Imaging in Cancer

Question 1

What is the basic principle of barium studies?

Answer 1

Barium sulphate is a contrast used for outlining the gastro-intestinal tract, the high atomic number of barium absorbs more X-ray photons than surrounding tissues.

Administered through barium meal or barium enema.

Barium appears white in the rasiograph

Question 2

How are CT scans produced?

Answer 2

X-rays produce a digital image of a slice of tissue, computer creates the image

Question 3

What is the hounsfield unit?

Answer 3

Expresses CT numbers in a standard form.

CT numbers express attenuation values of voxels

Question 4

What can be used as an oral contrast agent for a CT scan?

Answer 4

Oral - dilute iodine based contrast - outlines the gastrointestinal tract.

Question 5

What can be used as an intravenous contrast agent for a CT scan?

Answer 5

Iodine based contrast - omnipaque - demonstrate blood vessels or the vascularity of different tissues

Question 6

How does an MRI scan work?

Answer 6

Strong magnetic field aligns the H+ protons in the body in one direction

Radio pulse is applied and turns the nuclei 90 degrees away from the direction of the magnetic field.

Time is taken for the protons to relax and resume their initial alignment with the magnetic field

Image is created by measuring the time taken for the protons to relax to their original position

Lighter molecules take longer to come back to the rest state, higher mass returns to natural alignment quicker

Question 7

What are the MRI indications?

Answer 7

Excellent bone soft tissue detail
Vessels can be demonstrated
Brain, spine and musculoskeletal, abdomen pelvis can all be clearly observed.

Cardiac imaging possible

Does not involve exposure to ionizing radiation

Question 8

What MRI contraindications?

Answer 8

Claustrophobic and noisy

Cannot image patients with pacemakers

Question 9

Name a MRI contrast agent

Answer 9

Gadolinium

Question 10

What is the effect of Gadolinium

Answer 10

Causes changes in local magnetic field and so alters the tissue signal.

Question 11

What is the effect of contrast agents in MRI?

Answer 11

Reduces the time of relaxation of atoms within the body

Question 12

What is the purpose of screening?

Answer 12

Diagnose disease at an earlier stage before symptoms start and where treatment can alter the outcome

Cancer is therefore likely to be easier to treat

Question 13

What does the NHS have screening programmes for?

Answer 13

Bowel
Breast
Cervix

Question 14

What are the WHO principles of screening?

Answer 14

The condition should be an important health problem
There should be a latent stage of the disease
There should be a test or examination for the condition
Test acceptable to the population
There should be a treatment for the condition
Facilities for the diagnosis and the treatment should be available

Question 15

What are the Limitations of screening?

Answer 15

Test should cause no harm
Test should have high specificity and sensitivity
Benefit to the individual should outweigh the cost

Question 16

What is used to screen for breast cancer in women?

Answer 16

Mammograms (x-ray of the breast)

Question 17

What are the pros and cons of population breast screening?

Answer 17

Pros: Early diagnosis and resulting successful treatment. So increased rates of successful treatment since more cancers are found at curable stages

Cons: Overdiagnosis - finding tumours that would never have normally caused harm to the individual - unnecessary cancer treatment
Exposure to harmful radiation
Unnecessary anxiety

Question 18

What can a CT scan be used to see?

Answer 18

The precise location of a tumor, its shape, and whether it is solid or hollow. Although it can give clues as to whether or not a tumor is cancerous, only a biopsy can tell for sure. Unfortunately ,a CT scan is not reliable in helping to find tumors that are less than 2 cm.

Question 19

What is it hard to differentiate between on an MRI scan?

Answer 19

Inflammation and scar tissue from tumors

Question 20

What does a PET scan detect?

Answer 20

Differences in metabolic and chemical activity in the body

LOOKS AT FUNCTION NOT STRUCTURE

Cancer cells divide rapidly and have a very high metabolic activity

Scar tissue has a very low metabolic activity

Question 21

What is the added benefit of the CAT/PET scan combo?

Answer 21

You can clearly see the anatomical detail of the CT and the ability to find small clumps of cancer cells of the PET