| 31. |
- 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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| 32. |
- 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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| 33. |
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| 34. |
- Ebbers, Tino, et al.
(författare)
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Improving Computation of Cardiovascular Relative Pressure Fields From Velocity MRI
- 2009
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Ingår i: JOURNAL OF MAGNETIC RESONANCE IMAGING. - : Wiley. - 1053-1807 .- 1522-2586. ; 30:1, s. 54-61
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To evaluate a multigrid-based solver for the pressure Poisson equation (PPE) with Galerkin coarsening, which works directly on the specified domain, for the computation of relative pressure fields from velocity MRI data. Materials and Methods: We compared the proposed structure-defined Poisson solver to other popular Poisson solvers working on unmodified rectangular and modified quasirectangular domains using synthetic and in vitro phantoms in which the mathematical solution of the pressure field is known, as well as on in vivo MRI velocity measurements of aortic blood flow dynamics. Results: All three PPE solvers gave accurate results for convex computational domains. Using a rectangular or quasirectangular domain on a more complicated domain, like a c-shape, revealed a systematic underestimation of the pressure amplitudes, while the proposed PPE solver, working directly on the specified domain, provided accurate estimates of the relative pressure fields. Conclusion: Popular iterative approaches with quasirectangular computational domains can lead to significant systematic underestimation of the pressure amplitude. We suggest using a multigrid-based PPE solver with Galerkin coarsening, which works directly on the structure-defined computational domain. This solver provides accurate estimates of the relative pressure fields for both simple and complex geometries with additional significant improvements with respect to execution speed.
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| 35. |
- Erdogmus, Deniz, et al.
(författare)
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Image construction methods for phased array magnetic resonance imaging
- 2004
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1053-1807 .- 1522-2586. ; 20:2, s. 306-314
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Tidskriftsartikel (refereegranskat)abstract
- Purpose To study image construction in phased array magnetic resonance imaging (MRI) systems from a statistical signal processing point of view. Materials and Methods Three new approaches for image combination with multiple coils are proposed: 1) one based on the singular value decomposition of the measurement matrix, which is asymptotically optimal in the signal-to-noise ratio sense; 2) one based on a maximum-likelihood formulation, incorporating a priori information on the coil sensitivities in a Bayesian manner; and 3) one based on a least-squares formulation, which incorporates a smoothness constraint on the coil sensitivities. Results Numerical examples using synthetic and real data are presented to illustrate the performance of these new approaches. Results on the synthetic data show improvement in signal-to-error ratio, while results on the real data (a 4.7 T four-coil image of a cat spinal cord) show that the proposed methods can improve the SNR in the final image by up to 3 dB in the regions of interest compared to conventional sum-of-squares processing. Conclusion It is demonstrated that phased array MRI reconstruction performance can be improved by the use of more elaborate statistical signal processing algorithms. J. Magn. Reson. Imaging 2004;20:306–314. © 2004 Wiley-Liss, Inc.
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| 36. |
- Eriksson, Rolf, et al.
(författare)
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Contrast enhancement of manganese-hydroxypropyl-tetraacetic acid, an MR contrast agent with potential for detecting differences in myocardial blood flow
- 2006
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1053-1807 .- 1522-2586. ; 24:4, s. 858-863
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To determine whether the contrast agent MnHPTA has potential for detecting differences in myocardial blood flow. Materials and Methods: R1 in the myocardium was calculated from MR signal intensity measurements in 18 pigs after intravenous injection of 5, 15, or 25 mu mol MnHPTA/kg body weight. Measurements were made in each animal after administration at rest and during dobutamine-induced stress. Results: A difference of approximately 0.1 see(-1) in the R1 increase between rest and stress still remained 31 minutes after administration of 25 mu mol MnHPTA/kg body weight. When two consecutive MnHPTA injections were performed, the second injection induced a lower R1 increase than the corresponding first injection. Conclusion: MnHPTA at a dose of 25 mu mol/kg body weight (b.w.) has the potential to detect perfusion differences in myocardium. When two consecutive injections of MnHPTA were administered, the RI change after the second injection was affected by the earlier administration. Therefore, a protocol including more than one administration is not ideal for this contrast agent.
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| 37. |
- Eriksson, Rolf, et al.
(författare)
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Dobutamine-induced stress affects intracellular uptake of manganese : a quantitative magnetic resonance imaging study in pigs
- 2004
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1053-1807 .- 1522-2586. ; 21:4, s. 360-364
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To determine whether there are differences in increase in longitudinal relaxation rate (DeltaR1) in the myocardium between bolus administration of Mn(2+) ions during rest and during dobutamine-induced stress and, additionally, to determine whether there are differences in DeltaR1 between bolus injection and infusion of Mn(2+) ions during dobutamine-induced stress. MATERIALS AND METHODS: Pigs were divided into three groups with six pigs in each group. All animals received 15 mumol MnCl(2)/kg of body weight (b.w.) intravenously either as a bolus injection (groups 1 and 2) or as an infusion over one minute (group 3). The animals in groups 2 and 3 were subjected to dobutamine stress before injection of MnCl(2), while those in group 1 were not given dobutamine. T1 was quantified in the myocardium and left ventricular blood pool before contrast injection and repeatedly during a one-hour postinjection period. RESULTS: A significant difference in DeltaR1 between the groups with and the group without dobutamine stress was noted in the myocardium up to 45 minutes after contrast agent injection. No such significant difference was found between pigs that received the contrast agent as a bolus injection compared to infusion. CONCLUSION: Dobutamine stress increases uptake of manganese ions in the myocardium. This increase was independent of whether the contrast agent was administered as a bolus injection or as an infusion.
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| 38. |
- Eriksson, Rolf, et al.
(författare)
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Uptake of MnCl2 and mangafodipir trisodium in the myocardium : a magnetic resonance imaging study in pigs
- 2004
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1053-1807 .- 1522-2586. ; 19:5, s. 564-569
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To examine the changes in the longitudinal relaxation times (DeltaR1) induced in pig myocardium and blood following injections of 5, 10, and 15 micromol mangafodipir trisodium (Mn-DPDP) or MnCl2/kg of body weight (b.w.). MATERIALS AND METHODS: Twelve pigs were divided into two groups, one group receiving MnCl2 and the other receiving Mn-DPDP. Three consecutive doses of contrast agent (5, 10, and 15 micromol/kg of b.w.) were injected in each animal with a 40-minute time interval between each dose. Measurements of T1 in blood and myocardium were made 5, 15, 25, and 35 minutes after each injection. Additionally, relaxivity measurements in blood samples were performed. RESULTS: An increase in myocardial R1 was observed for both contrast agents at all concentration levels tested. This increase peaked 5 minutes after injection and then declined. An increase could still be detected 35 minutes after injection. The effect was larger when using MnCl2 than when using Mn-DPDP. CONCLUSION: The dissociation kinetics of Mn2+ from the DPDP ligand limits the relaxation increase of Mn-DPDP relative to that of MnCl2. On the other hand, the toxicity of MnCl2 may exclude it from clinical use.
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| 39. |
- 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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| 40. |
- Fagan, A. J., et al.
(författare)
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7T MR Safety
- 2021
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1053-1807 .- 1522-2586. ; 53:2333-346, s. 333-346
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic resonance imaging and spectroscopy (MRI/MRS) at 7T represents an exciting advance in MR technology, with intriguing possibilities to enhance image spatial, spectral, and contrast resolution. To ensure the safe use of this technology while still harnessing its potential, clinical staff and researchers need to be cognizant of some safety concerns arising from the increased magnetic field strength and higher Larmor frequency. The higher static magnetic fields give rise to enhanced transient bioeffects and an increased risk of adverse incidents related to electrically conductive implants. Many technical challenges remain and the continuing rapid pace of development of 7T MRI/MRS is likely to present further challenges to ensuring safety of this technology in the years ahead. The recent regulatory clearance for clinical diagnostic imaging at 7T will likely increase the installed base of 7T systems, particularly in hospital environments with little prior ultrahigh-field MR experience. Informed risk/benefit analyses will be required, particularly where implant manufacturer-published 7T safety guidelines for implants are unavailable. On behalf of the International Society for Magnetic Resonance in Medicine, the aim of this article is to provide a reference document to assist institutions developing local institutional policies and procedures that are specific to the safe operation of 7T MRI/MRS. Details of current 7T technology and the physics underpinning its functionality are reviewed, with the aim of supporting efforts to expand the use of 7T MRI/MRS in both research and clinical environments. Current gaps in knowledge are also identified, where additional research and development are required. Level of Evidence 5 Technical Efficacy 2
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