A Study on Hole Testing of Intramedullary Nail Based on Ultrasonic Sensor

Intramedullary nail internal fixation is the most prevalent method of treatment of fracture. The study on hole testing and localization of intramedullary nail is one of the most important research topics in present-day orthopedic medicine. This paper gives a new method for hole testing of intramedullary nail based on ultrasonic sensor. Considering the disadvantage, ultrasonic attenuates too fast in bone, it adopts special ultrasonic sensor and appropriate signal testing method to test the hole. It processes the acquired signal and improves conventional image enhancement algorithm. The method can get the clearest image to a great degree in the range of safe dosage of the ultrasonic to achieve testing and localization of the hole. It brings a new method and means to the navigator for intramedullary nail. The method overcomes the disadvantages of X-ray C-arm machine such as radiation damage, low precision and high fabricating cost. The simulation and clinical experiment indicate that the method has high sensitivity and good reproducibility. KEY WORD Intramedullary Nail, Ultrasonic Sensor, Hole Testing, Image Edge Detection, Image Enhancement Introduction: The fixation is the key point of three main principles in fracture treatment all the while. The development of fixation principle and method basically reflects the evolvement of fracture treatment. Intramedullary nail internal fixation is one of the important aspects. The latest data indicates: in occident developed country, the application of Intramedullary nail for treatments of long-tube fracture is above 90 percent. X-ray is mostly applied in actual orthopaedics operation for hole testing and localization of intramedullary nail. The application of X-ray in orthopaedics operation is a good method, but some inevitable disadvantages exist in Xray: (1) radiation damage. The radiation damage of X-ray for body is a sort of small-energy, many-frequency, long time, accumulated damage. If exposed to long time and big dosage X-ray, the apparatus and organization will get damage, sometimes result in cancer and even to death. (2) X-ray has low precision, blurry imaging, low resolving power etc, so high requirement is needed for the doctor. All these are disadvantageous for its popularization and easily result in false judgment. So the research of hole testing and localization of intramedullary nail, which is unharmful for physicians and suffers, is especially important. Hole Testing of Intramedullary Nail Based on Ultrasonic Sensor: 1. Mechanism of Ultrasonic Imaging Ultrasonic is a kind of machine vibration transmitted through flexibility medium(solid, liquid, gas). It’s frequency is above 20kHz. The range of ultrasonic for imaging is 10~5×10Hz. when ultrasonic transmits through symmetrical medium it can freely pass along its direction. If it transmits through heterogeneous medium or enters into another medium, reflection and refraction will come into being. The structure of body is a complicated medium whose apparatus and organization has respective and specifically acoustic impedance and decay characteristic. When ultrasonic enters into body, from the surface to the deep, it will pass some apparatus and organization which have different acoustic impedance and decay characteristic to produce different reflection and attenuation. According to strong and feebleness of received ultrasonic, light spots with different brightness display on the screen. Ultrasonic imaging comes into being. According to different imaging mode, ultrasonic imaging can be divided reflected ultrasonic imaging and transmitted ultrasonic imaging. The ultrasonic sensor is a kind of special sensor which makes use of the peculiarity of ultrasonic to generate and receive ultrasonic. The ultrasonic sensors include two parts: high frequency pulse generators and sensors. The high frequency pulse generators are used to generate ultrasonic frequency-electricity oscillation and the sensors transform electromagnetism energy into mechanical energy. The piezoelectricity sensors are in common use in medicine which make use of piezoelectricity effect of some crystal. 2. Research Content In order to realize hole testing and localization of intramedullary nail, the system adopts transmitted ultrasonic imaging: One probe for emission and one for receiver. The two probes scan the object in a concentric circle. The ultrasonic signal through body is received, amplified and imaged on the display. Thus the ultrasonic perspective image is acquired (see Figure 1) . 2.1 Ultrasonic attenuation and absorption Supposed that ultrasonic enters into symmetrical medium along X axis. At lamella dX whose intensity is I0 the decrement of intensity is dI − . According to experiment rule Idx dI α = − 1 here, α is called sound absorption coefficient. Through integral for both sides we can get