Passive screening of switched magnetic field gradients

Turner, Robert; Bowley, R. M.

doi:10.1088/0022-3735/19/10/023

Cited by 167 publications

(100 citation statements)

References 2 publications

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“…, 1986;Turner and Bowley , 1986) was used with a low-pass birdcage proton imaging coil (Stilbs and Moseley , 1978). Baseline diffusion-weighted and T2-weighted multi slice images were collected.…”

Section: Mr Imaging Methodsmentioning

confidence: 99%

Diffusion-Weighted Magnetic Resonance Imaging of Acute Focal Cerebral Ischemia: Comparison of Signal Intensity with Changes in Brain Water and Na⁺,K⁺ -ATPase Activity

Mintorovitch

Yang

Shimizu

et al. 1994

J Cereb Blood Flow Metab

191

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Summary: Diffusion-weighted magnetic resonance (MR) images from rats during acute cerebral ischemia induced by middle cerebral artery occlusion were analyzed for correspondence with changes in brain water, cation con centrations , and Na + ,K + -ATPase activity measured in vitro after 30 or 60 min of ischemia. In the ischemic hemi sphere, signal intensity was increased at 30 min (p < 0.05 vs contralateral hemisphere) and further increased at 60 min. Na + ,K + -ATPase activity was 34% lower in isch emic cortex and 40% lower in ischemic basal ganglia after 30 min (p < 0.05), but water content and Na + and K + concentrations were not significantly different between Diffusion-weighted magnetic resonance (MR) im aging can detect less severe and potentially revers ible cerebral ischemia much earlier than conven tional T2-weighted MR imaging (Moseley et aI., 1990; Mintorovitch et aI., 1991; Minematsu et aI., 1992; van Bruggen et aI., 1992 Abbreviations used: ADC, apparent diffusion coefficient; ANOV A, analysis of variance; MCA, middle cerebral artery; MR, magnetic resonance; TE, echo time; TR, repetition time. 332hemispheres. After 60 min , water content and Na + con centration were increased , and both Na + ,K + -ATPase activity and K + concentration were decreased in the ischemic hemisphere (p < 0.05). These findings are con sistent with the hypothesis that the early onset of signal hyperintensity in diffusion-weighted MR images may re flect cellular edema associated with impaired membrane pump function. Early in vivo detection and localization of potentially reversible ischemic cerebral edema may have important research and clinical applications.

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Section: Mr Imaging Methodsmentioning

confidence: 99%

Diffusion-Weighted Magnetic Resonance Imaging of Acute Focal Cerebral Ischemia: Comparison of Signal Intensity with Changes in Brain Water and Na⁺,K⁺ -ATPase Activity

Mintorovitch

Yang

Shimizu

et al. 1994

J Cereb Blood Flow Metab

191

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“…z' = (a + P cos 7, P + P sin 7, ~( 7 ) )~ where p is the (constant) radius of the cylinder, 7 is an angle that parameterizes a position on the arc, (a,P) are the z and y coordinates of the axis of the cylinder and z ( 7 ) is the position of the wire along the cylinder. Notice that the allowed geometries with this parameterization are arcs on the surfaces of cylinders which may or may not be concentric with the z axis, pieces of helicies, and sections of tilted loops.…”

Section: Methods and Resultsmentioning

confidence: 99%

Abstracts-part VIII (Continue in Part IX)

1987

Proc. Soc. Magn. Reson. Med.

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M a s s a c h u s e t t s I n s t i t u t e of Technology, Cambridge M A *, D e p t . o f C a r d i o l o g y # andDept. of Radiology $ , M a s s a c h u s e t t s G e n e r a l H o s p i t a l , Boston MA. I n t r o d u c t i o nWhen image v o x e l s c o n t a i n s i g n a l from m u l t i p l e s o u r c e s o f p r o t o n s i t i s of b i o l o g i c a l and p h y s i o l o g i c a l import a n c e t o c h a r a c t e r i z e t h e c o n t r i b u t i o n from t h e s e s o u r c e s i n d e p e n d e n t l y . Chemical s h i f t [ 1 , 2 ] imaging t e c h n i q u e s can p r o v i d e i n f o r m a t i o n a b o u t b u l k c h e m i c a l s h i f t r e s o l v e d f r a c t i o n s o f t h e t o t a l p r o t o n s i g n a l . W e p r o p o s e an a d d i t i o n a l c h a r a c t e r i z a t i o n b a s e d on s c a l a r c o u p l i n g w i t h i n e a c h c h e m i c a l l y s h i f t e d group.The amount and t y p e s o f s c a l a r c o u p l i n g c a n b e c h a r a c t e r i z e d by t h e i n t e n s i t i e s ( I . ) and r e l a t i v e i n te n s i t i e s ( C . . ) o f t h e v a r i o u s o r d e r s o f quantum t r a h d i t i o n s , where i and j r e pr e s e n t t h e o r d e r o f t h e quantum t r a ns i t i o n and i is g r e a t e r t h a n j . I1 and Cil r e c e i v e c o n t r i b u t i o n s from a l l s p i n s i n t h e s y s t e m . The o t h e r p a r a m e t e r s ( I . , C i . , j > 1) c o rr e s p o n d o n l y t o s p i d c o u d l e d f r a c t i o n s i n t h e sample. MethodsThe f o l l o w i n g p u l s e s e q u e n c e is c a p a b l e of g e n e r a t i n g a l l -o r d e r s o f quantum t r a n s i t i o n s : 90;-t -180'-t -90;-te-18O0-te-90~-td-P Y P Y 18O0-td-OBS Y T h i s s e q u e n c e i s maximized f o r t h e d o u b l e quantum t r a n s i t i o n by l e t t i n g t =t = 1 / 4 5 w i t h J b e i n g t h e s p i n -s p i n c g u p f i n g c o n s t a n t o f i n t e r e s t [ 3 , 4 ] . . The j t h o r d e r can be encoded d u r i n g t h e e v o l u t i o n p o r t i o n o f t h e s e q u e n c e (90;-t -180'-t ) by t h e a p p l i c a t i o n o f a mggnetyc F i e l d g r a d i e n t and decoded d u r i n g t h e d e t e c t i o n p e r i o d (90;-t-180'-OBS) by t h e a p p l i c a t i o n o f a n g t h e r m a g x e t i c f i e l d g r a d i e n t w i t h a n i n t eg r a t e d i n t e n s i t y o f j t i m e s t h a t o f t h e encode g r a d i e n t [ 5 ] . The p h a s e and f r e q u e n c y e n c o d i n g c a n a l s o be accomp l i s h e d d u r i n g t h e d e t e c t i o n p e r i o d a s i n c o n v e n t i o n a l spin-warp imaging. W e have s e l e c t e d s a m p l e s o f water ( n o c o u p l e d s p i n s ) , e t h a n o l (CH CH OH, f i v e c o u p l e d s p i n s ) and i s o p r o p z n o ? ((CH ) CHOH, s e v e n c o u p l e d s p i n s ) t o evalila3e t h e e f f e c t of c o u p l e d and nonc o u p l e d s p i n f r a c t i o n s on image s i g n a l i n t e n s i t y .Images were formed o f a phantom of c o n c e n t r i c c y l i n d e...

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“…5a was generated using Eq. [15] with c l ϭ ␦ l,2 (corresponding to a stream function of the form (P 2 (cos ) Ϫ P 2 (0)P 0 (cos )), while Fig. 5b was produced by applying the elemental Biot-Savart expression to the case of unit current flow in wirepaths, formed from contours of the stream function (with 20 turns in the coil).…”

Section: Methodsmentioning

confidence: 99%

“…[12]. Wirepaths that produce a pattern of current flow that mimics the required current distribution are given by contours of the stream function (15).…”

Section: Hemispherical Axial Gradient Coilsmentioning

confidence: 99%

Hemispherical gradient coils for magnetic resonance imaging

Green

Leggett

Bowtell

2005

Magnetic Resonance in Med

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Hemispherical gradient coils offer an open geometry that is well suited to imaging of the human brain. The windings of a hemispherical gradient coil are on average closer to the target region than those of a comparable cylindrical coil, and consequently hemispherical coils can produce higher efficiency at fixed inductance. The mathematical formalism needed for the design of hemispherical gradient coils is described here, including expressions relating the current distribution on the hemisphere to the magnetic field generated, as well as the stored energy and power dissipation.

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Passive screening of switched magnetic field gradients

Cited by 167 publications

References 2 publications

Diffusion-Weighted Magnetic Resonance Imaging of Acute Focal Cerebral Ischemia: Comparison of Signal Intensity with Changes in Brain Water and Na⁺,K⁺ -ATPase Activity

Diffusion-Weighted Magnetic Resonance Imaging of Acute Focal Cerebral Ischemia: Comparison of Signal Intensity with Changes in Brain Water and Na⁺,K⁺ -ATPase Activity

Abstracts-part VIII (Continue in Part IX)

Hemispherical gradient coils for magnetic resonance imaging

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Passive screening of switched magnetic field gradients

Cited by 167 publications

References 2 publications

Diffusion-Weighted Magnetic Resonance Imaging of Acute Focal Cerebral Ischemia: Comparison of Signal Intensity with Changes in Brain Water and Na+,K+ -ATPase Activity

Diffusion-Weighted Magnetic Resonance Imaging of Acute Focal Cerebral Ischemia: Comparison of Signal Intensity with Changes in Brain Water and Na+,K+ -ATPase Activity

Abstracts-part VIII (Continue in Part IX)

Hemispherical gradient coils for magnetic resonance imaging

Contact Info

Product

Resources

About

Diffusion-Weighted Magnetic Resonance Imaging of Acute Focal Cerebral Ischemia: Comparison of Signal Intensity with Changes in Brain Water and Na⁺,K⁺ -ATPase Activity

Diffusion-Weighted Magnetic Resonance Imaging of Acute Focal Cerebral Ischemia: Comparison of Signal Intensity with Changes in Brain Water and Na⁺,K⁺ -ATPase Activity