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Biomedical subjects

E Diessel

Publications and source records attributed to E Diessel.

9 recordsLinked to original sources
PubMed2000

Detailed analyses of periarticular osteoporosis in rheumatoid arthritis.

Periarticular osteopenia is the earliest radiographic sign of rheumatoid arthritis (RA). Recent studies using dual-energy X-ray absorptiometry (DXA) have indicated that the loss of periarticular BMD can be quantified by whole-hand bone mineral density (BMD) measurements. The aim of this study was to analyze periarticular BMD in more detail by DXA and quantitative ultrasound (QUS). In a cross-sectional study 23 women aged 30-76 years with early RA, mean disease duration 26 +/- 19 months, and 18 men aged 42-69 years, mean disease duration 24 +/- 25 months, were examined. All patients received antirheumatic therapy. The reference population consisted of 103 age-matched controls (68 females, 35 males) and young healthy controls. BMD measurements were performed using a DXA Expert XL densitometer (Lunar). BMD of the whole-hand and two subregions was determined: two subchondral regions of interest (S.CH.) were set within the trabecular bone, distal to the proximal interphalangeal joints of digits II and III excluding the dense subchondral bone of the metacarpophalangeal (MCP) joint and two metacarpal regions of interest (MCP) were set including the entire MCP joint of these fingers. QUS measurements at the proximal phalanges of digits II-V were performed using a DBM Sonic (Igea); amplitude-dependent speed of sound (Ad-SoS) was determined. In comparison with whole-hand BMD measurements, bone loss was pronounced in patients with a disease duration of 18-72 months at the subchondral regions of interest in both genders compared with age-matched controls (women: mean BMD loss S.CH. -23%, p<0.001, whole-hand -16%, p<0.001; men: mean BMD loss S.CH. -19%, p < 0.05, whole-hand -12%, p<0.05). The bone changes were also shown by QUS (women: Ad-SOS values of 1950 +/- 90 m/s in RA vs 2137 +/- 35 m/s in young healthy controls (p <0.005); men AD-SOS 1956 +/- 87 m/s in RA vs 2146 +/- 41 m/s in young healthy controls (p <0.05)). These results show that BMD and Ad-SOS values are significantly lowered in patients with early RA and indicate that periarticular osteoporosis in early RA might possibly be better detected using detailed hand scan analyses.

Absorptiometry, Photon↗
PubMed2000

Evaluation of a new body composition phantom for quality control and cross-calibration of DXA devices.

This study evaluated a new body composition phantom and its use for quality control and cross-calibration of dual-energy X-ray absorptiometry (DXA) instruments for measurements of body composition. We imaged the variable composition phantom (Lunar, Madison, WI) on eight different DXA devices. Deviations of up to 7% fat were observed when we compared the percent fat values measured by the different devices with the nominal values provided by the manufacturer. Absolute precision error of percent fat measurements for the phantom ranged from 0.6 to 0.8%. The phantom's percent fat values were also compared with whole body composition measurements from 130 female and male volunteers. The phantom detected differences in percent fat values that were similar to those found by comparing in vivo measurements with values from different DXA scanner models from the same manufacturer. When comparing different models of scanners from different manufacturers, such as the Hologic QDR-4500 and the Lunar DPX-IQ, the phantom showed a different relationship than was seen for patients. Therefore, corrections or comparisons based on the phantom data alone would be incorrect. In conclusion, the Lunar variable composition phantom is capable of accurately measuring the fat calibration of DXA devices and may be suitable for cross-sectional cross-calibration between scanners from the same manufacturer; however, for comparison of DXA scanners from different manufacturers, in vivo cross-calibration is still the only accurate method. The phantom may be used in longitudinal quality control to verify an instrument's temporal stability.

Absorptiometry, Photon↗
PubMed2000

Comparison of an imaging heel quantitative ultrasound device (DTU-one) with densitometric and ultrasonic measurements.

The purpose of this study was to evaluate a new imaging ultrasound scanner for the heel, the DTU-one (Osteometer MediTech, Denmark), by comparing quantitative ultrasound (QUS) results with bone mineral density (BMD) of the heel and femur from dual X-ray absorptiometry (DXA), and by comparing the DTU-one with another QUS device, the UBA 575+. The regions of interest in the DXA heel scan were matched with the regions evaluated by the two QUS devices. 134 healthy and 16 osteoporotic women aged 30-84 years old were enrolled in the study. In vivo short-term precision of the DTU-one for broadband ultrasound attenuation (BUA) and speed of sound (SOS) was 2.9% and 0.1%, respectively, and long-term precision was 3.8% and 0.2%, respectively. Highest correlations (r) between QUS and BMD measurements were achieved when comparing DTU-one results with BMD in matched regions of the DXA heel scan. Correlation coefficients (r) were 0.81 for BUA and SOS. Highest correlations with the UBA 575+ were 0.68 and 0.72, respectively. The comparison of BMD in different femoral sites with BUA and SOS (DTU-one) varied from 0.62 to 0.69 when including the entire study population. The correlation between BMD values within different sites of the femur tended to be higher (from r = 0.81 to 0.93). When comparing BUA with BUA and SOS with SOS on the two QUS devices, the absolute QUS values differed significantly. However, correlations were relatively high, with 0.76 for BUA and 0.82 for SOS. In conclusion, the results of the new quantitative ultrasound device, the DTU-one, are highly correlated (r = 0.8) with results obtained using the UBA 575+ and with BMD in the heel. The precision of the DTU-one is comparable to other QUS devices for BUA and is high for SOS.

Absorptiometry, Photon↗
PubMed1998

Linearity and accuracy errors in bone densitometry.

This investigation was undertaken to quantify accuracy errors and identify possible linearity errors in dual energy X-ray absorptiometry (DXA) of bone, based on studies of commercially available bone densitometers for planar densitometry. The following was found in a combination of in vitro phantom studies and in vivo investigations of human volunteers: (1) Pronounced differences between the instruments when measuring vertebral size and contours of the projected bone regions. (2) Falsely low bone mineral content (BMC in terms of g) in cases of low nominal bone mass, due to the fact that edge regions were omitted by the calculation software of some devices. (3) An increase in the projected bone area secondary to an increase in nominal bone mass with some instruments. (4) Clinically and statistically significant errors of accuracy of BMC and to a lesser extent bone mineral density (BMD). (5) Substantial linearity errors with some osteodensitometers for BMC, a phenomenon that reduces the usefulness of this parameter. It is concluded that DXA devices are affected by a combination of accuracy errors and linearity errors, some more than others, and that linearity errors influence their ability to monitor change in BMC and to a lesser extent in BMD, making system intercomparison difficult.

Adult↗
PubMed1997

Real-time observation of affinity reactions using grating couplers: determination of the detection limit and calculation of kinetic rate constants.

The use of integrated optical grating couplers for the analysis of bioaffinity reactions in order to calculate kinetic rate constants was investigated. The specificity of the sensor surface was determined by adsorptive or covalent attachment of the specific ligands. As an evanescent field sensor, the specific interaction of the corresponding ligand could be observed in real time and without labels. The detection limit in terms of the molecular weight of the analyte was studied by the specific binding of biotinylated proteins of different molecular weights to avidin-loaded sensors. It was shown that grating coupler sensors allowed detection of compounds of at least 2000 daltons using high-affinity receptors, while the direct sensing of low molecular analytes, such as biotin, could not be significantly achieved. Association rate constants were calculated for the interaction of the different biotinylated proteins to avidin-covered sensors from single binding curves. Due to the strong binding between avidin and biotin, the dissociation of the formed complex could not be observed. Kinetic rate constants and equilibrium constants were determined by studying the interaction of human immunoglobulin with the immobilized receptor, protein G. For the four human immunoglobulin subclasses a high affinity to protein G was determined with affinity constants ranging from 3.3 to 8.4 x 10(8) M-1.

Antibody Affinity↗
PubMed1997

[Vertebral morphometry with DXA/MXA equipment--an equipment comparison. Dual x-ray absorptiometry/morphometric x-ray absorptiometry].

PURPOSE: The accuracy and reproducibility of morphometric measurements (Morphometric X-ray Absorptiometry = MXA) of vertebrae were determined. The significant difference of the change in height of vertebral bodies in follow-up studies was computed for MXA methods and digitised spinal radiographs as well. MATERIAL AND METHODS: The measurements were carried out on two new Dual X-ray Absorptiometry (DXA) devices (device A = Expert, Lunar Corp., device B = QDR 2000 Plus, Hologic Inc.). The data were obtained by using the European Spine Phantom (ESP) and lumbar spine specimens. RESULTS: The accuracy of vertebral morphometry performed on radiographs is 2.0%, on the device A 2.3%, and on the device B 4.9%. Measurements taken with the ESP showed a reproducibility of 1.0 to 3.0%, whereas measurements of fractured vertebrae resulted in 5.1 to 6.0%. CONCLUSION: The results of the morphometric measurements demonstrate that a reliable fracture analysis in phantoms and specimens is possible. Further in-vivo studies are necessary.

Absorptiometry, Photon↗
PubMed1995

Recent developments in DXA. Quality of new DXA/MXA-devices for densitometry and morphometry.

The introduction of new devices demands the assessment of their capabilities in established terms. The accuracy, reproducibility and spatial resolution of in vitro (phantom) osteodensitometric and morphometric measurements of QDR 2000 Plus and EXPERT are presented. Design details of these DXA/MXA-devices are listed and discussed in combination with the data acquired in the test measurements and calculations. The image quality will improve with further software developments. The long-term reproducibility and in vivo reliability remains to be evaluated.

Absorptiometry, Photon↗