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NMR > Mark > Flashcards

Mark Flashcards

1
Q

Basis of magnetic resonance

A

RF applied in the X/y plane
B1 rotates at the Lamor frequency
Transfer from B1 to u
Flips from alpha to beta

Each isotope has a unique RF
By tuning the magnetic and gyromagnetic ration, can be tuned for an isotope

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2
Q

Spin populations at rest

A

E = hyBo

NB/NA = exp -E/kbT

Means that to get a high ratio, need big energy and magnetic field

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3
Q

Difference between T1 and T2

A 
T1 = Z recovery. Spin lattice relaxation
T2 = X/y decay. Spin-spin relaxation, energy lost between pairs of spins
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4
Q

NMR raw data transformation

A 
Collected in time domain
Converted to frequency domain
Time domain is induced current detected as magnetisation decays
Known as the FID
Fourier transformation
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5
Q

Lamor frequency equation

A

V = y Bo /2pi

Where y is the gyromagnetic ration and Bo is the magnetic field

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6
Q

Difference between fat and CSF

A

Fat-fast t1 and t2

CSF- slow T1 and medium T2

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7
Q

3 main methods of water suppression

A

Pre saturation
Water gate, 1ppm lost
Excitation sculpting, 0.5ppm lost

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8
Q

Positive markers in lung cancer

Negative markers

A

LDL, VLDL, lipids, pyruvate

HDL, glucose, methanol, citrate, choline, acetate

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9
Q

Prostate cancer

A

In a healthy peripheral zone, ZIPI uptake of Zn inhibits isomerisation of citrate by m-aconitase
Result is high Zn and citrate

In cancer, there is no Zn in, which promotes citrate through the TCA cycle
High levels of lactate
Alanine due to proteolysis (end of anaerobic metabolism)

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10
Q

Metabolic markers used in cancer

A

Metabolic rampage
Glycolysis elevated, but lack of oxidative metabolism
Warburg effect
More acetyl coa promotes fatty acid synthesis
More nucleotides made by the pentose phosphate pathway

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11
Q

How can NMR be used for cancer?

A

Single and combination therapies
Toxicology
Drug dosage
Resistance

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12
Q

FATE NMR

A

Uses glucose with either carbon 2 or 4 C13 carbons
‘Spin labelled’
Carbon. 2- glycolytic and PPP fluxes because DHAP becomes labelled in multiple positions

Carbon4- sole labelled carbon can only reach the first carbon of DHAP

Both follow the fate of pyruvate- but 2 follows citrate and 4 follows malic acid

Most popular label is 1,2 as can cover the glycolysis pathway and remainder

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13
Q

31P metabolomics using MRS

A

Tumour has higher phosphomonoesters
Higher PDE
Lower phopshocreatine

PME used as a marker for neonatal liver-infiltrating neoblastoma

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14
Q

Magic angle spinning

A

Spun at 1-80 kHz
Tilted at 54.74 degrees
Half width = 1/PI T2
Increases T2 so narrows lines

Solids have nuclear dipole coupling, when spun at angle =0
Hd u 3cos^2 theta-1, where at the Magic angle 3cos^2 theta-1 =0
And as the Hd is proportional to 1/T2, this means that when Hd is small that the T2 increases
Zirconium used

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15
Q

HR MAS in metabolism

A

4-6 kHz
Otherwise disrupt cells
Standard NMR

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16
Q

Other MAS methods

A

CRAMPS- combined rotation and multiple-pulse. Polymers and inorganic

DD-MAS- dipole decoupling

CP-MAS- cross polarisation. Non H, membrane proteins and lipids

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17
Q

HR MAS sample prep

A

12-65 uL

Zirconium oxide rotor

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18
Q

HR MAS and genomics

A

An aplastic gangliogliomas
Analyser by gene expression and hr MAS
Microarray
Agreed, multiomics technology

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19
Q

Brain tumour and Kennedy pathway

A

Produces phosphatidylcholine and phsophatidyethanolamine

Choline kinase up regulation increases flux

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20
Q

HR MAS for pathogen study

A

Drug sugar interactions
Mycobacterium smegmatis, c.jejuni and neisseria meningitidis
Drug ethambutol
Showed that emb separates the sugar from the cell wall but can be resigned in mutant

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21
Q

HR MAS and chemotherapy

A

Tumours had increases glutathione, creatine and phospholipids
Lower AAs
Tested the therapies docetaxel and fotemustine

Decreases in hypotaurine and GSH shows drug efflux activated
Can be used to measure drug resistance

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22
Q

Intrinsic contrast parameters

A

Cannot be changed
T1 and T2
Protein density
Flow

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23
Q

Extrinsic contrast parameters

A 
TR time, changes both
TE time, changes T2
Flip angle
TI changes T1
Turbo factor, as echo train increases the signal decreases
B value (gradient duration and interval)
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24
Q

Water and fat weighting

A

T1- water is larger, so the fat will recover quicker and give more signal. Fat will be brighter

T2- water is larger, so fat will decay quicker.

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25
Q

3 things that influence contrast

A

Energy of tissue- tissues that absorb energy have smaller T1 as are quick relaxing

Molecular packing- relaxation is more efficient when tissues are together. Higher density means short T2. Good contrast

Tumbling rate- optimal energy exchange at Lamor freq. t1 is minimum here, so recovery is optimum.

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26
Q

T1 weighting MRI

A

Large angle to saturate
Short TR to maximise sat
Short TE to minimise T2

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27
Q

T2 weighting MRI

A

Short angle
Long Tr
Long TE

28
Q

PD contrast MRI

A

Short angle
Long tr
Short TE

29
Q

Black blood imaging

A

Must be in the slice to be both 90 and 180
Flow phenomenon is called time of flight
After excitation with 90, signals depend on T2
Stationary tissue appears bright

30
Q

Factors that affect black blood imaging

A 
Velocity of flow
Slice thicknes
TE 
Slice orientation
Pre saturation of signal
31
Q

Pre saturation

A

90 pulse before imaging
The first proper 90 then saturates the blood into the -z
180 pulse will put it into +z
Already hypointense in T1 weighting as have a long T1

32
Q

Bright blood imaging

A 
Gradient rephrasing instead of spin echo
Entire imaging volume
Surrounding tissue needs to be saturated 
Imaging techniques are known as MRA
3 types:
TOF-MRA
PC-MRA
CE-MRA
33
Q

TOF-MRA

Determining blood direction

A

Entry slice phenomenon
60 degrees, short repetition
Stationary spins are saturated whereas in flow nuclei are not
Sensitivity best when perddendicular to blood flow

Nuclei entering the slice can be selectively saturated, so the presaturated will appear dark
Allows to determine the flow direction

34
Q

3D or 2D TOF MRA?

A

3D:
Higher signal to noise
Higher res
More tolerant of movement

2D:
Slow blood flow
Wider area coverage

MOTSA- multiple overlapping thin section angiography
Number of small scans to get a wider area, as volume limited by saturation

35
Q

TOF MRA disadvantages

A

Haemorrhaging lesions may mimic vessels
Conversion of oxyhemoglobin to methaemoglobin shorts the T1 time of nearby scans
Area limited by saturation, especially in plane flow

36
Q

Presentation of MRA images

3

A

Maximum intensity projection
Numberical value to each
Brightest pixel in each column
Viewed from two orthogonal directions

Shaded surface display
Treats boundaries between high and low signal as a surface
Solid and 3D

Radial MRA
Rotated and viewed from angle

37
Q

Phase contrast MRA

A

Two bipolar pulses
Stationary are returned to z
Moving pulses will be at the opposite end of the second gradient
Will not be returned to zero so will give signal
Phase advanced again
Applied in 3 axis

Too steep- only slow blood near to the vessels
Too shallow- only fast blood in centre

38
Q

PC MRA flow direction
2D and 3D MRA
Advantages
Disadvantages

A

Advance phase white
Retarded black

3D has better resolution and higher S/N
But does take a lot longer

Sensitive to flow direction and velocity
Good background suppression

Long time for 3D imaging
Sensitive

39
Q

CE-MRA

A

Gd reduces T1 of blood
Allows short can times, breath hold and short angle to saturate non blood T1s
Insensitive to turbulence and in plane flow
Digital subtraction
Gd reduces T1

40
Q

Administering contrast agent

A

Antecubital vein
30ml
RH -> lung -> LH -> arterial -> arterial venous
Could pass through aorta quicker than acquisition

In renal failure causes nephrogenic systemic fibrosis

41
Q

Centric K space filling

A

Central lines first
More scan to increase SN ratio
Shared peripheral
E.g. TWIST

42
Q

Spiral/elliptical k-space filling

A 
Single shot method
One excitation pulse
Train of gradient echoes (echo planar imaging)
Poor SNR but improved by data averaging
Large strain on gradients
43
Q

Optimisation of scan timing

3

A

Best guess- travel time + (injection time/2) - (imaging time/2)
Places scan at central arterial phase
Needs accurate estimate of travel time dependent on patient

Test bolus
3-4ml
Rapid low scans TWIST
Increases background

Automatic triggering
Simple pulse to detect leading edge
6s between leading edge and arterial phase for breath hold
Centric filling

44
Q

How to avoid phase mismapping

A

Swap the phase and frequency encoded axis
Respiratory compensation
Bellows attached and transducer picks up air movement

45
Q

Imaging planes for cardiac MRI

A

Two chamber- parallel to the inter-ventricular septum

Four chamber- perpendicular to

46
Q

Cardiac gating

A

Collection timed from ECG
Prospective gating- triggered by R wave
Single phase prospective- same phase of heart, static image
Trigger window- waits for next cycle
Trigger delay- length of time after R wave before start
Dark and bright blood
Averaging scans for arrythmias

47
Q

Multiphase imaging

A 
Heart physiology and function
Several stages of cardiac cycle
Played as loop
Prospective or retrospective gating
15-25 phases per heart beat to give 40-60 ms temporal resolutions
48
Q

Myocardial tagging

A

Spatial modulation of magnetisation (SPAMM)
Gradients used to null signal from stripes
Movement of grid is used to monitor the ventricular contraction
Measurements of boxes can be used to quantify function of systole

49
Q

What is fMRI?

A

Spotting proton changes in oxygenated and deoxygenated blood
Needs:
Activity
At rest

50
Q

How does fMRI work?

A

Oxygen-haemoglobin - diamagnetic, paired electron, T2 not influenced

Deoxygenated- paramagnetic (unpaired) -> T2 reduced

Observe paramagnetic broadening as the T2 changes
No oxygen -> broad peak

51
Q

BOLD

A

Blood oxygen level dependent
Blood with short T2 gives signal loss or retention
Long TE values (40-70) with echo trains to differentiate broad parts from narrow

52
Q

BOLD brain regions study

A

Faces- visual cortex
Houses- frontal lobes
Also applied to coma patients

53
Q

fMRI chronic stroke

A

Finger rolling
Showed that the brain could be retaught
Increased brain activity

54
Q

fMRI for brain injury

A

Indicate recovery

Looks for focal adhesions for repair and memory

55
Q

Doggy fMRI

A

In humans the same region is used for dogs and humans
Dogs have different areas for dogs and humans
And a. Much wider area
So that although initially they thought the brain was similar, more in depth it is not. So suggests there may be parallel evolution not divergent

56
Q

What is MRS?

A

MRI -> NMR signals
Used for cancer and heart attacks, shows chemicals without biopsies
Can compare normal and abonormal tissue identified by MRI

57
Q

MRS for Alzheimer’s

A

Biochemical changes associated with loss of neuronal integrity
A screen for dementia?
Creatine, choline, NAA. GABA, MI

Predicted by low NAA/Cr and high Cho/Cr and MI/Cr
NAA/Cr indicates mild cognitive impairment -> dementia

58
Q

MRS and magnetic fields

A

Runs 4-7 where MRI is 1-3
Improves resolution
Better to do high res, as GABA peaks can change at low tesla

59
Q

MRS and cancer

Metabolites

A

Diagnostic and monitoring
Choline- increased cellular activity and glial cell proliferation.
Glial cells -> neoplasm
Creatine- increased metabolism
Lactate- anaerobic glycolysis, Warburg effect
Myoinositol- glial hyper trophy and proliferation
N acetylaspartate- reduced suggests brain damage

60
Q

Foetal MRI

A

Planning of surgery
Cerebellum haemorrhage- T1 weighted
Peri ventricular modular heterotopia- fatal
Congenital diaphragmatic hernia- 50% mortality, surgery after birth
Hole in heart

61
Q

Age profiling of children

A

Metabolic fingerprint from urine
Creatine increases with age
H NMR
Creatinine as a disease biomarker

62
Q

Cold shock in CHO cells

A

Lower alanine levels
Lactate levels depend on cell line
Allows to identify rate limiting steps to improve flux
Antibody creation

63
Q

HR MAS biomarkers to grade tumours

New MRS for prostate cancer

A

Can observe by HR MAS for metabolites
Then Gleason score using microscope
GpCho/PCho correlates with % cancer in sample

New MRS can calculate volume and stage without invasion
High choline and low citrate

64
Q

Cardiac MRS study

A

PCr used for energy before ATP is
Means that the PCR/ATP ration drops rapidly in ischemia
Long term low PCR indicative of heart failure

65
Q

Role of fMRI in cognitive neuroscience

Ethical issues

A

Lie detection

Uncommitted voters showed anxiety in the amygdala

NMR (1 decks)

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