Applying very high resolution microfocus X-ray CT and 3-D reconstruction to the human auditory apparatus

Conventional high-resolution X-ray computed tomography (XCT) is an important medical technique because it provides sectional images (tomograms) of internal structures without destroying the specimen. However, it is difficult to observe and to analyze fine structures less than a few cubic millimeters in size because of its low spatial resolution of 0.4 mm. Overcoming this problem would not only enable visualization of human anatomical structures in living subjects by means of computer images but would make it possible to obtain the equivalent of microscopic images by XCT without making microscopic sections of biopsy material, which would allow the examination of the entire body and detection of focal lesions at an early stage. Bonse et al. and Kinney et al. studied absorption contrast microtomography by using synchrotron radiation(1-3) and achieved 8-mu m spatial resolution in human cancellous bone(1). Recently, Momose et al. reported examining the soft tissue of cancerous rabbit liver by a modification of the phase-contrast technique using synchrotron radiation with a spatial resolution of 30 mu m (ref. 4). However, the equipment for synchrotron radiation requires a great deal of space and is very expensive. Aoki et al., on a different tack, reported microtomography of frog embryos by using a conventional laboratory microfocus X-ray source with a spot size of about 2 mu m (ref. 5). As no human tomographic studies by superresolution microfocus XCT (MFXCT) using a normal open-type X-ray source have been reported, we tried using MFXCT with a maximum experimental spatial resolution of 2.5 mu m, especially designed for industrial use, on the auditory ossicles(6) of a human fetus, the smallest and lightest bones in the skeletal system. No XCT studies of fetal auditory ossicles have been reported to date. The fine tomograms with three-dimensional reconstructions obtained showed the existence of an apparently previously undescribed joint between the tympanic ring and the anterior process of the malleus. We hope the early development of this MFXCT for clinical use will make a great contribution to medicine.