MRI has a pretty unique value proposition for the brain, as it can detect and discern things that other modalities (CT, US) simply cannot. Even a poor quality MRI (essentially what this is) provides more information within the brain than a high resolution CT. Many of the brain pathologies are also very time-sensitive. So a good place to start.

Elsewhere in the body, MRI is less useful, and isn't really a workhorse as it is with neuroimaging. (Except maybe joint imaging.) Most emergent problems are detectable via those other cheaper, faster, & less onerous technologies.

Your guess about size is also likely correct; the positioning of the antenna/coils and relation to the magnet are very important (especially with a weak magnet) and much more challenging/variable if you're thinking about the range of abdomen sizes (for example) versus head sizes.

Do MRIs have any value in replacing physical examinations (prostate, colonoscopy) with diagnostic imaging? My understanding is that assay testing is getting better, but still no replacement for the physical procedures I mentioned.

For measuring spread of disease like prostate cancer imaging can be really helpful, see: PSMA PET-CT. I could imagine a world where imaging is really cheap and agents were safer, in which case we might opt to use imaging instead of physical exams, as they would offer way earlier detection. But for now the additional radiation (not present in MR), cost, risk, time, etc makes it a no go for standard of care screening.

Imaging in general has an important role in screening for certain diseases, and in some cases is already more important than physical examination. This mainly depends on how "well" physical examinations can detect an illness, the characteristics of a particular imaging study (cost, radiation exposure, etc), and the characteristics of a disease (prevalence in a population, potential benefit of early detection/treatment). So in short, for MRI to replace physical exam and/or lab testing in screening for a particular disease, the cost needs to come down or the benefit should outweigh the cost.

Prostate cancer screening in general is no longer officially recommended by the AAFP as a rule [1], but if a patient decides to opt-in to screening, the "assay" (PSA) is preferred over a digital rectal examination, which has been shown to be increasingly useless in the detection of prostate cancer. MRI doesn't currently have a role in prostate cancer screening, but Prostate MRI has an increasingly critical role in diagnosis.

CT colonography is currently a viable option for colon cancer screening instead of colonoscopy, though colonoscopy is still considered the gold standard.

Chest CT is currently recommended to screen for lung cancer in patient's that meet certain criteria (age, smoking history).

Mammography is obviously the workhorse of screening for breast cancer, rather than physical examination. But MRI is recommended as a screening mechanism for certain patient populations with very high risk of breast cancer (e.g. certain BRCA mutations). The small population, high prevalence, and benefit of early detection combine to make this a viable option.

[1] https://www.aafp.org/family-physician/patient-care/clinical-...

I think (I might be wrong) the brain might be a good target because there is not much motion. To get fast readings from an MRI you probably need the stronger magnets. MRI works not by capturing spatial variation directly like a camera, but collects a time series of aggregate magnetic field readings while a gradient field is used to create changing spatial variation. In essence, the time series gives the k-space of the image, which is then Fourier transformed into the original image. Consequently, the body must remain fairly still while this k-space time series is constructed. The heart, for instance, is notoriously hard to image.

The heart is hard to image but it’s impressive to see the results. Looking at cardiac cine series is impressive.

The size of the machine tends to scale more-than-linearly with the cross-section of the thing you're scanning. Small animal MRI machines are really tiny:

https://rs2d.com/en/mri/irm-1-5t/

You don't typically need an MRI in an ER setting except for the problem stated, differentiating between various reasons for a stroke. A CT can do the rest and is way cheaper and simpler to setup and operate.

There are other reasons an MR could be better though, for example no ionizing radiation, so you could argue you could send more patients through it than you would with an ER CT (you would only send patients you have a higher confidence of them requiring it to avoid spamming radiation).

Even for a stroke, the standard ED protocol is a CT in the majority of cases.

That has a lot to do with the difficultly and cost of siting an MRI close enough and keeping it open for for emergency protocols.

It also relates to the patient though. Stroke patients are often not very compliant and a morality that is slow and requires a still patient is ill suited to a lot of the work an ED sees.

True enough, but MRI is not inherently too slow for this use. If the economics otherwise made sense, an acceptably fast throughput stroke protocol MR is quite doable.

It is. The requirements of the MR environment make it a lot more difficult than CT though. For example a tubed patient is harder to manage in MR than CT, and while this is done regularly it isn't as easily done as CT.

True, but the improved contrast would probably make it a no-brainer if the other issues were taken care of .

Pun intended?

The contrast is so good.

You are probably aware, but there are 5 minute protocols (Siemens call their one a “go brain”) that are pretty reasonable, and probably not far off a gold standard routine protocol 10 years ago.

That just excludes haemorrhagic stroke rather than confirms most ischaemic strokes. It allows for antiplatlets to be safely given. MRI is still needed to diagnose all but severe or very late strokes as far as I’m aware (although this is not my field. Happy to be proven wrong)

CT is often done both as a non-contrast study (to exclude hemorrhage or large established stroke) and also as a CTA and sometimes with perfusion. This data at most stroke centers is all that is needed acutely to decide whether and how to treat, and MRI is often not done until days later to evaluate final extent of the stroke.

I saw a demo of this device at RSNA last year. It is quite small, which is their goal to make it as portable as it is. But, the opening where the body parts go is also small, and at this point too small I think to fit the whole body. It would work for head and extremities I should think.

I'm inquiring about using this in a veterinary hospital. Might be a ideal for this.

You need a lot of Tesla’s for animal work. Everything is so small that fine slices and high in-plane resolution is needed. The spinal cord on a small dog is not always easily imaged at 3T, 0.1T is going to be a problem.

Thanks. Makes sense why there's no info on their site regarding vet use.

They have video of knee, neck and foot. Evidently "works-in-progress" and not part of their FDA filing.

https://www.hyperfine.io/clinical