The birdcage resonator, well appreciated for its high signal-to-noise ratio and its magnetic field uniformity characteristics, operates efficiently in mid- to high-field MRI systems but, ...unfortunately not for low-field (< 0.4 T) applications. The inherently low inductance of the birdcage architecture is the main obstacle to achieving low-frequency resonance because of the need to use very high-value capacitors for the tuning. Small-case-size, high-value ceramic capacitors are known to have high dissipation factors which when used in the fabrication of RF coils could result in poor efficiency. To overcome this limitation, a novel technique known as multilayer self-capacitance (MLSC) construction has been developed and a prototype 2.5 MHz bird-cage resonator of length 25 cm and diameter 20 cm has been built. The technique involves the modification of the leg sections of the conductors constituting the bird cage into integrated capacitors using very low-loss materials as dielectrics. The observed unloaded Q-factor was 267 using the MLSC construction, and when loaded with a 16-cm-diameter bottle of 0.45% saline, its Q dropped to 246. The RF field uniformity plots have demonstrated that the MLSC technique has no adverse effects on the magnetic field homogeneity of the bird-cage resonator.
The observed rate of dissociation of radioactive estradiol from nuclear estrogen-receptor complexes from hen oviduct has been shown to depend to a large extent on the method used to initiate ...dissociation. The present study indicates that nuclear progesterone receptors display the same pattern of behavior. Dissociation kinetics of nuclear progesterone receptor extracted from hen oviducts were affected by the method of initiation of dissociation; the rate of dissociation at 25°C when dissociation was initiated with unlabeled steroid was three times that observed when dissociation was initiated by addition of a charcoal/dextran suspension. In contrast to nuclear receptors, both estrogen and progesterone receptors prepared from cytosol displayed only a single rate of dissociation, no matter what the method of initiation of dissociation. These results strengthen the idea that nuclear receptors contain a factor or subunit which may be removed by charcoal, which alters the rate of dissociation of steroid from the complex.
Continuous-wave NMR imaging of solids Lurie, D J; McCallum, S J; Hutchison, J M ...
Magma (New York, N.Y.),
03/1996, Letnik:
4, Številka:
1
Journal Article
Recenzirano
Current pulsed nuclear magnetic resonance methods of imaging samples such as solids with short spin-spin relaxation times are restricted to use with T2 values longer than approximately 10 ...microseconds. In the present study a method of imaging ultra-short T2 samples using continuous- wave, swept-field NMR is presented that, in principle, will be able to overcome this restriction. The technique is identical to that used in continuous-wave electron paramagnetic resonance imaging of paramagnetic species and involves irradiating the sample continuously with a radiofrequency excitation in the presence of a strong stationary magnetic field gradient. When the main magnetic field is swept over a suitable range, the variation of the NMR absorption signal with applied magnetic field yields a one-dimensional projection of the object under study along the gradient direction. Two- or three-dimensional image data sets may be reconstructed from projections that are obtained by applying the gradient in different directions. Signal-to-noise ratio can be improved by modulating the magnetic field and employing a lock-in amplifier to recover signal variations at the audio modulation frequency. Preliminary experiments were performed using a 7 Tesla magnet and a 300 MHz continuous-wave radiofrequency bridge with lock-in detection. The apparatus is described and the results of pilot experiments that employed vulcanized rubber samples are presented. The ability of the technique to detect short T2 samples was demonstrated by the presence of a background signal from the Perspex former of the birdcage resonator used for signal reception.
The Hand in Art: Petroglyph Polydactyly Hirthler, Maureen A., MD; Hutchison, Richard L., MD
The Journal of hand surgery (American ed.),
2012, 2012-1-00, Letnik:
37, Številka:
1
Journal Article
Background We assessed the current state of Canadian orthopedic resident research and the effect of protected block research time on the numbers of grants obtained, research projects completed, ...submissions for publication, publications and conference presentations. Methods We administered a 27-item cross-sectional survey containing quantitative and qualitative questions to postgraduate year (PGY)-3 to -5 residents in all 16 Canadian orthopedic training programs in the academic year of Jul. 1, 2005, to Jun. 30, 2006. Results There was an overall response rate of 45% (85/188) from residents in 15 of 16 orthopedic programs: 56% (48/85) of respondents took block research time of at least 1 month (mean 5 mo). The number of months taken was positively correlated with the number of grants obtained ( r = 0.28, p = 0.011) and publications ( r = 0.23, p = 0.031). Residents who took block time obtained more grants (Fisher exact test 3.54, p = 0.048) and publications (Fisher exact test 6.09, p = 0.012) than those who did not take block time. About 41% (35/85) of respondents said time was the biggest obstacle to research. Conclusion Providing protected block research time during residency allows Canadian orthopedic residents greater research success.
Thirty four patients suffering from chronic glomerulonephritides with and without the nephrotic syndrome and with an average age of 35 years were studied. Twenty eight of the patients underwent renal ...biopsy, as part of their management, and the histological classification was as follows: 7 membranous glomerulonephritis, 3 proliferative glomerulonephritis, 11 mesangiocapillary glomerulonephritis, 2 minimal change disease, 2 mesangial proliferative and 3 diffuse proliferative glomerulonephritis. Fourteen of the patients were on therapeutic diets mainly high protein - low salt and low cholesterol. Eighty three per cent of these patients were found to be biochemically deficient in vitamin B6 as judged by plasma pyridoxal-5-phosphate levels. No correlations were found between vitamin B6 and serum albumin, histological type of renal disease, duration of illness or serum cholesterol. By contrast, none of the patients with histologically similar disease that were daily receiving 25mg pyridoxine orally at the time of study were deficient. The importance of vitamin B6 deficiency in the nephrotic syndrome is discussed and it would appear that supplementary vitamin B6 should form part of the overall management of these patients.
