My problem with most of science is the “Who cares?” factor. Don’t get me wrong; I like science and all. It took us out of the Dark Ages and keeps me from getting small pox, but unfortunately most of science is boring. To be fair though, we won’t know until many years later if any of these “who cares?” studies turns out to be meaningful. Like how a famous artist might not be recognized for their brilliance at the time. I’d say that takes up 80% of science (N.B. that number was not derived in any scientific way).
The next layer of the science cake is “That’s cool … but so what." The ellipsis here is important, because it takes you a moment to think about it. There are a lot of studies out there that strike you immediately as really interesting. You might even share a link on Facebook. But when you think more about them you’re not really sure what they could be used for.
But every once in a while you encounter a new bit of science and think "Wow, the future is really here." Sadly there are no hoverboards yet, but I definitely got the feeling the first time I saw an iPhone, and then again seeing a video of Google's new self-driving car. Well, now on the horizon there’s the possibility of performing brain surgery without even making a single incision. I tend to lump a lot of things into “who cares” or “so what”, but when I first came across the field of high-intensity focused ultrasound I was amazed by the possibilities.
You’ve probably heard of regular, low-intensity unfocused ultrasound. You probably just call it “ultrasound”. That’s the kind where the OB/GYN lubes up a pregnant woman’s belly and takes a picture so she can post it on Facebook. The purpose of regular ultrasound is to bounce sound waves off tissue and listen for the echoes, which is very similar to SONAR. These echoes are computed into an image.
However, the sounds waves don’t just bounce off tissue, many of them are absorbed by the tissue. Sound waves are a physical energy, and when tissue absorbs energy it heats up. This fact is routinely made use of in physical therapists office. If you’ve ever done physical therapy for an injury, then you may be familiar with the use of ultrasound in that context. There they can use ultrasound to heat up the muscle tissue, and possibly even break up scar tissue. This might sound like a “that’s cool … but so what” technology, except it offers the possibility of doing surgery without making a single incision.
Surgery is possible with ultrasound, because of the fact that if you heat up tissue above a certain temperature, it dies. If you can heat tissue hot enough in a highly focused manner, then you can get rid of tissue you don’t want, and leave everything else untouched. This is possible through the use of high-intensity focused ultrasound (HIFU), because HIFU uses hundreds of small ultrasound speakers (called transducers) all sending ultrasound beams from different directions. Most of the brain only receives very low-intensity ultrasound, but at the tiny spot where all the ultrasound beams meet it can get pretty hot.
The first impressive use of HIFU is destroying tumors without touching other tissue. HIFU is already FDA-approved for this in non-brain applications, namely to obliterate benign tumors in the uterus called uterine fibroids. A woman with uterine fibroids can go in for “surgery” and the tumors are removed without having to even break the skin. That’s pretty cool that you could avoid cutting into the uterus, but it’ll be even cooler when you could go through the skull without having the break the skin. This has already been demonstrated in several patients (McDannold 2010).
Sometimes though tumors don’t have well defined borders, so you can’t just remove them easily. That’s where chemotherapy comes in. However, one problem with tumors in the brain (among the many problems) is that the blood-brain barrier often prevents chemo drugs from reaching the tumor. HIFU can also be used to selectively disrupt the blood-brain barrier and allow chemo drugs to reach the tumor (Liu 2010; Treat 2012).
HIFU can also be used in brain surgery. There’s a debilitating brain disorder called essential tremor. In essential tremor a person’s hands can shake uncontrollably. This might not seem so bad, unless they shake so much that the person can’t write or type or get dressed or even feed themselves. The neural circuitry that causes essential tremor is well understood, and it can be treated with surgery. Unfortunately the circuit is very deep in the brain, and most people I know would prefer to not have someone cut deep into their brain. However, recently a group of scientists and doctors at the University of Virginia showed that HIFU can be used get rid of the same deep brain target without invasive surgery. After being treated with HIFU essential tremor patients showed dramatic improvements (Elias 2013).
In addition to the treatments described above, many other applications of HIFU are being developed, including treatments for chronic pain (Jeanmonod 2012). While HIFU is not currently FDA-approved for any uses in the brain it’s still very exciting that we could soon have the possibility of brain surgery without the surgery. Yeah, it’s not a hoverboard, but to me it means the future is almost here.
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