3D Printed Pneumatic Headphones for 32 Ch. Headcoil

A common complaint when using the 32 channel head coil is that there are few options available for delivering auditory stimuli to subjects. The inner diameter of the coil is considerably smaller compared to that of the 12 channel coil and limits the use of the standard Siemens pneumatic headphones that come with the 3T Tim Trio. Some current alternatives are to purchase an expensive electronic ear bud system or to crank up the volume for the speaker inside the magnet room and hope that the subject can hear at least some of what you're saying. For most researchers neither of these are adequate solutions, so I was tasked to come up with an alternative that fit the following criteria:

• Integrates into existing pneumatic systems
• Durable
• Low cost
• Slim profile
• Comfortable
• Easily reproducible

If you've read my last few posts then it's no surprise that I decided to use Tinkercad and our in-house 3D printer to come up with a suitable solution. A link will be provided at the bottom of the post for those wishing to print their own.

The Siemens Option

The default Siemens headphones work wonderfully...if you are using the 12 channel coil. But when using the 32 channel it's useless to all but the smallest of heads. The headband and thick headphone chambers simply do not fit inside the coil along with a subject's head and adequate padding. Thankfully pneumatic systems like this don't have many components, so I won't have to alter the design too drastically to come up with a solution that fits our criteria. 

Figure 1 - Siemens pneumatic headphones 

Figure 2 - Siemens tube connector

The 3D Solution

Keeping in mind the aforementioned criteria, I used the Siemens system as a starting point. Eliminating the headband and slimming down the profile of the headphone chamber instantly gave us the extra space required. Creating a ridge in the headphone chamber is the simplest design solution (see Note 1) as it provides a means to secure the cushion in place and slim down the design even further. I moved the tube connection to the bottom of the headphone for a more streamlined appearance and to make it easier to attach the "Y" connector. The original Y connector never posed a problem, but I tapered the holes just slightly for a tighter fit around the tubing and slimmed down the design to save on material cost.

Figure 3 - Slim 32 Ch headphone chamber design

Figure 4 - Y connector solid and transparent

For those a bit more interested in the design details, I used a pair of Bose headphone cushions as the template for the shape. They are similar in size and shape to the Siemens cushions, though any cushions would work fine. It's mostly a matter of personal preference so long as all the proper measurements are taken to ensure a snug fit. Same goes for the tubing, though for the sake of easy integration I'd recommend sticking with the 1/4" and 1/2" tubing that is standard for this system.

Final Print

Due to the simple nature of these components, the material and settings for printing them is largely up to personal preference. Though because they're likely to take a bit of a beating I printed them out of ABS with 2 mm layers, 95% infill and supports. 95% infill may seem like overkill, but since we're dealing with a pneumatic system you have to make sure there are no holes that could reduce the quality of the audio (See Note 2). Plus the pieces are so thin and small that you don't want to run the risk of them being too brittle for every day use.

Figure 5 - Components w/supports on build plate

After a few hours of printing I got the following results:

Figure 6 - Headphone chamber printed with ABS

Figure 7 - Y Connector printed with ABS

The tubing fits securely inside the connectors without the need of any extra adhesive, though you can use a bit of superglue to make sure it stays put (see Note 3). It takes some effort to insert the 1/4 inch tubing into the Y connector, but that makes for a better fit!

Since I used a personal pair of headphones as the template, replacement cushions were ordered that match the dimensions. They are of higher quality than the Siemens headphones and serve multiple purposes; providing comfort, support, and ear protection. The cushions come with a black mesh that I super-glued to the inside to cover up the headphone chamber. Since I measured the dimensions of the hard plastic ring that shapes the cushion earlier it should fit snug on the ridge. Once satisfied that the fit was correct I went ahead and used superglue again to secure it in place.

Figure 8 - Headphone with cushion and mesh

Figure 9 - Pair of headphones with cushions installed

When it came time to integrate these into the Siemens system we purchased the following connectors and inserted them into the tubing for our new headphones as well as the originals. Some modification of the Siemens headphone tubing is required (See Note 4), but now it only takes a quick push of the button to switch between multiple pneumatic options.  As you can see in Figure 11, the quick release connector allowed us to created a microphone using a funnel. The possibilities are endless!

Figure 10 -  Quick release connector

Figure 11 - Siemens headphones (A), slim 32 ch headphones (B) and funnel microphone (C) 

Final Fitting

With the headphones finished it is time to test them out! As you can see below, even with the headphones inside the coil there is still room for more padding on the side of the head if needed. But the standard headphones only fit inside when set to the smallest setting and adding extra padding is no longer an option (see Note 5).

Figure 12 - New headphones inside 32 ch coil

Figure 13 - Siemens headphones inside 32 ch coil

OK so they fit, but do they work? Of course they do! Pneumatic systems like this are simple and straightforward. So long as you secure all the connections and there are no holes in the tubing then you're good to go.

You can access the original TinkerCAD model and download it here. If you are using the same cushions and tubing that I mentioned earlier, then you should not have to alter the models much if at all (See Note 3). But if you decide to go a different route then you'll have to use TinkerCAD and do a bit more in-depth adjustments. Thankfully they have several basic tutorials that should be enough to get you going.

Note 1: I went through several iterations before going with this design. Some required cutting holes in padding, while others proved difficult for my 3D printer to complete. You can't make an omelet without breaking a few eggs, but for the sake of simplicity I chose not to include every step.

Note 2: PLA, ABS, PETG or just about any other material would be suitable. It's mostly a matter of personal preference, but durability should definitely play a factor in your decision. I would even suggest printing out a few pairs and keeping them handy in case something should happen

Note 3: All 3D printers are not created equally. You may need to use adhesive or alter the size of the tubing holes in the STL model if the parts don't fit snug after you print them.

Note 4: The modifications are simple: 1) Cut a length of tubing roughly a foot long from the end of the 1/4" thick tubing that connects to the foot of the bed. Leave it plugged into the foot of the bed. 2) Insert the larger quick connector piece (the one with the button on it!) into it. 3) Insert the smaller quick release connector into the long piece of tubing that connects to the headphones. 4) Repeat for every pneumatic system you want to integrate (in case you design your own headphones later on!)

Note 5: The polystyrene head is by no means meant to show that everyone will have as much room when they use the slim headphones. It is meant to showcase that there is more room than if attempting to use the standard Siemens headphones. 

Designing and 3D Printing Custom Lens Holders

There are often times when subjects require corrective lenses in order to properly perform tasks while inside the MRI machine. We purchased a pair of MRI-safe goggles with interchangeable lenses some years back (see Note #1) and using them with our 12 channel head coil is easy because the inner diameter of the coil is large enough to comfortably fit the subject, a support pillow, and the goggles without any issue.

Figure 1 - MRI-safe goggles with prescription lenses

Using them with the 32 channel head coil however, is considerably more difficult to do. It is already hard enough to fit a subject comfortably inside the coil with support padding, so attempting to include the goggles as well is simply not an option. To solve this problem we designed and machined lens holders (Figures 2 and 3) that fit inside the eye sockets of the 32 channel coil. They're easy to set up and the fit is snug so that they don't move. Sometimes we use a velcro strap to keep them together but it's not required.

Figure 2 - 32 ch coil lens holder with velcro strap

Figure 3 - lens holders inserted into coil eye sockets

Problem solved, right? Ah but what if these holders break? What if other researchers have this same issue but don't have a mechanical engineer on staff who can design and machine pieces like these? The best solution to both of these scenarios (and many more!) is to create 3D CAD models and make them available for anyone to download. So let's get started!

Recreating Parts in Tinkercad and Blender

Tinkercad is a free, easy-to-use 3D CAD design tool that works in your browser and uses Boolean addition and subtraction of simple shapes to allow the creation of more elaborate models. I have to be honest, I am more comfortable with Blender, which is also free, but Tinkercad is far easier to pick up and ideal for (relatively) simple designs like these holders. I had zero experience with Tinkercad beforehand but doing their tutorials for about an hour familiarized me enough with their UI to complete the project. Using calipers to get as accurate as possible, I measured the various dimensions of one of the holders and after a few hours I came up with the following design:

Figure 4 - Lens holder in Tinkercad

Not too shabby, right? I know it's hard to get a sense for 3D models in pictures but hopefully you can make out some details. If not, no need to worry. I'll provide a link later on so you can download the model yourself and take a closer look. The next step is to export the model to Blender and bevel some edges to make for a smoother fit inside the eye socket. Beveling is not an option in Tinkercad (See Note #2) so importing the STL file to Blender is the easiest way to finish it up.

Figure 5 - Beveling in Blender

After beveling, the final step in this section is to duplicate the part and mirror it about the X axis to create the second holder.

Figure 6 - Duplicating and mirroring in Blender

The hardest part of this project is done, though we can always make changes should the need arise (See Note #3). Now it's time to manufacture the pieces.

3D printing the Holders

It's possible to take drawings to a machinist and have them create the parts out of nylon or some other plastic but if you've got a 3D printer handy than the best/easiest solution is to print them out yourself in just a few hours. I even printed a few versions using different material to see which one suited our needs best.

Figure 7 - Holders printed using PLA 

Figure 8 - Holders printed using PETG

Figure 9 - Holders printed using NylonX

Although it may look like all I did was print the same thing in three different colors, there's more than meets the eye! Figures 7, 8 and 9 are images of completed lens holders printed using PLA, PETG and NylonX, respectively (See Note #4). Printing the pieces in NylonX was the best solution because of its durability and flexibility, allowing for the holders to be crammed into the eye sockets and thicker lenses to be placed inside them without fear of breakage. Below are images of a thin lens and a thick lens held securely inside the holders (See Note #5).

Figure 10 - Top view of lens in NylonX holders

Figure 11 - Side view of lens with different thicknesses

There you have it! Hopefully these designs are a help to other research groups looking to use corrective lenses alongside their 32 channel coil. Here's the link to the original Tinkercad design for those that are interested, but be aware that the design would still need to be beveled, duplicated and mirrored before it's ready. This Dropbox link contains the Blender file with the two finished pieces as well as stl files for each individual piece. I would suggest bookmarking the link since I plan on adding the designs for our mirror holders soon. So be on the lookout for those blog posts in the future as well!

Notes

#1 The merchant we purchased the interchangeable MRI-safe goggles from has since gone out of business, but a quick Google search returns other vendors with similar products.

#2 Technically you CAN create a beveling effect using some tricks but it is far more trouble than it's worth.

#3 It's easy enough to go back and alter the dimensions of the piece if need be -- that's what I did! The design was revised several times before I found the best fit. You may have to do this as well depending on the shape of the lenses you are using, just make sure you edit the areas that hold the lens and not the ones that secure the holder to the eye socket.

#4 The only 3D printer setting worth changing from whatever default you have is upping the infill to 100%. As with any print that gets handled quite often, you'll want them to be dense and sturdy so it can take a bit of abuse.

#5 If you're still having trouble with fitting thicker lenses then increase the height of the small square in the middle of the Tinkercad piece by a few millimeters until you find a value that works

Printing in 3D, part one: Choosing, Building and Troubleshooting your own 3D Printer

In this first of a two-part series I’ll be diving into the topic of 3D printing. I'll start with a broad overview, move on to discuss available options for getting your own printer, and finally I'll pass along some troubleshooting tips I've learned along the way. In the second, arguably more interesting, post I’ll detail the process we use to create our own head cases that can drastically reduce subject head motion inside the MRI machine. 

A quick disclaimer before diving in, this post is NOT intended to be a comprehensive look at 3D printing and printers. This is a massive field with what can seem like unlimited design option and choices, many of which are still foreign to me as well! So whenever possible I will provide links with information for those interested in learning more and possibly want to build their own.

What's the deal with 3D printing?

Figure 1 - 3D printed prosthetic limb

There’s no doubt you’ve seen or heard about 3D printing before in some form or another. The technology has been around for some time now and is being utilized in new and exciting ways almost on a daily basis. Elaborate costumes, prosthetic limbs and tiny parts that are impossible to purchase are just the tip of the iceberg when it comes to the potential uses for this exciting technology.

Figure 2 - Unpainted 3D printed mask

Figure 3 - Fully painted 3D printed mask

  

Figure 4 - 3D printed gears. Almost impossible to buy but super easy to print!

Now that I’ve piqued your interest about possible uses, you’re probably wondering where someone even begins with setting up their own print station. Thankfully the open source 3D print community is thriving online. With the power of Google you don’t have to look too long in order to find general information on the topic. One could easily fall down a rabbit hole and the sheer amount of options available could turn you off to the idea all together.  But do not despair! I will fully admit that I knew next to nothing about 3D printing when the decision was made to build our own here. It was a learning process; it was frustrating, definitely caused some hair loss and at times I felt way over my head. But eventually one day the stars were aligned, kinks were ironed out, numbers were dialed in, and the world of 3D printing seemed a little less intimidating. I don’t have all the answers, and it would take me longer than I’d care to admit to detail the process of building a fully functional printer from start to finish, but I’m able to use our setup and troubleshoot the issues we come across. And because the online community is so active it is easy enough to search the internet for answers whenever I need them. Always remember that Google is your friend!

Printer styles and choosing what's right for you

I could write an entire post about the various styles of printer; describing the components needed and the software toolchain they follow, but that’s not within the scope of this blog. More importantly, people with far more knowledge than I on the topic have already done that! Follow the previous link and you’ll find information on various styles of printers and learn how to go from an STL file to a fully printed 3D model in no time. Well maybe not in "no time", but they will definitely get you there faster than I alone could!

Figure 5 - Kossel style 3D Printer

After various internal discussions my team decided on building our own Kossel, which is a delta style printer. Our reasons for going with this one were:

• A printer bed with a 300 mm radius for printing larger components
• A delta-style printer allows us to build tall pieces that aren't possible with other styles
• Fully open-sourced which allows us to custom pick the software we want to use
• A stationary printer bed which is more stable, especially when printing taller pieces
• A vertical build design, so takes up less space than other models
• Capable of printing at faster rates than other models due to it's stability
• Supports open source add-ons such as a headed bed for better model adhesion and automatic bed leveling before every print starts

 If all those features sound great to you then a Kossel or other delta style printer might be the way to go. You’re going to have to do some research and figure out which style is right for your facility. A few questions to consider before making your decision include:

•  Do you need a large printing platform?
• What sort of items will you be printing?
• What are the size limitations where you plan on setting it up?
• Does the speed at which it prints matter to you?
• Do you need an enclosed system?
• Can you machine the parts when necessary? Or have access to a machine shop?
• Does open-source sound appealing?
• What’s your comfort level when it comes to programming languages, EEPROM, etc.? Are you willing to learn?
• How much troubleshooting are you willing to do? And how complicated are you able to handle?

There are plenty of other questions to consider when deciding on a printer. Price, complexity, form, function, etc. can all be overwhelming! But focus on what you currently need AND try to plan for the future as much as possible. The great thing about building your own 3D printer is the potential to modify and add-on to it later on. Once you’ve become an expert, of course ;-)

Building a printer takes work

At the risk of trivializing the most time-consuming portion of the process, I won’t be spending much time describing the actual building and calibrating of our printer. There’s a great step-by-step video series that you could watch, and I’m sure others have done similar guides for other styles of printers as well, if you want to look those up. Assembling, programming different features, and calibrating can take an extraordinary amount of time and work. There are highly detailed wikis for individual printer design that outline all the steps. Long story short, be prepared to put in some work if you decide to go this route. There are also plenty of helpful people in the 3D printing online community that would be glad to answer questions and provide advice along the way, so you won’t be embarking on this adventure completely alone.

Lets fast forward through many many months of building, calibrating, and troubleshooting more issues than I care to remember, and take a look at our finished 3D printer. Below you'll find several pictures to give you an idea of what your setup might end up looking like. It's not the prettiest, but it's reliable, accurate and I've grown comfortable enough to fix the issues that arises.

Figure 8 - Our Kossel style delta printer finishing up a head case print

Figure 9 - 3D printer electronics, including RAMPS board and Raspberry Pi

As you can see, there's quite a lot going on with our printer! It would be easy enough to cover up all the wires and make the whole system easier on the eyes, but that limits access to the electronics. I need to be able to get in an out quite often when things break or need upgrading. 

Figure 10 - Printer bed, carriage w/extruder and an attached webcam for monitoring prints remotely

It's not as easy to tell from the photo, but our print bed has a glass plate on top and bed heating electronics underneath. The glass bed provides a more consistently flat, level surface than the regular aluminum plate alone and heating the bed helps dramatically with bed adhesion. Both of these features were added on after the printer was built.

Figure 11 - 3D printer station with control PC, custom built delta printer, and purchased Makerbot Replicator 2

Thankfully we have enough room in our electronics shop to keep both our printer, materials and control PC in the same area without taking up too much space. Although I haven't mentioned it yet, I am sure you have noticed the Makerbot Replicator 2 printer on the right. We did indeed purchase a prefabricated printer some years back to use as a backup of sorts for our own, but let's just say we are less than satisfied with it's performance. I'll discuss that a bit more in detail later on.

I completely understand going this route is an undertaking most researchers don’t have the time or resources to complete. But you get far more freedom to customize the device your own way and it can't be understated how much knowledge you'll gain by getting your hands dirty. It will do wonders for your confidence and building skills, not to mention troubleshooting is far easier and quicker when you know the machine inside and out. 

Don't wanna build your own printer? Thankfully you don't have to!

Now I know what some of you are thinking, especially those of you who absolutely have no background/interest/time etc. in building a printer; wouldn’t it be so much easier if I could just buy one and start using it right outta the box? Well of course! You can certainly but pre-fabricated, closed-system printers that are made with the non-enthusiast end consumer in mind. Meaning they are designed to be intuitive, easy to use, and convenient no matter what your prior experience with 3D printers may be. They usually come with proprietary software and parts, so they offer very little room for customization, but for some people this is the perfect solution.

Figure 6 - MakerGear M2 printer

These printers tend to be quite a bit pricier than other available options, but the convenience can be worth the cost for some. You won't spend hours and hours getting your printer up and running, but you might spend the same amount of time dealing with customer support and printer errors. The very nature of closed-system devices means home troubleshooting is limited to power cycling, restarting a print, or being convinced you have to buy new components. Mileage may vary though, so maybe your experience will be better than the one others have had, i.e. us! (Note 1)

If you’re like most people and caught somewhere in the middle between buying a pre-fabricated printer and completely building your own, well then have I got the solution for you. There are plenty of printer kits available for purchase online. This will likely be the go-to route for the majority of people. Nowadays kit manufacturers do a pretty decent job of explaining how to setup your printer after purchasing it. Simply find the one you want and they'll ship you the parts to build it. 

Figure 7 - Printrbot Simple Pro kit

They’re cheaper than the pre-fabricated printers and some models can even be comparable to building your own. In fact for all intents and purposes you ARE indeed building your own printer when you purchase one of these kits, just without the hassle of putting together a parts list and ordering from multiple vendors. Most kits I have seen don’t have proprietary software either, so you’re going to be using a bunch of free software to complete the toolchain and get the printer going; just like you would have to do if you built your own from scratch. It’s a relatively simple process once you’ve set it all up. Plus there are plenty of great open-source options to choose from, allowing for even more customization. I strongly recommend going this route if possible as it has the most benefit with the least amount of headaches. If I ever decide to build another printer I will definitely be buying a kit.

Helpful Tips & Tricks

The most useful advice I can offer is how we overcame many of the problems that popped up while building our printer. Information and solutions for all of the technical issues you'll likely come across can be found in handy guides online, but I am going to run through some specific issues we encountered frequently and helpful tips we learned along the way.

• This calibration technique for fine-tuning the extruder is extremely intuitive and easy to do
• For fine-tuning the entire system, including tower position, rod length, etc., this is a great calibration test piece. Fair warning, you’ll probably be printing this thing more times than you can count!
• Delta printers can be tricky to calibrate, but there are procedures out there that will walk you through it. Yet another fair warning, it can take a bit of time!
• When you first start calibrating and doing test prints, keep the temperature of your extruder on the lower end of the working range and slowly raise it as you continue. Temperature is a big factor when printing, but it's also one that can be easily changed, so focus on other factors first. The range is from 180° C to 220° C for PLA
• Applying blue painters tape to an unheated bed does wonders for initial print adhesion. Yes, it has to be blue. I don’t have the answer for why, but the online community has established that other colors just don’t work as effectively\
• This might sound even crazier than the previous tip, but if you are using a heated bed (I highly recommend it!) applying a thin coat of hairspray will help the print adhere better 
• Check connections and tighten screws, belts, tracks, etc. about once a month. During the calibration process specifically you’ll be printing so often and changing so many settings that things might shift out of place
• PLA is our filament of choice with whites, greys and blacks being the colors we usually stick with. While we do occasionally use other colors, the consensus online seems to be that colored filament tends to jam more often than blacks and whites do. You can always paint them any desired color afterwards anyways

Figure 12 - Various spools of PLA

• Store your filaments in airtight containers. Leaving them exposed to the open air can expose them to microscopic contaminants, which jam the extruder and lead to ugly prints
• Keep your active spool of filament on a roller so it feeds directly into the extruder – thus drastically reducing the possibly of it tangling up as it rolls out. We keep ours mounted above the printer. The last thing you want after printing for 15 hours is for a filament jam to ruin it all during the final minutes!

Figure 12 - Spool of PLA on roller being fed down into the extruder

• For the last step in the software toolchain we went with the free software Octoprint. Check out their website for a full rundown of features, but one of the coolest is the option to hook up a webcam and monitor your print in real time from anywhere. You can also adjust the settings from their online interface on a whim. I highly recommend going with this web-based route for printer control
• Consider adding a heated bed and glass plate if the printer you decided on doesn't already have them. Print adhesion and a level print surface are both major factors in determining the quality of the overall print and these two add-ons do wonders for addressing those issues
• Thankfully our university has a PLA recycling program. They take unwanted PLA prints, grind them up, and melt it back down into spools for use in student print labs. If you don't have a recycling system like this in your facility, consider setting it up. All those failed prints have to go somewhere, and they might as well be put to good use

Figure 13 - Recycle bad prints whenever possible

What's next?

Now that you're all experts on 3D printers and have your own set up, it's time to have some fun! In my next post I'll be diving into a unique project. I'll be going over the procedure used to turn a person's hi-resolution anatomical MRI scans into a custom 3D printed head case that fits inside our 12 channel head coil and drastically reduces subject movement inside the magnet. Stay tuned! (Note 2)

Figure 14 - Hi-res MPRAGE slice

Figure 15 - Custom 3D printed head case made from the above MPRAGE

Note 1: Unfortunately, I can attest from personal experience that purchasing a pre-fabricated printer is not without problems. We purchased a Makerbot Replicator 2 in our shop and have experienced problems almost from the get go. Granted we bought it several years ago and it's possible that the company has improved it's products, but it's customer service could still use some work. The extruder jams with filament most times it prints at this point and the only option available is to restart the print with different settings and hope for the best. There is no way of opening up the printer and tinkering without voiding the warranty, but even if we weren't concerned with the warranty it's still impossible to replace parts on our own because Makerbot doesn't sell them. The only solution we've ever gotten from customer service, when they bother to respond to our inquires, is to purchase a newer model of the extruder. I don't know about you, but having to purchase a new $150 part every couple months doesn't make a whole lot of sense considering the thousands of dollars this printer cost. They've also gone through two different proprietary softwares since our initial purchase and BOTH were lousy with crashes and bugs. To put it simply, I never use our Makerbot printer and exclusively use our custom built one. Take this experience with a grain of salt when purchasing your printer, but be aware that our experience is by no means an isolated incident.

Note 2: The