Clinical cancer imaging

Question 1

Why is cancer imaging important? 3 things

Answer 1

1. Early diagnosis through screening
2. Staging and location of tumors to guide surgeons and to help plan therapies
3. Therapeutic response and recurrence when patients are followed longitudinally

Question 2

what are 4 problems associated with breast cancer screening

Answer 2

Overdiagnosis, false positives, false negatives, radiation dose causes a small number of breast cancers.

Question 3

What is a barium swallow

Answer 3

Contrast agent

Question 4

How could a barium swallow show a tumour in the intestines or esophagus

Answer 4

CT scan following a barium swallow, you can observe the barium going down the esophagus and through the intestines. If there are areas where the flow of barium is interrupted, this may suggest the presence of a tumor at that location.

Question 5

What is seen in a CT scan during the arterial phase after iodine injection.

Answer 5

Soon after injection, the arterial phase shows iodine in the vessels surrounding the tumour. Shows tumour perfusion.

Question 6

What is seen in a CT scan during the venous phase after iodine injection

Answer 6

The venous phase is after iodine has passed out the blood and through the interstitial spaces before returning back into venous blood. If you image this at the right time, iodine uptake can be seen within the tumour.

Question 7

How can imaging of vascularisation of a tumour by CT help a patient

Answer 7

Helps in determining prognosis but also if a treatment has been effective. For example if a highly vascularised tumour loses contrast then the drug has had an effect.

Question 8

What is a complete response (RECIST)

Answer 8

Disappearance of all lesions

Question 9

What is a partial response (RECIST)

Answer 9

30% decrease in lesions

Question 10

What is a progressive disease (RECIST)

Answer 10

20% increase in lesions

Question 11

What is a stable disease (RECIST)

Answer 11

Small changes that don’t meet any of the other RECIST criteria

Question 12

True or false - Patients with a pacemaker can’t be given a CT scan?

Answer 12

False

Question 13

Rephasing of protons due to tissues during an MRI causes them to recover back to their original precessing frequency faster or slower?

Answer 13

Faster

Question 14

In T1, to protons recover faster in blood or bone, and what is the result of this

Answer 14

T1, protons in the blood take longer to revert back to the original frequency so produce a smaller signal. As a result they are dark in the image, compared to bone which is light.

Question 15

What is the relationship between T1 and T2?

Answer 15

T1 is the inverse of T2

Question 16

Is blood light or dark in a T2 MRI

Answer 16

Blood is light in T2, bone and fat are dark.

Question 17

What is the name of the process used to detect perfusion using an MRI

Answer 17

Arterial spin labeling - Protons are inverted 180 degrees.
Inverted nuclei flow into the imaging slice causing dephasing (darkening of the image)
There is a direct correlation between the amount of darkening and the amount of perfusion.

Question 18

How is diffusion imaging using an MRI relevant to cancer?

Answer 18

In tumours there are areas of necrotic cells which have perforated cell walls. As a result, these areas will exhibit a higher level of diffusion compared to surrounding normal cells. This can be used to determine if a suspected tumour is in fact cancerous.

Question 19

How is a signal produced by PET?

Answer 19

It’s the result of an annihilation event when an electron interacts with a positron which is emitted following nuclear decay.

Question 20

Do positrons used in PET have a short or long half life

Answer 20

Short, often minutes so following production of the positrons, a scan must be completed soon after.

Question 21

What is the result of the annihilation event in a PET scan

Answer 21

2 gamma ray photons emitted at 180 degrees and at 511keV. A ring of detectors measure coincidence events between 180 degrees to produce a tomographic image.

Question 22

Outline the way that 18FDG is used in PET imaging

Answer 22

FDG is taken up by normal glut1 transporters where it becomes stuck. This is because the deoxyglucose is not able to be processed further in the Krebs cycle. In cancer there is an upregulation of Glut 1 transporters and uptake of glucose due to a switch in metabolism which favors glycolysis. So in a PET scan, areas with a high uptake of glucose will be seen as a high uptake of 18FDG suggesting these are tumour cells.

Question 23

What other areas of the body exhibit background 18FDG signalling and why?

Answer 23

Brain and heart as they are highly metabolically active. Bladder and kidneys as this is the route FDG takes to be excreted.

Question 24

FDG can be used as a contrast agent to investigate brain tumours? true or false

Answer 24

False

Question 25

How is iodine used as a tracer in SPECT scans?

Answer 25

Used for thyroid cancer imaging. Iodine is imported into the thyroid as it is required for thyroid hormone production. (It’s imported by a sodium/iodine transporter). In thyroid cancer cases, the rate of uptake of iodine will change.