Radioisotope renography is a form of

medical imaging Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to revea ...

of the

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

s that uses

radiolabelling A radioactive tracer, radiotracer, or radioactive label is a synthetic derivative of a natural compound in which one or more atoms have been replaced by a radionuclide (a radioactive atom). By virtue of its radioactive decay, it can be used to exp ...

. A renogram, which may also be known as a MAG3 scan, allows a

nuclear medicine Nuclear medicine (nuclear radiology, nucleology), is a medical specialty involving the application of radioactivity, radioactive substances in the diagnosis and treatment of disease. Nuclear imaging is, in a sense, ''radiology done inside out'', ...

physician or a

radiologist Radiology ( ) is the medical specialty that uses medical imaging to diagnose diseases and guide treatment within the bodies of humans and other animals. It began with radiography (which is why its name has a root referring to radiation), but tod ...

to visualize the

s and learn more about how they are functioning. MAG3 is an acronym for

mercapto In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

acetyl In organic chemistry, an acetyl group is a functional group denoted by the chemical formula and the structure . It is sometimes represented by the symbol Ac (not to be confused with the element actinium). In IUPAC nomenclature, an acetyl grou ...

tri

glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...

, a compound that is

chelate Chelation () is a type of bonding of ions and their molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These l ...

d with a radioactive element –

technetium-99m Technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used Radiophar ...

. The two most common radiolabelled pharmaceutical agents used are ^99mTc-MAG3 (MAG3 is also called "mercaptoacetyltriglycine" or "mertiatide") and ^99mTc

DTPA Pentetic acid or diethylenetriaminepentaacetic acid (DTPA) is an aminopolycarboxylic acid consisting of a diethylenetriamine backbone with five carboxymethyl groups. The molecule can be viewed as an expanded version of EDTA and is used similarl ...

(diethylenetriaminepentacetate). Some other radiolabelled pharmaceuticals are EC (Ethylenedicysteine) and 131-iodine labelled OIH ( ''ortho''-iodohippurate).

Scan procedure

After injection into the

vein Veins () are blood vessels in the circulatory system of humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are those of the pulmonary and feta ...

s, the compound is excreted by the kidneys, and its progress through the

renal system The human urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressu ...

can be tracked with a

gamma camera A gamma camera (γ-camera), also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The applications of scintigraphy include early drug development ...

. A series of images are taken at regular intervals. Processing then involves drawing a

region of interest A region of interest (often abbreviated ROI) is a sample within a data set identified for a particular purpose. The concept of a ROI is commonly used in many application areas. Existing as a vicinity, or within one. For example, in medical imagin ...

(ROI) around both kidneys, and a computer program produces a graph of radioactivity inside the kidney with time, representing the quantity of tracer, from the number of counts measured inside in each image (representing a different time point). If the kidney is not getting blood for example, it will not be viewed at all, even if it looks structurally normal in

medical ultrasonography Medical ultrasound includes Medical diagnosis, diagnostic techniques (mainly medical imaging, imaging) using ultrasound, as well as therapeutic ultrasound, therapeutic applications of ultrasound. In diagnosis, it is used to create an image of ...

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and ...

. If the kidney is getting blood, but there is an obstruction inferior to the kidney in the bladder or ureters, the radioisotope will not pass beyond the level of the obstruction, whereas if there is a partial obstruction then there is a delayed transit time for the MAG3 to pass. More information can be gathered by calculating time activity curves; with normal kidney perfusion, peak activity should be observed after 3–5 minutes. The relative quantitative information gives the differential function between each kidney's filtration activity.

Tracers

MAG3 is preferred over ^99mTc DTPA in

neonate In common terminology, a baby is the very young offspring of adult human beings, while infant (from the Latin word ''infans'', meaning 'baby' or 'child') is a formal or specialised synonym. The terms may also be used to refer to Juvenile (orga ...

s, patients with impaired function, and patients with suspected obstruction, due to its more efficient extraction. The MAG3 clearance is highly correlated with the

effective renal plasma flow Effective renal plasma flow (eRPF) is a measure used in renal physiology to calculate renal plasma flow (RPF) and hence estimate renal function. Because the extraction ratio of PAH is high, it has become commonplace to estimate the RPF by divid ...

(ERPF), and the MAG3 clearance can be used as an independent measure of kidney function. After intravenous administration, about 40-50% of the MAG3 in the blood is extracted by the

proximal tubule The proximal tubule is the segment of the nephron in kidneys which begins from the renal (tubular) pole of the Bowman's capsule to the beginning of loop of Henle. At this location, the glomerular parietal epithelial cells (PECs) lining bowman’s ...

s with each pass through the kidneys; the proximal tubules then secrete the MAG3 into the tubular lumen. ^99mTc DTPA is filtered by the

glomerulus ''Glomerulus'' (; : glomeruli) is a common term used in anatomy to describe globular structures of entwined vessels, fibers, or neurons. ''Glomerulus'' is the diminutive of the Latin ''glomus'', meaning "ball of yarn". ''Glomerulus'' may refer to ...

and may be used to measure the

glomerular filtration rate Renal functions include maintaining an acid–base balance; regulating fluid balance; regulating sodium, potassium, and other electrolytes; clearance (medicine), clearing toxins; absorption of glucose, amino acids, and other small molecules; reg ...

(GFR) (in a separate test), making it theoretically the best (most accurate) choice for kidney function imaging. The extraction fraction of DTPA is approximately 20%, less than half that of MAG3. DTPA is the second most commonly used renal radiopharmaceutical in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

Clinical use

The technique is very useful in evaluating the functioning of kidneys. Radioisotopes can differentiate between passive dilatation and obstruction. It is widely used before kidney transplantation to assess the

vascularity Vascularity, in bodybuilding, is the condition of having many highly visible, prominent, and often extensively-ramified superficial veins. The skin appears "thin"—sometimes virtually transparent—due to an extreme reduction of subcutaneous fat ...

of the kidney to be transplanted and with a test dose of

captopril Captopril, sold under the brand name Capoten among others, is an ACE inhibitor, angiotensin-converting enzyme (ACE) inhibitor used for the treatment of hypertension and some types of congestive heart failure. Captopril was the first oral ACE inh ...

to highlight possible

renal artery stenosis Renal artery stenosis (RAS) is the narrowing of one or both of the renal arteries, most often caused by atherosclerosis or fibromuscular dysplasia. This narrowing of the renal artery can impede blood flow to the target kidney, resulting in r ...

in the donor's other kidney, and later the performance of the transplant. Post-transplantation renography can be used for the diagnosis of vascular and urological complications. Also, early post-transplantation renography is used for the assessment of delayed graft function. The use of the test to identify reduced kidney function after test doses of captopril (an

angiotensin-converting enzyme inhibitor Angiotensin-converting-enzyme inhibitors (ACE inhibitors) are a class of medication used primarily for the treatment of high blood pressure and heart failure. This class of medicine works by causing relaxation of blood vessels as well as a decr ...

medication) has also been used to identify the cause of

hypertension Hypertension, also known as high blood pressure, is a Chronic condition, long-term Disease, medical condition in which the blood pressure in the artery, arteries is persistently elevated. High blood pressure usually does not cause symptoms i ...

in patients with

kidney failure Kidney failure, also known as renal failure or end-stage renal disease (ESRD), is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney fa ...

. Initially there was uncertainty as to the usefulness, or best test parameter to identify renal artery stenosis, the eventual consensus was that the distinctive finding is of alteration in the differential function.

History

In 1986, MAG3 was developed at the University of Utah by Dr. Alan R. Fritzberg, Dr. Sudhakar Kasina, and Dr. Dennis Eshima. The drug underwent clinical trials in 1987 and passed Phase III testing in 1988. Before the development of tracers such as ^99mTc-MAG3, a range of other radiopharmaceuticals were employed. The test was first introduced in 1956, using

iodine-131 Iodine-131 (131I, I-131) is an important radioisotope of iodine discovered by Glenn Seaborg and John Livingood in 1938 at the University of California, Berkeley. It has a radioactive decay half-life of about eight days. It is associated with nu ...

diodrast Diodone is a radiocontrast agent that was used in urography. It was usually formulated as a salt with diethanolamine. See also * Iodinated contrast Iodinated contrast is a form of water-soluble, intravenous radiocontrast agent containing iodin ...

. Later developments included iodine-131, and then

iodine-123 Iodine-123 (123I) is a radioactive isotope of iodine used in nuclear medicine imaging, including single-photon emission computed tomography (SPECT) or SPECT/CT exams. The isotope's half-life is 13.2232 hours; the decay by electron capture to t ...

, labelled ortho-Iodohippuric acid (OIH, marketed as Hippuran). ^99mTc-MAG3 has replaced ¹³¹I-OIH because of better quality imaging regardless of the level of kidney function, and lower radiation doses.

References

{{Medical imaging Diagnostic nephrology Scintigraphy Urologic imaging