| 1. |
- Johansson, Edvin, et al.
(författare)
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Gradient echo imaging of flowing hyperpolarized nuclei : theory and phantom studies on 129Xe dissolved in ethanol
- 2002
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Ingår i: Journal of Magnetic Resonance. - 1090-7807 .- 1096-0856. ; 159:1, s. 68-75
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Tidskriftsartikel (refereegranskat)abstract
- The influence of flip angle and flow velocity on the signal intensity achieved when imaging a hyperpolarized substance with a spoiled gradient echo sequence was investigated. The study was performed both theoretically and experimentally using hyperpolarized xenon dissolved in ethanol. Analytical expressions regarding the optimal flip angle with respect to signal and the corresponding signal level are presented and comparisons with thermally polarized substances are made. Both experimentally and theoretically, the optimal flip angle was found to increase with increasing flow velocity. Numerical calculations showed that the velocity dependence of the signal differs between the cases of hyperpolarized and thermally polarized substances.
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| 2. |
- Johansson, Edvin, et al.
(författare)
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Perfusion assessment with bolus differentiation : a technique applicable to hyperpolarized tracers
- 2004
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 52:5, s. 51-1043
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Tidskriftsartikel (refereegranskat)abstract
- A new technique for assessing tissue blood flow using hyperpolarized tracers, based on the fact that the magnetization of a hyperpolarized substance can be destroyed permanently, is described. Assessments of blood flow with this technique are inherently insensitive to arterial delay and dispersion, and allow for quantification of the transit time and dispersion in the arteries that supply the investigated tissue. Renal cortical blood flow was studied in six rabbits using a 13C-labeled compound (2-hydroxyethylacrylate) that was polarized by the parahydrogen-induced polarization (PHIP) technique. The renal cortical blood flow was estimated to be 5.7/5.4 +/- 1.6/1.3 ml/min per milliliter of tissue (mean +/- SD, right/left kidney), and the mean transit time and dispersion in the renal arteries were determined to be 1.47/1.42 +/- 0.07/0.07 s and 1.78/1.93 +/- 0.40/0.42 s2, respectively.
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| 3. |
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| 4. |
- Månsson, S, et al.
(författare)
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Echo-planar MR imaging of dissolved hyperpolarized 129Xe : Potential for MR angiography
- 2002
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Ingår i: Acta Radiologica. - : SAGE Publications. - 0284-1851 .- 1600-0455. ; 43:5, s. 60-455
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The feasibility of hyperpolarized 129Xe for fast MR angiography (MRA) was evaluated using the echo-planar imaging (EPI) technique.MATERIAL AND METHODS: Hyperpolarized Xe gas was dissolved in ethanol, a carrier agent with high solubility for Xe (Ostwald solubility coefficient 2.5) and long relaxation times. The dissolved Xe was injected as a bolus into a flow phantom where the mean flow velocity was 15 cm/s. Ultrafast EPI images with 44 ms scan time were acquired of the flowing bolus and the signal-to-noise ratios (SNR) were measured.RESULTS: The relaxation times of hyperpolarized Xe in ethanol were measured to T1=160+/-11 s and T2 approximately 20 s. The resulting images of the flowing liquid were of reasonable quality and had an SNR of about 70.CONCLUSION: Based on the SNR of the obtained Xe EPI images, it was estimated that rapid in vivo MRA with 129Xe may be feasible, provided that an efficient, biologically acceptable carrier for Xe can be found and polarization levels of more than 25% can be achieved in isotopically enriched 129Xe.
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| 5. |
- Tingberg, Anders, et al.
(författare)
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Evaluation of lumbar spine images with added pathology
- 2000
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Ingår i: Proceedings of SPIE. - : SPIE. - 0819435988 ; 3981, s. 34-42
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Konferensbidrag (refereegranskat)abstract
- Optimisation of radiographic procedures require solid tools for evaluation of the image quality in order to ensure that it is sufficient to answer the clinical question at the lowest possible absorbed dose to the patient. Lumbar spine radiography is an examination giving a relatively high dose and good methods for evaluation of image quality as well as dose are needed. We have developed and used a method for the addition of artificial pathological structures into clinical images. The new images were evaluated in a study of detectability (free-response forced error experiment). The results from the study showed that the methodology can be used to detect differences in the screen-film systems used to produce the images, indicating that the method can be used in a study of image quality. The results of the study of detectability were compared with the outcome of a visual grading analysis based on the structures mentioned in the European Quality Criteria. The comparison indicated that a linear correlation exists between the two methods. This means that the simpler VGA can be used in the evaluation of clinical image quality.
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