paediatric renal imaging...what is the most important information supplied by the mag3 renogram?...

PAEDIATRIC RENAL

IMAGING

Dr A Brink

Causes of hydronephrosis includes:

Pelvi-ureteric obstruction

Vesico-ureteric reflux

Vesico-ureteric obstruction

Posterior uretral valves

Duplex kidneys

Radiopharmaceutical of choice:

99m Tc-MAG3 (mercaptoacetyl triglycine):

Taken up in the kidney via tubular secretion (98%)

and glomerular filtration (2%).

90% protein bound.

40 % of MAG3 in blood is taken up into the

kidneys every time the blood circulates through the

kidneys.

70% of the MAG3 is in the urine 30 minutes after

injection.

What do you need to get a good

quality MAG 3 scan ?

What do you need to get a good

quality MAG 3 scan ?

A WORKING KIDNEY! Difficult and sometimes

impossible to interpret if there is CRF.

MAG3 renogram = Dynamic study

What is the most important information

supplied by the MAG3 renogram?



The differential renal function.










Differential renal function only tells us how the

kidneys work in relation with each other. It does not

give us information on the global renal function.

If you want to calculate the absolute differential

renal function, adding a GFR is imperative.

Absolute GFR is valuable in cases with bilateral

disease.

How is Differential Renal Function (DRF)

calculated?

MAG3 cannot move through the nephron in under

2,5 minutes.

How is Differential Renal Function (DRF)

calculated?

MAG3 cannot move through the nephron in under

2,5 minutes.

DRF is calculated on the 1-2 minute image. Given

adequate time for mixing and uptake. None of the

counts (radioactivity) can be in the collecting system

jet.

How is DRF calculated?

Two accepted methods, Integral method and

Rutland Patlak plot.

Basic principle:

How is DRF calculated:

We draw regions of interest (ROI) to tell the

computer where the kidneys are.

These are not allowed to cut the kidneys.

Backgound ROI’s – More than one method, C-

shaped and peri-renal most acceptable.

Background ROI’s Must stay inside the patient!

So what does DRF measure?

So what does DRF measure?

We are comparing the two kidneys with each other.

Normal range is:45-55%

It does not give an indication of how well the

kidneys work as a unit. You can have 50/50% DRF

and renal failure.

Problematic if there is bilateral disease, then it is

useful to add a validated GFR measurement to

calculate absolute DRF.

The “Stages” of the renogram

Four “stages”:

Perfusion

Uptake

Excretion

Clearance

The curve

“Lasix response”

Lasix response = Non – obstructed system

The hydronephrosis dilemma

Causes of absent lasix response

Dehydration

Large collecting system

Full bladder

Renal insufficiency

Renal immaturity

Inadequate diuretic dose

Indications for Intervention

1. Infections/Complications.

2. Fall in differential renal function.

3. Increasing AP pelvis (relative indication).

Background

Prenatal hydronephrosis is found in approximately

0.25% of pregnancies(1).

There is spontaneous resolution in:

50% of cases with mild

15% with moderate and

0% with severe hydronephrosis(2).

1.Helin I, Person P.H. Prenatal diagnosis of urinary tract abnormalities by ultrasound.

Pediatrics, 78:879, 1986.

2.Feldman, D.M. et al: Evaluation and follow-up of fetal hydronephrosis. J

Ultrasound Med, 20: 1065,2001.

DRF 50/50%.

AP pelvis Calyceal

dilatation

Baseline

MAG3 at

Follow-up

MAG3 at

< 20 mm Seldom

marked

3/12 9/12

20 – 30mm Not marked 9/52 6/12 - 9/12

20 – 30mm Marked 6/52 3/12 – 6/12

30 - 40mm Not marked 6/52 6/52 – 3/12

30 – 40mm Marked 3/52 3/52 - 6/52

> 40 mm uncommon at 50/50% DRF

IMAGING IN HYDRONEPHROSIS

Ultrasound studies are booked between two MAG3

studies. If the ultrasound results are of concern the

MAG3 study is moved forward.

DRF 30/70%

DRF 30/70% follow-up MAG3 and ultrasound

studies are done earlier because the one kidney is

already compromised

As with DRF 50/50% the MAG3 renogram is moved

forward if the ultrasound results are of concern .

DRF 15/85% - 20/80%

The follow-up MAG3 is done 2/52 - 4/52 after

initial study.

Consider doing a MCUG here.

These patients are candidates for

nephrostomy

early surgery

early stent.

DRF of affected kidney < 10%.

Probably not salvageable, surgery often technically

very difficult.

Probably not worth saving.

Reproducibility:

0

2

4

6

8

10

12

14

0 10 20 30 40 50 60 70 80 90 100

PI

SI

SRP

HI

HRP

II

IRP

Percentile

Sta

nd

ard

devia

tion

Watch out if...

Vesico-ureteric reflux

06-07-2010 18-01-2011

VUR case study pt PG

VUR case study Pt PG

VUR case study Pt PG: indirect cystogram

Bilateral hydronephrosis

F A 40070567 10 June 2008 1-2

minute image

F A 40070567 10 June 2008

Fazili A 10 June 2008

F A 40070567 10 June 2008

paediatric renal imaging...what is the most important information supplied by the mag3 renogram?...

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