Overview of Nuclear Renal Scan
A nuclear renal scan, also known as renal scintigraphy, is a type of medical test that uses special substances called radiopharmaceuticals or radiotracers to examine the structure, function, and any disease in the kidneys. These substances, once injected into the body, are filtered out by the kidneys and produce a type of energy called gamma radiation. This radiation is then picked up by special cameras, to create images of the kidneys. These tests are generally straightforward to carry out, and there’s usually no need for the patient to be sedated.
The way nuclear renal scans are used has changed over time due to several factors. Firstly, the advancement in other imaging tests such as ultrasound, CT scan, and MRI has influenced their use. Secondly, the development and accessibility of different radionuclides – the substances used in the test. Lastly, the existing standard methods and preferred techniques for investigating various medical conditions have also affected its use.
Anatomy and Physiology of Nuclear Renal Scan
The kidneys are located on both sides of the body (bilaterally), roughly at the level of your upper waist, along your back. The left kidney typically sits a bit higher than the right one.
Each kidney is made up of two major parts: the renal parenchyma and the renal sinus. “Renal” just means it relates to the kidney.
The renal parenchyma is the functioning part of the kidney. It’s divided into two areas: the outer part (cortex) and inner part (medulla). The outer cortex contains structures like the glomeruli, which filter the blood, and renal tubules, which collect the filtered blood. The renal medulla has collecting ducts that concentrate the urine that the glomeruli begin producing. This urine then trickles down into urine drainage areas called renal calyces.
The renal sinus consists of these drainage areas called calyces, the renal pelvis, and the renal arteries and veins of the kidneys. The renal pelvis is a funnel-shaped structure that collects the urine from the renal calyces and sends it down to the urinary bladder through tubes called ureters.
The kidneys get their blood supply from the renal arteries, which start from the body’s main artery, the aorta, along your body. These arteries branch into smaller ones, eventually becoming tiny capillaries that supply blood to the kidneys. These capillaries also act as filters, helping to produce urine. They also capture back important substances from the filtered blood and concentrate the urine.
Medical imaging techniques like nuclear scintigraphy use these kidney structures to check how well your kidneys are working. Injected radioactive drugs enter the renal artery and to the kidneys’ capillaries. These radioactive tracers are used to measure how quickly your kidneys filter blood (glomerular filtration rate) and estimate the flow of blood plasma to your kidneys. Other tracers are used to check the structure of the kidneys and visualize them on scans.
Why do People Need Nuclear Renal Scan
Renal scintigraphy refers to a special imaging technique used to study kidney function and structure. It’s still used widely, despite the fact there are now many other methods for studying kidney health. Although these other methods may provide a better view of the kidney’s anatomy, renal scintigraphy continues to play an important role in examining kidney function. This imaging technique can help analyze various parts of the urinary system, which includes kidneys, tubes that drain the kidneys (pylocalyceal, ureteral), and the bladder.
Here are some medical conditions and situations where renal scintigraphy might be used:
1. Reno-vascular hypertension: A type of high blood pressure caused by narrowed blood vessels to the kidneys.
2. Obstructive uropathy: When something is blocking the normal flow of urine and causing it to back up into the kidney.
3. Renal anomalies: Abnormal features or qualities found in the kidney.
4. Renal transplant: If a person has undergone a kidney transplant surgery, doctors may use this technique to check if the new organ is working properly.
5. Renal parenchymal infections: These are infections in the kidneys, especially ones such as pyelonephritis and scarring caused by previous infections.
6. Renal masses: Tumors or growths in the kidneys.
7. Renal trauma: Injury to the kidneys.
8. Ureteric trauma: Injury to the ureter, which is the tube that carries urine from the kidneys to the bladder.
When a Person Should Avoid Nuclear Renal Scan
Getting a kidney scan while you’re pregnant is not recommended because it could expose the baby to radiation, which could be harmful.
The kidney scan uses a special type of medicine called Tc-99m labeled radiopharmaceuticals. This medicine can leave the body through breast milk. But according to a group called the Academy of Breastfeeding Medicine (ABM), these types of medicinal agents don’t require a mom to stop breastfeeding. This is because the amount of medicine the baby gets is less than 1 millisievert (mSvt), which is a very small dose. However, the ABM does suggest momma takes a small break from breastfeeding after getting this medicine. They suggest a 4-hour break if she got 99mTc-MAG3 and a 12-hour break if she got 99mTc-DTPA. This is just a safety measure to ensure moms feel confident about their baby’s safety.
Equipment used for Nuclear Renal Scan
A gamma scintillation camera system is a tool used to take images of your kidneys. It works by turning signals from a radioactive substance into pictures that doctors can look at on a monitor. This radioactive substance is safe for your body and is commonly used in different medical procedures.
The gamma camera system is composed of several parts, like a collimator, a scintillation crystal, photomultiplier tubes (sort of like very sensitive light sensors), and a computer that processes all the info.
The collimator, which is placed between you and the camera, helps focus on the specific area the doctors want to study. It absorbs any unnecessary radiation and blocks anything outside the wanted view from reaching the camera. The scintillation crystals turn the gamma rays (similar to X-rays but stronger) coming from your body into a flash of light. The photomultiplier tubes then turn this flash of light into a signal, kind of like turning the volume up and down on different light levels. Finally, the computer connected to the gamma camera system uses these signals to create a detailed image depending on how the radioactive substance has spread in your body.
Beyond just making these images, the computer also refines them for easier understanding. It can give important details that can help your doctor know more about your condition. These images and information go into a local or hospital-wide image-storage system called PACS (picture archiving and communications).
Sometimes, the information from the gamma camera is combined with anatomy images from a CT scan (a type of X-ray that gives detailed pictures of the inside of your body) in a process called single-photon emission computed tomography (SPECT). This provides an even more informative picture for your doctor.
Who is needed to perform Nuclear Renal Scan?
A nuclear medicine technologist is a healthcare worker with special training to do a test known as renal scintigraphy. This test is done under the supervision of a doctor who is a radiologist or a specialist in nuclear medicine. Like a coach guiding their team, these doctors oversee the procedure to make sure everything goes as planned.
Preparing for Nuclear Renal Scan
When having a kidney scan, it’s important for the patient to be well-hydrated. This helps reduce the amount of radiation that hits the bladder wall, which could be higher if the bladder was empty. Drinking plenty of water also ensures the kidneys function properly during the scan, as dehydration can slow down the time it takes for the kidneys to get rid of waste, which could skew the results of the test.
Typically, a kidney scan doesn’t require any medication or changes in diet beforehand. However, some specific types of kidney scans do have some preparations.
For example, in a type of kidney scan called a ‘diuretic renography’, used to check for blocked urine flow, drugs such as diclofenac (a type of non-steroidal anti-inflammatory drug or NSAID) are avoided. This is because they can decrease the production of prostaglandins – substances that widen blood vessels in the kidneys and help maintain the rate at which they filter waste from the blood. By reducing this filtration rate, diclofenac can delay kidney function and affect the results of the test. Using this kind of drug might also interfere with the normal contractions of the ureter (the tube that carries urine from the kidneys to the bladder) and further delay waste elimination.
In another type of kidney scan called ‘angiotensin-converting enzyme inhibitor (ACEI) renography’, which is used to check for kidney-related high blood pressure, the drug captopril is given before the test. This medication works better if taken on an empty stomach, so the patient is recommended to fast for at least 4 hours before the study. If the patient is already on an ACEI medication, they should stop taking it before the study. Captopril should be stopped at least 48 hours before, and other ACEIs like lisinopril or enalapril should be stopped at least 1 week before the ACEI renography examination. Long term usage of ACEI may decrease the effectiveness of the test.
How is Nuclear Renal Scan performed
Before starting a kidney scan, patients are asked to empty the bladder. This is because a full bladder would delay the drainage system of the upper urinary tract and interfere with the accuracy of the study. Sometimes, a medical device called a “foley catheter” may be used to keep the bladder empty. To ensure a smooth scan, patients are hydrated before and after the procedure.
The specific radioactive substance used in the scan, known as a “radiotracer”, depends on the type of kidney scan being performed. These include:
1. Technetium-99m DTPA: It is mainly cleared by the kidney through a process called glomerular filtration. This makes it useful for measuring kidney function and for evaluating the flow of the urine from the kidney to the bladder. The dose used for adults is up to 15 millicuries (mCi) and for children, it’s 0.1-0.2 mCi/kg (up to a maximum 5 mCi).
2. Technetium-99m DMSA: This agent mainly binds to cells in the kidney’s cortex making it useful for anatomy study and to check for conditions such as abnormal position of the kidney or scarring in the kidney. It binds to these cells for quite a long time exposing the kidney to greater radiation than other agents, therefore, other substances are often preferred. Additionally, the DMSA has a short shelf life after preparation. The dose for adults is 5 mCi while for children it’s 0.05 mCi/kg (up to a maximum 2.7 mCi).
3. Technetium-99m MAG3: This agent is mainly secreted by the renal tubules and a smaller amount is filtered by the glomeruli. Its dose is up to 10 mCi for adults and 0.15 mCi/kg for children with a maximum pediatric dosage of up to 4 mCi. It offers an efficient way to evaluate renal function and get additional information. Despite being less detailed in evaluating the structure of the renal cortex compared to DMSA, it allows additional functional information.
Once a dose of radiotracer is injected swiftly into the vein, the patient is then placed under a special camera (gamma camera) to capture images. The images provide a visual representation of kidney function. These images are captured in different stages of the study with a distinct purpose for each stage. Also, the particular technique to capture the image depends on the study being performed. An indwelling open bladder catheter is sometimes required if one is unable to urinate, as a full bladder blocks the drainage from the upper urinary tract.
The images of the kidney provide visual insight into the renal anatomy and function. A time-activity curve is generated based on the series of images, and renal function is quantified from this curve. For a detailed evaluation, a different time activity curve can be created where the kidney activity is compared with the aorta activity. The timing and peak of tracer presence in the aorta and kidneys are analyzed. It should be noted when evaluating kidney cortex function to exclude kidney pelvis activity because retained tracers in the renal pelvis can confuse cortical assessment.
A diuretic renal test is a special type of renal test that uses a diuretic (such as furosemide) to promote evacuation of the radiotracer from the kidney. It helps differentiate between a genuine blockage in the urinary tract and a non-obstruction urinary condition. Additional images beyond the mentioned anatomy images are acquired at 15 to 60-second intervals for an additional 20 to 30 minutes after diuretic use.
Possible Complications of Nuclear Renal Scan
Getting a nuclear renal scan has very few possible complications. One of these could be being exposed to some radiation, but this exposure is actually much less than what you would get from other types of scans, like an abdomen CT scan. To give you an idea, the amount of radiation you get from a renal scan is about the same as what you would get from 50 chest X-rays. In contrast, an abdominal CT scan exposes you to radiation equivalent to 500 chest X-rays. Techniques are being developed to reduce the amount of radiation in CT scans, but at the moment, the renal scan is still considerably lower.
Like any other injection, you might experience some pain or swelling where the renal scan injection was given.
Very rarely, a person may also have side effects from the radioactive materials used in the scan. These may include a reaction that causes a sudden drop in heart rate and blood pressure, a fever, or an allergic reaction. But these are typically mild and don’t usually require a stay in the hospital.
What Else Should I Know About Nuclear Renal Scan?
Renal scintigraphy is a test that’s used to examine the blood flow, function, and structure of the kidneys. However, with the advancement of other imaging techniques like CT scans and MRI, the role of renal scintigraphy has evolved. Nowadays, this test is mostly used to assess the blood flow and function of kidneys, while other imaging techniques are commonly used to study the structure.
In particular, renal scintigraphy is often used when a person can’t have a CT or MRI scan due to an allergy to the contrast material used, poor kidney function, or fear of enclosed spaces. This test is also chosen when it is suspected that there is a blockage in the urinary system and to distinguish real blockages from other conditions that can also cause the urinary tract to expand.
Renal scintigraphy can be used in specific circumstances. These include using a test with a blood pressure drug called captopril to diagnose high blood pressure caused by one kidney. It also includes using a variant of the test, DMSA cortical scintigraphy, to detect scars on the kidney or acute inflammation of the kidney (pyelonephritis), especially in children. This is because it is more sensitive than ultrasound and exposes the child to less radiation than a CT scan.
Renal scintigraphy is also very useful for assessing the function of a new kidney after a transplant. This test can detect complications and allow early treatment decisions if the transplant is not working properly. If the transplanted kidney is irrevocably damaged, it allows doctors to decide to remove it promptly, saving the patient from taking unnecessary immunosuppressive drugs.
Since renal scintigraphy exposes patients to significantly lower radiation compared to a CT scan, it is often preferred for examining the structure of children’s kidneys, irrespective of whether the kidneys are normal, if they are abnormally developed, or if there’s a disease condition.
