Genitourinary test out

Function of kidneys

- regulate concentration of blood

- remove waste

- maintaine acid base equilibrium, electrolytes, calcium, phosphorus, and water levels

- regulate blood pressure and volume of extracellular fluid

the kidneys receive ____ % of the cardiac output

25%

Kidney location:

retroperitoneal space between T12 and L3

Right kidney is slightly _____ than the left because of the _______

lower; liver

the renal system is comprised of the:

kidneys

ureters

bladder

urethra

the kidneys perform _______, ________, and ________ functions

excretory, regulatory, and secretory

kidney length, width, and thickness

length: 12 cm

width: 6 cm

thickness: 2.5 cm

kidneys weigh how much?

120-170g in normal adult

what is the kidneys basic function

to produce urine

list the 3 basic functions of the kidney

- Kidney EXCRETES the waste products of metabolism

- Kidney REGULATES the body’s content of water, sodium, and potassium

- The kidney MAINTAINS the appropriate acid-base balance of plasma

how does foreshortening affect kidney size

kidneys may appear smaller if the long axis is not parallel to the surface of the camera

what imaging modality is not a very accurate method for measuring kidney size

planar scintigraphy

what is the preferred method for determining kidney size

renal ultrasonography (US)

what would you do if one of the kidneys shows up deeper than the other?

take an anterior image - this will show the opposite of the posterior image

kidneys are well protected due to:

- their position

- protected by the renal capsule

what provides support to the kidneys?

renal fascia

what acts as a cushion for the kidneys

perirenal fat

urine flows away from the kidneys via:

peristalsis

urinary bladder can hold how much urine

300-500 mL

Each kidney has about ___ collecting ducts, each of which is fed by _____ nephrons

250; 4000

blood flow in a typical man is:

1200 mL/min

The fluid that filters out is called

glomerular filtrate

glomerular capillary bed function

-provides a barrier to larger particles

-leads fluid to leave the blood stream

pertibular capillary bed function

reabsorb water and solutes

as molecular weight increases, the amount filtered ________

decreases

Inulin molecular weight and permeability

MW: 5200

Permeability: 100%

Small proteins molecular weight and permeability

MW: 30000

Permeability: 50%

Albumin molecular weight and permeability

MW: 69000

Permeability: 0.5%

The _____ is the functional unit of the kidney

nephron

how many nephrons are in each kidney

~1 million

what are the 2 types of nephrons

cortical and juxtamedullary

cortical nephron function

(85%) perform excretory and regulatory functions

juxtamedullary nephron function

(15%) help to concentrate and dilute urine between the cortex and deep medulla

where is the juxtaglomerular apparatus located

between afferent and efferent arterioles

function of the juxtaglomerular apparatus

maintain system BP

maintain intraglomerular pressure

maintain glomerular filtration

synthesize and store renin

what is renin

a proteolytic enzyme

what is glomerular filtration

the first process in the formation of urine

what forms the glomerular filtrate

plasma (20%) that passes from the glomerulus into bowman's space

what is the glomerular filtration rate (GFR)

The rate of filtrate formed per minute in all nephrons of both kidneys

- good measure of kidney function

both kidneys combined can filter ______ per minute

125 mL

the GFR varies with ___, which in turn reflects:

BP; the volume of fluid which is effectively circulating

how many liters of blood get cleaned out a day and how many times?

5 liters; 56 times

what is tubular reabsorption

the movement of fluid and solutes from the tubular system into the peritubular capillaries

tubular reabsorption allows the body to:

retain fluid and desired solutes

through reabsorption, ____% of the glomerular filtrate is returned to the bloodstream

99%

what is the major site of reabsorption

proximal tubule

what is tubular secretion

the movement of solutes from the peritubular capillaries into the tubular system

- this is how the body secretes unwanted or excess substances

clinical indications of renal imaging

relative renal function

infection and inflammation

acute renal failure

renal transplant evaluation

renovascular hypertension

vesicoureteral reflux

list the functional agents

I-131 HIPPURAN (OIH)

Tc-99m DTPA

Tc-99m MAG3

list the morphologic agents

Tc-99m DMSA

Tc-99m Tc-GH

MOA of DTPA?

glomerular filtration

MOA of MAG3?

tubular secretion

MOA of I-131 and I-123 HIPPURAN?

tubular secretion (80%) and glomerular (20%)

MOA of DSMA?

cortical binding 50%

MOA of Tc-99m GH?

glomerular filtration (80%) and cortical binding (20%)

I-131 or I-123 Hippuran characteristics

High first pass extraction

high target to background ratio

total tubular secretion 80%

20% GFR

Adavantage of I-123 Hippuran

accumulates quicker

cleared 5 times faster than DTPA (out of kidneys by 20-30 mins)

I-123 Hippuran, MAG3, Tc-99m GH determine-

- size, shape, and position of kidneys

- demonstrate obstruction of collecting system

- post traumatic urine leaks

- calculate kidney function by doing ERPF (effective renal plasma flow)

Dose of I-123

1 mCi

Dose of I-131 Hippuran

150-300 uCi

characteristics of DTPA

inulin analog

freely filtered

no tubular secretion/resoprion

readily available

DTPA advanatges

good imaging characteristic

low radiation dose

great for demonstrating obstructions

DTPA disadvantage

does not show cortex (except first few mins)

DTPA dose

3-15 mCi

DTPA excretion percentages (2 hour, 4 hour, 24 hours)

2 hours= 50%

4 hours= 90%

24 hours = 95%

MAG3 characteristics

high first pass extraction

tubular secretion (80-90%)

no tubular resorption

MAG3 advantages

high target to background

rapid uptake and clearance

clearance % of MAG3 at 3 hours

90% in urine at 3 hours

DMSA characteristics

cleared slowly from the blood

40% of the dose accumulates in the cortex

agent doesn’t localize in the collecting system or renal pyramids

DMSA advantages

excellent for imaging cortical areas

DMSA disadvantages

higher radiation dose due to lack of excretion

DMSA dose

1-5 mCi

why do the RPxs need to be used within 30 min of prep?

introduction of air increases instability

Tc-99m glucoheptonate (GH) characteristics

looks like DTPA for first 30 min, except 10% remains in renal cortex

cleared quickly from circulation

50% of the dose gets protein bound

Tc-99m glucoheptonate (GH) dose

10-15 mCi

Tc-99m glucoheptonate (GH) advantage

excellent visualization of the renal parenchyma

Tc-99m glucoheptonate (GH) disadvantage

can get increased liver uptake in poorly functioning kidneys

imaging begins ___ hours post-injection

2-4

how will you image if there is poor renal function/clearance?

do delayed imaging

- can image up to 24 hrs when there is severely obstructed collection system

what are the imaging views?

posterior

LPO, RPO for 14-20 min/view

128x256 matrix

what collimator will you use for I-123 Hippuran and I-131?

high-resolution

a Tc agent is necessary for a _____ study

flow

what kind of agent is best for evaluating obstruction

one that is rapidly excreted into the collecting system (DMSA and Tc GH)

what kind of agent is preferred for optimal visualization of the parenchyma

an agent that is retained in the renal parenchyma (Tc GH)

Patient prep for functional imaging

- no contrast

- hydrate well

- if doing hippuran consider giving Lugols

- Off ACE inhibitors/diurectics for 1 week

functional imaging protocol

- pt supine (unless transplant)

- flow study 2-3 sec/fram for 1 min 64x64x8

- dynamic image for 20-30 sec frame for 20-30 mins 128x128

- take a pre and post void static image of the bladder

where will you draw your ROI's?

kidneys

bladder

aorta

background

what is a renogram

graphic expression of movement of RPx through kidneys

- Has 3 phases

Renogram phase 1

Initial Rise:

- arrival of RPx

- superior abdominal filling

- capillary phase, venous phase, early cortical phase

- 8 sec: continued plasma clearance

Renogram phase 2

Ascending Limb:

- 1-5 mins: concentration of RPx by kidney

- tracer is beginning to accumulate in the nephrons

Renogram phase 3

Descending Limb:

- drainage and excretion

- activity is leaving the kidneys via renal pelvises and ureters

what does the "peak time" identify

the point at which the ascending limb switches to the descending limb

When should peak activity occur?

2-6 (5) mins post injection

Height differences in curves can be caused by differences in-

- renal size

- depth

- pt positioning

- ROI drawings

The preferred agent for calculating GFR is

Tc DTPA

Calculating GFR: gates method protocol

- 3 mCi DTPA: count syringe for 1 min at 20 cm from camera face

- inject and acquire flow and dynamics

SAVE THE SYRINGE

- take 1 min post-inj count of syringe

- Draw ROI

Calculating GFR kidney depths: R & L

Right kidney depth (cm): [13.3 x weight/height] + 0.7]

Left kidney depth (cm): [13.2 x weight/height] + 0.7]

how to calculate % renal uptake of DTPA:

[(R kidney cts - bkd) / 0.153-kidney depth] + [(L kidney cts-bkd)/0.153-kidney depth] all divided by [Pre-injection counts - post-injection counts]

calculating GFR: plasma clearance method protocol

- obtain blood samples at 60 + 180 mins post-inj

- plot a time-activity curve

- extrapolate back to injection time

- (vol of plasma) x (slope of your curve) = plasma clearance

what is the Effective Renal Plasma Flow (ERPF)?

Represents the portion of blood that is presented to the renal secretory tissue