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Core > Nuclear: Genitourinary > Flashcards

Nuclear: Genitourinary Flashcards

1
Q

What are the main radio tracers used in renal scans?

A
  • Tc-99m DTPA
  • Tc-99m MAG3
  • Tc-99m DMSA
  • Tc-99m GH (glucoheptonate)
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2
Q

Which is the best radiotracer for estimating GFR?

A

Tc-99m DTPA

Note: Almost all of this radiotracer is filtered (not secreted) by the kidneys; however, since ~5% is not you are still slightly underestimating GFR.

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3
Q

What is the critical organ for Tc-99m DTPA?

A

Bladder

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4
Q

What is the critical organ for Tc-99m MAG3?

A

Bladder

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5
Q

What is the critical organ for Tc-99m GH (glucoheptonate)?

A

Bladder

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6
Q

What is the best radiotracer to estimate effective renal plasma flow?

A

Tc-99m MAG3

Note: Almost all of this radiotracer is secreted.

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7
Q

Which radiotracer is better for pts with poor renal function: DTPA or MAG3?

A

MAG3 is concentrated better by kidneys with poor renal function

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8
Q

Nuclear renal scans are usually obtained posteriorly. When would you want to obtain anterior images?

A
  • Transplanted kidney
  • Horseshoe kidney
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9
Q

What are the indications for a dynamic (functional) nuclear renal study?

A
  • Suspected obstruction
  • Evaluate differential function
  • Suspected renal artery stenosis
  • Suspected complication from renal transplant
  • Suspected urine leak
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10
Q

What are the 3 phases of a dynamic nuclear renal study?

A
  • Blood flow phase
  • Cortical phase
  • Clearance phase
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11
Q

Differential for symmetrically decreased renal flow on dynamic nuclear renal study

A

Technical error (e.g. poor bolus)

Note: Most pathologies will cause asymmetric flow problems.

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12
Q

Differential for asymmetrically decreased renal flow on dynamic nuclear renal study

A
  • Renal artery thrombosis
  • Renal vein thrombosis
  • Chronic high grade obstruction
  • Acute pyelonephritis
  • Acute rejection (transplant)

Note: ATN, interstitial nephritis, and cyclosporin toxicity will all have normal perfusion/flow.

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13
Q

Which phase of a dynamic nuclear renal study is used to calculate differential renal function?

A

The cortical (parenchymal) phase, after flow and before tracer reaches the collecting system

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14
Q

Where should you place the background area of interest for a dynamic nuclear renal study?

A

A background area that is not overlying the liver or spleen

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15
Q

How can you quantify tracer retention in the renal cortex?

A

20/3 ratio:

(peak count at 20 min)/(peak count at 3 min)

Note: The normal value should be < 0.8.

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16
Q

How do you decide whether to give furosemide during a dynamic nuclear renal study looking for obstruction?

A

If there is still tracer activity in the kidneys/collecting system at 30 minutes, then give the furosemide

Note: If there is true obstruction, the retained tracer won’t clear. If there is a dilated but non obstructed collecting system, then at least 50% of the remaining tracer should clear within 10-20 min of giving furosemide.

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17
Q

When should you call “no obstruction” on a dynamic nuclear renal study?

A

Radiotracer clears from collecting system without the need for Lasix

OR

> 50% reduction in radio-tracer from collecting system within 10 min of giving Lassix

Note: If there is less than 50% reduction after 20 min, call obstruction. Between 10-20 min to reach the 50% threshold is considered indeterminate.

18
Q

Common causes for false positive for obstruction on a dynamic nuclear renal study

A
  • Poor response to Lasix (e.g. poor renal function at baseline or dehydration)
  • Reservoir effect (very dilated renal pelvis)
  • Back pressure effects (full or neurogenic bladder)
19
Q

How long should it take 50% of collecting system radiotracer to washout after giving Lasix?

A

<10 min

Note: >20 min is considered obstruction. 10-20 min is considered indeterminate (most often due to a very dilated renal pelvis).

20
Q

How is a dynamic nuclear renal study performed to look for renal artery stenosis?

A

Standard dynamic study followed by a repeat study with an ACE inhibitor (e.g. captopril)

Baseline dynamic study with 1/2 dose captopril followed by full dose captopril study

Note: Normally there should be no difference between the baseline and full dose captopril studies. If captopril causes reduced renal function, this is suggestive of renal artery stenosis.

21
Q

Which radiotracers can be used for a renal artery stenosis dynamic nuclear renal study?

A
  • Tc-99m DTPA
  • Tc-99m MAG3
22
Q

How will renal artery stenosis affect the renogram in a captopril dynamic nuclear renal scan?

A

DTPA tracer: Decreased radiotracer uptake on RAS side (due to decreased perfusion)

MAG3 tracer: Tracer retention with delayed excretion on RAS side (due to decreased excretion)

23
Q

Pts should stop taking _____ 3-5 days prior to a dynamic nuclear renal study looking for renal artery stenosis

A

ACE inhibitors

24
Q

Do pts need to be NPO prior to a dynamic nuclear renal study?

A

Only if its looking for renal artery stenosis and you’re using a PO ACE inhibitor (in which case they should be NPO for 6 hours prior)

25
Q

What is the most common indication for a dynamic nuclear renal scan of a transplanted kidney?

A

To differentiate rejection (poor perfusion with delayed excretion) from acute tubular necrosis (good perfusion with delayed excretion)

Note: ATN usually gets better, rejection does not.

26
Q

How can you differentiate acute tubular necrosis from cyclosporin toxicity?

A

Timing:

ATN usually occurs within the first week after transplant; cyclosporin toxicity is more of a chronic finding

Note: Both will show normal perfusion with delayed excretion on dynamic nuclear renal study.

27
Q

Which of these studies is most consistent with renal transplant rejection?

A

The right (poor flow/perfusion and poor excretion)

28
Q

What do the arrowheads point to in this renal transplant pt?

A

Photopenic fluid collection surrounding the transplant:

  • Hematoma (usually within 2 weeks of transplant)
  • Lymphocele (usually 4-8 weeks after transplant)

Note: A urinoma would be hot on delayed images.

29
Q

Dynamic nuclear renal study shows no tracer uptake in a renal transplant…

A

Think arterial or venous thrombus

30
Q

What is the critical organ for Tc-99m DMSA?

A

Kidney

Note: All other tracers used in renal imaging have bladder as the critical organ.

31
Q

What radio tracers can be used for structural kidney imaging?

A
  • Tc-99m DMSA
  • Tc-99m GH (glucoheptonate)

Note: Both of these bind to the renal cortex, but DMSA is cleared more slowly (used more). GH is also filtered by the kidney and is cleared faster.

32
Q

Which radiotracer should be used for structural kidney imaging in pediatric pts?

A

Tc-99m DMSA

Note: Less radiation to the gonads than with Tc-99m GH.

33
Q

Indications for structural nuclear renal study

A
  • Suspected pyelonephritis
  • Differentiate renal mass from column of Bertin
34
Q

Imaging findings of acute pyelonephritis on a structural nuclear renal study

A
  • Focal ill-defined photopenia
  • Multifocal photopenia
  • Diffuse photopenia

Note: Renal scarring and masses can also appear this way.

35
Q

Imaging findings of column of Bertin on structural nuclear renal study

A

Column of Bertin will take up cortical tracers (e.g. Tc-99m DMSA), whereas a renal mass would not

36
Q

Tc-99m DMSA

A

Acute pyelonephritis (if acute renal issues)

Renal scarring (if no acute renal issues)

37
Q

Tc-99m DMSA: is there a renal mass or a column of Bertin?

A

Column of Bertin

Note: Central lesion takes up DMSA (renal masses are cold on DMSA cortical scans).

38
Q

What radiotracer is used for testicular blood flow studies?

A

Tc-99m pertechnetate

39
Q
A

Delayed (late) testicular torsion OR testicular abscess

Note: Peripheral rim of radiotracer uptake with central photopenia in the left scrotum.

40
Q
A

Normal testicular perfusion

41
Q
A

Right orchitis

Note: Increased blood flow to the right testicle (A).

42
Q
A

Acute left testicular torsion

Note: Absent flow to the left testicle.

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