1. Anatomy and physiology of the kidney
1. Pre-renal
1. Blood flows down the descending aorta to the abdominal aorta
2. Branches at the renal arteries
3. Supplies blood to the left and right kidneys
2. Blood arrives at the kidneys and receives approximately 20 - 25 % of the cardiac output

1. Renal artery enters the kidney and subdivides into the segmental artery, which goes to the 8 different Calyxes
2. In each renal calyx arterial blood flow branches as follows: interlobar arteries, arcuate arteries, interlobular arteries, to the afferent arterioles
3. Nice diagram of renal arterial blood flow (click it)
4. Afferent arterioles supplies the glomerulus (bowman's capsule)
5. Leaving the glomerulus the blood travels through the efferent arteriole with a network of peritubular capillaries that surround the convoluted tubules and loop of Henle
6. Capillaries converge into interlobular vein, arcuate vein, interlobular vein, that feeds into the renal vein

3. Nephron physiology (Intra-Renal)
1. The entire structure can be seen in the diagram below
2. Blood enters the nephron from the afferent arteriole at the Glomerulus/Bowman's capsule
1. Where 20% of the cardiac output arrives at approximately 1.2 L/min
2. One can make an assumption that 50% of whole blood is plasma, hence the Effective Renal Plasma Flow (ERPF) value would be 600 mL/min
3. About 20% of this plasma is filtered by the glomeruli resulting in a glomerular filtration rate (GFR) of 120 mL/min
4. This 20% is also know as the filtration fraction which is derived GFR/ERPF
5. 120/600 = 0.2 or 20%
6. Most of the filtered plasma is reabsorbed
7. Glomerulus is the first step in urine formation
3. Waste products, electrolytes, and water are filtered out by the proximal convoluted tubule
4. These by-products are then sent down the Loop of Henle and exit out the distal convoluted tubule
5. Certain by-products may re-enter or be reabsorbed along this tubule via the peritubular capillaries
6. The excreted by-products or urine that remain in the tubules continues out the collecting ducts and then enter the ureter
7. Between the afferent and efferent arterioles is the juxtaglomerular apparatus
1. This structure response to renal artery stenosis (RAS) and low sodium concentrations
2. It secrets rennin that starts the process of producing angiotensin, which when applied vasoconstricts the efferent arteriole
3. This process will occur with a patient that has renal artery stenosis. The body attempts to equalize the pressure by constricting the efferent arteriole (the process will discussed further under captopril renogram)

4. Kidney
1. Identify the location of the nephron within the kidney
2. Note the other sections of the kidney: Cortex, pyramid, medulla, calyx, and ureter
3. It is important to understand these structures when drawing the appropriate ROIs in a renogram
1. Lasix renogram includes the entire renal pelvis
2. Captopril (ACE inhibitor) renogram requires the ROI to only be drawn around the renal cortex
3. Lasix and Captopril will be discussed in the future


2. Radiopharmaceuticals used to image the kidney
1. Glomerular Filtration Rate (GFR)
1. As blood and plasma pass through the glomerulus, approximately 20% of the plasma is filtered out at 120ml/minute (as noted above)
2. Best agent to quantify GRF is ^99mTcDTPA
3. Only 3 to 5 % of this agent is protein bound, which results in a small error in the GRF value (if the error is known then this can be added to the calculation)
4. Increased rennin flow increases protein binding which falsely lowers the GFR
5. T_1/2 for DTPA are: 10, 90, and 600 minutes. In further assessment Sodee¹ states that less than 10% remains in the blood at 2 - 3 hours
6. Reducing agent in the DTPA kit is ascorbate which increases cortical binding of the agent (what happens to the GFR calculation if there is too much cortical binding?)
7. A dynamic imaging procedure is used to identify the passage of the radiopharmaceutical through the kidneys
8. Quantitatively, ROIs are drawn around the kidneys and time/activity curves is generated, which define renal function of the radiotracer passing through the kidneys
2. Effective Renal Plasma Flow (ERPF)
1. Identifies the amount of plasma that is filtered by the kidneys = 600 mL/minute
2. Agents used to quantify ERPF are ¹³¹ HIPP and ^99mTcMAG3
3. MAG-3 is the agent of choice
4. Tubular agents (radiopharmaceuticals) are used to determine ERPF
5. OIH is similar to paraaminonohippuric acid (PAH) which is the gold standard to determine ERPF (PAH is not an NMT procedure)
6. OIH - 80% is filtered by the tubules and 20% is filtered by the glomeruli
7. Jolles states that MAG3 filters 10% GFR and 90% EFPF
8. Clearance depends on the extraction efficiency and the blood flow to the kidneys
9. OIH - 96% is extracted from the arterial blood
10. OIH - Extraction fraction is approximately 65% at first pass with 70% cleared from the vascular pool in 30 minutes
11. In normal renal excretion maximum concentration occurs in the kidney at 3 - 5 minutes with 50% remaining at 7 - 10 minutes
12. Most of MAG-3 is excreted through the proximal convoluted tubule
13. MAG3 is not extracted by the kidneys as efficiency as OIH
14. In comparison of I¹³¹-OIH to MAG3
1. Rate of clearance 1.301/minute (MAG3) and 0.881/minute (OIH) - normal volunteers (NV)
2. Research has shown that renogram curves and 30 minute excretion rates were similar in NV
3. Image quality for MAG3 was significantly better than OIH (why?) - NV
4. Note I¹³¹-OIH dose is ~ 300 μCi and Tc99m-MAG-3 is ~ 10 mCi
5. MAG-3 is the superior agent in patients with renal impairment (RI)
6. 30-minute excretion was about the same for both (RI)
7. Time to peak was more rapid with MAG3 (RI)
8. MAG3 is 90% protein bound
9. MAG3 is 5.1% bound to RBC, while OIH was 15.3%
10. MAG3 may show hepatobiliary uptake (and GB)
11. Does hepatic uptake effect quantification?
12. Peak for both is between 2.5 to 3.4 minutes
15. Quantitatively, ROIs are drawn around the kidneys, and a time/activity curves is generated which displays renal function of the radiotracer passing through the kidneys
3. Perfusion image for static analysis
1. Identify space-occupying lesions
2. Agent of choice is ^99mTcDMSA
3. Considered a parenchymal imaging agent
4. 90% is bound to serum protein
5. Extraction fraction in to tubules is around 4 - 5%
6. 50% adheres to the tubules at 1 hour post dose
7. DMSA molecule splits when it reaches the kidney, in which part of it is secreted and part it binds to the tubules
8. DMSA expires 4 hours minutes after its reconstituted
9. Radiotracer perfuses into the kidneys and is retained by the renal cortex which allows for examination of renal anatomy
4. Perfusion and quantification
1. ^99mTc-glucoheptonate (GH) can be used for either cortical imaging and renal function
2. 50% is bound to the plasma protein
3. Tubules to glomeruli extraction is about 50/50
4. 10% binds to the renal cortex in 1 - 2 hours
5. Early analysis of the renal procedure yields function, however, delayed images better defines renal anatomy
6. Considering the above outline, how would you use these radiotracers to & image the kidneys?

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