MRI radiographers generally know what implants and devices can go into the scanner and those that can’t.
But there are some devices that can be a little puzzling.
Some staff members will scan a patient who has these ambiguous devices and implants, and for others it’s a hard no.
For a newbie this can be very confusing.
Here is my guide to the top 3 implants and devices, that seem to cause the most confusion for newbies.
- Cardiac loop recorders
- Heart valves and annuloplasty rings
- Body Piercings
You will find some general knowledge about these implants and devices and some info about how to manage them in the MRI environment.
Please remember, as the operator you are solely responsible for the safety and well being of your patients and anyone else that you expose to the MRI environment.
It is up to you to make the final decision about who and what is exposed to the magnetic field.
Implantable Cardiac Monitors and Loop Recorders
Over the last 5 years I have scanned increasing numbers of patients with implantable cardiac monitors.
Implantable loop recorders/implantable cardiac monitors are very small devices. They are inserted subcutaneously and record a patient’s ECG.
These devices are ideal for regular interval monitoring of patients, experiencing infrequent symptoms that may indicate that they have a cardiac arrhythmia. These symptoms can include –
- dizziness
- chest pain
- palpitations
- syncope (fainting)
The Reveal LINQ device is a commonly encountered insertable cardiac monitor in MRI departments. Information about this device can be found here at Medtronic–>>
Loop Recorders and the Magnetic Field
According to Shellock et al, 2014 patients with the Reveal Device and other loop devices can be safely scanned under certain conditions with no ill effects to the patient.
So these devices are considered CONDITIONAL.
Gimbel et al 2005, studied 10 patients with implantable loop recorders.
Between them they had a total of 11 MRI examinations including cranial, Lumabr spine, shoulder and knee scans on 1.5T magnets.
There was no reported harm to the patients or the ILR devices. No noted “sensations of tugging or warmth at the implant site” were also recorded.
Now even though loop devices are safe to scan under certain conditions, electro magnetic interference artifacts (caused by MRI) can be readily picked up by loop recorders.
The problem with that is this interference from MRI can be recorded on the loop device and misinterpreted as arrhythmias (Shellock et al, 2014).
Suggestions
1. Make sure that you have established whether the patient can be safely scanned.
Please check MRIsafety.com and or the manufacturer of the device. Also consult your local rules.
2. You can ask the patient if recent recordings have been taken from their loop recorder/monitor to ensure an up-to-date reading before you expose them to the magnetic field.
3. After the MRI scan you can suggest to the patient that their device is cleared.
This should avoid any electromagnetic interference artifacts being detected and interpreted as clinically significant arrhythmias.
Heart Valves and Annuloplasty Rings
Cardiac MRI and other MRI examinations are being offered at many more centres and demand continues to grow.
As a result we are seeing more patients with these devices in MRI.
Prosthetic heart valves are used to replace dysfunctional native valves.
The most common prosthetic heart valves are bio-prosthetic valves, mechanical valves and homografts.
1. Bioprosthetic valves
There are two main types of bioprosthetic valves – stented valves and stentless valves.
Stented valves
The leaflets of stented valves come from bovine pericardium or from the aortic valves of pigs (porcine). The leaflets are then attached to a plastic or titanium stent.
Stent-less
These valves consist of a section of aortic root (usually porcine in origin) and the aortic valve is given additional strength by an exterior cuff
2. Mechanical Valves
These valves are made from carbon and metal. They have many different configurations.
Caged ball valves –
These valves are no longer implanted but many existing patients still have them.
They are composed of a ball, a circular ring and a cage.
Bi-leaflet Valves –
The valves are 2 D shaped disks which are attached to a ring by hinges.
Monoleaflet valves
This type of valve only has 1 leaflet, which is a single disk attached to a ring by a central connecting rod.
3. Homografts
The patient’s aortic root is removed. It’s then replaced with a donor human aortic root which includes a portion of the ascending aorta and the aortic valve.
Homografts are rarely performed. It is a complex procedure and there is a lack of donor tissue.
Annuloplasty Rings
Annuloplasty rings are usually made of plastic, metal and surgical mesh.
They are used to strengthen the annulus that an existing valve is attached to.
The annulus is a ring of tissue found in the body that the leaflets of a valve are attached to.
The annulus helps the valve to open and close.
If the heart enlarges the annulus can become stretched and the leaflets may stop closing fully and allow blood to flow back in the wrong direction.
This is known as regurgitation.
Heart Valves, Annuloplasty Rings and the Magnetic Field
Lots of heart valves and annuloplasty rings have been tested up to 3 Tesla for heating effects and magnetic field interactions. Many demonstrated mostly minor magnetic field interactions (Shellock et al, 2014).
In fact the actual beating heart creates forces that are greater than the pulling forces created by the interactions of the magnetic field and the valves and or annuloplasty rings (Shellock et al, 2014).
So the force of the patient’s heart beat is considered stronger than the attractive forces of the magnetic field.
Shellock et al, 2014, state that “an MRI procedure is not considered to be hazardous for a patient that has any heart valve prosthesis or annuloplasty ring tested relative to the field strength of the MR system used for the evaluation”
For example this may mean that if a patient’s heart valve prostethesis or annuloplasty ring has been tested on a 1.5T magnet then they can have an examination on a 1.5T scanner.
According to Shellock et al 2014 “ with respect to clinical MRI procedures, there has been no report of a patient incident or injury related to the presence of a heart valve prosthesis or annuloplasty ring.”
However the authors do remind us that not all of these types of implants have been tested for MRI safety and compatibility.
Suggestions
1. Check your local rules.
2. Check MRISafety.com and see if the prosthesis or annuloplasty ring is listed there and follow the advice.
3. Consult with a more experienced member of staff and ask them for some advice.
4. If you have any doubts then remember you can choose to delay the patient’s scan until you have more information.
Body Piercings and Jewellery
Decorative body piercings are so common that radiographers will encounter them frequently.
They can be made of non-metallic materials but the majority of those that I have encountered have been metallic.
Some metallic piercings can be ferromagnetic or nonferromagnetic. It just depends.
And unless the patient can tell you exactly what the piercing is made from there is no guaranteed way of knowing.
Some departments keep a magnet nearby so they can check if a piercing is magnetic.
I was always a little sceptical of this practice in case you tested a really ferrous piercing and accidentally removed it or seriously displaced it.
I even know of one department that used a magnet to check for metallic foreign bodies in patient’s eyes!
Piercings and the Magnetic Field
The potential risks associated with piercings are discomfort and odd sensations due to movement or displacement from attractive forces caused by the magnetic field.
Heating and burns are also possible if the piercing is made from conductive materials (Shellock et al, 2014).
Suggestions
1. Because we cannot always be sure about what a piercing is made of, ideally all piercings should be removed before entering the MRI environment.
Inconveniently a lot of piercings cannot be removed so what options does the radiographer have?
2. If a piercing cannot be removed it is recommended that the piercing is wrapped in gauze or tape.
Gauze and tape can reduce the amount of contact that the piercing has with the skin thus reducing the likelihood of heating and burns
Taping the piercing down can help to reduce the likelihood of the piercing moving and causing discomfort while the patient is within the magnetic field (Shellock et al, 2014).
3. Always assess the piercing. If it is really big and looks like it is made of iron, you probably do not want to expose that to the magnetic field.
4. What area of the body are you going to scan? Modern scanners tend to be very well shielded. So the magnetic field is tightly bound to the vicinity of the bore.
If the patient is having an examination of their ankle and their piercing is on their lip, the piercing might be less affected by the magnetic field because of the distance of the piercing from the magnet bore.
5. Remember that the higher the field strength, the magnetic field will produce greater attractive forces. Please take that into consideration especially if you are working on a 3Tesla scanner.
6. Remember to tell the patient to inform you right away if they experience any heating, movement or strange sensations during their MRI examination. Then make sure that you investigate and take action from there.
I hope that this article has been helpful.
Please remember that if you are the operator the final decision about whether you will expose the patient to the magnetic field is up to you.
If in doubt, you can always delay the examination until you have more information.
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