MRI yog ib qho kev yees duab uas tsis muaj kev cuam tshuam uas tsim cov duab peb sab anatomical. Nws feem ntau yog siv rau kev kuaj kab mob, kuaj mob, thiab saib xyuas kev kho mob. Nws yog ua raws li cov cuab yeej siv thev naus laus zis uas zoo siab thiab tshawb pom qhov kev hloov pauv ntawm kev hloov ntawm cov axis ntawm cov protons pom hauv cov dej uas ua rau cov ntaub so ntswg nyob.
MRI ua haujlwm li cas?
MRIs siv cov hlau nplaum muaj zog uas tsim cov hlau nplaum muaj zog uas ua rau cov protons hauv lub cev kom haum rau qhov chaw ntawd. Thaum lub xov tooj cua zaus tam sim no yog rub tawm los ntawm tus neeg mob, cov protons tau txhawb nqa, thiab tig tawm ntawm qhov sib npaug, straining tawm tsam qhov rub ntawm cov hlau nplaum. Thaum lub chaw xov tooj cua raug kaw, MRI sensors tuaj yeem ntes lub zog tso tawm raws li cov protons rov zoo nrog cov hlau nplaum. Lub sij hawm nws yuav siv sij hawm rau cov protons realign nrog lub magnetic teb, raws li zoo raws li tus nqi ntawm lub zog tso tawm, hloov nyob rau hauv raws li ib puag ncig thiab cov tshuaj ntawm cov molecules. Cov kws kho mob tuaj yeem qhia qhov txawv ntawm ntau hom ntaub so ntswg raws li cov khoom sib nqus no.
Txhawm rau kom tau txais daim duab MRI, tus neeg mob tau muab tso rau hauv cov hlau nplaum loj thiab yuav tsum nyob twj ywm heev thaum lub sijhawm ua duab kom tsis txhob plam daim duab. Cov neeg sawv cev sib txawv (feem ntau muaj cov keeb gadolinium) yuav tau muab rau tus neeg mob uas muaj kev cuam tshuam ua ntej lossis thaum lub sijhawm MRI ua ntej ntawm cov protons uas muaj kev sib nqus. Qhov ceev ntawm cov protons realign, lub brighter duab.
Hom hlau nplaum twg siv MRIs?
MRI systems siv peb yam yooj yim ntawm cov hlau nplaum:
-Resistive hlau nplaum yog tsim los ntawm ntau coils ntawm hlau qhwv nyob ib ncig ntawm lub tog raj kheej los ntawm cov hluav taws xob tam sim no. Qhov no generates magnetic teb. Thaum hluav taws xob raug kaw, cov hlau nplaum tuag. Cov hlau nplaum no yog tus nqi qis dua los ua cov hlau nplaum superconducting (saib hauv qab), tab sis xav tau cov hluav taws xob loj heev los ua haujlwm vim yog lub ntuj tsis kam ntawm cov hlau. Cov hluav taws xob tuaj yeem tau txais kim thaum xav tau cov hlau nplaum hluav taws xob ntau dua.
-Ib daim hlau nplaum ruaj khov yog qhov ntawd - ruaj khov. Lub magnetic teb yeej ib txwm muaj thiab ib txwm muaj zog tag nrho. Yog li ntawd, nws tsis raug nqi dab tsi los tswj lub teb. Ib qho teeb meem loj yog tias cov hlau nplaum no hnyav heev: qee zaum ntau, ntau tons. Qee qhov chaw muaj zog yuav xav tau cov hlau nplaum hnyav li ntawd lawv yuav nyuaj rau kev tsim kho.
-Superconducting hlau nplaum yog nyob deb ntawm feem ntau siv hauv MRIs. Superconducting hlau nplaum yog me ntsis zoo ib yam li cov hlau nplaum resistive - coils ntawm hlau nrog ib tug dhau hluav taws xob tam sim no tsim lub magnetic teb. Qhov sib txawv tseem ceeb yog tias nyob rau hauv cov hlau nplaum superconducting cov hlau txuas ntxiv mus da dej hauv cov kua helium (ntawm qhov txias 452.4 degrees hauv qab xoom). Qhov no yuav luag tsis xav txog qhov txias txias ua rau cov xaim tsis kam mus rau xoom, txo qis hluav taws xob xav tau rau lub kaw lus thiab ua rau nws ua haujlwm ntau dua.
Hom hlau nplaum
Kev tsim ntawm MRI yog qhov tseem ceeb txiav txim siab los ntawm hom thiab hom ntawm cov hlau nplaum tseem ceeb, piv txwv li kaw, qhov-hom MRI lossis qhib MRI.
Cov hlau nplaum feem ntau siv yog superconducting electromagnets. Cov no muaj xws li cov kauj uas tau ua superconductive los ntawm helium kua txias. Lawv tsim muaj zog, homogeneous sib nqus teb, tab sis yog kim thiab yuav tsum tau tu tsis tu ncua (xws li topping lub helium tank).
Thaum poob ntawm superconductivity, hluav taws xob hluav taws xob yog dissipated li cua sov. Qhov cua sov no ua rau lub qhov kub kub sai sai ntawm cov kua Helium uas tau hloov mus rau hauv qhov ntim siab heev ntawm cov pa roj Helium (quench). Txhawm rau tiv thaiv kev kub nyhiab thiab asphyxia, cov hlau nplaum superconducting muaj kev nyab xeeb: cov kav dej tawm hauv cov pa, saib xyuas cov feem pua ntawm cov pa oxygen thiab qhov kub thiab txias hauv chav MRI, qhov rooj qhib tawm sab nraud (siab tshaj hauv chav).
Superconducting hlau nplaum ua haujlwm tsis tu ncua. Txhawm rau txwv kev txwv kev sib nqus hlau nplaum, cov cuab yeej muaj qhov thaiv kev tiv thaiv uas yog passive (hlau) lossis ua haujlwm (ib txheej txheej superconducting coil uas nws teb tawm tsam ntawm sab hauv coil) kom txo tau qhov tsis muaj zog.
Low field MRI kuj tseem siv tau:
-Resistive electromagnets, uas yog pheej yig dua thiab yooj yim los tswj dua superconducting hlau nplaum. Cov no tsis tshua muaj zog, siv zog ntau dua thiab xav tau lub tshuab cua txias.
-Cov hlau nplaum tas mus li, ntawm ntau hom, muaj li ntawm ferromagnetic metallic Cheebtsam. Txawm hais tias lawv muaj qhov zoo ntawm kev pheej yig thiab yooj yim los tswj, lawv hnyav heev thiab tsis muaj zog ntawm kev siv zog.
Txhawm rau kom tau txais qhov sib nqus sib nqus zoo tshaj plaws, cov hlau nplaum yuav tsum tau kho kom zoo ("shimming"), xws li passively, siv cov khoom txav ntawm cov hlau, los yog nquag, siv cov khoom siv hluav taws xob me me hauv cov hlau nplaum.
Cov yam ntxwv ntawm lub ntsiab hlau nplaum
Cov yam ntxwv tseem ceeb ntawm cov hlau nplaum yog:
- Hom (superconducting lossis resistive electromagnets, cov hlau nplaum ruaj khov)
-Lub zog ntawm daim teb tsim, ntsuas hauv Tesla (T). Hauv kev xyaum kho mob tam sim no, qhov no txawv ntawm 0.2 txog 3.0 T. Hauv kev tshawb fawb, cov hlau nplaum uas muaj zog ntawm 7 T lossis 11 T thiab tshaj yog siv.
- Homogeneity
