Objectives: MRI is of great clinical utility for the guidance of special diagnostic and therapeutic interventions. The majority of such procedures are performed iteratively (\"in-and-out\") in standard, closed-bore MRI systems with control imaging inside the bore and needle adjustments outside the bore. The fundamental limitations of such an approach have led to the development of various assistance techniques, from simple guidance tools to advanced navigation systems. The purpose of this work was to thoroughly assess the targeting accuracy, workflow and usability of a clinical add-on navigation solution on 240 simulated biopsies by different medical operators. Methods: Navigation relied on a virtual 3D MRI scene with real-time overlay of the optically tracked biopsy needle. Smart reference markers on a freely adjustable arm ensured proper registration. Twenty-four operators – attending (AR) and resident radiologists (RR) as well as medical students (MS) – performed well-controlled biopsies of 10 embedded model targets (mean diameter: 8.5 mm, insertion depths: 17-76 mm). Targeting accuracy, procedure times and 13 Likert scores on system performance were determined (strong agreement: 5.0). Results: Differences in diagnostic success rates (AR: 93%, RR: 88%, MS: 81%) were not significant. In contrast, between-group differences in biopsy times (AR: 4:15, RR: 4:40, MS: 5:06 min: sec) differed significantly (p<0.01). Mean overall rating was 4.2. The average operator would use the system again (4.8) and stated that the outcome justifies the extra effort (4.4). Lowest agreement was reported for the robustness against external perturbations (2.8). Conclusions: The described combination of optical tracking technology with an automatic MRI registration appears to be sufficiently accurate for instrument guidance in a standard (closed-bore) MRI environment. High targeting accuracy and usability was demonstrated on a relatively large number of procedures and operators. Between groups with different expertise there were significant differences in experimental procedure times but not in the number of successful biopsies.

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.

Introduction The goal of this work is to advance the production and use of 52Mn (t½ = 5.6 d, β+: 242 keV, 29.6%) as a radioisotope for in vivo preclinical nuclear imaging. More specifically, the aims of this study were: (1) to measure the excitation function for the natCr(p,n)52Mn reaction at low energies to verify past results [1–4]; (2) to measure binding constants of Mn(II) to aid the design of a method for isolation of Mn from an irradiated Cr target via ion-exchange chromatography, building upon previously published methods [1,2,5–7]; and (3) to perform phantom imaging by positron emission tomography/magnetic resonance (PET/MR) imaging with 52Mn and non-radioactive Mn(II), since Mn has potential dual-modality benefits that are beginning to be investigated [8]. Material and Methods Thin foils of Cr metal are not available commercially, so we fabricated these in a manner similar to that reported by Tanaka and Furukawa [9]. natCr was electroplated onto Cu discs in an industrial-scale electroplating bath, and then the Cu backing was digested by nitric acid (HNO3). The remaining thin Cr discs (~1 cm diameter) were weighed to determine their thickness (~ 75–85 μm) and arranged into stacked foil targets, along with ~25 μm thick Cu monitor foils. These targets were bombarded with ~15 MeV protons for 1–2 min at ~1–2 μA from a CS-15 cyclotron (The Cyclotron Corporation, Berkeley, CA, USA). The beamline was perpendicular to the foils, which were held in a machined 6061-T6 aluminum alloy target holder. The target holder was mounted in a solid target station with front cooling by a jet of He gas and rear cooling by circulating chilled water (T ≈ 2–5 °C). Following bombardment, these targets were disassembled and the radioisotope products in each foil were counted using a high-purity Ge (HPGe) detector. Cross-sections were calculated for the natCr(p,n)52Mn reaction. Binding constants of Mn(II) were measured by incubating 54Mn(II) (t½ = 312 d) dichloride with anion- or cation-exchange resin (AG 1-X8 (Cl− form) or AG 50W-X8 (H+ form), respectively; both: 200–400 mesh; Bio-Rad, Hercules, CA) in hydrochloric acid (HCl) ranging from 10 mM-8 M (anion-exchange) and from 1 mM-1 M (cation-exchange) or in sulfuric acid (H2SO4) ranging from 10 mM-8 M on cation-exchange resin only. The amount of unbound 54Mn(II) was measured using a gamma counter, and binding constants (KD) were calculated for the various concentrations on both types of ion-exchange resin. We have used the unseparated product for preliminary PET and PET/MR imaging. natCr metal was bombarded and then digested in HCl, resulting in a solution of Cr(III)Cl3 and 52Mn(II)Cl2. This solution was diluted and imaged in a glass scintillation vial using a microPET (Siemens, Munich, Germany) small animal PET scanner. The signal was corrected for abundant cascade gamma-radiation from 52Mn that could cause random false coincidence events to be detected, and then the image was reconstructed by filtered back-projection. Additionally, we have used the digested target to spike non-radioactive Mn(II)Cl2 solutions for simultaneous PET/MR phantom imaging using a Biograph mMR (Siemens) clinical scanner. The phantom consisted of a 4×4 matrix of 15 mL conical tubes containing 10 mL each of 0, 0.5, 1.0, and 2.0 mM concentrations of non-radioactive Mn(II)Cl2 with 0, 7, 14, and 27 μCi (at start of PET acquisition) of 52Mn(II)Cl2 from the digested target added. The concentrations were based on previous MR studies that measured spin-lattice relaxation time (T1) versus concentration of Mn(II), and the activities were based on calculations for predicted count rate in the scanner. The PET/MR imaging consisted of a series of two-dimensional inversion-recovery turbo spin echo (2D-IR-TSE) MR sequences (TE = 12 ms; TR = 3,000 ms) with a wide range of inversion times (TI) from 23–2,930 ms with real-component acquisition, as well as a 30 min. list-mode PET acquisition that was reconstructed as one static frame by 3-D ordered subset expectation maximization (3D-OSEM). Attenuation correction was performed based on a two-point Dixon (2PD) MR sequence. The DICOM image files were loaded, co-registered, and windowed using the Inveon Research Workplace software (Siemens).

Adequate placental function is essential for the growth and development of a healthy fetus. A major cause of abnormal placental function is thought to occur from inadequate maternal spiral artery remodelling, leading to maternal vascular malperfusion (MVM) of the placenta and ultimately fetal growth restriction (FGR) and stillbirth due to uteroplacental hypoxia. Current methods of investigating a pregnancy at risk of FGR rely on ultrasound estimations of fetal size and Doppler studies. A more informative measure may be to quantify placental function in-vivo. Magnetic resonance imaging (MRI) has the ability to assess placental oxygen saturation (sO2), using Blood Oxygen-Level Dependent (BOLD), and the partial pressure of oxygen (pO2) using Oxygen-Enhanced MRI (OE MRI). These MRI techniques have been shown to correlate with gestation and poor pregnancy outcomes in cross sectional studies. MRI measures of placental oxygenation are hypothesised to be a potential antenatal tool for the identification and stratification of high risk pregnancies at risk of FGR related to uteroplacental hypoxia. To address this hypothesis changes in placental oxygenation, following maternal hyperoxia, were calculated in normal and FGR pregnancies in a cross sectional study. The change in placental oxygenation was reproduced longitudinally to determine if the rate of change differed between normal and FGR pregnancies. Baseline placental MRI parameters (R1 and R2*) and measures of the change in oxygenation were incorporated into a diagnostic model to identify FGR related to uteroplacental hypoxia, which was provisionally tested in a group of high risk pregnancies to demonstrate its potential clinical utility. Placental measures of baseline R1 and R2* were significantly increased in FGR pregnancies. The change in placental pO2 following hyperoxia was found to be significantly lower in FGR pregnancies. The change in pO2 declined similarly with gestation in both cross sectional and longitudinal studies, in normal and FGR pregnancies. There were no significant correlations in the change in placental sO2 with gestation or pregnancy outcome. The use of a diagnostic model combining baseline R1 and R2* and pO2 measures identified FGR with a high specificity, and provided additional information to aid in disease stratification and decision making in a significant proportion of the high risk pregnancies tested. In conclusion, MRI parameters of placental pO2 following hyperoxia are significantly lower in FGR pregnancies, in keeping with the concept of uteroplacental hypoxia. MRI techniques show promise in the identification of FGR pregnancies related to MVM through measures of placental function, irrespective of fetal size, and may aid in the disease stratification of high risk pregnancies.

Este trabalho consistiu na implementação de um método de homogeneização de campo, denominado shimming passivo. Esse método é caracterizado pela inserção de pequenas peças ferromagnéticas no interior do magneto; a interação destas peças com o campo magnético principal produz campos locais capazes de corrigir inomogeneidades indesejadas, quando várias peças são estrategicamente combinadas. Embora esse método já tenha sido bem discutido, implementado e publicado por D.I.Hoult na década de 80, ele ainda não havia sido desenvolvido para um magneto resistivo com núcleo de ferro e peças polares, como é o caso do Artro-ToRM. Nosso objetivo era, através do Artro-ToRM, encontrar uma metodologia de modelagem e correção de campo que fosse útil para magnetos com a mesma geometria. Foram utilizados métodos computacionais de ajuste numérico que, a partir de mapas originais de campo, foram capazes de encontrar configurações de peças magnéticas que pudessem reduzir as inomogeneidades presentes. Um dos maiores desafios do trabalho, foi encontrarmos elementos passivos com comportamento previsível quando submetidos ao campo magnético principal, já que os programas de otimização presupunham que trabalhávamos com dipolos magnéticos, para efeitos de simplificação. Finalmente, considerando uma região cilíndrica com raio de 5 cm e comprimento de 10 cm, mostramos uma melhora de 390 ppm para 250 ppm na homogeneidade, após a correção passiva. / This work presents the implementation of a method for field correction, called passive shimming. The method is characterized by the insertion of small iron pieces in magnet bore; the interaction of these pieces with the main magnetic field produces local fields capable of correcting undesired inhomogenity, when some parts are strategically combined. Although this method has been already proposed by D.I.Hoult in the eighties, it still has not been developed for resistive magnets with polar pieces, such as the Artro-ToRM. Our objective were to find a method for field modeling and correction that could be useful for magnets with similar geometry. Computational methods of numerical adjustment were used from the original field maps, it was possible to find the optimal the configurations of magnetic parts for reducing the field inhomogenity. One of the biggest challenges of the work, was to find passive elements with previsible behavior when submitted to magnetic field main, since the optimization programs preassumed that we worked with magnetic dipoles, for the purpose of simplification. Finally, considering a cilindrical region, we show an improvement of 390 ppm to 250 ppm in the homogenity, after the passive correction.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20981号 / 医博第4327号 / 新制||医||1026(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 増永 慎一郎, 教授 辻川 明孝, 教授 溝脇 尚志 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

No description available.

Yes / Introduction : Rheumatoid arthritis (RA) affects 1% of the population and is principally associated with joint inflammation. It is suggested however that muscle involvement may be one of the earliest clinical features of RA. It is therefore important that techniques exist to accurately assess muscle health in those with RA to enable successful treatment. This study assesses the inter-rater and intra-rater repeatability of Diffusion Tensor MRI (DTI), 2-Point Dixon fat fraction, and T2 relaxation of the thigh muscle in patients with RA using manual regions of interest (ROI). Methods: Nineteen patients (10/19 males; mean age 59; range 18-85) diagnosed with RA had an MRI scan of their hamstrings and quadriceps muscles to obtain fat fraction (FF), mean diffusivity (MD), fractional anisotropy (FA), and T2 quantitative measurements. Two raters (R#1 & R#2) (initials removed for review) independently contoured ROIs for each patient. R#1 repeated the ROI for the same 19 patients after a 6-month hiatus to assess intra-rater repeatability. Inter-rater and intra-rater repeatability for the ROI measurements were compared using Inter Class Correlation (ICC) and Bland-Altman plots. Results: There was excellent agreement for both inter-rater and intra-rater repeatability. ICC results ranged from 0.900-0.998 (P<0.001), and intra-rater ICC results ranged from 0.977-0.999 (P<0.001). Bland-Altman plots also showed excellent agreement. Conclusions: ICC measurements and Bland-Altman plots showed excellent repeatability and agreement with no statistically significant differences when assessing the inter-rater and intra-rater repeatability of FF, MD, FA, and T2 relaxation of the thigh muscle using manual regions of interest in patients with RA. Implications for practice: Manual ROI drawing does not introduce significant errors obtaining FF, MD, FA, and T2 MRI measurements in an RA population. / This research is funded by the NIHR infrastructure at Leeds.

Although they share a number of clinical features, autism and schizophrenia are usually distinguished by their different ages of onset and certain discriminating features such as major impairments to communication in the former and positive psychotic symptoms in the latter. However, the recognition that these conditions are part of broader spectrums of impairment has led to the definition of disorders which do not show such marked and discriminating features, such as autism spectrum disorders (ASD) and schizotypal personality disorder (SPD). Reviewing the historical development of these concepts and areas of potential overlap or difference between them revealed that they have both shared and discriminating features, but no study to date has directly compared them. Three experiments were therefore conducted to compare ASD and SPD using clinical, neuropsychological and functional magnetic resonance imaging (fMRI) techniques. In the clinical experiment, standardised measures were used to determine if it was possible to distinguish between the groups, and to allow their quantitative comparison. It was possible to distinguish between ASD and SPD in most cases, although 17% of the population tested met criteria for both conditions. This ‘comorbid’ (CM) group were therefore considered separately. When a single diagnosis could be allocated, there were clear overlaps of clinical features between the conditions and each condition showed more traits of the other than were seen in controls. The overlaps were most prominent for negative schizotypal traits which did not differ between the groups. The CM group were more affected than either the ASD or SPD groups across multiple domains. All groups had high levels of previously undiagnosed psychopathology. In the neuropsychological experiment, tests of social cognition, executive function and central coherence / local-global processing bias were employed. The similarities between the ASD and SPD groups were striking. Both showed similar evidence of impairment in social cognition and executive function, although there was some evidence of greater impairment in working memory in the ASD group. Differences were seen using a test of local-global processing bias, although these were potentially confounded by differences in general intellectual ability. Two fMRI tasks were conducted: a working memory task (a letter based n-back task) and a social judgment task (where individuals made judgements of either gender or approachability from a picture of a face). The former did not distinguish between the ASD and SPD groups. In the latter, individuals with SPD showed significantly greater activation than the ASD group in several brain regions known to be associated with social cognition, with the controls scoring in-between the two. Although they show marked clinical and brain functional overlaps, the results of the fMRI task of social judgement suggest that it is correct to consider ASD and SPD as separate diagnostic entities. The findings are consistent with the idea that, although both conditions are associated with impairments in understanding the mental states of others (mentalising), the mechanism which underlies these differs between the groups, with ASD associated with hypo-mentalising and SPD associated with hyper-mentalising.

No description available.