Imaging modalities - miscellaneous

Question 1

How long does oral contrast take to opacify the bowel?

Answer 1

90 minutes

Question 2

By how much does a CT abdomen in pregnancy increase the risk of congenital abnormalities, and fatal congenital abnormalities?

Answer 2

Risk of congenital abnormalities after CT abdo in pregnancy is 1:200, and 1:400 of fatal congenital abnormalities. Check this

Question 3

List four features of a lymph node on ultrasound that suggest malignancy?

Answer 3

1. Round shape
2. Size >1cm
3. Hypoechoic/loss of echogenic hilum
4. distinct margins

Question 4

In what trimesters is the use of MRI safest for imaging pregnant women?

Answer 4

The second and third trimesters. Safety in the first trimester is unknown, so use is avoided.

Question 5

What IV contrast agent is used in MRI? When is this mainly used?

Answer 5

Gadolinium, mainly used for vascular imaging

Question 6

List two risks of using gadolinium? What group of patients is at higher risk of these?

Answer 6

1. NSF - nephrogenic systemic fibrosis
2. Interstitial fibrosis affecting kidneys and skin
   People with renal impairment are at higher risk.

Question 7

How much does MRI breast cost? Does this require a contrast agent? How long does it take?

Answer 7

Approx $1200.
Uses gadolinium.
Takes approximately 40 mins.

Question 8

What cases is MRI breast most useful for? (4 examples)

Answer 8

1. Lactating breasts
2. High risk screening
3. Evaluating extent of DCIS
4. Imaging lobular cancers.

Question 9

What is Riggler’s sign?

Answer 9

When you can see both sides of the bowel wall on AXR in the presence of free air/perforation

Question 10

What is Chilaiditi sign?

Answer 10

Rare anomaly involving interposition of the colon (usually hepatic flexure) between the liver and diaphragm. It is usually an asymptomatic radiological sign.

Question 11

What is the differential diagnosis for chilaiditi sign?

Answer 11

pneumoperitoneum

subphrenic abscess

Question 12

What is PET scanning?

Answer 12

Positron emission tomography

A nuclear medicine scan that reflects functional processes in the body

Question 13

List 3 functional principles underly PET scanning?

Answer 13

• Abnormal cellular metabolic activity tends to precede structural change
• cancer cells exhibit enhanced glycolysis
• tumours have increased glucose uptake compared to normal tissues

Question 14

Why do tumour cells have increased glucose uptake compared to normal cells?

Answer 14

they tend to express more glucose membrane transporters

Question 15

What contrast/marker is used in PET scanning?

Answer 15

F-18-FDG
Fluro-deoxy-glucose
This is a radiolabelled analogue of glucose

Question 16

Why is F-18-FDG concentrated in tumour cells?

Answer 16

1. They have increased uptake of glucose, and FDG is a glucose analogue
2. The FDG phosphorylated by hexokinase and then cannot diffuse out of the cell
   … so it becomes concentrated in malignant cells.

Question 17

How does a PET scanner detect FDG?

Answer 17

Positron emission on decay:
As the F-18-FDG decays it releases 2 photons, that travel at 180 degrees relative to one another. These are detected by the scanner which uses them to determine their position of origin.

Question 18

What 4 factors can influence PET scan results?

Answer 18

1. Tissue oxygenation
2. Glucose utilisation
3. Regional blood flow
4. Local inflammatory reaction

Question 19

What is the greatest risk of PET CT?

Answer 19

It has a very high radiation dose.