Rhenium-188 Labeled Hydroxyapatite and Rhenium-188 Sulfur Colloid

Aim: One therapeutic approach to rheumatoid arthritis and other inflammatory arthropathies besides surgical removal of inflamed synovium is radiation synovectomy using beta-emitting radionuclides to destroy the affected synovial tissue. Up to now the major problem associated with the use of labeled particles or colloids has been considerable leakage of radionuclides from the injected joint coupled with high radiation doses to liver and other non target organs. In this study we compared 188Re labeled hydroxyapatite particles and 188Re rhenium sulfur colloid for their potential use in radiation synovectomy. Methods: To this end we varied the labeling conditions (concentrations, pH-value, heating procedure) and analyzed the labeling yield, radiochemical purity, and in vitro stability of the resulting radiopharmaceutical. Results: After optimizing labeling conditions we achieved a labeling yield of more than 80% for 188Re hydroxyapatite and more than 90% for the rhenium sulfur colloid. Both of the radiopharmaceuticals can be prepared under aseptic conditions using an autoclav for heating without loss of activity. In vitro stability studies using various challenge solutions (water, normal saline, diluted synovial fluid) showed that 188Re labeled hydroxyapatite particles lost about 80% of their activity within 5 d in synovial fluid. Rhenium sulfur colloid on the other hand proved to be very stable with a remaining activity of more than 93% after 5 d in diluted synovial fluid. Conclusion: These in vitro results suggest that 188Re labeled rhenium sulfur colloid expects to be more suitable for therapeutic use in radiation synovectomy than the labeled hydroxyapatite particles.

Stability of radiomic features in CT perfusion maps

This study aimed to identify a set of stable radiomic parameters in CT perfusion (CTP) maps with respect to CTP calculation factors and image discretization, as an input for future prognostic models for local tumor response to chemo-radiotherapy. Pre-treatment CTP images of eleven patients with oropharyngeal carcinoma and eleven patients with non-small cell lung cancer (NSCLC) were analyzed. 315 radiomic parameters were studied per perfusion map (blood volume, blood flow and mean transit time). Radiomics robustness was investigated regarding the potentially standardizable (image discretization method, Hounsfield unit (HU) threshold, voxel size and temporal resolution) and non-standardizable (artery contouring and noise threshold) perfusion calculation factors using the intraclass correlation (ICC). To gain added value for our model radiomic parameters correlated with tumor volume, a well-known predictive factor for local tumor response to chemo-radiotherapy, were excluded from the analysis. The remaining stable radiomic parameters were grouped according to inter-parameter Spearman correlations and for each group the parameter with the highest ICC was included in the final set. The acceptance level was 0.9 and 0.7 for the ICC and correlation, respectively. The image discretization method using fixed number of bins or fixed intervals gave a similar number of stable radiomic parameters (around 40%). The potentially standardizable factors introduced more variability into radiomic parameters than the non-standardizable ones with 56-98% and 43-58% instability rates, respectively. The highest variability was observed for voxel size (instability rate  >97% for both patient cohorts). Without standardization of CTP calculation factors none of the studied radiomic parameters were stable. After standardization with respect to non-standardizable factors ten radiomic parameters were stable for both patient cohorts after correction for inter-parameter correlations. Voxel size, image discretization, HU threshold and temporal resolution have to be standardized to build a reliable predictive model based on CTP radiomics analysis.

The relation of urinary Tamm-Horsfall-protein on CaOx-crystallization under the scope of the Bonn-Risk-Index

In previous papers we introduced the Bonn-Risk Index (BRI) as a new method of evaluating an individual's actual risk of forming calcium oxalate (CaOx). A comparison of our results with the calculated urinary relative supersaturations (RS) with respect to CaOx, showed that samples with similar values of RS can have different values of BRI. We suggested that this may reflect the individual influence of the urinary macromolecular constituents which are not taken into account at the calculation of RS. To estimate the role of macromolecules on the value of BRI, we examined 45 unprepared 24-h urine samples from 24 persons (16 healthy subjects, eight CaOx stone-formers) with respect to BRI, RS, and the concentration of urinary Tamm-Horsfall-protein ([THP]). The crystallization experiments were carried out by the use of a laser-probe. Based on the data of BRI and RS, the effect of THP may shift from a minor promoter in stone-formers and persons "at risk", to an inert urinary constituent in healthy subjects and persons "without risk". However, the observed effects are small and at least in the latter group close to zero.

Reproducibility of a single-sample method for 99Tcm-MAG3 clearance under clinical conditions

The aim of this study was to assess the intra-individual reproducibility of 99Tcm-mercaptoacetyltriglycine (99Tcm-MAG3) clearance in routine clinical practice in various circumstances using a single-sample method. Three groups of 30 patients each were enrolled in the study. Investigations were repeated on the same day with two different levels of activity (group A), within 1 week (group B), or after 1 year (group C). Blood samples were taken after 20 and 25 min and clearance values were averaged to minimize incidental errors after calculation according to the formula proposed by Bubeck et al. For clearance estimation on the same day, time-dependent background correction for residual activity was carried out. The mean difference was -2.0%, +6.0% and -1.5% (S.D. = 6.3%, 15.7% and 11.7%) for groups A, B and C respectively, taking into account values > 100 ml min-1 only. We demonstrated that 99Tcm-MAG3 clearance is highly reproducible under the same conditions. However, a repeat clearance measurement on a separate day revealed large differences. Therefore, in follow-up studies for evaluation of changing kidney function (e.g. surgery or chemotherapy), differences should exceed 30% (i.e. 2 S.D. of group B) to be statistically significant.

Rhenium-188 labeled hydroxyapatite and rhenium-188 sulfur colloid. In vitro comparison of two agents for radiation synovectomy

AIM

One therapeutic approach to rheumatoid arthritis and other inflammatory arthropathies besides surgical removal of inflamed synovium is radiation synovectomy using beta-emitting radionuclides to destroy the affected synovial tissue. Up to now the major problem associated with the use of labeled particles or colloids has been considerable leakage of radionuclides from the injected joint coupled with high radiation doses to liver and other non target organs. In this study we compared 188Re labeled hydroxyapatite particles and 188Re rhenium sulfur colloid for their potential use in radiation synovectomy.

METHODS

To this end we varied the labeling conditions (concentrations, pH-value, heating procedural and analyzed the labeling yield, radiochemical purity, and in vitro stability of the resulting radiopharmaceutical.

RESULTS

After optimizing labeling conditions we achieved a labeling yield of more than 80% for 188Re hydroxyapatite and more than 90% for the rhenium sulfur colloid. Both of the radiopharmaceuticals can be prepared under aseptic conditions using an autoclave for heating without loss of activity. In vitro stability studies using various challenge solutions (water, normal saline, diluted synovial fluid) showed that 188Re labeled hydroxyapatite particles lost about 80% of their activity within 5 d in synovial fluid. Rhenium sulfur colloid on the other hand proved to be very stable with a remaining activity of more than 93% after 5 d in diluted synovial fluid.

CONCLUSION

These in vitro results suggest that 188Re labeled rhenium sulfur colloid expects to be more suitable for therapeutic use in radiation synovectomy than the labeled hydroxyapatite particles.

Ganzkörperverteilung von Tc-99m-Sestamibi nach pharmakologischer Belastung mit Arbutamin und Dipyridamol im Vergleich zum Ruhezustand

Ziel: Der neue Beta-adrenerge Rezeptoren-Agonist Arbutamin (GenESA®, Gensia Europe Ltd., Berkshire, England) wurde speziell für den pharmakologischen Streß zum Nachweis einer koronaren Herzerkrankung entwickelt und stellt damit auch für die Belastungsmyokardszintigraphie eine Option dar. Die pharmakologische Wirkung kann im Vergleich zum Vasodilatator Dipyridamol anhand der Ganzkörper-Aktivitätsverteilung nach Applikation von Tc-99m-Sestamibi bestimmt werden. Methoden: Untersucht wurden 9 Patienten nach Applikation von Tc-99m-Sestamibi unter Ruhebedingung, nach Steigerung der myokardialen Perfusion durch Infusion von Arbutamin und unter maximaler Vasodilatation durch Infusion von Dipyridamol. Ergebnisse: Nach Gabe von Arbutamin bestand eine szintigraphisch meßbare verminderte Radiotracereinlagerung in der unteren Extremität. Gegenüber Dipyridamol war die myokardiale Akkumulation von Tc-99m-Sestamibi trotzdem vermindert, was sich neben dem relativen Anteil des Herzens an der Ganzkörperaktivität (2,1% ± 0,5% gegenüber 2,4% ± 0,4%, p <0,05) auch an einem niedrigeren Herz-Lungen-Quotienten (2,5 ± 0,4 gegenüber 2,8 ± 0,5, p <0,05) zeigte. Schlußfolgerung: Nach Infusion von Arbutamin ist sowohl der Anteil von myokardial deponiertem Tc-99m-Sestamibi als auch der Kontrast des Myokards zur umgebenden Lunge geringer als nach Gabe von Dipyridamol. Ob dieser Unterschied für die Diagnose myokardialer Perfusionsstörungen mit Tc-99m-Sestamibi relevant ist, muß noch überprüft werden.

[Whole body distribution of Tc-99m-sestamibi after pharmacological stress with arbutamine and dipyridamole compared with resting conditions]

AIM

Arbutamine is a new catecholamine that has been developed as a pharmacologic stress agent for the diagnosis of coronary artery disease. Optionally, it can be used in myocardial scintigraphy. The pharmacologic effect compared to dipyridamole was assessed looking at the whole body distribution of Tc-99m-Sestamibi.

METHODS

9 patients were investigated after injection of Tc-99m-Sestamibi during rest, after infusion of arbutamine, and after vasodilatation with dipyridamole.

RESULTS

Infusion of arbutamine results in a measurable diminished radiotracer deposition in the lower limb as compared to dipyridamole. The amount of myocardial activity of Tc-99m-sestamibi, however, is also reduced as shown by the percentage of myocardial activity compared to the whole body distribution (2.5% +/- 0.4% for arbutamine vs. 2.8% = 0.5% for dipyridamole) in addition, the heart/lung ratio is lower after application of arbutamine (12.1% +/- 0.5% vs. 2.4% +/- 0.4%).

CONCLUSION

After infusion of arbutamine the percentage of myocardial activity as well as the contrast of the myocardium to the surrounding lungs is decreased as compared to dipyridamole. Further studies should reveal whether this difference is relevant in diagnosing coronary artery disease.