Determination of ultrasound phase velocity in trabecular bone using time dependent phase tracking technique

Ultrasound velocity is one of the key acoustic parameters for noninvasive diagnosis of osteoporosis. Ultrasound phase velocity can be uniquely measured from the phase of the ultrasound signal at a specified frequency. Many previous studies used fast Fourier transform (FFT) to determine the phase velocity, which may cause errors due to the limitations of FFT. The new phase tracking technique applied an adaptive tracking algorithm to detect the time dependent phase and amplitude of the ultrasound signal at a specified frequency. This overcame the disadvantages of FFT to ensure the accuracy of the ultrasound phase velocity. As a result, the new method exhibited high accuracy in the measurement of ultrasound phase velocity of two phantom blocks with the error less than 0.4%. 41 cubic trabecular samples from sheep femoral condyles were used in the study. The phase velocity of the samples using the new method had significantly high correlation to the bulk stiffness of the samples (r = 0.84) compared to the phase velocity measured using fast Fourier transform FFT (r = 0.14). In conclusion, the new method provided an accurate measurement of the ultrasound phase velocity in bone.     

Determination of serum thyroxine enantiomers in patients by liquid chromatography with a chiral mobile phase

A chromatographic method for the separation and determination of D- and L-thyroxine enantiomers (D-, and L-T4) in human serum with a chiral ligand ion-exchange system using a chiral mobile phase additive and a silica column was established. An aqueous eluent containing L-proline (L-pro) sufficiently complexed copper II ions and triethylamine (TEA) was used. It was monitored with a UV detector. The separation was completed in 12 min. The method has acceptable sensitivity, precision and accuracy for analysis. The limit of detection and the limit of quantitation for both D- and L-T4 were 0.1 microg/ml and 0.8 microg/ml, respectively. Calibration curves were linear within 1-100 microg/ml; the mean correlation coefficients were r(D-T4)=0.9986 for D-T4 and r(L-T4)=0.9978 for L-T4. T4 enantiomers were separated on baseline under the optimum condition. L-T4 eluted before D-T4. The concentration of D-T4 and L-T4 in 45 thyroid patients serum (hyperthyroid, hypothyroid, thyroidectomy, goitre or thyroiditis) using HPLC was determined, those results showed that D,L-T4 concentration varied in different thyroid patient. Attention should be paid to this result in treating thyroid disease in the clinic.     

A third type of serum cholinesterase deficiency in Eskimos.

A new type of serum cholinesterase deficiency with less than 10% of the normal activity was found in an Alaskan Eskimo. The new type of deficiency appeared to be allelic with two types previously described in this population.     

Determination of 25-hydroxycholecalciferol in serum

A precise specific method for measuring 25-hydroxycholecalciferol (25-OH CC) in 2 ml of human serum is described. It includes extraction with acetonitrile, separation with Sep-Pak C-18 cartridges, purification through HPLC and a further quantitation by means of a protein-binding assay. An exhaustive study of this protein-binding method has been performed. The sensitivity of the protein-binding assay is 20 pg/tube and the inter and intra-assay coefficients of variation are 9.6% and 8.7% respectively. The precision of the overall process has been assessed by calculating the inter and intra-assay coefficients of variation, 15.5 and 10.4% respectively. Mean serum value of 25-OH CC in normal subjects (18-50 years old, during spring) is 11.2 +/- 5.5 ng/ml.     

Face to phase: pitfalls in time delay estimation from coherency phase

Coherency phase is often interpreted as a time delay reflecting a transmission delay between spatially separated neural populations. However, time delays estimated from corticomuscular coherency are conflicting and often shorter than expected physiologically. Recent work suggests that corticomuscular coherence is influenced by afferent sensory feedback and bidirectional interactions. We investigated how bidirectional interaction affects time delay estimated from coherency, using a feedback model of the corticomuscular system. We also evaluated the effect of bidirectional interaction on two popular directed connectivity measures: directed transfer function (DTF) and partial directed coherence (PDC). The model is able to reproduce the range of time delays found experimentally from coherency phase by varying the strengths of the efferent and afferent pathways and the recording of sensory feedback in the cortical signal. Both coherency phase and DTF phase were affected by sensory feedback, resulting in an underestimation of the transmission delay. Coherency phase was altered by the recording of sensory feedback in the cortical signals and both measures were affected by the presence of a closed loop feedback system. Only PDC phase led to the correct estimation of efferent transmission delay in all simulated model configurations. Coherency and DTF phase should not be used to estimate transmission delays in neural networks as the estimated time delays are meaningless in the presence of sensory feedback and closed feedback loops.     

Determination of anti-AGE antibodies in human serum

The aim of this study was to develop an immunoenzyme method for the determination of anti-AGE antibodies in human serum. Human aortic elastin glycatedin vitro (AGE-elastin) was used as an antigen, expressing AGE-epitopes, common to all glycated proteins.Polyclonal serum from guinea-pig against AGE-Hemocyanin was obtained according to Nakayamaet al. [(1989)Biochem Biophys Res Commun 162: 740–45] and its specificity was tested via direct and competitive ELISA. Sera of 20 type 1 diabetic patients and 20 healthy subjects were tested using the method described. Seventeen patients had elevated levels of competing factors that may be anti-AGE antibodies, compared with the healthy group. The method could be used for investigation of different clinical groups of type 1 diabetic patients. Such a study would help in understanding the pathogenic role of autoantibodies against advanced glycation end products of proteins for the development of long-term diabetic complications.