This is precisely what saved my father's life last year.
16 years ago he had some kind of brain cyst. Totally benign. But as a follow up, the doctor ordered yearly MRIs, much to his annoyance.
Last year those yearly routine MRIs spotted a brain tumor- before it had time to get dangerous or cause any damage to him. It was growing quickly though and was right near his eye. Quick surgery got it out.
I want to live in a world where everyone has access to that.
PET scans are limited in resolution when you get down to the sub-5 mm or so range due to scanner technology and fundamental limits of the physics of positron/electron annihilation & photon emission.
A typical MRI (i.e. alas, not what this article is describing) can usually resolve something at that size and identify characteristics like diffusion restriction or contrast enhancement which can confirm metastasis.
Also, in the brain, PET scans (at least the most common, FDG, which is based on glucose) are extremely limited in utility because of the baseline high glucose metabolism of the brain, which makes it hard to distinguish from the metabolic activity of a tumor.
The flip-side of that is that PET is vastly multiple orders of magnitude far more sensitive than MRI. So while PET may not be able to localize as well as MRI, it can detect smaller things if the targeting of the radioisotope is good.
FDG PET/CT is not used to stage intracranial metastases due to background brain activity significantly reducing sensitivity. You’re likely only detecting lesions 1cm or greater in the brain, or ones which demonstrate low metabolic activity and appear dark.
MRI is much more sensitive and specific and is the standard of care for staging in my practice and as per the NCCN clinical guidelines. I haven’t been to any institution or heard of one where PET is used for staging of brain metastases.
I am unsure of the exact state of play but believe that small mets (eg a few mm in size) are better seen with MRI. MR is probably easier to get than PET too.
There are usually a few radiologists lurking here and they would have better knowledge than me (I’m an MR tech).
That's absolutely true. We work with a lot of technical founders who are turning their research into a diagnostic medical devices. One of the first questions we always ask is: how will the information produced by your device help clinical decision making? More data is _nice_ but if it doesn't alter the course of treatment, it's pointless. Sometimes it's okay if the doctor doesn't know if the problem is A or B if the treatment for A and B is the same.
I’ve spent a long time around scanners and re-read this book before helping students. It’s remarkable easy to lose track of the fundamentals, though maybe that’s just me.
(vastly simplified) MRI basically functions on two fundamental mechanisms--"spin echo" and "gradient echo". Spin echo signal is described by T1 and T2. Gradient echo signal is described by T1 and T2*. The difference between T2 and T2* relate to local magnetic properties of the tissue which is called "susceptibility". Blood contains iron so its presence alters T2* and this is exploited clinically. A good example of T2* imaging used clinically is susceptibility-weighted imaging (SWI).
T2* effects increase with higher MRI main field strength. From what I can tell so far these ultra low-field scanners have to rely on spin echoes.
These are different MRI sequences that are weighted differently to produce a specific contrast that show different characteristics of the tissue that is imaged.
I really liked ‚MRI made easy‘ as an introduction to MRI physics. Just google it, it’s a free Book
16 years ago he had some kind of brain cyst. Totally benign. But as a follow up, the doctor ordered yearly MRIs, much to his annoyance.
Last year those yearly routine MRIs spotted a brain tumor- before it had time to get dangerous or cause any damage to him. It was growing quickly though and was right near his eye. Quick surgery got it out.
I want to live in a world where everyone has access to that.