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- Carlsson, Åsa, 1978, et al.
(författare)
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Accurate and sensitive measurements of magnetic susceptibility using echo planar imaging.
- 2006
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Ingår i: Magnetic resonance imaging. - : Elsevier BV. - 0730-725X. ; 24:9, s. 1179-85
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Tidskriftsartikel (refereegranskat)abstract
- Susceptibility differences are common causes for artifacts in magnetic resonance (MR); therefore, it is important to choose phantom materials in a way that these artifacts are kept at a minimum. In this study, a previously proposed MR imaging (MRI) method [Beuf O, Briguet A, Lissac M, Davis R. Magnetic resonance imaging for the determination of magnetic susceptibility of materials. J Magn Reson 1996; Series B(112):111-118] was improved to facilitate sensitive in-house measurements of different phantom materials so that such artifacts can more easily be minimized. Using standard MRI protocols and distilled water as reference, we measured magnetic volume susceptibility differences with a clinical MR system. Two imaging techniques, echo planar imaging (EPI) and spin echo, were compared using liquid samples whose susceptibilities were verified by MR spectroscopy. The EPI sequence has a very narrow bandwidth in the phase-encoding direction, which gives an increased sensitivity to magnetic field inhomogeneities. All MRI measurements were evaluated in two ways: (1) manual image analysis and (2) model fitting. The narrow bandwidth of the EPI made it possible to detect very small susceptibility differences (equivalent susceptibility difference, Deltachi(e)> or =0.02 ppm), and even plastics could be measured. Model fitting yielded high accuracy and high sensitivity and was less sensitive to other image artifacts as compared with manual image analysis.
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- Carlsson, Åsa, 1978, et al.
(författare)
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Degraded water suppression in small volume ¹H MRS due to localised shimming.
- 2011
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Ingår i: Magma (New York, N.Y.). - : Springer Science and Business Media LLC. - 0968-5243. ; 24:2, s. 97-107
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Tidskriftsartikel (refereegranskat)abstract
- High quality, artifact free, ¹H MRS require a homogeneous magnetic field over the volume of interest (VOI) and an effective global water suppression (WS). However, the shim coils act globally and, hence, affect the resonance frequency over the entire object, making the frequency selective WS spatially selective. Unsuppressed water signal may cause spurious echo artifacts. Aim: Study and visualise the effect localised shimming has on WS.
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- Carlsson, Åsa, 1978, et al.
(författare)
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The influence of cardiac triggering time and an optimization strategy for improved cardiac MR spectroscopy.
- 2017
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Ingår i: Zeitschrift fur medizinische Physik. - : Elsevier BV. - 1876-4436 .- 0939-3889. ; 27:4, s. 310-317
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Tidskriftsartikel (refereegranskat)abstract
- To study how cardiac motion affects the spectral quality in cardiac MR spectroscopy and to establish an optimization strategy for the cardiac triggering time for improved quality and success rate of cardiac MRS.Water spectra were acquired while the cardiac triggering time was varied over the cardiac cycle, and five different spectral quality parameters were studied (frequency, phase, linewidth, amplitude and noise). Furthermore, three different optimization strategies for the cardiac triggering time were tested, and finally, a comparison was made between water suppressed lipid spectra acquired in systole and diastole.The cardiac triggering time had a high impact on the spectral quality, especially on the mean signal amplitude and the standard deviation of the signal amplitude, phase and linewidth. Generally, the highest spectral quality was observed for spectra acquired in mid to end systole, at approximately 23% of the cardiac cycle. The exact optimal triggering time differed between subjects and needed to be individually optimized. To optimize the triggering time with our proposed MRS-method gave in average 13% higher signal than when the triggering time was determined through imaging. Lipid spectra acquired in systole demonstrated higher quality with improved SNR compared with acquisitions made in diastole.This study shows that the spectral quality in cardiac MRS is strongly dependent on the cardiac triggering time, and that the spectral quality as well as the repeatability between acquisitions is greatly improved when the cardiac triggering time is individually optimized in mid to end systole using MRS.
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- Ivarsson, Tord, 1946, et al.
(författare)
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Neurochemical properties measured by H-1 magnetic resonance spectroscopy may predict cognitive behaviour therapy outcome in paediatric OCD: a pilot study
- 2021
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Ingår i: Journal of Neural Transmission. - : Springer Science and Business Media LLC. - 0300-9564 .- 1435-1463. ; 128, s. 1361-1370
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Tidskriftsartikel (refereegranskat)abstract
- To identify neurochemical factors measured pre-treatment that may predict cognitive behavioural treatment (CBT) outcome, aiming at understanding possible causes of poor CBT response. 1H magnetic resonance spectroscopy was used before treatment with CBT in treatment naive 11-18 year-old patients with moderate-severe OCD. Diagnoses and assessment of OCD severity were based on semi-structured interviews. Linear mixed effects models were used to analyse the association between metabolite level and treatment outcome. Worse CBT outcome was associated with higher concentration of glutamine and glutamate combined (Glx) in middle cingulate cortex (MCC) (F = + 3.35, p = 0.004) and of N-acetylaspartate and N-acetylaspartylglutamate combined (tNAA) (F = + 2.59, p = 0.019). Also, we noted a tendency towards higher thalamic Glx concentration (F = + 1.91, p = 0.077) to be associated with worse CBT outcome. In general, the findings of the current pilot study are compatible with the hypothesis of an overweight of excitatory to inhibitory factors in brain circuits driving goal-directed behaviours (GDB). Higher MCC Glx and tNAA may be involved in the selection of GDB. A more detailed understanding of how these brain areas function in health and illness is needed.
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