Conventional Magnetic Resonance Imaging (MRI) is a qualitative method for obtaining images of softtissues in patients. Conventional MRI is the standard method used today and it results in gray-scaleimages in which the different magnetic properties of biological tissues determine the image contrast. However, the magnitude of the measured signal is only relative and therefore not directlycomparable between images. Synthetic MRI is a relatively new technique which can be used to postsynthesizedifferent images based on absolute measurement of several magnetic properties oftissues. Synthetic MRI can therefore provide quantitative information together with the contrastimages. In order to use synthetic MRI clinically an evaluation of the image quality and diagnostic ability isrequired. The purpose of this thesis is to evaluate if synthetic MRI and conventional MRI produceimages with equal contrast. A study was designed and conducted for statistical evaluation of contrast and Contrast-to-Noise Ratio(CNR) generated with different imaging methods. A total of 22 patients were examined using bothconventional MRI and synthetic MRI and the results were pairwise analyzed. The contrast and CNR could not be stated as equal for the imaging methods. Typically the contrastwas higher in the synthetic images for the T1 and T2 weighted images. This was not observed withCNR which suggests that the noise is higher in the synthetic images. The higher contrast obtained insynthetic images resulted in a better separation of different tissues using synthetic MRI. Thesynthetic T2 FLAIR images contained artifacts that are not good for clinical use. However the fact thatthe different imaging methods produce different image quality is not proven to be clinically decisive.

The purpose of this thesis was to implement and quantitatively test a quantitative MRI (qMRI) method, from which synthetic MR images are created and also evaluated. The parameter maps of T1, T2*, and effective proton density (PD*) were tested with reference tubes containing different relaxation times, and concentrations of water (H2O) and heavy water (D2O). Two normal volunteers were also used to test qMRI method, by performing regional analysis on the parameter maps of the volunteers. The synthetic FLASH MR images were evaluated by: using the relative standard deviation of a region of interest (ROI) as a measure for the signal-to-noise ratio (SNR), implanting artificial multiple sclerosis (MS) lesions in the parameter maps used to create the synthetic images, and an MRI radiologist opinion of the images. All MRI measurements were conducted on a 3.0 Tesla scanner (Siemens MAGNETOM Skyrafit). The results from reference tube testing, shows that the implementation was reasonably successful, although the T2* maps can not display values on voxels which have T2 exceeding 100 ms. In vivo parameter map ROI values were consistent between volunteers. The SNR and contrast-to-noise ratio of synthetic images are comparable to their measured counterparts depending on TE. The artificial MS lesions were distinguishable from normal appearing tissue in a T1-weighted synthetic FLASH. The radiologist thought the a synthetic T2*-weighted FLASH was somewhat promising for clinical use after further research and development, however a synthetic T1-weighted FLASH had clinical value. / Syftet med detta arbete var att implementera och kvantitativt undersöka en kvantitativ MR (qMRI) metod, för att sedan skapa och utvärdera syntetiska MR-bilder. qMRI-metodens parameterkartor (T1, T2* och effektiv proton densitets PD*) undersöktes med olika typer av referensprover. Dessa prover innehöll skilda relaxationstider, samt olika koncentrationer av vatten (H2O) och tungt vatten (D2O). In vivo parameterkartor från frivilliga granskades genom att jämföra T1, T2* och PD* värdena på intresseområden (ROIs) mellan frivilliga och publicerade värden. Syntetiska FLASH MR-bilder utvärderades genom att: använda relativa standardavvikelsen av ett intresseområde (ROI) som ett mått på signal-brusförhållande (SNR), implantera artificiell multipel skleros (MS) lesioner i de frivilligas parameterkartor för att se ifall dessa kan identifieras i de syntetiska MR-bilder, och slutligen utvärderade en MR-radiolog bilderna. MR-mätningarna utfördes på 3.0 Tesla MR-kamera (Siemens MAGNETOM Skyrafit). Resultaten från referensproverna visar att implementeringen var rimligen framgångsrik, även om beräknade T2* för voxlar som har T2 över 100 ms inte är pålitliga. Frivilligas parameterkartor visade på bra överensstämmelse, dessvärre inte med publicerade. SNR och kontrast-till-brus-förhållandet (CNR) för syntetiska bilder är jämförbara med deras uppmätta motsvarigheter, beroende på TE. De artificiella MS-lesionerna kunde tydligt skiljas från normal omgivande vävnad i en T1-viktad syntetisk FLASH. Radiologen tyckte att en syntetisk T2*-viktad FLASH var något lovande för klinisk användning efter ytterligare förbättringar, medan en syntetisk T1-viktad FLASH hade kliniskt värde.

This thesis describes the bene ts and disadvantages of using synthetic Magnetic Resonance Imaging (MRI) instead of conventional MRI. The thesis is based on a clinical study performed at Orebro University Hospital were 11 patients diagnosed with Multiple Sclerosis (MS) went through a brain examination with both methods. The examination time was measured and compared between the two methods, and the quality of the images was analysed by two radiologists. The study shows that the examination time can be reduced using the synthetic method instead of the conventional. The image quality is however not as good with the synthetic method which opens a discussion whether the time reduction is worth the loss of image quality. However, the conclusions are that the method can be useful for patients diagnosed with MS who are examined yearly and especially useful as a complement to the conventional sequence to gain as much information as possible that can be compared between the patients yearly exams. To completely replace other conventional examination types, the method has to be further evaluated and equipped with functions that are present in the conventional sequences, such as correction for motion artefacts. / Denna rapport beskriver de fördelar och nackdelar som finns med att använda syntetisk magnetresonanstomografi (MRI) istället för konventionell MRI. Rapporten är baserad på en klinisk studie som har genomförts vid Universitetssjukhuset i Örebro där 11 patienter diagnostiserade med Multipel Skleros (MS) genomförde en undersökning av hjärnan med båda metoderna. Undersökningstiden mättes och jämfördes metoderna emellan, och bildkvaliteten analyserades av två radiologer. Den kliniska studien visar att undersökningstiden kan förkortas när den syntetiska metoden används i jämförelse med den konventionella. Bildkvaliteten för de konventionella bilderna anses vara av högre kvalitet i denna studie vilket öppnar en diskussion gällande huruvida det är värt att förlora en viss bildkvalitet mot förkortat undersökningstid. Slutsatsen är att metoden är användbar för patienter diagnostiserade med MS som undersöks årligen, och speciellt användbar som ett komplement till de konventionella sekvenserna för att generera så mycket information som möjligt. Denna information är sedan användbar vid jämförelse av bilderna från patienternas återkommande undersökningar. För att helt ersätta de konventionella sekvenserna krävs vidare utvärderings av den syntetiska metoden samt att den kompletteras med er funktioner, exempelvis för att korrigera för rörelseartefakter.

Multiple sclerosis is a neurological disease causing a degeneration of myelin around the axons in the central nervous system. This process leaves traces in the form of lesions, which can be distinguished in an MRI examination. It is important to detect these at an early stage to state diagnosis and initiate medication.  In this Master's Thesis, an automatic segmentation algorithm was developed, with the purpose of segmenting possible multiple sclerosis lesions. Secondly, a progression model was developed with the purpose of estimating the state of each individual lesion. The implementation was based on synthetic contrast weighted images, segmentation maps and quantitative relaxation maps produced by SyMRI (SyntheticMR, Linköping, Sweden). The automatic segmentation algorithm has a relatively high sensitivity but low precision, causing a large number of false positives. The algorithm performed better in the cerebrum compared to the cerebellum. The large number of false positives appeared mainly due to partial volume effects, creating hyperintense artifacts in synthetic T2W FLAIR images. A larger amount of data would have been desirable to create a more robust algorithm. The progression model showed promising results, with a clear correlation to the synthetic contrast-weighted images and segmentation maps available in SyMRI. The progression model could be useful in disease monitoring, medical decisions and diagnosis of Multiple Sclerosis.