Imaging Modality: Bone Densitometry

The radiology department within the health care field is very complex. There are a number of imaging modalities that are used throughout the field. Imaging modalities are able to view and image different parts of the body. Bone densitometry is an imaging modality that scans the bones in order to detect osteoporosis. Osteoporosis is a skeletal disorder that affects the strength of bones. It is a disease in which the bone density and quality are affected, and the bone becomes thinner and more porous.

The bone being more porous is demonstrated in figure 1. Due to thinner bones, a person with osteoporosis has an increased risk of fracturing their bones. There are different stages of this disease, the first stage is osteopenia. Osteopenia is low bone mass and is considered as pre-osteoporosis.

Another category of osteoporosis is severe osteoporosis, where a fracture is present . Throughout the world, 44 million people have low bone mass and 10 million people have osteoporosis. Out of the 10 million people who have this disease, 8 million of them are women.

This statistic shows that osteoporosis is more common in women than it is in men. Osteoporosis can be detected with the use of bone densitometry. Bone densitometry uses a low dose of ionizing radiation to assess low bone mass and detect any deterioration within the skeletal system. It uses two energies in order to separate bone from the surrounding soft tissue. Due to the use of two energies, bone densitometry uses a dual-energy x-ray absorption unit. Bone densitometry is often referred to as a DXA scan and the terms are used interchangeably.

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Just like any imaging modalities, there is a purpose for the scan. Bone densitometry has a number of different purposes. Some of the purposes are measuring bone mineral density (BMD), detecting bone loss, establishing the diagnosis of osteoporosis, assessing the risk of fractures, assessing the response to therapy being done for osteoporosis, and performing an assessment of a vertebral fracture. If a fracture is already present or suspected, a bone density scan can be done to confirm the diagnosis. A bone density scan can be used to do any one of these things or all of them depending on the patient’s condition. Before bone densitometry was invented and first used, standard x-rays were used in the process of diagnosing osteoporosis.

Since general x-rays were used, radiologists had to evaluate the scans performed differently than any other x-rays. They took x-rays of the thoracic and lumbar spine and used those images to detect any visible changes in the density of the patient’s bone. Due to these images not being as accurate as the scans used today, the disease was not diagnosed till later. Osteoporosis was normally diagnosed after a fracture was detected or suspected. The most common areas scanned during a bone densitometry are the hips and lumbar spine. The hips and lumbar spine are also known as the “gold standard” due to them withholding most of the body’s weight and enduring the most stress. When the lumbar spine is scanned, the scanning is done on L1-L5 but only L1-L4 is analyzed. The positioning and centering for both of the exams are similar to those in general x-ray. For the l-spine, the patient is supine with no pelvic rotation and the legs are elevated and at a 60-90 degrees angle from the trunk of the body.

For the hips, the patient is supine with their legs extended and rotated 15-20 degrees internally. The hip used for the exam is determined by if the patient has had a previous hip fracture. Each bone densitometry machine may vary depending the manufacturer who made the machine. Most machines have a flat table with an arm suspended over it . Due to each machine being different, a patient must have their scans performed on the same machine in order to get accurate results  Patients may have to have a bone density scan done more than once depending on their results. The scans will be done every few years, which will be determined by the results. Since the patient will more than likely have to have more than one scan, the positioning of the patient is key.

Every imaging modality has their own indications and contraindications. The indications for a bone density scan are also the risk factors for osteoporosis. These include being female, increased age, an estrogen deficiency, Caucasian, low body weight, family history, smoking, and any previous adult fractures. Certain diseases may also be risk factors for osteoporosis. Some of these include diabetes, rheumatoid arthritis, and some gastrointestinal conditions. Individuals should have a bone density scan performed if they are a post-menopausal woman who is not taking estrogen, smoker, have a previous hip fracture or evidence of a vertebral fracture, osteoporosis runs in their family, or are taking certain medications. These medications include steroids, and any thyroid or anti-seizure medication. Individuals should also have this scan done if they have one of the following diseases: type 1 diabetes, liver or kidney disease, or hyperthyroidism.

There are a couple of reasons in which an individual should not have a bone density scan done. These include being pregnant, or if they have had an exam done in which contrast was administered within a week prior to the scan. When a patient is getting ready for their scan, their prep may vary on the facility. Before the scan is performed, the patient must inform the technologist if there is any chance of pregnancy. If the patient has any metal that may interfere with the images, they may be asked to remove those objects. These objects may include belts, zippers, jewelry, or anything in the pockets. The patient will be instructed to wear loose or comfortable clothing for their exam. If the patient has to remove any clothing, they will be given a gown, but this depends on the facility’s protocol.

Once the patient is prepped for the exam, they will be asked to lay down on the table. The technologist will correctly position them based on the area being examined. Once the patient is positioned, the scan will begin. After the scan is complete, the results will appear on the technologist’s computer. These results will show two different scores that will provide the patient’s diagnosis. The first score is the T-score, which is where the patient’s data is compared to young, healthy adults of the same gender. A normal T-score is greater or equal to -1.0. Osteopenia can be categorized as a T-score of less than -1.0 but greater than -2.5. Osteoporosis can be categorized as less than -2.5 but severe osteoporosis has the same T-score but also has fracture present.

The other score is the Z-score, which compares the patient’s data to someone of the same age, gender, and size. If someone is below the expected range for their age, their Z-score will be less than -2.0. If someone is within the expected range for their age, the Z-score will be greater than -2.0. The results from the bone density scan, will be recorded and sent to the patient’s primary care physician. Bone densitometry is very complex but is a very accurate way of diagnosing osteoporosis. Osteoporosis is a skeletal disorder which is more common than some may realize. Due to this disease being so common, there has to be an accurate test in order to diagnose it. Bone densitometry does just this but can also be used to assess any fractures within the vertebral column. This is just one of the many imaging modalities within the radiology department and can be performed within a clinic or a hospital. Something that is unique about this imaging modality is that the results are not sent to the radiologist and are only sent to the primary care physician