An ultrasound may be used to find a tumor. It can also help a doctor perform a biopsy  because it shows the tumor’s exact location in the body. A biopsy is the removal of a small amount of tissue for examination.
How does an ultrasound work?
An ultrasound, also called sonography or ultrasonography, is an imaging test. It uses high-frequency sound waves to create pictures of internal organs. The sound waves hit the organs and bounce back to a device called a transducer. The transducer turns them into images for the doctor to examine on a computer.
The sound waves echo differently when bouncing off abnormal tissue and healthy tissue. This helps the doctor detect a potential tumor.
Who does my ultrasound?
An ultrasound may be done in a doctor's office or at a hospital.
The test is usually performed by an ultrasound technologist. An ultrasound technologist is also called a sonographer. This person is specially trained to use the ultrasound machine.
A radiologist interprets the results of an ultrasound. A radiologist is a medical doctor who specializes in using imaging tests to diagnose disease.
Getting ready for an ultrasound
When you schedule your ultrasound, you will get detailed instructions.
How you need to prepare for an ultrasound depends on the part of the body being examined. For example, these are potential instructions for an ultrasound of certain parts of the abdomen:
Eat a fat-free meal the night before.
Avoid eating or drinking for up to 12 hours before.
Drink a quart of water an hour before, and keep a full bladder.
Sometimes, preparation is as simple as wearing comfortable, loose-fitting clothing to the appointment.
Additionally, check with your insurance provider in advance. Find out whether the cost of the test will be covered and whether you may need to pay for part of it.
Once you arrive at the doctor's office or hospital, you will be asked to sign a consent form. The consent form states that you understand the benefits and risks and agree to undergo the test.
Talk with your doctor about any concerns you have about the ultrasound.
During the test
When you arrive for your ultrasound, you will remove some or all of your clothing. This depends on which the part of the body needs to be examined. In some cases, you will wear a hospital gown. You may also need to take off jewelry.
You will lie on an examination table next to the ultrasound scanner. The scanner includes a computer, a screen, and a transducer. The transducer is a hand-held device that is attached to the scanner by a long cord.
The ultrasound technologist will spread a gel on your skin over the body part being examined. The gel helps eliminate air pockets between the transducer and your skin. This allows the ultrasound to produce better images.
Next, the technologist will press the transducer firmly against the gel and move it back and forth. The screen will display images of your organs and blood vessels. The technologist will use the computer to save images during the test.
You will need to lie still during the ultrasound. The technologist may ask you to hold your breath for several seconds at a time. Additionally, you may need to change your position on the table.
In some cases, the transducer is attached to a lubricated probe. The technician gently inserts the probe into the body. For example, the probe may be inserted into a man’s rectum to see the prostate. Or, it may be inserted into a woman’s vagina to see the uterus or ovaries.
Ultrasounds are usually painless. However, you may feel some discomfort when the transducer is pressed on your body. A full bladder may contribute to the discomfort.
The test can take 20 to 60 minutes to complete. The time depends on the body part under examination.
At the end, a radiologist may enter the exam room to review the images.
After the test
When the procedure is over, the technologist will wipe the gel off your body. Then, you may get dressed.
After your ultrasound, you may return to your usual activities. This includes driving.
If the test results show something concerning, you may additional tests. Additional tests will provide more information.
Questions to ask your doctor
Before having an ultrasound, consider asking the following questions:
What will happen during the ultrasound?
Who will perform the ultrasound?
Is the radiologist certified by the American Board of Radiology?
How long will the procedure take?
How accurately can an ultrasound find cancer?
When will I learn the results? How will they be communicated to me?
Who will explain the results to me?
What other tests will I need if the ultrasound finds evidence of cancer?
What is Cancer? 
National Library of Medicine: Ultrasound 
RadiologyInfo.org: General Ultrasound