NMR Spectroscopy Flashcards
What is chemical shift?
Small changes in resonant frequency due to different molecular environments of nuclei.
How can we take adavantage of nuclear spin?
By subjecting a molecule to an external magnetic field and then irradiate with light and gather information about how light interacts with that compound
What is Prodium?
A hydrogen isotope of mass 1
What can spectroscopy tell us?
Tells us the precise chemical environment of every single protin in the molecule and we can use this information to discern the precise structure of the molecule
What do we get?
Distinct resonances from all the different compounds
What is a limitation of spectroscopy?
Can getting splitting where we dont get a single resonant frequency
Thats because we have degeneracy in the energy levels and it causes coupling between adjacanet proteins on the molecule, causing a splitting in the line shape
Means some of the line shapes we then see in the spectra arent straight forward to quantify as they’re not single peaks, they’ve got double or triple peaks
but these tend nto to affect the primary metabolites of interest in brain spectroscopy like GABA or Lactate of Glutamate and Glutamine
In what setting can spectroscopy be useful?
In a diagnostic setting
We can image the shifts- integrate the area under the primary resonances and then using phase encoding in two or three dimensions, we can spectroscopically sample the whole of the brain
Why is metabolic information from spectroscopy useful?
We can get complimentary metabolic information about molecular uptake and distribution of different brain metabolites and this is used clinically
The applications are usually in relation to brain tumours- loooking at the metabolism of different chemicals in the brain, its complimentary to strcutural information that we see with proton MRI
Most atoms in the periodic table have what?
Nucear spin
What are the easiest atoms to pick up?
Those with nuclear spin 1/2
Hydrogen is the most straight forward
We can pick up lots of atoms with MR- about 10 or 11 that are useful medically
To pick up the signals from different atoms in MR what do we do ?
Tune the scanner to different frequencies
This is because the resonant frequency of the nucleus depends on the gyromagnetic ratio - the ratio of the magnetic moment to the angular momentum of a spinning charged particle
What can we do to measure the different signals?
Build spearate radiofrequency coils to pick up the signals from them
What do we need to account for when building these different radiofrequency coils?
Natural abundance and concentration- dealing with weaker signals which make noiser images
Endogenous vs exogenous (contrast agents) - is it present in the human body or not? We can inject people with traces of nuclei that arent found in the body that are MR sensitive
Hyperpolarisation ‘signal boosting’ of low concentration atoms - can be magnetised to quite strong high levels using strong magnetic fields etc, there are ways of boosting the signal of low concentration atoms to amplify the signal
What is Deuterium?
An isotope of water, but its got a proton and neutron in the nucleus, essentially its heavy water
This resonates at a lower frequncy than water but what we can do with infusions of heavy glucose is monitor the uptake and turnover of these spectroscopically as we infuse them in the brain and monitor in time the wash in and washout of glucose
What is 3Helium?
An intert gas
3He is a rare isotope of He
We amplify the signal from the gas using laser hyperpolarisation equipment - can use lasers to highly magnetise the nuclei of the He atoms and when we inhale the gas we can image lung function with it, can see different levels of ventilation heterogeineity acorss people
We can also measure the oxygen partial pressure in the lungs and that has an impact on brian oxygenation
