Understanding tests used to detect bone problems

X-ray examinations are used to “look through” different parts of your body. Different amounts of radiation are able to pass through different types of tissue, and this produces the x-ray image. Bones absorb almost all the radiation because they are so dense – so they appear as white or grey outlines on the x-ray image. Soft tissues like fat or muscles let almost all radiation pass through them – they do not appear on the x-ray image.

This is why x-ray examinations are particularly useful for examining the skeleton, but not very good for examining soft tissues. X-ray examinations always involve exposure to radiation, which is why they should only be done if medically necessary. Pregnant women only have x-rays in very rare cases.

X-ray examinations are used to detect or rule out problems like fractures, signs of wear and tear, abnormal positions of bones or bone inflammations.

Before having an x-ray you are asked to remove any clothing and jewelry from the part of the body that is to be x-rayed. Depending on the part of the body to be examined, you may need to lie down, sit, or stand. While the x-ray is being taken, your body is positioned between the radiation source and the x-ray film. Genitals are protected from radiation by a lead apron if possible. The medical staff will usually also wear lead aprons for protection. It only takes a few seconds to get the image.

Computed tomography (CT) makes it possible to get more exact x-ray images of the body. The x-rays are sent through the body from different directions. CT scans do not consist of one x-ray image of the part of the body that is being examined. Instead, different x-ray images are taken in thin layers (“slices”).

A computer uses the data from these individual images to put together a multidimensional cross-sectional image of the part of the body that was scanned. In CT examinations people are exposed to considerably higher levels of radiation than in simple x-ray examinations.

Computed tomography may be used to see changes in the bones that cannot be seen, or can only be seen very poorly, using conventional x-ray images.

During the examination, you are moved through a ring-shaped CT scanner while lying down. An X-ray source in the CT scanner rotates around the part of your body that is being scanned. Depending on how much of the body is scanned, the procedure takes about 5 to 30 minutes in total.

Magnetic resonance imaging (MRI or MRT) also produces detailed cross-section images of the body. Instead of x-rays, this technique uses magnetic fields and radio waves, hence the name.

Put in simple terms, the MRI scanner measures the activity of the body’s hydrogen atoms. The signals measured during this procedure are converted into visual information and can be seen on a computer as two- or three-dimensional images of bones, joints and soft tissues.

MRI scans are especially useful for examining soft tissues like muscles, ligaments or cartilage because these tissues contain a lot of water.

MRI examinations are used for things like knee, shoulder or spine problems. MRI imaging can show signs of wear and tear, ligament and meniscus injuries and inflammations in bones.

An MRI scanner is a large, tunnel-like device containing special coils that produce magnetic fields and radio waves. To do the examination you are asked to lie down on an examination table which is then moved into the machine as far as needed, depending on which part of your body is being examined. While the images are being taken you will hear loud tapping noises. Some people may find the small space and unusual sounds distressing. An MRI examination can take about 15 to 30 minutes in total.

People with implants that are affected by magnetic fields (like pacemakers) cannot have MRI scans. Nowadays some practices and hospitals have open MRI scanners, which can be helpful for people who are frightened of being in a confined space or who are very overweight.

Bone density tests (also called bone densitometry or osteodensitometry) measure the amount of minerals in the bones. The results tell us how resistant the bones are to fractures. Bone density is commonly measured using a special x-ray technique called dual energy x-ray absorptiometry (DXA or DEXA). Weak x-rays are usually sent from below, through the bones of the spine and the top of the thigh bone.

If someone has a lot of wear and tear in their spine, this approach is only used to look at their thigh bone. If someone has an artificial hip joint, it is only used to look at their spine. People who undergo DXA are exposed to less radiation than in a conventional x-ray examination, and to a lot less radiation than in computed tomography.

Bone density tests do not produce x-ray images, but instead measure how easily x-rays pass through the bones. The more porous and brittle the bones are, the more x-rays pass through them. The amount of x-rays that pass through the bones is expressed in a measurement called the T-score. The T-score compares the measured bone density with the bone density of young, healthy adults.

A T-score higher than -1 is considered to be normal, and a T score between -1 and -2.5 is low. According to current definitions, people are considered to have osteoporosis if they have a T-score of -2.5 or lower.

Sometimes ultrasound examinations or computed tomography (CT) are also used to measure bone density of the heel. But there is not enough good research to say whether these measurements are more or less reliable than those obtained using DXA. Besides, as already mentioned, computed tomography exposes people to far more radiation.

Bone densitometry can be used to find out whether someone has osteoporosis and how high their risk of bone fractures is. It is also used to monitor the effects of treatment.

To have a DXA scan, you will be asked to lie flat on your back. If the density of the bones in your spine is being measured, your legs will be raised and bent at a 90° angle. To measure the neck of the femur, your legs will lie flat.

A generator below the examination table produces x-rays while a scanner moves above your body to measure how much radiation was absorbed by your body. The examination takes about 5 to 10 minutes.

Bone scans (bone scintigraphy) produce images of bone metabolism. To get a clear image, a weak radioactive substance is injected into your body before the examination. This substance accumulates in the bones, making it easier to see the different bone structures in the image. Things like cancer metastases or inflamed tissue often store more of this substance than healthy tissue, and this is seen in the image. Bone scans also involve exposure to radiation.

Bone metabolism may change, for instance if a tumor is growing in the bone or if there is an inflammation in the bone. Bone scans can be used if it is thought that someone might have one of these problems. They may also be used to look at poorly-healing fractures.

To prepare for the examination, the doctor injects the radioactive substance into a vein. It takes a few hours for this substance to spread throughout your body. Then you lie down and a special camera takes images as it moves over your body.

In bone biopsies, the doctor takes some tissue out of the bone using a thin needle in order to test it for certain disease-related changes. In bone marrow biopsies, the tissue is not taken from the bone itself, but from the bone marrow inside of the bone.

Bone biopsies are done to examine things like tumors, inflammations and bone structure problems like osteoporosis. Bone marrow biopsies might be considered in people who are thought to have a problem with blood production, like anemia.

After the skin above the bone is anesthetized locally, a small cut is made to insert the biopsy needle. In bone biopsies, tissue is often taken from the pelvic bone, but it can also be taken from the patella (kneecap) or femur (thigh bone). In bone marrow biopsies, the sample is usually taken from the upper part of the pelvic bone (the iliac crest) or from the breastbone. The sample is then tested in a laboratory.

Blood tests are another method used to diagnose certain bone diseases. One example is osteoporosis, where blood tests are used to determine risk factors and rule out other illnesses. For instance, blood calcium levels can be measured to find out whether someone is getting enough calcium, but this does not provide any information about how much calcium there is in their bones. Another important blood parameter is “alkaline phosphatase,” a protein that increases if someone has certain bone diseases.

Other blood parameters may be used to detect signs of inflammations, tumors or metabolic diseases which can affect the condition of the bones.