Understanding tests used to detect bone problems

X-ray examinations are especially useful for examining the skeleton, but less so for examining soft tissues. This is because the different types of tissue allow different amounts of radiation to pass through. Bones absorb almost all the radiation because they are so dense – so they appear as white or gray outlines on the x-ray image. Soft tissues like fat or muscles let almost all the radiation pass through – they appear as black areas on the x-ray image.

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 emergency situations.

X-ray examinations are used to detect problems like fractures, abnormal positions of bones, or bone diseases like osteoarthritis. They are also used to plan surgery or to check the position of a prosthesis after an operation. Dentists use x-rays to detect things like diseases in the roots of the teeth.

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 or briefly leave the x-ray room. 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 dye is sometimes put into the body before the scan to make certain structures more visible on the x-ray image.

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. Things like fractures, bone tumors and dead bone tissue can be shown in more detail and their position can be described more accurately.

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.

MRI scans are particularly useful for examining soft tissues like muscles, ligaments or joint cartilage.

Magnetic resonance imaging also produces detailed cross-sectional 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 examinations are used for things like knee, shoulder or spine problems. MRI imaging can show slipped discs, meniscus injuries, and tendon injuries in the shoulder.

People with metallic implants might not be able to have MRI scans, like people who have a pacemaker.

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 scan can take about 15 to 30 minutes in total. 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 stable the bones are. Bone density is measured using a special x-ray technique called dual energy x-ray absorptiometry (DXA or DEXA).

DEXA sends weak x-rays through the bones of the lumbar spine and the top of the thigh bone. The test measures how easily x-rays pass through the bones. The lower the bone density, the more x-rays pass through them. People who undergo DEXA are exposed to less radiation than in a conventional x-ray examination.

Age-related changes to the spine can affect the reliability of the bone density measurements. That is why measurements are usually done on the thigh bone, unless somebody has two artificial hips.

Bone densitometry can be used to find out whether someone has osteoporosis. But the risk of a fracture doesn’t only depend on bone density. That is why the bone density measurement should always be looked at together with other risk factors and a person’s general state of health.

To have a DEXA 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 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. A weak radioactive substance is injected into your body before the examination. It accumulates in the bones, making it easier to see the bones’ metabolic activities in the image.

Bone scintigraphy is used to detect cancerous metastases and inflammations in the bones. Because cancerous and inflamed tissues have especially active metabolisms, they store more of the radioactive substance than healthy tissue. But the scan can also be used to detect dead tissue: It can no longer be seen in the image because it no longer has a metabolism. Bone scans also involve exposure to radiation.

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 bone marrow biopsies, the tissue is taken from the bone marrow. The bone marrow is inside the bone and contains the blood stem cells that produce new blood cells. The bone marrow also produces immune cells for the body’s immune system.

Bone biopsies are special tests that are used in particular to examine rare bone tumors.

Bone marrow biopsies are mainly used to diagnose different types of blood cancer such as leukemia.

The skin above the bone is first numbed using a local anesthetic. A small cut is then made to insert the biopsy needle.

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.