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DEVELOPMENT OF AN IN-VIVO ACOUSTIC DIAGNOSTIC FOR LITHOTRIPTER-INDUCED SHOCK-TISSUE INTERACTION
Part 4: Hear for yourself the sounds, and see whether you can distinguish a successful treatment.
Click on the following links for:
1. Homepage for lithotripsy project
2. Introduction to lithotripsy (Tutorial) 3. Formal report on the project 5. Publications
Click here for Biomedical Ultrasonics page
The signals from the device described in this project contain energy across a wide range of frequencies, from almost d.c. (0 Hz) to greater than a million cycles per second (1 MHz). Much of this is at frequencies higher than the upper limit of human hearing (generally taken to be 20,000 Hz). However by a process called decimation, it is possible to provide a representation of that original 0-1 MHz signal in the frequency range 0-8 kHz, which is well within the frequency range of normal human hearing.
The objective results described in 3. Formal report on the project suggest that if the lithotripter is on-target and the stone is intact, the echoes should be strong, but diminish in amplitude if the treatment is successful and the stone breaks up. The echoes will remain strong if the treatment is unsuccessful and the stone does not fragment. If the lithotripter focus moves off-target (perhaps as a result of patient motion), the echoes should become suddenly less strong. The idea is that, in addition to the objective measure of the success of the treatment with is provided through the quantitative testing described in 3. Formal report on the project, in addition we would provide the surgeon with a real-time representation of these echoes so that he/she can obtain a subjective impression of the quality of treatment as it progresses.
To give you an idea of what these sounds are like, this page provides you with pre-recoded sequences of decimated sounds recorded from three patients during their treatment. These three treatments were judged by the clinicians to have the following degree of success:
These sounds come from a treatment whose outcome was declared to be unsuccessful (the X-ray image of the stone at the end of the treatment was very similar to the image at the start, implying that probably only minor fragmentation occurred).
These sounds come from a treatment was clearly successful, as determined by the clinician who could clearly make out a single stone in the X-ray at the start of the procedure, and multiple stone fragments in the X-ray at the end of the procedure.
These sounds come from a treatment whose outcome was declared to be partially successful (the X-ray image of the stone at the end of the treatment looked somewhat smaller and less dark, implying a change in density).
The judgement you must make is on the following basis: For a given patient, does the start at the end of the treatment sound like a 'pale echo' of the sound you can hear at the start of the treatment? If so, the procedure would be deemed 'successful'.
Click on the buttons 1,2,3 below to see if you can tell which relates to A, which to B, and which to C (above). After you have done this, you may view the correct answer by clicking here.
What are you listening for? When you click on a sequence you will hear two sounds, one from the start of the treatment, closely followed by one from the end. If the treatment is successful, the second should be a 'pale echo' of the first (as highlighted above in yellow), and as a result the recording should sound like 'tick tock'. But if the treatment has been unsuccessful, the second echo will sound similar to the first, and you will hear 'tick tick'. Listen to the recordings from these three patients: one should sound like 'tick tock' and that indicates a successful treatment. On should sound a little like 'tick tock', and that indicates a partially successful treatment. One should sound nothing like 'tick tock', and that indicates a failed treatment.
Simple analogy for the occurrence of 'tick tock': It is and imperfect analogy, but consider a railwaymen walking along the length of the train, hitting the metal wheels with a hammer. If the wheel rings nicely, he knows that it is not cracked. If the wheel is cracked, it gives a duller sound. We are looking for the stone to go from being intact at the start of the treatment (when it will give a nice ring in "tick" sound), to being fragmented at the end of the treatment (when it will give a duller "tock" sound). Hence a successful treatment should be indicated by a "tick-tock" sound.
Note that these sounds contain information from the ultrasonic frequency range: in order for you to hear them, the frequencies have been compressed into an audio range signal. (Specifically, the data has not been resampled but simply played back at a slower rate (akin to reducing the play back rate on a tape recorder). Wav files are stored with header information that defines the playback rate. The software we used just changes that playback rate from 5 MHz to 11 kHz.)
This page was last updated by TG Leighton, 20 August 2004