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Biomedical subjects

J B Weaver

Publications and source records attributed to J B Weaver.

At least 19 recordsLinked to original sources
PubMed1992

Wavelet-encoded MR imaging.

Wavelet encoding is presented and compared to phase encoding. In wavelet encoding a distribution of spins is excited by a slice selective RF pulse; for each repetition time the distribution excited has the profile of a wavelet at different scale and translation. The spin density can be reconstructed with an inverse wavelet transform. Wavelet encoding has three advantages over phase encoding: (1) there is no Gibb's ringing from partial volume effects, (2) the effective repetition time can be 36 times the repetition time for a 256 x 256 image, and (3) motion artifacts are local and dramatically reduced. Using wavelet encoding, a 256 x 256 T2-weighted projection image can be acquired in 33 s.

Artifacts↗
PubMed1991

Filtering noise from images with wavelet transforms.

A new method of filtering MR images is presented that uses wavelet transforms instead of Fourier transforms. The new filtering method does not reduce the sharpness of edges. However, the new method does eliminate any small structures that are similar in size to the noise eliminated. There are many possible extensions of the filter.

Artifacts↗
PubMed1991

Limited field of view spin echo MR imaging.

Several groups have reported using a method of limiting the field of view (FOV) where the slices excited by the 90 and 180 degree pulses are perpendicular. However, only one slice can be excited during each repetition time, so multislice imaging is not possible. We present a modification of this method that allows multislice imaging. The slices excited by the 90 degrees and 180 degrees pulses are at a small angle; the field of view is limited and multislice imaging is possible. The modifications also allow the center of the FOV to be offset to any position. We describe the conditions that yield optimal images for the given FOV, slice thickness, and interslice gap. Representative images demonstrating the features of the technique are presented. The technique can be used to reduce the number of phase-encoding steps resulting in reduced imaging time, or it can be used to increase the spatial resolution without increasing the imaging time.

Humans↗
PubMed1988

Simultaneous multislice acquisition of MR images.

The simultaneous multislice technique is a method of imaging multiple parallel slices with the number of echoes normally used to image a single slice. Images of 16 slices have been obtained from a single 128-echo acquisition. The distance between the slices can be decreased to approximately 15% of the field of view in the readout direction with the cost of significant image blurring. The image blurring is negligible when the distance between the slices approaches the field of view in the readout direction. The trade-offs are described, and equations and images are presented.

Magnetic Resonance Imaging↗
PubMed1988

An assessment of the value of biochemical fetoplacental function tests in detecting intrauterine growth retardation.

Four serum biochemical fetoplacental function tests (HPL, unconjugated and total oestriol and AFP) were used to screen for intrauterine growth retardation in 793 patients attending an antenatal clinic. The birthweight corrected for sex, birth ranking and maternal size was used as an index of growth. The sensitivity and specificity of each test was calculated at varying cut-off points and plotted as 'Receiver Operator Curves'. HPL is clearly better than the oestriols or AFP with 80% sensitivity in detecting birth weights of less than the 5th centile when the 25th HPL centile is used as the cut-off point. However, the sensitivity of HPL is sufficiently low to make the value of screening questionable, particularly since 40% of all growth retarded infants were in mothers who did not attend antenatal clinic for screening and 25% of all growth retarded infants were detected by clinical examination.

Female↗
PubMed1985

Effect of alcoholic intoxication on the appreciation of different types of humor.

Male subjects were placed into one of three intoxication conditions (no ethanol, low dose, high dose) and were exposed to humorous segments from television programs. During manifest intoxication or the corresponding period in the no-intoxication control condition, they were exposed, in a balanced order, to a segment containing blunt (i.e., unsophisticated, raw) humor and to a segment containing subtle (i.e., sophisticated, refined) humor. Subjects' facial reactions to the humorous stimuli were unobtrusively recorded and later analyzed by judges who were naive about the experimental conditions. Subjects also rated the funniness of the segments. The perceived funniness of blunt humor was found to increase with ethanol intoxication. For subtle humor, in contrast, perceived funniness was found to decrease with intoxication. This divergent interaction of reported humor appreciation was less apparent in the analysis of facial expressiveness. Although correlations between ratings and aspects of facial expression were generally positive, clearly corroborative support for the humor appraisals was found only in the frequency of smiles in response to subtle humor.

Adult↗
PubMed1978

A six-point scoring system for antenatal cardiotocographs.

A six-point scoring system for antenatal cardiotocography based upon baseline fetal heart rate (FHR) ad FHR response to fetal movements and Braxton-Hicks contractions has been described and tested in 89 patients. The 'six-point score' obtained within 24 hours of delivery or death of the fetus (D--1) was shown to be strongly associated both with the one-minute Apgar score and the nutritional status of the infant as reflected by centile birth weight. In 21 patients whose D--1 'six-point score' was 4 or less, analysis ofthe cardiologicographs performed on the previous day (D--2) showed that 14 infants already showed evidence of hypoxia. In the remaining seven patients, however, the previous day's six-point score had been normal (5 or 6); in six of these patients a persistently low daily fetal movement count or placental abruption led to repeat cardiotocography. Hypoxia affected the three components of the score in a progressive manner. Firstly there were alterations in the response of the FHR to Braxton-Hicks contractions followed by changes in the FHR response to fetal movements. Finally, fetal movements ceased and baseline FHR changes occurred mainly in the form of a trachycardia. The method of scoring was simple to use and could standardize reporting.

Female↗
PubMed1977

Response to a Valsalva manoeuvre before and after epidural block.

In pregnant patients at term the cardiovascular response to a Valsalva manoeuvre has been evaluated in the lateral and supine positions, before and after epidural block (T8-S5). There was no difference in the pattern of response under these four conditions. After epidural block, there was a tendency to a greater degree of hypotension and a slower recovery. In labour such repeated hypotension could account for the increase in fetal acidosis when the second stage of labour is conducted in the supine position.

Anesthesia, Epidural↗