Weight estimate for MRI contrast?

[grebes4lyfe]

Venturing over here from pre-vet for a quick question...

I'm wondering how exact a weight is actually needed to calculate an IV contrast dose for a brain MRI? Can an estimated weight that is within 10-15 pounds be used to calculate a contrast dose? Is there any research supporting the ability to estimate this dose that you all could possibly direct me towards, please?
Or, is an exact weight really that important?

I've tried to google scholar the **** out of this and I'm just getting a lot of stuff about the efficacy of contrast with different magnetic field strengths, or something completely unrelated, or something that I just can't understand since I'm not a radiologist.

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[maxxor]

Multiply the recommended dose (mmol/kg) by weight (kg) and divide by concentration (mmol/mL).

Or use a chart
https://www.radiology.wisc.edu/wp-c...0/gadolinium-based-contrast-dosing-charts.pdf

 

[grebes4lyfe]

Thanks for the response! my question though is actually if an estimate that’s within 10-15 lbs could be used without actually weighing the patient?

 

[maxxor]

Thanks for the response! my question though is actually if an estimate that’s within 10-15 lbs could be used without actually weighing the patient?

I’ll answer a question with a question and ask why do you want to know this?

How much of a percentage of their weight does that amount represent? That’s the intrinsic error you are introducing by using an estimate vs actual weight.

In the early days of MR, unit doses were used. It can be done, but because of Gadolinium deposition concerns, it’s best to use the proper dose rather than give more than necessary.

 

[grebes4lyfe]

I’ll answer a question with a question and ask why do you want to know this?

How much of a percentage of their weight does that amount represent? That’s the intrinsic error you are introducing by using an estimate vs actual weight.

In the early days of MR, unit doses were used. It can be done, but because of Gadolinium deposition concerns, it’s best to use the proper dose rather than give more than necessary.

I had a pediatric brain tumor and my follow up MRI is tomorrow. I’m 12 years out with no recurrence, q3year MRIs now and this should be my last one. I also have an eating disorder and I don’t get weighed. Like, ever. Giant trigger, reduced to tears, it’s ugly and I want to avoid it at all costs. I’m confident that my weight has not fluctuated too much from my last known weight from 2 years ago (still wear the same clothes, etc), but the nurses won’t accept it (Oncologist said the estimate was probably fine, charge nurse in radiology said no).
I’m not asking for treatment advice or anything, I know that’s not what this site is for at all. I just wanted to know a little more about how the dosing works for this, if dosing someone 10-15 pounds off (~8-10% body mass) was within an acceptable range and if there was any research showing this that I could present to plead my case.
Or if I just need to prepare myself for some ugly crying tomorrow.
Also because now I’m just curious about it in general and haven’t been able to find any information online that I can decipher.

 

[deleted109597]

Alternatively, you could have the weigh you without telling you the amount. It's important for them to know, not as much for you. It can be done tactfully.