Germination of field dodder (Cuscuta campestris Yunck.) was investigated in field and laboratory studies. Germination plots established to simulate field conditions showed a rapid decline in the ...number of seedlings emerging over a 5-yr period. Less than 10% of the seeds planted emerged. Time of germination was correlated with temperature. The dormancy of seeds buried at various depths was found to be broken by overwintering. Older seeds and those close to the surface germinated best. Scarified seeds did not germinate at 15 C nor at temperatures of 39 C or above. Maximum germination occurred at 30 and 33 C. Scarified seeds planted at various depths failed to emerge from 3.8, 4.0, or 7.6 cm in the three soil types evaluated; the majority emerged from 3 cm or less. Seeds stored outdoors, at 3 to 8 C, or −3 to 0 C declined in dormancy with time compared to seeds stored at 15 to 25 C.
A novel magnetic field and radio frequency (1.7 MHz) pulse sequence is described for a whole body n.m.r. imaging machine under construction. Selective excitation is used to obtain signals from ...successive lines of proton spins (water) across the body to build up an image of a transverse section. The images display spin concentration and spin-lattice relaxation time, T1, separately. For a 50% change in T1 to be discerned in the human trunk, a spatial resolution of 2 cm3 is expected for a 2 min scan and 0.5 cm3 for a 30 min scan. Very preliminary images at the present incomplete stage of development show the geometrical accuracy and T1 discrimination: an in vivo image demonstrates some of the difficulties to be overcome. In vitro measurements of normal rabbit tissue samples have been made at 24 MHz to map the T1 distributions that can be expected from normal subjects. The transposition of this information from rabbit to man, and from 24 MHz to 2.5 MHz have been checked and the comparison shown to be meaningful. Of pathological samples, human breast tumour and human liver metastases offer a good contrast to their surrounding tissue, and an experimental investigation has shown that tissue immediately surrounding a tumour also has an elevated T1 value. A wide range of abnormalities that are associated with abnormal fluid formation in the body may be amenable to imaging by the n.m.r. technique. Potential hazards are believed to be small in the present generation of equipment.
Abstract In the ongoing debate about gender-specific (GS) vs. traditional knee implants, there is limited information about patella-specific outcomes. GS femoral component features should provide ...better patellar tracking, but techniques have not existed previously to test this accurately. Using novel computed tomography and radiography imaging protocols, 15 GS knees were compared to 10 traditional knees, for the 6 degrees of freedom of the patellofemoral and tibiofemoral joints throughout the range of motion, plus other geometric measures and quality of life (QOL). Significant differences were found for patellar medial/lateral shift, where the patella was shifted more laterally for the GS femoral component. Neither group demonstrated patellar maltracking. There were no other significant differences in this well-functioning group.
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.
