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  • Engellau, Lena, et al. (författare)
  • MR evaluation ex vivo and in vivo of a covered stent-graft for abdominal aortic aneurysms: ferromagnetism, heating, artifacts, and velocity mapping
  • 2000
  • Ingår i: Journal of Magnetic Resonance Imaging. - : John Wiley and Sons. - 1522-2586. ; 12:1, s. 112-121
  • Tidskriftsartikel (refereegranskat)abstract
    • Magnetic resonance imaging (MRI) safety was evaluated at 1.5 T in a covered nickel titanium stent-graft (Vanguard) used for endovascular treatment of abdominal aortic aneurysms (AAAs). Imaging artifacts were assessed on MRI with contrast-enhanced (CE) three-dimensional (3D) MR angiography (MRA) and spiral computed tomography (CT) in 10 patients as well as ex vivo. Velocity mapping was performed in the suprarenal aorta and femoral arteries in 14 patients before and after stent-graft placement. For comparison it was also performed in six healthy volunteers. No ferromagnetism or heating was detected. Metal artifacts caused minimal image distortion on MRI/MRA. The artifacts disturbed image evaluation on CT at the graft bifurcation and graft limb junction. No significant differences in mean flow were found in patients before and after stent-graft placement. Our study indicates that MRI at 1.5 T may be performed safely in patients with the (Vanguard) stent-graft. MRI/MRA provides diagnostic image information. Velocity mapping is not included in our routine protocol.
  • Svensson, Jonas, et al. (författare)
  • Image artifacts due to a time-varying contrast medium concentration in 3D contrast-enhanced MRA
  • 1999
  • Ingår i: Journal of Magnetic Resonance Imaging. - : John Wiley and Sons. - 1522-2586. ; 10:6, s. 919-928
  • 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.
  • Bjerner, Tomas, et al. (författare)
  • Evaluation of nonperfused myocardial ischemia with MRI and an intravascular USPIO contrast agent in an ex vivo pig model
  • 2000
  • Ingår i: Journal of Magnetic Resonance Imaging. - 1053-1807 .- 1522-2586. ; 12:6, s. 866-872
  • Tidskriftsartikel (refereegranskat)abstract
    • The ultrasmall superparamagnetic iron oxide (USPIO) preparation NC100150 Injection (Clariscan; Nycomed Imaging, Oslo, Norway) was tested for its ability to delineate nonperfused myocardium under steady-state conditions. An experimental animal model of focal myocardial ischemia induced by ligation of the distal part of the left anterior descending artery was used. The contrast agent was administered in four doses: 0, 4, 8, and 12 mg Fe/kg body weight. Magnetic resonance examination ex vivo, including T1-, T2-, and T2*-weighted sequences, was performed. Nonperfused myocardium was determined by fluorescein. The best delineation of nonperfused myocardium was found with a T1-weighted inversion recovery/turbo spin-echo sequence and doses of 4 and 8 mg Fe/kg body weight, where 95% of the volume was discernible at the dose of 4 mg Fe/kg body weight. The results suggest that steady-state imaging by T1-weighted sequence with the use of NC100150 Injection to delineate nonperfused myocardium is feasible. J. Magn. Reson. Imaging 2000;12:866-872.
  • Meaney, James F M, et al. (författare)
  • Pulmonary magnetic resonance angiography
  • 1999
  • Ingår i: Journal of Magnetic Resonance Imaging. - 1053-1807 .- 1522-2586. ; 10:3, s. 326-338
  • Tidskriftsartikel (refereegranskat)abstract
    • Early attempts to image the pulmonary vasculature with spin-echo magnetic resonance (MR) imaging were hampered by severe image degradation related to respiratory and cardiac pulsation artifact, susceptibility at interfaces between lung parenchyma and vessel wall, and poor contrast between flowing blood and intravascular filling defects of emboli. With the development of gradient-echo MR angiographic techniques some of these limitations were overcome; however, the need for multiple breath-holds and the frequent occurrence of flow-related artifacts that could simulate pulmonary emboli diminished their clinical utility. With the development of contrast-enhanced MR angiography, many of the limitations of earlier techniques were addressed. Images of both lungs with high signal-to-noise ratios and high contrast between flowing blood and pulmonary emboli could be acquired in a single breath-hold, during "first-pass" imaging with extracellular contrast agents in the coronal plane. However, subsegmental vessels could not be assessed with this approach. The technique has been refined further by imaging each lung separately in the sagittal plane; this offers higher resolution and total lung coverage and requires a shorter breath-hold. Finally, several investigators have reported preliminary data on imaging of the pulmonary vasculature with blood pool agents, exploiting respiratory triggering or navigator echoes to eliminate the need for breath-holding for the detection of pulmonary emboli.
  • Wang, Chen, et al. (författare)
  • Sequence optimization in mangafodipir trisodium-enhanced liver and pancreas MRI
  • 1999
  • Ingår i: Journal of Magnetic Resonance Imaging. - 1053-1807 .- 1522-2586. ; 9:2, s. 280-284
  • Tidskriftsartikel (refereegranskat)abstract
    • To find an optimal magnetic resonance (MR) sequence for mangafodipir trisodium-enhanced liver and pancreas imaging, six healthy volunteers were studied using a 1.5 T MR system with different T1-weighted abdominal imaging sequences. These were turbo field (gradient)-echo (TFE), fast field (gradient)-echo (FFE), and spin-echo sequences before and after mangafodipir trisodium administration. Various parameter combinations were investigated within each sequence type, and then the best combination was found and compared with those of the other sequences. Signal intensity (SI) measurements were made in regions of interest in the liver, pancreas, and a reference marker with a known T1 value. Contrast index (CI, SItissue/SImarker) and contrast-to-noise ratio (CNR, [SItissue/SImarker]/SDbackground) were calculated, and percentage CI increase and CNR in the postcontrast images were used for the best sequence evaluation. Regarding CI, the TFE sequence with a TR/TE/flip angle of 15 msec/4.6 msec/20 degrees and inversion time of 300 msec had the largest pre- to postcontrast percentage increase. The FFE sequence with a TR/TE/flip angle of 140 msec/4.6 msec/90 degrees had the highest postcontrast CNR and is considered to be the optimal sequence for mangafodipir trisodium-enhanced MR imaging of the liver and pancreas.
  • Alamidi, Daniel, et al. (författare)
  • Variable flip angle 3D ultrashort echo time (UTE) T1 mapping of mouse lung: A repeatability assessment
  • 2018
  • Ingår i: Journal of Magnetic Resonance Imaging. - : John Wiley and Sons. - 1053-1807 .- 1522-2586. ; 48:3, s. 846-852
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Lung T1is a potential translational biomarker of lung disease. The precision and repeatability of variable flip angle (VFA) T1mapping using modern 3D ultrashort echo time (UTE) imaging of the whole lung needs to be established before it can be used to assess response to disease and therapy. Purpose: To evaluate the feasibility of regional lung T1quantification with VFA 3D-UTE and to investigate long- and short-term T1repeatability in the lungs of naive mice. Study type: Prospective preclinical animal study. Population: Eight naive mice and phantoms. Field strength/Sequence: 3D free-breathing radial UTE (8 μs) at 4.7T. Assessment: VFA 3D-UTE T1calculations were validated against T1values measured with inversion recovery (IR) in phantoms. Lung T1and proton density (S0) measurements of whole lung and muscle were repeated five times over 1 month in free-breathing naive mice. Two consecutive T1measurements were performed during one of the imaging sessions. Statistical Tests: Agreement in T1between VFA 3D-UTE and IR in phantoms was assessed using Bland–Altman and Pearson 's correlation analysis. The T1repeatability in mice was evaluated using coefficient of variation (CV), repeated-measures analysis of variance (ANOVA), and paired t-test. Results: Good T1agreement between the VFA 3D-UTE and IR methods was found in phantoms. T1in lung and muscle showed a 5% and 3% CV (1255 ± 63 msec and 1432 ± 42 msec, respectively, mean ± SD) with no changes in T1or S0over a month. Consecutive measurements resulted in an increase of 2% in both lung T1and S0. Data Conclusion: VFA 3D-UTE shows promise as a reliable T1mapping method that enables full lung coverage, high signal-to-noise ratio (∼25), and spatial resolution (300 μm) in freely breathing animals. The precision of the VFA 3D-UTE method will enable better design and powering of studies. Level of Evidence: 1. Technical Efficacy: Stage 2. J. Magn. Reson. Imaging 2018;48:846–852.
  • Andersson, Thord, et al. (författare)
  • Consistent intensity inhomogeneity correction in water–fat MRI
  • 2015
  • Ingår i: Journal of Magnetic Resonance Imaging. - : John Wiley & Sons. - 1053-1807 .- 1522-2586. ; 42:2, s. 468-476
  • Tidskriftsartikel (refereegranskat)abstract
    • PURPOSE:To quantitatively and qualitatively evaluate the water-signal performance of the consistent intensity inhomogeneity correction (CIIC) method to correct for intensity inhomogeneities METHODS: Water-fat volumes were acquired using 1.5 Tesla (T) and 3.0T symmetrically sampled 2-point Dixon three-dimensional MRI. Two datasets: (i) 10 muscle tissue regions of interest (ROIs) from 10 subjects acquired with both 1.5T and 3.0T whole-body MRI. (ii) Seven liver tissue ROIs from 36 patients imaged using 1.5T MRI at six time points after Gd-EOB-DTPA injection. The performance of CIIC was evaluated quantitatively by analyzing its impact on the dispersion and bias of the water image ROI intensities, and qualitatively using side-by-side image comparisons.RESULTS:CIIC significantly ( P1.5T≤2.3×10-4,P3.0T≤1.0×10-6) decreased the nonphysiological intensity variance while preserving the average intensity levels. The side-by-side comparisons showed improved intensity consistency ( Pint⁡≤10-6) while not introducing artifacts ( Part=0.024) nor changed appearances ( Papp≤10-6).CONCLUSION:CIIC improves the spatiotemporal intensity consistency in regions of a homogenous tissue type. J. Magn. Reson. Imaging 2014.
  • Bergvall, Erik, et al. (författare)
  • A fast and highly automated approach to myocardial motion analysis using phase contrast magnetic resonance imaging.
  • 2006
  • Ingår i: Journal of Magnetic Resonance Imaging. - : John Wiley and Sons. - 1522-2586. ; 23:5, s. 652-661
  • Tidskriftsartikel (refereegranskat)abstract
    • Purpose: To develop a fast and highly automated method for calculating two-dimensional myocardial motion and deformation using velocity encoded magnetic resonance imaging. Materials and Methods: Two-dimensional phase contrast magnetic resonance imaging was used to acquire time resolved velocity maps of the myocardium. Cardiac motion was calculated by an iterative integration-regularization scheme of low computational cost. Image segmentation was performed using active appearance models. Results: Validation of motion tracking was performed in N = 47 subjects using saturation grid-tagging and closely followed "tag-lines." Image segmentation was validated vs. manual delineation. Conclusion: The speed and limited user interaction gives the method good potential for use in clinical practice.
  • Briley Saebo, Karen, et al. (författare)
  • Long-term imaging effects in rat liver after a single injection of an iron oxide nanoparticle based MR contrast agent
  • 2004
  • Ingår i: Journal of Magnetic Resonance Imaging. - 1053-1807 .- 1522-2586. ; 20:4, s. 622-631
  • Tidskriftsartikel (refereegranskat)abstract
    • PURPOSE: To investigate the duration of liver R2* enhancement and pharmacokinetics following administration of an iron oxide nanoparticle in a rat model.MATERIALS AND METHODS: Rats were injected with 0, 1, 2, or 5 mg Fe/kg of NC100150 Injection, and quantitative in vivo 1/T2* liver measurements were obtained between 1 and 133 days after injection. The concentration of NC100150 Injection was determined by relaxometry methods in ex vivo rat liver homogenate.RESULTS: At all dose levels, 1/T2* remained greater than control values up to 63 days after injection. In the highest dose group, 1/T2* was above control levels during the entire 133 day time-course investigated. There were no quantifiable amounts of NC100150 Injection present 63 days after injection in any of the dose groups. The half-life of NC100150 Injection in rat liver was dose dependent. For the lowest dose group, the degradation of the particles could be defined by a mono-exponential function with a half-life of eight days. For the 2 and 5 mg Fe/kg dose groups, the degradation was bi-exponential with a fast initial decay of seven to eight days followed by a slow terminal decay of 43-46 days.CONCLUSION: NC100150 Injection exhibits prolonged 1/T2* enhancement in rat liver. The liver enhancement persisted at time points when the concentration of iron oxide particles present in the liver was below method detection limits. The prolonged 1/T2* enhancement is likely a result of the particle breakdown products and the induction of ferritin and hemosiderin with increasing iron cores/loading factors.
  • Burtscher, Isabella M, et al. (författare)
  • Proton MR spectroscopy in clinical routine
  • 2001
  • Ingår i: Journal of Magnetic Resonance Imaging. - : John Wiley and Sons. - 1522-2586. ; 13:4, s. 560-567
  • Tidskriftsartikel (refereegranskat)abstract
    • In vivo magnetic resonance spectroscopy (MRS) addresses metabolic pathways and their steady states in different tissue types. The brain has by tradition, and due to technical limitations in other organs, been one of the tissues most studied by MRS, and both 1H- and 31P-MRS have been used. Although 31P-MRS is outstanding for the evaluation of sources of metabolic energy in the brain, 1H-MRS has become the major clinically applied method in neurospectroscopy, as it provides information on markers of neuronal function, myelin, cell membranes, and metabolic active compounds. Furthermore, MR sensitivity is much greater for protons than it is for phosphorus and 1H-MRS, therefore allowing better spatial resolution. This review focuses on neurospectroscopy and diagnostic insights into diverse neurological problems provided by 1H-MRS applied as a clinical tool.
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