Advances in F19 MRI: Imaging Drugs in Living Organisms

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Discussion Overview

The discussion revolves around recent advancements in fluorine-19 (F19) MRI technology, particularly its application in imaging drugs within living organisms, such as rats. Participants explore the sensitivity challenges of F19 MRI compared to traditional hydrogen MRI, the potential for hyperpolarization techniques, and the use of fluorinated compounds as contrast agents.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant questions the feasibility of producing a good image with F19 MRI due to the low abundance of fluorine compared to hydrogen and the typical therapeutic doses of drugs.
  • Another participant mentions hyperpolarization schemes that have shown promise in enhancing F19 MRS/MRI sensitivity, suggesting that these may have potential clinical applications.
  • It is noted that increasing the number of fluorine atoms in a compound could improve the signal-to-noise ratio in F19 MRI.
  • A participant references a paper discussing a CF3 group complexed with a lanthanide that significantly increases F19 sensitivity and inquires about the potential of using boron instead of lanthanide for similar effects.
  • Concerns are raised regarding the relaxation times of boron nuclei, with one participant speculating that quadrupolar nuclei may facilitate faster relaxation times, but uncertainty remains about their effectiveness compared to lanthanide complexes.

Areas of Agreement / Disagreement

Participants express varying opinions on the effectiveness of F19 MRI and the potential of different chemical strategies to enhance imaging. There is no consensus on the best approach or the feasibility of using boron in place of lanthanides.

Contextual Notes

Participants acknowledge limitations related to the sensitivity of F19 MRI and the complexities of using different isotopes and chemical structures, but these remain unresolved within the discussion.

gravenewworld
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What kind of advances have been made in this field (since I don't stay on top of it)? If I wanted to image, say, where my fluorinated drug is going within a rat, is it possible? NMR is inherently not a sensitive modality. Hydrogen is vastly more abundant in a living organism than fluorine (typical MRI vs F19 MRI), so given the fact that most therapeutic doses of drugs occur probably in the millimolar to nanomolar range, is it even possible to produce a good image with F19 MRI? Is it practically impossible to produce a decent S/N ratio? What if I incorporated more fluorines into my compound?
 
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I recall people were fiddling around with hyperpolarization schemes in relation to 19F MRS/MRI at an Experimental NMR Conference a few years back, but they were able to get the model system/proof of concept looking fairly convincing, so you might want to poke around to see if they've made the jump to the clinic (or at least the diagnostic radiology research labs).

Otherwise, more fluorines = more signal. Jeff Bulte at Johns Hopkins has been using extensively fluorinated compounds as contrast agents/tracers that I can also muster up from memory within the last few years. Also, in general, fluorine has some particularly interesting advantages - it's about 80% to 85% as sensitive as 1H, the only stable isotope is 19F (in contrast to hydrogen and deuterium), and it's a spin-1/2 nucleus.
 
Thanks for the response. My PI just sent me this paper in which they have a moiety containing a CF3 group complexed with a lanthanide metal

http://onlinelibrary.wiley.com/doi/10.1002/mrm.22881/abstract

Sensitivity for 19F increases by 10,000 fold. Would this work for boron instead of a lanthanide? For example a compound containing a BF2 group? My quantum chemistry is quite rusty (took it almost 10 years ago), so I'm not sure if using boron would also work to decrease relaxation times too.
 
The most common boron nuclei are quadrupolar, so my initial suspicion is that they would indeed facilitate faster relaxation times. Relative to a comparable lanthanide complex...not sure off the top of my head. I would suspect probably not, although it would depend on which one. I'm mostly thinking that you may find naturally occurring lanthanides to be a mix of isotopes, some of which are themselves quadrupolar (for example - "natural abundance" gadolinium is actually composed of 5 or 6 isotopes, some of which are spin-3/2 nuclei). I think there are some lanthanides which are mostly just spin-1/2 nuclei (thulium, I think, as it's used in the shift reagent TmDOTP), but my rare-earth chemistry is a bit dusty.
 

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