MRI Homogeneity

Magnetic field uniformity (homogeneity), yomwe imadziwikanso kuti magnetic field uniformity, imatanthawuza chidziwitso cha mphamvu ya maginito mkati mwa malire a voliyumu, ndiko kuti, ngati mizere ya maginito kudutsa dera lonselo ndi yofanana. Voliyumu yeniyeni apa nthawi zambiri imakhala danga lozungulira. Chigawo cha maginito ofanana ndi ppm (gawo pa miliyoni), ndiko kuti, kusiyana pakati pa mphamvu yamagetsi yamagetsi ndi mphamvu yochepa ya mphamvu ya maginito mu danga linalake logawidwa ndi mphamvu zapakati zomwe zikuchulukitsidwa ndi milioni imodzi.

MRI imafunika kufananiza kwamphamvu kwa maginito, komwe kumatsimikizira kusintha kwa malo ndi chiŵerengero cha chizindikiro ndi phokoso la chithunzi muzojambula. Kusafanana kwamphamvu kwa maginito kumapangitsa kuti chithunzicho chisawoneke bwino komanso chisokonezeke. Kufanana kwa maginito kumatsimikiziridwa ndi mapangidwe a maginito okha ndi chilengedwe chakunja. Kukula kwa malo ojambulira a maginito, m'munsimu maginito a maginito ofanana amatha kutheka. Kukhazikika kwa mphamvu ya maginito ndi index yoyezera kuchuluka kwa kutengeka kwa mphamvu ya maginito ndi nthawi. Munthawi ya katsatidwe ka kujambula, kutengeka kwa mphamvu ya maginito kumakhudza gawo la siginecha ya echo yoyezedwa mobwerezabwereza, zomwe zimapangitsa kupotoza kwa chithunzi ndi kuchepa kwa chiŵerengero cha maginito. Kukhazikika kwa maginito kumagwirizana kwambiri ndi mtundu wa maginito ndi khalidwe la mapangidwe ake.

Zomwe zimaperekedwa ndi maginito ofanana muyeso zimayenderana ndi kukula ndi mawonekedwe a malo oyezera omwe atengedwa, ndipo nthawi zambiri amagwiritsa ntchito malo ozungulira okhala ndi mainchesi ena ndi pakati pa maginito monga muyeso woyezera. Nthawi zambiri, chifaniziro cha mphamvu ya maginito ya maginito ndi malo oyezera, kusintha kwa mphamvu ya maginito mu malo operekedwa (ppm value), ndiko kuti, gawo limodzi mwa magawo miliyoni a mphamvu ya magnetic field (ppm) monga gawo lopatuka kuti lifotokoze mochulukira, nthawi zambiri gawo lopatukali limatchedwa ppm, lomwe limatchedwa kuyimira mtengo wathunthu. Mwachitsanzo, kufanana kwa mphamvu ya maginito mkati mwa silinda yonse yoyang'ana cheke ndi 5ppm; Kufanana kwa maginito mu gawo la 40cm ndi 50cm kokhazikika ndi maginito apakati ndi 1ppm ndi 2ppm, motsatana. Itha kufotokozedwanso motere: kufanana kwa mphamvu ya maginito mu danga la cubic centimita iliyonse m'dera lachitsanzo lomwe likuyesedwa ndi 0.01ppm. Mosasamala kanthu za muyeso, poganizira kuti kukula kwa gawo loyezera ndi kofanana, kucheperako kwa ppm kumawonetsa kufananiza kwa maginito.

Pankhani ya chipangizo cha 1.5-tMRI, kusinthasintha kwamphamvu kwa mphamvu ya maginito yomwe imayimiridwa ndi gawo limodzi la kupatuka (1ppm) ndi 1.5 × 10-6T. Mwa kuyankhula kwina, mu dongosolo la 1.5T, kufanana kwa maginito a 1ppm kumatanthawuza kuti mphamvu ya maginito yaikulu imakhala ndi kusinthasintha kwa 1.5 × 10-6T (0.0015mT) kutengera maziko a mphamvu ya maginito ya 1.5T. Mwachiwonekere, mu zipangizo za MRI zokhala ndi mphamvu zosiyana siyana, kusinthasintha kwa mphamvu ya maginito yomwe imayimiridwa ndi gawo lililonse lopatuka kapena ppm ndi yosiyana, kuchokera pamalingaliro awa, machitidwe otsika amatha kukhala ndi zofunikira zochepa kuti zikhale zofanana ndi maginito (onani Table 3-1) . Ndi makonzedwe otere, anthu amatha kugwiritsa ntchito mulingo wofananira kuti afanizire mosavuta machitidwe omwe ali ndi mphamvu zakumunda zosiyanasiyana, kapena machitidwe osiyanasiyana okhala ndi mphamvu yamunda womwewo, kuti athe kuwunika momwe maginito amagwirira ntchito.

Pamaso pa muyeso weniweni wa maginito maginito kufanana, m`pofunika molondola kudziwa pakati pa maginito, ndiyeno kukonza munda mphamvu kuyeza chida (Gauss mita) kafukufuku pa danga la utali wozungulira ena, ndi kuyeza maginito mphamvu yake. mfundo ndi mfundo (njira ya ndege 24, njira ya ndege 12), ndipo potsiriza sungani deta kuti muwerengere kufanana kwa maginito mkati mwa voliyumu yonseyo.

Kufanana kwa mphamvu ya maginito kudzasintha ndi malo ozungulira. Ngakhale maginito afika muyezo wina (factory kutsimikizika mtengo) asanachoke pafakitale, Komabe, pambuyo unsembe, chifukwa cha chikoka cha zinthu zachilengedwe monga maginito (kudzikonda) kutchinga, RF shielding (zitseko ndi Windows), waveguide mbale. (chubu), kapangidwe kachitsulo pakati pa maginito ndi zothandizira, zokongoletsera zokongoletsera, zowunikira, mapaipi olowera mpweya, mapaipi amoto, mafani otulutsa mwadzidzidzi, zida zam'manja (ngakhale magalimoto, zikepe) pafupi ndi nyumba zapamwamba ndi zapansi, kufanana kwake kudzasintha. Choncho, ngati kufanana kumakwaniritsa zofunikira za kujambula kwa magnetic resonance ziyenera kukhazikitsidwa pa zotsatira zenizeni za kuyeza panthawi yovomerezeka yomaliza. Kusanja kumunda komanso kuwongolera kwamphamvu kwa koyilo ya superconducting kochitidwa ndi mainjiniya oyika opanga maginito opanga maginito mu fakitale kapena chipatala ndi njira zazikulu zosinthira kufananiza kwa maginito.

Kuti tipeze ma signature omwe asonkhanitsidwa pakupanga sikani, zida za MRI zimafunikanso kukulitsa mphamvu ya maginito △B ndikusintha kosalekeza kotengera gawo lalikulu la maginito B0. Ndizotheka kuti gawo la gradient △B loyikidwa pamwamba pa voxel imodzi liyenera kukhala lalikulu kuposa kupatuka kwa maginito kapena kusinthasintha kwa maginito chifukwa cha gawo lalikulu la maginito B0, apo ayi lisintha kapena kuwononga chizindikiro chomwe chili pamwambapa, zomwe zimapangitsa kuti pakhale zinthu zakale komanso kuchepetsa khalidwe lajambula.

Kupatuka kwakukulu ndi kusinthasintha kwamphamvu kwa maginito komwe kumapangidwa ndi mphamvu ya maginito B0, kumakhala koipitsitsa kwambiri kwa mphamvu ya maginito, kutsika kwa chithunzicho, komanso kukhudzana kwambiri ndi kutsatizana kwa lipid (kusiyana kwafupipafupi kwa resonance pakati pawo. madzi ndi mafuta m'thupi la munthu ndi 200Hz okha) ndi kupambana maginito resonance spectroscopy (MRS) anayendera. Choncho, kufanana kwa maginito ndi chimodzi mwa zizindikiro zazikulu zoyezera momwe zida za MRI zikuyendera.

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