Differences in SPET analysis of thyroid-associated orbitopathy.
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Algorithms↗
Biomedical subjects
József Varga
Publications and source records attributed to József Varga.
Limitations of bi-linear regression analysis for the determination of receptor occupancy with positron emission tomography.
BACKGROUND AND OBJECTIVES: Linear/multilinear regression methods are widely used in quantitative neuroreceptor positron emission tomography. A reference tissue method based on a bi-linear operational equation, the bi-linear reference tissue method, has been introduced in order to overcome the need for arterial blood sampling. The aim of the present paper was to investigate the sensitivity of the bi-linear reference tissue method to statistical noise, with special regard to the assessment of receptor occupancy. In addition, improvement of the bi-linear reference tissue method by regularization using physiological constraints was evaluated. METHODS: Application of the bi-linear method to dynamic positron emission tomography using the serotonin transporter ligand C-(+)McN5652 was considered. Investigations were performed by computer simulations and analysis of 29 patient studies. RESULTS: The equilibrium specific-to-non-specific partition coefficient V"3 was significantly underestimated by the bi-linear reference tissue method. At realistic noise levels the extent of the underestimation ranged from 25% to 75% for partition coefficients ranging from 0.3 to 0.3, respectively. This caused a 15-60% underestimation of changes in receptor occupancy after simulated intervention. The noise dependence of the bias was confirmed in the patient studies. Regularization significantly reduced the underestimation of the occupancy. CONCLUSIONS: When receptor status or noise level vary substantially, as in receptor occupancy studies, the bias of the bi-linear reference tissue method should be taken into account.
Adult↗
Age dependence of serum beta-N-acetylhexosaminidase (NAG) activity.
Serum N-acetyl-beta-D-glucosaminidase (NAG; EC 3.2.1.30) is a hexosaminidase and may be a predictor of vascular injury, e.g., in infant respiratory distress syndrome, pneumonia, broncho-pulmonary dysplasia and necrotizing enterocolitis. To estimate the new diagnostic prospects we have modified our urinary NAG assay. In this sensitive colorimetric micro-assay, VRA-GlcNAc was used as a substrate. In the present study the age dependence of serum NAG activity was investigated in newborn babies, infants (1-24 months), children (2-18 years) and adults (19-80 years). Serum NAG activity was found to be age-dependent; it is higher in early childhood (11-59 U/l) but decreases to a constant value at the age of 1-2 years. After the age of 2 years it is similar to adults' NAG (10-30 U/l). In pediatrics age-matched reference ranges must be taken into consideration.
Acetylglucosamine↗
[Assessment of autoimmune disease activity in endocrine orbitopathy: comparison of SPECT using 99m-Tc-DTPA or 99m-Tc-depreotide and MRI scores].
INTRODUCTION: Currently there is no ideal imaging technique which could estimate the degree of inflammation in thyroid eye disease. AIM: A new, rapid and cost-effective method, using 99mTc-labelled DTPA and 4-headed SPECT, was developed which is able to diagnose inflammatory activity in patients with endocrine orbitopathy (EOP). METHODS: The MRI T2 relaxation time was used as reference. Comparative orbital SPECT with the more specific 99mTc-Neospect (depreotide) was also performed in the same patients. RESULTS: Visual evaluation of orbital SPECT frames of patients suffering from active EOP could be easily distinguished from inactive EOP patients'. Despite the supposedly different characteristics of the two tested radiopharmaceuticals, there was essentially no difference between their accumulation in the orbit and the information obtained. The MRI activity scores correlated well with 99mTc-DTPA activity uptake (AU). The mean AU value in patients with inactive EOP was 6.26 +/- 1.6 10(-6) ID/cm3, while in active EOP 10.78 +/- 0.61 10(-6) ID/cm3, significantly higher. The 99mTc-DTPA accumulation in the orbital region in active disease was similar to that of depreotide. There was a good correlation (r = 0.91, P < 0.0001) between the two methods. CONCLUSION: The authors concluded that 99mTc-DTPA orbital SPECT is a potentially useful method, which--after initial clinical and MRI staging--gives useful quantitative estimation of disease activity in endocrine orbitopathy. It may provide important visual and quantitative information during the follow up of patients.
Adult↗
Experimental results of donor site filling for autologous osteochondral mosaicplasty.
PURPOSE: Autologous osteochondral mosaicplasty has become a treatment option for focal chondral and osteochondral defects in recent years. Excessive postoperative bleeding from the donor site was reported as a possible complication of the procedure. The purpose of this study was to investigate different biodegradable materials for donor site filling, which could prevent excessive postoperative bleeding from these sites but would allow reasonable blood clot formation on the articular surfaces of donor tunnels. TYPE OF STUDY: Basic science evaluation. METHODS: In an experimental model, "donor site plugs" made from hydroxylapatite, carbon fiber, polyglyconate-B, compressed collagen, and 2 versions of polycaprolactones were used to fill the bony tunnels created by harvesting. These materials were tested in 100 knees of 50 German Shepherd dogs to determine the quality of the repair tissue formation on the surfaces of the harvesting holes filled by these materials. Arthroscopies of the dogs were performed at several intervals, from 4 weeks to 26 weeks, and macroscopic studies were performed on euthanized animals between 8 weeks and 30 weeks to evaluate donor site filling and coverage. Empty donor tunnels served as controls for the evaluation of the different filling materials. RESULTS: All tested materials effectively decreased postoperative bleeding. Hydroxylapatite, carbon rods, polyglyconate-B, and melted polycaprolactone materials showed a good integration to the surrounding cancellous bone, but these fillings showed only a limited repair tissue formation, even at 30 weeks postoperatively. Second-look arthroscopy and histologic evaluation of necropsies showed the best fibrocartilage coverage after filling by compressed collagen. Technical details of the filling also had certain importance in the quality of the repair tissue formation. CONCLUSIONS: According to histologic results, compressed collagen appears to be a good material to fill donor tunnels of osteochondral graft harvest. This material is substituted gradually by bone formation and its articular surface can serve as an appropriate scaffold for fibrocartilage coverage created by the natural intrinsic repair process.
Animals↗
Active retrobulbar inflammation in Graves' ophthalmopathy visualized by Tc-99m DTPA SPECT.
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Graves Disease↗
Urinary homogentisic acid in alkaptonuric and healthy children.
To detect and follow-up the metabolic status of patients with alkaptonuria (AKU), urinary homogentisic acid (HGA) was measured by gas chromatography. These results were close to values we obtained by colorimetric method (linearity: upto 700 mg/l, detection limit: 1 mg/l, within-run imprecision (CV): 1.2% at 100 mg/l HGA, 4.9% at 10 mg/l, between-run CV: 6.8% at 100 mg/l). To determine urinary reference ranges of HGA, 84 healthy children (age: 2 months-18 years) were divided into five age groups. HGA and creatinine were measured in their morning urine. Statistical analysis proved that urinary HGA/creatinine ratio is age-dependent. The ratio is relatively high between 1 and 6 years of age, with large scatter (upper limit of reference ranges given as mean + 2 SD: 5.5-7.2 mg/mmol = 0.03-0.04 mmol/mmol creatinine), and it decreases with age. Approximately at the age of 7 years, HGA/creatinine ratio becomes constant, and later it is similar to the adult value (upper limit: 2.8 mg/ mmol = 0.017 mmol/mmol creatinine). We monitored a patient during her 1-5th year of life, and her urinary HGA was 80-200 times higher than the upper limit of the age-matched reference ranges. The measurement of HGA supports the decision for starting restricted protein diet and is useful for the evaluation of the effectiveness of therapy.
Adolescent↗
[PET and SPECT scans in autistic children].
The authors have analyzed and compared the results of the 99mTc-ECD-SPECT and FDG-PET examinations, performed in alert state, of 12 children suffering from infantile (9 subjects) or atypical (3 subjects) autism. In addition to frontally increased FDG metabolism, a decreased blood flow with left-sided dominance was found bifrontally and bitemporally in the infantile form (perfusion-metabolism mismatch). The regional differences in cortical FDG uptake were not significant in atypical autism, although both the blood flow and the metabolism of the thalami were decreased. Based on the results, the authors suggest that, beyond the usually inconclusive structural (CT or MR) examinations, cerebral blood flow SPECT and metabolic FDG-PET investigations may be useful in classifying the disease.
Adolescent↗
Modified regression model for the Logan plot.
Logan's graphical model is a robust estimation of the total distribution volume (DVt) of reversibly bound radiopharmaceuticals, but the resulting DVt values decrease with increasing noise. The authors hypothesized that the noise dependence can be reduced by a linear regression model that minimizes the sum of squared perpendicular rather than vertical (y) distances between the data points and fitted straight line. To test the new method, 15 levels of simulated noise (repeated 2,000 times) were added to synthetic tissue activity curves, calculated from two different sets of kinetic parameters. Contrary to the traditional method, there was no ( P > 0.05) or dramatically decreased noise dependence with the perpendicular model. Real dynamic 11C (+) McN5652 serotonin transporter binding data were processed either by applying Logan analysis to average counts of large areas or by averaging the Logan slopes of individual-voxel data. There were no significant differences between the parameters when the perpendicular regression method was used with both approaches. The presented experiments show that the DVt calculated from the Logan plot is much less noise dependent if the linear regression model accounts for errors in both the x and y variables, allowing fast creation of unbiased parametric images from dynamic positron-emission tomography studies.
Artifacts↗