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P Rüegsegger

Publications and source records attributed to P Rüegsegger.

10 recordsLinked to original sources
PubMed1992

[Loss of bone mass in patients with anorexia on tube feeding and its prevention with biphosphonates].

Women with long-lasting anorexia nervosa often display osteopenia. Furthermore, we have observed additional marked loss of bone mass under tube feeding in underweight anorexia patients. Such loss of bone substances can lead to spontaneous fractures. Therefore, we investigated in this study whether this undesirable effect of tube-feeding might be prevented by administration of bisphosphonates (Didronel), a substance that inhibits the activity of osteoclasts. Bone density was assessed by a high-precision, low dose, quantitative computed tomography of the distal radius and the distal tibia. A group of 6 anorexia patients (tube feeding with an initial underweight of 74.9 +/- 10.3% of ideal weight, mean +/- SD) treated with bisphosphonates showed only slight loss of trabecular bone (0.8 +/- 0.2%, mean +/- SEM) after 2 months of observation, whereas in 2 control groups a marked diminution of trabecular bone was observed (4.4 +/- 0.7% and 7.6 +/- 1.1% respectively, p less than 0.001 for each comparison). Cortical bone was unchanged throughout. Treatment with bisphosphonates provides effective prevention of bone loss observed in tube-feeding.

Adult↗
PubMed1979

Loss and recovery of trabecular bone in the distal radius following fracture--immobilization of the upper limb in children.

Computed tomography of the human radius is performed using a special purpose scanning device which incorporates a radionuclide (125I) as radiation source. Parameters decribing the trabecular bone and the compact bone are determined at a distal and a diaphyseal measuring site respectively. Using this measurement technique changes in bone mineralization in the radius were studied in a group of 23 children following immobilization of an upper limb for fracture healing. An immobilization period of between three to six weeks resulted in a reduction of the relevant parameter value of up to 44% (mean 16%) in the distal part of the radius, whereas no significant change could be seen in the diaphyseal part of the same bone. Rapid remineralization of trabecular bone is indicated by the increase of the corresponding parameter value at a rate of up to several percent per week. However, in some of the patients studied complete normalization was not attained during the first six months following cast removal.

Bone Regeneration↗
PubMed1979

Bone densitometry using computed tomography. Part I: selective determination of trabecular bone density and other bone mineral parameters. Normal values in children and adults.

Gamma-ray computed tomography (gamma-ray CT), using a special purpose scanner, enables in-vivo quantitative analysis of bone mineralization. Trabecular bone density (TBD), the relative amount of compact bone (bone density, BD) and the total absorption (TA) for a cross-section of the radius are determined from measurements of local linear absorption coefficients. A preliminary study of normal children (n = 49) and adults (n = 34) indicated that TBD is independent of age and sex in the age range 4 to 40 years. DB remains constant throughout childhood but increases after puberty in both women and men. TA is higher for adults than for children, and also higher for men than for women. A correlation between TA and parameters relating to body size indicates a relationship between body weight and bone mass.

Adolescent↗
PubMed1979

Computed tomography reconstruction from hollow projections: an application to in vivo evaluation of artificial hip joints.

The long-term mechanical stability of total hip arthroplasties limits the application of this widely used surgical procedure in cases of severe coxarthroses. A noninvasive method of assessing the tissue distribution in the vicinity of the implant--bone interface is needed to identify early signs of implant loosening and to evaluate new prosthetic solutions. In order to develop such a method, a modified computed tomography technique has been devised that yields cross-sectional images without the usual artifacts caused by metallic implants. This technique provides information on bone mineral and bone cement distributions as well as on the precise position and orientation of the implant within the femur shaft. Results obtained from excised human femurs and preliminary data from measurements on patients made 3 months postoperatively reveal that the bone cement distribution is much less favorable than is indicated by radiographs.

Aged↗
PubMed1978

Standardization of computed tomography images by means of a material-selective beam hardening correction.

Polychromaticity of the X-rays used in computed tomography (CT) has made it difficult to establish an absolute scale for CT values and has made quantitative comparisons between patients unreliable. The spectral shift of the X-rays depends on the material distribution within the structure measured and is significant if substantial amounts of bone, fat, or injected contrast material are present. A material-selective beam hardening correction procedure has been developed that allows the reconstruction of good approximations of linear attenuation coefficients with respect to a reference energy. With the aid of mathematical simulations and measurements on a physical phantom, the feasibility of the procedure and its insensitivity with regard to energy settings and other machine parameters are documented.

Humans↗
PubMed1976

Quantification of bone mineralization using computed tomography.

Computed tomography was used to find a sensitive parameter for bone mineralization. A precision scanning instrument was constructed for determination of the mineral distribution in sections of the forearm. The quality of the reconstructed images allows separate quantification of compact and spongy bone even when gamma rays are used. Computer simulation and measured of models and macerated human bones showed that under clinical conditions it is possible to quantify spongy bone density within an accuracy of +/-2%.

Adolescent↗
PubMedDate not supplied

High-contrast resolution of CT images for bone structure analysis.

The modulation transfer function (MTF) of an imaging system may be used as a figure of merit to assess its geometrical resolution. As such it is often derived from the point spread function (PSF) through a Fourier transformation, or through a FFT in case of digital images. Using the special features of the convolution-backprojection algorithm and making some simplifying assumptions about the number of rays, it is shown that the desired MTF is also obtainable without a Fourier transformation of the PSF, different shapes and sizes of the beam-profile are then analyzed, and finally it is shown that calculated and measured MTF functions are in good agreement. The effects of aliasing on the cutoff frequency are also discussed.

Aged↗