Medical imaging

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Medical imaging is a very important tool to diagnose cancer. It involves taking a picture (scan) of the inside of your child’s body. Several different types of imaging can be used, depending on what type of cancer is suspected and where it is in the body. The doctor uses these tests to determine exactly where the cancer is, how big it is and whether it has spread.

In many cases, several different types of medical imaging tests are done to get an accurate diagnosis.

Medical imaging itself is not painful, but, for some tests, your child may need to be given a contrast agent – a dye that helps to give a clearer picture. In some cases, this is an injection; in others, it is a liquid for the child to drink.

In very rare cases, the contrast agent may cause an allergic reaction. If your child has ever had a reaction to contrast agents or dyes before, or has any allergies (especially to iodine), be sure to let the health professionals know.

For most medical imaging tests, the child has to be very still while the images are being taken. This can be difficult for children, especially young children. Encourage your child to stay very still during the tests so the health professionals can take good images. Infants or young children may be given a medicine (a sedative) to calm them down and help them stay still, or may be given a general anaesthetic so that they sleep through the test.

Some medical imaging tests use radioactivity or radiation to give a picture of the inside of the body. Tests such as X-rays and CT scans are done in radiology departments. Tests that use an injection of radioactivity are done in nuclear medicine departments – these tests include PET scans, MIBG scans and bone scans.

Because medical imaging scans are complex and detailed, it will be a few days before you find out the results.

X-ray

X-rays are a type of radiation that are used to look inside the body. They create a black-and-white picture of the inside of the body.

X-rays can help diagnose different types of cancer, such as bone cancer. Chest X-rays are used to see whether there is cancer in the lungs or around the heart.

X-rays are painless. Your child will be asked to stand in front of the X-ray machine and keep very still while the images are being taken.

Sometimes, depending on the type of cancer that is suspected, your child might be given a contrast agent to make other body structures (e.g. their bladder or stomach) appear on the X-ray. Contrast agents for X-rays are usually given as a liquid for the child to drink.

X-rays are a very important tool for diagnosing cancer. The amount of radiation that your child is exposed to during an X-ray is very small. However, because X-rays are a type of radiation, there is an extremely small chance that they can contribute to the development of cancer. This risk is very low, but, if you are concerned about it, discuss it with your child’s doctor.

Ultrasound

Ultrasound uses sound waves to create black-and-white images of the inside of the body. It can be used to detect lumps, masses or tumours. It is a completely painless test. The doctor will let you know if there is anything your child needs to do to prepare for the ultrasound.

During the ultrasound procedure, a small wand is covered with gel and then moved slowly over your child’s body part. There is no pain, but the wand may be pressed down firmly to get a better picture, which might be uncomfortable.

Your child might need a follow-up CT scan or MRI if the ultrasound suggests that there is a tumour or growth. These other scans can confirm what the ultrasound found.

The sound waves used in an ultrasound cannot be heard by the human ear. They are completely safe, and there are no long-term effects or risks to your child.

Computed tomography (CT) scan

CT scans (also called CAT scans) are a very complex series of X-rays that provide a highly detailed picture of the inside of the body. CT scans can be used to create three-dimensional images.

CT scans are used to:

  • detect abnormal growths, including tumours, in the body
  • determine the stage of a tumour (how big it is and whether it has spread)
  • guide where a biopsy should be taken
  • help the health care team decide on the best treatment.

A CT machine is shaped like a large doughnut ring with a table that slides in and out of the middle. The ring contains the X-ray machine. Your child will be asked to lie very still on the table while the images are being taken.

Because the child needs to stay very still during the scan, they may be given a medicine (a sedative) before the scan to keep them calm. If the child is young or nervous, they may be given a general anaesthetic so that they sleep through the scan.

CT scans are painless.

Contrast agents are often used for CT scans. These make soft tissues and organs appear on the image, as well as bones. Contrast agents can be given as an injection or a drink, or both may be given.

The amount of radiation that your child is exposed to during a CT scan is very small, but more than the amount of radiation from a standard X-ray. Because X-rays are a type of radiation, there is an extremely small chance that they can contribute to the development of cancer. This risk is very low, but, if you are concerned about it, discuss it with your child’s doctor.

The Australian Radiation Protection and Nuclear Safety Agency has fact sheets on CT imaging and children, and what parents should know about CT scans.

Magnetic resonance imaging (MRI)

MRI scans use radio waves and magnets to create an image of the inside of the body.

An MRI can provide specific information about the body that other scans may not detect. MRIs are used to:

  • detect abnormal growths, including tumours, in the body
  • help determine the stage of a tumour (how big it is and whether it has spread)
  • help the health care team decide on the best treatment.

An MRI machine is shaped like a long, narrow tube. Your child will be asked to lie very still on a table that slides into the tube. This might be distressing for the child, especially if they are not comfortable with closed or confined spaces. The machine also makes loud noises, which can be scary for children. Your child will be given earplugs or headphones to block out these noises.

MRI scans take longer than X-rays or CT scans, and your child might need to be in the machine for up to an hour, depending on the parts of the body that need to be scanned.

Because the child needs to stay very still during the scan, they may be given a medicine (a sedative) before the scan to keep them calm. If the child is young or nervous, they may be given a general anaesthetic so that they sleep through the scan.

You will be able to talk to your child through an intercom during the scan, which can help them relax.

MRI scans are painless.

Contrast agents are often given before an MRI scan, which can make different parts of the body stand out better in the image. These are usually given as an injection.

Positron emission tomography (PET) scan

PET scans use radioactivity to create images of the body. Before the scan, your child will be injected with a very small amount of radioactivity. Because cancer cells tend to absorb more radioactivity than normal cells, they will look different on the scan.

A PET scan is used to:

  • detect cancer
  • help determine the stage of a tumour (how big it is and whether it has spread)
  • help the health care team decide on the best treatment.

Together with other types of imaging, PET scans are used to provide a more accurate picture of what is happening in your child’s body.

A PET scanner is similar in shape to a CT scanner. It is a ring-shaped machine that slides back and forth over a table. Your child will be asked to lie very still on the table while the images are being taken by the ring. The scan can take up to an hour.

Because the child needs to stay very still during the scan, they may be given a medicine (a sedative) before the scan to keep them calm. If the child is young or nervous, they may be given a general anaesthetic so that they sleep through the scan.

The radioactivity given to your child before the scan only stays in their body for a short time, and the risk to your child from exposure to the radioactivity is very low. If you are concerned about this risk, discuss it with your child’s doctor.

Metaiodobenzylguanidine (MIBG) scan

An MIBG scan is a test used to diagnose neuroblastoma, a particular type of cancer in children. MIBG is a radioactive dye that attaches specifically to neuroblastomas anywhere in the body, so they can be easily seen on a scan.

If your child needs an MIBG scan, they will have an injection of MIBG on one day and will have the scan the next day. The scan takes about 90 minutes. Your child might need more than one scan over a day or two, but they will only need one injection of MIBG. They will also need to drink a small amount of liquid that contains iodine 2 days before and 4 days after the MIBG scan.

The scanner looks similar to a CT scanner or a PET scanner. Your child will be asked to lie on a table while a ring-shaped camera moves back and forth over their body.

Because the child needs to stay very still during the scan, they may be given a medicine (a sedative) before the scan to keep them calm. If the child is young or nervous, they may be given a general anaesthetic so that they sleep through the scan.

MIBG scans are painless.

The radioactivity given to your child before the scan only stays in their body for a short time, and the risk to your child from exposure to the radioactivity is very low. If you are concerned about this risk, discuss it with your child’s doctor.

Bone scan

Bone scans provide specific and detailed information about your child’s bones. They are used to diagnose bone cancer and to determine whether a cancer has spread to the bones. They can also help to diagnose other bone disorders or injuries.

If your child needs a bone scan, they will first have an injection of a radioactive dye. A few hours later, they will have the scan. The radioactivity settles in areas of damaged bone, which appear as ‘hot spots’ on the scan.

The machine is very similar to a CT scanner. Your child will be asked to lie on a table while a ring-shaped camera moves back and forth over their body. The scan takes about an hour.

Because the child needs to stay very still during the scan, they may be given a medicine (a sedative) before the scan to keep them calm.

Bone scans are painless.

The radioactivity given to your child before the scan only stays in their body for a short time, and the risk to your child from exposure to the radioactivity is very low. If you are concerned about this risk, discuss it with your child’s doctor.

published: Sunday, 23 August, 2015