Medical applications for Acoustic Emission
Quality control in orthopaedic diagnostics requires methods of non-destructive processes which do not harm the patient either by radiation or by an invasive examination. There is currently no non invasive evaluation method for the state of wear regarding human joints, and it is not possible to quantify joint condition from patient report as every patient has different levels of tolerance to pain.
Initial trials shows that the analysis of Acoustic Emission (AE) signals from sensors attached to human joints that it may be possible to grade levels of joint degradation.
Although there is a desired frequency range for AE signals sensor selection was determined by size of sensor. A large sensor limited knee movement and was difficult to attach. Noise due to sensor slipping was also problematic (above). A sensor with a small height was selected for practicality.
Sensor attachment was achieved using medical tape, a medical grease was used as a couplant. As the sensor is attached to the skin near to the joint there is no evasive process also the process causes no pain and no harm to the body unlike x-rays.
Loading of Joint
The joint was loaded by natural body movements. The loading of the knee was achieved by a simple squat process. The rotation of the knee joint was monitored using motion analysis (fluorescent balls above). Results showed that the greatest AE signals occurred at the point of maximum load of the joint.
Bone Cement Samples
Samples of bone cement cast into compact test specimens were fatigued under conditions found in the human body. AE showed that it was possible to detect and locate small changes in crack length.
Design of Low Profile Sensors
Initial trials showed that sensor design and attachment was fundamental for good results. The design of a low profile sensor with a suitable frequency range will further work, allowing simple attachment and it would create less noise due to movement of the skin under the sensor.
Re-Trial and Further Tests
The initial trials should be repeated using the developed low profile sensor. This would allow the designed frequency range to be evaluated. In addition other joints in the body should be studied. In addition a study of the attenuation of signals through body tissue should be completed.
To validate the technique a clinical trial would have to be completed. Patients with known levels of damage, including no damage would have to be tested and AE results quantified to those levels of damage. This would allow future examinations to be classed into ranges of joint damage (above).
Design of Testing Machine
The fruition of the project would be the design and build of a dedicated AE testing machine with a guide to testing different joints in the body. Results should be outputted in terms of the level of joint degradation, allowing patients to be prioritised for treatment.