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| 2. |
- Engström, Maria, et al.
(author)
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High Proton Relaxivity for Gadolinium Oxide Nanoparticles
- 2006
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In: Magnetic Resonance Materials in Physics, Biology and Medicine. - : Springer Science and Business Media LLC. - 0968-5243 .- 1352-8661. ; 19:4, s. 180-186
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Journal article (peer-reviewed)abstract
- Objective: Nanosized materials of gadolinium oxide can provide high-contrast enhancement in magnetic resonance imaging (MRI). The objective of the present study was to investigate proton relaxation enhancement by ultrasmall (5 to 10 nm) Gd2O3 nanocrystals.Materials and methods: Gd2O3 nanocrystals were synthesized by a colloidal method and capped with diethylene glycol (DEG). The oxidation state of Gd2O3 was confirmed by X-ray photoelectron spectroscopy. Proton relaxation times were measured with a 1.5-T MRI scanner. The measurements were performed in aqueous solutions and cell culture medium (RPMI).Results: Results showed a considerable relaxivity increase for the Gd2O3–DEG particles compared to Gd-DTPA. Both T 1 and T 2 relaxivities in the presence of Gd2O3–DEG particles were approximately twice the corresponding values for Gd–DTPA in aqueous solution and even larger in RPMI. Higher signal intensity at low concentrations was predicted for the nanoparticle solutions, using experimental data to simulate a T1-weighted spin echo sequence.Conclusion: The study indicates the possibility of obtaining at least doubled relaxivity compared to Gd–DTPA using Gd2O3–DEG nanocrystals as contrast agent. The high T 1 relaxation rate at low concentrations of Gd2O3 nanoparticles is very promising for future studies of contrast agents based on gadolinium-containing nanocrystals.
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| 3. |
- Leupold, Jochen, et al.
(author)
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Fast chemical shift mapping with multiecho balanced SSFP
- 2006
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In: Magma. - : Springer Science and Business Media LLC. - 1352-8661. ; 19:5, s. 267-273
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Journal article (peer-reviewed)abstract
- Object: A method is proposed that provides spectroscopic images with high spatial resolution and moderate spectral resolution at very short total data acquisition times. Materials and methods: Balanced steady-state free precession (bSSFP, TrueFISP, FIESTA, b-FFE) is combined with a multiecho readout gradient and frequency-sensitive reconstruction such as Fourier reconstruction known from echo-planar spectroscopic imaging (EPSI) or matrix inversion. Balanced SSFP imaging requires short repetition times to minimize banding artefacts, thereby restricting the achievable frequency resolution. Results: Two-dimensional (2D) high-resolution spectroscopic images were produced of three H-1 resonances (water, acetone and fat) on phantoms and water/fat separation in vivo within 1-2 s. Additionally, fast P-31 spectroscopic images were acquired from a phantom consisting of two resonances within 195 ms. Conclusion: Frequency-sensitive reconstruction of multiecho bSSFP data can provide spectroscopic images with high spatial and temporal resolution while the frequency resolution is moderate at around 100 Hz. The method can also separate more than three resonances, allowing for hetero-nuclei metabolite mapping, for example C-13 and P-31.
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| 4. |
- Leupold, Jochen, et al.
(author)
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Fast multiecho balanced SSFP metabolite mapping of H-1 and hyperpolarized C-13 compounds
- 2009
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In: Magma. - : Springer Science and Business Media LLC. - 1352-8661. ; 22:4, s. 251-256
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Journal article (peer-reviewed)abstract
- To investigate the feasibility of multiecho balanced steady-state free precession (bSSFP)-based fast chemical shift mapping hyperpolarized C-13 metabolites. The overall goal was to reduce total imaging time and to increase spatial resolution compared to common chemical shift imaging (CSI). A multiecho bSSFP sequence in combination with an iterative reconstruction algorithm was implemented. H-1 experiments were performed on phantoms and on a human volunteer in order to investigate the feasibility of the method on a system with metabolite maps that are known beforehand. C-13 experiments were performed in vivo on pigs, where CSI images were acquired also for comparison. Chemical shift images of three and four distinct H-1 resonance frequencies as well as chemical shift images of up to five hyperpolarized C-13 metabolites were successfully obtained. Fast metabolite mapping based on multiecho balanced SSFP in combination with an iterative reconstruction approach could successfully separate several H-1 resonances and hyperpolarized C-13 metabolites.
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| 5. |
- Stenman, Katarina, et al.
(author)
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Detection of polyunsaturated omega-6 fatty acid in human malignant prostate tissue by 1D and 2D high-resolution magic angle spinning NMR spectroscopy
- 2009
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In: Magnetic Resonance Materials in Physics, Biology and Medicine. - Berlin : Springer. - 0968-5243 .- 1352-8661. ; 22:6, s. 327-331
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Journal article (peer-reviewed)abstract
- OBJECT: Polyunsaturated omega-6 fatty acids (PUFAs) have been shown to promote prostate cancer. Here, we describe the use of HRMAS NMR spectroscopy to detect omega-6 PUFA species in prostate tissues. MATERIALS AND METHODS: Samples originating from non-malignant (n = 54) and malignant (n = 27) prostate tissues (from 27 prostatectomized men) were studied by 1D (1)H, 2D (1)H-(1)H and (1)H-(13)C HRMAS NMR spectroscopy followed by histopathological characterization. RESULTS: HRMAS NMR proved to be a powerful, non-destructive method to identify and characterize PUFAs. The omega-6 PUFA was found in 15% of examined human prostate tumors. CONCLUSION: It is possible to detect PUFAs in prostate tissues using our NMR-based spectroscopic approach.
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| 6. |
- Weis, Jan, et al.
(author)
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A simple method for mapping the B(1) field distribution of linear RF coils
- 2005
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In: Magnetic Resonance Materials in Physics, Biology and Medicine. - : Springer Science and Business Media LLC. - 0968-5243 .- 1352-8661. ; 18:6, s. 283-287
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Journal article (peer-reviewed)abstract
- Inhomogeneity of the radio frequency (RF) field B1 leads to intensity variations in MR images and to spatial dependence of spectral line amplitudes. In this paper, a simple method of measuring the B1 field components of an unsegmented linear coil is described. The method is designed for the coils operating up to 20 MHz. The B1 field distribution is replaced by the static magnetic field caused by DC current flowing through the coil. The technique involves rotating the coil 90° so that measured B1 component is aligned with B0 and measuring the shift of resonance frequency using a spectroscopic imaging sequence. Experimental results were in good agreement with the theoretical computations.
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| 8. |
- Weis, Jan, et al.
(author)
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Chemical-shift micro-imaging of subcutaneous lesions
- 2005
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In: Magnetic Resonance Materials in Physics, Biology and Medicine. - : Springer Science and Business Media LLC. - 0968-5243 .- 1352-8661. ; 18:2, s. 59-62
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Journal article (peer-reviewed)abstract
- A chemical-shift imaging technique was used for the study of small subcutaneous lesions. This study concerns micro-imaging of two females suffering from a tenosynovial giant cell tumor and an epidermal cyst. High-resolution water, fat and chemical-shift artifact-free images were obtained on a whole-body MR unit (1.5 T) equipped with a 23-mm microscopy surface coil and standard gradients (23 mT/m). A significant improvement in signal-to-noise ratio was achieved by reducing the receiver bandwidth to values below ±10 kHz. The image data sets were acquired with resolution 0.1×0.13 mm in the plane, slice thickness 0.5 mm and with acquisition time less than 3 min. Spatial resolution, fat suppression, image texture and edge delineation were improved on spectroscopic images compared with those on conventional MR images.
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| 9. |
- Wirestam, Ronnie, et al.
(author)
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Wavelet-based noise reduction for improved deconvolution of time-series data in dynamic susceptibility-contrast MRI.
- 2005
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In: Magma. - : Springer Science and Business Media LLC. - 1352-8661. ; 18:3, s. 113-118
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Journal article (peer-reviewed)abstract
- Dynamic susceptibility-contrast (DSC) MRI requires deconvolution to retrieve the tissue residue function R(t) and the cerebral blood flow (CBF). In this study, deconvolution of time-series data was performed by wavelet-transform-based denoising combined with the Fourier transform (FT). Traditional FT-based deconvolution of noisy data requires frequency-domain filtering, often leading to excessive smoothing of the recovered signal. In the present approach, only a low degree of regularisation was employed while the major noise reduction was accomplished by wavelet transformation of data and Wiener-like filtering in the wavelet space. After inverse wavelet transform, the estimate of CBF.R(t) was obtained. DSC-MRI signal-versus-time curves (signal-to-noise ratios 40 and 100) were simulated, corresponding to CBF values in the range 10-60 ml/(min 100 g). Three shapes of the tissue residue function were investigated. The technique was also applied to six volunteers. Simulations showed CBF estimates with acceptable accuracy and precision, as well as independence of any time shift between the arterial input function and the tissue concentration curve. The grey-matter to white-matter CBF ratio in volunteers was 2.4 +/- 0.2. The proposed wavelet/FT deconvolution is robust and can be implemented into existing perfusion software. CBF maps from healthy volunteers showed high quality.
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| 10. |
- Lätt, Jimmy, et al.
(author)
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Effects of restricted diffusion in a biological phantom: a q-space diffusion MRI study of asparagus stems at a 3T clinical scanner
- 2007
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In: Magma. - : Springer Science and Business Media LLC. - 1352-8661. ; 20:4, s. 213-222
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Journal article (peer-reviewed)abstract
- Introduction The aim of this work was to study the effects of restricted diffusion in a biological phantom consisting of green asparagus stems using q-space MRI at a clinical scanner. Method Measurements of the full width at half maximum (FWHM) of the displacement distribution were performed with varied diffusion time (T d). The accuracy of the measurements was investigated with respect to the degree of violation of the short gradient pulse (SGP) condition, partial volume effects and a FWHM-based tensor model. Results The measurements showed a reasonably constant FWHM perpendicular to the capillaries in the vascular bundles and an increased FWHM parallel with the bundles when the T d was increased. A 15% decrease in FWHM perpendicular to the bundles was observed when the diffusion encoding duration was prolonged from 24 to 74 ms, owing to the violation of the SGP condition. For a population of different confinement sizes, simulations indicated that the FWHM reflects the smaller sizes rather then the mean size of the confinements. Conclusion A new method allowing tensor analysis of FWHM was derived and yielded accurate results. In conclusion, we found it possible to measure the effects of restricted diffusion with q-space MRI using a clinical MRI scanner.
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