| 1. |
- Svensson, Jonas, et al.
(författare)
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Image artifacts due to a time-varying contrast medium concentration in 3D contrast-enhanced MRA
- 1999
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Ingår i: Journal of Magnetic Resonance Imaging. - 1522-2586. ; 10:6, s. 919-928
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this work was to study image effects due to time-varying contrast medium concentration in contrast-enhanced three dimensional (3D) magnetic resonance angiography (MRA) images. Two different simulation models (1D and 3D) and two different contrast medium variation schemes were used. Phantom measurements were also performed. Experiments were performed for several different bolus timings. Similar sequence and image object parameters were used in both simulations and measurements (TE/TR 2. 1/7.8 mses, flip angle 30 degrees, T1/T2 1200-80/150-40 msec, flow velocity 100 cm/sec). A small variation in bolus timing yielded large variations in the appearance of the image effects, especially if the center of k-space was sampled in the vicinity of rapid contrast medium concentration variation. For a typical bolus injection in a patient, a severe signal loss but only minor ringing and edge artifacts appeared if the bolus injection was poorly timed. Effects of pulsatile flow were minor. The 3D model proved to be a useful tool in these studies.
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| 2. |
- Hawezi, Zana, et al.
(författare)
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In vivo transport of Gd-DTPA(2-) in human knee cartilage assessed by depth-wise dGEMRIC analysis.
- 2011
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 34, s. 1352-1358
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To investigate the transport of Gd-DTPA(2-) in different layers of femoral knee cartilage in vivo. MATERIALS AND METHODS: T(1) measurements (1.5 Tesla) were performed in femoral knee cartilage of 23 healthy volunteers. The weight-bearing central cartilage was analyzed before contrast and at eight time points after an intravenous injection of Gd-DTPA(2-) : 12-60 min (4 volunteers) and 1-4 h (19 volunteers). Three regions of interest were segmented manually: deep, middle, and superficial. RESULTS: Before contrast injection, a depth-wise variation of T(1) was observed with 50% higher values in the superficial region compared with the deep region. In the deep region, the uptake of Gd-DTPA(2-) was not detected until 36 min and the concentration increased until 240 min, whereas in the superficial region, the uptake was seen already at 12 min and the concentration decreased after 180 min (P < 0.01). There was a difference between medial and lateral compartment regarding bulk, but not superficial Gd-DTPA(2-) concentration. The bulk gadolinium concentration was negatively related to the cartilage thickness (r = -0.68; P < 0.01). CONCLUSION: The depth-wise and thickness dependent variations in Gd-DTPA(2) transport influence the interpretation of bulk dGEMRIC analysis in vivo. In thick cartilage, incomplete penetration of Gd-DTPA(2) will yield a falsely too long T(1) . J. Magn. Reson. Imaging 2011;. © 2011 Wiley-Liss, Inc.
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| 3. |
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| 4. |
- Mannfolk, Peter, et al.
(författare)
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Can resting-state functional MRI serve as a complement to task-based mapping of sensorimotor function? A test-retest reliability study in healthy volunteers.
- 2011
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 34, s. 511-517
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To investigate if resting-state functional MRI (fMRI) reliably can serve as a complement to task-based fMRI for presurgical mapping of the sensorimotor cortex. MATERIALS AND METHODS: Functional data were obtained in 10 healthy volunteers using a 3 Tesla MRI system. Each subject performed five bilateral finger tapping experiments interleaved with five resting-state experiments. Following preprocessing, data from eight volunteers were further analyzed with the general linear model (finger tapping data) and independent component analysis (rest data). Test-retest reliability estimates (hit rate and false alarm rate) for resting-state fMRI activation of the sensorimotor network were compared with the reliability estimates for task-evoked activation of the sensorimotor cortex. The reliability estimates constituted a receiver operating characteristics curve from which the area under the curve (AUC) was calculated. Statistical testing was performed to compare the two groups with respect to reliability. RESULTS: The AUC was generally higher for the task experiments, although median AUC was not significantly different on a group level. Also, the two groups showed comparable levels of within-group variance. CONCLUSION: Test-retest reliability was comparable between resting-state measurements and task-based fMRI, suggesting that presurgical mapping of functional networks can be a supplement to task-based fMRI in cases where patient status excludes task-based fMRI. J. Magn. Reson. Imaging 2011;. © 2011 Wiley-Liss, Inc.
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| 5. |
- Siversson, Carl, et al.
(författare)
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Local Flip Angle Correction for Improved Volume T1-Quantification in Three-Dimensional dGEMRIC Using the Look-Locker Technique
- 2009
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 30:4, s. 834-841
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To present an evaluation method for three-dimensional Look-Locker (3D-LL) based T1 quantification, calculating correct T1 values independent of local flip angle (FA) variations. The method was evaluated both in phantoms and in vivo in a delayed Gadolinium Enhanced MRI of Cartilage (dGEMRIC) study with 33 subjects. Materials and Methods: T1 was measured with 3D-LL, using both local FA correction and a precalculated FA slice profile. and compared with standard constant FA correction, for all slices in phantoms and in both femur condyles in vivo. T1 measured using two-dimensional Inversion Recovery (2D-IR) was used as gold standard. Results: Due to the FA being slice dependent, the standard constant FA correction results in erroneous T1 (systematic error = 109.1 ms in vivo), especially in the outer slices. With local FA correction. the calculated T1 is excellent for all slices in phantoms (<5% deviation from 2D-IR). In vivo the performance is lower (systematic error = -57.5ms), probably due to imperfect inversion. With precalculated FA correction the performance is very good also in vivo (systematic error = 13.3 ms). Conclusion: With the precalculated FA correction method, the 3D-LL sequence is robust enough for in vivo dGEMRIC, even outside the centermost slices.
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| 6. |
- Siversson, Carl, et al.
(författare)
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Repeatability of T1-quantification in dGEMRIC for three different acquisition techniques: two-dimensional inversion recovery, three-dimensional look locker, and three-dimensional variable flip angle.
- 2010
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 31:5, s. 1203-1209
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To evaluate the repeatability of the dGEMRIC (delayed gadolinium enhanced MRI of cartilage) method in osteoarthritis-prone knee joints for three different T1 quantification techniques: two-dimensional inversion recovery (2D-IR), three-dimensional Look-Locker (3D-LL), and three-dimensional variable flip angle (3D-VFA). MATERIALS AND METHODS: Nine subjects were examined twice, with a 2-week interval, using all three measurement techniques. Four regions of interest were defined in the central medial and lateral femoral cartilage. The repeatability was evaluated for each measurement technique. For the 3D techniques, the variation between different slices was also evaluated. RESULTS: Repeatability expressed by root-mean-square coefficient of variation (CV(RMS)) showed similar results for 2D-IR and 3D-LL (5.4-8.4%). For 3D-VFA CV(RMS) was higher (9.3-15.2%). Intraclass correlation coefficient showed both 2D-IR and 3D-LL reliability to be moderate, while 3D-VFA reliability was low. Inter-slice CV(RMS) and ICC was of the same magnitude as the repeatability. No clear differences could be interpreted between the condyles. CONCLUSION: Both 2D-IR and 3D-LL perform well in generating repeatable dGEMRIC results, while 3D-VFA results are somewhat inferior. Furthermore, repeatability results in this study are similar to previously published results for healthy subjects. Finally, the positioning of the analyzed images is crucial to generate reliable repeatability results.
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