Krzysztof Kacperski

Performance evaluation of D-SPECT: a novel SPECT system for nuclear cardiology.

D-SPECT (Spectrum Dynamics, Israel) is a novel SPECT system for cardiac perfusion studies. Based on CZT detectors, region-centric scanning, high-sensitivity collimators and resolution recovery, it offers potential advantages over conventional systems. A series of measurements were made on a beta-version D-SPECT system in order to evaluate its performance in terms of energy resolution, scatter fraction, sensitivity, count rate capability and resolution. Corresponding measurements were also done on a conventional SPECT system (CS) for comparison. The energy resolution of the D-SPECT system at 140 keV was 5.5% (CS: 9.25%), the scatter fraction 30% (CS: 34%), the planar sensitivity 398 s(-1) MBq(-1) per head ((99m)Tc, 10 cm) (CS: 72 s(-1) MBq(-1)), and the tomographic sensitivity in the heart region was in the range 647-1107 s(-1) MBq(-1) (CS: 141 s(-1) MBq(-1)). The count rate increased linearly with increasing activity up to 1.44 M s(-1). The intrinsic resolution was equal to the pixel size, 2.46 mm (CS: 3.8 mm). The average reconstructed resolution using the standard clinical filter was 12.5 mm (CS: 13.7 mm). The D-SPECT has superior sensitivity to that of a conventional system with similar spatial resolution. It also has excellent energy resolution and count rate characteristics, which should prove useful in dynamic and dual radionuclide studies.

Iterative deconvolution of simultaneous 99mTc and 201Tl projection data measured on a CdZnTe-based cardiac SPECT scanner

We present a method of correcting self-scatter and crosstalk effects in simultaneous technetium-99m/thallium-201 stress/rest myocardial perfusion (single photon emission computed tomography) SPECT scans. The method, which is in essence a hybrid between the triple energy window method and scatter modelling, is based on a model of spatial and spectral distribution of projection counts in several selected energy windows. The parameters of the model are determined from measurements of thin rod sources in air when no in-object scatter or attenuation effects are present. The model equations are solved using the iterative maximum likelihood expectation maximization algorithm in the projection space to find estimates of the primary photopeak counts of both radionuclides. The method has been developed particularly for a novel dedicated cardiac camera based on CdZnTe pixellated detectors, although it can also be adapted to a conventional scintillator camera. The method has been validated in anthropomorphic phantom experiments. Significant improvement in defect contrast has been observed with only moderate increase in image noise. The application of the method to patient data is illustrated.

Three-gamma annihilation imaging in positron emission tomography

It is argued that positron annihilation into three photons, although quite rare, could still be used as a new imaging modality of positron emission tomography. The information gained when the three decay photons are detected is significantly higher than in the case of 511 keV two-gamma annihilation. The performance of three-gamma imaging in terms of the required detector properties, spatial resolution and counting rates is discussed. A simple proof-of-principle experiment confirms the feasibility of the new imaging method.

Performance of three-photon PET imaging: Monte Carlo simulations

We have recently introduced the idea of making use of three-photon positron annihilations in positron emission tomography. In this paper, the basic characteristics of the three-gamma imaging in PET are studied by means of Monte Carlo simulations and analytical computations. Two typical configurations of human and small animal scanners are considered. Three-photon imaging requires high-energy resolution detectors. Parameters currently attainable by CdZnTe semiconductor detectors, the technology of choice for the future development of radiation imaging, are assumed. Spatial resolution is calculated as a function of detector energy resolution and size, position in the field of view, scanner size and the energies of the three-gamma annihilation photons. Possible ways to improve the spatial resolution obtained for nominal parameters, 1.5 cm and 3.2 mm FWHM for human and small animal scanners, respectively, are indicated. Counting rates of true and random three-photon events for typical human and small animal scanning configurations are assessed. A simple formula for minimum size of lesions detectable in the three-gamma based images is derived. Depending on the contrast and total number of registered counts, lesions of a few mm size for human and sub mm for small animal scanners can be detected.

Three-gamma annihilations as a new modality in PET

We argue that the positron annihilations into three photons, although quite rare, might still be used as a modality in positron emission tomography imaging. This is possible, because the amount of information gained when the three decay photons are detected is significantly larger than in the case of 511 keV two-gamma annihilation. Feasibility and performance of the new technique is assessed by numerical calculations. Examples of three-gamma images obtained in Monte Carlo simulations are presented.

Iterative deconvolution of simultaneous dual radionuclide projections for CdZnTe based cardiac SPECT

We propose a method of separating primary 99mTc and 201Tl photons in projections acquired on a SPECT camera based on CdZnTe detectors during a simultaneous dual radionuclide rest-stress myocardial perfusion scan. The method is based on a model of spectral and spatial distribution of counts in the measured projections. We use the Maximum Likelihood Expectation Maximisation (ML-EM) iterative algorithm to solve the model equations for the pure primary counts. The deconvolved primary count projections are then reconstructed using the standard OSEM algorithm. Considerable improvement of defect contrast can be observed in anthropomorphic phantom scans.