[Constancy check of system linearity for dose calibrators. Effect of molybdenum impurities at high start activities of 99mTc]. / Konstanzprüfung der Systemlinearität von Aktivimetern mittels 99mTc. Einfluss der Molybdän-Verunreinigung bei hohen Startaktivitäten.

UNLABELLED: Dose calibrators are one of the most important and most frequently used instruments for the determination of activities in nuclear medicine. For guaranteeing a constant quality of the dose calibrators' measurements, constancy checks including the examination of the system linearity have to be performed regularly, usually measured using 99mTc. The 99mTc eluate extracted from a 99Mo/99mTc generator is contaminated with molybdenum. Not accounting for the molybdenum impurity might lead to an exceed of the tolerance limit of 5% deviation to the reference value for this constancy check. The reason for this effect is the contamination of the 99mTc eluate with 99Mo, whose impact depends on both the amount of the impurity and on the total measurement time (high start activities). RESULT: In this work, the influence of the molybdenum impurity on the results of the constancy check of the system linearity was investigated and maximum start activities for certain impurities were determined providing that the deviation to the reference values is below 5%. CONCLUSION: Provided that certain boundary conditions are observed, a correction of the results with respect to the molybdenum contamination is not necessary.

Calibration test of PET scanners in a multi-centre clinical trial on breast cancer therapy monitoring using 18F-FLT.

UNLABELLED: A multi-centre trial using PET requires the analysis of images acquired on different systems We designed a multi-centre trial to estimate the value of 18F-FLT-PET to predict response to neoadjuvant chemotherapy in patients with newly diagnosed breast cancer. A calibration check of each PET-CT and of its peripheral devices was performed to evaluate the reliability of the results. MATERIAL AND METHODS: 11 centres were investigated. Dose calibrators were assessed by repeated measurements of a 68Ge certified source. The differences between the clocks associated with the dose calibrators and inherent to the PET systems were registered. The calibration of PET-CT was assessed with an homogeneous cylindrical phantom by comparing the activities per unit of volume calculated from the dose calibrator measurements with that measured on 15 Regions of Interest (ROIs) drawn on 15 consecutive slices of reconstructed filtered back-projection (FBP) images. Both repeatability of activity concentration based upon the 15 ROIs (ANOVA-test) and its accuracy were evaluated. RESULTS: There was no significant difference for dose calibrator measurements (median of difference -0.04%; min = -4.65%; max = +5.63%). Mismatches between the clocks were less than 2 min in all sites and thus did not require any correction, regarding the half life of 18F. For all the PET systems, ANOVA revealed no significant difference between the activity concentrations estimated from the 15 ROIs (median of difference -0.69%; min = -9.97%; max = +9.60%). CONCLUSION: No major difference between the 11 centres with respect to calibration and cross-calibration was observed. The reliability of our 18F-FLT multi-centre clinical trial was therefore confirmed from the physical point of view. This type of procedure may be useful for any clinical trial involving different PET systems.

[External radiation exposure and effective half-life in Lu-177-Dota-Tate therapy]. / Äußere Strahlenexposition und effektive Halbwertszeit bei Therapie mit Lu-177-Dota-Tate.

The aim of the study was to estimate the external radiation exposure emitted by the patient to his surroundings after discharge. Being in compliance with legal requirements is especially important when doing multiple therapies. To estimate the effective half-life to be used quite realistically, the individual effective half-lives for 41 patients with 52 therapies were calculated. From the resulting histogram the maximum value was determined to be 100 h. Substituting the physical half-life by this maximum effective half-life results in dose estimates, which are lower but still conservative. In addition, the analysis of dose related parameters for patients who underwent multiple therapies demonstrates that the parameters estimated for the first therapy cannot be transferred to the subsequent ones.

[Radioembolization with (90)Y-labeled microspheres: post-therapeutic therapy validation with Bremsstrahlung-SPECT]. / Radioembolisation mit (90)Y-markierten Mikrosphären: Posttherapeutische Therapievalidierung mit Bremsstrahlungs-SPECT.

During the last years angiographic Selective Internal Radiotherapy (SIRT) with (90)Y-labelled microspheres has become a common technique for the local-ablative treatment of cancer patients. SIRT is a palliative therapy concept for the treatment of liver malignancies. As a result of (90)Y-decay as ß(-)-emitter without a concomitant gamma radiation, Bremsstrahlung imaging is needed to validate the distribution achieved by radioembolisation. This article demonstrates the method of imaging through phantom measurement and shows the advantages of post-therapeutic tomography by means of a patient study. Approaches for further optimization of Bremsstrahlung imaging are discussed.

Estimation of glomerular filtration rate in liver-transplanted children: comparison of simplified procedures using 51Cr-EDTA and endogenous markers with Sapirstein's method as a reference standard.

This study evaluated simple procedures for GFR determination in 48 liver-transplanted children. After injection of (51)Cr-EDTA, blood samples were obtained up to four h, and activity retention in the body was measured for 60 min with scintillation probes. As a reference, GFR was calculated according to Sapirstein. Simplified calculations were performed according to Brochner-Mortensen, Russel, Devaux and Oberhausen. Additionally, GFR was determined using plasma creatinine and cystatin C according to Schwartz and Filler, respectively. The reference revealed mildly reduced GFR (62 +/- 20 mL/min/1.73 m(2)). Russel's method provided the highest degree of correlation (r(2) = 0.95), the smallest bias in GFR determination (-2%), and only one false exclusion plus one false diagnosis of chronic kidney disease. Oberhausen's method with blood sampling at one h post-injection performed slightly worse (r(2) = 0.67, bias: 3%). All other methods resulted in significantly different GFR estimates compared to the reference. Nevertheless, notably, the second narrowest 95% limits of agreement (-31% to 45%) was observed using cystatin C. In conclusion, this data implies to prefer Russel's method as a simplified procedure, and if patients cannot be available long enough (four h) for measurements, Oberhausen's method instead. If radiotracer methods are not available at all or for screening GFR, cystatin C appears to be the procedure of choice.

[123I]AM281 single-photon emission computed tomography imaging of central cannabinoid CB1 receptors before and after Delta9-tetrahydrocannabinol therapy and whole-body scanning for assessment of radiation dose in tourette patients.

BACKGROUND: The cannabinoid CB1 receptor agonist Delta9-THC has been suggested for treatment of Tourette syndrome (TS). Based on animal studies, the CB1 antagonist [123I]AM281 (N-(Morpholin-4-yl)-1-(2,4-dichlorophenyl)-5-(4-[123I]iodophenyl)-4-methyl-1H-pyrazole-3-carboxamide) has been proposed for single photon emission computed tomography (SPECT) in humans. Our aims were to 1) evaluate specific binding of [123I]AM281 to CB1 receptors in TS patients and 2) assess radiation exposure associated with the use of AM281 labeled with 123I for SPECT and 124I for positron emission tomography. METHODS: We employed [123I]AM281 in six TS patients before and after Delta9-THC treatment. Dynamic SPECT, plasma measurements (including metabolite analysis with thin layer chromatography), and whole-body imaging were performed. Regions of interest derived from magnetic resonance images were used to extract from SPECT uptake in an area with high CB1 density (lentiform nuclei) and reference regions. Specific over nonspecific partition coefficients V3" were calculated. Whole-body images were carried out for dosimetric analysis. Data obtained with [123I]AM281 were used to predict doses from [124I]AM281. RESULTS: Mean V3" ranged from .19 to .31 and did not change significantly after Delta9-THC treatment. Nevertheless, in the only patient with a marked clinical response, V3" clearly declined. Thin layer chromatography revealed biexponential kinetics of tracer metabolism; about 60% remained nonmetabolized after 3 hours. Effective doses of .011 mSv/MBq for [123I]AM281 and .34 for [124I]AM281 were computed. CONCLUSIONS: This study suggests that specific binding of [123I]AM281 to CB1 receptors can be detected in patients using SPECT. Radiation exposure with [123I]AM281 is low; that with [124I]AM281 is higher but acceptable for single investigations.

[Testing cross-calibration between positron emission tomographs and their peripheral devices]. / Uberprüfung der Kreuzkalibrierung von Positronen-Emissions-Tomographen zu ihren peripheren Geräten.

The aim of this study was to evaluate the cross-calibration of positron emission tomographs and their peripheral devices prior to a multicenter study. The instrumentation of 22 sites (including 24 dedicated PET scanners), including 21 that could be operated in 2D mode and 20 in 3D mode, was investigated according to standardized acquisition and reconstruction protocols, and the cross-calibration was checked against the dose calibrators (22 instruments) and the sample changer (20 instruments). The deviation of the cross-calibration to the dose calibrators was below 5% for 10 of 21 PET scanners (2D mode) and 6 of 20 (3D mode). For 6 (2D mode) and 6 (3D mode) scanners, the corresponding error was up to 10%. In turn, the deviation between dose calibrator and standard was less than 8% for 19 devices, and even less than 5% for 14 devices. In most of the well counters evaluated, the cross-calibration error was less than 10%. Although required in general, the cross-calibration between positron emission tomographs and their peripheral devices becomes even more critical when pooling data in the framework of quantitative clinical multicenter studies.

Use of recovery coefficients as a test of system linearity of response in positron emission tomography (PET).

Quantitative determination of activity concentration has always been regarded as a goal of PET scanner design. Therefore, a linear response with respect to activity concentration is essential. To prove system linearity of response a test is proposed based on the determination of recovery coefficients (RC) for different object geometries. If all degrading effects, especially scatter and attenuation, are corrected to a sufficient degree of accuracy, the system behaves linearly resulting in a theoretical relationship between hot (HSRC) and cold spot recovery coefficients (CSRC). Therefore this relationship, applied to appropriate phantom data containing hot or cold spheres, combined with the constraints on asymptotic behaviour of RC can be used as a test of system linearity of response. After applying the system's standard corrections RC were determined using both 2D and 3D data acquisition modes. For both 2D and 3D data, HSRC directly measured showed an excellent agreement with the HSRC calculated from the CSRC. The analysis was extended to radionuclides of different positron ranges, to the effect of data smoothing, and to that of iterative reconstruction. The agreement between the RC determined under varying border conditions demonstrates the effectiveness of the corrections used in constituting system linearity. Therefore, the method proposed is used as a test of system linearity of response.

Multicenter comparison of calibration and cross calibration of PET scanners.

UNLABELLED: The purpose of this study was to compare the calibration of PET scanners and their cross calibration to peripheral devices in a multicenter study. METHODS: Twenty-three dedicated PET scanners were investigated, applying standardized protocols. To ensure exact determination of the activity used, dose calibrators were checked using (68)Ge standards. RESULTS: Nine of 19 and 11 of 20 scanners displayed an error of <5% in 3-dimensional and 2-dimensional acquisition modes, respectively. Four and 5 scanners displayed an error of 10% in 3-dimensional and 2-dimensional modes, respectively. All other scanners yielded errors of 5% to <10%. Because of hardware and software problems, the measurements performed on 1 scanner could not be adequately analyzed. CONCLUSION: An investigation of calibration is mandatory. Especially for quantitative analyses in clinical multicenter trials, identification of potentially miscalibrated scanners is necessary.