ʻO MRI kahi ʻenehana kiʻi non-invasive e hana ana i nā kiʻi anatomical kikoʻī ʻekolu. Hoʻohana pinepine ʻia no ka ʻike ʻana i ka maʻi, ka ʻike, a me ka nānā ʻana i ka mālama ʻana. Hoʻokumu ʻia ia ma luna o ka ʻenehana loea e hoʻohauʻoli a ʻike i ka hoʻololi ʻana i ke ala o ka axis rotational o nā protons i loaʻa i loko o ka wai e hana ai i nā ʻiʻo ola.
Pehea ka hana MRI?
Hoʻohana nā MRI i nā magnet ikaika e hoʻohua ai i kahi māla magnetic ikaika e hoʻoikaika i nā protons i loko o ke kino e kūlike me kēlā kahua. Ke hoʻokau ʻia ke au o ka radiofrequency i ka mea maʻi, hoʻoulu ʻia nā protons, a wili ʻia i waho o ke kaulike, e hoʻoikaika ana i ka huki ʻana o ke kahua magnetic. Ke hoʻopau ʻia ke kahua radiofrequency, hiki i nā mea ʻike MRI ke ʻike i ka ikehu i hoʻokuʻu ʻia i ka wā e hoʻoponopono hou ai nā protons me ke kahua magnetic. ʻO ka manawa e pono ai nā protons e hoʻoponopono hou me ka māla magnetic, a me ka nui o ka ikehu i hoʻokuʻu ʻia, e loli ana ma muli o ke kaiapuni a me ke ʻano kemika o nā mole. Hiki i nā kauka ke haʻi i ka ʻokoʻa ma waena o nā ʻano kikoʻī like ʻole e pili ana i kēia mau waiwai magnetic.
No ka loaʻa ʻana o kahi kiʻi MRI, hoʻokomo ʻia ka mea maʻi i loko o kahi magnet nui a pono e noho mālie i ka wā o ke kaʻina hana kiʻi i ʻole e pohō ke kiʻi. Hiki ke hāʻawi ʻia nā mea ʻokoʻa (ʻo ia ka mea i loaʻa pinepine i ka Gadolinium) i ka mea maʻi ma mua a i ʻole i ka wā o ka MRI e hoʻonui i ka wikiwiki o ka hoʻohuli ʻana o nā protons me ke kahua magnetic. ʻOi aku ka wikiwiki o ka hoʻoponopono hou ʻana o nā protons, ʻoi aku ka mālamalama o ke kiʻi.
He aha nā ʻano magnet e hoʻohana ai nā MRI?
Hoʻohana nā ʻōnaehana MRI i ʻekolu ʻano kumu magnet:
-Hoʻohana ʻia nā magnet resistive mai nā wili uea he nui i ʻōwili ʻia a puni ka cylinder kahi e hele ai kahi au uila. Hoʻopuka kēia i kahi māla magnetic. Ke pani ʻia ka uila, make ke kahua magnetic. ʻOi aku ka haʻahaʻa o kēia mau magnet ma mua o ka superconducting magnet (e ʻike i lalo), akā pono ka nui o ka uila e hana ai ma muli o ke kūpaʻa kūlohelohe o ka uea. Hiki ke piʻi ka uila ke makemake ʻia nā magnet mana kiʻekiʻe.
-ʻO ka magnet mau loa ʻo ia wale nō -- mau loa. Aia mau ke kahua magnetic a me ka ikaika piha. No laila, ʻaʻohe uku no ka mālama ʻana i ke kahua. ʻO kahi hemahema nui, ʻo ia ke kaumaha loa o kēia mau magnet: i kekahi manawa he nui a nui nā tona. Pono kekahi mau māla ikaika i nā magnet no ke kaumaha a paʻakikī ke kūkulu ʻia.
- ʻO nā magnet superconducting ka mea maʻamau i hoʻohana ʻia ma MRI. He ʻano like nā mea magnet superconducting me nā magnet resistive - ʻo nā wili uea me kahi au uila e hele nei e hana i ke kahua magnetic. ʻO ka ʻokoʻa koʻikoʻi ʻo ia i loko o kahi superconducting magnet e ʻauʻau mau ʻia ka uea i ka helium wai (ma kahi anuanu 452.4 degere ma lalo o ka ʻole). ʻO kēia anuanu ʻaneʻane hiki ʻole ke hoʻoheheʻe i ke kū ʻana o ka uea i ka zero, e hōʻemi nui ana i ka pono uila no ka ʻōnaehana a ʻoi aku ka maikaʻi o ka hana.
Nā ʻano magnet
Hoʻoholo ʻia ka hoʻolālā o MRI e ke ʻano a me ke ʻano o ka magnet nui, ʻo ia hoʻi i pani ʻia, tunnel-type MRI a i ʻole MRI wehe.
ʻO ka mea maʻamau i hoʻohana pinepine ʻia he superconducting electromagnets. Aia kēia mau mea i kahi coil i hana ʻia e ka hoʻoheheʻe wai helium. Hoʻopuka lākou i nā māla magnetic ikaika, homogeneous, akā he pipiʻi a pono e mālama mau ʻia (ʻo ia hoʻi ka hoʻonui ʻana i ka pahu helium).
Inā nalowale ka superconductivity, hoʻopau ʻia ka ikehu uila e like me ka wela. Hoʻomaka kēia hoʻomehana i ka hoʻoheheʻe wikiwiki ʻana o ka wai Helium i hoʻololi ʻia i ka leo kiʻekiʻe loa o ke kinoea Helium (quench). I mea e pale aku ai i ka wela wela a me ka asphyxia, ua loaʻa i nā mea hoʻokele superconducting nā ʻōnaehana palekana: nā paipu hoʻokuʻu kinoea, ka nānā ʻana i ka pakeneka o ka oxygen a me ka mahana i loko o ka lumi MRI, wehe ʻia ka puka i waho (overpressure i loko o ka lumi).
Ke hana mau nei nā magnet superconducting. No ka hoʻopaʻa ʻana i nā kaohi o ka hoʻokomo ʻana i ka magnet, loaʻa i ka hāmeʻa kahi ʻōnaehana pale i ka passive (metallic) a i ʻole ka hana (kahi superconducting coil o waho e kūʻē ana ke kahua i ko ka coil i loko) e hōʻemi i ka ikaika o ka māla.
Hoʻohana pū ka MRI haʻahaʻa haʻahaʻa:
- ʻO nā electromagnets resistive, ʻoi aku ka maʻalahi a maʻalahi hoʻi e mālama ma mua o nā magnet superconducting. ʻAʻole ikaika loa kēia, hoʻohana i ka ikehu hou aʻe a koi i kahi ʻōnaehana hoʻomaha.
- Nā magnet mau, o nā ʻano like ʻole, i haku ʻia me nā ʻāpana metala ferromagnetic. ʻOiai ua loaʻa iā lākou ka pōmaikaʻi o ka maʻalahi a me ka maʻalahi o ka mālama ʻana, ua kaumaha loa lākou a nāwaliwali i ka ikaika.
No ka loaʻa ʻana o ke kahua mākia homogeneous, pono e hoʻokani maikaʻi ʻia ka magnet ("shimming"), me ka hoʻohana ʻana i nā ʻāpana metala hiki ke hoʻoneʻe ʻia, a i ʻole me ka ikaika, me ka hoʻohana ʻana i nā coils electromagnetic liʻiliʻi i puʻunaue ʻia i loko o ka magnet.
Nā hiʻohiʻona o ka magnet nui
ʻO nā hiʻohiʻona nui o kahi magnet:
-ʻAno (superconducting a i ʻole resistive electromagnets, mau magnet mau)
-Ka ikaika o ke kahua i hana ʻia, ana ʻia ma Tesla (T). Ma ka hoʻomaʻamaʻa lapaʻau o kēia manawa, ʻokoʻa kēia mai 0.2 a 3.0 T. Ma ka noiʻi, hoʻohana ʻia nā magnet me nā ikaika o 7 T a i ʻole 11 T a ʻoi aku.
-Homogeneity
