Quality control methods for magnetic resonance imaging in a multi-unit medical imaging organization

Quality control methods and test objects were developed and used for structural magnetic resonance imaging (MRI), functional MRI (fMRI) and diffusion-weighted imaging (DWI). Emphasis was put on methods that allowed objective quality control for organizations that use several MRI systems from different vendors, which had different field strengths. Notable increases in the numbers of MRI studies and novel MRI systems, fast development of MRI technology, and international discussion about the quality and safety of medical imaging have motivated the development of objective, quantitative and timeefficient methods for quality control. The quality control methods need to be up to date with the most modern MRI methods, including parallel imaging, parallel transmit technology, and new diffusion-weighted sequences. The methods need to be appropriate to those organizations that use MRI for quantitative measurements, or for the participation in multicenter studies. Two different test object methods for structural MRI were evaluated in a multi-unit medical imaging organization, these were: the Eurospin method and the American College of Radiology (ACR) method. The Eurospin method was originally developed as a part of European Concerted Action, and five standardized test objects were used to create a quality control protocol for six MRI systems. Automatic software was written for image analysis. In contrast, a single multi-purpose test object was used for the ACR method, and image quality for both standard and clinical imaging protocols were measured for 11 MRI systems. A previously published method for fMRI quality control was applied to the evaluation of 5 MRI systems and was extended for simultaneous electroencephalography (EEG) and fMRI (EEG–fMRI). The test object results were compared with human data that were obtained from two healthy volunteers. A body-diameter test object was constructed for DWI testing, and apparent diffusion coefficient (ADC) values and level of artifacts were measured using conventional and evolving DWI methods. The majority of the measured MRI systems operated at an acceptable level, when compared with published recommended values for structural and functional MRI. In general, the measurements were repeatable. The study that used the test object revealed information about the extent of superficial artifacts (15 mm) and the magnitude of signalto-noise ratio (SNR) reduction (15%) of the simultaneous EEG–fMRI images. The observations were in accordance with the data of healthy human volunteers. The agreement between the ADC values for different methods used in DWI was generally good, although differences of up to 0.1 x10-3 mm2/s were observed between different acquisition options and different field strengths, and along the slice direction. Readout-segmented echo-planar imaging (EPI) and zoomed EPI in addition to efficient use of the parallel transmit technology resulted in lower levels of artifacts than the conventional methods. Other findings included geometric distortions at the edges of MRI system field-of-view, minor instability of image center-of-mass in fMRI, and an amplifier difference that affected the EEG signal of EEG–fMRI. The findings showed that although the majority of the results were within acceptable limits, MRI quality control was capable of detecting inferior image quality and revealing information that supported clinical imaging. A comparison between the different systems and also with international reference values was feasible with the reported limitations. Automated analysis methods were successfully developed and applied in this study. The possible future direction of MRI quality control would be the further development of its relevance for clinical imaging. Preface and acknowledgements This research was carried out in the HUS Medical Imaging Center and was supported by the State Subsidy for University Hospitals. It has been a forward-looking environment in which to work and advance one’s scientific aims. I especially want to thank CEO Jyrki Putkonen, chief physician Pekka Tervahartiala and former MRI process owner Juha Halavaara for developing this environment and creating its positive atmosphere. I wish to thank both the current and former Heads of the Department of Physics at the University of Helsinki, Professor Hannu Koskinen and Professor Juhani Keinonen, for providing favorable conditions for me to build upon my knowledge of science. I also wish to thank the management of MATRENA doctoral school for the development of a wellorganized and a fruitful scientific environment. The supervisors of this thesis have shown considerable patience with this research for which I am very grateful. Professor Sauli Savolainen has continuously encouraged me to proceed with the thesis, and given invaluable help with his extensive insight into the fascinating world of medical physics. Adjunct Professor Outi Sipila has provided in-depth guidance in planning the studies and effectively taught me how to write scientific papers, always reading the drafts carefully and squeezing the last drop of literary contamination and vagueness out of my texts. I wish to thank the official reviewers of this thesis, Professor Miika Nieminen and Adjunct Professor Eveliina Lammentausta, who have given their extremely valuable and constructive comments. My co-authors also deserve thanks and I am especially grateful to Nadja Lonnroth. Cooperation with her showed me how inspiring writing a scientific article can actually be, and this effectively revived the pulse of my scientific life. Linda Kuusela was a great coauthor in three papers we co-authored as she was willing to help and give a sensible opinion whenever needed. Sampsa Turunen kindly provided his expertise in electroencephalography into the research. Marjut Timonen, Jouni Uusi-Simola, Touko Kaasalainen and Juha Peltonen have been enthusiastic about the subject of this thesis and great colleagues throughout the years. Adjunct Professor Sami Heikkinen introduced me to the world of genuine MR science, and later gave his invaluable help in planning and preparing the test objects, together with the kind help and valuable contribution of Maiju Soikkeli. Eila Lantto and Ali Ovissi provided the radiologists’ perspective into the last paper of this thesis, for which I am very grateful. I feel much obliged to all the colleagues and friends who have encouraged me in my research work. Miia Pitkonen, an inspiring and cheerful colleague, has encouraged me at crucial times, which gave me the important spurts of energy to complete this project. Laura Tuomikoski, who is currently also preparing her PhD thesis, has been my warm and encouraging peer supporter during the finalizing phase of my project. The hilarious company of my friends of the YL Male Voice Choir, where we originally met, kept me lively and open-minded throughout the years. These are Antti, Hannes, Heikki, Jukka, Mikko, Risto, Sampo, Tommi and Tuomas. I am deeply grateful to my parents Tauno and Tuulikki who provided me with a safe home where education was appreciated, and ensured that I had the possibility to study the things I wanted. Finally, I owe my deepest gratitude to my wife Suvi for persistently but lovingly driving me to complete the project, and while I was writing this thesis, for taking care of our wonderful little daughters Linnea and Sylvia.