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DXA-skanning à BMD Peter S. Oturai M.D. Department of Clinical Physiology, Nuclear Medicine & PET Rigshospitalet, University of Copenhagen, Denmark

•  Knogle – mineral - BMC – BMD •  DEXA/DXA

§  Princip §  BMD à T/Z à Osteoporose/Osteopeni

§  Apparatur §  Praktisk – Dosimetri §  Rigtighed - Præcision §  Diverse

§  Fejlkilder - artefakter §  VFA, TBS

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D(E)XA skanning

• D -

• E -

• X -

• A -

 D - Dual

 E - Energy

 X - X-ray

 A - Absorptiometry

38 KeV + 70 KeV

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DXA-scanner and thus provides a more accurate representation of bonemineral losses.9

The NOF recommends dual-energy X-ray absorptiometry(DXA) testing for the early detection and treatment of osteo-porosis. The organization particularly recommends DXAtesting of the spine and hip because these are the most fre-quent fracture sites. Investigators from the National Healthand Nutrition Examination Survey III (NHANES III) col-lected DXA test results between 1988 and 1994 and com-piled a standard set of normal bone density measurements ofthe hip for different genders, ethnicity, and age groups in theUnited States, with which the test result of a patient can becompared for immediate diagnosis of osteoporosis.10 In2008, the NOF reported that it adopted the World HealthOrganization’s (WHO) newly developed fracture predictionalgorithm (FRAX) for the U.S. population. The algorithmenables physicians to calculate the probability of osteoporo-sis-related fractures with a particular patient.11

For the diagnosis of osteoporosis, quantitative computedtomography (QCT) has also been used—particularly to mea-sure the BMD of trabecular bone within the vertebral bodyexcluding its cortical bones, and, more recently, peripheralQCT has been used for the measurement of BMD with pe-ripheral bones.12 Quantitative ultrasound also has been usedfor the measurement of calcaneal bone (Os calcis) BMD withspeed of sound and broadband ultrasound attenuation.13

Bone DensitometryDevices and MethodsSPA and DPAIn 1963, single-photon absorptiometry (SPA) was intro-duced. This device could quantitatively measure the BMD ofthe peripheral bones.14 SPA, however, could not measure theBMD of central skeletal sites (lumbar spine and hip). Theradionuclide source (125I), which SPA used, emitted an aver-age energy of 27 keV. The energy level was sufficient for theBMD measurement of appendicular bones but not for that ofcentral skeletal sites.15 Dual-photon absorptiometry (DPA)was then developed.16 Both SPA and DPA used radionuclidesources that decayed and required regular replacement. SPAand DPA also took considerable scanning time (15-30 min)because of low photon flux. With the slow scanning, thereoccurred undesirable incidents, such as the patients movingduring the scan, rendering poor quality of the image andlimiting reproducibility.

DXAIn the mid-1980s, DXA was developed. Unlike the 2 previousdevices, DXA used low-energy x-ray beam with high photonflux that permitted faster scanning. First-generation DXAequipment used pencil beams and took 5-10 minutes to scana skeletal site. Recent generations use fan beams, and takeonly 10 to 30 seconds to scan. Modern DXA devices offerimproved spatial resolution, image quality, and precision17-20

and can be used to scan both central and peripheral bonesites.

DXA uses highly collimated beams. The beams passthrough soft tissues and bony parts of the body and are cap-tured by a detector placed on the opposite side. The intensityof the beam exiting the body and thereafter being reflected onthe detector is inversely related to the density of the bodyparts being evaluated (Fig. 1). For the measurement of bonemass and BMD, the intensity of the beam that exited a bodypart is compared with that of the beam that exited from thestandard phantoms of known density. The results of BMD areexpressed in grams per square centimeter. The beam thatexited a body part is displayed as an image on the monitorscreen or on a plain paper. To check the stability of theequipment and to ensure the quality and control of the pro-cesses, the phantoms are calibrated daily.

The selection of the optimal skeletal site for the diagnosisof osteoporosis is not well defined because bone minerallosses do not progress at the same rate at different parts of thebody.21-23 Therefore, the measurement of hip BMD is per-formed for the evaluation of hip fracture risk, whereas themeasurement of spine BMD is performed for the evaluation ofspine fracture risk.24 Because the spine has the most trabec-ular content, it best represents patient’s bone metabolismand, for the reason, vertebral bodies are generally regarded asbeing better for monitoring responses to treatment than otherskeletal sites.25,26

DXA can perform many different functions, exposing pa-tients to very low radiation doses (1-10 !Sv).19

Posteroanterior (PA) Spine and Hip BMDDXA uses 2 different x-ray beams with high- and low-photon energies and can measure the BMD of PA spine andhip with correction of the interference from overlying softtissues (Fig. 2).

Peripheral Skeletal BMD (Forearm Bones)Unlike other densitometry methods, the DXA results of bothcentral and peripheral skeletal BMD can be evaluated withthe WHO criteria for the diagnosis of osteoporosis and fol-low-up studies. DXA can measure the BMD of forearm,which is significant in the evaluation of hyperparathyroidismor in obese patients who are heavier than the table limit of thedevices (Fig. 3).

Figure 1 Diagram showing principles of DXA technology. Reprintedwith permission from the International Society for Clinical Densi-tometry.

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Dual-Energy X-ray Absorptiometry (DXA)

•  Collimated beams through soft tissue+bone à detector on opposite side •  Beam intensity on the detector is inversely related to

density of the body parts.

•  Image on the monitor screen.

•  BMD results: g/cm2 PSO 2013

Osteoporose = Porøs knogle

•  Osteoporose: Systemisk skelet sygdom (hyppigste metaboliske knoglelidelse) •  lav knogle masse • mikroarkitekturel ødelæggelse af knoglevæv • øget knogle skørhed og følsomhed for fraktur uden traume

Knogle-brudstyrke:

•  80 % BMC •  20 % elasticitet (grundsubstans + geometri)

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Bone Mineral Mass – Bone Mineral Content (BMC)

•  Plain X-ray •  RA

radiographic absorptiometry

•  DPA dual energy photon absorptiometry

•  DXA (2D) - 1987

•  QCT (3D) quantitative CT

•  QUS quantitative ultrasound

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Bone Mineral Mass - Bone Mineral Density

•  DXA creates a planar (2 dimensional) image – combination of low+high energy attenuation

•  BMC (bone mineral content) – hydroxyapatite – Ca10(PO4)6(OH)2

•  BMD (bone mineral density) §  BMC – g §  vBMD (volume) – g / cm3

§  BA (bone area; projected area onto the image plane) – cm2

§  aBMD (areal) – g / cm2

•  aBMD = BMC / BA – g / cm2

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Bone Mineral Mass Image

X-ray

2-D

3-D

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Bone Densitometry

I  =  I0  x  e-­‐μt  I:  intensity  after  absorber  I0  :  intensity  before  absorber  μ:  linear  attenuation  coeff.  (cm-­‐1)  t:  absorber  thickness  (cm)  

•  µ decreases with increasing X-ray energy •  µ increases with increasing tissue density •  µ increases with atomic number

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Bone Densitometry

I  =  I0  x  e-­‐μt  μt  x  ρ/ρ  =  (μ/ρ)  x  t  x ρ  =  MAC  x  σ      I  =  I0  x  e-­‐MAC  σ        ρ  :  density  (g/cm3)    

   μ/ρ:  mass  attenuation  coefAicient  (MAC)  (cm2  /  g)      txρ  =  σ  :  areal  mass  density  (g/cm2)    

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Bone Densitometry - MAC

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Basic Physics of Nuclear Medicine/Dual-Energy Absorptiometry: Wikis http://www.thefullwiki.org/Basic_Physics_of_Nuclear_Medicine/Dual-Energy_Absorptiometry

Bone Densitometry – MAC

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DXA – BMD – Two body compartments

X-ray

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DXA Absorptiometry

38 KeV + 70 KeV

IH0 ¨¨¨¨¨¨¨¨¨ IH

IL0 ¨¨¨¨¨¨¨¨¨ IL

Measuring • Low energy – L • High energy – H

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DXA Absorptiometry

Bone-Mineral-Density (BMD) = (g/cm2)

•  Low energy – L •  High energy – H •  Soft – S •  Bone – b

M A C

M A C

M A C

M A C

M A C

M A C

M A C

M A C

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DXA Absorptiometry – Two compartments

Bone Soft tissue

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DXA – Scanner

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DXA - Scanner

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Two X ray energies: 1.  Voltage switching (Hologic) – between low/high voltage 2.  K edge filtering (GE, Norland) – constant tube voltage à filter à low+high voltage

Detector

Bone Densitometry – X ray tube

Table Collimation Cerium Filter Lead barrel Fixed anode tube 76 kVp

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DXA-scanner – Pencil- and Fan- Beam

Pencil Fan Detectors 1 (2-3 mm / pixel) > 10

Scan time Hip/Spine 3-5 min 30 sec Whole body 20 min 3 min

Advantages • Higher image resolution • No magnification • Low pt.-dose

• Short examination time

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DXA-praktisk: metal, lejring, lift m.m.

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•  Optimal skeletal site for OP is not well defined - bone mineral losses do not progress at same rate at different body parts.

•  Hip BMD for the evaluation of hip fracture risk Spine BMD for the evaluation of spine fracture risk.

•  The spine has the most trabecular content à best represents bone metabolism à vertebral bodies are better for monitoring responses to treatment than other skeletal sites.

per cubic centimeter rather than in grams per square centi-meter, as for DXA. Recently, peripheral DXA was also devel-oped for the scanning of peripheral skeletal sites, such asfinger, calcaneus, and forearm bones. These scanners are lessexpensive than central DXA devices and have the advantageof being small and portable. However, peripheral DXA is notyet fully established as a method to monitor treatment re-sponses for lack of reference data to compare. PeripheralQCT has also been used for the study of BMD with children,adolescents, and adults, but it similarly suffers from lack ofreference data for comparison.

Indications for BMD TestingThe following conditions are commonly mentioned as clini-cal indications for bone density testing with adults:

1. all women age 65 and older;2. all men age 70 and older;3. adults with a fragility fracture;

4. adults with a disease or condition associated with lowbone density;

5. adults taking medication associated with low bone den-sity;

6. anyone being treated for low bone density to monitortreatment effect;

7. anyone not receiving therapy, in whom evidence ofbone loss would lead to treatment; and

8. women discontinuing osteoporosis treatment.

Interpretations of BMD StudyManufacturers of BMD devices usually provide built-in facil-ity to compare the BMD result of a patient with the BMD dataof the young normal population (T-score) or with the BMDdata of an age-matched control group (Z-score). These com-parisons are expressed as units of standard deviation from themean or as percentiles of the mean of the young normalpopulation.

Figure 3 An 85-year-old woman with a BMD test with lumbar spine T-score of !1.3, total hip T-score of !1.8,femoral neck T-score of !2.0, total left forearm BMD T-score of !3.9, distal 1/3 forearm T-score of !4.3, becauseof degenerative changes in spine and hip. Diagnosis of osteoporosis was made only from the forearm BMDmeasurement. The patient’s vitamin D and parathyroid hormone levels were normal.

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Bone Densitometry - DXA

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DXA-scanning – Images – ROIs

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48-w

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DXA – T-, Z-score

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BMD - T-Score

•  T-score (for given BMD-værdi) = antal SD fra gennemsnits BMD-værdi hos ung voksen af samme køn (peak bone mass)

7D A N S K K N O G L E M E D I C I N S K S E L S K A B

høj alder, tidligere lavenergifraktur, abnorm tidlig menopause (� 45 år), rygning, alkoholoverforbrug og øget faldtendens [17-22].

Dual X-ray Absorptiometry (DXA)-scanning og røntgen af columna thoracolumbalis regnes for guldstandarder ved undersøgelse for osteoporose. Blodprøver anvendes differen-tialdiagnostisk mhp. udredning af sekundære årsager til osteo-porose (Afsnit 3.1).

5.1. Osteodensitometri (DXA-scanning)Ved en DXA-scanning måles, i hvor stort omfang røntgen-stråler afsvækkes under deres passage gennem knoglevævet, hvorved knoglens mineraltæthed (Bone Mineral Density, gram/cm2 BMD), kan estimeres.

T-scoreMåleresultatet anføres som en T-score, der angiver, hvor mange standarddeviationsenheder (SD) BMD-målingen afvi-ger fra middelværdien hos yngre normalpersoner (peak bone mass) af samme køn.

(BMDaktuel måling – BMDpeak bone mass)T-score = SDBMD

I henhold til WHO’s definition er en T-score d -2,5 diagnostisk for osteoporose hos postmenopausale kvinder. En tilsvarende tærskelværdi kan anvendes for mænd ældre end 50 år (Tabel 2).

Valg af målestedI klinisk sammenhæng anbefales det at anvende BMD-målin-ger i columna lumbalis og proksimale femur til diagnostik af osteoporose og til kontrol af behandlingseffekt.

– I columna beregnes T-score ud fra det gennemsnitlige BMD i lændehvirvlerne.

– I proksimale femur anbefales det at T-score beregnes ud fra BMD-målinger i områderne »total hip« eller alternativt »femoral neck«.

T-score som prædiktor for frakturrisikoBMD er en væsentlig determinant for knoglernes brudstyrke. For hver gang BMD mindskes med 1 SD (sv.t. 1 T-score), øges risikoen for fraktur med en faktor 2,3-2,6 på det sted, hvor scanningen er udført (dvs. i ryg eller hofteregionen) og med ca. en faktor 1,5 på andre steder i skelettet [23].

5. Undersøgelsesmetoder

Tabel 1. Risikofaktorer for fraktur. Hvis der tillige med én eller flere risikofaktorer foreligger en T-score d -2,5, anbefales det, at der iværksættes behandling med antiresorptive lægemidler.

– Arvelig disposition i lige linje for osteoporose – Alder over 80 år– Kvinder med lav kropsvægt (BMI < 19 kg/m2)– Tidligere lavenergifraktur– Osteogenesis imperfecta– Abnormt tidlig menopause (< 45 år)– Systemisk glukokortikoidbehandling (se Afsnit 11)– Rygning– Stort alkoholforbrug– Ældre med øget risiko for fraktur på grund af faldtendens– Sygdomme associeret med osteoporose*, herunder: – Anorexia nervosa – Malabsorption (herunder tidl. gastrektomi) – Primær hyperparathyreoidisme – Hyperthyreoidisme – Organtransplantation – Kronisk nyreinsufficiens – Langvarig immobilisation – Mb. Cushing – Mastocytose – Rheumatoid artrit – Myelomatose – Mb. Bechterew – Behandling med aromatasehæmmere

Yderligere forhold som kan begrunde iværksættelse af behandlingDer kan opnås enkelttilskud til antiresorptiv behandling ved T-score < -4 (selvom der ikke foreligger andre risikofaktorer)

*) En lang række andre sygdomme er associeret med en øget risiko for at udvikle osteoporose og pådrage sig fraktur – en oversigt over disse sygdomme kan ses på selskabets hjemmeside (www.dkms.dk) . Det anbefales, at behandlende læge vurde-rer, om patienter med sådan sygdomme bør udredes med en DXA-scanning, og om der efter en konkret risikovurdering evt. skal iværksættes antiresorptiv behandling. I så fald anbefales det at forsøge at opnå enkelttilskud til behandlingen via en kon-kret begrundet ansøgning til Lægemiddelstyrelsen.

Tabel 2. Tolkning af T-score i ryg eller hofte baseret på måling af BMD ved DXA-scanning.

T-score > -1 NormalT-score mellem -1 og -2,5 OsteopeniT-score d -2,5 Osteoporose*

*) Bemærk at én patient med lavenergifraktur i ryg eller proksimale femur per defi-nition har osteoporose uanset resultatet af DXA-scanningen (jf. Afsnit 1).

0,7 0,8 0,9 1,0 1,1 1,2 1,3 g/cm2

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BMD - T-Score - Ostoporosis

0,7 0,8 0,9 1,0 1,1 1,2 1,3 g/cm2

4. history of corticosteroid use (5 mg or more for 3months or more);

5. parental history of hip fracture;6. rheumatoid arthritis;7. Secondary osteoporosis (eg, type 1 diabetes, osteogen-

esis imperfecta in adults, longstanding hyperthyroid-ism, hypogonadism, premature menopause, chronicmalabsorption, chronic liver disease and hyperparathy-roidism);

8. current smoker and heavy alcohol use; and9. body mass index.

By incorporating these 9 risk factors, the FRAX improves thechances of early detection and intervention of osteoporosis,even when the BMD values are not in the range of osteopo-rosis by the WHO definition. The software estimates the 10-year probability of hip fracture as well as the 10-year proba-bility of major osteoporotic fracture (vertebral, forearm, hip,and shoulder). The NOF recommends initiating treatment ifthe 10-year hip fracture probability computed by the FRAX is3% or greater or if the 10 year major osteoporosis-relatedfracture probability is 20% or greater.

There, however, is no hard-and-fast rule for the interven-tion threshold from the cost-benefit viewpoint or from theeconomic perspective, ie, in the United States, treatment isconsidered cost-effective when the 10-year risk probability ofa hip fracture is 3% or greater, whereas in the United King-dom and Sweden, for instance, treatment is considered cost-effective when the 10-year risk probability of hip fracture is4% or greater.39-41

Recommendationsfor Bone Health CareThe current consensus is that central DXA bone densitometryis the standard for assessing fracture risk and diagnosingosteoporosis. In March 2008, the NOF released an update tothe 1999 NOF published guidelines, which included the fol-lowing recommendations: (1) counseling on osteoporosisand related fracture risk; (2) checking for secondary causes;(3) advising dietary intake of adequate amounts of calcium

(at least 1200 mg per d, including supplements) and vitaminD (800-1000 IU per d for individuals at the risk of insuffi-ciency); (4) recommending regular weight-bearing activityand muscle-strengthening exercise to reduce the risk of fallsand fractures; (5) advising avoidance of tobacco smoking andexcessive alcohol intake; (6) recommending BMD testing forwomen aged 65 years and older and men aged 70 years andolder; (7) recommending BMD testing for postmenopausalwomen and men aged 50-70 years old with high risk profiles;(8) recommending BMD testing to patients who have alreadysuffered a fracture to determine the degree of disease severity;(9) initiating therapy for patients with hip or vertebral frac-tures; (10) initiating therapy for patients with BMD T-scoresless than –2.5 at the femoral neck, total hip, or spine by DXA;(11) initiating treatment for postmenopausal women andmen aged 50 and older with low bone mass (T-score -1 to–2.5 for osteopenia) at the femoral neck, total hip, or spine if10-year hip fracture probability is 3% or greater or if 10-yearmajor osteoporosis-related fracture probability is 20% orgreater (these selection criteria are based on the WHO abso-lute fracture risk model, the FRAX, adapted for the U.S. pop-ulation; http://www.shef.ac.uk/FRAX); (12) listing of currentFood and Drug Administration-approved pharmacologic op-tions for osteoporosis prevention, such as bisphosphonates(alendronate, ibandronate, risedronate and zoledronate), cal-citonin, estrogens, and/or other hormone therapy, raloxifene,and parathyroid hormone 1-34; and (13) recommendingBMD testing at DXA centers that meet accepted quality con-trol standard. The guidelines also recommend the patients onpharmacotherapy to take BMD test every 2 years after initialtherapy and the patients on steroid therapy to take the testevery 6 months.

The process of bone loss is silent until it becomes apparentwith a bone fracture. It is, therefore, important to diagnoselow bone mass and osteoporosis as early as possible andinitiate fracture prevention therapy. DXA offers an accuratemethod of measuring both central and peripheral skeletalBMD via the use of very low doses of radiation to the patients.DXA is currently the most favored method of detecting lowbone mass, diagnosing osteoporosis, and monitoring treat-ment responses, because of cost-effectiveness, precision andlow radiation burden.

References1. Melton LJ, 3rd, Wahner HW: Defining osteoporosis. Calcif Tissue Int

45:263-264, 19892. Frost HM: The pathomechanics of osteoporosis. Clin Orthop 200:198-

225, 19853. Consensus Development Conference: Diagnosis, prophylaxis, and

treatment of osteoporosis. Am J Med 94:646-650, 19934. Cummings SR, Kelsey JL, Nevitt MC, et al: Epidemiology of osteopo-

rosis and osteoporotic fractures. Epidemiol Rev 7:178-208, 19855. Kanis JA, Delmas P, Burckhart P, et al: Guidelines for diagnosis and

management of osteoporosis. On behalf of the European Foundationfor Osteoporosis and Bone Disease. Osteoporos Int 7:390-406, 1997

6. Assessment of fracture risk and its application to screening for post-menopausal osteoporosis. Report of a WHO Study Group. WorldHealth Organ Tech Rep Ser 843:1-129, 1994

7. van Staa TP, Dennison EM, Leufkens HG, et al: Epidemiology of frac-tures in England and Wales. Bone 29:517-522, 2001

Figure 6 Relationship between fracture risk and T-score. Reprintedwith permission from the International Society for Clinical Densi-tometry.

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BMD – T/Z-score

70-woman spine

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52-m

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DXA – Dosimetry

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DXA – Dosimetry – Patients

IAEA_DEXA_Pub1479_2010

0.003 mSv

10 mSv

Effective dose (mkrSv)

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DXA – Dosimetry - Patients

mkrSv Tynd Std Tyk

AP Spine 0,18 0,7 1,4

Femur 0,17 0,68 1,35

APS+DualFem 0,54 2,06 4,10

Underarm 0,01

Total body 0,5 0,5 1

Ge Lunar Prodigy Pro Advance

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DXA – Accuracy and Precision

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Bone mineral mass, consisting of hydroxyapatite - mineral component of bone that is left after a bone is defleshed, lipids extracted and ashed.

1.  DXA cannot tell the difference between thick low density and thin high density bone

2.  Surrounding soft tissue composition (head, hands, feet upper torso) – The fat error

3.  Artefacts (degenerative, aortic, fracture) à 4.  ROI placement 5.  Lack of standardization (e.g. Hologic vs GE)

• BMD 10%

DXA – Accuracy - BMC

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•  Quality control •  Phantom (spine) •  Calibration

•  Standardized BMD (sBMD)

DXA – Accuracy - BMC

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Repeated BMD measurements – risk factors, treatment indication, treatment control

Lack of reproducibility of BMD determinations is due to variation in operator(s) handling, a lack of consistency in data analysis, and the inherent precision error of the technique.

Common operator errors include: 1)  poor patient positioning 2)  inconsistent selection of vertebral levels 3)  poor placement of disk markers for the lumbar spine 4)  improper hip rotation 5)  inconsistent determination of ROIs of the hip

Intra patient variation to be determined: Facility / Scanner / Personel (training)

DXA – Precision - BMD

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Precision testing •  Rate of change in BMD is slow, 0.5-2% per year.

Steroid à10-20%. •  Precision SD, CV à Least Significant Change (LSC)

•  Test: Each operator individually à Facility precision

•  2 measurements in each of 30 patients / (3 measurements in each of 15 patients)

•  Exlude: pregnant, < 21y, radiation workers •  Hip / Spine - total •  Time interval: (< 2-4 wks) same day •  The patient taken off the examination table after initial

BMD à repositioned for subsequent scan

Quality control - Not research

DXA – Precision – BMD – Assessment

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•  LSC = 2.77 x CV% (or SD-g/cm2)

•  Monitoring Time Interval: MTI = LSC (g/cm2) / expected rate of change (g/cm2/y)

DXA – Precision – LSC – MTI

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DXA – Precision – BMD – ISCD.org Calculator

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DXA – Various

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1.  Degenerative bone disease 2.  Aortic calcifications 3.  Fracture 4.  Previous bone surgery 5.  Anomalies 6.  Obesity 7.  Metal (piercing, buttons, arthroplasty, pacemaker) 8.  Catheters 9.  Tablets 10. Imaging contrast 11. Radioactive isotopes

DXA – Artefacts

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•  Sala A. J Clin Densitom 2006, Effect of diagnostic radioisotopes and radiographic contrast media on measurements of lumbar spine bone mineral density and body composition by DXA. Hologic. Table 10.

•  Fosbøl M,.J Clin Densitom 2012, The Effect of 99mTc on DXA Measurement of Body Composition and BMD. GE Lunar. Nukl.med.: 2d pause (Tc-99m). Check dose rate limit (1 m): BMD: <0,77 mkrSv/h; BC: < 0,21 mkrSv/h.

DXA – Radiographic Contrast - Radioisotopes

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Obs!

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Obs!

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Vertebral Fracture Assessment - VFA

In contrast to the WHO definition, clinicians observed thatthere were incidents of osteoporosis-related fractures, evenwhen the T-score is greater than !2.5 (for example, theT-score is !2.0). The reason was perhaps that there are othersignificant factors to take into account for a more accurateassessment of bone fracture risk. For instance, patients ofdifferent age, despite the same BMD values, may have differ-ent chances of incurring bone fracture because of differencesin brittleness, quality, and architectural stability of bones.

The clinical observations, perhaps, led the WHO and theNOF to adopt the FRAX, which estimates the probability ofpatients’ fracture risks, incorporating femoral neck BMD and9 clinical fracture risk factors. The factors, according to theWHO, are as follows:

1. age;2. sex;3. previous fragility fracture after age 50;

Figure 5 (A) Illustrations of densitometric VFA. The left-most picture without C-arm shows the patient changingposition so the technologist can obtain a lateral view. The middle picture shows the DXA machine equipped withC-arm. The right-most picture shows spinal compression fracture detected by DXA method. Reprinted with permissionfrom the International Society for Clinical Densitometry. (B) Illustrations demonstrating various types of spinalfractures. (Reprinted with permission from Lenchik et al.31) (Color version of figure is available online.)

226 K.J. Chun

In contrast to the WHO definition, clinicians observed thatthere were incidents of osteoporosis-related fractures, evenwhen the T-score is greater than !2.5 (for example, theT-score is !2.0). The reason was perhaps that there are othersignificant factors to take into account for a more accurateassessment of bone fracture risk. For instance, patients ofdifferent age, despite the same BMD values, may have differ-ent chances of incurring bone fracture because of differencesin brittleness, quality, and architectural stability of bones.

The clinical observations, perhaps, led the WHO and theNOF to adopt the FRAX, which estimates the probability ofpatients’ fracture risks, incorporating femoral neck BMD and9 clinical fracture risk factors. The factors, according to theWHO, are as follows:

1. age;2. sex;3. previous fragility fracture after age 50;

Figure 5 (A) Illustrations of densitometric VFA. The left-most picture without C-arm shows the patient changingposition so the technologist can obtain a lateral view. The middle picture shows the DXA machine equipped withC-arm. The right-most picture shows spinal compression fracture detected by DXA method. Reprinted with permissionfrom the International Society for Clinical Densitometry. (B) Illustrations demonstrating various types of spinalfractures. (Reprinted with permission from Lenchik et al.31) (Color version of figure is available online.)

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DXA – TBS Trabecular Bone Scan

http://www.medimaps.fr/ definition-tbs

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SLUT - Tak