The body receives nutrients from food and converts them into energy. After the necessary food enters the body, metabolic waste remains in the intestine and is absorbed into the blood.
The kidneys and urinary system contain chemicals (electrolytes) such as potassium and sodium, as well as water. They remove metabolites from the blood called urea.
Urea is produced when foods containing proteins, such as meat, poultry and some vegetables, are destroyed in the body. It is carried into the bloodstream and further into the kidneys.
The functions of the kidneys are as follows:
- removal of liquid waste from the blood in the form of urine;
- maintaining a stable balance of salts and other substances in the blood;
- the production of erythropoietin - a hormone that promotes the formation of red blood cells;
- blood pressure adjustment.
The kidneys remove urea from the blood through tiny filtering units called nephrons. Each nephron consists of a network formed by small vessels - capillaries called glomeruli, and a small renal tube.
Urea, together with water and other waste products, forms urine when it passes through the nephrons and through the renal tubules.
What is an ultrasound
Ultrasound diagnostics (ultrasound of the kidneys) is a safe and painless method that is based on the conversion of acoustic waves to create a gray-scaled (black and white) image of organs, including the kidneys, ureters and bladder. The method is used to assess the size, shape and location of organs.
Acoustic signals move at different speeds, depending on the type of tissue being examined: they penetrate most quickly through solid (solid) tissue and most slowly through air. Air and gases are the main enemies of ultrasound.
The kidneys are a pair of bean-shaped organs located behind the abdominal cavity, just above the waist (the region of the lumbar vertebrae). Moreover, the right kidney is located slightly higher than the left (the region of the last two thoracic vertebrae). They perform the function of removing excess metabolic products from the blood and produce urine.
The ureters are thin paired connective tissue tubes that carry urine from the kidneys to the bladder. Urine is formed continuously at all times of the day.
At the time of examination, the ultrasound scanner through a special sensor transmits ultrasonic signals of different frequencies to the studied area. They are reflected or absorbed by the tissue, and the resulting image is displayed on the monitor. Images in the form of black, gray and white objects reflect the internal structure of the kidneys and related organs. Ultrasound is also used to evaluate blood flow in the kidneys.
Another type of ultrasound is Doppler scanning, sometimes called a duplex scan, which is used to determine the speed and direction of blood flow in the kidneys, heart, and liver.
Unlike standard ultrasound, acoustic signals can be heard during Doppler imaging.
Indications for ultrasound
Doctors prescribe an ultrasound scan - a kidney test - for certain complaints and anxiety in the kidneys and bladder.
- Recurrent acute lower back pain.
- Difficult and painful urination.
- Urination with blood.
- Frequent urination in small portions.
- Inability to urinate.
Ultrasound is also recommended for monitoring the condition of existing problems with the kidneys or bladder, for example:
- urolithiasis (urolithiasis);
- kidney stone disease (nephrolithiasis);
- acute and chronic cystitis (inflammation of the bladder);
- acute and chronic nephritis;
- nephrosclerosis, polycystic, pyelonephritis, etc.
An ultrasound scan may also show:
- kidney size;
- signs of kidney and bladder injury;
- developmental abnormalities from the moment of birth;
- the presence of obstruction or stones in the kidneys and bladder;
- complications of urinary tract infections (UTIs);
- the presence of a cyst or tumor, etc.
Ultrasound can detect any abscesses, foreign bodies, swelling and infections in or around the kidneys. The calculi (stones) of the kidneys and ureters can also be detected using ultrasound.
Ultrasound of the kidneys can normally be done to help locate the needles used in the biopsy. It is done to get a sample of kidney tissue, to remove fluid from cysts or abscesses, or to place a drainage tube.
An ultrasound scan of the kidneys can also be used to determine blood flow in the kidneys through the renal arteries and veins. Ultrasound can also be used after transplantation to assess organ survival.
Among other conditions, such an ultrasound scan can detect kidney stones, cysts, tumors, congenital malformations of the kidney tract (these are abnormalities at birth), prostate problems, the effects of infection and organ trauma, and kidney failure.
There may be other reasons for the appointment of an ultrasound of the kidneys, normal and pathological.
Special training
Usually, kidney preparation is not required for an ultrasound scan, although it may be possible to prescribe an 8–10-hour fasting diet before starting. As a rule, filling the bladder is required, therefore it is recommended to drink as much water as possible before the test.
Be sure to inform your doctor about taking any medications - this is very important for the interpretation of subsequent research results.
Abdominal pain is the most common indication for ultrasound scanning of the kidneys. However, the doctor may also refer you to the procedure if you suffer from other symptoms. Or if you are worried about the results of your recent blood and urine tests.
Ultrasound of the bladder and ureters
The bladder is a hollow organ consisting of smooth muscle muscle. He stores urine until it is "evacuated" at the request of the body.
The most common cause of an ultrasound examination of the bladder is to check its emptying. Urine that remains in the bladder after urination (“post-void”) is measured.
If it stagnates in the bladder for a long time, then problems may arise, for example:
- enlarged prostate (prostate gland in men);
- urethral stricture (narrowing of the urethra);
- organ dysfunction.
An ultrasound of the bladder can also provide information about:
- walls (their thickness, contours, structure);
- diverticula (sacs) of the bladder;
- the size of the prostate;
- stones (uroliths) in the cavity;
- large and small neoplasms (tumors).
During an ultrasound of the bladder, the ovaries, uterus or vagina are not examined.
Preparation for ultrasound of the kidneys and bladder includes a fasting diet (about 10 hours) and regular bowel movement.
If you do not check for residual urine after urination, a full bladder is needed. You may be asked to drink plenty of water an hour before the test.
An ultrasound transducer is placed between your navel and the pubic bone. The image is viewed on a monitor and read in place. To check your bladder drainage, you will be asked to go out and empty it. When you return, research will resume.
In order for your bladder to be full, you will need to drink at least 1 liter of fluid 1 hour before the appointed time. Avoid milk, sodas and alcohol.
If you have a permanent urinary (urethral) catheter installed , you need to check with a specialist for preliminary preparation before scanning.
How is ultrasound performed
After preparing for ultrasound of the kidneys and bladder, the procedure itself will be carried out in a separate room equipped with the necessary equipment. During the procedure, the light in the room is turned off so that the visual structure of the abdominal organs is clearly visible on the monitor of the device.
A specially trained ultrasound imaging specialist in sonography will apply a clear, warm gel to the required area of your body. This gel serves as a conductor for the transmission of sound waves to ensure smooth movement of the sensor across the skin and eliminate air between them, for better sound conductivity. When performing an ultrasound of the kidneys, the child’s parents are usually allowed to be around to instill confidence and support in the baby.
You or your child will be asked to take off their upper or lower clothes and lie on the couch. Then the technician will place the sensor on top of the gel on a highlighted area of your body. The sensor emits signals of various frequencies (it is selected according to the weight of the patient), and the computer detects the absorption or reflection of acoustic waves from organs. The waves are echoed and come back to the sensor. The speed with which they return, as well as the volume of the reflected sound wave are converted into readings of various types of tissues.
The computer transforms these audio signals into black and white images, which the ultrasound specialist subsequently analyzes.
What to expect from the study
Ultrasound of the kidneys in women and men is painless. You or your child may feel light pressure on the abdomen or lower back as the sensor moves through the body. Nevertheless, you are required to lie still for a while during the procedure so that the acoustic waves reach the desired organ more efficiently.
The specialist may also ask you to lie down in another position or hold your breath for a short while.
Obtaining and interpretation of the results
Sonography should be performed in all patients with CKD (chronic kidney disease), primarily to recognize a progressive, irreversible kidney disease, which is not visible on any other additional diagnostics, including biopsy.
On ultrasound, negative signs include a decrease in kidney size, a thin cortical layer, and sometimes cysts. The specialist needs to be careful when making a diagnosis based solely on the size of the kidney.
Although the echogenicity of the cortical layer often increases with CKD, its normal value also does not exclude the presence of the disease. Also, echogenicity may increase with reversible (acute) kidney disease. Thus, only a change in this indicator is not a reliable guarantee of the presence of CKD.
Sonography can also identify specific causes of urological and nephrological abnormalities, such as urethra obstruction, polycystic kidney disease, reflux nephropathy, and interstitial nephritis.
Acute renal failure
While sonography may be useful in acute renal failure, its use should be limited to those patients for whom the cause is not obvious or to those who may have bladder obstruction.
The kidneys often turn out to be normal in acute tubular necrosis (OTH), but can be enlarged and / or echogenic.
An increase in kidney size can also occur with other causes of acute renal failure. Echogenicity is non-specific and may increase for other reasons, including glomerulonephritis and interstitial nephritis.
Cystic Kidney Disease
Cystic kidney disease is either genetic or acquired. Polycystic is the most common genetic type of mutation and is characterized by an increase in renal mass, in addition to multiple cysts. Ultrasound is enough to make a final diagnosis.
Pain and hematuria
A CT scan is usually recommended to determine the causes of pain and hematuria, but in some cases the diagnosis can be made using ultrasound, and this is not unreasonable.
Stones are usually visible, but up to 20% can be missed by a specialist, especially when they are small or inside the ureter.
Thus, computed tomographic scanning is more suitable to determine the causes of acute renal colic.
Carcinoma screening
Some people are at increased risk for kidney malignancies, especially those with previous tumors and patients with a kidney transplant. Sonography, in comparison with other methods, may be less sensitive, but it is more accessible and is not associated with radiation exposure.
Transplant Nephrology
Sonography is indicated in most cases of acute renal failure due to the only remaining functioning kidney and the frequency of urological complications. Normal surgical use of ureteral stents reduces obstruction, but bladder dysfunction remains common. Sonography is not used in the diagnosis of acute organ rejection, unless it is serious, in which case the allograft will be swollen and echogenic.
However, this picture can also be seen with acute tubular necrosis and nephritis.
An ultrasound specialist will identify all necessary measurements of organs in a special protocol and record a conclusion on the condition of the kidneys, bladder and other organs. He will then give it to you or your healthcare provider.
If, according to the results of the study, any pathologies or abnormalities are revealed, then additional examinations (general and biochemical blood tests, urine tests, and other tests) are prescribed to clarify the diagnosis.
In emergency cases, ultrasound results may be available for a short period of time. Otherwise, they usually cook within 1-2 days.
In most cases, the results after the examination are not given directly to the patient or family.
What can interfere with objective research?
Sometimes patients neglect the preparation for the study with ultrasound of the kidneys. Therefore, certain factors or conditions may affect the test results. These include, for example, the following factors.
- Severe obesity.
- Barium in the gut from recent radiography with barium.
- Intestinal gas.
Ultrasound Risks
There are no serious risks associated with ultrasound of the abdomen and kidneys. Ultrasound does not cause discomfort from the application of the gel and the sensor to the skin.
Unlike x-rays, the degree of exposure of which can adversely affect the body, ultrasound is completely safe.
Ultrasound can be used during pregnancy and even in the presence of an allergy to a contrast dye, since no radiation or contrast agents are used in the process.
Other related procedures that can be performed to evaluate the kidneys include x-ray and computed tomography (CT) scans, magnetic resonance imaging of the kidneys, antegrade pyelogram, intravenous pyelogram and renal angiogram.
Help child
Young children may be afraid of the very prospect of going for examination and working equipment. Therefore, before leading a child to an ultrasound of the kidneys, try to explain to him in simple terms how this procedure will be carried out and why it is done. A regular conversation can help alleviate your child’s fears.
For example, you can tell your baby that the equipment will simply take pictures of him or his kidneys.
Encourage the child to ask questions to the doctor and specialists, try to relax him during the procedure, as muscle tension and trembling can make it difficult to obtain accurate results.
Infants, as a rule, cry during ultrasound of the abdominal cavity and kidneys, especially if they are kept, but this will not interfere with the procedure.