Ultrasound is used to examine different parts of the body. It is pain-free, although the patient may feel some pressure if the sonographer needs to press harder with the transducer, the camera that transmits and receives sound waves. It is often done to evaluate the kidneys and is called a renal ultrasound.
Prior to Exam
There is generally no preparation that needs to be done by the patient prior to the exam. If the bladder is examined, the patient will have to drink 32 ounces of water one hour before the exam to ensure that the bladder is full. While fasting is not necessary, it may be helpful in reducing the amount of bowel gas that may otherwise cause difficulty with visualizing the kidneys.
The patient may be asked to undress from the waist up and put on a gown. Some ultrasound departments will allow the patient to leave his or her clothes on. The patient will be asked to lie on his or her back, but may have to roll onto either side for better visualization of the kidneys. Towels will be tucked into the clothing or gown to protect them from the ultrasound gel.
Ultrasound gel is either colorless, light green, or blue. Many departments warm the gel prior to the ultrasound exam. It is placed onto the skin for several reasons. The gel allows the sonographer, the person who does the ultrasound, to easily move the camera over the skin while he or she acquires the necessary pictures. Ultrasound gel also allows the ultrasound waves to transmit into the body and to return from the body to the transducer.
A series of images is taken of each kidney. Images are taken in the longitudinal plane, which shows a splice of the kidney from front to back, and head to toe. At least three images are taken in the longitudinal plane from the outside to the inside, or toward the spine: lateral, mid, and medial. Transverse images are two-dimensional splices from front to back and side to side. A series of transverse images are taken from up to down: superior, mid, and inferior. Doppler images are taken to demonstrate the blood flow within the kidney.
Renal ultrasound can detect several problems with the kidneys. Kidney stones may or may not be seen, which often depends on the size of the stone. Small stones can look like fatty deposits, which may be normal. Cysts are seen on ultrasound, especially in the elderly population. Hydronephrosis can be seen as a fluid collection in the renal pelvis. The kidneys may show signs of infection on ultrasound. The ureters cannot be examined using ultrasound.