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Biomedical subjects

P Rüegsegger

Publications and source records attributed to P Rüegsegger.

At least 73 records · Page 4Linked to original sources
PubMed1991

[The use of bone density measurements in the diagnosis and therapy of osteoporosis].

Bone firmness and risk of fracture depend on factors like bone density, bone structure, elasticity of bone materiel and many others. Bone density is an important single factor which has moreover the advantage of being measureable rather precisely today. Unfortunately, the individual values of bone density scatter very much, i.e. the range of normal values is very large so that bone density values alone do not allow a very fine graduation of osteoporosis. At least as important as bone density is its change in the course of time. Three procedures which complete each other partially are primarily at our disposal today for the determination of bone density. The double energy X-ray absorption (DXA) is a plain procedure for the examination of the lumbar spine and/or the femoral neck. The resulting content of bone minerals comprises both cortical and trabecular bone and can be influenced by superimposed tissue. The exposure to irradiation by DXA is small, however the pictures are not of diagnostic quality and supplementary X-rays are recommended in order to avoid erroneous interpretations. In favorable cases a reproducibility of 1% can be achieved. At least 5% change are however necessary in the osteoporotic patient in order to be recognized with certainty. In quantitative computerised tomography (QCT) we distinguish between procedures for the examination of trabecular bone density in vertebral bodies (axial OCT) and procedures for the separate determination of trabecular and cortical bone density in the extremities (pQCT). Axial QCT is also used for the examination of the lumbar spine. Its reproducibility is comparable with that of DXA, the sensitivity of QCT is however higher than that of DXA.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1990

Does alternate-day cloprednol therapy prevent bone loss? A longitudinal double-blind, controlled clinical study.

Osteoporosis is a serious side effect of systemic treatment with steroids. Cloprednol, a synthetic glucocorticoid with an anti-inflammatory potency twice that of prednisone, causes less calcium and nitrogen excretion than does prednisone in equipotent doses. Therefore a double-blind study was undertaken comparing the effects of alternate-day cloprednol and prednisone therapy on bone mineral density in 39 patients (cloprendol: 13 men and 8 women aged 48.5 +/- 2.8 years; prednisone: 9 men and 9 women aged 49.7 +/- 1.7 years) with lung diseases. Ten patients with asthma (9 men and 1 woman aged 37.8 +/- 3.7 years) inhaling daily beclomethasone served as control subjects. Trabecular and total bone density of the distal tibia and radius was determined quarterly during 1 year with a special-purpose computed tomographic system. Initial mean trabecular bone density of the patients receiving cloprednol and prednisone was 17% below normal. After a treatment period of 1 year, we found a loss of radial trabecular bone density (mean +/- SEM) of 1.33% +/- 0.49% in the cloprednol group and 2.38% +/- 0.69% in the prednisone group. In postmenopausal women, prednisone but not cloprednol therapy caused significant (p less than 0.01) trabecular bone loss (5.29% +/- 0.99% versus 0.70% +/- 0.65%). The control group lost 0.91% +/- 0.79%. Loss of cortical bone was insignificant in all three groups. In post-menopausal women, 1 year of alternate-day cloprednol therapy was associated with significantly less bone loss than was prednisone therapy in equipotent dosages.

Administration, Inhalation↗
PubMed1989

Peripheral QCT: a low-risk procedure to identify women predisposed to osteoporosis.

A low-risk procedure is described for the precise quantitation of changes of trabecular and cortical bone density at peripheral measuring sites. The method is based on quantitative computed tomography (QCT). Bone parameters are calculated for a sample volume common to all examinations of a patient. This is achieved by matching stacks of tomograms according to the cross sectional area of the bone measured. With the help of a special-purpose CT system the described procedure enables a reproducibility for trabecular and cortical bone parameters of 0.3% (1 SD) at a local radiation dose of 0.1 mSv (10 mrem). The method was used to assess the individual changes in bone density of 39 perimenopausal women during an observation period of 2 to 3 years. The results are grouped according to their menstrual state. Regularly menstruating women experience minute or no changes in bone density. After menopause the interindividual differences are considerable: some women lose bone excessively, others remain relatively stable. The frequency distribution of the rate of bone loss appears to be bimodal. Hence women can be classified in fast losers and slow losers. We conclude that the rate of bone loss may be most helpful in the identification of those women predisposed to osteoporosis.

Disease Susceptibility↗
PubMed1988

[Bone loss in female patients with anorexia nervosa].

Osteoporosis is occasionally seen in young women with episodes of anorexia nervosa. To study anorectic osteopenia we have examined 10 patients aged 18 to 37 years before, during and after treatment. Treatment consisted of hospitalization for correction of underweight by tube feeding and subsequent psychotherapy. Bone-density measurements performed with high-precision, low-dose, quantitative computed tomography of the distal radius and the distal tibia before treatment showed an age-dependent pattern. Linear regression suggests a trabecular bone loss of approximately 3% per year. This loss might be caused by low estrogens, because all patients were amenorrheic. After tube-feeding periods of 27 to 89 days (5 patients), trabecular bone density of the tibia was further reduced by 10.3% (range 6-13%) below pretreatment values. One year later average trabecular bone diminution was 17.3% (range 8-28%). Such rapid bone loss may cause osteoporosis within a few years, and treatment is therefore required for prevention of this skeletal deterioration.

Adolescent↗
PubMed1988

Quantitative computed tomography of the rheumatic knee.

A good noninvasive means to quantitate the extent and course of bone loss in rheumatoid arthritis (RA) is currently not available. We report on ways of assessing arthritic bone changes by means of quantitative computed tomography (QCT). The visualization of lesions and the quantitation of bone density diminutions are based on a stack of forty thin computed tomograms and 3D reconstructions. A pilot study shows that QCT may be a useful tool in the noninvasive assessment of the progression of RA and that it may help to evaluate the efficacy of therapeutic procedures.

Adult↗
PubMed1988

Quantitative computed tomography at peripheral measuring sites.

Three most frequently used noninvasive procedures for bone quantitations are dual photon absorptiometry [DPA, DPX] and quantitative computed tomography [QCT]. The peripheral QCT allows trabecular and cortical bone to quantitated separately, radiation dose is very low and precision very high.

Absorptiometry, Photon↗
PubMed1987

Changes in local bone density after knee arthroplasty. The use of quantitative computed tomography.

Loosening is a serious problem in total arthroplasty and early detection of bone loss in the vicinity of an implant would help in its investigation. We present a method for the objective evaluation of bone adjacent to metallic implants in which a modified technique of quantitative computed tomography (QCT) is used to reconstruct cross-sectional images with few artefacts. We have used this technique in 19 patients with knee arthroplasties to monitor the changes in bone density around the tibial stem of the prosthesis. In the first weeks after operation all patients showed a decrease in bone density ranging from 0.4% to 3.6% per month. One year after arthroplasty bone density had stabilised and only minor changes were observed. Our work indicates that modified QCT is a sensitive method for the long-term monitoring of the anchorage of implants and allows the early detection of osteolytic changes.

Aged↗
PubMed1986

Disuse osteoporosis in patients with total hip prostheses.

Aseptic loosening of total hip arthroplasty is still a serious problem. Bone quality might be one of the major factors influencing loosening. In a previous study, bone loss during the reparation phase was evaluated with modified computed tomography at the site of the implant. The present study documents the degree of disuse osteoporosis prior to and after surgery. Bone density of both tibiae of patients with unilateral artificial hip joints was evaluated longitudinally. Preoperatively a significant right-left difference was found, that has to be attributed to the preoperative unloading of the diseased leg. After surgery a slight but significant bone loss was found in both legs attributable to the immobilization following surgery and the reduced activity in the first 6 months. In successfully operated cases this loss is temporary. In one patient bone loss continued; after 1 year there are now clinical signs of implant loosening. Although the spectrum of physical activity in our group was wide, no correlation between activity and bone loss has been found so far.

Aged↗
PubMed1986

Reduced parathyroid hormone response to peroral phosphate in osteoporotic patients.

To determine whether PTH secretion can be stimulated in osteoporosis by peroral phosphate (1.5 g phosphorus), we have compared serum PTH and urinary cyclic AMP responses in 8 osteoporotic patients with vertebral compression fractures to those of 7 age-matched control subjects. While there was no statistically significant difference in the rise of serum phosphate and urinary phosphate excretion and in the fall of serumionized calcium concentrations, serum PTH and urinary cyclic AMP were increased in control subjects, but not in osteoporotic patients (osteoporotics vs. control group: PTH, p less than 0.01; cyclic AMP/glomerular filtrate, p less than 0.05). Moreover, plasma levels of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were the same in the 2 groups of subjects. Serum levels of the carboxyl-terminal flanking peptide (PDN-21) encoded by the calcitonin gene and cosecreted with calcitonin were similar in normal and osteoporotic subjects before and 3 min after 1-min intravenous calcium infusions (2 mg/kg body weight), and of calcitonin after the calcium infusions. We conclude that calcitonin and PDN-21 responses to intravenous calcium are the same in normal and osteoporotic subjects, whereas stimulation of PTH secretion by peroral phosphate is impaired in some osteoporotic patients.

Administration, Oral↗
PubMed1985

Optimal CT settings for bone evaluations.

In CT densitometry the precision, sensitivity and accuracy of the procedure are limited by photon noise, the degree of tissue differentiation and artefacts caused by the finite size of the x-ray beam, hardening of the x-rays and scattered radiation. These artefacts are highly dependent on the CT settings, such as x-ray spectrum and effective energy, intensity of photon flux and collimation of the beam. To monitor the progression of a disease or the efficacy of a therapy, longitudinal studies are necessary; thus the radiation dose per examination should be kept at a minimum. For bone evaluation of the peripheral skeleton it is shown that there is a narrow optimal energy range of 30-40 keV where a dose below 150 mu Sv is sufficient to detect a change of 1% in trabecular bone density at the 0.1 confidence level. Concomitantly accuracy might be better than 1% if adequate beam collimation is applied.

Absorptiometry, Photon↗
PubMed1985

Reconstruction algorithm for incomplete projections in the framework of linear operators in normed linear spaces.

Based on the linearity of the Radon transform and the convolution-backprojection reconstruction algorithm, a new linear-vector space notation is introduced that is of general use in computed tomography (CT). Using this notation, a consistency condition for the completion of incomplete projection data is described. This consistency condition leads to singular or ill-conditioned systems of linear equations for the unknown projection data. Using regularization methods, an algorithm for the consistent projection completion is presented that can exploit symmetries of the missing data region. The performance of the new algorithm is documented with simulated and actualy measured CT-projection data. The algorithm quantitatively improves CT reconstructions with realistic amounts of data and noise and can be used for the completion of arbitrary regions of missing projections.

Fourier Analysis↗
PubMed1983

Corticosteroid-induced bone loss. A longitudinal study of alternate day therapy in patients with bronchial asthma using quantitative computed tomography.

Treatment with corticosteroids can produce osteoporosis. It is generally held that bone loss occurs when steroids are administered daily, but recent findings indicate that bone may also be lost on alternate day therapy. Cortical and trabecular bone, which may be affected differently, can be assessed independently, by quantitative computed tomography. This technique has been applied to the appendicular skeleton in following 20 patients with bronchial asthma during one year of chronic alternate day corticosteroid therapy. The trabecular bone loss was considerable; prednisone 25 mg on alternate days caused an average reduction in trabecular bone of 3.5% over one year. Bone loss was dose- and age-dependent. Young patients on 50 mg/2 days lost up to 17% trabecular bone in one year. Cortical bone was not significantly affected over the same period.

Adrenal Cortex Hormones↗
PubMed1982

Anchorage of femoral implants visualized by modified computed tomography.

Metallic implants produce a great deal of artifacts in standard CT images. These artifacts cover tissue structures and impede visualization of the anchorage of the implant within the bone. Thus a modified CT procedure has been developed to permit reconstructions free from artifacts. It is an iterative procedure using a maximum of measured projection data. Using this modified CT technique, the anchorage of a titanium-alloy femoral prosthesis implanted without cement was examined. Good contact of the implant with the cortical bone has documented. This promises good initial stability. The CT examinations were performed by using a special-purpose CT scanner. It is hoped that the modified CT technique will allow a quantification of bony tissue in the close vicinity of implants and thus provide a non-invasive procedure that will allow the long-term stability of implants to be evaluated.

Aged↗