Saturday, January 18, 2014

Waterjetting 17c - Discriminate cutting of tissue

In the last two posts I have noted that, by tailoring the pressure at which a waterjet is aimed at a surface, it is possible to discretely remove different layers that cover that surface, while leaving the underlying layers undamaged. The examples extend from removing individual layers of paint to the rubber left on a runway after planes have landed. But this idea also works in the removal of damaged concrete from bridge decks and garage floors. Here it is the ability of the jet to grow the longer cracks in the damaged concrete that makes it able to discriminate between the good and bad parts of the deck.

The idea can be extended into other areas that are not quite as obvious. And it began with a conversation with my dermatologist – Dr. Van Stoecker. We were discussing the change in state of different tumors when I brought up the discriminatory ability of waterjets. And so I went home and tried a simple experiment. I took an apple and bruised it – and left it for a couple of days. (The pictures come from a repeat of the experiment that I carried out today).

Figure 1. Bruised apple, showing the darkened damaged flesh under the skin

Then I removed the skin over the bruise and using a water pick washed away the soft damaged tissue, while leaving the healthy tissue undamaged, since the jet did not have enough power to remove it.

Figure 2. Showing the peeled region around the damaged part of the apple, and the old model WaterPik used for the demonstration.

The process was a little slow, and since the tip was hand-held and not rotating (the better way to ensure total areal coverage) took longer than it would with a spinning jet.

Figure 3. Partially cleaned apple.

The pulsating jet is manually oscillated over the apple surface, and cuts down through the softer flesh, but is not powerful enough to remove the healthy apple tissue beneath it.

Figure 4. The apple after the damaged flesh had been removed. Because of the simple manual manipulation the cleaning of the final surface was not quite as thorough as is achieved with a spinning head. The procedure takes varying amonts of time depending on the pulsation setting and the type of apple being used – this was a Granny Smith.

A water pick operates at a relatively low pressure, but the demonstration was sufficient that Dr Stoecker obtained an excised human skin tumor and we carefully cleaned the tumor surface, aspirating the spent water and debris using a small version of the vacuum system that we used to collect radioactive waste from underground storage tanks. When the tissue was then sent away for analysis it turned out that the water had effectively removed all the diseased tissue – which is softer – while leaving the healthy tissue in place.

Testing progressed through testing on dogs, and the concept was ultimately patented and was licensed.

One of the advantages of the tool, and the approach is that the jet will penetrate and remove the small tendrils of cancer that can spread out from the main tumor since the jet will follow these paths and remove the soft tissue content, while leaving the stronger healthy flesh. This has the benefit of reducing the scarring of the flesh in the vicinity of the tumor, and thus the amount of subsequent cosmetic treatment.

The argument for reduced excision of healthy tissue is equally or perhaps of more concern where the tumor lies in the brain, and colleagues in Germany have carried out operations on individuals to evaluate how effective waterjet removal (hydro-surgery) (Waterjet dissection of the brain: experimental and first clinical results. Technical note. Piek J, Wille C, Warzok R, Gaab MR.) No complications were found with the first nine patients who received this treatment.

The use of pulsating jets, of the WaterPick variety and at higher pressures has found increasing use for other purposes. Before the recent popularity of chemical washes it was, for example, shown that the use of a pulsating jet to flush wounds helped both remove any foreign matter still in the wound (particularly with “gravel rash” type injuries) and to lower the bacterial count.

Figure 5. Change in relative bacterial counts after conventional and pressure washed wound treatment (From PTJournal)

For this to be effective jet pressures had to be higher than 25 psi. Specialized equipment has now been developed for these uses, which have been shown to provide the benefits of: - shortening of the wound healing process, - reduction of the scar tissue, - low stress effects for the patients because the treatment is relatively painless.

Two different tools, the Debritom and the Versajet have been marketed for use in cleaning skin injuries (and while photos exist – for example here, I will recognize that some readers may be sensitive and will forego showing them.

The Versajet is a slightly different concept in which a very small high-pressured jet cuts across the face of the instrument and back into a collection chamber, so that it can peel off thin layers of necrotic and other undesired tissue and clean up wounds, particularly with burn injuries, more positively. The vacuum created by the jet passage into the chamber helps collect the debris.

Figure 6. Schematic showing the operation of the Versajet system.(Smith and Nephew )

Precision cutting and discriminatory cutting of flesh and other parts of the body have grown in application as the ability to manufacture smaller and more precise component,s that can operate at higher pressure, have been developed.

I will conclude this short section on some of these developments in the next post.

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