X-Ray

Question 1

What is attenuation?

Answer 1

the reduction of the force/ energy of X-rays

- increases with higher atomic number and density

Question 2

What is the difference between transmission and emission imaging?

Answer 2

Transmission = radiation is directed through the patient. Transmission is collected essentially showing a map of attenuation. Good at showing structure, especially between tissues of different densities or atomic number
Emission imaging = radiation is administered to a patient as a tracer. Emitted radiation is detected outside the patient.

Question 3

What are the different detectors in planar X-ray?

Answer 3

Film hardcopy - film processor with tanks of chemicals. High resolution.
Computed radiology computer copy - digital enhancement and archiving
Digital radiology - flat panel detector, fully digitalised.

Question 4

How are mammography X-rays done?

Answer 4

• use a compression plate to reduce breast thickness, improving the resolution and lowing radiation dose.

Question 5

What is fluoroscopy?

Answer 5

Real-time imaging involving injecting dye into an artery. Allows you to see blood flow inside vessels.

Question 6

Limitations of planar x-ray

Answer 6

• cant distinguish between overlying tissues

- tissues other than those being observed reduce the contrast

Question 7

How is a CT scan carried out?

Answer 7

Patient lays inside the aperture of the machine.
An X-ray tube rotates around the patient very quickly - helical scanning
Fires x-rays each rotation - detected to give image.

Question 8

How can CT be used to measure disease progression?

Answer 8

• measure the size of the left inguinal lmyph node

Question 9

How does nuclear medicine/emission imaging work?

Answer 9

• radioactive tracer is injected - patient emits gamma rays

- imaging depends on metabolism of the tracer.

Question 10

What is gamma camera imaging?

Answer 10

• uses single photon emitting radionuclides - decay with direct emission of gamma rays
• can operate in 2d (planar) or 3d (SPECT)
• most common radionuclide is Tc-99m
• records gamma rays and collects image over time

Question 11

What is SPECT?

Answer 11

• single-photon emission computed tomography

- Acquires up to 64 images from around the head

Question 12

What is FDG?

Answer 12

• the most commonly used tracer in PET scans

- a glucose analogue, enters the cells in the same way

Question 13

How does PET scanning work?

Answer 13

• Injected radionuclides emit a positron as they decay. When the positron meets an electron, there is an annihilation event, where two gamma rays are produced.
• These are detected by a ring of scintillation detectors

Question 14

What combinations of imaging can you do in hybrid imaging?

Answer 14

PET-CT
SPECT - CT
PET-MR

Question 15

Which technique has the best resolution?

Best to worst

Answer 15

• X-RAY
• CT
• PET
• PLANAR- NM
• SPECT

Question 16

Which technique has the best contrast?

Best to worst

Answer 16

• PET
• SPECT
• PLANAR-NM
• CT
• X-RAY

Question 17

What is attenuation correction?

Answer 17

Occurs in PET-CT.

• gamma rays coming from the centre of the patient will travel through more tissue, meaning they are attenuated more
• CT image is used as an attenuation map to correct the PET image.