The incudo-malleolar joint and sound transmission losses.

The question as to whether the incudo-malleolar joint (IMJ) is mobile or immobile at moderate sound pressure levels (SPLs) is addressed. Referring to the mechanical properties of elastic tissue, we suggest that the IMJ is mobile at any SPL. In order to test this hypothesis, we investigated the dynamics of the IMJ in nine temporal bones by means of laser scanning doppler vibrometry. The dynamic behavior of both ossicles, malleus and incus is described by three degrees of freedom, and transfer functions (TFs) are shown for each motion component [corrected]. We show that there is indeed relative motion between the malleus and the incus. This transmission loss affects the middle ear TF and results in a frequency dependent sound transmission loss. Some characteristics of our results are in agreement with middle ear TFs described in the literature. The increasing transmission loss towards higher frequencies is caused by relative motion between malleus and incus at the IMJ. The concept that the IMJ is functionally mobile is consistent with the physical properties of elastic tissues which most likely define the mechanics of this joint. Since the IMJ is indeed mobile at moderate sound intensities and audible frequencies the theory of the lever ratio being responsible for the characteristics of the middle ear TF must be reconsidered.

Pelvimetry and patient acceptability compared between open 0.5-T and closed 1.5-T MR systems.

Our objective was to compare maternal pelvimetry and patient acceptability between open low-field (0.5-T) and closed 1.5-T MR systems. Thirty women referred for pelvimetry (pregnant: n=15) were scanned twice in the supine position, once in the vertical open system and once in the closed system. Each patient completed a comfort and acceptability questionnaire. Pelvimetric and questionnaire data were compared between systems. Total scan time was double in the open system (7:52+/-1:47 vs 3:12+/-1:20 min). Poor image quality in the open system prevented assessment of interspinous and intertuberous diameters in one woman and all measurements in another, both pregnant, with abdominal circumferences >120 cm. The open system was much more acceptable in terms of claustrophobia and confinement (both p<0.01). Claustrophobia interrupted one closed examination. Thirty-three percent of pregnant women in both systems reported fear of fetal harm. Sixty percent of all women preferred the open system, 7% the closed system, and 33% had no preference. Limits of agreement of 3-5% from the mean for all diameters confirmed good pelvimetric reproducibility. Women's preference for open-system MR pelvimetry is feasible with abdominal circumferences