The measurement of bone mineral content is important for diagnosis of demineralization diseases such as
osteoporosis. A reliable method of obtaining bone mineral images using a digital magnification
mammography system has been developed. The full-field digital phase contrast mammography (PCM)
system, which has a molybdenum target of 0.1mm focal spot size, was used with 1.75 x magnification. We
have performed several phantom experiments using aluminum step wedges (0.2 mm - 6.0 mm in thickness)
and a bone mineral standard phantom composed of calcium carbonate and polyurethane (CaCO3
concentration: 26.7 - 939.0 mg/cm3) within a water or Lucite phantom. X-ray spectra on the exposure field
are measured using a CdTe detector for evaluation of heel effect. From the equations of x-ray attenuation and
the thickness of the subjects, quantitative images of both components were obtained.
The quantitative images of the two components were obtained for different tube voltages of 24 kV to 39
kV. The relative accuracy was less than 2.5% for the entire aluminum thickness of 0.5 to 6.0 mm at 5 cm
water thickness. Accuracy of bone mineral thickness was within 3.5% for 5cm water phantom. The
magnified quantitative images of a hand phantom significantly increased the visibility of fine structures of
bones. The digital magnification mammography system is useful not only for measurement of bone mineral
content, but also high-resolution quantitative imaging of trabecular structure.
We have developed a photon-counting 256ch CdTe line detector system for a monochromatic x-ray CT system using fluorescent x-rays generated by synchrotron radiation. The size of each detector element is 1.98 mm(w) X 1.98 mm(h) X 0.5 mm(t). Each element has two discriminators (an upper and a lower discriminator) and two 16-bit counters (an upper and a lower counter). Each discriminator rejects pulses having a pulse height lower than the chosen voltage limits. All pulses in between the upper and lower voltage limits were obtained by subtracting the upper counter value from the lower counter value. By changing the voltage limits, we can obtain an incident x-ray energy spectrum. Several energy spectra for the fluorescent x-ray and standard (gamma) -ray sources were measured by using this detector. The detector showed a sufficient energy resolution, and has been found to be suitable as a detector of monochromatic x-ray CT.
We, a user group for medical applications of the SPring-8, have proposed the introduction of white X-rays from insertion devices to BMIC (BioMedical Imaging Center) for clinical uses so that enough photon fluxes to a subject is guaranteed. The photon flux, depending on various monochromatizing methods, was compared at the surface of the subject 200 m from a light source.
Monochromatic x-ray CT has several advantages over conventional CT, which utilizes bremsstrahlung white x-rays from an x-ray tube. Although various types of monochromatic x-ray CT systems using synchrotron radiation have been developed using a parallel x-ray beam for imaging of small samples with a high spatial resolution, imaging of large objects such as the human body have not been developed yet. We have developed a fan-beam monochromatic x-ray CT using fluorescent x-rays generated by irradiating metal targets by synchrotron radiation. A CdTe linear array detector of 512 mm sensitive width was used in the photon counting mode. We made phantom experiments using fluorescent x-rays ranging from 32 to 75 keV. Monochromatic x-ray CT images of a cylindrical lucite phantom filled with several contrast media have been obtained. Measured CT numbers are compared with linear attenuation coefficients, and they showed a good linearity over a wide range of contrast media concentrations.
In this paper, we describe a 3D computed tomography (3D CT) using monochromatic x-rays generated by synchrotron radiation, which performs a direct reconstruction of 3D volume image of an object from its cone-beam projections. For the develpment of 3D CT, scanning orbit of x-ray source to obtain complete 3D information about an object and corresponding 3D image reconstruction algorithm are considered. Computer simulation studies demonstrate the validities of proposed scanning method and reconstruction algorithm. A prototype experimental system of 3D CT was constructed. Basic phantom examinations and specific material CT image by energy subtraction obtained in this experimental system are shown.