| 1. |
- Brockstedt, Sara, et al.
(författare)
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High-resolution diffusion imaging using phase-corrected segmented echo-planar imaging
- 2000
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Ingår i: Magnetic Resonance Imaging. - 1873-5894. ; 18:6, s. 649-657
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion magnetic resonance imaging (MRI) was performed with a high-resolution segmented echo-planar imaging technique, which provided images with substantially less susceptibility artifacts than images obtained with single-shot echo-planar imaging (EPI). Diffusion imaging performed with any multishot pulse sequence is inherently sensitive to motion artifacts and in order to reduce motion artifacts, the presented method utilizes navigator echo phase corrections, performed after a one-dimensional Fourier transform along the frequency-encoding direction. Navigator echo phases were fitted to a straight line prior to phase correction to avoid errors from internal motion. In vivo imaging was performed using electro cardiographic (ECG) triggering. Apparent diffusion coefficient (ADC) maps were calculated on a pixel-by-pixel basis using up to seven diffusion sensitivities, ranging from b = 0 to 1129 x 10(6) s/m(2).
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| 2. |
- Brockstedt, Sara, et al.
(författare)
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SchnelleMagnetresonanz-Bildgebung
- 2002
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Ingår i: Radiologie Up2Date. - : Georg Thieme Verlag KG. - 1616-0681 .- 1617-8300. ; :4, s. 413-438
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in German Die Verkürzung der Untersuchungszeiten bei der klinischen Magnetresonanztomographie (MRT) bietet für den Patienten den Vorteil einer angenehmeren und schnelleren Untersuchung und erhöht gleichzeitig den Patientendurchsatz. Dies erfordert schnelle und robuste Aufnahmetechniken, welche beispielsweise auch bei der Aufnahme bewegter Organe oder für atemangehaltene Messungen eingesetzt werden können. Durch die Entwicklung leistungsfähiger Gradientensysteme konnten in den letzten Jahren neue und schnelle Pulssequenzen entwickelt werden. Die rasante Entwicklung neuer Aufnahmemethoden und Rekonstruktionstechniken macht es für den Anwender immer wichtiger, die grundlegenden Prinzipien schneller Aufnahmetechniken zu verstehen. In diesem Übersichtsartikel wird versucht, die Grundlagen der schnellen Pulssequenzen und deren klinische Anwendungsbereiche darzustellen. Dies beinhaltet die schnelle Spin-Echo-Technik und deren Kombination mit selektiven Präparationstechniken, die schnelle und ultraschnelle Gradienten-Echo-Technik sowie die echoplanare Bildgebung. Abschließend werden kurz neueste Entwicklungen wie die parallele Bildgebung beschrieben.Zusammenfassung auf S. 434
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| 3. |
- 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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| 4. |
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| 5. |
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| 6. |
- Geijer, Bo, et al.
(författare)
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Persistent high signal on diffusion-weighted MRI in the late stages of small cortical and lacunar ischaemic lesions
- 2001
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Ingår i: Neuroradiology. - : Springer Science and Business Media LLC. - 1432-1920 .- 0028-3940. ; 43:2, s. 115-122
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion-weighted imaging (DWI) is very sensitive to early brain infarcts. However, the late stages have been insufficiently studied. Infarcts in small vessel disease are often multiple and of different ages, and differentiation between new and old lesions might be difficult. We have therefore studied the change with time in DWI of small (< 3 ml) ischaemic lesions. We imaged 21 patients with an acute lacunar syndrome and a lesion visible on early DWI. They all had three MRI examinations 12-58 h (early), 7-16 and 54-144 days after the onset of stroke; 10 patients with high DWI signal on the third examination had a fourth examination 12-28 months after the stroke. MRI was performed at 1.5 T, using echo-planar DWI with 7 b-values from 0 to 1200 x 10(6) s/m2 and conventional T2-weighted imaging. After 7-16 days 18 of 21 lesions gave high signal on DWI, and 12/16 measurable lesions had a decreased apparent diffusion coefficient (ADC). After 54-144 days ten lesions still gave high DWI signal and two still had an ADC below normal. On the fourth examination there was no remaining high DWI signal and all ADC were higher than normal.
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| 7. |
- Geijer, Bo, et al.
(författare)
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The value of b required to avoid T2 shine-through from old lucunar infarcts in diffusion-weighted imaging
- 2001
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Ingår i: Neuroradiology. - : Springer Science and Business Media LLC. - 1432-1920 .- 0028-3940. ; 43:7, s. 511-517
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Tidskriftsartikel (refereegranskat)abstract
- Multiple small infarcts of different ages are common in small-vessel disease. Diffusion-weighted imaging (DWI) is a powerful method for discriminating new from chronic lesions. This can be done on the diffusion-weighted images provided that b is sufficiently high. Our purpose was to determine that critical value of b. We reviewed DWI from a previous study of acute, mainly lacunar strokes, and selected 18 old lacunar infarcts, well defined on uncoded images with b 0 s/m2 (i. e., T2-weighted images) but invisible on DWI with b 1,200 x 10(6) s/m2. We used a 1.5 tesla imager and single-shot echo-planar technique. We had seven separate acquisitions with echo time 123 ms and b in steps between 0 and 1,200 x 10(6) s/m2. Two neuroradiologists blinded to the selection of lesions carried out two different lesion-detection procedures, thereby testing each lesion four times, giving a total of 72 tests of b values. The results were consistent, indicating a level for detection of 800 x 10(6) s/m2 in two tests, 400-600 x 10(6) s/m2 in 65 tests and at lower values in the remainder. For imagers up to 1.5 tesla, at long repetition times and an echo time up to 120 ms T2-shine through of old lacunar infarcts can be avoided using b of 1,000 x 10(6) s/m2.
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| 8. |
- Holmqvist, Catarina, et al.
(författare)
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Pre-operative evaluation with MR in tetralogy of fallot and pulmonary atresia with ventricular septal defect
- 2001
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Ingår i: Acta Radiologica. - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 42:1, s. 63-69
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To assess whether MR imaging could replace angiography in preoperative evaluation of patients with tetralogy of Fallot and pulmonary atresia with ventricular septal defect (VSD), especially since the surgical correction was done earlier than was previously the rule. MATERIAL AND METHODS: Fourteen patients with tetralogy of Fallot (n = 10) or pulmonary atresia with VSD (n = 4), mean age 7.5 +/- 4.4 months, were evaluated with angiocardiography and MR before definitive surgical correction. RESULTS: There was good diagnostic agreement between the two modalities when evaluating right ventricular outflow obstruction; 86% for valvular and 93% for supravalvular stenosis, but the agreement was somewhat lower for the subvalvular obstruction (57%). Surgery findings, however, were in favour of MR in 5 patients concerning the subvalvular right ventricular outflow tract obstruction. MR images identified all stenoses in the right and left pulmonary arteries, but overlooked one stenosis in the main pulmonary artery. MR could evaluate patency in all palliative shunts. CONCLUSION: Even in this young age group, MR imaging offers a good alternative to angiocardiography for the pre-operative evaluation of the right ventricular outflow tract, the main pulmonary artery and the proximal right and left pulmonary arteries, before definitive surgical correction of tetralogy of Fallot and pulmonary atresia with VSD.
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| 9. |
- Larsson, Elna-Marie, et al.
(författare)
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MRI with diffusion tensor imaging post-mortem at 3.0 T in a patient with frontotemporal dementia.
- 2004
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Ingår i: Dementia and Geriatric Cognitive Disorders. - : S. Karger AG. - 1420-8008 .- 1421-9824. ; 17:4, s. 316-319
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Tidskriftsartikel (refereegranskat)abstract
- The formalin-fixed brain of a patient with clinically diagnosed frontotemporal dementia (FTD) was examined post-mortem using magnetic resonance imaging (MRI) with diffusion tensor imaging (DTI) at 3.0 T. Frontotemporal atrophy as well as bilateral frontal white matter abnormalities were seen. The white matter changes were slightly more extensive on DTI than on conventional MRI. Correlation with histopathology of the corresponding regions revealed typical frontal lobe degeneration of non-Alzheimer type, with mild frontotemporal degeneration in the outer cortical layers and a moderate frontal white matter gliosis with demyelination. Post-mortem MRI/DTI with histopathologic correlation will enhance our understanding of the basis of white matter changes observed in dementia patients and may improve the in vivo MRI/DTI diagnostic assessment in FTD.
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| 10. |
- Lindgren, Arne, et al.
(författare)
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Clinical lacunar syndromes as predictors of lacunar infarcts. A comparison of acute clinical lacunar syndromes and findings on diffusion-weighted MRI
- 2000
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Ingår i: Acta Neurologica Scandinavica. - : Hindawi Limited. - 1600-0404 .- 0001-6314. ; 101:2, s. 128-134
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To evaluate if patients with acute lacunar syndromes have acute lacunar infarcts or other types of cerebral lesions on diffusion-weighted MRI. METHODS: Patients with acute lacunar syndromes underwent echo-planar diffusion MRI of the brain within 3 days after stroke onset. Localization and size of lesions with hyperintense signal were determined, compared with clinical characteristics and with findings on follow-up T2-weighted MRI. RESULTS: Twenty-three patients participated in the study. Thirteen patients had pure motor stroke, 1 pure sensory stroke, 8 sensorimotor stroke, and 1 ataxic hemiparesis. Twenty-two patients had at least one lesion with increased signal on diffusion-weighted MR images. These acute lesions were in the internal capsule/ basal ganglia/thalamus in 13 patients, subcortical white matter in 5 patients, brainstem in 2 patients, cortex (multiple small lesions) in 1 patient, and cortex + basal ganglia in 1 patient. The median volume of the lesions was 0.6 ml on the initial examination and on follow-up, of 17 patients after 1 to 5 months, 0.5 ml. CONCLUSIONS: Almost all patients with acute ischemic lacunar syndromes have acute lesions on echo-planar diffusion-weighted MRI within 3 days after stroke onset. These lesions are mostly small and subcortical, compatible with lacunar infarcts caused by single penetrating artery occlusion, but in a minor proportion of patients (2 of 23 in our study) a cortical involvement is found.
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