Efficient high-frequency body coil for high-field MRI.

The use of body coils is favored for homogeneous excitation, and such coils are often paired with surface coils or arrays for sensitive reception in many MRI applications. While the body coil's physical size and resultant electrical length make this circuit difficult to design for any field strength, recent efforts to build efficient body coils for applications at 3T and above have been especially challenging. To meet this challenge, we developed an efficient new transverse electromagnetic (TEM) body coil and demonstrated its use in human studies at field strengths up to 4 T. Head, body, and breast images were acquired within peak power constraints of <8 kW. Bench studies indicate that these body coils are feasible to 8 T. RF shimming was used to remove a high-field-related cardiac imaging artifact in these preliminary studies. P41RR13230     

A principal components analysis self-organizing map.

We propose a new self-organizing neural model that performs principal components analysis. It is also related to the adaptive subspace self-organizing map (ASSOM) network, but its training equations are simpler. Experimental results are reported, which show that the new model has better performance than the ASSOM network.     

The diminished efficiency and altered dynamics of respiration in experimental pulmonary congestion

Quantitative measurements of the relative efficiency of respiration in the normal lung, as contrasted with the congested lung, have not been made in the intact experimental animal. In 1934 Christie and Meakins,¹ utilizing simultaneous determinations of dynamic intrapleural pressure and of tidal exchange in patients with congestive heart failure, demonstrated a marked decrease in pulmonary distensibility. With appropriate treatment, distensibility was found to increase as the patient improved. In the present study, an approach similar to that of these authors has been used, and studies of the efficiency of respiration have been made on normal dogs at rest and during hyperpnea (produced by the inhalation of carbon dioxide) and contrasted with the relative efficiency of respiration after pulmonary congestion induced by rapid venous infusion. With this approach, a quantitative comparison of the work necessary to achieve a given amount of tidal exchange has been possible in an animal with normal lungs and in the same animal after severe pulmonary congestion. From measurements of tidal exchange, ventilation, and intrapleural pressure fluctuations, a representation of the dynamic changes in these factors during progressive pulmonary congestion has been obtained.