<P> In IVP, the contrast agent is given intravenously, allowed to be cleared by the kidneys and excreted through the urinary tract as part of the urine . If this is contraindicated for some reason, a retrograde pyelogram, with the contrast flowing upstream, can be done instead . </P> <P> IVP was previously the test of choice for diagnosing ureteral obstruction secondary to urolithiasis but in the late 1990s non-contrast computerized tomography of the abdomen and pelvis replaced it because of its increased specificity regarding etiologies of obstruction . </P> <P> An injection of X-ray contrast medium is given to a patient via a needle or cannula into the vein, typically in the antecubital fossa of arm . The contrast is excreted or removed from the bloodstream via the kidneys, and the contrast media becomes visible on X-rays almost immediately after injection . X-rays are taken at specific time intervals to capture the contrast as it travels through the different parts of the urinary system . This gives a comprehensive view of the patient's anatomy and some information on the functioning of the renal system . </P> <P> Immediately after the contrast is administered, it appears on an X-ray as a' renal blush' . This is the contrast being filtered through the cortex . At an interval of 3 minutes, the renal blush is still evident (to a lesser extent) but the calyces and renal pelvis are now visible . At 9 to 13 minutes the contrast begins to empty into the ureters and travel to the bladder which has now begun to fill . To visualize the bladder correctly, a post micturition X-ray is taken, so that the bulk of the contrast (which can mask a pathology) is emptied . </P>

What type of patient preparation is required for an ivp
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