able to determine the position and orientation of a tracking device, at least four markers  1404  need to be applied. The size of the markers  1404  helps to determine the optimal tracking distance. The optical tracking system  1400  supports flat retro-reflective markers  1404  for the construction of tracking devices. Such flat retro-reflective markers  1402  do not hamper manipulation. 
     In an embodiment, the markers  1404  are locatable by tracking systems, devices, and methods that can operate in the radio frequency (RF) range. The markers  1404  can be positioned on the interior of the testing tool  110  for tracking systems  1400  that operate through use of RF illumination, such as the technology known as radio-frequency identification (RFID). Advantageously, the RF energy is able to be transmitted through the tissue of the injector&#39;s hand, arm and other portions of the injector&#39;s body that may obstruct the required line-of-site view between an optical tracking system  1400  and the testing tool  110  during injection training, when implemented using optical tracking systems  1400  based on infrared illumination. 
     In an embodiment, the reflective markers  1404  comprise corner reflectors. Corner reflectors can operate in a wide range of electromagnetic frequencies including the infrared and the radio spectrums. A corner reflector is a retro-reflector comprising three mutually perpendicular, intersecting flat surfaces. The corner reflector reflects waves back directly towards the source, but shifted (translated). The three intersecting surfaces often have square shapes. Optical corner reflectors, called corner cubes, made of three-sided glass prisms, are used in surveying and laser range-finding. The incoming ray is reflected three times, once by each surface, which results in a reversal of direction. The three corresponding normal vectors of the corner&#39;s perpendicular sides can be considered to form a basis (a rectangular coordinate system) (x, y, z) in which to represent the direction of an arbitrary incoming ray, [a, b, c]. When the ray reflects from the first side, say x, the ray&#39;s x component, a, is reversed to −a while the y and z components are unchanged, resulting in a direction of [−a, b, c]. Similarly, when reflected from side y and finally from side z, the b and c components are reversed. So the ray direction goes from [a, b, c] to [—a, b, c] to [—a, —b, c] to [—a, —b, —c] and it leaves the corner reflector with all three components of direction exactly reversed. The distance traveled, relative to a plane normal to the direction of the rays, is also equal for any ray entering the reflector, regardless of the location where it first reflects. 
     In an embodiment, the optical tracking system  1400  views the testing tool  110  and the needle tip  233  as it approaches and penetrates the injection apparatus  105 . The optical tracking system  1400  can operate in the visual and infrared spectrums. For optical tracking systems  1400  using the infrared spectrum, an improvement in resolution and differentiation is available by altering the temperature of the testing tool  110  and/or the needle tip  233  to be different (hotter or colder) than ambient temperature. Infrared thermography (IRT), thermal imaging, and thermal video are examples of infrared imaging science. Thermographic cameras detect radiation in the infrared range of the electromagnetic spectrum (roughly 9,000-14,000 nanometers or 9-14 μm) and produce images of that radiation, called thermograms. Since infrared radiation is emitted by all objects above absolute zero according to the black body radiation law, thermography makes it possible to see one&#39;s environment with or without visible illumination. The amount of radiation emitted by an object increases with temperature; therefore, thermography allows one to see variations in temperature. When viewed through a thermal imaging camera, warm objects stand out well against cooler backgrounds. 
     The testing tool  110  and needle tip  233  can be clearly resolved against the ambient temperature background when using thermal imaging. In an embodiment, the 3D sensor(s)  502  from the interior of the injection apparatus  105  can be configured to sense both light emitting from the testing tool  110  and thermal energy emitted from the testing tool  110  and/or needle tip  233  by use of infrared, or other forms of thermal imaging. Multiple methods for achieving temperature variation of the testing tool  110  relative to ambient temperature can be used, including, without limitation, resistive heating on the testing tool  110  interior with conductive heat transfer to the hollow needle  232 , and routing gas of a controlled temperature through a tube into the testing tool  110  interior and exhausting the gas through the needle tip  233 . In an embodiment, thermal imaging is available by including temperature markers on the injection apparatus  105  to be viewable by a the optical tracking system  1400 , which can support accurate resolution of the testing tool&#39;s  110  position relative to the injection apparatus  105 . In an embodiment, the depth of penetration of the needle tip  233  into the injection apparatus  105  can be determined by measuring the length of the needle  232  remaining exterior to the injection apparatus  105 , thereby exposed to the view of the optical tracking system  1400 . By knowing the orientation and position of the testing tool  110  relative to the injection apparatus  105 , along with the measured length of the needle  232  remaining exterior to the injection apparatus  105 , the depth of penetration of the needle tip  233  in the injection apparatus  105  may be determined. 
     In an embodiment, position information provided by the 3D sensor(s)  502  and the optical tracking system  1400  can be combined to determine the position and orientation of the testing tool  110  and the needle tip  233  relative to the injection apparatus  105  during injection training. Combination of position data corresponding to the light emitting needle tip  233  as the needle tip  233  passes through the opaque layer of artificial skin, as sensed by the 3D sensor(s)  502  from the interior of the injection apparatus  105 , with the length of the needle  232  remaining exterior to the injection apparatus  105 , as sensed by the optical tracking system  1400 , can be combined to determine the position and orientation of the testing tool  110  and the needle tip  233  relative to the injection apparatus  105 . 
     An injection training system has been disclosed in detail in connection with various embodiments. These embodiments are disclosed by way of examples only and are not to limit the scope of the claims that follow. One of ordinary skill in the art will appreciate from the disclosure herein any variations and modifications. 
     Terminology/Additional Embodiments 
     The term “injection” as used herein includes it usual and customary meaning of an injection, but is also to be interpreted broad enough to encompass, for example, the insertion of a catheter device or the use of simple needles, such as would be used in an acupuncture therapy. The techniques involved, particularly a camera embedded in a model of a living subject and a tool with a light emitter can be applied to any therapeutic procedure. For example, the tool can be a catheter and the procedure can be a minimally invasive procedure requiring the catheter to be located in a particular location. 
     Conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. 
     Depending on the embodiment, certain acts, events, or functions of any of the methods described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the method). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores, rather than sequentially. 
     The various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein can be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The described functionality can be implemented in varying ways for each particular application, but such embodiment decisions should not be interpreted as causing a departure from the scope of the disclosure. 
     The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein can be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, microcontroller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The blocks of the methods and algorithms described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of computer-readable storage medium known in the art. An exemplary storage medium is coupled to a processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The processor and the storage medium can reside in an ASIC. The ASIC can reside in a user terminal. In the alternative, the processor and the storage medium can reside as discrete components in a user terminal. 
     While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices or algorithms illustrated can be made without departing from the spirit of the disclosure. As will be recognized, certain embodiments of the disclosures described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others. The scope of certain disclosures disclosed herein is indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.