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SEM 4:Cellular Pathology > X-ray, CT, PET > Flashcards

X-ray, CT, PET Flashcards

1
Q

What is ionising radiation?

A

Radiation that causes ionisation when it interacts with matteras it adds charge to particles

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2
Q

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

A
  • Gamma rays

- X-rays

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3
Q

Why is ionising radiation used?

A
  • Penetrating into the body
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4
Q

What is action of direct ionising radiation?

A
  1. When the ionising energy interacts with the cell directly, it causes DNA damage and leads to a mutation.
  2. This can lead to death by promoting apoptosis.
  3. It can lead to cancer which is abnormal proliferation of the cell, or it can not lead to any change apart from the DNA sequence.
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5
Q

What is the action of indirect ionising radiation?

A
  1. When the ionising energy interacts with water molecules (H2O), it breaks it down into free radicals which are very reactive.
  2. These then acts on the DNA in cell leading to a mutation.
  3. This can lead to death by promoting apoptosis, it can lead to cancer which is abnormal proliferation of the cell, or it can not lead to any change apart from the DNA sequence.
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6
Q

What are the direct effects of radiation damage and risk?

A
  • Only at high radiation dose, therefore no damage is normally seen at usually diagnostic doses.
  • Very high radiation levels beyond the threshold effect to see the damage
  • Damage includes erythema and hair loss
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7
Q

What are the indirect effects of radiation damage and risk?

A
  • Risk of cancer induction, which is proportional to the level of radiation exposure
  • This means that higher the exposure, the higher the chance of cancer.
  • There is no threshold limit like in direct effects.
  • Risk of genetic change in subsequent population
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8
Q

What are positrons?

A
  • Positive electrons interact with matter to create gamma rays
  • Used in PET scanning
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9
Q

What are gamma rays?

A
  • Rearrangement of the nucleus
  • Penetrating radiation
  • Gamma Camera Imaging SPECT
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10
Q

What are X-rays?

A
  • Very similar to Gamma rays
  • Spectrum of electromagnetic radiation
  • X-ray imaging e.g. radiographs, CT
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11
Q

What is the difference between positrons, gamma rays and x-rays?

A

In positrons and gamma rays, the patients are administered with radioactive traces which will be emitted all the time all around. X-rays howver, are artifically produced in an X-ray tube.

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12
Q

Why is the attenuation of the X-ray important?

A

It increases with higher atomic number and higher density. Therefore, in bone, there is almost no attenuation which means the signals do not go through, this is why it comes up as white on the X-ray. However, in the lungs which are mostly air, the signals go through easily and therefore they show up as black.

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13
Q

What is transmission imaging?

A
  1. Radiation is directed through the patient.
  2. A transmission map collected is an attenuation map.
  3. Therefore, it looks at how much signal is absorbed by the tissue.
  4. It is good at showing structure, especially between tissues of different densities or atomic number.
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14
Q

What is emission imaging?

A
  1. The radiation is administed to a patient in the form of a tracer.
  2. Emitted radiation is detected outside the patient.
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15
Q

What are the elements of an X-ray?

A
  • Elements of a tube are filament, target and a vacuum
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16
Q

Describe the action of X-ray

A
  1. Between the filament and the target, there is a voltage difference which accelerates with energy.
  2. When the machine is switched on, a heating circuit is set up, which causes the filament to fire electrons at the target.
  3. These electrons will then produce a beam of X-ray.
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17
Q

How is the X-ray beam controlled?

A
  • High voltage controls the energy of the of the X-ray
  • Current controls, control the amount of X-ray. This means that we have control over the amount of energy of X-rays produced.
  • The machine can be switched on and off meaning only the X-ray is produced when the tube is in action.
18
Q

What fractures can X-ray be used to diagnose?

A
  • Clavicle
  • Proximal phalanx of the index finger
  • Radius/ulna
19
Q

What can an X-ray be used to diagnose?

A
  • Dental radiology
  • Fractures
  • Chest X-ray
  • Mammography
20
Q

What can X-rays diagnose in the chest?

A
  • Lung cancer
  • Pulmonary embolism - wedge shapes defect
  • Only large pulmonary embolism however, can be seen on an X-ray
21
Q

What is a mammography?

A

X-ray of the breast tissue that contains compression plates to reduce the breast thickness. It can improve resolution and lower the radiation dose. This is why it is used as a screening tool.

22
Q

What is real time X-ray?

A

Fluoroscopy

23
Q

How does a Fluoroscopy work?

A
  1. A catheter is fed inside an artery and radio opaque dye is injected.
  2. It shows blood flow inside vessels and can be used to assist with interventions.
  3. This helps identify areas of occlusions.
24
Q

Give an example of a fluoroscopy and how it works

A

A coronary angiography

  1. Real time imaging using an image intensifier called fluoroscopy
  2. A cardiac catheter is fed inside the aorta.
  3. The radio-opaque contrast agent is used to identify areas of occlusion
  4. Treatment may be either balloon angioplasty or insertion of a stent.
25
Q

What are the limitations of planar X-ray?

A
  • Cannot distinguish between overlying tissues
  • Tissues other than those being observed reduce contrast in the image
  • This is compromised by tomography which is now CT
26
Q

What is a CT scanner?

A
  • A rotating X-ray tube which is able to identify 3D slices
  • The machine is made of X-ray beam, fan beam, detectors and aperture
  • the patient sits in the aperture and the X-ray beam rotates around them.
27
Q

What are the types of scanning that an X-ray uses?

A

Helical scanning:

  • this is also known as spiral scanning
  • continuous rotation and every rotation one image is made
  • it moves along the patient

Helical MSCT:

  • More advanced Helical scanning
  • However, now technology has advanced that now multiple images are taken per rotation
  • This is known as multi-slice and is a faster scan
  • This means there is more coverage at each rotation
28
Q

When is a CT used for urgent diagnosis?

A

Required if a patient has a haemorrhage or a clot
This is important because depending on the pathology, you can administer the drugs which have opposite effects. With the X-ray, you can’t tell but with a CT you can.

29
Q

How can a CT be used to identify disease progression?

A

It can be used to measure and monitor response to therapy such as measurement of the size of the left inguinal lymph node shows progression of disease.

30
Q

How can a CT be used to define area to be treated?

A

CT can show the direction of the radiotherapy beams that are used. This is so normal tissues don’t get damaged. External beam radiotherapy irradiates normal tissue as well as tumours. Multiple beams are used to spare normal tissue.

31
Q

How does emission imaging work?

A
  • Involved in nuclear medicine
  • Injecting radioactive material which the patient emits out (the gamma rays)
  • Not the same as imaging but involves looking at the emission of the patient
  • The image depends on the metabolism of the tracer
  • This is why it is functional imaging because it measures the functionality of an organ
32
Q

What camera is used in emission imaging?

A

A gamma camera

  • Using a single photon emitting radionuclides
  • Detects the gamma rays the patient gives off
  • Can operate in 2D (planar) or 3D (SPECT)
33
Q

What is an example of emission imaging?

A

PET (Positron emission tomography)

34
Q

What is PET?

A
  • Uses positron emitting radionucleotides
  • Always 3D
  • If the area highlighted in PET scan is bright, that means there is high uptake of the injected material, meaning there is high metabolism in that area and therefore the functionality is high.
35
Q

Why is it important to consider radioactive delay when working with radioactive material?

A

Overtime, the radioactive material will get weaker and smaller with time. It decays according to half-life.

36
Q

What is half-life?

A

This is the time taken for a radioactive material to reduce its radioactivity by 50%.

37
Q

What is the most common radionucleotide?

A

Technetium-99 (Tc-99)

  • Half-life of 6 hours
  • When used, it is paired with a biological molecule that is specific to a certain organ to find out the functionality of a certain organ
  • Good for detecting metastasis in cancer
38
Q

How is Tc-99 used in scans?

A
  • In bone scan, it is Tc-99m MDP
  • In kidney scans, it is Tc-99m DTPA
  • In infection or inflammation, it is Tc-99m white cells
39
Q

What is the difference between PET and nuclear medicine?

A

Between PET and nuclear medicine is that in PET 2 gamma rays are given off.

40
Q

What is hybrid medicine?

A

When the imaging techniques are combined:

  • PET-CT shows the exact location of the hot spot
  • SPECT-CT: most common
  • PET-MR: nonionizing
41
Q

Compare the dose, cost, resoultion and contrast of different techniques

A

Planar X-ray: Dose and Cost are Low; Resolution are very good and Contrast is poor

CT: Dose is high; Cost is medium, resolution good and contrast good.

Planar Nuclear Medicine: Dose Medium, Cost Medium, Resolution Poor and Contrast Good

SPECT: Dose Medium, Cost High, Resolution Very Poor and Contrast Very Good

PET: Dose High, Cos Very High, Resolution Medium and Contrast V. Good

SEM 4:Cellular Pathology (13 decks)

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