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P Rüegsegger

Publications and source records attributed to P Rüegsegger.

90 records · Page 5Linked to original sources
PubMed1982

Quantitative computed tomography of bone.

Computed tomography (CT) is well accepted as an imaging procedure, but comparatively little effort has been made to utilize the potential capability of CT to quantify tissue densities and composition. There are two reasons for this. First, precision and accuracy of quantification are limited by nonlinear effects. These effects are nonlocal and are object and scanner dependent. Second, intraindividual and interindividual variations of tissue compositions are considerable. Single energy measurements require restrictive assumptions on tissue compositions. The diagnosis and treatment monitoring of osteopenic bone diseases with low-dose CT is given as an example of a successful application of quantitative CT. With a special-purpose CT system and an analytic procedure for the quantification of bone at peripheral measuring sites, longitudinal examinations were performed. Low-dose quantitative CT permitted quantification, on an individual basis, of the bone loss of immobilization osteoporosis on a week-by-week basis. Changes due to postmenopausal osteoporosis are less drastic, and so measurement at intervals of months is adequate. In women after menopause, 3-month intervals were used in evaluating the natural course of osteoporosis and in quantifying the effects of sodium fluoride treatment on trabecular bone. Low-dose quantitative CT has proved to be a sensitive and highly reproducible procedure for the noninvasive evaluation of bone loss or bone accretion. During a disease or therapy, each patient can be evaluated individually.

Adult↗
PubMed1981

Quantification of trabecular bone with low dose computed tomography.

Computed tomography (CT) has the potential of providing a precise quantification of trabecular bone. A special purpose low dose CT system for applications at peripheral measuring sites has been developed. With this system, the quantification of trabecular bone can be achieved with a reproducibility on the order of 0.3%. It has been used successfully in pilot studies of immobilization osteoporosis in children and adults on a week by week basis. Currently, the method is being used in a preliminary investigation of bone loss in women in an attempt to differentiate normal changes from changes due to postmenopausal osteoporosis. Results obtained so far indicate that intervals of 3 months are adequate for following the natural course of osteoporosis or its response to therapy on an individual basis.

Adult↗
PubMed1980

[Determination of morphine and codeine in urine by high-pressure liquid chromatography (author's transl)].

A sensitive and specific method for the determination of morphine and codeine is described. The drugs are adsorbed from urine on Amberlite XAD-2 resin at pH 8.5 and eluted from it with organic solvent. After a clean up the residue is separated by high-pressure-liquid-chromatography on reversed phase column using 0.1 M NaH2PO4 in 25% CH3CN/H2O as mobile phase. The eluted drugs are detected by uv-absorption at 230 nm. The method is sensitive, specific and precise.

Chromatography, High Pressure Liquid↗
PubMed1980

Hypophosphatemic vitamin D resistant rickets (phosphate diabetes): bone mineral problems studied by 125I-computed tomography and microradiography.

125I-computed tomography (CT) for the bone mineral analysis of the radius was performed on 9 children with vitamin D resistant hypophosphatemic rickets (VDRR) treated with vitamin D in pharmacological doses. Trabecular bone density was increased in 1 patient and normal in all others. The cortical width of the diaphysis of the radius was decreased, and the cross sectional area of the bone increased, but the total amount of compat bone mineral in the cross section was normal. Measurements of the second metacarpal bone on X-rays of the hand revealed similar findings. Microradiographic and histological examinations of the fibula on 9 different patients also treated with vitamin D showed grossly abnormal mineralization of bone tissue with a perilacunar mineral deficit. It is concluded, that the amount of compact bone and trabecular bone is not decreased in children with VDRR. The normal mineral content determined by CT and the impaired mineralization of the bone material examined by microradiography indicate an over-abundance of incompletely mineralized bone.

Adolescent↗
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

Comparison of structure extraction methods for in vivo trabecular bone measurements.

In vivo trabecular bone structure measurements have become available recently using high resolution quantitative computed tomography (3D-QCT) or magnetic resonance imaging. In this work different structure extraction and morphometric evaluation techniques are compared, which are of potential use for in vivo assessment of human cancellous bone structure. Given the spatial resolution of actual in vivo examination procedures, best results are obtained by extracting first the skeleton of the structure and applying model independent 3D techniques to calculate trabecular number, then deriving mean trabecular thickness and separation from densitometric bone volume fraction and Tb.N*. Traditional histomorphometric methods based on bone surface and volume ratios and assuming a plate model performed less well.

Bone Density↗
PubMedDate not supplied

[Pathogenesis, prevention and therapy of steroid osteoporosis].

The pathogenesis of glucocorticoid osteoporosis is complex. Numerous, controversial mechanisms have been postulated. However, there is certainly both a reduction in bone formation as well as an increase in resorption. The increase in resorption probably occurs before the reduction in formation. As of a threshold dose of approx. 7.5% prednisone equivalents per day, administered for approx. 1 year, a loss of cancellous bone occurs; the reduction in compact bone is far less pronounced. Histologically, bone matrix synthesis appears to be uniformly reduced, while resorption varies considerably. The cancellous bone structure has a filigree appearance which is also recognizable by the glass-like appearance on radiographs. The development of new glucocorticoid preparations such as Deflazacort, which promotes osteoporosis less than, e.g., prednisone, is very promising. For the prevention and treatment of glucocorticoid-induced osteoporosis, frequently used drugs today are fluorides, ossein-hydroxy-apatite complexes and, especially in acute glucocorticoid osteoporosis, calcitonin.

Bone Development↗
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↗
PubMedDate not supplied

Cancellous bone structure: analysis of high-resolution CT images with the run-length method.

Quantitative computed tomography is extensively used to assess bone density; its potential to quantify bone structure, however, remains to be explored. In this work we present the modifications of the run-length method necessary to enable an analysis of the trabecular bone structure at the distal radius and the distal tibia. Furthermore, the close relationship between histomorphometric values and the run-length parameters is shown. The procedure may be regarded as a noninvasive, reproducible biopsy. For an adequate analysis, high resolution CT images are required. To obtain such images, we modified a special purpose CT system and achieved a high contrast resolution of 0.25 mm. The procedure was applied to groups of normal volunteers and osteoporotic patients, and the results are interpreted with the help of simple two- and three-dimensional models of the trabecular architecture.

Adult↗