A bone scan is an imaging test that examines bone for irregularities that could indicate infection or cancer. A bone density test specifically looks at the density of bone and evaluates how likely a person is to develop osteoporosis.

What is Bone Scan?

Definition:

A bone scan, or bone scintigraphy, is used to describe an imaging technique in which bone is examined to look for pathological conditions. 

Purpose of a bone scan:

A bone scan is done to check for possible infection or cancer in the bone tissue. It can also be completed to look for fractures and arthritis.

Procedure for a bone scan:

A bone scan is categorized as a nuclear medicine method because it involves a small amount of radiation entering the body. A radioactive tracer is first injected into the person. A few hours later the person will then have their body scanned with a device designed to detect the radioactive material. The tracer can show abnormalities on the scan that could indicate a bone problem. A score below -1 but not at -2.5 means osteopenia. Osteoporosis is when the score is -2.5 and worse.

Advantages:

A big benefit of a bone scan is that it is a sensitive test. It can detect very small irregularities in the bone that may not be evident on a regular X-ray. This means that a defect in the bone caused by cancer or infection is more likely to be detected if you have a bone scan than a general X-ray.

Disadvantages:

Bone scans use radioactive chemicals as tracers. The problem with this is that it does expose a person to radiation, although at a low level. The other issue is that some people may have an allergic reaction to the radiation in the tracer.

What is Bone Density Scan?

Definition:

A bone density scan is also called a dual energy X-ray absorptiometry (DEXA) and is a test done to look at the density of the bone tissue. 

Purpose of a bone density scan:

A bone density scan is done to look at how dense your bone tissue is. The scan is done to evaluate a person’s risk of getting osteoporosis. Osteoporosis is porous bones, which makes a person likely to break a bone.

Procedure for a bone density scan:

The DEXA is similar to an X-ray and you lie on a table. The machine, though, uses two different types of X-ray beams. It produces both a high-energy and a low-energy X-ray beam. The idea is to measure how well the rays pass through the bone so as to estimate the density of the tissue.

Advantages:

The bone density test is useful for looking at how dense bone tissue is. It also uses very little radiation.

Disadvantages:

There is variation in the values obtained from different DEXA machines. 

Difference between Bone Scan and Bone Density Scan

Definition

A bone scan is a scan of bone to look for problems like cancer or infection. A bone density scan is imaging done to look at the density of the bone.

Purpose

The purpose of a bone scan is to check for problems like infection and cancer. The purpose of a bone density scan is to look at the density of bone and assess the risk of osteoporosis.

Method

With a bone scan, a radioactive tracer is injected into the person and then the scan done. With a bone density scan, both low-energy and high-energy X-ray beams are used.

Advantages

A bone scan is sensitive to even small changes in bone tissue that can allow rapid detection of problems like bone cancer or infection. A bone density scan is quick and does not use radioactive tracers.

Disadvantages

A drawback of a bone scan is it uses radioactive tracers that people may be allergic to. A drawback of a bone density scan is that DEXA machines are not all standardized.

Table comparing Bone Scan and Bone Density Scan

Summary of Bone Scan Vs. Bone Density Scan

• A bone scan and bone density scan are both commonly used imaging techniques.
• A bone scan is a test to look for problems like fractures, infections, or bone cancer.
• A bone density scan is used to look at the level of mineral density in bones and to assess a person’s risk of osteopenia and osteoporosis.

FAQ

Does a bone scan show bone density?

A bone scan does not accurately show bone density. This is why a bone density test is recommended when the doctor is interested in seeing how thick the bones are.

What is the difference between bone density and bone quality?

Bone density is how thick bone is while bone quality refers to attributes of bone that are separate from bone density.

Which scan is best for bone?

The type of scan that is best depends on what is being diagnosed. For bone cancer and bone infection a bone scan is best while for bone density a DEXA scan is best.

Why would a doctor order a bone scan?

A bone scan is ordered when a doctor suspects something is wrong and a patient has symptoms such as pain in the bone. It is also possible that a person who was previously diagnosed with cancer may have metastases that have spread into the skeleton. A scan can show if this has happened.

How accurate are bone density scans?

Bone density scans have a high accuracy allowing doctors to determine what amount of bone loss has occurred and if the person has osteopenia or osteoporosis.

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