Bone Densitometry for Technologists (None)

9781588290205 - Bone Densitometry for Technologists (None) by Lori Ann Lewis

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In addition to the T -scores, DXA reports also provide Z -scores, which are calculated similarly to the T -score, except that the patient's BMD is compared with an age-matched and race- and gender-matched mean, and the result expressed as a SD score.

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Most official groups recommend screening healthy women for osteoporosis at age 65, and testing higher-risk women earlier. The International Society for Clinical Densitometry ISCD recommends screening men without risk factors for osteoporosis at age 70, and screening higher-risk men earlier. Of course, BMD testing is an appropriate tool in the evaluation of patients who have diseases e.

Bone Density Technologist

Recently, many epidemiological studies have validated risk assessment indices for osteoporosis in women. The purpose of the risk assessment indices is not to diagnose osteoporosis or low BMD, but to identify women who are more likely to have low BMD. The calculated risk index is based on self-reported age and weight: It was developed and validated in several studies in Asian and White women 23—25 and men. Evidence suggests that the femur neck or total hip is the optimum site for predicting the risk of hip fracture and the spine is the optimum site for monitoring response to treatment.

Thus, many authors recommend hip measure alone for the fracture risk assessment. The most important informations to check are the correct identification of the patient, his date of birth and also the sex and ethnicity which are mandatory to calculate T -scores. Sex is used by all manufacturers to calculate T -scores i. T -scores for women are calculated using a female normative database, while T -scores for men are calculated using a male normative database. Although, all manufacturers use race in calculating Z -scores, there is inconsistency in the way race is handled when calculating T -scores.

Common mistakes in the clinical use of bone mineral density testing

Norland and Hologic are using race in calculating T -scores i. T -scores for Caucasians are calculated using a Caucasian normative database, T -scores for Blacks are calculated using a normative database for Blacks ; however, GE Lunar and recent Hologic machines use the database for young-normal Caucasians to calculate T -scores, regardless of the race of the subject. The main purpose of the DXA scan image is to check if the patient is positioned correctly, something that the technologist must determine before the patient leaves the testing center.

Positioning should also be doublechecked by the clinician who interprets the test. A scan with correct positioning of the spine is shown in Figure 1 a the patient is straight on the table spine is straight on the image , not rotated spinous processes are centered , and centered in the field roughly equal soft tissue fields on either side of the spine. Patients with scoliosis cannot be positioned with the spine straight on the table; moreover with severe scoliosis degenerative changes can occur that invalidate the spine measurement.

The scan should extend up sufficiently far to include part of the lowest vertebra with ribs which is usually T12 and low enough to show the pelvic brim which is usually the level of the L4—L5 interspace. Internal rotation may be improved by having the patient flex the foot before doing the internal rotation, and then relaxing the foot after the strap is in place. This amount of internal rotation presents the long axis of the femoral neck perpendicular to the X-ray beam, providing the greatest area and the lowest BMC and the lowest BMD , and is confirmed on the scan by seeing little or none of the lesser trochanter Figure 1 b.

Correct positioning and analysis of the L1—L4 spine a and the proximal femur Lunar b and Hologic c.

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The software marks regions of interest in the spine and hip, but the technologist can and should make adjustments if needed. The spine region of interest consists of the L1 through L4 vertebrae Figure 1 a. The intervertebral lines can be moved or angled, if necessary. There must be sufficient soft tissue on both sides of the spine; otherwise BMD will be under estimated.

Job Description of a Bone Densitometry Technologist

The hip regions of interest include the femoral neck, trochanter and total hip Figure 1 b. Ward's region and the intertrochanteric region are not relevant and can be deleted from the results reports.

The default hip analysis includes a midline that must be placed correctly for the other sites to be identified correctly. The preferred position for the rectangular femoral neck box differs for different manufacturers. For GE Lunar, the femoral neck box is located by the analysis program at the narrowest and lowest density section of the neck; typically this will be about half way between the femoral head and the trochanter Figure 1 b.

For Hologic the box is on the distal part of the femoral neck Figure 1 c. This induces a large difference among these two measurements, because of a gradient of BMD all along the femoral neck the proximal being the highest, the distal being the lowest. Thus careful checking of the femoral neck box is mandatory. The image should be evaluated for artifacts e.

Almost all artifacts and local structural change will spuriously elevate BMD. In the spine, absent bone laminectomy or spina bifida or vertebral rotation idiopathic scoliosis will spuriously lower BMD. All evaluable vertebrae should be used, but vertebrae that are affected by local structural change should be deleted from the analysis. Most agree that decisions can be based on two vertebrae; the use of a single vertebra is not recommended. Figures 2 and 3 show examples from common spine and hips scanning problems.

Examples among some common spine scanning problems: Finally, physicians must keep in mind to actively look for secondary osteoporosis in front of low BMD value, either by thorough history taking or with biochemical studies before stating about postmenopausal osteoporosis. Examples among some common hip scanning problems: For assessing vertebral heights also called vertebral morphometry , a special software is used to determine vertebral body dimensions. The computer with the help of the technologist places points on the superior and inferior endplates of each vertebra.

The vertebral heights are calculated and compared with each other as well as to the expected normal dimensions. With the advent of higher-resolution DXA systems, visual assessment of fractures is also possible from DXA-based lateral spine images Figure 4. In this situation, the DXA system essentially functions as a digital X-ray imaging device. Visual assessment is performed from a computer monitor or high-resolution printout. To optimize the assessment, the use of high-definition dual-energy images has been recommended. The evaluation of spine fractures can be performed without a conventional lateral spine X-ray.

This can be done at the same time and at the same place as the BMD measurement, with much less radiation than a conventional spine X-ray. Moreover, VFA is a technology for diagnosing vertebral fractures that may alter diagnostic classification, improve fracture risk stratification, and identify patients likely to benefit from pharmacological therapy who otherwise might not be treated. Skeletal radiologists have criticized the technique for being insensitive and inaccurate for detecting vertebral fractures in particular at the upper thoracic spine. A DXA image is of lower resolution than a conventional X-ray and might fail to identify other potential problems or diseases that would be apparent on a spine film.

However, VFA allows ruling out vertebral fracture at levels where vertebral fracture is most common, i. At this time, DXA devices are not generally accepted as a surrogate for spinal X-rays, though they may provide a useful screening tool in higher-risk patients when spinal X-rays are unavailable. For example, individuals over 65, subjects reporting significant height loss or patients on long-term glucocorticoid therapy who have not had previous vertebral fractures or spinal radiographs could benefit from a VFA. It is recommended to measure the PA lumbar spine and proximal femur and classifying the patient based on the lowest T -score from three sites lumbar spine, femoral neck and total hip.

Although, the BMDs at different anatomic regions are correlated, the agreement between sites is low when it comes to classifying individual subjects as osteoporotic or not. Thus, T -score discordance between the lumbar spine and hip testing sites is a commonly observed phenomenon in densitometery.

T -score discordance is the observation that the T -score of an individual patient varies from one key measurement site to another. Various studies have analyzed the prevalence and impact of T -score discordance on the management of osteoporosis.

Physiologic discordance is related to the skeleton's natural adaptive reaction to normal external and internal factors and forces. Mechanical strain especially related to weight bearing plays a key role in this kind of discordance. An example of this type of discordance is the difference observed between the dominant and nondominant total hip.

Moreover, the spine and hips usually start out with different T -scores the spine is said to reach peak at least 5 years before the hip. The second type of discordance described as pathophysiologic discordance is seen secondary to a disease. Common examples observed in the elderly include vertebral osteophytosis, vertebral end plate and facet sclerosis, osteochondrosis, and aortic calcification. A second subtype is a true discordance resulting from a more decreased BMD in the lumbar spine than the hips.

Indeed, most of the etiologiess of the secondary osteoporosis such as glucocorticoid excess, hyperthyroidism, malabsorption, liver disease and rheumatoid arthritis first affect spinal column. Anatomic discordance is owing to differences in the composition of bone envelopes tested. An example is the difference in T -scores found for the posteroanterior lumbar spine and the supine lateral lumbar spine in the same patient.

Bone Densitometry 101

Artifactual discordance occurs when dense synthetic manmade substances are within the field of ROI of the test: We demonstrated in a previous study that DXA in vivo reproducibility is 2-fold better in the hips than the spine especially when measuring both hips. The high prevalence of T -score discordance could induce some problems for the physicians in decision-making regarding these patients. In general, high prevalence of discordance between lumbar spine and hip T -scores suggests some defects in the cut-off values for definition of osteoporosis and osteopenia proposed with the WHO.

The inconsistencies in the diagnostic classification of osteoporosis between skeletal sites lend credence to the notion that BMD should be used as only one of the factors in making therapeutic decisions when evaluating patients with osteoporosis. Biblio is a marketplace for book collectors comprised of thousands of independent, professional booksellers, located all over the world, who list their books for sale online so that customers like you can find them!

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The latest Canadian Cancer Statistics report found that of all newly diagnosed cancers in , half are expected to be lung, colorectal, breast and prostate cancers. Learn what you can do to reduce the burden of cancer. Select the text below and copy the link. Bone density scan A bone density scan is an imaging test that uses x-rays to measure how strong your bones are. Why a bone density scan is done A bone density scan may be done to: You can eat normally but should not take calcium supplements for 24 hours before the test.

Side effects Bone density scans use low levels of ionizing radiation. What the results mean A bone density scan tells your doctor how strong your bones are by using a numbered score. What happens if the results are abnormal Your doctor will decide whether further tests, procedures, follow-up care or additional treatment are needed. Special considerations for children Preparing children before a test or procedure can help lower their anxiety, increase their cooperation and develop their coping skills.

In most cases, contrast medium is injected into or around the structure to be examined. Also called contrast dye or contrast agent.

Stories Slowly, it dawned on me that I, too, could be a survivor. Links to help you Living with cancer Your healthcare team Publications Talk to an information specialist Talk to someone who's been there Connect with our online community Questions to ask. Taking action against all cancers The latest Canadian Cancer Statistics report found that of all newly diagnosed cancers in , half are expected to be lung, colorectal, breast and prostate cancers.

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