MRI ndi ukadaulo wojambula wosasokoneza womwe umapanga zithunzi zatsatanetsatane zamitundu itatu. Nthawi zambiri amagwiritsidwa ntchito pozindikira matenda, kuzindikira, komanso kuyang'anira chithandizo. Zimachokera ku teknoloji yamakono yomwe imakondweretsa ndikuwona kusintha kwa kayendetsedwe ka kayendedwe ka ma protoni omwe amapezeka m'madzi omwe amapanga minyewa yamoyo.
Kodi MRI imagwira ntchito bwanji?
Ma MRIs amagwiritsa ntchito maginito amphamvu omwe amapanga mphamvu yamaginito yomwe imakakamiza ma protoni m'thupi kuti agwirizane ndi gawolo. Pamene mphamvu ya radiofrequency idutsa mwa wodwalayo, ma protoni amakokedwa, ndikutuluka molingana, ndikukankhira kukoka kwa maginito. Gawo la radiofrequency likazimitsidwa, masensa a MRI amatha kuzindikira mphamvu zomwe zimatulutsidwa pomwe ma protoni amalumikizana ndi maginito. Nthawi yomwe ma protoni amatenga kuti agwirizanenso ndi mphamvu ya maginito, komanso kuchuluka kwa mphamvu zomwe zimatulutsidwa, zimasintha malinga ndi chilengedwe komanso chilengedwe cha mamolekyu. Madokotala amatha kusiyanitsa pakati pa mitundu yosiyanasiyana ya minofu kutengera maginitowa.
Kuti mupeze chithunzi cha MRI, wodwala amaikidwa mkati mwa maginito akuluakulu ndipo ayenera kukhala chete panthawi yojambula kuti asasokoneze chithunzicho. Zofananira (nthawi zambiri zimakhala ndi gawo la Gadolinium) zitha kuperekedwa kwa wodwala kudzera m'mitsempha isanakwane kapena panthawi ya MRI kuti awonjezere liwiro lomwe ma protoni amayenderana ndi mphamvu ya maginito. Mapulotoni akamasinthasintha mwachangu, chithunzicho chimawala kwambiri.
Ndi maginito amtundu wanji omwe ma MRIs amagwiritsa ntchito?
Makina a MRI amagwiritsa ntchito mitundu itatu ya maginito:
-Maginito osamva amapangidwa kuchokera ku ma waya ambiri okulungidwa pa silinda yomwe magetsi amadutsamo. Izi zimapanga mphamvu ya maginito. Magetsi akatsekedwa, mphamvu ya maginito imafa. Maginitowa ndi otsika mtengo kuti apange kusiyana ndi maginito a superconducting (onani m'munsimu), koma amafunikira magetsi ambiri kuti agwire ntchito chifukwa cha kukana kwachilengedwe kwa waya. Magetsi amatha kukhala okwera mtengo ngati pakufunika maginito apamwamba.
-Maginito okhazikika ndizomwezo - zokhazikika. Mphamvu ya maginito imakhalapo nthawi zonse ndipo imakhala ndi mphamvu zonse. Choncho, kusamalira mundawu sikuwononga ndalama zambiri. Choyipa chachikulu ndichakuti maginitowa ndi olemera kwambiri: nthawi zina matani ambiri. Minda ina yolimba ingafunike maginito olemera kwambiri moti n’zovuta kupanga.
- Superconducting maginito ndi omwe amagwiritsidwa ntchito kwambiri mu MRIs. Maginito a Superconducting ndi ofanana ndi maginito olimbana ndi maginito - ma waya amagetsi odutsa amapangira mphamvu ya maginito. Kusiyanitsa kofunikira ndikuti mu maginito a superconducting waya amasambitsidwa nthawi zonse mu helium yamadzimadzi (kuzizira kwa madigiri 452.4 pansi pa ziro). Kuzizira kosayerekezekaku kumachepetsa kukana kwa waya mpaka zero, kumachepetsa kwambiri kufunikira kwa magetsi pamagetsi ndikupangitsa kuti ikhale yotsika mtengo kwambiri kuti igwire ntchito.
Mitundu ya maginito
Mapangidwe a MRI amatsimikiziridwa ndi mtundu ndi mawonekedwe a maginito akuluakulu, mwachitsanzo otsekedwa, MRI yamtundu wa ngalande kapena MRI yotseguka.
Maginito omwe amagwiritsidwa ntchito kwambiri ndi superconducting electromagnets. Izi zimakhala ndi koyilo yomwe yapangidwa kukhala superconductive ndi kuzizira kwamadzi a helium. Amapanga maginito amphamvu, osakanikirana, koma ndi okwera mtengo ndipo amafunikira kusamalidwa nthawi zonse (ndiko kukweza thanki ya helium).
Pakachitika kutayika kwa superconductivity, mphamvu yamagetsi imatayidwa ngati kutentha. Kutentha kumeneku kumayambitsa kuwira mwachangu kwamadzi amadzimadzi a Helium omwe amasandulika kukhala wokwera kwambiri wa mpweya wa Helium (kuzimitsa). Pofuna kupewa kutentha kwa kutentha ndi asphyxia, maginito a superconducting ali ndi chitetezo: mapaipi otulutsa mpweya, kuyang'anira kuchuluka kwa mpweya ndi kutentha mkati mwa chipinda cha MRI, chitseko chotsegula kunja (kupanikizika kwambiri mkati mwa chipinda).
Superconducting maginito amagwira ntchito mosalekeza. Kuti muchepetse kutsekera kwa maginito, chipangizocho chimakhala ndi njira yotchinjiriza yomwe imakhala yopanda kanthu (chitsulo) kapena yogwira ntchito (koyilo yakunja ya superconducting yomwe munda wake umatsutsana ndi koyilo yamkati) kuti muchepetse mphamvu yakumunda yosokera.
Low field MRI imagwiritsanso ntchito:
-Ma electromagnets okana, omwe ndi otsika mtengo komanso osavuta kuwasamalira kuposa maginito a superconducting. Izi ndizochepa mphamvu, zimagwiritsa ntchito mphamvu zambiri ndipo zimafuna njira yozizirira.
-Maginito osatha, amitundu yosiyanasiyana, opangidwa ndi zida zachitsulo za ferromagnetic. Ngakhale ali ndi mwayi wokhala wotchipa komanso wosavuta kusamalira, ndi olemera kwambiri komanso ofooka kwambiri.
Kuti mupeze mphamvu ya maginito yofanana kwambiri, maginito amayenera kuchunidwa bwino ("shimming"), mwina mosasamala, pogwiritsa ntchito zidutswa zachitsulo zosunthika, kapena mwachangu, pogwiritsa ntchito makoyilo ang'onoang'ono amagetsi omwe amagawidwa mkati mwa maginito.
Makhalidwe a maginito waukulu
Makhalidwe akuluakulu a maginito ndi awa:
-Mtundu (ma electromagnetic superconducting kapena resistive, maginito osatha)
-Kulimba kwa gawo lopangidwa, kuyeza mu Tesla (T). Muzochita zamakono zamakono, izi zimasiyana kuchokera ku 0.2 mpaka 3.0 T. Pofufuza, maginito okhala ndi mphamvu za 7 T kapena 11 T ndi kupitirira amagwiritsidwa ntchito.
-Homogeneity
