Cellular pathology: X-Ray, CT, PET Flashcards

1
Q

What is ionising radiation?

A
  • Radiation that causes ionisation, acquiring of a negative or positive charge by an atom as a result of gaining or losing electrons, when it interacts with matter
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the different types of ionising radiation used in medical imaging?

A
  • Gamma rays - Penetrating electromganetic radiation
  • X-rays - Part of the spectrum of electromagnetic radiation
  • Positrons - An electron with a positive charge
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why is ionising radaition used in medical imaging?

A
  • It’s penetrating so can travel through tissues easily and provide a clear image of what’s happeneing inside the body
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe the different effects of ionising radiation on the body

A
  • Indirect effect - ionising radiation can produce free radicals and hydrogen peroxide from the water molecules within our bodies. These species are highly reactive and can cause our cells to mutate
  • Direct effect - ionising radiation can break down DNA of our cells leading to these cells to mutate.
  • Mutation within our cells can lead to a biological response which include cell death, that cell becoming cancerous or a a chnage in the genetic code within DNA of that cell
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the risks of the direct effect of ionising radiation?

A
  • Only at high radiation dose, above threshold, will direct effect cause any damage to an individual
  • Not noticed at usual diagnostic doses
  • Examples of risks of direct effect include:
    • ​​​Erythema (redness of the skin or mucous membranes due to increased blood flow)
    • Hair loss
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the risks of the indirect effect of ionising radiation?

A
  • Risk of cancer induction
  • Risk of genetic change in subsequent population
  • Unlike with the direct effect, the risks of the indirect effect of ionising radiation are proportional to radiation dose, no threshold
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the radaition doses for some of the medical imaging techniques that use ionising radiation?

A
  • Chest X-ray: 0.02 mSv
  • CT pelvis: 7 mSv
  • CT head: 2 mSv
  • PET scan: 10 mSv
  • mSv = microsievert
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the calculated risk of contracting fatal cancer from ionisig radiation?

A
  • 5% per Sievert
  • 1 in 20000 per mSv
  • 1 in 2000 per PET scan
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Briefly explain how the different types of ionising radiation used in medical imgaing are produced?

A
  • Positrons - Emitted following radioactive decay of an unstable nucleus
  • Gamma rays - Emitted as a result of positrons interacting with matter
  • X-rays - Artificially produced in an X‑ray tube
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Give an example of a medical imaging technique that each type of ionising radiation used medical imaging is used for

A
  • Positrons - PET scanning
  • Gamma rays - Gamma camera imaging
  • X-rays - X-ray imaging, CT scanning
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What factors affect the attenuation of X-rays by a particular tissue?

A
  • Atomic number - The higher the atomic number, meaning the higher the no. of protons in the nucleus, the more the X-ray will be attenuated by that tissue
  • Density - The higher the density, the more the X-ray will be attenuated
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the major difference between transmission imaging and emission imaging?

A
  • In transmission imaging the patient lies between radiation source, e.g. X ray tube, and detector and radiation is directed through the patient
  • However, in emission imaging the radiation is administered to a patient in the form of a tracer and the radiation emitted from the patient is detected
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Explain how an X-ray tube works?

A
  • The X-ray tube is a vaccum and within it there’s a:
    • Filament
    • Target (anode)
  • Between the filament and the target (anode) there’s a high voltage difference - this is used to accelerate electrons
  • When X-ray tube is turned on a current will flow through a heating circuit which will cause electrons to be fired from the filament and hit the target (anode).
    • As they travel to target these electrons are accelerated by the voltage
  • When they hit the target it causes an X-ray to be produced
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What elements of an X-ray tube are used to control the X-rays that are produced?

A
  • Voltage controls the speed and therefore the energy of the x-rays
  • Current controls the amount of x-rays produced
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are some of the clinical uses of X-rays?

A
  • Diagnostic X-ray - fracture, chest X-ray
  • Veterinary X-ray
  • Dental radiology
  • Mammography
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

On a chest X-ray if you see a white wedge-shaped area within a lung what might that indicate?

A
  • Indicates that this person may have a pulmonary embolism
  • Only large pulmonary embolisms can be seen on X-ray
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

When performing a mammography why is a compression plate used?

A
  • Compression plate used to reduce breast thickness
  • This Improves resolution of image produced
  • It also allows for a Lower radiation dose to be used as the X-rays have to travel a shorter distance
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Explain how fluoroscopy (real-time X-ray imaging) works?

A
  • Fluoroscopy is usually used during a medical procedure
  • A catheter is fed inside an artery and radio opaque dye is injected
  • During the procedure the patient is kept within an X-ray imgaing machine which produces X-rays continously throughout the procedure
  • The real-time X-ray images produced are usually used to show blood flow inside vessels, which makes it easier to identify areas of occlusion (blockage of a blood vessel)
  • Can also be used to assist with interventions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is coronary angiography?

A
  • Coronary angiography is a technique that uses the process as fluoroscopy to see how blood flows through the coronary arteries
  • The cardiac catheter is fed inside the aorta and the dye is first injected into the aorta
20
Q

What are the treatments available if an area of occlusion is identified in the coronary arteries?

A
  • Balloon angioplasty - specially designed catheter with a tiny balloon is placed in area to of occlusion, then inflated to widen vessel and increase blood flow
  • Insertion of a stent - Re-inforces vessel and allows blood flow to re-start
21
Q

What are some limitations of normal X-rays?

A
  • Cannot distinguish between overlying tissues
  • Tissues other than those being observed reduce contrast in the image
  • Superseded by Computed Axial Tomography (CT)
22
Q

Explain how CT scans work?

A
  • Patient lies within the CT scanner between the X-ray tube and detector
  • As X-rays are produced by X-ray tube it rotates around the patient so that X-rays travel through patient at different angles
  • As this occurs the patient bed also moves up and down
    • These 2 processes allow for “slices” of the patient to be produced
  • This also allows for overlaying tissues to be distinguished
23
Q

What are the differences between CT and MSCT (Multi-slice CT)?

A
  • MSCT is able to produce multiple slices of the patient for every rotation around the patient while CT is only able to produce one
  • MSCT is faster than CT
  • MSCT has more coverage per rotation
24
Q

What are some of the clinical uses of CT?

A
  • Acute diagnosis - e.g. distinguishing between intracerebral haemorrhages and intracerebral blood clots
  • Disease progression - Imaging is used for monitoring response to therapy e.g. chemoterapy in cancer treatment
  • Treatment planning for radiotherapy - CT is used to define area to be treated and the direction of the radiotherapy beams that are used in order to avoid damage to normal tissues
25
Q

What are the 2 types of imaging technique that use emission imaging?

A
  • Gamma camera
    • Uses single photon emitting radionuclides
    • Can operate in 2D (planar) or 3D (SPECT)
  • PET (positron emission tomography)
    • Uses positron emitting radionuclides
    • Always 3D
26
Q

Gamma cameras and PET are both used in nuclear medicine imaging. What are the general pronciples of nuclear medicine imaging?

A
  • Nuclear medicine imaging results in the production of an image of the distribution of a radioactive tracer
  • Nuclear Medicine usually only shows function of area that’s scanned
  • It may reflect anatomy but without metabolism, the tracer will not be taken up
27
Q

As they are radioactive all tracers used in nuclear medicine imaging have a half-life. What is a half-life?

A
  • The time taken for the radioactivity of a radioactive substance to reduce to 50%
28
Q

How can the half-life of a radioactive substance be calculated?

A
  • Calculated using the following equation:
  • A = A0et
    • Where:
    • A = Activity remaining
    • A0 = Initial Activity
    • t = decay time
    • λ = Decay constant
    • λ = ln2/half-life (t1/2)
29
Q

What is the most common radionuclide tracer that’s used in gamma camera imaging?

A
  • Tc-99m (technetium-99m)
30
Q

What is the half-life of Tc-99m?

A
  • 6 hours
31
Q

As as well as a radionuclide a radioactive tracer also has a biological marker, why is this?

A
  • When using nuclear medicine imaging you’e scanning a particular organ so the biological marker is used to target the radioactive tracer to a particular organ
32
Q

Give some examples of radioactive tracers used in gamma camera imaging and the organs they’re used to image

A
  • Tc-99m MDP - bone scans
  • Tc-99m DTPA - kidneys
  • Tc-99m White Cells - infection/inflammation
33
Q

How can gamma camera imaging be used to diagnose cancer (metastatic disease)?

A
  • For a cancer that has infiltrated into bone you can administer the Tc-99m MDP radioactive tracer and then place the person into a gamma camera
  • The image produced will show the bones as dark which indicates that bones are they only area of the body that metabolise the Tc-99m MDP
  • If you see small black spots that show up darker than the normal bones it means the person has metastases within their bones
  • This is because the metastases have a greater metabolic rate than normal bone and so metabolise the Tc-99m MDP more and therefore these areas show up darker than normal bone
34
Q

Explain how a dynamic renal transplant scan works

A
  • Gamma camera positioned above the patient
  • Tc-99m DTPA injected Intravenously
  • Tc-99m DTPA taken up by kidneys
  • Gamma camera records gamma rays produced via radioactive decay of Tc-99m DTPA and collects image over time
  • These images are used to produce a functional time curve of the transplanted kidney to see if it will function normally or if it’s rejected
35
Q

What is SPECT (Single-photon emission computed tomography)?

A
  • It’s a nuclear medicine imaging technique that uses a radioactive tracer administered to the patient to detect gamma rays and produce an image
  • The detector used rotates around the patient and produces transaxial slices which are used to produce a 3D image
36
Q

How can SPECT be used to diagnose someone with parkinson’s disease?

A
  • Administer the radioactive tracer Ioflupane (I-123 FP-CIT) to the patient
  • SPECT scan is then performed to view the patients brain
  • The image produced looks at the amount of binding to the dopamine transporters on the neurons within the brain by the Ioflupane
  • In Parkinson’s disease you will see reduced uptake in the Putamen of the Ioflupane which differentiates it from an essential tremor
37
Q

What is the major difference between the way radiation is produced by PET and by Gamma cameras?

A
  • In PET a positron within the radioactive tracer will collide with an electron in our bodies annihilating both
  • This produces 2 gamma rays at 180o to each other
  • However, with gamma cameras the radioactive tracer will only produce 1 gamma ray
38
Q

What is the most common radioactive tracer used in PET scans?

A
  • FDG (fluorodeoxyglucose)
39
Q

What is FDG and why is it used as a radioactive tracer in PET scans?

A
  • FDG is a glucose analogue which enters cells in the same way as glucose
  • Good reflection of the distribution of glucose uptake and phosphorylation by cells in the body
  • This is because after phosphorylation FDG-6P, unlike G-6P, is unable to take part in glycolysis and so stays within the cell
40
Q

Explain how a PET scanner works

A
  • A ring of scintillation detectors supported in a fixed gantry are used to detect gamma rays produced from radioactive tracer inside the patient
  • Operated in “coincidence mode” - only photons emitted from an annihilation event are recorded
41
Q

Explain the concept of PET coincidence

A
  • 2 gamma rays originate from one annihilation event
  • Both are detected within a short time (a few ns)
  • Defines ray path for subsequent reconstruction of image
42
Q

How can a PET scan be used to diagnose types of neurodegenative disease?

A
  • FDG administered to patient and then a PET scan of that patients brain is performed
  • FDG is taken up by cells of the brain and reflects metabolic activity
  • In Alzheimer’s disease you’ll see hypometabolism, mostly in temporal and parietal regions of brain - FDG taken up more in these areas
  • In Pick’s disease you’ll see fronto-temporal hypometabolism - FDG taken up more in these areas
43
Q

Most modern scanners are hybrid scanners, name some of the different combinations that mae up hybrid scanners

A
  • PET-CT
  • SPECT-CT
  • PET-MR
44
Q

Why does attenuation correction need to occur in a PET image?

A
  • Gamma rays originating from the centre of the patient will travel through more tissue which mean they are attenuated more
45
Q

How is attenuation correction performed?

A
  • A CT image of same area scanned using PET is used as an attenuation map to correct the PET image