Dental magnetic resonance imaging

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Trabecular Bone Assessment Using Magnetic-Resonance Imaging : A Pilot Study

Trabecular Bone Assessment Using Magnetic-Resonance Imaging : A Pilot Study

Briefly, porcine ribs were prepared by removing soft tissue and periosteum, and then sectioned into bone pieces measuring approximately 3 cm in width. On each sample, a conical perforation was prepared according to the manufacturer instructions using dental-implant surgical drills (Straumann). For this study, dental implants were not placed. Instead, the perforation was used as a reference marker for the determination of the measurement site. All samples were immersed into a 3.5% formaldehyde bath 4 weeks prior to the study.

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Magnetic Resonance Imaging on Patients with Implanted Cardiac Pacemakers

Magnetic Resonance Imaging on Patients with Implanted Cardiac Pacemakers

In 1994, the American Society for Testing and Materials (ASTM) had proposed a stan- dard test method for evaluating the effects of passive implants on MR images [5]. For small objects like dental implants made of titanium or gold, Klock et al. were able to show translational forces on orthodontic wires, that were 9.1–27.6 times higher than normal gravity [6]. Compared to the low weight of the wires, the effect was regarded as not hazardous. Regier et al. evaluated the heating near fixed orthodontic appliances in a 3 Tesla environment, but they only found miniature temperature changes of –0.3 to +0.2 ◦ C degrees, which was seen as not dangerous at all for the patient [7]. One publica- tion covering dental implants and their magnetic susceptibility in MRI nevertheless still recommended a per-case evaluation, because most but not all recent tested materials had been unaffected by the RF fields [8].
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Improvements of Magnetic Resonance Imaging techniques for clinical diagnosis
in cerebrovascular disease

Improvements of Magnetic Resonance Imaging techniques for clinical diagnosis in cerebrovascular disease

For Subproject 3 (Publications II and VII), patients were included in a prospective imaging study (7.0 Tesla Ultra-High Field Project, “7UP-Study”, WHO International Clinical Trials Registry No. DRKS00003193, http://apps.who.int/trialsearch/Trial.aspx?TrialID=DRKS00003193). Inclusion criteria were: (1) subacute/chronic ischemia or transitory ischemic attack (TIA), (2) age 18–80 years, (3) ability to give informed consent and (4) legal competence. Exclusion criteria were: (1) cardiac pacemakers or any other electronic implants, (2) any metallic implant, (3) pregnancy or breast feeding period, (4) claustrophobia, (5) chronic or episodic vertigo, (6) retinal diseases and (7) dental bridges and more than two metallic dental crowns in a row. Neurological status was assessed using the National Institute of Health Stroke Scale (NIHSS) at time of admission for index stroke and before MR imaging. Imaging was performed first at 3.0 T, immediately followed by 7.0 T. A neurologist specialized in stroke supervised the patients during MRI. In total, 18 patients were eligible for Publication II and 6 patients for Publication VII, which was performed on the subset of Moya-Moya-patients (n=6).
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Movement model of a human hand based on magnetic resonance imaging (MRI)

Movement model of a human hand based on magnetic resonance imaging (MRI)

1) CT imaging (Computed Tomography) is a medical imaging method employing tomography where digital geometry processing is used to generate a three- dimensional image from a large number of two- dimensional X-ray images taken around a single axis of rotation. The nature of X-ray imaging makes it very well suited for bone imaging, and high-resolution 3D images can be obtained in a matter of seconds or minutes. However, CT relies on ionising radiation, which in high doses can cause cancer. Therefore, we exclude CT from our investigations.

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Foci on breast magnetic resonance imaging in high-risk women: cancer or not?

Foci on breast magnetic resonance imaging in high-risk women: cancer or not?

MRI is also able to detect very small enhancing lesions, with 5 mm or lower maximum diameter, which might be difficult to further characterize. These small lesions are defined by the American College of Radiology Breast Imaging Reporting and Data System (ACR BI-RADS) as foci. A focus is a small dot of enhancement that stands out from parenchymal enhancement. Per definition, foci cannot be accurately assessed with respect to margin or internal enhancement: if these characteristics can be assessed, the finding should be considered a small mass [ 11 ]. Foci are frequently associated with an increased hormonal stimula- tion, and they can sometimes be seen when a benign lesion is present (fibroadenoma, cyst and fibrocystic changes, lymph node), but they can also represent the early onset of a malignant lesion [ 12 , 13 ]. Studies addressing the malig- nancy rate of foci found in the general population showed highly variable results, with percentages ranging from 0.6 to 23 % [ 12 , 14 ]. Thus, the best management of foci is still under discussion. The issue is of particular interest in high-risk women, especially considering the importance of early diagnosis in this group of patients. Despite this, not many studies addressed the frequency of foci detected dur- ing screening MRI in high-risk patients and the malignancy rate of foci in this population.
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Efficient Simulation of Magnetic Resonance Imaging

Efficient Simulation of Magnetic Resonance Imaging

N ow that the simulation methods are described, justified, and exemplified, they can be discussed more generally. The goal of this work is to find efficient and accurate means to simulate full MR imaging experiments. No tool that is currently available is able to handle this task adequately or even attempts to do so. Therefore, the procedures that are defined in the methods chapter should be consid- ered the main result of this work. The common approaches, namely the Direct Bloch equation simulation (see Section 2.1) and extended phase graph algorithm [34], have been used as a starting point and were then further developed to suit the task. That development gave rise to the Sequence Response Kernel approach (see Section 2.4), which is a completely novel and very task-centered way to perform MRI simulation. The potential of this approach was showcased in some derived algorithms (see Sec- tion 3.6).
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Three-dimensional In vivo magnetic resonance imaging (MRI) of mouse facial nerve regeneration

Three-dimensional In vivo magnetic resonance imaging (MRI) of mouse facial nerve regeneration

weighted MRI sequence allowing to longitudinally visualize the same facial nerve branches of an individual mouse before and at several time-points within 3 weeks after injury. In accordance with previous findings, we observed nerve hyperintensity in the MR images after injury. We provide a cellular source for this hyperintensity by performing correlative immunehistological inspection, demonstrating accumulation of fibrotic material and several cell types including immune and Schwann cells in such hyperintense nerve areas. In summary, we provide a novel MRI protocol allowing for longitudinal high-resolution imaging of smallest nerve branches at identical positions in the same animal over several weeks.
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Exploring novel magnetic resonance imaging markers for ischemic stroke in the
application of vessel size imaging and amide proton transfer imaging

Exploring novel magnetic resonance imaging markers for ischemic stroke in the application of vessel size imaging and amide proton transfer imaging

One study has published a quantitative Q assessment in human brain tissue [100]. The Q values in our study are somewhat lower than those found by Jensen et al. [100], in which a triple dose of CA has been administered and only the maximum signal drop points are used to estimate Q. Although such an implementation leads to a smaller underestimation of Q in the circumstance of intrinsic blood paramagnetism, it is not suitable for acute stroke imaging: first, such a high dose of CA is not commonly used in clinical routine; second, maximum signal drops between ischemic and normal tissue are not comparable, as the maximum drop in ischemic tissue is reached much later than in normal tissue with a significantly lower concentration of CA. Therefore, we have fitted the whole dynamic passage for the estimation of Q to achieve a relatively equivalent influence of CA dosage in both the ischemic and the normal tissue. Moreover, linear fitting avoids the accidental errors that often occur in picking a single signal drop.
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Evaluation of multi-parametric Magnetic Resonance Imaging for the detection of
prostate cancer

Evaluation of multi-parametric Magnetic Resonance Imaging for the detection of prostate cancer

Material and Methods: Institutional review board approval and informed consent were obtained in all studies. In the first study ex vivo intact-tissue spectroscopy at 14 T was used to estimate the risk of PCa recurrence after prostate surgery from 48 individual patients. Further in the second study MRI-guided prostate biopsy was performed on 54 patients and diagnostic parameters were calculated for all combinations of T2-weighted imaging with MP-MRI. The third study compared detection rates for PCa from 32 patients with indication for a systematic re-biopsy. These patients underwent 3 T MP-MRI without endorectal coil and subsequent targeted biopsies were performed in MRI/Ultrasound (US) fusion mode followed by a systematic standard transrectal ultrasound (TRUS) guided biopsy.
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Accuracy of various lymph node staging criteria in rectal cancer with magnetic
resonance imaging

Accuracy of various lymph node staging criteria in rectal cancer with magnetic resonance imaging

Die radiologische Befundung der MRT-Untersuchungen im Rahmen unserer Studie erfolgte durch Prof. Taupitz, stellvertretender Leiter der Klinik für Radiologie, CBF, Charité Universitätsmedizin Berlin, denen ich beisaß und sie schriftlich in dem o.g. Formblatt festhielt. Prof. Taupitz stand während der ganzen Zeit der Studie ebenfalls für Rückfragen zur Verfügung und war maßgeblich beteiligt an dem Abschnitt „MR Imaging“ des Material- und Methodenteils der o.g. Publikation. Dr. C. Schmidt führte mich in das radiologische PACS-System ein und wohnte einem Großteil der Auswertungssitzungen durch Prof. Taupitz ebenfalls bei.
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Analysis of functional magnetic resonance imaging time series by independent component analysis

Analysis of functional magnetic resonance imaging time series by independent component analysis

Magnetic resonance tomography (MRT) is based on the principle of magnetic spin reso- nance. Atomic nuclei with odd spin numbers (essentially, an unpaired proton and neutron) have a spin and therefore a magnetic dipole moment. Since the hydrogen nuclei has a rela- tively large magnetic moment and often appears in biological systems, this hydrogen nuclei is used for imaging in humans. In a magnetic field the spins within the tissue all arrange in one of two opposite directions, namely parallel or antiparallel to the magnetic field. Since the parallel arrangement is energetically more efficient the dipoles most frequently arrange in parallel direction. The magnetic dipole moments of the nuclei then precess around the axial field. Precessing is the slow movement of the nuclei around their axes. The frequency with which the dipole moments precess is called the Lamor frequency. This frequency in- creases proportional to the strength of the magnetic field. Common used field strength for human research ranges from 0.5 to 3 Tesla. For comparison, the average earth’s magnetic field is only around 50 µTesla.
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Optimisation of Phase Data Processing for Susceptibility Reconstruction in Magnetic Resonance Imaging

Optimisation of Phase Data Processing for Susceptibility Reconstruction in Magnetic Resonance Imaging

7.4. RECONSTRUCTING SUSCEPTIBILITY DISTRIBUTIONS 7.4 Reconstructing Susceptibility Distributions All strategies for estimating susceptibility distributions in soft tissue are based on the a priori estimation of fieldmaps, and thus on phase imaging. Single-echo GRE measurements are not useful for this aim, since fieldmaps derived of such data may contain deviations from the true field due to unconsidered phase offsets (see Section 6.1). Fieldmaps used for susceptibility recon- struction should at least rely on double-echo, or offset-corrected phase data. Furthermore it is evident, that the estimation of susceptibility requires knowledge of the magnetic field in all spatial dimensions. Ideally, an isotropic sampling of space should be attempted. This is best achieved using an isotropically sampled, full 3D GRE sequence with slab- or non-selective excitation. Sev- eral strategies for the reconstruction of tissue magnetic susceptibility were introduced during the last years. Two main categories can be defined, single and multiple orientation measurements. Furthermore, reconstruction can be performed directly or by using a minimisation approach. All methods presented below use the model of scalar susceptibility (Section 7.3.1), and will be shown in application examples using optimised parametrisation. Parameter optimisation will be discussed later on in Section 7.6. A comprehensive discussion of the current reconstruction techniques and applications for susceptibility imaging in MRI can be found in Reichenbach [ 2012 ].
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Optimisation of Phase Data Processing for Susceptibility Reconstruction in Magnetic Resonance Imaging

Optimisation of Phase Data Processing for Susceptibility Reconstruction in Magnetic Resonance Imaging

7.4. RECONSTRUCTING SUSCEPTIBILITY DISTRIBUTIONS 7.4 Reconstructing Susceptibility Distributions All strategies for estimating susceptibility distributions in soft tissue are based on the a priori estimation of fieldmaps, and thus on phase imaging. Single-echo GRE measurements are not useful for this aim, since fieldmaps derived of such data may contain deviations from the true field due to unconsidered phase offsets (see Section 6.1). Fieldmaps used for susceptibility recon- struction should at least rely on double-echo, or offset-corrected phase data. Furthermore it is evident, that the estimation of susceptibility requires knowledge of the magnetic field in all spatial dimensions. Ideally, an isotropic sampling of space should be attempted. This is best achieved using an isotropically sampled, full 3D GRE sequence with slab- or non-selective excitation. Sev- eral strategies for the reconstruction of tissue magnetic susceptibility were introduced during the last years. Two main categories can be defined, single and multiple orientation measurements. Furthermore, reconstruction can be performed directly or by using a minimisation approach. All methods presented below use the model of scalar susceptibility (Section 7.3.1), and will be shown in application examples using optimised parametrisation. Parameter optimisation will be discussed later on in Section 7.6. A comprehensive discussion of the current reconstruction techniques and applications for susceptibility imaging in MRI can be found in Reichenbach [ 2012 ].
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Development and application of electrical conductivity mapping using magnetic resonance imaging

Development and application of electrical conductivity mapping using magnetic resonance imaging

88 Abstract To develop an imaging modality for the quantification of brain tissue sodium concentration (TSC) calculated from magnetic resonance electrical properties tomography (MR-EPT) based on the correlations between conductivity and sodium concentration in saline solutions. Conductivity maps were reconstructed using the transceive phase of the combined signal at 3T while sodium concentration scans were acquired at 4T both in phantom and in 8 healthy subjects. The brain conductivity and sodium concentration maps were co-registered and normalised to 1mm 152 MNI brain atlas. So-called pseudo tissue sodium maps (pTSC) were generated by performing a linear transform of conductivity maps based on saline solution model at 37°C. Statistical analysis was performed to investigate the discrepancy between pTSC and TSC. A strong linear correlation between pTSC and TSC was found when all brain regions were included (r=0.60, p<0.001). The same trend was found in gray matter (r=0.58, p<0.001) and in white matter (r=0.43, p<0.05), respectively. The slope of the overall linear regression was 0.72, which indicates that pseudo- sodium concentration tends to underestimate TSC values obtained by sodium MRI. Moreover, Bland-Altman analysis revealed that the mean difference between the two methods was ~4mMol/L. The underestimation of pTSC is likely due to the lower water content of brain tissue relative to the saline solution. Despite an overall underestimation compared to sodium MRI, pseudo sodium concentration correlated well with sodium MRI measurement. This provides evidence that sodium ion concentration is the dominant source of electrical conductivity, the latter being accessible with MR-EPT.
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Development of a novel spherical navigator-based motion measurement technique in magnetic resonance imaging

Development of a novel spherical navigator-based motion measurement technique in magnetic resonance imaging

1.1 Motivation MRI is a fascinating example of how physical knowledge can be applied for the good of humanity. In this particular case, the understanding of the physical properties of atomic nuclei and their interactions with external electromagnetic fields enabled the development of a technology for medical imaging. In contrast to other imaging methods, such as, for instance, computed tomography, MRI is entirely non-invasive, meaning that no harm whatsoever is inflicted on the patient. In addition, MRI is an inherently multi-modal imaging technique, because it offers a large variety of different image contrasts providing insights into various aspects of the human body, e. g. anatomical structures or diffusion properties of the brain [3, 4]. These benefits have made MRI one of the most important and widely-used medical imaging techniques in both research and clinics around the world.
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Quantitative magnetic particle imaging

Quantitative magnetic particle imaging

Cellular MPI is of high interest for several biomedical applications such as cell tracking or diagnosis of inflammatory diseases and cancer [ 25 , 31 , 154 , 156 ]. Previous studies characterized magnetic signal changes of MNPs interacting with living cells [ 58 , 62 , 64 , 157 – 160 ]. These effects are caused by several factors including MNP aggregation, "size-filtering" during the cellular uptake and increasing dipole-dipole interactions due to a smaller distance and decreased mobility of the MNPs. In most cases, these signal changes result in a deterioration of the MPI image quality and quantification errors. Section 7.1 focuses on the possibility to incorporate these signal changes in the MPI image reconstruction by using multi-color MPI (see section 2.2.3). The incorporation not only prevents image quality degradations but also allows the extraction of information about the MNP environment. This feature is utilized in combination with the high temporal resolution of MPI to demonstrate the potential for imaging and quantification of MNPs interacting with living cells in section 7.2. Although the experiments are focused on MNPs interacting with cells, the fundamental principle can easily be adapted to include the influence of other environmental factors.
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Comparability of size measurements of the pancreas in magnetic resonance imaging and transabdominal ultrasound

Comparability of size measurements of the pancreas in magnetic resonance imaging and transabdominal ultrasound

The visual plane of the pancreas on ultrasonography may also impact measurements. Some authors have used other approaches such as a sagittal (Niederau et al., 1983) or cranio-caudal view (Pochhammer, Szekessy, Frentzel-Beyme, & Hollstein, 1984) or even an inclined position originating from a transversal view (Kolmannskog, Vatn, Swensen, Aakhus, & Gjone, 1983) instead of anterior –posterior measurements. These inconsistencies of capturing US images bear measurement variations as well, making comparisons of studies more complicated and should be kept in mind by the clinicians when draw- ing conclusions based on imaging results. Although the size of a healthy pancreas is mostly irrelevant in daily clinical routine, the dis- crepancies between US and MRI should not be disregarded, especially in the case of potentially pathological pancreatic lesions.
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Combined Amino Acid Positron Emission Tomography and Advanced Magnetic Resonance Imaging in Glioma Patients

Combined Amino Acid Positron Emission Tomography and Advanced Magnetic Resonance Imaging in Glioma Patients

4. Amino Acid PET and PWI PWI is a non-invasive MRI technique to measure blood flow quantitatively. In Neuro-Oncology, the parameters relative cerebral blood volume (rCBV) and cerebral blood flow (rCBF) are frequently assessed. Most commonly, a gadolinium-based contrast agent is used to assess tissue perfusion. After i.v. injection, the passage of the contrast agent leads to i) a local magnetic field distortion (susceptibility effect) in the vicinity of the vessels causing a signal drop in T2- or T2*-weighted MRI, also called dynamic susceptibility contrast (DSC), or ii) a shortening of T1-relaxation time causing a signal increase in T1-weighted MRI, also called dynamic contrast-enhanced (DCE) MRI. While DSC data requires only the first pass of intravascular contrast agent for assessing tissue perfusion, DCE additionally evaluates information about the continuous accumulation of the contrast agent in the extracellular space. Consequently, the acquisition times for DCE are longer than for DSC.
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Quantitative assessment of the equine hoof using digital radiography and magnetic resonance imaging

Quantitative assessment of the equine hoof using digital radiography and magnetic resonance imaging

Following MR imaging, the distal extremities were sectioned in a sagittal plane using a band saw. (Figure 8 a) Tissue specimens were collected from the distal half of the dorsal hoof wall and lateral, medial and mid-sagittal aspects of the sole. The samples were fixed in 10% neutral-buffered formalin for at least 48 hours, trimmed for paraffin embedding and tissue sectioning. Slides were stained with hematoxylin and eosin and contained the stratum lamellatum and stratum reticulare. Histopathologic evaluation was performed by a board-certified veterinary pathologist to confirm absence of lamellar disease. Only feet without lamellar disease were included in the study.
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Elucidating the ionic liquid distribution in monolithic SILP hydroformylation catalysts by magnetic resonance imaging

Elucidating the ionic liquid distribution in monolithic SILP hydroformylation catalysts by magnetic resonance imaging

Monolithic silicon carbide supported ionic liquid-phase (SILP) Rh-catalysts have very recently been introduced for gas-phase hydroformylation as an important step toward industrial upscaling. This study investigates the monolithic catalyst system in combination with di fferent impregnation procedures with non-invasive magnetic resonance imaging (MRI). The findings were supported by X-ray microtomography (micro-CT) data of the monolithic pore structure and a catalytic performance test of the catalyst system for 1-butene gas-phase hydroformylation. MRI con firmed a homogeneous impregnation of the liquid phase throughout the full cross-section of the cylindrical monoliths. Consistent impregnations from one side to the other of the monoliths were achieved with a stabilizer in the system that helped preventing inhomogeneous rim formation. External in fluences relevant for industrial application, such as long-term storage and temperature exposure, did not a ffect the homogeneous liquid-phase distribution of the catalyst. The work elucidates important parameters to improve liquid-phase catalyst impregnation to obtain e fficient monolithic catalysts for industrial exploitation in gas-phase hydroformylation as well as other important industrial processes.
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