Bone Density Scan
Bone density generally refers to the strength of a bone and its ability to bear weight. Doing a bone density scan therefore measures a bone’s strength, its ability to bear weight, and its risk of fracture. The most common and accurate way to measure bone density is to use a Dual-Energy X-ray Absorptiometry (DEXA) scan. (Medlineplus, 2014). Before the use of DEXA was introduced, osteoporosis could be determined only when a patient broke a bone, and by then, the bone may have become very weak. With a bone density scan however, it can be determined if a patient is at risk of bone fracture, or at risk of osteoporosis. The bone density scan is done with Dual Energy X-ray Absorptiometry (DEXA) equipment. The DEXA technology became available for clinical use in 1987, but before then, there were the Single Photon Absorptiometry (SPA), and Dual Photon Absorptiometry (DPA), both of which are no longer in use. (Dasher, Newton, & Lenchik, 2010). The bone density scan is usually done on the following patients:
• Post menopausal women not taking estrogen.
• Patients with personal or maternal history of hip fracture or smoking.
• Post menopausal women who are tall (over 5ft 7inches), or thin (less than 125lbs).
• Men with clinical conditions associated with bone loss.
The DXA Scanner
Driver, (2013), described the DEXA scanner as a machine that produces two x-ray beams of high and low energy levels. Much like fluoroscopy, the x-ray from the DEXA scanner comes from underneath the patient, and the scanner has a very low x-ray dose. Earlier versions of the DEXA scanner emitted radiation which required up to five minutes to scan an area of interest, but the more advanced machines can take as little as five seconds to scan the same area. The amount of x-ray that passes through the bone is measured at each of these energy levels. The computer eliminates the soft tissue, and the bone mineral density is measured based on the difference between the two beams. DEXA scan usually measures bone loss (osteoporosis), and Bone Mineral Density (BMD). According to Dasher et al. (2010), DEXA is not only used for diagnosis of osteoporosis, but it is also used to help assess fracture risk to help select patients for pharmacology therapy, and to help monitor therapy or disease progression. So, when the whole body is scanned, DEXA scanners also allow for measurements of the total body calcium content and body composition. (Papp, 2011). Just like the x-ray machines, the DEXA scanner is manufactured by different manufacturers, so the machines may not look exactly alike, but the technology is the same. There are two types of DEXA scanners: Central DEXA scanner and Peripheral DEXA scanner.
Central DEXA Scanner
The central DEXA scanner has a long table and a detector above the table which looks like a C-arm. The radiation comes from underneath the patient just like in fluoroscopy. This particular scan predicts the bone density in...