I-MRI yitekhnoloji ye-imaging engeyiyo invasive evelisa imifanekiso emithathu eneenkcukacha ze-anatomical. Ihlala isetyenziselwa ukufumanisa isifo, ukuxilongwa, kunye nokujonga unyango. Isekelwe kwi-teknoloji eyinkimbinkimbi evuyisayo kwaye ibone utshintsho kwicala le-axis ejikelezayo yeeproton ezifumaneka emanzini okwenza izicubu eziphilayo.
Isebenza njani iMRI?
Ii-MRIs zisebenzisa iimagnethi ezinamandla ezivelisa indawo eyomeleleyo yamagnetic enyanzela iiprotons emzimbeni ukuba zihambelane naloo ntsimi. Xa i-radiofrequency current ityhalwa kwisigulana, iiprotons ziyavuselelwa, kwaye zijikelezwe ngaphandle kokulingana, zitsala nzima ngokuchasene nokutsalwa kwemagnethi. Xa i-radiofrequency field icinyiwe, ii-sensors ze-MRI ziyakwazi ukubona amandla akhutshiweyo njengoko iiprotoni zihambelana nomhlaba wemagnethi. Ixesha elithathayo ukuba iiprotons zilungelelanise kunye nomhlaba wamagnetic, kunye nobungakanani bamandla akhululiwe, utshintsho ngokuxhomekeka kokusingqongileyo kunye nobume bekhemikhali yeemolekyuli. Oogqirha bayakwazi ukuxelela umahluko phakathi kweentlobo ezahlukeneyo zezicubu ezisekelwe kwezi zixhobo zamagnetic.
Ukufumana umfanekiso weMRI, isigulana sifakwa ngaphakathi kwemagnethi enkulu kwaye kufuneka sihlale sithe cwaka ngexesha lenkqubo yokucinga ukuze singawufiphalisi umfanekiso. Ii-agent zokuchasana (ezihlala ziqulethe i-element Gadolinium) zinokunikwa isigulane nge-intravenously ngaphambi okanye ngexesha le-MRI ukwandisa isantya apho iiproton zihambelana ne-magnetic field. Ukukhawuleza kweeprotoni zilungelelaniswa, umfanekiso ukhanya ngakumbi.
Zeziphi iintlobo zemagnethi ezisetyenziswa ziiMRIs?
Iinkqubo zeMRI zisebenzisa iintlobo ezintathu ezisisiseko zemagnethi:
-Iimagnethi ezixhathisayo zenziwe ngeekhoyili ezininzi zocingo ezibhijelwe kwicylinder apho kudlula umsinga wombane. Oku kuvelisa umhlaba wemagnethi. Xa umbane uvaliwe, imagnethi iyafa. Ezi magnethi zinexabiso eliphantsi ukwenza kunemagnethi egqithisayo (jonga ngezantsi), kodwa kufuneka izixa ezikhulu zombane ukuze zisebenze ngenxa yokuxhathisa kwendalo kocingo. Umbane unokubiza kakhulu xa kufuneka iimagnethi eziphezulu zamandla.
-A umazibuthe osisigxina kanye ukuba -- esisigxina. Intsimi yamagnetic ihlala ikhona kwaye ihlala inamandla apheleleyo. Ngoko ke, akubizi nto ukugcina intsimi. Ingxaki enkulu kukuba ezi magnethi zinzima kakhulu: ngamanye amaxesha zininzi, zininzi iitoni. Amanye amasimi awomeleleyo angafuna iimagnethi ezinzima kangangokuba kuya kuba nzima ukuwenza.
Iimagnethi zeSuperconducting zezona zisetyenziswa kakhulu kwiiMRIs. Iimagnethi ezinkulu zifana nje neemagnethi ezixhathisayo - iikhoyili zocingo ezinombane odlulayo zidala umhlaba wemagnethi. Umahluko obalulekileyo kukuba kwimagnethi ye-superconducting ucingo luhlala luhlamba kwi-helium yolwelo (kwiqondo elibandayo le-452.4 degrees ngaphantsi kwe-zero). Le ngqele ephantse ingakholelekiyo yehlisa ukuxhathisa kocingo ukuya ku-zero, inciphisa ngokumangalisayo imfuneko yombane kwisixokelelwano kwaye iyenza ingabizi kakhulu ukusebenza.
Iintlobo zemagnethi
Uyilo lwe-MRI lugqitywa luhlobo kunye nefomathi yemagnethi ephambili, oko kukuthi, i-MRI evaliweyo, i-tunnel-type okanye i-MRI evulekileyo.
Ezona magnethi zisetyenziswa ngokuqhelekileyo zizizibuthe ze-superconducting. Ezi ziquka ikhoyili eye yenziwa i-superconductive ngokupholisa ulwelo lwe-helium. Zivelisa amandla anamandla, alinganayo, kodwa ayabiza kwaye afuna ukugcinwa rhoqo (oko kukuthi ukukhupha itanki ye-helium).
Kwimeko yokulahlekelwa kwe-superconductivity, amandla ombane achithwa njengobushushu. Oku kufudumeza kubangela ukubila ngokukhawuleza kolwelo lweHelium oluguqulwa lube ngumthamo ophezulu kakhulu wegesi yeHelium (ukucima). Ukuze kuthintelwe ukutshisa kwe-thermal kunye ne-asphyxia, i-superconducting magnets ineenkqubo zokukhusela: iipayipi zokukhupha igesi, ukubeka iliso kwipesenti ye-oksijini kunye nobushushu ngaphakathi kwegumbi le-MRI, ukuvula umnyango ngaphandle (uxinzelelo olungaphezulu ngaphakathi kwegumbi).
Iimagnethi zeSuperconducting zisebenza ngokuqhubekayo. Ukucutha imiqobo yokufakela umazibuthe, isixhobo sinenkqubo yokukhusela enokuba yi-passive (intsimbi) okanye esebenzayo (ikhoyili ye-superconducting yangaphandle enentsimi echaseneyo nekhoyili yangaphakathi) ukunciphisa amandla entsimi alahlekileyo.
I-MRI yendawo ephantsi ikwasebenzisa:
-Ii-electromagnets ezixhathisayo, ezinexabiso eliphantsi kwaye kulula ukuzigcina kunemagnethi ephezulu. Ezi azinamandla kangako, zisebenzisa amandla amaninzi kwaye zifuna inkqubo yokupholisa.
-Imagnethi ezisisigxina, zefomathi ezahlukeneyo, ezenziwe ngezinto zetsimbi ze-ferromagnetic. Nangona zinenzuzo yokungabizi kwaye kulula ukuyigcina, zinzima kakhulu kwaye zibuthathaka ngamandla.
Ukufumana eyona ntsimi yamagnetic i-homogeneous, umazibuthe kufuneka ucocwe kakuhle ("shimming"), nokuba ingashukumi, usebenzisa amaqhekeza esinyithi ashukumayo, okanye ngokusebenzayo, usebenzisa iikhoyili ezincinci zombane ezisasazwe kwimagnethi.
Iimpawu zemagnethi ephambili
Iimpawu eziphambili zemagnethi zezi:
-Uhlobo (i-superconducting okanye i-electromagnetic resistive, imagnethi esisigxina)
-Amandla entsimi eveliswayo, alinganiswe kwiTesla (T). Kwinkqubo yangoku yeklinikhi, oku kuyahluka ukusuka kwi-0.2 ukuya kwi-3.0 T. Kuphando, iimagnethi ezinamandla ze-7 T okanye i-11 T nangaphezulu zisetyenziswa.
-Homogeneity
