Ultrasound Phantoms: War were declared

The ultrasound phantoms work.  They have a few limitations, but for certain applications, these cheap DIY phantoms are going to be far superior to expensive commercial phantoms.  In fact, part of their DIY nature makes them inherently superior.  Creating a phantom for a special purpose, such as vessel cannulation, foreign body identification, or needle procedures, is simple.

One of the big issues that has come up is bacterial/fungal growth on the phantom.  This should be expected, as the phantom is constructed of gelatin and sugar-free psyllium.  The system is essentially a giant petri dish.  I needed to find a way to inhibit microbial growth.  Not just inhibit, but stop.  Completely and totally.

I lucked out in a couple of ways.  I tried mixing some bleach into the material when it was on the stovetop.  The mixture foamed up a fair amount.  This wasn't a big issue with the first two layers, as pouring the next layer seemed to dissolve the previously settled foam.  The final layer settled with a very large amount of foam.  This foam is a random mixture of air and gelatin, and almost completely sono-opaque.

This is the external surface of the simulant, and represented a major problem for the phantom.  It was impossible to image past this interfering layer.  I tried scraping the surface foam off, but to no avail.
I spent three shifts at the hospital trying to find a way to make the system workable.  At this point I had intentionally inoculated the surface with dust and dirt to attempt encourage microbial growth. At the three day point, no growth, but no apparent solution.

Ending my shift one morning, I had my "Eureka" moment.  One of the workmen was removing floor tiles by heating them with a propane torch.  Between my broken Spanish and his broken English, I was able to convey that I wanted to borrow his propane torch.  I quickly heated the surface of the phantom, melting the top foam layer.  It liquified and appeared to completely remove the foam layer.

I waited ten anxious minutes, visibly bouncing.  I placed the ultrasound transducer and was rewarded with two easily visible vessel simulants.  Cannulation was almost exactly the same (the new material seems somewhat more friable).

Six weeks later, the phantom was still visibly free of microbial growth (I don't have the patience or material to actually test for microbial growth beyond naked eye visualization).

I'm stuck at the next step.  I'm either casting a human arm and making a mould, or I'm developing some method to snake the vessels through the simulant to increase the difficulty in cannulation.

DIY Ultrasound Phantoms: Recipes, Part 1

I'm now on the fourth generation homemade ultrasound phantom. The recipe is pretty simple and low cost. I'm using store bought Knox gelatin, generic sugar-free psyllium fiber (Metamucil), and vein simulators (5mm Penrose drains). Before I link to the articles I used, I'm going to shoot the authors a quick email (The idea of using the above recipe is not my original idea). Right now I'm building the phantoms in cheap, flat food containers (ultra cheap tupperware clones). Each phantom is currently constructed of three "pours". Each pour uses the following recipe: 250-300cc's of boiling water 3 packets of Knox gelatin 1-2 tablespoons of sugar free psyllium fiber With the water at a boil, add the packets of Knox gelatin slowly. Some will probably clump up (This isn't a big deal. I'll go into that in a bit). While adding the gelatin, watch the boil, as it may boil over. Stir continuously. Once the gelatin is added, slowly add the psyllium fiber, again watching carefully and stirring continuously. If the mixture clumps a little bit, don't worry too much. If you are looking to create a relatively clear ultrasound phantom, pour the mixture into the mold (in my case, the cheap food storage container) through a strainer. This will catch most of the lumps. If you are looking to create a "Dirty" looking phantom, leave the clumps in. These clumps will sonographically appear as areas of varying tissue density. These inclusions mimic the appearance of real tissue. Our goal (at my hospital) is to create a better arm simulation for US guided IV insertion techniques. These inclusion bodies mimic scar tissue, varying tissue densities/types, and present a sonographic picture that is not as "cut and dried" as other vascular simulators. The cheap food containers that I am using hold 3-4 gelatin "pours". I have been using three pours for my prototypes. After each pour, I'm allowing the gelatin to firm up in the fridge for two hours, before pouring the next layer. After the first pour has firmed up, but before pouring the second pour, I'm putting down two penrose drains, filled with water/saline, to simulate vessels. One of the vessels I'm overfilling/pressurizing with 30% more fluid, to simulate an artery. My vessel simulators occasionally leak, so I'm not having tremendous success with the arterial simulation. Still, with the slight pressurization, the vessel does have a slightly different appearance when visualized sonographically. This is a practice, that once perfected, will enable students to differentiate between arteries and veins. I'm working on a method to create an automated pulse, so that the vessel is maintained under pressure and appears to pulsate.

DIY Ultrasound Phantoms

I've got a lot of projects kicking around. This one kinda got pushed to the front because one of my colleagues said "We need to be able to perform this skill, but we don't have the resources to develop our techniques". Ordinarily, this would warrant some kind of project, slow and methodical like. However, I'm now one of the guys that responsible for fixing problems like this. It's not just an issue, it's "my" issue. The glove was thrown down, so to speak. The issue is that we need to place IV (intravenous) lines in our patients. It seems pretty simple: you come to the ER, sick/broken/in pain, and we need to take care of you. One of the ways that we address this is by starting an IV line and drawing blood. If you are going to do either of those things, you can do them both (in theory). Most of the time, this is a simple matter of getting a skilled provider, with the right equipment, to the bedside. Veins are typically pretty easy to find (it helps if you have sensitive fingertips, not sensitive eyes), and then it's just a matter of a quick poke. The complicating factor is the condition of the patient. Some folks don't have great veins (for that matter, some folks don't have shallow veins, demonstrated sonographically). If you can't find a shallow vein, you need to find a deep one. Beyond a few millimeters, you simply can't feel a deep vein. You need some way to visualize those deep veins. Enter in the bedside ultrasound system. We use these during traumas to examine patients for internal bleeding. Occasionally we use it to check on pregnant women and the health of the fetus. Other than that (this comprises maybe an hour or two a day, at most) our bedside sono units are dormant. They're like any other medical imager: not cheap. A couple of docs figured out that we can use these things to visualize deeper veins (and arteries). From there it was a simple trick to guide an angiocath (an IV needle) into one of these veins. It's a pretty cool solution. It's not as invasive as a PICC Line (Peripherally Inserted Central Catheter), or other central line (subclavian, femoral, etc), and it's more comfortable than a jugular line. It's also a guided solution. No blind sticking, and you can see the structures in the patient's arm to avoid complications (inadvertent arterial puncture). However, it's also a bigger deal than a simple IV stick. You're taking an angiocath that you would normally poke a couple of millimeters down, and going 10-20 millimeters down into someone's arm. You're asking more of your patient. More to the point, if all you have done, to date, is a standard IV placement, you're asking a lot of yourself. I know that the folks that I work with care for their patients. Or they're crazy. No one would work under these conditions (low pay, constant threat of bodily harm, verbally abusive clients, incredible work loads) for years. They all seem highly functional, so I'm going to stick with "Compassionate". I think my colleagues generally care for their patients, like they would care for their own family. So it's a lot to ask them to jam a needle two to three inches into someone's arm, using a technique they're uncertain of. In fact, it's just wrong. We have ultrasound simulators, called phantoms, that we borrow from the medical school. They're around $300-$400 dollars, and they're simple blocks of gel (silicone? dunno) with vessels suspended within them. The sonographic image looks pretty nice: a couple of straight vessels a couple of centimeters deep. It's not what a patient's arm looks like: vessels that are all over the place, twisting and turning, with various inclusions scattered through the arm. We needed to come up with a way to transition from the perfection of the standard ultrasound phantom to the reality of patient care. Oh yeah, one more thing: No budget. Solutions will start in the next post. (I'm going to try out a cliffhanger ending for this one)