| 1. |
- Engellau, Lena, et al.
(författare)
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MR evaluation ex vivo and in vivo of a covered stent-graft for abdominal aortic aneurysms: ferromagnetism, heating, artifacts, and velocity mapping
- 2000
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Ingår i: Journal of Magnetic Resonance Imaging. - 1522-2586. ; 12:1, s. 112-121
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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.
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| 2. |
- 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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| 3. |
- Holmqvist, Catarina, et al.
(författare)
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Collateral flow in coarctation of the aorta with magnetic resonance velocity mapping: correlation to morphological imaging of collateral vessels.
- 2002
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 15:1, s. 39-46
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To correlate quantification of collateral flow in aortic coarctation with the morphological visualization of the collateral vessels and to compare different approaches to measurement of collateral flow. MATERIALS AND METHODS: Thirteen children with coarctation were examined with T1-weighted spin-echo (T1-W SE) imaging and 3D contrast-enhanced magnetic resonance angiography (MRA). MR velocity mapping was performed at four levels in the descending aorta. RESULTS: The flow immediately above and below the coarctation did not differ significantly. Measuring within the coarctation resulted in flow overestimation. The increase of flow from proximal to distal aorta was 12 +/- 21% in patients with no or uncertain collaterals and 69 +/- 55% in patients with pronounced collaterals. Spin-echo images and MRA were comparable in visualizing collateral vessels. The visual estimation of collaterals correlated reasonably well with flow quantification MR velocity mapping. CONCLUSION: Collateral flow assessment with MR velocity mapping is an accurate technique for evaluating the hemodynamic importance of a coarctation and is recommended if abundant collaterals are not visualized with spin echo or MRA.
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| 4. |
- Knutsson, Linda, et al.
(författare)
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Absolute quantification of cerebral blood flow in normal volunteers: Correlation between Xe-133SPECT and dynamic susceptibility contrast MRI
- 2007
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 26:4, s. 913-920
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To compare, absolute cerebral blood flow (CBF) estimates obtained by dynamic susceptibility contrast MRI (DSC-MRI) and Xe-133 SPECT. Materials and Methods: CBF was measured in 20 healthy volunteers using DSC-MRI at 3T and Xe-133 SPECT. DSC- MRI was accomplished by gradient-echo EPI and CBF was calculated using a time-shift-insenisitive deconvolution algorithm and regional arterial input functions (AIFs). To improve the reproducibility of AIF registration the time integral was rescaled by use, of a venous output function. In the Xe-133 SPECT experiment, Xe-133 gas was inhaled over 8 minutes and CBF was calculated using a biexponential analysis. Results: The average whole-brain CBF estimates obtained by DSC-MRI and Xe- 133 SPECT were 85 +/- 23 mL/(min 100 g) and 40 +/- 8 mL/(min 100 g), respectively (mean +/- SD, n = 20). The linear CBF relationship between the two modalities showed a correlation coefficient of r = 0.76 and was described by the equation CBF(MRI) = 2.4 CBF(Xe) - 7.9 (CBF in units of mL/(min 100 g)). Conclusion: A reasonable positive linear correlation between MRI-based and SPECT-based CBF estimates was observed after AIF time-integral correction. The use of DSC-MRI typically results in overestimated absolute perfusion estimates and the present study indicates that this trend is further enhanced by the use of high magnetic field strength (3T).
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| 5. |
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| 6. |
- Malmgren, Lars, et al.
(författare)
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Improved receiver coil for upper thoracic spine imaging in a vertical magnetic field
- 1992
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 2:2, s. 191-195
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Tidskriftsartikel (refereegranskat)abstract
- To improve image quality in the upper thoracic spine, an anatomically shaped copper wire loop coil, made to fit over the patient's shoulders, was constructed. The coil was permanently mounted on a foam-rubber vest to facilitate attachment to the patient. Phantom and in vivo studies of the performance of the coil in healthy volunteers showed as much as a two times greater signal-to-noise ratio relative to that of standard coils for the upper thoracic spine. In a patient with lesions in the upper thoracic cord, the coil gave better image quality in the region of interest than did the standard coils. The coil has been integrated into the authors' routine imaging equipment and has been the coil of choice for imaging of the upper thoracic spine on their 0.3-T vertical field system.
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| 7. |
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