3 ms·

I have a heart stent that is only rated to 3T, so I'm kind of sad that I can't make use of the newer MRI technologies (granted, this particular MRI imaging does

I have a heart stent that is only rated to 3T, so I'm kind of sad that I can't make use of the newer MRI technologies (granted, this particular MRI imaging doesn't seem to be a thing for humans yet). I'm wondering if, at some point, I'll be able to have it replaced with a newer material that isn't ferromagnetic (or wouldn't be affected like mine is)

KennyBlanken 4y ago
Your stent is only rated to 3T because that's about the absolute maximum field strength used by human clinical MRI systems, with the vast majority being half to a quarter that. As you noted, this imaging was done at much higher field strengths, ~10T. That sort of field strength is practical at the scale of a system sized for a mouse. For a human, it's likely to never be practical for a whole slew of reasons related to the energy needed, forces on the machine, the increase field size and strength affecting room construction, safety thresholds, etc.
- hansvm 4y ago
  1.5T and 3T are very common, and 4-7T are definitely used in a number of hospitals. UMN has a 10.5T magnet they've shoved humans into. Their stent is rated to 3T for a variety of reasons including: 1. That's all they've tested (as you alluded to). 2. It might actually fail at higher fields. 3. Stents act as antennas and can focus RF into unwanted places like cooking the middle of the brain, and it's a lot more likely that the stent is rated for exactly 3T than up to 3T since the relevant frequencies are proportional to field strength, and the associated wavelengths can coincide more or less with the length of the stent (kind of like how the Tacoma Narrows bridge could have experienced a lot more wind, but that particular set of factors was problematic). It _might_ be certified for 0-3T, but that takes additional research to actually do. 4. Any number of other reasons. High fields have a variety of counter-intuitive properties.
  - MPSimmons 4y ago
    For what it's worth, most of the concern seems to be migration (movement of the stent) and temperature increase, and there's also a passive optical artifact introduced by the stent in the image itself. The manufacturer docs are here: https://www.cardiovascular.abbott/int/en/hcp/products/percutaneous-coronary-intervention/xience-family/freqently-asked-questions.html https://www.cardiovascular.abbott/int/en/hcp/products/percut... Nonclinical testing has shown that the XIENCE Sierra™ Stent, in single and in overlapped configurations up to 71 mm in length, are MR conditional. A patient with this device can be scanned in an MR system under the following conditions:\* Static magnetic field of 1.5 or 3 Tesla Maximum spatial gradient field of 3000 Gauss/cm or less Maximum MR system reported whole-body-averaged specific absorption rate (SAR) of 2.0 W/kg (normal operating mode) Under the scan conditions defined above, XIENCE Sierra™ Stents are expected to produce a maximum temperature rise of of less than 4.5°C after 15 minutes of continuous scanning. The XIENCE Sierra™ Stent should not migrate in this MRI environment. MRI at 1.5 or 3 Tesla may be performed immediately post-implantation. In non-clinical testing, the image artifact caused by the device extends approximately 6 mm from the XIENCE Sierra™ Stent when imaged with a gradient echo or spin echo pulse sequence and a 3T MRI system. It may be necessary to optimize the MRI parameters to account for the presence of XIENCE Sierra™ Stents.
    - lostlogin 4y ago
      Cardiac stents are fine in MR and most others are too. As the document you have provided says, it won’t move. One did once but it seems it wasn’t related to the MR. You can scan them to immediately after insertion - I used to. Massive amounts of overlapping stents should get people thinking a bit though. The force from a beating heart is more than the MR exerts and the cooling provided by flowing blood are factors. The funny thing is, most scanners aren’t what it says on the label. Scan water, get the centre frequency and work back to get the field. The most recent one I tested was 2.89T. http://www.ismrm.org/smrt/safety_page/2019.Shellock.Coronary.Stent.MRI.Guidelines.pdf http://www.ismrm.org/smrt/safety_page/2019.Shellock.Coronary...
  - ramraj07 4y ago
    I’m not getting into a 7T ever. You feel loopy when you get up from it so it clearly does something to your brain. No way.
    - lostlogin 4y ago
      I haven’t tried 7T. Move slowly near the entrance to the bore and it’s fine at 3T. It isn’t permanent or anything. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4409466/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4409466/
- lostlogin 4y ago
  Clinical systems are mostly 3T where I live, but you can buy clinical 7T scanners (see recent RSNA and Siemens Terra). Heart stents are rated to 3T as that’s what was tested - it’ll almost certainly be fine at a higher field, but no one has tested it. I’m an MR tech. https://www.siemens-healthineers.com/magnetic-resonance-imaging/7t-mri-scanner/magnetom-terra https://www.siemens-healthineers.com/magnetic-resonance-imag... https://www.ismrm.org/smrt/safety_page/2021.Shellock.Coronary-Stent.MRI.Guidelines.pdf https://www.ismrm.org/smrt/safety_page/2021.Shellock.Coronar...

KennyBlanken 4y ago

Your stent is only rated to 3T because that's about the absolute maximum field strength used by human clinical MRI systems, with the vast majority being half to a quarter that. As you noted, this imaging was done at much higher field strengths, ~10T. That sort of field strength is practical at the scale of a system sized for a mouse. For a human, it's likely to never be practical for a whole slew of reasons related to the energy needed, forces on the machine, the increase field size and strength affecting room construction, safety thresholds, etc.

hansvm 4y ago
1.5T and 3T are very common, and 4-7T are definitely used in a number of hospitals. UMN has a 10.5T magnet they've shoved humans into. Their stent is rated to 3T for a variety of reasons including: 1. That's all they've tested (as you alluded to). 2. It might actually fail at higher fields. 3. Stents act as antennas and can focus RF into unwanted places like cooking the middle of the brain, and it's a lot more likely that the stent is rated for exactly 3T than up to 3T since the relevant frequencies are proportional to field strength, and the associated wavelengths can coincide more or less with the length of the stent (kind of like how the Tacoma Narrows bridge could have experienced a lot more wind, but that particular set of factors was problematic). It _might_ be certified for 0-3T, but that takes additional research to actually do. 4. Any number of other reasons. High fields have a variety of counter-intuitive properties.
- MPSimmons 4y ago
  For what it's worth, most of the concern seems to be migration (movement of the stent) and temperature increase, and there's also a passive optical artifact introduced by the stent in the image itself. The manufacturer docs are here: https://www.cardiovascular.abbott/int/en/hcp/products/percutaneous-coronary-intervention/xience-family/freqently-asked-questions.html https://www.cardiovascular.abbott/int/en/hcp/products/percut... Nonclinical testing has shown that the XIENCE Sierra™ Stent, in single and in overlapped configurations up to 71 mm in length, are MR conditional. A patient with this device can be scanned in an MR system under the following conditions:\* Static magnetic field of 1.5 or 3 Tesla Maximum spatial gradient field of 3000 Gauss/cm or less Maximum MR system reported whole-body-averaged specific absorption rate (SAR) of 2.0 W/kg (normal operating mode) Under the scan conditions defined above, XIENCE Sierra™ Stents are expected to produce a maximum temperature rise of of less than 4.5°C after 15 minutes of continuous scanning. The XIENCE Sierra™ Stent should not migrate in this MRI environment. MRI at 1.5 or 3 Tesla may be performed immediately post-implantation. In non-clinical testing, the image artifact caused by the device extends approximately 6 mm from the XIENCE Sierra™ Stent when imaged with a gradient echo or spin echo pulse sequence and a 3T MRI system. It may be necessary to optimize the MRI parameters to account for the presence of XIENCE Sierra™ Stents.
  - lostlogin 4y ago
    Cardiac stents are fine in MR and most others are too. As the document you have provided says, it won’t move. One did once but it seems it wasn’t related to the MR. You can scan them to immediately after insertion - I used to. Massive amounts of overlapping stents should get people thinking a bit though. The force from a beating heart is more than the MR exerts and the cooling provided by flowing blood are factors. The funny thing is, most scanners aren’t what it says on the label. Scan water, get the centre frequency and work back to get the field. The most recent one I tested was 2.89T. http://www.ismrm.org/smrt/safety_page/2019.Shellock.Coronary.Stent.MRI.Guidelines.pdf http://www.ismrm.org/smrt/safety_page/2019.Shellock.Coronary...
- ramraj07 4y ago
  I’m not getting into a 7T ever. You feel loopy when you get up from it so it clearly does something to your brain. No way.
  - lostlogin 4y ago
    I haven’t tried 7T. Move slowly near the entrance to the bore and it’s fine at 3T. It isn’t permanent or anything. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4409466/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4409466/
lostlogin 4y ago
Clinical systems are mostly 3T where I live, but you can buy clinical 7T scanners (see recent RSNA and Siemens Terra). Heart stents are rated to 3T as that’s what was tested - it’ll almost certainly be fine at a higher field, but no one has tested it. I’m an MR tech. https://www.siemens-healthineers.com/magnetic-resonance-imaging/7t-mri-scanner/magnetom-terra https://www.siemens-healthineers.com/magnetic-resonance-imag... https://www.ismrm.org/smrt/safety_page/2021.Shellock.Coronary-Stent.MRI.Guidelines.pdf https://www.ismrm.org/smrt/safety_page/2021.Shellock.Coronar...