Signal-to-noise optimization and observed volume localization with circular surface coils

Evelhoch, Jeffrey L.; Crowley, Michael; Ackerman, Joseph J. H.

doi:10.1016/0022-2364(84)90195-1

Cited by 70 publications

(32 citation statements)

References 14 publications

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“…1,6 SC have the inconvenience of having a different sensitivity at each point depending on the depth. [1][2][3] If the correlation between the obtained image and the tissues real distribution has to be high (image fidelity) the sensitivity map must be as uniform as possible. Ideally, the sensitivity should be the same everywhere in such a way that the image would only depend on the sample characteristics.…”

Section: The Signalmentioning

confidence: 99%

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MRI Visualization of Small Structures Using Improved Surface Coils

Rivera¹,

Vaquero²,

Santos³

et al. 1998

Magnetic Resonance Imaging

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In this paper we present the spatial resolution enhancement and noise reduction level achieved with an optimized inductively coupled surface coil specificall designed for our experiments. The technique of designing and implementing customized coils for magnetic resonance imaging of very small structures is described. We have designed a low cost prototype of an inductively coupled circular surface coil, tuned for 1 H magnetic resonance imaging at 200 MHz. The coil is mounted on a customized teflo support. The inductive coupling used in this coil improves the signal-to-noise ratio by reducing various loss mechanisms (specially the dielectric losses). Test images have been acquired to determine the evolution of induced articular lesions in a rabbit animal model, as well as brain tumors in rats. The images show high spatial resolution, excellent B 1 fiel homogeneity and no ''hot spots''. Comparing these images with those acquired with conventional coils, one find better spatial resolution and signal-to-noise ratio, as well as larger fiel of view with less intense illumination artifact. The methodology can be used in any application that requires high quality imaging of small structures.

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Section: The Signalmentioning

confidence: 99%

“…[1][2][3][4][5] This signal (s) is contaminated by undesired noise (r) at the detector input. The relationship between signal and noise is described by a dimensionless variable known as the signal-to-noise ratio (SNR); the higher the SNR is, the better the image quality.…”

Section: Introductionmentioning

confidence: 99%

MRI Visualization of Small Structures Using Improved Surface Coils

Rivera¹,

Vaquero²,

Santos³

et al. 1998

Magnetic Resonance Imaging

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“…Rapid pulsing was used to optimize sensitivity per unit time (13),even thou gh comparisons of relative amounts of metabolites are thus invalid due to differential partial saturation of the peaks of interest. Serial concentration changes of individual metabolites may be reliably obtained if it is assumed that T 1 values are relatively independent of physiological state (6,8,(13)(14)(15)(16). Since PCr T I'S of brain in vivo are in the range 2.2-4.4 s (15, 16), precise quantitation would require pulse delays of at least 6.6-13.2 s.…”

Section: Systemic Changes Experiments Were Carri Ed Out In Neonatalmentioning

confidence: 99%

31P Nuclear Magnetic Resonance Study of the Effect of Hypoxemia on Neonatal Status Epilepticus

et al. 1986

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METH ODSbolic perturbat ion imp osed by hypoxia, by seizures during normoxia, and by seizures during hypoxia. The se are topi cs of major clinical relevance since seizures in the neon ate are frequ entl y manifested by apnea and cyanosis (2).In measuring cerebral metabolic state , we employed high resolution 31P_NMRspectroscopy, a powerful technique for noninvasi ve, sequential measurement of brain energy change s in vivo (6-9). These in vivo measur ements were corro borated by in vitro determ inati on of brain metabolite concentratio ns. Systemic changes. Experiments were carri ed out in neonatal(1-to 10-day old) mongrel dogs as previously described (8). Halothane (0.5-3.0%) in oxygen was administered to allow tracheostom y. Haloth ane was then discontinued and the animals were paral yzed with pan curonium (0.2 ml admi nistered intraperitoneally) and mechanically ventilated with a gas mixture of 30% O2/7 0% N20 . In add ition to the use of nitrou s oxide for analgesia, all sites of incision were infiltrated with local anesthetic (xylocaine, 1%). The femoral art eries were catheterized to continuously monitor blood pressure and to anaerobically withdraw sampl es for determination of blood gases. The femoral vein was cath eterized to allow infusion of dru gs. Wounds were periodically infiltrated with xylocaine.Carbon dioxide tensions were normalized (PC0 2, 30-40 mm Hg) by adju sting minute ventilation. Thereafter, ventilator settings were not changed. Animals who had abno rmal acid-base statu s (base deficit> 5 mm ol HC0 3 / liter) were not entered into the study. Following a 30-min normalization period, animals were randomly assigned to one of four stud y groups: control group , hypoxia group, seizure-normox ia or seizure-hypoxia group. Th e durat ion of hypoxia, seizure, or seizure and hypoxia was 45 min. Animals in the hypoxia group or seizure-hypoxia group were ventilated with a gas mixtu re containing 8% O 2 / 92% N2• Animals in the contro l group or seizure-norm oxia group were ventilated with a gas mixtu re consisting of 30% O 2 / 70% N20. Seizures were induced in the seizure-normo xia and seizurehypoxia group s with an intravenous infusion of the 'Y amino but yric acid blocking agent , bicuc ulline (Sigma Co.), 2 mg/kg intravenou sly. Animals in the contro l and hypoxia groups received an equ ivalent volume of 0.9% saline intravenously.Blood gases were measured with a Radiom eter microblood gas analyzer. Plasma glucose levels were measured using a Beckm an G lucose Analyzer II; plasma lactate levels were measured spectrophotometrically using standard enzymatic anal yses (10). Plasma catech olamine concentratio ns were determined by radioenzymati c analysis (1 1).Cerebral phys iology. Th e EEG was continuo usly recorded with scalp electrodes and a Beckman polygraph ic recorder. An auto-58 1 Abbreviations 3IP_NM R, phosphorus-31 nuclear magnetic resonance CBF, cerebral blood flow PCr, phosphocreatine ABSTRACf. Prolonged neonatal seizures are often accompanied or exacerbated by hypoxemia. To determine the e...

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“…A pulse width of 36 ps provided optimal signal to noise (approximately 12.5: 1 for ATP after 300 one-s scans). Rapid pulsing was performed to increase sensitivity per unit time (14). Optimization of the homogeneity of the magnet was performed by observing the proton signal of water.…”

Section: Methodsmentioning

confidence: 99%

The Effect of Hypotension on Brain Energy State during Prolonged Neonatal Seizure

et al. 1987

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Clinical and experimental evidence show that systemic hypotension may occur during the course of prolonged seizure (1-3). Nonetheless, the physiologic and metabolic consequences of hypotension on the outcome of neonatal seizure is unclear (4). Because metabolic demands on the brain increase greatly during seizure, it is hypothesized that even a modest reduction in CBF produces relative ischemia and further tissue damage.Autoregulation of CBF ordinarily maintains cerebral perfusion during systemic hypotension (5, 6), but may be impaired during seizure (4, 7). However, use of the term, autoregulation, may be inappropriate since the response of the cerebral circulation to seizure is not a simple maintenance of blood flow, but rather a sustained increase of 150-200% (8,9). The goal of this study was to determine whether the expected compensatory increase in CBF which occurs during seizure is affected by moderate hypotension and whether there is subsequent compromise of brain energy state.

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Signal-to-noise optimization and observed volume localization with circular surface coils

Cited by 70 publications

References 14 publications

MRI Visualization of Small Structures Using Improved Surface Coils

MRI Visualization of Small Structures Using Improved Surface Coils

31P Nuclear Magnetic Resonance Study of the Effect of Hypoxemia on Neonatal Status Epilepticus

The Effect of Hypotension on Brain Energy State during Prolonged Neonatal Seizure

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