Treatment monitoring and thermometry for therapeutic focused ultrasound

If the title above doesn’t sound like it belongs on Fractals of Change, that’s because it’s from a paper co-authored by son-in-law Hugh Morris which has just been published by the International Journal of Hyperthermia. Last year I blogged about the research Hugh is doing in London on using ultrasound for non-invasive surgery. This paper is an outgrowth of that research.

The technique they’re using to zap cancers is an interesting one: a number of high-frequency sound waves are beamed into the body.  None of the waves by itself has enough energy to do any damage as it passes through skin and other tissue. Aimed right, the beams converge at the site of malignity.  When focused, the beams together have enough energy to heat up bad cells and cause them to die.

The problem Hugh has been working on is how to measure the actual temperature being produced so that treatment can be best calibrated to kill all the bad cells with minimal damage to surrounding tissue. Sticking a thermometer into the patient is one option but this is invasive and also can interfere with the treatment since the thermometer itself may scatter or affect the beams and interaction between the beams and the probe may actually change the temperature you’re trying to monitor.

So it would be better to use MRI or some other non-invasive technique to measure temperature indirectly.  In fact, ultrasound itself can be used to measure the temperature by reporting on tissue changes. But how do you know what MRI or ultrasound reading corresponds to what temperature? How do you know which temperatures are most effective in the first place if you don’t know what temperature you’re operating at?

Hugh has been working on using probes in bovine liver (he buys the livers without the cows) to measure temperature induced and calibrate that with the readings given by non-invasive techniques. The problem he’s had to contend with are that the probes do affect the temperature being measured.  You could correct for that if you only knew how much effect is induced over how much time.

In case you didn’t guess the solution: “Morris et al. proposed a refinement to this [earlier] technique. Instead of assuming an arbitrary time for the end of the first phase [of induced heating] , the time was chosen from analysis of the second differential of the temperature with respect to time…. Morris et al. have also used thin-film thermocouples as a viscous-free reference, and calculated the viscous effect for a wire thermocouple as a function of time by subtracting the TFT measurement from the wire measurement.” Makes sense to me (not really).

What I do understand (because we saw it) is the dedication of young scientists constructing experiments, failing, correcting, trying again, avoiding false positives, questioning, retesting, and (sometimes) coming up with something very exciting.

We’re proud of Hugh.