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Endocytosis is a common internalization pathway for cellular labeling with MRI contrast agents. However, the entrapment of the Gd(III) complexes into endosomes results in a "quenching" of the attainable relaxivity when the number of Gd(III) complexes reaches the number of ca. 1 × 10(9)/cell. Herein we show that the use of the newly developed photochemical internalization technique provides an efficient method for attaining the endosomal escape of GdHPDO3A molecules entrapped by pinocytosis into different kind of cells. Furthermore, it has been found that a new "quenching" limit is observed when the number of Gd-HPDO3A complexes is ca. five times higher than the value observed for the endosome entrapped conditions. The observed behavior is explained in terms of the attainment of the conditions in which the difference in proton relaxation rates between the cytoplasmic and the extracellular compartment is higher than the exchange rate of water molecules across the cellular membrane. The experimental data points have been reproduced by using a properly designed theoretical compartment T(1)-relaxation model.

There is no single technique for reconstruction of the canal wall following radical mastoidectomy. Autograft tissues may be unsuitable because of resorption and limited availability. An ideal foreign implant material should be bone-like in quality, non-ototoxic, readily available and malleable. Plaster of Paris, a degradable ceramic powder of CaSO4, may be regarded as a bone mineral. But a certain amount of heat develops during its solidifying process and may present a risk for injury to the facial nerve and the labyrinth. We studied the temperature rise with respect to added solution, to volume, and to surroundings, and investigated its biocompatibility when implanted in soft tissue in guinea pigs. The investigations suggested no risk of thermal injury and the biocompatibility was excellent. Hence plaster of Paris may constitute an alternative implant material for mastoid obliteration and reconstruction of the canal wall in ear surgery.

Many techniques have been proposed for reconstruction of the posterior canal wall and/or obliteration of the mastoid bowl after radical mastoidectomy. The variety of materials that have been used, biological as well as foreign materials of different kinds, indicates that the ideal solution has yet to be found. Plaster of Paris, a biocompatible, degradable ceramic material prepared from CaSO4, may have an osteogenic property and become an alternative implant material for ear surgery. However, its possible ototoxicity has not been studied previously. Plaster was implanted in the tympanic cavity of guinea pigs. On investigation in the scanning electron microscope after 4.5 to 8 months, no toxic damage to the hair cell morphology was observed. Thus, from an ototoxic point of view, plaster of Paris would seem suitable for use as an implant material in ear surgery. Studies concerning the possible osteogenic property of plaster of Paris and its clinical application in human ear surgery are in progress.

Many techniques for obliteration of the mastoid cavity after cholesteatoma and mastoid surgery, are known. Also the materials used are numerous, differing from organic autogenous and homogenous grafts, to synthetic alloplastic materials like acrylic plastic, porous polyethylene and ceramics. The ideal solution is still concealed, also indicated by the number of methods and materials used.

Unilaterally severely hearing impaired persons, who may experience substantial communication problems in situations of high acoustic demands, would in theory benefit from contralateral routing of signals (CROS). However, reports of failure because of too much disturbing noise and distortion have been common. The reason for a low success rate in CROS, though, is an inappropriate fitting procedure, due to lack of understanding of the basic principle of CROS among both patients and audiologists. The precondition for success in CROS is an accurate description of the individual hearing deficit and a correctly balanced adjustment of the CROS aid through testing under sound field conditions, combined with a comprehensive follow-up.