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Biomedical subjects

P Seitz

Publications and source records attributed to P Seitz.

9 recordsLinked to original sources
PubMed1991

Partial characterization of rat marrow stromal cells.

Fibroblast-like rat marrow stromal cell (CFU-F) cultures have been characterized in terms of their responsiveness to calciotropic hormones, metal ions, the nonsteroidal antiinflammatory drug, and by their putative paracrine role in the maintenance of active populations of osteoblasts at the marrow-bone interface. These studies indicate that CFU-Fs lack a complete osteoblast signature. Subconfluent CFU-Fs grown in the presence or absence of 10(-7) M dexamethasone lack receptors for PTH and calcitonin, and fail to show enhanced cAMP or cGMP responses to 10(-7) M 1-34 PTH (rat), or any evidence of osteocalcin production [+/- 10(-9) M 1,25-(OH)2D3]. Low concentrations of fluoride [10(-12) and 10(-9) M] stimulated CFU-F grown in vitro in serum-free media, though higher levels (10(-7) and 10(-6) M), inhibited growth in vivo and in vitro. Aluminum (10(-12)-10(-7) M) and ibuprofen (10(-7) M) did not alter normal growth patterns, indicating an action on bone cells more differentiated than CFU-Fs. Serum-free conditioned medium (CM) from control and ovariectomized (OVX)/OVX+ dihydrotachysterol-Rx rat CFU-F cultures was mitogenic for neonatal rat calvarial osteoblasts in vitro, but not for ROS 17/2.8 cells. The studies affirm the mesenchymal-like character of CFU-Fs and project their significant role in sustaining functional endosteal osteogenic cell populations.

Animals↗
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↗
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↗
PubMed1980

Mitochondrial water in myocardial ischemia: investigation with nuclear magnetic resonance.

Nuclear magnetic resonance studies of mitochondria isolated from ischemic hearts after coronary vessel occlusion indicated a decrease in water proton relaxation times. This change coincided with a decrease in the hydration of the samples. It is suggested that in ischemia, changes in macromolecular hydration may be one of the first mechanisms to alter function in the mitochondria, which are vital to the energy-transducing process in heart muscle.

Animals↗
PubMed1979

A new tocograph with cassette recording system and separate servo graphic recorder.

In order to register contractional activity, especially in the case of high-risk pregnancies, a tocograph was develop by means of which the contractions are registered by a small cassette recorder, which the patient can carry by about with her. A separate graphic recorder is responsible for the playback and this recorder remains at the doctor's practice. The patient is able to register her contractions herself as the unit is so simple to use. The recording section weighs only 500 grams, including the specially developed pressure transducer with optical distance-meter. The tocograph is produced in series.

Female↗