{"id":5081,"date":"2019-01-23T11:46:01","date_gmt":"2019-01-23T08:46:01","guid":{"rendered":"https:\/\/umram.bilkent.edu.tr\/?p=5081"},"modified":"2019-01-24T10:31:57","modified_gmt":"2019-01-24T07:31:57","slug":"doktora-tez-sunumu-koray-ertan","status":"publish","type":"post","link":"https:\/\/umram.bilkent.edu.tr\/index.php\/tr\/2019\/01\/23\/doktora-tez-sunumu-koray-ertan\/","title":{"rendered":"Doktora Tez Sunumu: Niyazi Koray Ertan"},"content":{"rendered":"\n<p><a href=\"https:\/\/umram.bilkent.edu.tr\/index.php\/tr\/\">UMRAM<\/a>&#8216;da<a href=\"https:\/\/umram.bilkent.edu.tr\/index.php\/teams\/koray-ertan\/\"> Koray Ertan<\/a> 3 Ocak 2019 tarihi itibariyle doktora tez sunumunu ba\u015far\u0131l\u0131 bir \u015fekilde ger\u00e7ekle\u015ftirdi. <a href=\"http:\/\/www.ee.bilkent.edu.tr\/tr\/page.php?id=12\">Bilkent \u00dcniversitesi Elektrik ve Elektronik M\u00fchendisli\u011fi B\u00f6l\u00fcm\u00fc<\/a>&#8216;nde doktora \u00e7al\u0131\u015fmalar\u0131n\u0131 <a href=\"https:\/\/umram.bilkent.edu.tr\/index.php\/teams\/ergin-atalar\/\">Ergin Atalar<\/a> ile birlikte s\u00fcrd\u00fcrd\u00fc. \u00d6n\u00fcm\u00fczdeki d\u00f6nem <a href=\"https:\/\/www.stanford.edu\/\">Stanford \u00dcniversitesi<\/a>&#8216;nde post-doc \u00e7al\u0131\u015fmalar\u0131na devam edecektir.<\/p>\n\n\n\n<p><strong>Tez&nbsp;Ba\u015fl\u0131\u011f\u0131<\/strong>: Z-Gradyan Dizisinin Tasar\u0131m\u0131 ve Manyetik Rezonans G\u00f6r\u00fcnt\u00fclemedeki Uygulamalar\u0131<\/p>\n\n\n\n<p><strong>Abstract:<\/strong>  Ba\u011f\u0131ms\u0131z gradyan g\u00fc\u00e7 y\u00fckselte\u00e7leri taraf\u0131ndan s\u00fcr\u00fclen gradyan sarg\u0131 dizileri dinamik olarak ayarlanabilen manyetik alan profilleri yaratabilirler. Bu do\u011frultuda, 25 cm \u00e7ap\u0131nda 9 kanall\u0131 bir gradyan sarg\u0131 dizisi tasarlanm\u0131\u015f ve \u00fcretilmi\u015ftir. Daha \u00f6nceden tasarlanan, 50 V voltaj ve 20 A ak\u0131m sa\u011flama kapasitesine sahip g\u00fc\u00e7 y\u00fckselte\u00e7leri, sarg\u0131lar\u0131 ba\u011f\u0131ms\u0131z olarak beslemek i\u00e7in kullan\u0131lm\u0131\u015ft\u0131r. Gradyan sar\u0131mlardaki y\u00fcksek ak\u0131m hassasiyetini sa\u011flayabilmek i\u00e7in bu sarg\u0131lardaki kar\u015f\u0131l\u0131kl\u0131 kuplaj de\u011ferlendirilmistir. Kar\u015f\u0131l\u0131kl\u0131 kuplaj etkisini de i\u00e7eren birinci dereceden bir devre modeli \u00f6nerilmi\u015ftir. Bu model, verilen bir gradyan ak\u0131m seti ve g\u00fc\u00e7 y\u00fckselte\u00e7 limitleri i\u00e7in gerekli olan voltajlar\u0131 ve elde edilebilecek minimum \u00e7\u0131k\u0131s s\u00fcresini analitik olarak hesaplanmas\u0131n\u0131 sa\u011flamaktad\u0131r. Kar\u015f\u0131l\u0131kl\u0131 kuplaj ve kanallar aras\u0131ndaki empedanslar \u00f6l\u00e7\u00fclm\u00fc\u015f ve \u00f6nerilen birinci devre modeli ile g\u00fc\u00e7 y\u00fckselte\u00e7lerinin \u00e7al\u0131\u015fma band\u0131 i\u00e7erisinde (&lt;10kHz) uyumluluk g\u00f6zlenmi\u015ftir. \u00d6rnek bir z-gradyan alan\u0131 i\u00e7in eniyile\u015ftirme yap\u0131lm\u0131\u015f ve bu alan Manyetik Rezonans G\u00f6r\u00fcnt\u00fcleme (MRG) deneylerinde frekans kodlay\u0131c\u0131 gradyan olarak kullan\u0131lm\u0131\u015ft\u0131r. Gradyan dizisi donan\u0131m\u0131n\u0131n uygun bir \u015fekilde \u00e7al\u0131st\u0131\u011f\u0131 ak\u0131m \u00f6l\u00e7\u00fcmleri ve MRG deneyleri ile tasdiklendikten sonra dinamik olarak ayarlanabilen alan profillerinden kaynakl\u0131 avantajlar ara\u015ft\u0131r\u0131lm\u0131\u015ft\u0131r. <\/p>\n\n\n\n<p>\u0130lk olarak, farkl\u0131 boyutlardaki hedef hacimlerde olu\u015fturulan do\u011frusal gradyanlar, de\u011fi\u015fken do\u011frusall\u0131k hatalar\u0131 belirlenerek d\u00f6rt parametre i\u00e7in eniyile\u015ftirme yap\u0131lm\u0131\u015ft\u0131r. Bu parametreler birim y\u00fckselte\u00e7 ak\u0131m\u0131 ile olu\u015fturulabilecek maksimum gradyan g\u00fcc\u00fc, birim y\u00fckselte\u00e7 voltaj\u0131 ile olu\u015fturulabilecek olan maksimum \u00e7\u0131k\u0131\u015f h\u0131z\u0131 (slew rate), birim gradyan g\u00fcc\u00fc i\u00e7in gerekli olan minimum ak\u0131m normu ve minimum manyetik alan tepe de\u011feridir. Daha k\u00fc\u00e7\u00fck hacimlerde ve daha y\u00fcksek do\u011frusall\u0131k hatalar\u0131 ile bu parametrelerinde her birinde simulasyonlarda s\u00fcp\u00fcr\u00fclen de\u011ferler aras\u0131nda 5 kattan fazla art\u0131\u015f g\u00f6zlenmi\u015ftir. Buradan kaynaklanan avantaj dif\u00fczyon a\u011f\u0131rl\u0131kl\u0131 g\u00f6r\u00fcnt\u00fclemeye uygulanm\u0131\u015ft\u0131r. Do\u011frusal gradyan alan\u0131 yaln\u0131zca ilgili kesit i\u00e7erisinde eniyile\u015ftirildi\u011finde, sarg\u0131n\u0131n b\u00fct\u00fcn hacminde yap\u0131lan eniyile\u015ftirmeye oranla, gradyan g\u00fcc\u00fcnde 4 kat art\u0131\u015f elde edilmi\u015ftir. Bu dif\u00fczyon gradyan s\u00fcresini 3 kat azaltm\u0131\u015ft\u0131r ve eko zaman\u0131n\u0131 yar\u0131ya indirmi\u015ftir. Artan sinyal g\u00fcr\u00fclt\u00fc oran\u0131 sayesinde fantom i\u00e7in hesaplanan ADC haritalar\u0131nda daha iyi tahminler yap\u0131lm\u0131\u015ft\u0131r.<\/p>\n\n\n\n<p>\u0130kinci olarak, gradyan dizileri do\u011frusal olmayan gradyanlar \u00fcretebilirler. Do\u011frusal olmayan gradyanlar sayesinde iki yenilik\u00e7i uygulama geli\u015ftirilmi\u015ftir. \u0130lk uygulamada, do\u011frusal olmayan gradyanlar birden \u00e7ok kesit pozisyonunu tek bir frekansa \u015fifrelemek i\u00e7in kullan\u0131lm\u0131\u015ft\u0131r. Bu sayede, tek bantl\u0131 bir RF darbe ile \u00e7oklu kesit se\u00e7imi ger\u00e7ekle\u015ftirilmi\u015ftir. Geleneksel \u00e7oklu kesit se\u00e7imlerinde kullan\u0131lan RF darbelerinden kaynaklanan SAR ve RF tepe g\u00fcc\u00fc art\u0131s\u0131 gibi dezavantajlar engellenmi\u015ftir. Bu tekni\u011fi ger\u00e7ekle\u015ftirebilmek i\u00e7in iki farkl\u0131 tasar\u0131m y\u00f6ntemi \u00f6nerilmi\u015ftir. \u0130ki y\u00f6ntem de kesit kal\u0131nl\u0131\u011f\u0131 hatas\u0131, merkez nokta kaymas\u0131, gradyan g\u00fcc\u00fc ve g\u00fc\u00e7 t\u00fcketimi a\u00e7\u0131s\u0131ndan incelenmi\u015f ve kar\u015f\u0131last\u0131r\u0131lm\u0131\u015ft\u0131r. Fantom MRG deneylerinde, tek bantl\u0131 RF darbe ile iki ve \u00fc\u00e7 kesit uyar\u0131m\u0131 sa\u011flanm\u0131st\u0131r. \u0130kinci uygulamada, tek kanall\u0131 bir do\u011frusal olmayan gradyan, do\u011frusal gradyanlar ile spoke uyar\u0131m\u0131 s\u0131ras\u0131nda e\u015fzamanl\u0131 kullan\u0131larak B<sup>+<\/sup>1 d\u00fczensizliklerinden kaynakl\u0131<sup> <\/sup>uzaysal uyar\u0131m d\u00fczensizliklerini azaltmak i\u00e7in kullan\u0131lm\u0131\u015ft\u0131r. Do\u011frusal olmayan gradyanlar i\u00e7in ba\u011f\u0131ms\u0131z bir k-uzay de\u011fi\u015fkeni tan\u0131mlanarak, problem bir boyut geni\u015flemi\u015f uyar\u0131m k-uzay\u0131nda tekrar ifade edilmi\u015ftir. Tek boyutlu, iki boyutlu, RF g\u00fc\u00e7 limitli ve RF g\u00fc\u00e7 limitsiz olmak \u00fczere simulasyonlar yap\u0131lm\u0131\u015ft\u0131r. \u00d6nerilen y\u00f6ntem MRG deneylerindeki uyar\u0131m d\u00fczensizliklerini sadece do\u011frusal gradyanlar\u0131n kullan\u0131ld\u0131\u011f\u0131 duruma oranla 2.3 kat daha fazla azaltm\u0131\u015ft\u0131r. <\/p>\n\n\n\n<p><\/p>\n\n\n\n<p><\/p>\n\n\n\n<p><a rel=\"noreferrer noopener\" href=\"https:\/\/umram.bilkent.edu.tr\/index.php\/2019\/01\/23\/phd-thesis-defence-koray-ertan\/#print\" target=\"_blank\"><\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>UMRAM&#8216;da Koray Ertan 3 Ocak 2019 tarihi itibariyle doktora tez sunumunu ba\u015far\u0131l\u0131 bir \u015fekilde ger\u00e7ekle\u015ftirdi. Bilkent \u00dcniversitesi Elektrik ve Elektronik M\u00fchendisli\u011fi B\u00f6l\u00fcm\u00fc&#8216;nde doktora \u00e7al\u0131\u015fmalar\u0131n\u0131 Ergin Atalar ile birlikte s\u00fcrd\u00fcrd\u00fc. \u00d6n\u00fcm\u00fczdeki d\u00f6nem Stanford \u00dcniversitesi&#8216;nde post-doc \u00e7al\u0131\u015fmalar\u0131na devam edecektir. Tez&nbsp;Ba\u015fl\u0131\u011f\u0131: Z-Gradyan Dizisinin Tasar\u0131m\u0131 ve Manyetik Rezonans G\u00f6r\u00fcnt\u00fclemedeki Uygulamalar\u0131 Abstract: Ba\u011f\u0131ms\u0131z gradyan g\u00fc\u00e7 y\u00fckselte\u00e7leri taraf\u0131ndan s\u00fcr\u00fclen gradyan sarg\u0131 [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":5111,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[445,447],"tags":[],"_links":{"self":[{"href":"https:\/\/umram.bilkent.edu.tr\/index.php\/wp-json\/wp\/v2\/posts\/5081"}],"collection":[{"href":"https:\/\/umram.bilkent.edu.tr\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/umram.bilkent.edu.tr\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/umram.bilkent.edu.tr\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/umram.bilkent.edu.tr\/index.php\/wp-json\/wp\/v2\/comments?post=5081"}],"version-history":[{"count":8,"href":"https:\/\/umram.bilkent.edu.tr\/index.php\/wp-json\/wp\/v2\/posts\/5081\/revisions"}],"predecessor-version":[{"id":5131,"href":"https:\/\/umram.bilkent.edu.tr\/index.php\/wp-json\/wp\/v2\/posts\/5081\/revisions\/5131"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/umram.bilkent.edu.tr\/index.php\/wp-json\/wp\/v2\/media\/5111"}],"wp:attachment":[{"href":"https:\/\/umram.bilkent.edu.tr\/index.php\/wp-json\/wp\/v2\/media?parent=5081"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/umram.bilkent.edu.tr\/index.php\/wp-json\/wp\/v2\/categories?post=5081"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/umram.bilkent.edu.tr\/index.php\/wp-json\/wp\/v2\/tags?post=5081"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}