The different methods of imaging the kidneys
Ultrasound, CT Scan, MRI, IVP (Intravenous Pyelogram), Renal scan, Renal Arteriogram are some commonly used methods to image the kidneys.

Imaging studies of kidney are used to

1. Study the location and size of the kidneys.
2. To identify presence and the size of obstruction.
3. To visualize blood supply to the kidneys.
4. To detect and characterize any malformations such as cysts, tumors.

Intravenous pyelogram (IVP)
The IVP is called as intravenous pyelogram. It involves the intravenous injection of iodinated contrast material which is filtered at the glomerulus and gets concentrated within the tubules. It is finally excreted into the ureters and finally through the bladder into the urine. X–rays are taken at different time intervals from the injection of the dye. The dye usually appears from 1 to 3 minutes after the contrast material is injected.

It provides an opportunity to determine the number of kidneys, their size, their configuration and if there are any filling defects. The second phase occurs between five minutes and it allows visualization of the ureters and the bladder. IVP exposes one to radiation and therefore not advised when it comes to pregnant women or very young children. In addition, the radiocontrast can be a toxin to the kidney and especially in some people who already have some renal impairment.

Ultrasound image
Ultrasonography represents a major advance in the non-invasive visualization of the kidney. The principal used is that of ultrasound waves which generate an echo when their passage is impeded by tissues air fluid etc. The significant differences in this impedance occurs among tissues which differ in the content of water fats, minerals solids etc. The waves that are reflected are recorded as signals.
The main uses are to

• Determine the size of the kidneys.
• See if there is any obstruction to the flow of urine
• Evaluate cysts and tumors. Numerous cysts in both kidneys usually signifies polycystic kidney disease. Solid renal masses may signify the presence of tumor.

CT Scan
Useful in imaging cysts and tumors, hemorrhage or infections.

Renal Arteriography
Renal arteriography means the visualization of the renal arteries by the injection of dye into the arteries. It is mainly used to diagnose any narrowing of the renal arteries (renal artery stenosis) which are commonly seen in advanced atherosclerosis or people who are smokers.

Renal scan
The renal scan involves intravenous injection of a radionuclide labeled agent that emits radiation. Use of a scintillation camera picks up this radiation as the agent passes through the kidney. The radio pharmaceutical agents generally used are I–31 or technetium 99.

The renal scan provides information about the blood flow within the kidney. Delayed excretion of the agent which may signify intrinsic renal disease, decreased blood flow or obstruction to the flow of urine.

This is mainly used to evaluate patients who are at high risk for an adverse reaction to contrast material in whom a renal arteriogram or IVP cannot be done.