| 1. |
- Covaciu, Lucian, et al.
(författare)
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Human brain MR spectroscopy thermometry using metabolite aqueous-solution calibrations
- 2010
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1053-1807 .- 1522-2586. ; 31:4, s. 807-814
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To estimate absolute brain temperature using proton MR spectroscopy ((1)H-MRS) and mean brain-body temperature difference of healthy human volunteers. MATERIALS AND METHODS: Chemical shift difference between temperature-dependent water spectral line position and temperature-stable metabolite spectral reference was used for the estimations of absolute brain temperature. Temperature calibrations constants were obtained from the spectra of the N-acetyl aspartate (NAA line at approximately 2.0 ppm), glycero-phosphocholine (GPC line at approximately 3.2 ppm), and creatine (Cr line at approximately 3.0 ppm) aqueous solutions with pH values within physiologically pertinent ranges. Single-voxel PRESS sequence (TR/TE 2000/80 ms) was used for this purpose. Brain temperature was determined by averaging the temperatures computed from water-Cho, water-Cr, and water-NAA chemical shift differences. RESULTS: The mean brain temperature of 18 healthy volunteers was 38.1 +/- 0.4 degrees C and mean brain-body (rectal) temperature difference was 1.3 +/- 0.4 degrees C. CONCLUSION: Improved accuracy of the temperature constants and averaging the temperatures computed from water-Cho, water-Cr, and water-NAA chemical shift differences increased the reliability of the brain temperature estimations.
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| 2. |
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| 3. |
- Dyverfeldt, Petter, et al.
(författare)
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Hemodynamic aspects of mitral regurgitation assessed by generalized phase-contrast MRI
- 2011
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Ingår i: Journal of Magnetic Resonance Imaging. - : John Wiley and Sons. - 1053-1807 .- 1522-2586. ; 33:3, s. 582-588
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Mitral regurgitation creates a high velocity jet into the left atrium (LA), contributing both volume andpressure; we hypothesized that the severity of regurgitation would be reflected in the degree of LA flowdistortion.Material and Methods: Three-dimensional cine PC-MRI was applied to determine LA flow patterns andturbulent kinetic energy (TKE) in seven subjects (five patients with posterior mitral leaflet prolapse, two normalsubjects). In addition, the regurgitant volume and the time-velocity profiles in the pulmonary veins weremeasured.Results: The LA flow in the mitral regurgitation patients was highly disturbed with elevated values of TKE.Peak TKE occurred consistently at late systole. The total LA TKE was closely related to the regurgitant volume.LA flow patterns were characterized by a pronounced vortex in proximity to the regurgitant jet. In some patients,pronounced discordances were observed between individual pulmonary venous inflows, but these could not berelated to the direction of the flow jet or parameters describing global LA hemodynamics.Conclusion: PC-MRI permits investigations of atrial and pulmonary vein flow patterns and TKE in significantmitral regurgitation, reflecting the impact of the highly disturbed blood flow that accompanies this importantvalve disease.
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| 4. |
- Dyverfeldt, Petter, et al.
(författare)
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Reduction of motion artifacts in carotid MRI using free-induction decay navigators
- 2014
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Ingår i: Journal of Magnetic Resonance Imaging. - : John Wiley & Sons. - 1053-1807 .- 1522-2586. ; 40:1, s. 214-220
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE:To develop a framework for prospective free-induction decay (FID)-based navigator gating for suppression of motion artifacts in carotid magnetic resonance imaging (MRI) and to assess its capability in vivo.MATERIALS AND METHODS:An FID-navigator, comprising a spatially selective low flip-angle sinc-pulse followed by an analog-to-digital converter (ADC) readout, was added to a conventional turbo spin-echo (TSE) sequence. Real-time navigator processing delivered accept/reject-and-reacquire decisions to the sequence. In this Institutional Review Board (IRB)-approved study, seven volunteers were scanned with a 2D T2-weighted TSE sequence. A reference scan with volunteers instructed to minimize motion as well as nongated and gated scans with volunteers instructed to perform different motion tasks were performed in each subject. Multiple image quality measures were employed to quantify the effect of gating.RESULTS:There was no significant difference in lumen-to-wall sharpness (2.3 ± 0.3 vs. 2.3 ± 0.4), contrast-to-noise ratio (CNR) (9.0 ± 2.0 vs. 8.5 ± 2.0), or image quality score (3.1 ± 0.9 vs. 2.6 ± 1.2) between the reference and gated images. For images acquired during motion, all image quality measures were higher (P < 0.05) in the gated compared to nongated images (sharpness: 2.3 ± 0.4 vs. 1.8 ± 0.5, CNR: 8.5 ± 2.0 vs. 7.2 ± 2.0, score: 2.6 ± 1.2 vs. 1.8 ± 1.0).CONCLUSION:Artifacts caused by the employed motion tasks deteriorated image quality in the nongated scans. These artifacts were alleviated with the proposed FID-navigator.
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| 5. |
- Escobar Kvitting, John-Peder, et al.
(författare)
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In Vitro Assessment of Flow Patterns and Turbulence Intensity in Prosthetic Heart Valves Using Generalized Phase-Contrast MRI
- 2010
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Ingår i: JOURNAL OF MAGNETIC RESONANCE IMAGING. - : John Wiley and Sons, Ltd. - 1053-1807 .- 1522-2586. ; 31:5, s. 1075-1080
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To assess in vitro the three-dimensional mean velocity field and the extent and degree of turbulence intensity (TI) in different prosthetic heart valves using a generalization of phase-contrast MRI (PC-MRI). Materials and Methods: Four 27-mm aortic valves (Bjork-Shiley Monostrut tilting-disc, St. Jude Medical Standard bileaflet, Medtronic Mosaic stented and Freestyle stentless porcine valve) were tested under steady inflow conditions in a Plexiglas phantom. Three-dimensional PC-MRI data were acquired to measure the mean velocity field and the turbulent kinetic energy (TKE), a direction-independent measure of TI. Results: Velocity and TI estimates could be obtained up and downstream of the valves, except where metallic structure in the valves caused signal void. Distinct differences in the location, extent, and peak values of velocity and TI were observed between the valves tested. The maximum values of TKE varied between the different valves: tilting disc, 100 J/m(3); bileaflet, 115 J/m(3); stented, 200 J/m(3); stentless, 145 J/m(3). Conclusion: The TI downstream from a prosthetic heart valve is dependent on the specific valve design. Generalized PC-MRI can be used to quantify velocity and TI downstream from prosthetic heart valves, which may allow assessment of these aspects of prosthetic valvular function in postoperative patients.
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| 6. |
- Gifford, Aliya, et al.
(författare)
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Canine body composition quantification using 3 tesla fat–water MRI
- 2014
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1053-1807 .- 1522-2586. ; 39:2, s. 485-491
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Tidskriftsartikel (refereegranskat)abstract
- PurposeTo test the hypothesis that a whole-body fat–water MRI (FWMRI) protocol acquired at 3 Tesla combined with semi-automated image analysis techniques enables precise volume and mass quantification of adipose, lean, and bone tissue depots that agree with static scale mass and scale mass changes in the context of a longitudinal study of large-breed dogs placed on an obesogenic high-fat, high-fructose diet.Materials and MethodsSix healthy adult male dogs were scanned twice, at weeks 0 (baseline) and 4, of the dietary regiment. FWMRI-derived volumes of adipose tissue (total, visceral, and subcutaneous), lean tissue, and cortical bone were quantified using a semi-automated approach. Volumes were converted to masses using published tissue densities.ResultsFWMRI-derived total mass corresponds with scale mass with a concordance correlation coefficient of 0.931 (95% confidence interval = [0.813, 0.975]), and slope and intercept values of 1.12 and −2.23 kg, respectively. Visceral, subcutaneous and total adipose tissue masses increased significantly from weeks 0 to 4, while neither cortical bone nor lean tissue masses changed significantly. This is evidenced by a mean percent change of 70.2% for visceral, 67.0% for subcutaneous, and 67.1% for total adipose tissue.ConclusionFWMRI can precisely quantify and map body composition with respect to adipose, lean, and bone tissue depots. The described approach provides a valuable tool to examine the role of distinct tissue depots in an established animal model of human metabolic disease.
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| 7. |
- 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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| 8. |
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| 9. |
- Horn, Michael, et al.
(författare)
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Dynamic Contrast-Enhanced MR Imaging for Differentiation of Rounded Atelectasis From Neoplasm
- 2010
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1053-1807 .- 1522-2586. ; 31:6, s. 1364-1370
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Tidskriftsartikel (refereegranskat)abstract
- Purpose To characterize rounded atelectasis (RA) with dynamic contrast-enhanced MRI in the differential diagnosis of solitary peripheral pulmonary neoplasm. Materials and Methods Twenty-four patients with diagnostically equivocal peripheral pulmonary nodules were examined with dynamic contrast-enhanced MRI. 13 patients had a total of 16 rounded atelectases and 11 had a neoplasm. The final diagnosis was made either by histology (n = 14) or follow-up examinations of at least 24 months (n = 10). The peripheral nodules were evaluated concerning their morphology and contrast-enhancement dynamics. Curves for signal intensity (SI) versus time were produced and the relative increase in SI, slope of SI during wash-in, and slope of SI during wash-out calculated. Additionally, SI time curves were evaluated using a two compartment model where the ratio for the SI of the fast and the slow component were calculated. Mean values from different tissues of interest were compared by an unpaired two-sided t-test. Results Analysis of the SI-time curves of the RAs revealed a curve shape similar to the pulmonary artery, but a magnitude in SI between artery and normal lung tissue. Linear curve fit showed a significantly steeper slope during wash-in and wash-out, and higher relative signal increase in atelectases as compared to neoplasms. Results from the two compartment model showed increased flow and a high ratio of the slow to the fast components with a long mean transit time in neoplasms. Conclusion Three parameters, slope of SI during wash-in and wash-out, and the slow/fast ratio can be used as diagnostic tools for discrimination of RA and neoplasm
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| 10. |
- Kullberg, Joel, et al.
(författare)
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Adipose tissue distribution in children: automated quantification using water and fat MRI.
- 2010
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Ingår i: Journal of magnetic resonance imaging : JMRI. - : Wiley. - 1522-2586 .- 1053-1807. ; 32:1, s. 204-10
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To develop and validate a method for rapid acquisition and automated processing of magnetic resonance (MR) images for analysis of abdominal adipose tissue distribution in children. Materials and Methods: The study included 21 (10 girls, 11 boys) healthy 5-year-old children. Rapid water and fat MR imaging (6 sec) was performed using a 2-point-Dixon technique on a 1.5T MR scanner using an 8-channel cardiac coil. An automated image processing algorithm was developed for automated segmentation of visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT), respectively. The results from the fully automated analysis were compared to those from a semiautomated analysis, performed by three operators, from the same images. Results: The automated analysis was seen to give results with strong correlation to the reference measurements (r ≥ 0.997); however, the SAT volume was underestimated by 9.4 ± 3.8%. The accuracy of the automated segmentation of VAT and SAT (TP: true positive, FP: false positive, mean ± SD, %) was TP: 83.6 ± 8.5, FP: 12.7 ± 6.8; and TP: 89.9 ± 3.6, FP: 0.7 ± 0.3, respectively.
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