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Zusammenfassung Die intraarterielle Selektive Interne Radiotherapie (SIRT) mit 90 Y-markierten Mikrospharen ist mittlerweile eine wichtige lokal-ablative Therapieoption fur die Behandlung onkologischer Patienten geworden. Die SIRT stellt gegenwartig einen palliativen Therapieansatz fur die Behandlung von Lebermalignomen dar. Infolge der Art des 90 Y-Zerfalls als β - -Strahler ohne eine begleitende Gammaemission, bedarf es zur Validierung der erzielten Verteilung des Radioembolisates einer Bremsstrahlungsbildgebung. Dieser Artikel demonstriert durch eine Phantommessung diese Art der Bildgebung und zeigt anhand einer Patientenstudie die Vorteile einer posttherapeutischen Schnittbildgebung. Es werden Ansatzpunkte fur weitere Optimierungen der Bremsstrahlungsbildgebung aufgezeigt.

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.

Zusammenfassung PET-Untersuchungen werden heute fast ausschlieslich mit PET/CT-Hybridsystemen durchgefuhrt. Wahrend Abnahme- und Konstanzprufung fur die Einzelkomponenten PET bzw. CT durch entsprechende Vorschriften geregelt sind, fehlen Regelungen fur die Schnittstelle der Hybridgerate. Diese Schnittstelle beinhaltet die Justage beider Gantries und der Liege zueinander sowie die Energieskalierung von Absorptionskoeffizienten von der CT-Energie auf 511 keV. Bis jetzt werden Kontrollmessungen bezuglich der mechanischen Justage (Bestimmungen von Offset-Parametern) nach den Empfehlungen des Herstellers durchgefuhrt typischerweise halbjahrlich. An einem Biograph 16 (Fa. Siemens) wurde die Stabilitat dieser Offsetbestimmungen systematisch durch wochentliche Messungen uber einen Beobachtungszeitraum von zehn Monaten untersucht, erganzt durch Messungen mit einer zusatzlichen Belastung der Liege bis zu 135 kg und bei verschiedenen vertikalen Liegenpositionen. Nach den vorliegenden Ergebnissen beim getesteten Geratetyp kann von uber die Herstellerempfehlung hinausgehenden Konstanzprufungen des Offsets abgesehen werden. Auch die Energieskalierung der Absorptionskoeffizienten ist abhangig von Methodik und Softwareimplementierung und somit nicht Gegenstand der Konstanzprufung. Notwendig hingegen ist die Entwicklung geeigneter Methoden der Abnahmeprufung, sowohl zur Erfassung und Feststellung aller Freiheitsgrade der mechanischen Justage als auch zur Ermittlung der Gute der Absorptionskorrektur der Emissionsdaten.

SummaryIn nuclear medicine therapy the treatment of tumours by radiation exposure from internally deposited labelled antibodies or labelled peptides is currently an active field of investigation. To permit the efficient delivery of high amounts of radiation dose to tumours while limiting the radiation dose to critical organs dosimetry calculations have to be performed. These are relying on scintigraphic data being input to the well known MIRD formalism.This paper focuses on the methods and the difficulties associated with the scintigraphic determination of organ kinetics. The physical properties of the well-known scintigraphic imaging modalities, PET, SPECT and planar scintigraphy, are discussed thereby taking into account the properties of the appropriate radionuclides currently being available for therapy and dosimetry. Several arguments are given and disputed for the limited clinical use of PET and SPECT in dosimetry and the ongoing preference of planar whole-body imaging as the method of choice. The quantitative restrictions still inherent to this method are also discussed in detail. Procedural recommendations are proposed covering all processes related to data acquisition, data correction and data analysis which finally lead to reliable estimations of organ dose.

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.

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.

In emission tomography, the spread of regional tracer uptake to surrounding areas caused by limited spatial resolution of the tomograph must be taken into account when quantitating activity concentrations in vivo. Assuming linearity and stationarity, the relationship between imaged activity concentration and true activity concentration is only dependent on the geometric relationship between the limited spatial resolution of the tomograph in all three dimensions and the three-dimensional size and shape of the object. In particular it is independent of the type of object studied. This concept is characterized by the term "recovery coefficient". Recovery effects can be corrected for by recovery coefficients determined in a calibration measurement for lesions of simple geometrical shape. This method works on anatomical structures that can be approximated to simple geometrical objects. The aim of this study was to investigate whether recovery correction of appropriate structures is feasible in a clinical setting. Measurements were done on a positron emission tomography (PET) scanner in the 2D and 3D acquisition mode and on an analogue and digital single-photon emission tomography (SPET) system using commercially available software for image reconstruction and correction of absorption and scatter effects. The results of hot spot and cold spot phantom measurements were compared to validate the assumed conditions of linearity and stationarity. It can be concluded that a recovery correction is feasible for PET scanners down to lesions measuring about 1.5xFWHM in size, whereas with simple correction schemes, which are widely available, an object-independent recovery correction for SPET cannot be performed. This result can be attributed to imperfections in the commercially available methods for attenuation and scatter correction in SPET, which are only approximate.

SummaryIn 58 patients with Parkinsonism or dystonia striatal dopamine D2 receptors were investigated using 123l-iodobenzamide (123I-IBZM) single-photon emission computed tomography (SPECT). The influence of SPECT reconstruction methodology on semiquantification and the clinical value of 123I-IBZM SPECT were evaluated. Delineation of the striatal uptake and striatum/frontal cortex (ST/FC) ratios were improved by the use of compensation procedures for scatter and attenuation as well as the choice of an adequate filter. Satisfactory results were achieved using a Metz prefilter with a comparatively high order number (i. e. high cut-off and low suppression of higher frequencies via roll-off). Regarding clinical diagnoses it was not possible to differentiate between advanced idiopathic Parkinson’s disease (IP) and Parkinsonism of other aetiology (OP) on the basis of 123I-IBZM SPECT. But patients with IP and favourable response to L-Dopa showed significantly higher ST/FC ratios than those with fluctuating response. In patients with dystonia ST/FC ratios were significantly higher compared to patients with IP or OP.

TO THE EDITOR: With interest we read the recent publication of Scheuermann et al. ( [1][1] ), who reported on the experience of the American College of Radiology Imaging Network in qualifying PET scanners to participate in multicenter trials. The network does so by analyzing submitted PET scans of

A new method for quantifying regional variations in extravascular lung water (rELW) has been developed. The positron source 15O (T1/2 = 2.0 min.) was provided as H215O 'on line' by constant intravenous injection. Tomographic images (PET) of the water distribution were obtained during equilibrium. The distribution of blood volume was obtained by marking erythrocytes (carboxyhaemoglobin) using a bolus inhalation [C-11)-CO; T1/2 = 20.4 min). Absorption is calculated from transmission tomography. The rELW is defined as: total lung water minus intravascular space. The method was carried out in five intubated and anaesthetised dogs before and after induction of pulmonary oedema with oleic acid (0.06 ml./kg.). Mean ELW (PET) rose from 0.13 +/- 0.02 g./cm.3 to 0.24 +/- 0.04 g./cm.3. There was good correlation with a simultaneously performed thermo-dye method (7.1 +/- 1.3 ml./kg. KG to 13.3 +/- 1.9 ml./kg. KG; r = 0.94). Gravimetric estimations resulted in 13.7 +/- 2.6 ml./kg. KG. The development and distribution of the pulmonary oedema was non-homogeneous and varied regionally.

One dimensional profile scans with a whole body counter are refocused with a linear space invariant filter in the frequency domain, 'Hanning' window and inverse system transfer function. Artifacts are eliminated in a way that a clinically applicable method is developed. Topographic information is achieved with the highly energetic nuclide 82bromide. The bromide space (extracellular volume) in patients with liver cirrhosis (n = 9) compared to normal subjects (n = 10) is increased most in the upper abdominal thoracic region.

A proposal is made for the test conditions to evaluate PET count rate performance. This performance depends in a complex manner on the spatial distribution of activity and scattering material. Therefore, a combined body phantom is proposed, which is as simple as possible but which adequately simulates the range of clinical application of a whole body tomograph. Taking into account the special properties of the new block detector design, a comprehensive test procedure is developed. This includes not only the common count rate characteristic, but also checks for the accuracy of randoms estimation and count loss correction schemes, and for the occurrence of pulse pile up. This is done for different source and scatter configurations, simulating brain, cardiac, and abdominal imaging, respectively. Examples are given, based on measurements of the latest generation PET scanners, namely the CT1 PT 931/08-12 and the Scanditronix PC 2048-07WB.

There are two competitive measuring techniques in emission tomography: SPECT and PET. The superiority of PET is founded not only on using physiological radionuclides and tracers such as carbon 11, oxygen 15, and nitrogen 13, but also on achieving a physical performance far in excess of that of SPECT. Considering the demands of cardiac studies, the performance of both methods is analyzed and compared and the inherent limitations are stated.