Computed Tomography

Question 1

Of all the phases of CT scans, what is the best for detecting calculi?

Answer 1

Unenhanced (non-contrast)

*also get baseline enhancement for renal masses

Question 2

What are the 3 enhancement phases (i.e IV contrast phases) of the kidney

Answer 2

1. Corticomedullary
2. Nephrographic (aka Nephrogenic)
3. Excretory

Question 3

Which IV contrast phase is best for analyzing a renal mass?

Answer 3

Nephrographic

Question 4

What phases are essential/required for full work up of a renal mass?

Answer 4

1. Unenhanced (non-contrast)
   - get the baseline of the mass
2. Corticomedullary
3. Nephrogenic

Question 5

In cases of Contrast induced nephropathy, (CIN) when do you see acute tubular necrosis (ATN)?

Answer 5

24-72 hours after contrast

Question 6

What are preventive strategies against CIN?

Answer 6

• IV fluids before and after contrast
• Steroids at least 12 hours before and q4h and anti-histamine prior to contrast
• N-acetylcysteine may be beneficial

Question 7

What is the Hounsfield unit for water, which we based all other substances against?

Answer 7

HU water = 0

Question 8

Air and fat have HU’s that are what compared to water?

Answer 8

HU air = -1000 (dark black)

HU fat = -20 to -100

Question 9

Compare the HU’s of acute blood vs. clotted blood

Answer 9

HU acute bleed = 30-45

HU clotted blood = > 60 (brighter due to increased Hgb concentration)

Question 10

Bone and metal have HU’s of what?

Answer 10

HU bone = >400

HU metal = >1500 (causes artifact)