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Table 1 Statements from the Official Position of the Brazilian Association of Bone Assessment and Metabolism (ABRASSO) regarding technical aspects of body composition measurements using dual-energy X-ray absorptiometry (DXA), along with the levels of agreement (interrater reliability) among the statement’s collaborators

From: Official position of the Brazilian Association of Bone Assessment and Metabolism (ABRASSO) on the evaluation of body composition by densitometry: part I (technical aspects)—general concepts, indications, acquisition, and analysis

Question

Statement

Level of agreement (%)

1. What other parameters and methods are available for body composition assessment in addition to DXA?

Available non-DXA methods for assessment of body composition parameters include anthropometric measurements (weight, height, BMI, skinfold thickness, waist circumference, hip circumference, mid-upper arm circumference, calf circumference), air-displacement plethysmography, bioelectrical impedance, ultrasonography, computed tomography, and magnetic resonance imaging

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2. What are the indications and contraindications of body composition assessment using densitometry?

Considering aspects of accuracy, precision, cost, duration, and regional distribution of fat and lean mass, DXA is considered the gold-standard method for body composition assessment. This method is recommended for assessment of fat mass even in patients with different diseases but remains under investigation for assessment of lean mass

The clinical indications for body composition measurements using DXA are several, but the main ones are obesity, weight loss, dietary protein supplementation in athletes, sarcopenia, use of antiretroviral agents associated with risk of lipodystrophy in individuals with acquired immunodeficiency virus (HIV) infection, stratification of cardiovascular risk, physical training, injury rehabilitation, nutritional disturbances, growth hormone deficiency, thyroid disorders, hypogonadism, estrogen/androgen therapy, glucocorticoid therapy, malabsorption syndromes, eating disorders, and measurement of lean mass for drug dose calculation

Contraindications for DXA scanning include pregnancy, patient's weight or height above the limit allowed for the equipment or inability to remain still throughout the examination, recent administration of contrast material, and image artifacts

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3. What are the technical principles of DXA for body composition assessment?

Total body DXA acquisition is relatively fast and takes on average 5–20 min depending on the equipment and the individual's body proportions. The radiation emitted during body composition assessment varies by equipment from 0.15 to 4.7 µSv

The equipment for DXA scanning consists of a computer system, an exam table, detectors, and a tube that emits X-rays at two different intensities (high = above 70 keV; low = 39–50 keV). The attenuation coefficient of the difference between the two dual-energy levels (R value) estimates the bone mineral content based on the atomic level of each compartment of the body (mineral, soft tissue, and water)

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4. Which precautions should be taken before DXA scanning?

The principles of X-ray protection are based on the duration of exposure, distance from the source, and shielding (protection barriers), according to the ALARA principle. The DXA examination involves a low effective radiation dose (1 mSv for the entire body); therefore, radiation protection is not necessary for professionals involved in whole-body DXA scanning. However, identification, evaluation, analysis, and implementation of measures to reduce the time of direct exposure and increase the distance between the radiation source and the operator are recommended

 Weight and height should be measured using a medical scale

 The room temperature is recommended to be maintained between 21 and 24 °C, and the humidity between 20 and 60%

 Overnight fasting offers the best condition for reproducible DXA scanning results. Heavy fluid intake and large meals should be avoided before the exam

 During DXA scanning, the patient must wear light clothes (e.g., sports clothing) or a gown provided by the densitometry service. Clothing with dense metal or plastic should be avoided, and accessories (e.g., earrings, rings, watch, bracelets, etc.) should be removed

 Patients with large breasts projecting over the upper limbs (e.g., those with obesity or gigantomastia) may use a breast adjustment band without a zipper or metal. Bladder emptying is also recommended. Potential artifacts should be removed whenever possible

 Patients who recently received oral barium contrast, which interferes with DXA results, should be asked to postpone the scanning until 1 week after the use of the contrast. Additional time may be required for complete intestinal cleaning in patients with constipation. Iodinated contrasts used for CT scanning and radioisotopes also interfere with DXA results and require a 1-week delay before scanning

 In patients with external non-removable artifacts (e.g., cardiac pacemaker and vascular, orthopedic, mammary, or gluteal prostheses), consistent positioning and analysis are important for longitudinal reproducibility

 Motion artifacts should be avoided, and when present, the scanning should be performed again

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5. How is the image acquisition protocol?

The patient should be positioned with the body centered on the DXA scanning table, with the center table line used as a reference for aligning the patient. The patient's hand palms should face down and be placed at least 1 cm from the body; if this is not possible, the hands can be placed sideways. The feet must be kept in a neutral position, the upper limbs in a straight or slight angle, the chin upwards in a neutral position, and the head close to the upper limit of the examination table, without exceeding it. Consistency in hand placement at each center is essential for longitudinal monitoring since changes in hand placement could result in changes in tissue measurement

The manufacturer Hologic recommends that both legs are kept apart and in internal rotation throughout the entire exam. In contrast, the legs must be kept together with the use of a Velcro strap to reduce movement in GE-Lunar DXA systems

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6. How is the analysis protocol?

Consistent patient positioning and analysis are the most important factors to minimize measurement errors. Despite slight differences between manufacturers regarding DXA analysis software in terms of movement and segmentation of subregions in ROI markers, the recommendations for the positioning of subregion ROIs are comparable between manufacturers

The ROI lines must be positioned as follows:

1. Head: immediately below the chin

2. Arms: in both glenoid joints, verifying that the lines are separating the arms and hands from the rest of the body, passing through the glenoid

3. Spine: adjusted as close as possible to the vertebrae

4. Pelvis: the upper line must touch the iliac crests, and both oblique lines must pass through the femoral necks without contact with the ischium

5. Legs: hands and forearms must be separated from the legs

6. Between-legs: should follow the division between the legs

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