Dual-Energy X-Ray Absorptiometry in the Diagnosis of Osteoporosis: A Practical Guide

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1 Nuclear Medicine and Molecular Imaging Pictorial Essay Lorente-Ramos et al. DEX of Osteoporosis Nuclear Medicine and Molecular Imaging Pictorial Essay Rosa Lorente-Ramos 1 Javier zpeitia-rmán raceli Muñoz-Hernández José Manuel García-Gómez Patricia Díez-Martínez Miguel Grande-árez Lorente-Ramos R, zpeitia-rmán J, Muñoz- Hernández, García-Gómez JM, Díez-Martínez P, Grande-árez M Keywords: bone mineral density, DEX, dual-energy x-ray absorptiometry, osteoporosis DOI: /JR Received July 30, 2010; accepted after revision October 14, ll authors: Unidad Central de Radiodiagnóstico de la CM, Hospital Infanta Leonor, v gran Vía del Este 80, Madrid, Spain. ddress correspondence to R. Lorente-Ramos (rosa.lorenteramos@salud.madrid.org). JR 2011; 196: X/11/ merican Roentgen Ray Society Dual-Energy X-Ray bsorptiometry in the Diagnosis of Osteoporosis: Practical Guide OJECTIVE. The purpose of this essay is a quick and comprehensive review of dualenergy x-ray absorptiometry in the diagnosis of osteoporosis that shows how to achieve the best performance in three steps. CONCLUSION. The three-step procedure for dual-energy x-ray absorptiometry includes image acquisition emphasizing proper patient positioning and regions of interest; analysis, including areas to scan and detection of artifacts that should be excluded from the analysis and noted in the report because they can necessitate additional imaging; and interpretation of results. D ual-energy x-ray absorptiometry (DEX) is the technique of choice in the assessment of bone mineral density (MD) [1], the average concentration of mineral in a defined section of bone [2]. DEX is a quick method that is accurate (exact measurement of MD), precise (reproducible), and flexible (different regions can be scanned) and is performed with a low radiation dose [3, 4]. lthough other factors, such as trabecular bone structure, are important, central MD measurements are helpful in the diagnosis of osteoporosis for estimating the risk of nontraumatic fracture and in choosing and monitoring treatments. Understanding every step of the procedure is important for maximizing the usefulness of the imaging evaluation to patients and referring clinicians. DEX scanner consists of a low-dose x-ray tube with two energies for separating mineral and soft-tissue components and a high-resolution multidetector array. The devices have one of two different systems: a fanbeam device that emits alternating high (140 kvp) and low ( kvp) x-rays and sweeps across a scan area or a constant x-ray beam with a rare-earth filter and energy-specific absorption, which separates photons of higher (70 kev) and lower (40 kev) energy [5]. Image cquisition reas Scanned In adult patients, central DEX measurements of the lumbar spine and proximal femur are recommended [6]. Two regions should be measured so that if one is unevaluable, the forearm can be imaged. For children (younger than 20 years) only the lumbar spine is studied [7] because variability in femoral maturation results in lack of reproducibility in the hip region, so the reference database is available only for the spine. Lumbar spine Posteroanterior images of the lumbar spine include vertebral bodies L1 L4 (Fig. 1). Proximal femur Either hip may be used for DEX of the proximal femur. The lowest-level data on the femoral neck and total hip are used for diagnosis (Fig. 1). Total hip is the most reproducible measurement of the hip. Forearm The forearm is used in three conditions when the hip and spine cannot be measured or the data interpreted, in examinations of patients with hyperparathyroidism and those whose weight exceeds the limit for the table. Primary hyperparathyroidism decreases MD, which is greater in structures with predominantly cortical bone as opposed to trabecular bone. Recommendations include measurement at the three sites (hip, spine, and radius) for diagnosis and for follow-up after surgical and medical treatment. The areas imaged are total bone, one third of the radius, the ultradistal radius, and the ulna. The most useful measurements are the ultradistal portion of the radius as an indicator of trabecular bone loss and the distal one third of the radius (distal radial diaphysis, excluding the ultradistal portion) as an indicator of cortical bone mineral loss. ccording to the International Society JR:196, pril

2 Lorente-Ramos et al. for Clinical Densitometry [6], the distal one third (33% radius) of the nondominant forearm is the region of choice in the assessment of osteoporosis (Fig. 1C). ppropriate Patient Positioning ppropriate patient positioning is essential for optimizing MD measurement. The patients are placed in the supine position for posteroanterior imaging of the lumbar spine (Fig. 2) and femoral neck (Fig. 2) and sitting next to the table for imaging of the forearm (Fig. 2C). Image ssessment Images are assessed for patient movement. The area of interest exceeding 1 2 cm and superior and inferior limits should be included to verify that the complete anatomic region is scanned. The bone axis should be straight and centered (Fig. 1), and the lesser trochanter should not be seen on images of the proximal femur (Fig. 1). nalysis Placement of Region of Interest Equipment from various manufacturers generates automatic ROIs, which should be reviewed. Correct numbering of vertebral bodies is the main goal in DEX of the lumbar spine. The indicators of correct positioning are as follows: the ribs appear at T12, the largest transverse processes are L3, the vertebral area values increase from L1 to L4, MD increases from L1 to L3, and the MD of L4 is similar to or slightly less than that of L3. Sometimes radiographs are necessary for correlation. ltered vertebrae (deformed or with lesions or artifacts in them) should be excluded from the analysis. If only one vertebral body is left, the region is not useful for diagnosis. In hip scanning, it is important to avoid undesired bone. The anatomic landmark selected for femoral neck ROI placement is the greater trochanteric notch (Figs. 3 and 3). Pitfalls Inappropriate patient positioning The most important source of false MD measurements is inappropriate patient positioning (Figs. 4 and 4). Longitudinal in vivo precision reflects variability due to positioning: spine, 1.1%; femoral neck, 1.2%; trochanter 1.3% [8]. rtifacts Images should be assessed for artifacts, which should be excluded from the ROI [9]. rtifacts include dense objects such as piercings (Fig. 5), catheters (Fig. 5), and surgical material (Fig. 5C); retained contrast medium, such as barium (Fig. 6) and myelographic agents (Fig. 6);and vertebroplasty cement (Fig. 6C). Calcifications that do not affect the analysis, such as calcified kidneys (Fig. 7), hydatid cysts (Fig. 7), myomas, and lithiasis, should be noted in the report as incidental findings. Calcifications superimposed on the ROI, such as dermatomyositis (Fig. 8) and bone grafts (Fig. 9), should be noted as causes of increased MD. Disorders Many diseases spuriously alter MD measurement. In analysis of the lumbar spine, a greater than 1 point difference in T-score between two adjacent vertebrae indicates a vertebra is abnormal, and radiography is mandatory for diagnosis. Degeneration due to osteoarthrosis artifactually increases spinal MD in elderly patients and causes several morphologic changes, such as osteophytes (bone growths) and vertebral endplate reactions to degenerative disks (Fig. 10). In the presence of fractures, MD is altered owing to higher bone density with a smaller surface (Fig. 11). Lytic and sclerotic bone lesions, such as metastatic lesions, lymphoma, bone islands (Fig. 12), lesions due to Paget disease, hemangiomas, and dense pedicles (Fig. 13), also are impediments to MD measurement. Diffuse diseases, such as ankylosing spondylitis and osteopetrosis, alter osseous structure and bone density (Fig. 14). Interpretation The scanner calculates MD in grams per square centimeter. reference database is consulted, and values and curves are obtained. The main parameters are T-score, which represents the SD by which the MD differs from the mean MD of a young adult reference population of the same ethnicity and sex, and Z-score, which is the SD by which the MD differs from the mean MD of a healthy population of the same ethnicity, sex, and age as the person undergoing DEX. For estimation of fracture risk, it is generally accepted that each SD in T-score increases risk by a factor of 2 [10]. ccording to the World Health Organization, among postmenopausal women and men 50 years old and older, diagnosis is based on T-score, normal being greater than 1.0; osteopenia, 1 to 2.5; and osteoporosis, less than 2.5. Z-scores are used in evaluations of premenopausal women, men younger than 50 years, and children and teenagers (younger than 20 years) [6]. Osteoporosis should not be diagnosed on the basis of densitometric criteria alone [5]. Z-score less than 2 indicates the diagnosis is below the expected range for age (adults) or low bone density for chronologic age (children). Conclusion DEX is a quick, accurate, low-cost imaging method for the diagnosis of osteoporosis. It comprises adequate performance (symmetry, morphology, positioning), ROI placement, detection of artifacts, pathologic evaluation (incidental findings and those affecting analysis), and evaluation of bone mineral density. References 1. Lewiecki EM, Watts N, McLung MR, et al. Official positions of the International Society for Clinical Densitometry. J Clin Endocrinol Metab 2004; 89: Wahner H. Technical aspects and clinical interpretation of bone mineral measurements. Public Health Rep 1989; 104[suppl]: Cummings SR, ates D, lack DM. Clinical use of bone densitometry. JM 2002; 288: Lentle C, Prior JC. Osteoporosis: what a clinician expects to learn from a patient s bone density examination. Radiology 2003; 228: dams JE. Single and dual energy X-ray absorptiometry. Eur Radiol 1997; 7:S20 S31 6. aim S, inkley N, ilezikian JP, et al. Official position of the International Society for Clinical Densitometry and executive summary of the 2007 ISCD position development conference. J Clin Densitom 2008; 11: aim S, Leonard M, ianchi ML, et al. Official positions of the International Society for Clinical Densitometry and executive summary of the 2007 ISCD pediatric position development conference. J Clin Densitom 2008; 11: Orwoll ES, Oviatt SK. Longitudinal precision of dual-energy x-ray absorptiometry in a multicenter study. The Nafarelin/one Study Group. J one Miner Res 1991; 6: Jacobson J, Jamadar D, Hayes CW. Dual X-ray absorptiometry: recognizing image artifacts and pathology. JR 2000; 174: [No authors listed]. ssessment of fracture risk and its application to screening for postmenopausal osteoporosis: report of a WHO study group. World Health Organ Tech Rep Ser 1994;843: JR:196, pril 2011

3 DEX of Osteoporosis Fig year-old woman with hyperparathyroidism. Region of interest (ROI) and image assessment., Posteroanterior dual-energy x-ray absorptiometric (DEX) image of lumbar spine includes T12 and ribs, L5 and iliac bone, and straight and centered spine., DEX image of left proximal femur shows four ROIs are femoral neck, trochanter, intertrochanteric region, and Ward triangle. Total hip image comprises four ROIs. Image includes all of femoral head and at least 1 cm under region of lesser trochanter, which should not be seen owing to rotation. Femoral axis is straight. C, DEX image of left forearm. Most important ROI is one-third (1/3) radius (arrow). Image should include 2 cm of diaphysis over one third of forearm and part of carpal bones. xis is straight and centered. MD = bone mineral density, UD = ultradistal. C JR:196, pril

4 Lorente-Ramos et al. C Fig. 2 Patient positioning., Photograph shows position for posteroanterior imaging of lumbar spine: supine with hips and knees flexed over support to reduce lordosis., Photograph shows position for imaging of proximal femur: supine with lower extremity internally rotated and slightly abducted to keep femoral axis straight. C, Photograph shows position for imaging of forearm: sitting beside table with forearm resting on table, hand pronated and held by straps. Fig year-old menopausal woman with osteopenia. Green = normal, yellow = osteopenia; red = osteoporosis, MD = bone mineral density, MC = bone mineral content, Sup = superior, Inf = inferior, Ward = Ward triangle., Dual-energy x-ray absorptiometric (DEX) image shows incorrect placement of region of interest (ROI) in which boundary includes bone other than area of interest (femoral neck T-score, 2,6; total femur, 2)., DEX image shows correct ROI placement. Equipment allows operator to reduce ROI size and change angulation according to morphologic features of femoral neck or exclude area from analysis. T-score decreases with correct ROI placement (femoral neck T-score, 2.1; total femur, 1.8). 900 JR:196, pril 2011

5 DEX of Osteoporosis Fig year-old woman with osteopenia. Green = normal, yellow = osteopenia; red = osteoporosis, MD = bone mineral density, MC = bone mineral content, Sup = superior, Inf = inferior, Ward = Ward triangle., Dual-energy x-ray absorptiometric (DEX) image of proximal femur shows inappropriate positioning of femoral head resulting in depiction of lesser trochanter (arrow) and normal femoral neck T-score of 0.9., DEX image shows appropriate rotation in that lesser trochanter is not depicted (arrow). Modification of hip rotation to proper position results in femoral neck T-score of 1.3, indicating presence of osteopenia. Fig. 5 rtifacts caused by dense objects., 18-year-old girl with anorexia nervosa. Dualenergy x-ray absorptiometric (DEX) image shows density superimposed on L4 (arrow) found to be metallic removable piercing not noticed by technologist. Examination was repeated after removal of object, and L4 Z-score decreased from 1.6 to 3 and L1 L4 Z-score from 1.7 to 3., 65-year-old woman with enteric tube. DEX image shows dense structure (arrow) superimposed over L1 vertebral body. Exclusion of L1 from analysis changed T-score from 1 for L1 L4 to 1.2 for L2 L4. C, 68-year-old woman with spinal fixation. DEX image shows presence of surgical material over L4 L5 increases bone mineral density values (L3 T-score, 2.8; L4, 1.2). Exclusion of L4 changes T-score from 1.8 for L1 L4 to 2.7 for L1 L3. Green = normal, yellow = osteopenia; red = osteoporosis, MD = bone mineral density, MC = bone mineral content, D11 and D12 = T11 and T12. C JR:196, pril

6 Lorente-Ramos et al. Fig. 6 rtifacts caused by contrast material. Green = normal, yellow = osteopenia; red = osteoporosis, MD = bone mineral density., 65-year-old woman who underwent barium examination of upper gastrointestinal tract day before dual-energy x-ray absorptiometric (DEX). DEX image shows higher of T-score in L3 (1.6) than in adjacent vertebrae (L2, 3.3; L4, 1.1). Exclusion of L3 changes L1 L4 T-score from 1.4 to 2.3. ecause artifacts can be caused by retained contrast material from previous examinations, every patient should be asked whether barium examination has been performed within past few days, and DEX should be postponed if it has., 72-year-old woman with remote history of myelography. DEX image shows densities overlying L3 and L5 caused by retained myelographic contrast medium from examination performed 25 years ago. rea should be excluded from analysis. With exclusion of L3, L1 L4 T-score changes from 2.1 to 2.5. C, 75-year-old woman with osteoporotic L1 and L3 fractures sustained 1 year ago and managed with vertebroplasty. DEX image shows T-scores are higher than for adjacent vertebrae (L1, 0.2; L2, 3.5; L3, 1.2; L4, 4). Excluding L1 and L3 from analysis changes L1 L4 T-score from 2.1 to 3.8. C 902 JR:196, pril 2011

7 DEX of Osteoporosis Fig. 7 Calcifications not affecting analysis., 67-year-old-woman with calcified kidney. Dual-energy x-ray absorptiometric (DEX) image shows previously unknown calcified nonfunctioning kidney. Radiograph confirms finding., 54-year-old woman with calcified hydatid cyst. DEX image and radiograph show calcification that proved to be hepatic hydatid cyst. Fig year-old woman with dermatomyositis. Dual-energy x-ray absorptiometric image and radiograph show multiple seeming calcifications superimposed on left hip. Erroneous increase in bone mineral density (arrow) precludes analysis. Fig year-old woman with bone graft. Dual-energy x-ray absorptiometric image and radiograph show area of laminectomy and calcified bone graft over L4 L5 vertebral bodies. Exclusion of L3 and L4 changes L1 L4 T-score of 1.8 to L1 L2 T-score of 1.6. Fig year-old woman with osteoarthrosis. Dual-energy x-ray absorptiometric image shows artifactual increase in bone mineral density (arrow) in affected vertebrae due to osteophytes and vertebral endplate reaction to degenerative disk. ffected vertebrae have higher bone mineral density and T-score (L2, 1.0; L3, 0.8) than adjacent vertebral bodies (L1, 1.7; L4, 2.4). MD = bone mineral density, green = normal, yellow = osteopenia; red = osteoporosis. Fig year-old woman with vertebral fracture. Dual-energy x-ray absorptiometric image shows high-density L1 vertebral body of reduced size consistent with vertebral fracture (arrow). Lateral radiograph of lumbar spine confirms presence of fracture (arrow). Top = normal, center = osteopenia; bottom = osteoporosis, MD = bone mineral density. JR:196, pril

8 Lorente-Ramos et al. Fig year-old woman with sclerotic vertebral pedicle. Dual-energy x-ray absorptiometric image and radiograph show dense round area overlying L4 vertebral body (solid arrows) that turned out to be left L4 sclerotic pedicle. Cholecystectomy clips (open arrows) are evident. Green = normal, yellow = osteopenia; red = osteoporosis, MD = bone mineral density. Fig year-old woman with sclerotic bone island. Dual-energy x-ray absorptiometric image and radiograph depict dense round area in trochanteric region Fig year-old woman with osteopetrosis. Posteroanterior dual-energy x-ray absorptiometric (DX) image of lumbar spine shows dense vertebrae with high T-score at all levels. MC = bone mineral content, MD = bone mineral density, CV = coefficient of variation, CF = autocorrelation function, CF = bias correction factor, TH = total hip. 904 JR:196, pril 2011