An overview of Renography - the medical imaging of kidneys using Nuclear Medicine - including its advantages and disadvantages over other Radiographic imaging modalities.
3. DEFINITION
Renography is the medical imaging of the kidney
using radionuclide material (such as Tc-99m-
MAG3), and viewed with a Gamma camera.
4. There are other methods of imaging the kidney, such as KUB X-
ray (Kidney-Ureter-and-Bladder X-ray) Computed Tomography
(CT), MRI, Ultrasound, etc.
However, Renography refers specifically to the use of
radionuclides. It is therefore sometimes called Nuclear
Renography or Radioisotope Renography or Renal
Scintigraphy.
KIDNEY IMAGING
5. HOW IS A RENOGRAPHY SCAN DONE?
After injection of radionuclide material (or radioactive
tracer/radiopharmaceutical) into the intravenous system,
the compound is usually localized/excreted by a specific
organ (in this case, the kidneys) and its progress
through the renal system/urinary tract can be tracked
using a gamma camera.
Radionuclides contains radioactive atoms. When those
atoms decay, they emit gamma rays that are detected
by the gamma camera.
6. POSITIONING
• Posterior: This camera may be placed posterior to the
patient because the kidneys are closer to the back.
• RPO: Right Posterior Oblique is used to view the right
kidney better, with the patient lying sideward on his/her
RIGHT side.
• LPO: LEFT Posterior oblique is used to view the LEFT
kidney better, with the patient lying sideward on his/her
7. POSITIONING (CONTD.)
The patient will lie supine for the test. Otherwise, he/she will be
seated. The detector is then brought as close as possible to the
patient’s back.
Detector
8. Fig: Image of Left and Right Kidney taken from the Right Poste
Oblique (RPO) position.
9. RADIONUCLIDES
• Tc-99m-MAG3 (Mercapto Acetyl Tri Glycine)
• Tc-99m-DTPA (Diethylene Triamine Pent Acetate)
• EC (Ethyl Cysteine)
• 131-Iodine labelled OIH (Ortho-Iodo-Hippurate)
Tc-99m is the most commonly used radionuclide, because of its low
half life for gamma emission of 6 hours (meaning about 93.7% of it
decays in 24 hours).
The relatively ‘short’ Physical Half Life of the isotope allows for
scanning procedure, which collects data rapidly but keeps total
patient exposure low.
10. CLASSES OF RADIONUCLIDES USED
• Filtered Agents:- used in evaluating vascular supply, measuring
renal function (filtration rate), drainage (detects obstruction).
Time–Activity (dynamic) studies are usually used.
• Excreted Agents:- they are excreted by the renal tubules.
These agents are helpful with evaluating patients with
diminished renal function and kidney transplant.
• Cortical Imaging Agents:- used in evaluating patients with
renal scarring from chronic infection and renal mass.
11. Technetium-99m is most widely used radionuclide. It readily emits
easily detectable 140 keV gamma rays (about the same wavelength
as those emitted by conventional X-ray machines. For adults, about
8 mCi IV of Tc-99m is given.
12. Fig: Injection of radionuclide intravenously
A Gamma Camera tracks the radioisotopes and measures how the kidneys
process it, producing 2D images or 3D images (using SPECT – Single Photon
Emission Computed Tomography).
13. GAMMA CAMERA
(also called Scintillation/Anger/Nuclear Medicine Camera)
The gamma camera consists of
• Collimators: made of Lead, and helps to maintain image quality. Gamma
rays emitted in line with the collimator holes are transmitted to the crystal,
whereas rays emitted obliquely are absorbed by the collimator septa.
• Scintillator (Image Crystal, e.g. NaI), which converts the gamma ray
photons to visible light.
• PhotoMultiplier Tube (PMT), which converts the visible light to electrical
signals, as it detects and amplifies the electrons produced by its
photocathode.
• Pre-amplifier is usually attached to the back of the PMT to amplify the
electrical signal, and send to the computer for encoding and image
formation (renogram).
14.
15. AREAS/REGIONS OF
INTEREST
This is the area from which the
radioactivity is measured in the
analysis. We have 2 areas of
interest:
• Kidney Area, and
• Background Area.
The radioactivity detected from the
background data is subtracted from
the kidney to eliminate background
16. Three phases are described for quantifying the renogram by
analysis of time-activity curves of the Left and Right kidney Areas of
Interest.
• Perfusion Phase (0-30 sec) - first passage of the radioactive
bolus into the kidney.
• Parenchymal Phase (40-160 sec) - filtration and/or secretion
before any excretion - slope of curve
• Excretory Phase (3-20 min).
Time to peak on the renogram curve, or Tmax, is defined as the
absolute maximum of each renal curve. This peak should occur by 5
minutes after injection.
RENOGRAM DATA
ANALYSIS
17. ADVANTAGES
• It is useful in evaluating the physiology/functioning of the kidney by monitoring
flow of radioisotope and how efficiently the kidneys absorb and pass it. Other
modalities provide info mainly about anatomy of organs.
• It shows abnormalities in structure, size and shape of the kidneys.
• The radioisotope material helps to differentiates between passive dilation and
obstruction.
• It is important to be done before and after renal transplantation to check for the
vascularity of the kidney to be transplanted, success of kidney treatment,
rejection of a kidney transplant.
• It is a good option if the patient has had an allergic reaction to the contrast dye
used in KUB X-rays.
18. DISADVANTAGES
• It produces lower contrast images than KUB X-ray, CT and MRI, and
may require further tests to clarify a diagnosis.
• Renography may not reliably differentiate between cysts (abnormal
sac filled with fluid) and tumours (abnormal mass of tissue/swelling)
.
• Time consuming. A typical scan takes 30 mins – 2 hours.
• Requires nuclear reactor producing radionuclide to be close.
19. CONCLUSION
During/after treatment, diuretics may be given to the
patient to enhance urine production / kidney metabolism
and to help excrete the radionuclide from the patient’s
body as urine.
