B5.079 Prework 1: Renal Imaging Flashcards
pros and cons of conventional radiographs
pros: cheap and quick
cons: poor soft tissue detail & radiation
pros and cons of CT
pros: high spatial and contrast resolution, relatively short exam, easy to access
cons: high radiation dose, risks of iodinated contrast
pros and cons of nuclear scintigraphy
pros: provides functional data
cons: poor resolution, radiation exposure
pros and cons of ultrasound
pros: relatively cheap and quick, no radiation
cons: cant visualize ureters, operator dependent
is MRI used for kidney imaging?
not often
2nd or 3rd line only
2 main categories of renal imaging
structural: xray, CT, US
functional: nuclear medicine
how does a CT of the kidney work
produce cross sectional images of the kidney utilizing an xray source and detector on a rotating gantry
often performed with IV contrast
can produce images in any plane
4 phases of renal imagining w contrast
- pre contrast
- post contrast: corticomedullary
- post contrast: nephrogenic
- delayed: pylographic
why are there different phases of renal imaging?
each phase highlights a different portion of the kidney and allows detection of different disease processes
pre-contrast imaging uses
renal calcifications
no differentiation
corticomedullary phase imaging description
20-40 s after contrast admin
cortex brighter than medulla/pelvis (kidneys perfuse from outside in)
nephrogenic phase imaging description
60-120 s after contrast admin
equal distribution of contrast between cortex and medulla
pyelographic phase imaging description
minutes to hours after contrast admin
contrast in calices and pelvis
early post contrast imaging uses
detects and characterizes solid vs cystic cortical masses
i.e. RCC vs simple cyst
delayed contrast imaging uses
evaluates renal pelvis and ureter for mass lesions
i.e. UCC
appearance of cyst on post contrast CT
dark, homogenous mass
appearance of RCC on post contrast CT
mass with mixed densities throughout, lighter than cyst
how does an ultrasound work for kidney imagine
high frequency sound waves are produced by a piezoelectric crystal in a transducer and transmitted into the tissues via a gel medium
transducer also receives reflected sound waves and converts them back into electrical currents for image reconstruction
2 main factors in ultrasound image reconstruction
travel time for a reflected beam of sound (depth)
degree to which it is reflected (acoustic impedance)
high acoustic impedance on US
fat, air, bone, metal
appear whiter
hyperechoic
low acoustic impedance on US
water
appear dark
hypoechoic
normal kidney appearance on US
edge is lighter
cortex darker
collection of renal sinus fat in center appears light
hydronephrosis on US
dark circles in center of kidney due to urine filled calices
use of Doppler imaging on kidney
can determine direction and speed of blood flow within the structure
helps determine is there is vasculature in a mass (RCC vs fluid filled cyst)
how does nuclear medicine imaging of the kidney work
utilizes selective binding and/or filtering of various radioactive compounds (radionuclides)
most common renal scintigraphic study is a MAG-3 renal scan
what is MAG-3
compound which is partially filtered from the blood via the glomerulus and partially secreted from the tubules
labeled with radioactive technicium
uses of renal scintigraphy
can construct an image with radioactivity and also quantitate amount of activity in a given structure over time
evaluates renal function and can be used to determine GFR
normal activity vs time curve for a kidney
activity rises to a peak and then begins to decline steadily
decreases faster with administration of Lasix
activity vs time curve during hydronephrosis
activity constantly rises and never falls, even with Lasix administration
radioactive material cannot be excreted due to blockage
activity vs time curve in nonobstructed but dilated kidney
rises to a peak, but eventually falls off with Lasix infusion
