Introduction: Magnetic resonance (MR) imaging is one of the most important diagnostic tools in modern medicine. Compared to other imaging modalities, it provides superior soft tissue contrast of all parts of the body and it is considered to be safe for patients. Today almost all MR is performed in a nonquantitative manner, only comparing neighboring tissue in the search for pathology. It is possible to quantify MR-signals and relate them to their physical entities, but time consuming and complicated calibration procedures have prevented this being used in a practical manner for clinical routines. The aim of this work is to develop and improve quantification methods in MRspectroscopy (MRS) and MR-imaging (MRI). The techniques are intended to be applied to diffuse diseases, where conventional imaging methods are unable to perform accurate staging or to reveal metabolic changes associated with disease development. Methods: Proton (1H) MRS was used to characterize the white matter in the brain of multiple sclerosis (MS) patients. Phosphorus (31P) MRS was used to evaluate the energy metabolism in patients with diffuse liver disease. A new quantitative MRI (qMRI) method was invented for accurate, rapid and simultaneous quantification of B1, T1, T2, and proton density. A method for automatic assessment of visceral adipose tissue volume based on an in- and out-ofphase imaging protocol was developed. Finally, a method for quantification of the hepatobiliary uptake of liver specific T1 enhancing contrast agents was demonstrated on healthy subjects. Results: The 1H MRS investigations of white matter in MS-patients revealed a significant correlation between tissue concentrations of Glutamate and Creatine on the one hand and the disease progression rate on the other, as measured using the MSSS. High accuracy, both in vitro and in vivo, of the measured MR-parameters from the qMRI method was observed. 31P MRS showed lower concentrations of phosphodiesters, and a higher metabolic charge in patients with cirrhosis, compared to patients with mild fibrosis and to controls. The adipose tissue quantification method agreed with estimates obtained using manual segmentation, and enabled measurements which were insensitive to partial volume effects. The hepatobiliary uptake of Gd-EOB-DTPA and Gd-BOPTA was significantly correlated in healthy subjects. Conclusion: In this work, new methods for accurate quantification of MR parameters in diffuse diseases in the liver and the brain were demonstrated. Several applications were shown where quantitative MR improves the interpretation of observed signal changes in MRI and MRS in relation to underlying differences in physiology and pathophysiology.

In radiotherapy, cancer is treated with ionizing radiation, most commonly bremsstrahlung photons from electrons of several MeV. Secondary electrons produced in photon-interactions results in dose deposition. The treatment response is low for low doses, raises sharply for normal treatment doses and saturates at higher doses. This response pattern applies to both eradication of tumors and to complications in healthy tissues. Well controlled treatments require accurate dosimetry since the uncertainty in delivered dose will be magnified 1 to 5 times in treatment response variations. Techniques that superpose many small radiation fields to concentrate the dose to a localized target are becoming increasingly used. A detector with high spatial resolution suitable for such fields is a silicon diode. To maintain the current accuracy of the dosimetric calibration of 1.5%, diode measurements relative to this calibration should preferably be possible at 0.5% accuracy level. The main limitation of silicon diodes is their over-response to low-energy photons. This problem has been adressed with the insertion of a high atomic number filter in diodes. For modeling diode detector response one must quantify the spectral variations in the irradiated medium resulting from variations of the beam parameters. This requires understanding of the particle transport and can be achieved by Monte Carlo simulations. However, the small dimensions of the detector geometry compared to surrounding medium makes a direct application of Monte Carlo impractical due to the large amount of CPU time necessary to reach statistically satisfactory results. In this work a fast method for spectra calculations is used, based on superposition of mono-energetic fluence pencil kernels. Building on this base a general model for silicon response functions in photon fields is developed. The incident photons are bipartitioned into a low and a high energy component. The high energy part is treated with the Spencer-Attic cavity theory while the low energy part and scattered photons are treated with large cavity theory. The deviations from electron equilibrium are investigated and handled with correction factors. The result is used to correct unshielded diode measurements, with an overall uncertainty less than 0.5%, except for very small fields where the precision is around 1-2%, thus eliminating the need for less predictable shielded diodes for measurements in photon fields.

BACKGROUND: Because of superior soft tissue contrast, the use of magnetic resonance imaging (MRI) as a complement to computed tomography (CT) in the target definition procedure for radiotherapy is increasing. To keep the workflow simple and cost effective and to reduce patient dose, it is natural to strive for a treatment planning procedure based entirely on MRI. In the present study, we investigate the dose calculation accuracy for different treatment regions when using bulk density assignments on MRI data and compare it to treatment planning that uses CT data. METHODS: MR and CT data were collected retrospectively for 40 patients with prostate, lung, head and neck, or brain cancers. Comparisons were made between calculations on CT data with and without inhomogeneity corrections and on MRI or CT data with bulk density assignments. The bulk densities were assigned using manual segmentation of tissue, bone, lung, and air cavities. RESULTS: The deviations between calculations on CT data with inhomogeneity correction and on bulk density assigned MR data were small. The maximum difference in the number of monitor units required to reach the prescribed dose was 1.6%. This result also includes effects of possible geometrical distortions. CONCLUSIONS: The dose calculation accuracy at the investigated treatment sites is not significantly compromised when using MRI data when adequate bulk density assignments are made. With respect to treatment planning, MRI can replace CT in all steps of the treatment workflow, reducing the radiation exposure to the patient, removing any systematic registration errors that may occur when combining MR and CT, and decreasing time and cost for the extra CT investigation.

Dose assessments produced using the computer code MCNP are important to simulate events that are difficult to recreate experimentally. An emergency scenario involving whole-body skin contamination is one example of such an event. For these scenarios, an anthropomorphic phantom of a 10-year-old male with uniform skin contamination was created and combined with MCNP for dose calculations. Activity on the skin was modeled with gamma-ray sources at energies of 50 keV, 100 keV, 250 keV, 500 keV, 750 keV, 1 MeV, 1.25 MeV, 1.5 MeV, and 2 MeV. The radionuclides 60Co, 137Cs, and 131I were also modeled. The effective dose to the body and major organs was calculated for each scenario. Exposure rate contour lines were also produced around the body. The activity required to result in a dose equal to the legal limit of 0.1 mSv for minors was calculated for each scenario. The highest activity required to produce this limit was from the 50 keV gamma-ray source. This activity was increased by an arbitrary value, approximately tenfold the current value, to represent an emergency scenario. This new activity concentration of 1 mCi per 100 cm2 was used to produce doses for each of the scenarios. The lowest effective dose for the body was 0.82 mSv, produced from the 50 keV source. The highest effective dose was 19.59 mSv, produced from the 2 MeV source. The exposure rates nearest the body were approximately 1.25 R/h, decreasing to100 mR/h approximately 60 cm from the body. The data points were found to be dependent on the energy of the gamma ray. These data can also be improved by deriving solutions previously assumed in this scenario. For example, the skin may be broken down into multiple regions to allow for independent calculations for regional contamination. The activity on the skin can also be derived from air concentration models, allowing for the use of other models to be used in conjunction with this research.

No description available.

Magister Chirurgiae Dentium (MChD) / Robinson and Martinez first introduced the entity of unicystic ameloblastoma in 1977. Since then numerous case reports and series have been published. The evidence suggests that a more conservative approach can be used successfully to treat the unicystic ameloblastoma. The term unicystic is derived from the macro- and microscopic appearance of the lesion, whereas the term unilocular is used in radiological interpretation to describe a radiolucency having one loculus or compartment. Much confusion stems from the fact that a unicystic ameloblastoma might appear not only as a unilocular lesion, but also as what is often interpreted as a multilocular bone defect.

Radiation therapy is an important method to treat cancer with the aim to deliver as high doses as reasonably achievable to the tumor while protecting the surrounding healthy tissue and organs at risk, OARs. Therefore, it is essential to have high accuracy in the dose delivered clinically and quality assurances are required. In the meantime, radiation therapy techniques are becoming more advanced and complex, introducing a significant risk of random and systematic errors that needs to be investigated. Hence, the need of independent dose verifications has increased. The purpose of the present work is to design and create a mailed audit system for external evaluation of the dose to water in relevant points in a phantom, including influences from the whole treatment chain, from computed tomography, CT, scanning, to contouring of structures, treatment planning and treatment delivery. The measurements were performed using an anthropomorphic Polymethyl methacrylate, PMMA, phantom designed to be relevant for the head-and-neck region containing inserts corresponding to tumour, salivary glands and medulla made of PMMA and that are easily distinguishable from the surroundings for contouring. Inhomogeneities of both Teflon, corresponding to the spinal cord, and air were also included. Pellet shaped electron paramagnetic resonance, EPR, dosimeters made of lithium formate with a diameter of 4.5 mm and height of 5 mm were made for the measurements. The dosimeters can be placed in various positions in the different structures of the phantom using PMMA tubes and can be analyzed using a spectrometer. In order to test the precision and accuracy of the EPR dosimetry method, measurements with three blind tests were performed simultaneously with an ionization chamber for comparison of absorbed doses. For the audit measurement, the audit phantom was CT scanned twice both with a Siemens CT scan and GE (General Electric)) CT scan for comparison of Hounsfield Units, HU, and dose distributions. The target and the OARs were contoured in the treatment planning system, TPS, (Varian, Eclipse) and a dynamic Intensity modulated radiation therapy, IMRT, treatment plan was created. The treatment plan consisted of seven coplanar 6 MV fields giving the target a dose of 5 Gy delivered with a Varian, Clinac iX accelerator. The absorbed doses to water were determined in seven locations: three points in the target, one in each parotis, one in the medulla and one in the air cavity. The absorbed doses were determined using the signal from the EPR dosimeters and were compared to the planned doses. Also, the measured and reconstructed volumes of the structures were compared. The blind tests doses obtained from the EPR dosimeters agreed with the results obtained from the ionization chamber within 1% and are well below the calculated uncertainties (1 SD) in the EPR measurements. The absorbed doses and the dose distributions were not affected by any spread in HU and the absorbed doses had an agreement within 0.5% in comparison between the Siemens and GE CT studies. The determined doses agreed with planned doses within 4% for all the structures except the air cavity. This deviation is not covered by the calculated standard uncertainty. However, the deviation does fall within two standard deviations, corresponding to a confidence interval of 95%. Also the measured and planned volumes had an agreement within 2.5% for smaller structures and within 5% for larger structures. Repeating the whole measurement chain with other dosimeter batches is required using two or three dosimeters in each measurement point for higher precision. A conclusion can be made that this work showed promising initial results for an audit system for evaluation of the dose to water in relevant points in a phantom, including influences from the whole treatment chain.

Com a liberação do uso da energia nuclear para aplicações pacíficas, a Comissão Internacional de Proteção Radiológica, CIPR, fundada em 1928, criou em 1958 um sistema de proteção às doses de radiação ionizante indesejáveis causadas aos trabalhadores, indivíduos de público e meio-ambiente para viabilizar a introdução dessas aplicações. Esse sistema de proteção é adotado pelo Organismo Internacional de Energia Atômica, OIEA, que publica recomendações em séries de segurança, SS e pela Comissão Nacional de Energia Nuclear, CNEN, que publica regulamentações em normas. Essas recomendações internacionais e regulamentações nacionais passaram por adaptações e necessitam ser aplicadas dessa forma. O presente trabalho utiliza recomendações da publicação 75 da CIPR, da publicação 115 da SS e regulamentações da norma NN 3.01 da CNEN para apresentar, através de medidas de radioproteção, o controle das doses de radiação ionizante para trabalhadores em uma instalação radiativa que trabalha com pesquisa, produção, fracionamento e embalagem de fontes não-seladas para uso clínico. Dessa forma, é possível prevenir adequadamente as doses indesejáveis e confirmar as doses recebidas. / With the liberation of the use of the nuclear energy for peaceful applications, International Commission Radiological Protection, ICRP, founded in 1928, created a system of protection of the undesirable doses of ionizing radiation in 1958. This has been received by workers, members of the public and environment and hence it became possible for the introduction of these applications. This protection system is adopted by the International Agency of Energy Atomic, IAEA, that publishes recommendations in safety series, SS and by the Comissão Nacional de Energia Nuclear, CNEN, which publishes these regulations. The international recommendations and national regulations were adapted and they need to be applied in this way. The present paper uses recommendations of the publication 75 from ICRP, of the publication 115 from SS and regulations of the regulation NN 3.01 from CNEN to present, through radiological protection measures, the ionizing radiation dose control for workers in a nuclear plant that works in the research, production, division and packing of unsealed sources to be used in clinical applications. In that way it is possible to prevent appropriately the undesirable doses and to confirm the received doses.

<p>In order to improve the diagnosis of coronary artery disease, better methods for detection of myocardial perfusion defects would be useful. One of the methods used for myocardial perfusion evaluation today is magnetic resonance imaging. </p><p>This method could be improved if a contrast agent that induced long-lasting contrast enhancement in the myocardium could be developed. The paramagnetic manganese(II) ion has promising properties for meeting this need, since it enters cardiomyocytes through voltage-gated calcium channels and remains inside the cells for a long time after an intravenous injection. If these properties can be utilized, manganese-enhanced MRI has potential for detecting transient periods of ischemia in a manner similar to the conventional SPECT stress test.</p><p>To investigate the contrast-enhancing properties of the manganese(II) ion, a series of experiments was performed in pigs, using a manganese salt (MnCl₂) and two manganese-based chelates (MnDPDP and MnHPTA) and measuring the longitudinal relaxation rates before and after contrast agent administration. This was done in normal pig myocardium at rest and during dobutamine-induced stress with several different doses of contrast agent, and in a model for coronary artery stenosis using MnCl₂ administered during dobutamine stress to determine whether transient ischemia could be detected with this contrast agent.</p><p>The results of these experiments showed that of the three contrast agents, MnCl₂ induces the greatest increase in ΔR1, followed by MnHPTA. Using MnCl₂ it was possible to produce images on which transient myocardial ischemia was visible, but only during the first 30 minutes after contrast agent injection.</p><p>The stenosis model is still far from the clinical situation and several complications, including the potential toxicity of the manganese(II) ion, remain to be overcome. However, the results from this model are promising for the future development of manganese- enhanced magnetic resonance imaging of transient myocardial ischemia.</p>

In order to improve the diagnosis of coronary artery disease, better methods for detection of myocardial perfusion defects would be useful. One of the methods used for myocardial perfusion evaluation today is magnetic resonance imaging. This method could be improved if a contrast agent that induced long-lasting contrast enhancement in the myocardium could be developed. The paramagnetic manganese(II) ion has promising properties for meeting this need, since it enters cardiomyocytes through voltage-gated calcium channels and remains inside the cells for a long time after an intravenous injection. If these properties can be utilized, manganese-enhanced MRI has potential for detecting transient periods of ischemia in a manner similar to the conventional SPECT stress test. To investigate the contrast-enhancing properties of the manganese(II) ion, a series of experiments was performed in pigs, using a manganese salt (MnCl2) and two manganese-based chelates (MnDPDP and MnHPTA) and measuring the longitudinal relaxation rates before and after contrast agent administration. This was done in normal pig myocardium at rest and during dobutamine-induced stress with several different doses of contrast agent, and in a model for coronary artery stenosis using MnCl2 administered during dobutamine stress to determine whether transient ischemia could be detected with this contrast agent. The results of these experiments showed that of the three contrast agents, MnCl2 induces the greatest increase in ΔR1, followed by MnHPTA. Using MnCl2 it was possible to produce images on which transient myocardial ischemia was visible, but only during the first 30 minutes after contrast agent injection. The stenosis model is still far from the clinical situation and several complications, including the potential toxicity of the manganese(II) ion, remain to be overcome. However, the results from this model are promising for the future development of manganese- enhanced magnetic resonance imaging of transient myocardial ischemia.