PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 9178243

Improved automatic off-resonance correction without a field map in spiral imaging.

L C Man·J M Pauly·A Macovski
View original source ↗Export metadata ↓

Abstract

Non-2DFT k-space readout strategies are useful in fast imaging but prone to blurring when reconstructed off resonance. Field inhomogeneities or susceptibility variations, coupled with a long readout time, are the major sources of this artifact. Correction methods based on a priori off-resonance information such as an acquired field map have been proposed in the literature. An alternative approach estimates the spatially varying off-resonance frequency from the data itself before applying a correction. In this latter approach there is a trade-off between the extent of correction and the chance of increased artifact due to estimation error. This paper introduces an improved algorithm for field map estimation which is both faster and more robust than the existing method. It uses a multi-stage estimation of the field map, starting from a coarse estimate both in frequency and space and proceeds towards higher resolution. The new algorithm is applied to phantom and in vivo images acquired with radial and spiral sequences to give sharper images.

Explore related subjects

AbdomenAlgorithmsArtifactsHumansImage Processing, Computer-AssistedMagnetic Resonance ImagingPhantoms, ImagingJournal ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, P.H.S.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

L C Man, J M Pauly, A Macovski. 1997. Improved automatic off-resonance correction without a field map in spiral imaging.. https://doi.org/10.1002/mrm.1910370616

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2007

A case of scirrhous gastric cancer with peritonitis carcinomatosa controlled by TS-1 + paclitaxel for 36 mo after diagnosis.

A 34-year-old female complaining of abdominal fullness was diagnosed as scirrhous gastric cancer (type 4') with peritonitis carcinomatosa in July 2002. A combined chemotherapy regimen was selected to control massive ascites; TS-1 80 mg/m(2) was given orally on d 1-14, 22-35, and paclitaxel 50 mg/m(2) was administered intravenously on d 1, 8, 22 and 29. After 2 courses of this regimen, the primary tumor was markedly reduced, and ascites completely vanished. Alopecia (grade 1, since d 30), leukocytopenia (grade 2, on d 34) and anemia (grade 2, on d 34) were the only adverse events throughout the following courses. The chemotherapy was effective for 28 mo, and then it was discontinued upon the patientos own request, and she survived for 36 mo after diagnosis.

Abdomen↗
PubMed2007

Endocrine role of the renin-angiotensin system in human adipose tissue and muscle: effect of beta-adrenergic stimulation.

The renin-angiotensin system has been implicated in obesity-related hypertension and insulin resistance. We examined whether locally produced components of the renin-angiotensin system in adipose tissue and skeletal muscle play an endocrine role in vivo in humans. Furthermore, the effects of beta-adrenergic stimulation on plasma concentrations and tissue release of renin-angiotensin system components were investigated. Systemic renin-angiotensin system components and arteriovenous differences of angiotensin II (Ang II) and angiotensinogen (AGT) across abdominal subcutaneous adipose tissue and skeletal muscle were assessed in combination with measurements of tissue blood flow before and during systemic beta-adrenergic stimulation in 13 lean and 10 obese subjects. Basal plasma Ang II and AGT concentrations were not significantly different between lean and obese subjects. Ang II concentrations were increased in obese compared with lean subjects during beta-adrenergic stimulation (12.6+/-1.5 versus 8.1+/-1.0 pmol/L; P=0.04), whereas AGT concentrations remained unchanged. Plasma renin activity increased to a similar extent in lean and obese subjects during beta-adrenergic stimulation (both P<0.01). No net Ang II release across adipose tissue and skeletal muscle could be detected in both groups of subjects. However, AGT was released from adipose tissue and muscle during beta-adrenergic stimulation in obese subjects (both P<0.05). In conclusion, locally produced Ang II in adipose tissue and skeletal muscle exerts no endocrine role in lean and obese subjects. In contrast, AGT is released from adipose tissue and muscle in obese subjects during beta-adrenergic stimulation, which may contribute to the increased plasma Ang II concentrations during beta-adrenergic stimulation in obese subjects.

Abdomen↗
PubMed2007

Absence of selective brain cooling in unrestrained baboons exposed to heat.

To test whether baboons are capable of implementing selective brain cooling, we measured, every 5 min, the temperature in their hypothalamus, carotid arterial bloodstream, and abdominal cavity. The baboons were unrestrained and exposed to 22 degrees C for 7 days and then to a cyclic environment with 15 degrees C at night and 35 degrees C during the day for a further 7 days. During the latter 7 days some of the baboons also were exposed to radiant heat during the day. For three days, during heat exposure, water was withheld. At no time was the hypothalamus cooler than carotid arterial blood, despite brain temperatures above 40 degrees C. With little variation, the hypothalamus was consistently 0.5 degrees C warmer than arterial blood. At high body temperatures, the hypothalamus was sometimes cooler than the abdomen. Abdominal temperature was more variable than arterial blood and tended to exceed arterial blood temperature at higher body temperatures. Hypothalamic temperature cooler than a warm abdomen is not evidence for selective brain cooling. In species that can implement selective brain cooling, the brain is most likely to be cooler than carotid arterial blood when an animal is hyperthermic, during heat exposure, and also dehydrated and undisturbed by human presence. When we exposed baboons to high ambient temperatures while they were water deprived and undisturbed, they never implemented selective brain cooling. We conclude that baboons cannot implement selective brain cooling and can find no convincing evidence that any primate species can do so.

Abdomen↗