Vpliv gostote magnetnega polja na popačenja zaradi kovine in načini za zmanjševanje popačenj : diplomsko delo

Stražišar, Leon (author), Jeločnik, Žiga (author), Podobnik, Janez (mentor), Robida, Tina (comentor), Alukić, Erna (reviewer)

Uvod: Slikanje z magnetno resonanco je neinvazivna metoda, s katero pridobimo tri dimenzionalne anatomske slike. Ob slikanju se lahko pojavijo popačenja, ki nam kvarijo sliko. Osredotočili smo se na popačenja, ki nastajajo zaradi kovin. Namen: Namen je preučiti vpliv različnih dejavnikov na pojavnost in zmanjševanje popačenj zaradi kovine pri MR slikanju. Metode dela: Izbrali smo magnetno resonančna tomografa 1,5 T in 3 T. Preuredili smo star fantom, v katerega smo vstavili vijaka izdelana iz titana in jekla. Izbrali smo različna pulzna zaporedja, pri katerih smo nato izvedli meritve. Nato smo vsako pulzno zaporedje čim bolj optimizirali na tak način, da bi bila popačenja zaradi kovine čim manjša. Pridobljene slike smo interpretirali in izvedli meritve s pomočjo programa ImageJ. Rezultati: Prikazali smo slike fantoma z vstavljenimi vijaki v različnih pulznih zaporedjih in v različnih ravninah. Prikazali smo rezultate meritev popačenj. Predstavili smo tudi tabele s parametri, ki smo jih spreminjali. Razprava in zaključek: Ugotovili smo, da ima na izgled in velikost popačenj zaradi kovine zelo velik vpliv vrsta kovine. Če je kovina feromagnetna (jeklo), povzroča veliko večja popačenja od tistih, ki jih povzroča kovina, ki ni feromagnetna (titan). Razlik v popačenjih zaradi kovine pri pulznem zaporedju T1 TSE in T2 TSE skorajda ni, velik vpliv na popačenja pa ima gostota magnetnega polja. V vseh primerih z izjemo enega smo dokazali, da so popačenja zaradi kovine pri gostoti magnetnega polja 3T večja od tistih pri 1,5T. Ugotovili smo tudi, da se z ustreznim spreminjanjem parametrov, kot so pasovna širina, TE, velikost matrike in debelina reza lahko zmanjša negativen vpliv kovinskih popačenj. Predvsem lahko s tem uspešno zmanjšamo vpliv popačenja zaradi kovine na okoliške strukture, manj pa je uspešno pri zmanjševanju velikosti izpada signala zaradi kovine. Na koncu smo naše ugotovitve primerjali tudi z ugotovitvami treh sorodnih raziskav ter ugotovili, da smo prišli do enakih zaključkov.

• Language: Slovenian
• Keywords: diplomska dela, radiološka tehnologija, popačenje zaradi kovine, 1, 5T, 3T, vpliv gostote magnetnega polja, titan, jeklo, vpliv vrste kovine, zmanjševanje popačenj zaradi kovine
• Work type: Bachelor thesis/paper
• Organization: ZF - Faculty of Health Sciences
• Place of publishing: Ljubljana
• Publisher: [L. Stražišar : Ž. Jeločnik]
• Year: 2023
• Number of pages: 46 str.
• PID: 20.500.12556/RUL-151565
• COBISS.SI-ID: 166136579
• Publication date in RUL: 09.10.2023

Secondary language

• Language: English
• Title: Influence of magnetic field density on metal artifacts and methods of reducing them : diploma work

Abstract

Introduction: Magnetic resonance imaging is a non-invasive method to obtain three - dimensional anatomical images. The distortions that are created spoil our images. We have focused on the distortions caused by metals. Purpose: The aim is to investigate the influence of different factors on the incidence and reduction of metallic distortion in MR imaging. Methods: We have selected a 1. 5 T and a 3 T MRI scanner. We have rebuilt an old phantom into which we have inserted two screws; the first one was made from titanium and the second one from steel. We selected different pulse sequences and made the measurements. We then optimised each pulse sequence in such a way as to minimise the distortion due to metal. The acquired images were then interpreted and measurements were taken using ImageJ. Results: Display of images and results of measurements. Tables with the modified parameters are also presented. Discussion and conclusion: We found out that the type of metal has a very strong influence on the appearance and size of metal artefacts. If the metal is ferromagnetic (steel), it causes much greater distortions than those caused by a non-ferromagnetic metal (titanium). There is almost no difference in the distortion due to metal in the T1 TSE and T2 TSE pulse sequences. Besides the type of metal, magnetic field density has also a lot of influence on the occurrence of metal artefacts. We have shown in all but one case that the distortions due to metal at a magnetic field density of 3T are larger than those at 1. 5T. We have also found that by appropriately varying parameters such as bandwidth, TE, matrix size and slice thickness, the negative impact of metal artefacts can be reduced. This is very successful at reducing the impact of metallic distortion on surrounding structures, but less successful at reducing the signal loss because of metal. Finally, we also compared our findings with the findings of three related studies and found that we reached the same conclusions.

• Keywords: diploma theses, radiologic technology, metal artefacts, 1, 5T, 3T, influence of magnetic field density, titanium, steel, influence of metal type, methods of reducing metal artefacts