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Magnetic response image plane nonuniformity and stochastic noise are properties that greatly influence the outcome of quantitative magnetic resonance imaging (MRI) evaluations such as gel dosimetry measurements using MRI. To study these properties, robust and accurate image analysis methods are required. New nonuniformity level assessment methods were designed, since previous methods were found to
A safe and reproducible mixing procedure for the manufacture of a polymerization-based dosemeter gel evaluated using MRI (PoMRI) is presented. The dose response, obtained by irradiating gel-filled vials with absorbed doses in the interval 0-20 Gy and evaluated with respect to 1/T2, was found to be linear in the interval 0-8 Gy, with a sensitivity of 0.211 s-1Gy-1 (r2 = 0.998) at 1.5 T. Evaluation
MR image nonuniformity can vary significantly with the spin-echo pulse sequence repetition time. When MR images with different nonuniformity shapes are used in a T1-calculation the resulting T1-image becomes nonuniform. As shown in this work the uniformity TR-dependence of the spin-echo pulse sequence is a critical property for T1 measurements in general and for ferrous sulfate dosimeter gel (FeGe
A method for analysing and comparing treatment planning system (TPS) data and ferrous dosimeter gel measurements evaluated with MRI (FeMRI) was developed, including image processing to final absorbed dose images. Measurements were analysed according to this method and FeMRI data were thereby compared with the TPS-calculated dose distribution. For photons, differences between FeMRI- and TPS dose da
A ferrous gel, based on ferrous (Fe) sulphate and agarose, was used with a clinical magnetic resonance imaging (MRI) scanner to obtain relative dose distribution data from therapeutic photon and electron beams. The FeMRI gel was scanned using a new MRI acquisition protocol optimized for T1 measurements. Thorough comparisons with silicon semiconductor detector and ionization chamber measurements, a
A dosimeter gel, based on an agarose gel infused with a ferrous sulphate solution and evaluated in a magnetic resonance scanner, was used for complete verification of calculated dose distributions. Two standard treatment procedures, treatment of cancer in the urinary bladder and treatment of breast cancer after modified radical mastectomy, were examined using pixel-by-pixel and dose volume histogr
A new method has been investigated for the mapping of dose distributions in three dimensions delivered by the Leksell gamma knife. The irradiation unit is used to selectively treat small volumes in the brain with single high doses of ionising radiation--a treatment procedure known as radiosurgery. The dosimetry method investigated utilises a dosimeter gel consisting of ferrous sulphate solution an
A method for the production of a tissue-mimicking phantom material for MR imaging is described. The material consists of a nickel-doped agarose gel. The T1 and T2 values of the gel can be varied independently by changing the relative amounts of nickel and agarose. Practically any T1 and T2 combination of clinical interest can be obtained. The long-term stability was studied and found to be good. T
The measurement of absorbed dose distributions using dosemeter gel and magnetic resonance imaging (MRI) in a standard geometry has been investigated. Absorbed depth-dose curves and profiles measured with this new technique show good agreement with corresponding measurements using diodes. This was proven in a 60Co beam as well as an electron beam. The dosemeter gel is made of agarose and ferrous su
When a pinhole collimator is to be used for tomographic studies the standard SPECT software has to be modified so as to avoid serious image distortion outside the axis of rotation. The MTF measured at the axis of rotation shows that the better resolution of the pinhole collimator as compared with that of a parallel-hole collimator improves the tomographic image. The low sensitivity of the pinhole
In 50 patients with primary hyperparathyroidism, investigation before initial neck exploration included ultrasonography, computed tomography and 99technetium-201thallium subtraction scintigraphy. The sensitivity for correct preoperative localization was 50%, 54% and 56%, respectively. There was marked inter-observer variation in assessment of ultrasonography and computed tomography, while scintigr
Two gels have been found to be suitable to load with ferrous sulphate solution. In these soft tissue equivalent phantoms, the absorbed dose distribution can be measured after irradiation in clinically used MR imaging equipment. The present studies were carried out using a 0.25 T NMR analyser without imaging properties. A ferrous sulphate solution, 0.05 M with respect to sulphuric acid, can be gell
Activation products which contribute significantly to the exposure of the staff operating the accelerator were found in the accelerator head in the transparent holder for the lead blocks and in the 60 degrees wedge filter made of lead. A proper choice of material in these parts of the accelerator could easily reduce this exposure without excessive changes in the construction. The absorbed dose-rat
BACKGROUND: Ulcerative colitis and Crohn's disease are the major chronic inflammatory bowel diseases affecting the gastrointestinal tract in humans. Imaging techniques such as endoscopy and computed tomography are used to monitor disease activity. Magnetic resonance imaging (MRI) is emerging as a diagnostic modality, and studies have shown that MRI can be used in the diagnostic procedure of patien
The purpose of this research was to investigate the geometrical accuracy of magnetic resonance (MR) images used in the radiation therapy treatment planning for lung cancer. In this study, the capability of MR imaging to acquire dynamic two-dimensional images was explored to access the motion of lung tumors. Due to a number of factors, including the use of a large field-of-view for the thorax, MR i
