雙光子吸收法

thedifferen tsarebasedon athreecompartmen

概述

雙光子吸收法(DPA)採用能發射兩種不同能量光子的核素作放射源，利用高能和低能射線通過被測部位的不同衰減分布來計算骨的能量衰減分布，故可用來測量一些軟組織變異大的部位如脊椎、髖等全身部位的骨礦含量，從而消除軟組織及脊髓對測量結果的影響。

英文名

dualX-rayenergyabsorptiometry

equipmentrequired:

DEXAmachine,whichdifferentiatesbodyweightintothecomponentsofleansofttissue,fatsofttissueandbone,basedonthedifferentialattenuationbytissuesoftwolevelsofx-rays.

description/procedure:

Thepersonlaysonthewholebodyscanner,withthex-raysourcesmountedbeneathatableandadetectoroverhead.Thepersonisscannedwithphotonsthataregeneratedbytwolow-dosex-raysatdifferentenergylevels.Thebody'sabsorptionofthephotonsatthetwolevelsismeasured.Theratioscanbethenusedtopredicttotalbodyfat,fat-freemass,andtotalbodybonemineral.Theprocedurecantakeabout10-20minutes.

advantages:

Thismethodisprecise,accurate,andreliable.DEXAmeasurementsarebasedonathreecompartmentalmodel(totalbodymineral(frombones),fat-freesoft(lean)mass,andfattissuemass)ratherthantwocompartmentasinmostothermethods.DEXAcanalsodistinguishregionalaswellaswholebodyparametersofbodycomposition.Assuch,itisconsideredareferencestandard,andthelatestbodycompositionresearchusesthismethod.

disadvantages:

Theequipmentisexpensive,andoftenrequirestrainedradiologypersonneltooperate.

othercomments:

Ifnotforthelimitingpriceofmeasurement,DEXAwouldbeconsideredthecriterionmethodofbodycompositionanalysis