Ukufana kwe-MRI

Ukufana kwensimu yamagnetic (homogeneity), okwaziwa nangokuthi ukufana kwensimu yamagnetic, kubhekisela ekwazini kwensimu yamagnetic ngaphakathi komkhawulo othile wevolumu, okungukuthi, ukuthi imigqa yensimu yamagnetic endaweni yeyunithi iyafana yini. Umthamo othize lapha ngokuvamile uyisikhala esiyindilinga. Iyunithi yokufana kwensimu yamagnetic yi-ppm (ingxenye ngesigidi), okungukuthi, umehluko phakathi kwamandla ensimu aphezulu kanye namandla ensimu amancane ensimu yamagnetic endaweni ethile ehlukaniswe ngamandla ensimu ajwayelekile aphindwe ngesigidi esisodwa.

I-MRI idinga izinga eliphezulu lokufana kwensimu yamagnetic, okunquma isinqumo sendawo kanye nesilinganiso sesiginali kuya komsindo sesithombe ebangeni lokuthwebula izithombe. Ukufana okungekuhle kwensimu yamagnetic kuzokwenza isithombe sifiphale futhi siphendukezelwe. Ukufana kwensimu yamagnetic kunqunywa ukwakheka kwemagnet uqobo kanye nendawo yangaphandle. Lapho indawo yokuthwebula izithombe yemagnet inkulu, kulapho ukufana kwensimu yamagnetic kungafinyelelwa khona kuphansi. Ukuqina kwensimu yamagnetic kuyinkomba yokukala izinga lokuhamba kokuqina kwensimu yamagnetic ngokuhamba kwesikhathi. Phakathi nesikhathi sokulandelana kwezithombe, ukuzulazula kokuqina kwensimu yamagnetic kuzothinta isigaba sesignali ye-echo ephindaphindwayo elinganisiwe, okuholela ekuphazamisekeni kwesithombe kanye nokwehla kwesilinganiso sesiginali kuya komsindo. Ukuqina kwensimu yamagnetic kuhlobene eduze nohlobo lwemagnet kanye nekhwalithi yomklamo.

Izinhlinzeko zezinga lokufana kwensimu yamagnetic zihlobene nosayizi kanye nesimo sesikhala sokulinganisa esithathwe, futhi ngokuvamile zisebenzisa isikhala esiyindilinga esinobubanzi obuthile kanye nendawo ephakathi kwemagnet njengobubanzi bokulinganisa. Ngokuvamile, ukumelwa kokufana kwensimu yamagnetic kusesimweni sesikhala esithile sokulinganisa, ububanzi bokushintsha kokuqina kwensimu yamagnetic esikhaleni esinikeziwe (inani le-ppm), okungukuthi, ingxenye eyodwa kwesigidi samandla amakhulu ensimu yamagnetic (ppm) njengeyunithi yokuphambuka ukuze iveze ngokwenani, ngokuvamile le yunithi yokuphambuka ibizwa ngokuthi i-ppm, ebizwa ngokuthi ukumelwa kwenani eliphelele. Isibonelo, ukufana kwensimu yamagnetic ngaphakathi kwesilinda sonke sokuhlola ukuskena kungu-5ppm; Ukufana kwensimu yamagnetic esikhaleni sesphere esingu-40cm no-50cm esigxile nesikhungo samagnet kungu-1ppm no-2ppm, ngokulandelana. Kungabuye kuboniswe kanje: ukufana kwensimu yamagnetic esikhaleni se-cube sesentimitha ngayinye ye-cubic endaweni yesampula evivinywayo ngu-0.01ppm. Kungakhathaliseki ukuthi iyiphi indinganiso, ngaphansi kwesisekelo sokuthi usayizi wesiyingi sokulinganisa uyafana, uma inani le-ppm lincane libonisa ukuthi ukufana kwensimu yamagnetic kungcono.

Uma kukhulunywa ngedivayisi engu-1.5-tMRI, ukuguquguquka kwamandla e-magnetic field okumelwe yiyunithi eyodwa yokuphambuka (1ppm) kungu-1.5×10-6T. Ngamanye amazwi, ohlelweni lwe-1.5T, ukufana kwe-magnetic field okungu-1ppm kusho ukuthi insimu eyinhloko yamagnetic inokuguquguquka kwe-drift okungu-1.5×10-6T (0.0015mT) ngokusekelwe ngemuva kwamandla e-magnetic field angu-1.5T. Ngokusobala, emishinini ye-MRI enamandla ehlukene ensimu, ukuhlukahluka kwamandla e-magnetic field okumelwe yiyunithi ngayinye yokuphambuka noma i-ppm kuhlukile, kusukela kulo mbono, izinhlelo ze-low field zingaba nezidingo eziphansi zokufana kwe-magnetic field (bheka Ithebula 3-1). Ngalesi lungiselelo, abantu bangasebenzisa indinganiso yokufana ukuze baqhathanise kalula izinhlelo ezinamandla ensimu ahlukene, noma izinhlelo ezahlukene ezinamandla ensimu afanayo, ukuze bahlole ngokunembile ukusebenza kwe-magnet.

Ngaphambi kokulinganisa kwangempela ukufana kwensimu yamagnetic, kubalulekile ukunquma ngokunembile isikhungo samagnethi, bese uhlela ithuluzi lokulinganisa ukujula kwensimu (i-Gauss meter) probe endaweni yesikhala serediyasi ethile, bese ulinganisa ukujula kwayo kwensimu yamagnetic iphuzu ngephuzu (indlela yendiza engu-24, indlela yendiza engu-12), bese ekugcineni ucubungula idatha ukuze ubale ukujula kwensimu yamagnetic ngaphakathi kwevolumu yonke.

Ukufana kwensimu yamagnetic kuzoshintsha ngokuhambisana nendawo ezungezile. Ngisho noma imagnethi isifinyelele izinga elithile (inani eliqinisekisiwe lemboni) ngaphambi kokushiya ifektri, Nokho, ngemva kokufakwa, ngenxa yethonya lezici zemvelo ezifana nokuvikela i-magnetic (self-), ukuvikela i-RF (iminyango namafasitela), ipuleti lokuqondisa amagagasi (ithubhu), isakhiwo sensimbi phakathi kwamamagnethi nezisekelo, izinto zokuhlobisa zokuhlobisa, izinto zokukhanyisa, amapayipi okungenisa umoya, amapayipi omlilo, abalandeli bokukhipha umoya ophuthumayo, imishini yeselula (ngisho nezimoto, ama-lifti) eduze kwezakhiwo ezingenhla nezingezansi, ukufana kwayo kuzoshintsha. Ngakho-ke, ukuthi ukufana kuyahlangabezana yini nezidingo ze-magnetic resonance imaging kufanele kusekelwe emiphumeleni yokulinganisa yangempela ngesikhathi sokwamukelwa kokugcina. Ukulinganisa insimu engasebenzi kanye nokulinganisa insimu esebenzayo ye-superconducting coil eyenziwe unjiniyela wokufaka womkhiqizi we-magnetic resonance efektri noma esibhedlela yizinyathelo ezibalulekile zokuthuthukisa ukufana kwensimu yamagnetic.

Ukuze kutholakale izimpawu eziqoqwe ngokwendawo enkambisweni yokuskena, imishini ye-MRI idinga futhi ukufaka insimu yamagnetic ye-gradient △B ngaphezulu ngezinguquko eziqhubekayo nezikhulayo ngokusekelwe ensimini yamagnetic eyinhloko B0. Kungenzeka ukuthi insimu ye-gradient △B ebekwe phezu kwe-voxel eyodwa kumele ibe nkulu kunokuphambuka kwensimu yamagnetic noma ukuguquguquka kokukhukhuleka okubangelwa yinsimu yamagnetic eyinhloko B0, ngaphandle kwalokho izoshintsha noma ibhubhise isignali yokuma kwendawo engenhla, okuholela ezintweni zobuciko kanye nokunciphisa ikhwalithi yokuthwebula izithombe.

Uma ukuphambuka nokuguquguquka kwensimu yamagnetic ekhiqizwa yinsimu yamagnetic eyinhloko i-B0 kukhulu, kulapho ukufana kwensimu yamagnetic kuba kubi khona, ikhwalithi yesithombe iba phansi, futhi kuhlobene ngqo nochungechunge lokucindezela kwe-lipid (umehluko wemvamisa ye-resonance phakathi kwamanzi namafutha emzimbeni womuntu ungama-200Hz kuphela) kanye nempumelelo yokuhlola i-magnetic resonance spectroscopy (MRS). Ngakho-ke, ukufana kwensimu yamagnetic kungenye yezinkomba ezibalulekile zokulinganisa ukusebenza kwemishini ye-MRI.

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