Nuclear Medicine Senior Ii 2013 Renal Functional Imaging

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Physiologic renal with Tc-99m DTPA or Tc-99m MAG3

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Eval of renal perfusion/function
Detect/eval hydronephrosis (obstructive or nonobstructive)
Quantify regional renal function
Diagnose renovascular hypertension

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Morphologic renal assessment with Tc-99m succimer/DMSA

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Diagnose acute or chronic pyelonephritis
Differentiate renal masses from normal variants

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Renal Anatomy includes

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Renal cortex, medulla, renal pyramids, renal pelvis, renal artery

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Renal Hilum

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A fissure indenting the medial border of the kidney
Blood vessels, nerves, & ureters pass through this fissure into the kidney

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Renal cortex

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Outer layer of the kidney
Contains both vascular & tubular components

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Renal medulla

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Inner layer of the kidney
Contains tubular structures

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Renal pyramids

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Sections of the medulla

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Renal pelvis

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The upper end of the ureter as it leaves the kidney
Outer border is convex & divided into major & minor calyxes

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Nephron

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Primary unit of the kidney (approx. 1 mil/kidney)
Can be separated into both tubular & vascular anatomical components
Renal filtration occurs due to pressure gradients between the vascular & tubular components

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Tubular anatomy includes:

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Bowman's capsule/space
Proximal/distal convoluted tubules
Loop of Henle
Collecting ducts
Renal pelvis
Macula Densa

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Macula Densa

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Part of the tubule that passes between the afferent & efferent arterioles
Wall of the afferent arteriole at this point contains secretory cells called granular cells

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Granular cells

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Wall of the afferent arteriole at the point of the Macula densa

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Juxtaglomerular apparatus (JGA)

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Where the macula densa touches the granular cells of the arteriole

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JGA Functions

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Granular cells secrete renin

Macula densa senses tubular fluid flow & sends info back to the kidney so renin secretion/GFR can be regulated

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Vascular anatomy includes:

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Renal artery
Smaller arteries
Afferent arterioles
Glomerulus
Efferent arterioles
Peritubular capillaries
Veins of increasing size
Renal vein

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Renal filtration route

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Glomerulus forms protein free filtrate from blood --> collected in Bowman's capsule --> flows through the proximal tubule, Loop of Henle, & distal tubule --> needed substances absorbed back into vascular system --> remaining filtrate (urine) drawn into the renal pyramid, minor calyces, major calyces --> into renal pelvis --> to the bladder

Filtered plasma returned to renal hilum & into the renal veins for transport back to the heart

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Key renal functions

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Regulation of water & inorganic ion balance
Removal of metabolic waste & foreign chemicals
Secretion of hormones

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Erythropoietic factor

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Hormone secreted by the kidney
Controls RBC production in marrow

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Renin

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Regulates arterial blood pressure

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Vitamin D3 (Renal)

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Role in calcium synthesis & metabolism

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Functions of nephron

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Glomerular filtration
Tubular secretion
Tubular reabsorption

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Glomerular filtration facts

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Fluid in Bowman's capsule filtered by the glomerulus is virtually PROTEIN FREE
20% of total fluid is filtered this way
Small amount that is filtered is put back into the blood
Anything in the blood stream bound to a protein is generally not filtered at the glomerulus either

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Tubular secretion facts

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Process whereby substances move from the vascular capillaries into the tubule lumen
Approx. 80% of fluid filtered this way

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Tubular reabsorption facts

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Regulatory mechanism that moves substances from the tubule back into blood to meet bodily needs
Must occur for homeostasis purposes
Process by which substances undergo tubular reabsorption varies by substance (i.e. active transport, passive diffusion)

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Tc-99m DTPA Facts with Renal Imaging

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Should not bind to plasma proteins or be absorbed or secreted by the tubules for accurate GFR
5% of dose binds to proteins so imperfect (but still the best for GFR assessment)
Rapid renal clearance with max renal concentration at 3-5 min post-injection
3-20 mCi

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Tc-99m DTPA Incorporation, Excretion, & RAD

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Incorporation: Glomerular filtration (method of pressure mediated filtration)
Excretion: Renal
RAD: Bladder wall

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Tc-99m mertiatide (MAG3) facts (Renal)

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Binds to plasma proteins
90% clearance by tubular secretion (active transport), remainder by GF
10 mCi dosage

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Tc-99m MAG3 incorporation, excretion, & RAD

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Incorporation: Primarily by tubular secretion (active transport filtration process)
Excretion: Renal
RAD: Bladder wall

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MAG3 vs DTPA

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MAG3 has 3 different reasons for being a better agent than DTPA:
Better extraction rate (3xs or 50-60% higher)
Better target to nontarget ratio & better differentiation of cortex & collecting system
More sensitive for abnormalities/pathologies

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I-131/I-123 orthoiodohippuran

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80% clearance by tubular secretion
Poorer indicator of tubular secretion than MAG3
Issues of iodine (safety, energy, collimator)
Dosage: 300 uCi

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Tc-99m gluceptate (glucoheptonate)

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Dose becomes loosely bound to tubules demonstrating anatomy
Filtered by both GF & TS
1/2 dose is excreted in urine at 2 hrs post-injection

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Tc-99m DMSA Facts

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Binds tightly to the tubules in the cortex demonstrating anatomy
Filtered by both GF & TS
1/3rd dose is excreted in the urine by 24 hrs post-injection
Dosage: 2-5 mCi

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Tc-99m DMSA Incorporation, Excretion, & RAD

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Incorporation: GF & TS
Excretion: Renal
RAD: Renal cortex receives highest exposure

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Renal GFR Study Prep & Equipment

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Prep: Well-hydrated so excretion & washout are not delayed; void prior to beginning of study

Camera & Collimator: LFOV camera with HR, GAP, LEAP; 140 keV peak & 15-20% window

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Renal GFR Acquisition Parameters

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Renal perfusion: 60 sec dynamic flow @ 1 sec/frame

Parenchymal uptake & clearance: 30-60 min dynamic study @ 60 sec/frame

Typical study duration is 20-30 min unless lasix is administered then it is lengthened to 40-60 min

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Renal GFR Patient Positioning

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Supine with arms to side; Camera posterior with native kidneys OR Anterior with transplant

Mark xiphoid process at Top center FOV & pubic symphysis at bottom center FOV

Kidneys approx. at elbow

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GFR Additional views

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Pre- & Post-injection syringe counts necessary for processing & quantification

Inj. site static

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GFR Processing

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Draw ROI around each kidney CORTEX on early frame (may/may not include renal pelvis)

Semilunar background ROI at inferolateral poles of both kidneys on same frame

Only ones to calculate GFR

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Renal Tubular Secretion Study Facts

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Same prep, camera & collimator, Acquisition parameters, patient positioning as GFR

Processing: Same ROIs as GFR but calculate ERPF or % uptake of dose

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Renal Anatomy Study Prep & Equipment

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Prep: Hydration (not as critical); patient should void prior to starting the study

Equipment: LFOV with SPECT; Pinhole/HR collimator; 140 keV peak 15-20% window

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Renal Anatomy Acquisition Parameters

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Flow: may not be performed with DMSA because bkgd clearance is slow

Statics: 2-3 hrs post-injection 400kcts of POST, LPO, & RPO

SPECT: Follow statics, 360 degrees, 64 stops @ 20 sec/stop

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Renal Anatomy Positioning & Processing

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Supine for SPECT acquisition with arms above head & Prone for posterior & oblique views to get as close to patient as possible

Processing: Renal & Bkgd ROIS to create flow & function curves

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Normal Renal Physiologic Parameters

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GFR: 125 ml/min for TWO young healthy kidneys (normal decreases with age)

ERPF: 500-600 ml/min for TWO young healthy kidneys (normal decreases with age; will have age based values)

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Other renal diagnostic tools

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Renal ultrasound with Doppler of blood flow
Voiding cystourethrogram (VCUG)
Intravenous pyelogram (IVP) for stones, enlarged prostate, tumors
CT of kidneys

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Renal Lab Values

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BUN: Elevated indicates renal obstruction or failure; 7-20 mg/dL or 16 is optimal

Serum creatinine: Elevated indicates renal failure, obstruction or decreased blood perfusion to kidneys; normal = 0.8-1.4 mg/dL or 1.05 mg/dL is optimal

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Hydronephrosis

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Excess fluid in kidneys
Typically due to obstruction
Can also have non-obstructed hydronephrosis

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Chronic renal failure (end stage renal disease - ESRD)

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Patient put on dialysis until a transplant is available

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Wilm's tumor

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Pediatric renal carcinoma

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Polycystic kidney disease

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Multiple, focal cold spots on scan with poor function

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Horseshoe kidney

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Image from anterior since spine attenuates the connection from a posterior view

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Renal Diuretic Interventional Agent

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Differentiate dilation of collecting system from obstruction
1 mg/kg of furosemide/lasix given over 1 min (max of 40 is recommended)
Admin with, 15 min, or 20 min post- radiopharmaceutical injection

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Diuretic Intervention Evaluation

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Physicians may look for
1) Retained RP in collecting system
2) Sufficient renal function for diuresis (urine production)
3) Adequate hydration of patient before intervention admin

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ACE-Inhibitor intervention

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Administered to aid in the diagnosis of Renovascular Hypertension due to renal artery stenosis

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Renovascular Hypertension

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Type of hypertension caused by renal artery stenosis of 60% or greater in the AFFERENT arterioles
Constriction causes decrease pressure & blood flow to the glomerulus causing GFR to drop

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Low Renal Blood flow problems

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Kidney will become scarred & contracted overtime

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Main causes of RVH

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Atherosclerosis & fibromuscular dysplasia (disease that causes stenosis of the arteries)
Not all causes of renal artery stenosis cause RVH

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RVH Diagnostics & Treatment

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CT & MRI angiography are other best option for diagnostic imaging but do not account for the functional effects of any lesions

Treatment: Angioplasty, arterial stenting, or surgery

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RVH Mechanism

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When patient has RVH the body naturally compensates for the decrease is afferent arteriole BP by stimulating renin secretion --> renin converts circulating angiotensinogen to AG I --> AG I is acted upon by ACE & converted to AG II --> AG II causes vasoconstriction of the efferent arterioles which improves GFR & tubular secretion & also increases BP

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Aldosterone

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Hormone that causes the tubules of the kidneys to retain sodium & water which INCREASES the fluid volume in body & INCREASES BP
Spironolactone - lowers BP by blocking the aldosterone receptor
Part of the renin-angiotensin system

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RVH Chain

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Low afferent BP --> renin secretion --> Angiotensinogen --> angiotensin I --> angiotensin II --> increase efferent BP

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ACE Inhibitor on RVH chain

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ACE inhibitor admin causes AG I to NOT BE CONVERTED to AG II which breaks the cycle of natural compensation & allows visualization of RVH by noting a decrease in function, lower, & slower dose uptake in affected kidney & delayed washout of dose qualitatively for DTPA & MAG3
GFR will also decrease qualitatively

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ACE Inhibitor study Prep

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Off regular ACE-inhibitors 1 day-1 week
Well hydrated
NPO morning of study
BP Monitored constantly
Saline IV should be started & kept at an open rate in case of hypotension

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ACE Inhibitor Study Contraindications

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Severe renal insufficiency & stenosis since ACE-inhibitor admin may induce acute renal failure

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ACE Inhibitor Acquisition Protocol

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Baseline DTPA or MAG3 study is performed to assess renal function followed by administration of ACE-inhibitor & a repeat renal-function study
Some are a two day study but not necessary if done in correct order

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Catopril Info

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Orally administered
Dose: 25-50 mg
Timing: 1 hour before study

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Enalaprilate Info

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IV administered over 5 minutes
0.04 mg/kg (max 2.5 mg)
15-20 minutes before study

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Diagnostic Criteria used by Physician for ACE-Inhibitor Study

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1.) Decreased dose uptake in affected kidney after ACE admin compared to baseline
2.)Delay in max uptake of dose after ACE
3.) Cortical retention of dose with delayed washout after ACE-inhibitor
4.) Functional parameter, GFR, will decrease from baseline level; increase in time to peak with ERPF

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Assessment of Transplanted Kidney

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DTPA or MAG 3: patency of vascular supply, urine leaks, or clearance capabilities

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Problems with transplants

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Acute tubular necrosis (ATN) & rejection
ATN: necrosis of the tubules but vasculature remains normal; presents as decreased renal functon & prolonged cortical retention

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3 Types of Kidney Transplant Rejection

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Hyperacute: Strong Ab response within 24 hrs of transplantation
Acute: Common, reversible with drug tx, happens 5-10 days post-transplant
Chronic: Irreversible progressive loss of renal function
With Rejection the blood supply is poor to absent & renal function & transit is prolonged