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Techniques of Molecular Medicine > Imaging techniques > Flashcards

Imaging techniques Flashcards

1
Q

What is a preclinical modality?

A

Related to modalities investigating animal models

Pre-therapeutic

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2
Q

Which pre-clinical modalities can imaging techniques be applied to?

A

Neurology

Oncology

Cardiology

Cell tracking

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3
Q

What can clinical imaging be used for?

A

Diagnosis

Prognosis

Determine the location of the disease

Monitor the response to therapy

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4
Q

What can preclinical imaging be used for?

A

Validating clinical imaging methods - confirm using histology

Interpreting mechanisms of human disease and therapy - look at uptake of therapeutic cells, combine with other imaging technique to look at therapeutic response

Developing new clinical imaging technology

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5
Q

What is light?

A

A form of electrical radiation

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6
Q

What are the two states light can be found?

A

At some wavelengths it takes form in visible light

At some wavelengths it takes a form of radiation we cannot see

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7
Q

What type of light are X-rays?

A

Short wavelengths

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8
Q

Why can X-rays be used to observe the body?

A

Some X-rays are absorbed by the body

Some X-rays are attenuated by the body

Bones contain calcium, making them denser than other tissues = shadows

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9
Q

What are X-rays usually used for?

A

Revealing fractures

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10
Q

What are CT scans?

A

Multiple cross-sectional images of the body using X-rays

Computer processing techniques bring them together

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11
Q

How are CT scans better than X-rays?

A

More detailed

Can reveal bones, tissues and organs

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12
Q

How do CT scans produce more detailed images than X-rays?

A

X-rays use a fixed tube that sends X-rays in one direction

CT scanner uses a motorised X-ray source that shoots beams of X-rays as it revolves around the patient

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13
Q

How is image reconstruction of a CT carried out?

A

Digital X-ray detectors detect the signal

These are found opposite to the X-ray source

As the X-ray passes through the patient, they are picked up by detectors and transmitted to a computer

2D image slices are stacked together into 3D images

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14
Q

What are the advantages of CT scans?

A

Great bone-soft tissue contrast

High spatial resolution

Whole body coverage

Non-invasive

Cheap compared to MRI

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15
Q

What are the limitations of CT scans?

A

Ionising

Limited soft tissue contrast

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16
Q

Why are CT scans often used in neurology?

A

Cheaper than MRI

Broad diagnosis of neurological disorders

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17
Q

What are ways to improve CTs?

A

Contrast agents

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18
Q

Definition of radioactivity

A

Process in which unstable atomic nuclei spontaneously emit ionizing radiation

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19
Q

What type of scan is a PET scan?

A

Nuclear scan

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20
Q

What techniques do PET scans use to obtain an image?

A

Radioactive techniques

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21
Q

What does PET stand for?

A

Positron Emission Tomography

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22
Q

What are alpha particles?

A

He nuclei

Large

Don’t travel far in space

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23
Q

What are gamma rays?

A

Highly energetic photons

Similar properties to X-rays

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24
Q

What are beta particles?

A

Electrons

Don’t travel far

Absorbed by the body

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25
Q

What are positrons?

A

Antimatter of electrons = positive electron

Similar properties to electrons

Don’t cause damage until they collide and cause annihilation

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26
Q

What is annihilation?

A

When a positron and an electron collide

Causes the release of two gamma rays at 180 degrees from one another

Allows to pinpoint the place in the body where annihilation occurs

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27
Q

How do PET scans produce images?

A

Uses positrons and electron interactions

Tracers are made up of carrier molecules covalently bonded to radioactive isotopes

The gamma rays 180 degrees apart formed through annihilation are detected by coincidence

Detectors measure these photons and use the information to create a 3D image

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28
Q

How are tracers administered to the body?

A

Intravenously

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29
Q

Advantages of PET scans

A

Sensitive (nM-pM)

Half-life of tracers is long (20 minutes - few hours)

Large range of tracers

30
Q

Disadvantages of PET scans

A

Single signal

Resolution is relatively low

Ionising radiation

High cost due to the use of tracers

31
Q

What do radiotracers target?

A

Biomarkers

32
Q

What are biomarkers?

A

Anything biological that is of interest in disease states

33
Q

What criteria must a target fulfill in order to be considered a biomarker?

A

The target should be biologically informative

The target must be differentially expressed over the background

The unbound radiotracer should be cleared quickly by the body

The radiotracer must be delivered to and specifically interact with the target

Background activity should clear within the lifetime of the radioactivity : contrast

34
Q

Examples of multimodal imaging in PET

A

PET-CT

PET-MRI

35
Q

Uses of PET-CT and PET-MRI

A

CT dosen’t show biochemistry of disorder

PET retained in tumour cells show the regions of cancer

CT = anatomy 
PET = glow of cancer cells
36
Q

How can PET be used to image cancer?

A

Through cancer metabolism

Tumour cells have enhanced metabolic activity, as both glycolysis and oxidative phosphorylation are turned on

37
Q

Example of PET scan tracer used in cancer

A

FDG

38
Q

What is FDG?

A

Modified form of glucose with unstable fluorine 18 used as a radioactive tracer

Since FDG can no longer undergo metabolic degeneration, it is trapped inside the tissues

39
Q

What is the distribution of FDG?

A

Brain - takes up 60% of glucose in normal functioning

Salivary

Myocardium

Renal excretion

40
Q

Applications of FDG in oncology

A

Diagnosis

Staging

Response monitoring

41
Q

What are the problems with FDG?

A

Cannot detect tumour types in organs with glucose as primary source of energy (prostate, brain cancer)

FDG is taken up by inflammatory cells

42
Q

What is the goal of future biomarkers?

A

Aim at complex biochemical pathways involved in cancer metabolism

Try to find associated radiotracers

43
Q

What do MRI use?

A

Protons which are abundant in the human body

Manipulate the magnetisation of the hydrogen protons to create an image

44
Q

What is the major source of protons in the body?

A

Water

45
Q

What are the three components of an MRI machine?

A

A big magnet (3T in hospitals, 9.4T preclinically)

Radio frequency pulse transmitter and receiver

Magnetic field

46
Q

Explain how MRIs work

A
  1. All protons spin, creating a small magnetic charge
  2. When a strong magnetic field is introduced, the protons align with the field
  3. The MRI generates a stable magnetic field parallel to how the patient lies
  4. The MRI technician then introduces a radiofrequency pulse using a radiofrequency pulse transmitter in the opposite direction to the magnetic field
  5. This disrupts the proton and forces it either into a 90 degree or 180 degree realignment
  6. Since the radiofrequency pulse push the proton against its nature, once the force is turned off, the protons realign with their magnetic field in a process called precessing
  7. As the nuclei are precessing, there is release of electromagnetic energy
47
Q

How does MRI distinguish between tissues?

A

Detection of the electromagnetic energy as they precess

Differentiation of the tissues based on how quickly they release energy after the pulse is turned off

48
Q

What does the Larmor equation explain?

A

The magnetic field strength emitted from the CT machine increases with distance

49
Q

What is the importance of the Larmor equation?

A

Allows to differentiate between the front and back of the brain

The lower magnetic frequencies come fro the front of the brain

50
Q

What is another name for precession?

A

Relaxation

51
Q

Why do different tissue types have different relaxation?

A

Relaxation is determined by the environment of the water molecules

52
Q

What does T1 measure?

A

The time required for the spins to go back to their original axis (applied magnet)

Water spins quickly = more time needed to go back to axis = darker T1

Lipids spin slowly = more time needed to go back to axis = lighter T1

53
Q

What does T2 measure?

A

The coordination of the H+ spins

Water spins quickly = quicker for the spins to be random = lighter T2

Lipids spin slower = more time needed for spins to be random = darker T2

54
Q

What are the advantages of MRI?

A

Great soft tissue contrast

High spatial resolution

Non-invasive

Non-ionising

Can image structure and function

55
Q

What are the disadvantages of MRI?

A

Expensive

Can lack specificity

Lack of temporal resolution

56
Q

What is functional MRI?

A

Indirectly measures neuronal firing

57
Q

What is measured in fMRI?

A

NOT measure neuronal firing

But rather the blood flow changes that happens in response through the neurovascular coupling in the brain

More active brain regions = more blood flow

58
Q

What signal is measured in fMRI?

A

BOLD

Blood Oxygen Dependent Signal

BOLD increases with neronal firing

59
Q

How is fMRI useful?

A

Differences in the T2 signal between oxygenated and deoxygenated blood

T2 of oxygenated is longer than T2 in deoxygenated blood

60
Q

What is requires to capture the BOLD signal?

A

Fast imaging

Gradient-Echo Planar Imaging

61
Q

What type of system underlies the ultrasound?

A

Acoustic based system

Works between 1-100 mHz

62
Q

What is needed to carry an fMRI out?

A

Task - neuronal stimuli

Increased neuronal firing

Vessel dilation

Increased cerebral blood flow from the baseline

Increased BOLD signal

63
Q

Describe how an ultrasound works

A

Transducer uses an array of pizoelectrical crystals

These vibrate when an electric signal is applied

Produce a high frequency sound or compressional waves called ultrasounds

Crystals also work in reverse, producing electric signals when sensing high frequency of compressional sounds

64
Q

What ate sound waves?

A

Propagating fluctuations in pressure, density, temperature and particle motion

65
Q

How does an ultrasound use sound waves to create an image?

A

Some tissues with high densities echo sound waves

Some tissues with lower densities allow sound waves to pass through the body

The echoed sound waves are captured by the pizoelectric crystal, transducing the signal into an electric one

66
Q

What does ultrasund measure?

A

The boundaries between materials which have different acoustic impedance

67
Q

What changes the electric signals into points of brightness on the image?

A

Computer

68
Q

What is the image formed by an ultrasound called?

A

A sonogram

69
Q

What allows a sonogram to form a real time motion?

A

Crystals are repeatedly activated many times so a complete image frame is completed 20 times per second

70
Q

What are sonograms used for?

A

Looking at babies during pregnancies

Heart during cardiac investigations

71
Q

What are the advantages of ultrasound?

A

Cheap

Portable

Non-invasive

Non-ionising

72
Q

What are the disadvantages of ultrasound?

A

Spatial resolution and contrast

Depth

Cannot image the adult brain because of the skull

Techniques of Molecular Medicine (12 decks)

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