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. At the end of the test, a person is asked to pass urine and a final X-ray is taken. Before the test, a person is asked to pass urine so that their bladder is emptied. They are asked to lie flat during the procedure.
Normal appearances
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 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 is emptied. An IVP can be performed in either emergency or routine circumstances.
Emergency IVP
This procedure is carried out on patients who present to an Emergency department, usually with severe renal colic and a positive hematuria test. In this circumstance the attending physician requires to know whether a patient has a kidney stone and if it is causing any obstruction in the urinary system. Patients with a positive find for kidney stones but with no obstruction are sometimes discharged based on the size of the stone with a follow-up appointment with a urologist. Patients with a kidney stone and obstruction are usually required to stay in hospital for monitoring or further treatment. An Emergency IVP is carried out roughly as follows:
delayed abdominal X-ray, taken at roughly 15 minutes post injection.
If no obstruction is evident on this film a post-micturition film is taken and the patient is sent back to the Emergency department. If an obstruction is visible, a post-micturition film is still taken, but is followed up with a series of radiographs taken at a "double time" interval. For example, at 30 minutes post-injection, 1 hour, 2 hours, 4 hours, and so forth, until the obstruction is seen to resolve. This time delay can give important information to the urologist on where and how severe the obstruction is.This is very useful.
Routine IVP
This procedure is most common for patients who have unexplained microscopic or macroscopic hematuria. It is used to ascertain the presence of a tumour or similar anatomy-altering disorders. The sequence of images is roughly as follows:
plain or Control KUB image;
immediate X-ray of just the renal area;
5 minute X-ray of just the renal area.
15 minute X-ray of just the renal area.
At this point, compression may or may not be applied. In pyelography, compression involves pressing on the lower abdominal area, which results in distension of the upper urinary tract.
If compression is applied: a 10 minutes post-injection X-ray of the renal area is taken, followed by a KUB on release of the compression.
If compression is not given: a standard KUB is taken to show the ureters emptying. This may sometimes be done with the patient lying in a prone position.
A post-micturition X-ray is taken afterwards. This is usually a coned bladder view.
Image assessment
The kidneys are assessed and compared for:
Regular appearance, smooth outlines, size, position, equal filtration and flow.
The ureters are assessed and compared for:
Size, a smooth regular and symmetrical appearance. A 'standing column' is suggestive of a partial obstruction.
Metformin use: Historically, the drug metformin has been required to stop 48 hours pre and post procedure, as it known to cause a reaction with the contrast agent. However the newest guidelines published by the Royal College of Radiologists suggests this is not as important for patients having <100mls of contrast, who have a normal kidney function. If kidney impairment is found before administration of the contrast, metformin should be stopped 48 hours before and after the procedure.
Contrast allergy: If the patient has any previous history of adverse or moderate reactions to contrast medium.
Patient with significantly decreased kidney function ;because contrast media can be nephrotoxic and worsen kidney function
Other tests
An IVP can and should be used in conjunction with the following tests:
Ultrasound
Cystoscopy
CT
MRI
Video cystometrography or VCMG
Blood test
Urine analysis
Treatment
Depending on the outcome and diagnosis following an IVP, treatment may be required for the patient. These include surgery, lithotripsy, ureteric stent insertion and radiofrequency ablation. Sometimes no treatment is necessary as stones <5mm can be passed without any intervention.
Future
IVP is an affordable yet useful imaging modality and continues to be relevant in many parts of the world. In the developed world, however, it has increasingly been replaced by contrast computed tomography of the urinary tract, which gives greater detail of anatomy and function.
History
The technique of IVP was originally developed by Leonard Rowntree of the Mayo Clinic in the 1920s. IVP was previously the test of choice for diagnosing ureter 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. Now, because of increased accuracy computed tomography and ultrasounds of the renal tract are used; ultrasounds additionally do not involve radiation. Etymologically, urography is contrast radiography of the urinary tract, and pyelography is contrast radiography of the renal pelvis, but in present-day standard medical usage, they are synonymous.
