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Saturday, May 24, 2008

MRI scans Q&As

My daughter is pregnant and she has just had cancer diagnosed. If she needs any x-rays and scans will she still be able to have these even though she is pregnant?

Cancer is diagnosed during about 1 in every 1000 pregnancies. This means that the combination of cancer and pregnancy is uncommon. However, when it does occur it is a situation which raises many questions.

The benefits to the mother of any scans and x-rays must be balanced against the possibility of any harm to her unborn child. Another issue is that because cancer during pregnancy is so unusual there is relatively little information available and this can lead to uncertainty over the best way to handle the problem.

So the pattern of care for anyone who is found to have cancer during her pregnancy is likely to be worked out on an individual basis. The doctors will take account of such things as

  • the type of cancer
  • how big it is
  • whether it has spread
  • the stage of the pregnancy
  • the different types of treatment that could be used
  • and the feelings and wishes of the mother, her partner and their relatives.

Having said this, it is possible to make some general comments about the use of scans and x-rays during pregnancy. But before this it might be helpful to describe the various stages in the progress of a normal pregnancy. These are:

  • preimplantation: this is the time from when fertilisation of the female egg (ovum) takes place until the fertilised egg becomes firmly attached to the wall of the womb (the uterus). This usually takes about 8 days.
  • embryonic stage: this is the period during which the embryo develops and all the major organs of the body are formed (so it is also known as the period of organogenesis). This usually lasts from the 8th day to about the 8 the week of the pregnancy).
  • foetal stage: during this time, the various organs that have been formed grow in size and become increasingly mature. Although most of the body's organs will have been formed during the embryonic phase a few important tissues are still developing during the foetal period, these include the nerves, the lung tissue and the bone marrow. The foetal stage lasts from the 8th week until the time of birth, at about 38 weeks.
A normal pregnancy lasts about 38 weeks and another way that is used to describe its progress is to talk about three 'trimesters', each trimester being about twelve weeks. So the first trimester covers the period of preimplantation, the development of the embryo and the beginning of foetal growth. The second trimester covers the early and middle stage of foetal growth and third trimester covers the final three months, til birth.

Any damage to the unborn child can lead to a number of different outcomes. These include:
  • spontaneous abortion during the early part of the pregnancy
  • a child born with congenital malformations or birth defects
  • premature birth with the child being delivered early
  • a low birth weight
  • problems which appear during childhood or adolescence, such as delayed growth, difficulties with learning and infertility
  • an increased risk of cancer development in later life.

This list looks alarming but it is important to remember that many of these problems occur with 'normal' pregnancies when there are no other illnesses or treatments involved. For example, it is estimated that between 1 in 8 to 1 in 10 pregnancies end in a miscarriage or spontaneous abortion, that about 1 in 50 babies are born with obvious birth defects or congenital abnormalities and about 1 in 10 have very minor, less obvious abnormalities.

Tests for someone with cancer are used to check on the size of the growth and whether or not is has spread. They may include: ordinary x-rays (like a chest x-ray), ultrasound scans, CT scans (also known as CAT scans or computerised scans), magnetic resonance imaging (MRI scans), radio-isotope scans (like bone scans) and positron emission tomography (PET scans).

The main concern over tests in pregnancy is whether they involve the use of ionising radiation. In high doses, radiation can be damaging to the unborn child, particularly during the first few weeks of pregnancy.

X-rays, CT scans, radio-isotope scans and PET scans involve the use of ionising radiation. The doses of radiation involved are small so the risk of damage to the unborn child is likely to be small. However, doctors try to avoid using these tests during pregnancy, especially during the first trimester. The one exception is a chest x-ray with protective shielding to the pelvic region. The dose to the foetus from this is so tiny that it is considered to be a 'safe' test.

Ultrasound scans and MRI scans do not use ionising radiation and there is no recorded evidence that they can cause any harm to the embryo or the foetus. So usually any 'imaging' tests that need to be done for a woman who is pregnant and who has cancer can be safely and effectively done using a combination of a chest x-ray and appropriate ultrasound and MRI scans.

Sentinel node biopsy testing is sometimes used in breast cancer or malignant melanoma to discover whether the cancer has spread to nearby lymph nodes. During this test a very small dose of radioactive material may be used. Specialists hold different views on whether this test is safe for use in pregnancy. Some feel that as the dose is so tiny the risk to the unborn child is negligible and the test is safe to use. Other doctors feel that this test should be avoided in pregnant women.

For each woman the doctors will work towards a safe and effective, pattern of tests, to get the information needed to plan her treatment. Obviously the woman and her family should be involved in discussions about what choices there are. In this way the final plan of action will offer the best possible chances of success for the mother with the least possible risk of harm to her unborn child.

Can you tell me the difference between a CT scan and an MRI scan? Is one better than the other?

CT scans became widely available in the UK about 20 years ago. The initials CT stand for computerised tomography. CT-scanners produce a specialised type of x-ray which builds up a three-dimensional picture of the inside of the body. The scan is painless. It takes longer than an ordinary x-ray (about 30 minutes) and involves lying on a couch which moves through a short tunnel, which houses the scanner. Most people who have a CT-scan are given a drink or injection of dye to allow particular areas to be seen more clearly. For a few minutes this may make you feel hot all over.

MRI scans became widely available in Britain during the 1990s. The initials stand for magnetic resonance imaging. The test is similar to a CT-scan but uses magnetic fields rather than x-rays to build up a series of cross-sectional pictures of the body. During the test, which may take longer than a CT-scan, you will be asked to lie very still on a couch inside a metal cylinder. It can be slightly uncomfortable and some people find it claustrophobic. The scan is also very noisy but you may be given earplugs or headphones to wear. Once again drinks or an injection of dye may be used to show up particular parts of your body.

Both types of scanner use computers to produce the pictures of your body and it usually takes a day or two to get the results of the scans.

At the present time there are many more CT-scanners in the country than MRI scanners but the numbers of both types of scanner are increasing all the time.

CT and MRI scanners are used to help diagnose and assess many different medical conditions. In cancer they are of great help in showing the exact position of tumours and helping to see whether or not they have spread.

In diagnosing and assessing cancers the two sorts of scanner are complimentary: for some cancers CT-scans will give more accurate information whilst for others an MRI scan is better. So the choice of which sort of scan is used depends on which type of cancer is suspected, or being investigated, and your medical team will be able to decide which of the tests is needed. Sometimes both CT and MRI scans are used to get even more information.

Via: http://www.cancerbackup.org.uk

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