Renal Functional Imaging Flashcards
prep
well hydrated - minimum 300-500 ml water prior to scan
void before imaging
RP(s) and dose
MAG3 or DTPA
90-370 MBq
imaging protocol
flow and dynamic, then statics of pre-void, post-void and injection site
what are the 2 sequential phases that are imaged?
- renal perfusion (flow)
- function (dynamic)
normal renal scan
- prompt and symmetrical perfusion in both kidneys within 2-5 secs of seeing the abdominal aorta
- peak activity seen at 2-5 min
bladder visible by ____
4-8 mins
time to peak (Tmax)
2-5 mins
what is the 20 min/peak ratio?
measures residual cortical activity (transit time in kidney) at t=20 mins and at max counts
then cts at 20 mins divided by max cts
20 min/max ratio
<0.35 normal
what is the differential cortical retention?
% retained in each kidney at 15 or 20 mins
what is considered abnormal differential cortical retention?
difference of more than 20%
normal value of T1/2 excretion
=< 20 mins
8-12 mins is typical
what is the T1/2 excretion?
time for half the peak activity to be cleared from the kidney
what range is appropriate for differential/relative renal function?
45:55
pathologies seen in diuretic renal scan (lasix)
- hydronephrosis (obstructive or non-obstructive)
- horseshoe kidney
- renal/crossed ectopia
pathologies seen in regular renal scans
- acute glomerulonephritis
- renal artery
- vein thrombosis
- renal trauma (contusion, rupture, urine leak)
pathologies seen in ACEI/captopril scans
RVH caused by RAS
symptoms of acute glomerulonephritis
- oliguria, proteinuria, hematuria
- HTN
- edema
what does acute glomerulonephritis look like with MAG3/DTPA?
uni/bilateral delayed excretion = elongated excretory phase on the renogram
what does acute glomerulonephritis look like with DMSA/Gluco?
photopenic cortex = poor function
NM appearance of renal artery embolus
with MAG3/DTPA = absent flow, function, and uptake
NM appearance of RVT
- with MAG3/DTPA: decreased flow, enlarged kidneys, prolonged renal parenchymal transit time
NM appearance of renal contusion/trauma
- infarcted area that improves over time!
nm appearance of renal rupture or fx
tearing = break in continuity of renal contour
what RP is best to determine renal rupture/fx?
delayed morphological imaging = DMSA
indications for diuretic renal imaging
- hydronephrosis
- eval distension of renal pelvis and ureter
- differentiating cause of distension: functional vs. mechanical obstruction
hydronephrosis
dilation of renal pelvis and ureters
what causes hydronephrosis?
- congenital malformations
- mechanical obstruction
- inflammatory obstruction
- nerve damage
- VUR, UTIs
which diuretic is most commonly used for functional renal scintigraphy? when do we use it? what is its mechanism of action?
lasix
various times, can be F15, F20 or right away (F0)
it inhibits absorption of sodium in loop of henle = less water going back to blood so more is excreted
what is used if the patient has a sulpha allergy?
ethancrynic acid
mechanical causes of distension
- nephrolithiasis
- extrinsic masses that press on the ureter
- infection
- mechanical obstruction
functional causes of distension
- VUR
- previous obstruction
- infection
- congenital disorders
dose of Lasix
max 40 mg IV over 1-2 mins
when does administering lasix result in better discrimination between obstruction and non obstruction? why?
F15
allows for maximal diuresis effect
when does administering lasix result in better visualization or natural urinary drainage? why?
F20, 30 or Fmax
non obstructed hydronephrosis is seen as…
post lasix, collecting system washes out = renogram curve declines
obstructed hydronephrosis is seen as…
post lasix, little change in collecting system activity = rising renogram changes very little or not at all
T1/2 excretion post lasix
T1/2 <10 = …
no obstruction
T1/2 excretion post lasix
T1/2 10-20 = …
indeterminate
T1/2 excretion post lasix
T1/2 >20 = …
obstruction
difference between acute/subacute high-grade and chronic high-grade obstruction
acute = blood flow and function is maintained
chronic = decreased blood flow and function
false positives for diuretic scans
- dehydration
- poor underlying renal function
- back pressure from noncompliant bladder
- interstitial dose
- large volume in dilated pelvis
- use of diclofenac
what is renovascular hypertension (RVH)?
HTN caused by blockage/occlusion of renal artery
what is HTN?
BP >140/90
symptoms of RAS
- uncontrollable HTN (nonresponsive to meds)
- headache
- stroke
- BP wildly erratic (exceeds sys 200 mmHg)
- common under 30 or over 55
causes of RAS
- atherosclerosis
-thromboembolism - fibromuscular dysplasia
- pressure from external mass on renal artery
prep
discontinue ACE, how long? why?
short acting 3 days
long acting 5-7 days
it can reduce sensitivity of test
prep
discontinue diuretics, how long? why?
2-3 days
volume depletion cna reduce specificity of test
why does fasting need to be done for captopril studies?
it interferes with absorption of captopril therefore false neg can happen
dose of captopril
50 mg, PO
when do you give captopril?
1 hr prior to RP injection
dose of enalapril
0.04 mg/kg, max 2.5 mg IV over 3-5 mins
when do you give enalapril?
10-15 mins prior to RP injection
ACEI Neg exam
peak activity …
<5 mins
ACEI Neg exam
half time excretion
8-12 min
ACEI Neg exam
20min:peak ratio
<0.35
RVH with MAG3
post capto
renogram results
post captopril = adequate uptake and secretion but decreased excretion due to decreased GFR
RVH with MAG3
NM image results
increase cortical retention
RVH with DTPA
post capto
renogram results
post captopril = fall in peak function, decrease in uptake and excretion
scale for renograms
grade 0
normal
scale for renograms
grade 1
mild abnormalities
time to peak >5 min
delayed excretion, 20 min: max >0.3
scale for renograms
grade 2
more exaggerated delay in Tmax and parenchymal washout
scale for renograms
grade 3
progressive parenchymal accumulation
(no washout)
scale for renograms
grade 4
renal failure with measurable kidney uptake
scale for renograms
grade 5
no uptake
false negatives for ACEI scans
- didn’t stop ACEI therapy
- didn’t fast
ACEI Renography
high probability
unilateral deterioration of renogram curve post captopril
ACEI Renography
intermediate probability
- small or poorly functioning kidney
- abnormal baseline renogram that is unchanged after ACEI
ACEI Renography
low probability
- normal ACEI renogram with normal indices
- grade 2 renogram that’s unchanged or improves after ACEI
generic name ethacrynic acid
Edecrin
generic name furosemide
lasix
trade name Vasotec
enalapril
blocks conversion of angiotensin I to angiotensin II
captopril and enalapril
administered IV 40 ug/kg over 3-5 mins
enalapril
1 mg/kg administered IV for peds
Lasix
