Overview of Radionuclide Cystography
Radionuclide cystography (RNC) is a type of medical imaging test that doctors use to check for problems in the tubes (ureters) that carry urine from the kidneys to the bladder, as well as the bladder itself. In this test, they use a special kind of medicine called a radiopharmaceutical agent to help them see these areas more clearly.
This test can be done in two ways. In one method, they can inject the medicine directly into your bladder using a small tube called a catheter. The other way involves injecting the medicine into a vein. Once in your body, the medicine eventually makes its way to your kidney and bladder area. Because your body naturally flushes out this medicine in your urine, it can help show how your bladder and ureters are working.
The doctors then use a device called a gamma camera to take pictures of your bladder and ureters. This camera works by detecting the small amounts of radiation that the medicine gives off.
RNC is most often used to diagnose a condition called vesicoureteric reflux (VUR). This is when urine flows backwards from the bladder into the ureters. If not treated, VUR can cause kidney damage, frequent infections, and high blood pressure.
Anatomy and Physiology of Radionuclide Cystography
The process of performing a radionuclide cystography (RNC), a type of imaging test, involves looking at different parts of the urinary system. These parts typically include the kidneys, the ureters (tubes that carry urine from the kidneys to the bladder), the bladder (that stores urine) and the urethra (the duct which carries urine from the bladder to outside the body).
The resolution of modern imaging equipment is very good, allowing us to see details as small as a few millimeters, or nearly a centimeter. This means that anything smaller than this might not be detected during the RNC test.
Typically, the kidneys produce urine that then collects in the renal pelvis, a funnel-like part which then drains into the ureters. The ureters have muscular walls that contract in a wave-like motion, pushing the urine forward and down into the bladder. The ureters enter the bladder at an angle, a key feature that generally ensures the flow of urine is only one-way, from the ureters into the bladder and not the other way around. If this one-way flow fails, urine can flow back into the ureters, a condition known as vesicoureteric reflux (VUR), which can cause kidney damage if not diagnosed early.
When your bladder is full of urine, your body triggers a reflex known as the micturition reflex. This causes the bladder wall to tightly squeeze and the muscles (internal urethral sphincter) at the connection to the urethra to relax, allowing urine to flow out. The process of urination is controlled by another muscle (external urethral sphincter), which you can contract or relax to start or stop urinating.
During an RNC examination, the bladder should generally appear round, tapering slightly towards the bottom. If VUR is happening, the imaging test will show increased tracer activity, which looks like thin curvy extensions from the bladder up to the renal pelvis. Severe or chronic VUR can cause the ureters to widen and twist. If the test shows increased activity outside where it’s expected or a strange shape of the bladder, further tests may be required to look for other issues, such as bladder diverticula (abnormal pouches in the bladder wall), or pressure on the bladder from adjacent structures.
RNC is also commonly done in cases of kidney transplant, where the new kidney is usually placed in the pelvis and connected to the iliac vessels (the main blood vessels in the pelvis). This might cause a bulging in the bladder’s appearance during the RNC. Also, VUR is common in kidney transplants because the standard valve at the UVJ is not present.
Why do People Need Radionuclide Cystography
Radionuclide cystography (RNC) is a type of test that uses a small amount of radioactive material to look at the bladder and the tubes that carry urine from the kidneys to the bladder (ureters). It may be performed for several reasons:
1. Evaluating urinary tract infections in female patients: Doctors use this test to check for a condition called vesicoureteric reflux (VUR), which happens when urine flows back from the bladder into the ureters. This can be a cause of urinary tract infections.
2. Diagnosing VUR in children with a family history: If there’s a family history of VUR, this test can be used to diagnose if the child has VUR.
3. Checking the effect of a treatment for VUR: If a patient has had medical or surgical treatment for VUR, doctors can use the test to see if it worked.
4. Checking for reflux in people with a neurogenic bladder: This test can help doctors see if urine is flowing back into the ureters in people with a neurogenic bladder. A neurogenic bladder is a condition where someone cannot control their bladder because of nerve damage.
5. Diagnosing VUR in renal transplant recipients: For those who’ve received a kidney transplant, this test is used to diagnose VUR.
6. Diagnosing and checking on VUR in patients with persistent prenatal hydronephrosis: This is a condition where the area of the kidney that collects urine is enlarged in a fetus. This test helps diagnose and monitor VUR in such cases.
7. Measuring the amount of urine left in the bladder after urinating: This helps doctors see how well the bladder is functioning.
When a Person Should Avoid Radionuclide Cystography
Radionuclide cystography (RNC) is a safe procedure used to look at your bladder and lower urinary tract, but there are still some reasons why a person might not be able to have it. Those reasons include:
1. A person might have had an allergic reaction or other problem when given a radiopharmaceutical (a type of medicine that has a small amount of radiation) in the past, although this is rare. These reactions are usually caused by allergies and sometimes cause a drop in heart rate and blood pressure.
2. If a person currently has a urinary tract infection that hasn’t been treated, the radiopharmaceutical, specifically sodium pertechnetate, which is sometimes used in the procedure, could get absorbed into their system.
There are other factors that doctors will need to carefully consider before performing an RNC, although they don’t necessarily mean the procedure can’t be done. Doctors may need to make some adjustments to ensure the procedure will give them a clear enough picture to make a diagnosis.
1. Pregnancy – Although the amount of radiation the fetus would be exposed to during an RNC is very low, if a person is pregnant, doctors should try to avoid it if possible. Instead, they may use another type of test that uses a contrast agent and ultrasound. If there are no other options, the doctors will try to use the lowest amount of radiation possible without making the test results unclear.
Issues with the structure of the urinary system – If there are known abnormalities that could result in the radiopharmaceutical getting trapped in the bladder, vagina, rectum, or elsewhere, doctors may want to avoid an RNC. Also, if an abnormality might cause a significant leak or loss of the radiopharmaceutical, the doctors will need to be very careful to avoid contamination.
The most successful RNC tests involve the patient actively participating, particularly during the parts of the test where the patient needs to empty their bladder. Some conditions might not show up unless they happen while the bladder is being emptied. If a patient can’t participate in this part of the test, they could get test results that seem normal but aren’t.
Equipment used for Radionuclide Cystography
The following is a breakdown of the tools and materials required for a type of medical test known as radionuclide cystography (RNC):
1. Various tools needed to insert a medical device called a foley catheter (a flexible tube used to drain urine from the bladder).
2. A radiopharmaceutical, which is a radioactive substance that helps create clearer images in the scan.
3. Sterile saline, a type of clean salt water.
4. A device called a gamma camera which captures the images from the radiopharmaceutical.
5. Other necessary items for safely storing, collecting, and disposing of any leftover radioactive materials.
The radiopharmaceuticals often used in this test are called technetium-99m sodium pertechnetate, Tc-99m sulfur colloid, or Tc-99m diethylenetriamine penta-acetic acid (DTPA). The appropriate dose differs, but generally should not exceed 1 mCi per cycle of urination in children. Certain patients, particularly those with medical alterations to the bladder or certain inflammation conditions, should avoid some of these substances.
For a slightly different type of RNC, the radiopharmaceuticals can be given through an injection into a vein, then they travel to the urinary tract, avoiding the need for a catheter in the bladder. This method can also help doctors understand how well the kidneys are functioning. The typical radiopharmaceuticals in this case are technetium-99m-mercaptoacetyltriglycine (Tc-99m-MAG3) or technetium-99m-DTPA.
Technetium-99 emits particles of light called photons, which the gamma camera can capture. To make sure enough photons are present for the camera to capture an image, the amount of technetium-99m activity is checked before giving it to the patient. This amount can be quantified by tracking how many radioactive atoms fall apart every second, which is equal to the number of photons emitted.
A gamma camera is a special tool that captures images of gamma radiation in a process known as scintigraphy. Basic parts of this camera include a device called a collimator, a large crystal made of a substance called sodium-iodide (NaI), multiple light detection tubes, and image enhancing electronics. The collimator helps increase the clarity of the images by absorbing scattered gamma rays. The NaI crystal absorbs the gamma photons and emits light, which is caught by the light detection tubes and sent to a computer to create the final image.
How is Radionuclide Cystography performed
Before any medical exam, it’s crucial to clearly explain what will happen to the patient or their parents if the patient is a child. A complete health history can help the doctor understand why the exam is needed, check for any ongoing infections, and find out about any previous surgeries involving the urinary tract. It’s also helpful to look at any past imaging tests for any specific anatomical details or other findings.
In a test known as a retrograde radionuclide cystography (RNC), a tube, called a Foley catheter, is inserted into the bladder while taking care to keep everything sterile. In some situations, a small puncture above the pubic bone might be made instead. Once the catheter is in place, the patient is seated on a bedpan if possible, and a special camera is positioned behind them. If the patient can’t sit upright, the images can be taken while they lie down.
Next, a small amount of radioactive material is injected into the bladder. This can be done by mixing the radioactive material with a saltwater solution (250-500 mL), or it can be injected straight into the catheter followed by the saltwater solution. If the second method is chosen, 10-20 mL of saltwater should be added to the catheter before the radioactive material to ensure that the lining of the bladder isn’t directly exposed to the radioactive material.
The bladder is filled either until it can’t take any more fluid or until it reaches the volume that’s normal for the patient’s age. For children, the bladder volume is approximated by the formula (in milliliters): [age (years) + 2] x 30 mL. For adults, the typical bladder capacity can be from 300 to 400 mL. Filling the bladder slowly can decrease spasms, and using body-temperature salt water can make the patient more comfortable.
If any radioactivity is seen above the bladder or within the system that collects urine from the kidneys, it means the urine is flowing back into the kidneys. This flow back can occur during, before, or after urination. The RNC test is very good at spotting this issue. It can even detect a flow back volume as low as 1 mL. If no activity is seen above the bladder, images are taken while the patient is urinating because the flow back might only be visible during this stage of the exam. Typically, 5-second images are acquired during filling and urinating with 30-second front-view images before and after urination. The flow back on RNC is graded as mild, moderate, or severe:
– Mild: The flow back is limited to the tube that carries urine from the kidney to the bladder (ureter).
– Moderate: The flow back reaches the area in the kidneys where urine is collected.
– Severe: The flow back reaches the area in the kidneys where urine is collected and is associated with dilation and twisting of the ureter and the kidney structures involved in urine collection.
A similar procedure, called the antegrade RNC, involves injecting the radioactive material into a vein and then taking images of the kidneys and the related structure until the bladder is fully distended. Like in the retrograde technique, the patient is placed in an upright position to urinate with the gamma camera at their back, if possible. If the patient can’t cooperate, images are obtained in the supine position. If the patient fails to hold their urine until requested, the test might not provide useful results.
The amount of urine left in the bladder after urination is determined by studying pre- and post-urination images. Here is the formula used to calculate this volume:
Residual volume = [voided volume in ml X post-void bladder counts] / [Initial bladder counts – post-void bladder counts]
Possible Complications of Radionuclide Cystography
Going through a procedure called radionuclide cystography (RNC), which examines how the bladder and urinary tract are working, rarely results in complications. Yet, there’s always a small chance of developing a urinary tract infection (UTI) due to the placement of a catheter in the urethra, a tube that carries urine out of the body. Based on a recent study, about 1% of patients get a UTI after RNC, especially if they already have issues with their urinary system, like reflux of urine back into kidneys (VUR) or swelling in kidneys due to urine buildup (hydronephrosis).
Despite this slight risk, routinely using antibiotics to prevent infections before the procedure isn’t typically recommended. Additionally, there could be minor issues like injury to the urethra. But rest assured such problems are infrequent and usually minor.
What Else Should I Know About Radionuclide Cystography?
Vesicoureteral reflux (VUR) is a condition where urine flows backward from the bladder to the kidneys. Detecting this early and correctly is very important to avoid long-term kidney damage. VUR is often discovered in children who may need several follow-up checks, so it’s essential to limit their exposure to radiation, which could have harmful effects.
Doctors use two main types of X-ray tests to detect VUR: radionuclide cystography (RNC) and micturating cystourethrograms (MCU). MCU involves using X-rays to examine a contrast dye that’s put into the bladder through a tube. This test uses still and moving images to view the flow of urine. Both X-rays and gamma rays can cause DNA damage.
However, RNC is not just more accurate at detecting VUR but also uses about 1/20th of the radiation dose that MCU uses. To understand how low the radiation dose is, it’s almost ten times less than a regular chest X-ray.
There are newer tests, such as contrast-enhanced voiding urosonography (ceVUS), which use high-frequency sound waves (much like an ultrasound) and a special dye to capture clear images of the bladder, urethra, and ureters. This test doesn’t use harmful radiation, but it might be hard to perform in some rare cases, and things like gas in the intestine can distort the images.
So in certain situations, RNC might be the best test to use. It’s safe, accurate, and crucial for detecting any problems with the urinary system while minimizing risks.
