have developed a "smart stethoscope" that can hear when a kidney
stone has been successfully broken down by treatment.
The device listens to echoes created by shock wave therapy
(lithotripsy) to let the doctor know if therapy has worked.
Trials at Guy's Hospital in London have showed promising results,
saving patients unnecessary repeat therapy and x-ray monitoring.
The device was developed along with scientists from Southampton
Lithotripsy works by focusing thousands of shock waves onto the
kidney stones in an effort to break them into pieces small enough to
urinate out of the body or be dissolved by drugs.
But there is no way of monitoring how the process is getting on.
X-ray image after
X-ray image before
Doctors can take an x-ray before and after treatment to see if
there is any change in the appearance of the stone.
But it is often difficult to tell from these pictures and is more
a case of trial and error - if the symptoms return then the patient
will need more shock wave therapy.
Professor Tim Leighton and colleagues at the Institute of Sound
and Vibration Research at Southampton University, along with kidney
experts at Guy's, decided to see whether the echoes produced by the
shock waves could be interpreted in some way.
Prof Leighton said: "It's a bit like the man on the railway who
walks along the length of the train, hitting the metal wheels with a
hammer to find out if any are cracked.
"If the wheel is cracked it gives a duller sound.
"What we are looking for is a stone to go from being intact at
the start of treatment to fragmented at the end of the treatment."
The smart stethoscope is a small probe, similar to those used to
trace heart patterns using an ECG, which is taped to the flank of
Just like a normal stethoscope, it picks up sound. From here, the
sounds are transmitted to a box the size of a packet of biscuits
which amplifies and changes the frequency of the sounds so the
doctor can hear them.
When the stone is intact the sound given off is a 'tick'. When it
has been shattered into small pieces the sound changes to a 'tock'.
Prof Leighton said the device could also be wired up to a
computer that would analyse the sounds and display the results using
a traffic light system - red for no success, amber for some success
and green for fully successful treatment.
So far, they have used the device to monitor treatment in 50
patients with kidney stones.
With funding from the Engineering and Physical Science Research
Council, the researchers have developed a prototype they say works
Prof Leighton said: "It's been superbly successful. I have been
astounded by how effective it is as a monitor.
"Plus, it's completely non-invasive. It does not expose you to
He said it would reduce rather than replace the need for x-rays,
which would still be used to locate the stone within the kidney.