7.7 Imaging

Question 1

• Who discovered the properties of X-rays?

Answer 1

Willhelm Conrad Roentigen in 1895

Question 2

What are X-rays and how are they generated?

Answer 2

• Part of the EM spectrum, very short wavelength (0.1-1 angstrom units)
• Generated by high energy electrons striking a tungsten target within a vacuum tube

Question 3

What are the different types of imaging?

Answer 3

• Plain X-ray
• Barium radiology
• Ultrasound
• Angiography
• Computed tomography (CT)
• Magnetic resonance imaging (MRI)

Question 4

How do X-rays work?

Answer 4

• Transmitted beam is recorded on an X-ray film
• Image phosphor read by a computer (CR)
• Direct digitisation (DR)
• Image intensifier
• Stored on the picture archiving and communication system (PACS)

Question 5

What are the advantages of plain X-rays?

Answer 5

• Quick
• Cheap
• Great detail
• Widely available

Question 6

What are the disadvantages of plain X-rays?

Answer 6

• 2D representation only

Question 7

How are the risks of diagnostic radiology managed?

Answer 7

• Doses are kept As Low As Reasonably Achievable (ALARA)
• Radiation techniques should be avoided in pregnant and potentially pregnant women
• Non-radiation techniques should be used where possible and appropriate

Question 8

What units are used to measure effective doses of radiation?

Answer 8

mSv (milli-Sieverts) - lifetime risk of fatal cancer 5-5.9% per Sv - there is a small risk, but it is managed

Question 9

What is the frequency used in high frequency ultrasound?

Answer 9

2-15MHz

Question 10

What is doppler ultrasound techniques?

Answer 10

Use the doppler effect to measure the movement and volume of blood through veins and arteries

Question 11

What are the advantages of ultrasound?

Answer 11

• High quality information about soft tissues
• No ionising radiation
• Inexpensive (5-50% cost of a CT)
• Flow information available
• Easily portable and lots of variable sizes

Question 12

What are the disadvantages of ultrasound?

Answer 12

• Gas and bone block US beam
• Obesity degrades image quality
• Operator dependant
• Pixel brightness is not quantitative

Question 13

What is scintigraphy?

Answer 13

Where a scintillation counter or similar methods are used to obtain images of organs that have taken up radioactive tracers, or records of their activity.

Question 14

What is the most common radionucleotide used in scintigraphy?

Answer 14

Technetium - 99m

Question 15

What are the principles of scintigraphy?

Answer 15

• Radiation emitting
• External solid state detector
• Data collection, then image generation and display

Question 16

Why is ^99m Tc used?

Answer 16

Short half life, but long enough to allow for uptake and detection within the body (6 hours)

Question 17

• What is bone scintigraphy?

Answer 17

A method of viewing bones as ^99m Tc is taken up by osteoblasts, just need to wait for the soft tissue phase to pass. Take image 3-4 hours after injection.

Question 18

• What else can scintigraphy be used for?

Answer 18

Renal imaging - able to detect whether kidneys are obstructed or not

Question 19

What is PET imaging?

Answer 19

Positron Emission Tomography

• A radioactive dye is ingested that accumulates at areas of increased metabolic activity
• Dye emits positrons that will annihilate with electrons and release photons which can then be detected

Question 20

What is PET-CT?

Answer 20

This is where PET and CT scans are combined together in a POWERFUL diagnostic tool

Question 21

• Who created CT??

Answer 21

Godfrey Hounsfield, won the Nobel prize in 1979

Question 22

What is CT?

Answer 22

Computed Tomography

• Attenuation of transmitted X-rays measured by electronic detectors
• Produces detailed images of internal structures, including bone and soft tissue

Question 23

What is multi-slice CT?

Answer 23

This is where multiple CT solid state detectors rotate around the patient (0.5s rotation speed, 0.5-0.625mm slice thickness).

Question 24

What units are used in CT?

Answer 24

Hounsfield units

Question 25

What are the HU principles for CT?

Answer 25

Bone: +1000 HU Water: 0 HU Air: -1000 HU

Question 26

What is MRI?

Answer 26

``` Magnetic Resonance Imaging - 1.5 Tesla (30000x Earth's field) - Radiofrequency of 63.9MHz - 2D and 3D images A large magnet aligns the protons of hydrogen atoms within the body, then the radio waves causes them to rotate. Once turned off, the protons relax and emit radio waves which can be picked up by the detectors, forming an image - different hydrogen atoms in different tissues have different energies, resulting in different results/colours and consistencies on the image. ```

Question 27

What are the basics of MRI?

Answer 27

- High strength magnet - Shim coils - Gradient coils - Radiofrequency coils - Computers are used to control gradient and RF coils, reconstruct images - Creates both 2D and 3D images

Question 28

What is functional MRI/fMRI?

Answer 28

A variation of MRI that looks at blood flow, as oxyHB and deoxyHB have different signal intensities - can be used to see which areas of the brain are used to control different actions, as when activated will have a higher blood flow to that area.

Question 29

What is x-ray attenuation?

Answer 29

The reduction of intensity of the beam as it is absorbed by/transverses matter.

Question 30

What are the colours of different tissues in CT and x-ray?

Answer 30

Bone: White (absorbs most) Fat: Varied shades of grey Soft tissues: Varied shades of grey Air: Black (absorbs least) CT works on x-ray principles so same colours seen

Question 31

What is radiography?

Answer 31

The use of ionising and non-ionising radiation in imaging and viewing the internal forms of objects.

Question 32

What is angiography?

Answer 32

A method of imaging the inside/lumen of various body cavities, in particular blood vessels and chambers of the heart. Uses x ray imaging - contrast agents are used to allow the lumen to show up

Question 33

What are contrast agents?

Answer 33

Substances used to increase contrast of different structures within the body, absorbs or alters electromagnetism or ultrasound, resulting in a different colour seen in the screen.

Question 34

What are radiopharmaceuticals?

Answer 34

Substances used for imaging that emit radiation themselves, so are able to be viewed using specific detectors (almost always gamma radiation).

Question 35

What is the main use of radiography/x-rays?

Answer 35

Most frequently used to image bones, but chest x-rays are also common.

Question 36

What is the main use of CT scans?

Answer 36

To take highly detailed images of the brain and other internal soft tissues.

Question 37

What is the main use of ultrasound?

Answer 37

Imaging and visualising (done live) of foetuses and other soft tissues when high quality is necessarily needed.

Question 38

What is the main use of nuclear medicine?

Answer 38

Imaging of digestive systems or other circulatory systems, often to look for blockages