Editing Pathophysiology of Urinary Tract Obstruction (section)

==== Nuclear renography ====

* '''<span style="color:#ff0000">Tracers commonly used in urology (3): MAG3, DTPA, DMSA'''
*# '''MAG3'''
*#* '''Tracer properties'''
*#** High extraction by the kidneys
*#*** Renal uptake is 55% compared with 20% uptake by DTPA
*#** Rapid clearance
*#** Low radiation dose
*#** '''Tubular secretion'''
*#* '''Preferred radiopharmaceutical in the evaluation of the obstructed collecting system'''
*# '''DTPA'''
*#* '''Tracer properties'''
*#** '''Removed almost exclusively by glomerular filtration'''
*#*** MAG3 actively secreted by the tubules
*#* '''Preferred radiopharmaceutical in the evaluation of GFR'''
*#** '''Adequate imaging of the collecting system, however, is GFR-dependent with DTPA and is therefore limited in patients with renal insufficiency and those <6 months of age because of the immaturity of renal function'''
*# '''DMSA'''
*#* Tracer properties
*#** Binds to the proximal convoluted tubules in kidney so the excretion pattern of the kidneys cannot be assessed§
*#** '''Best tissue to background activity ratio'''
*#* '''Preferred radiopharmaceutical in the evaluation of renal Scarring and prediction of renal recovery (superior to DTPA and MAG-3)'''

{| class="wikitable"
|'''<span style="color:#ff0000">Tracer'''
|'''<span style="color:#ff0000">Clinical question'''
|'''<span style="color:#ff0000">Clearance'''
|'''<span style="color:#ff0000">Useful in renal failure'''
|-
|'''<span style="color:#ff0000">MAG3'''
|'''<span style="color:#ff0000">Obstruction</span>, differential renal function, perfusion, effective renal plasma flow'''
|'''95% secretion, <5% glomerular filtration'''
|'''<span style="color:#ff0000">Yes'''
|-
|'''<span style="color:#ff0000">DTPA'''
|'''<span style="color:#ff0000">Obstruction</span>, differential renal function, perfusion, filtration (GFR)'''
|'''>95% glomerular filtration'''
|'''<span style="color:#ff0000">No</span> (since tracer has to be filtered)'''
|-
|'''<span style="color:#ff0000">DMSA'''
|'''<span style="color:#ff0000">Morphology</span> (cortical defects, ectopic or aberrant kidneys) and differential renal function'''
|'''60% tubular filtration, some glomerular filtration'''
| 
|}
§§

* '''Phases of a nuclear scan (3):'''
*# '''Flow (initial) phase'''
*#* '''Characterized by rapid renal uptake''' of the radiopharmaceutical, reflecting renal perfusion
*#* '''Shows renal uptake, background clearance, and abnormal vascular lesions'''
*# '''Renal phase'''
*#* '''Characterized by a more gradual rise in uptake over time, usually peaking after 2-5 minutes'''
*#* '''Primarily evaluates renal function'''
*#** '''Most sensitive indicator of renal dysfunction'''
*#* '''Urinary obstruction can diminish the rate of uptake of the radiotracer during the second phase and can therefore alter the assessment of differential renal function'''
*# '''Excretory phase'''
*#* '''Characterized by a gradual decrease in renal counts''' over time
*#* Often augmented by the administration of a diuretic (diuretic renogram) to induce high urine flow and prevent the false positive results that can be caused by urine stasis in a dilated collecting system
*#** The diuretic (usually furosemide 0.5 mg/kg) is administered when maximum collecting system activity is visualized.
*#* '''<span style="color:#ff0000">The T1/2 is the time it takes for collecting system activity to decrease by 50% from that at the time of diuretic administration'''
*#** '''<span style="color:#ff0000">T1/2 < 10 minutes: normal, non-obstructed collecting system'''
*#** T1/2 10-20 minutes: mild to moderate delay, may be a mechanical obstruction
*#** '''<span style="color:#ff0000">T1/2 > 20 minutes: high-grade obstruction'''
*#*** '''The level of obstruction can usually be determined, as can abnormalities such as ureteral duplication'''
*#* '''Causes of false-positive results (6): High Definition Nuclear Renography Can Deceive'''
*#*# '''Hepatobiliary excretion''' if the area of intestinal activity or gallbladder activity is included in the area of study
*#*# '''Dehydration''' because of the suboptimal response to a diuretic agent
*#*# '''Neonates''' because of renal immaturity
*#*# '''High-grade Reflux'''
*#*# '''CKD (poor renal function)'''
*#*# '''Presence of massive collecting system Dilation with urinary stasis'''
* Measurement of differential renal function and tracer washout will vary depending on the protocol and radiopharmaceutical used, and care should be taken when interpreting results if comparative studies have been performed using different protocols or radiopharmaceuticals.