Depth of interaction detection for gamma-ray imaging

Research areas:
Authors:
Lerche, C. W.; Döring, M.; Ros, A.; Herrero, V.; Gadea, R.; Aliaga, R. J.; Colom, R.; Mateo, F.; Monzo, J. M.; Ferrando, N.; Toledo, J. F.; Martinez, J. D.; Sebastia, A.; Sanchez, F.; Benlloch, J. M.
Year:
Type of Publication:
Journal:
Volume:
Number:
Pages:
Month:
2009
Article
Instrum. Meth. Phys. Res. A
600
3
624-634
March
Keywords:
Depth of interaction detection, gamma-ray imaging, Center of gravity algorithm

Abstract:
A novel design for an inexpensive depth of interaction capable detector for γ-ray imaging has been developed. The design takes advantage of the strong correlation between the width of the scintillation light distribution in monolithic crystals and the interaction depth of γ-rays. We present in this work an inexpensive modification of the commonly used charge dividing circuits which enables the instantaneous and simultaneous computation of the second order moment of light distribution. This measure provides a good estimate for the depth of interaction and does not affect the determination of the position centroids and the energy release of γ-ray impact. The method has been tested with a detector consisting of a monolithic LSO block sized View the MathML source and a position-sensitive photomultiplier tube H8500 from Hamamatsu. The mean spatial resolution of the detector was found to be View the MathML source for the position centroids and View the MathML source for the DOI. The best spatial resolutions were observed at the center of the detector and yielded View the MathML source for the position centroids and View the MathML source for the DOI.

Online version

Analysis of time resolution in a dual head LSO+PSPMT PET system using low pass filter interpolation and digital constant fraction discriminator techniques

Research areas:
Authors:
Monzó, José M.; Lerche, Christoph W.; Martínez, Jorge D.; Esteve, Raúl; Toledo, José; Gadea, Rafael; Colom, Ricardo J.; Herrero, Vicente; Ferrando, Néstor; Aliaga, Ramón J.; Mateo, Fernando; Sánchez, Filomeno; Mora, Francisco J.; Benlloch, José M.; Sebastiá, Ángel
Year:
Type of Publication:
Journal:
Volume:
Number:
Pages:
Month:
2009
Article
Nuclear Instr and Meth in Physics A
604
1-2
347–350
June
Keywords:
Positron emission tomography, Event time detection, Digital algorithms, System simulation, Position sensitive detector

 

Abstract:
PET systems need good timeresolution to improve the true event rate, random event rejection, and pile-up rejection. In this study we propose adigital procedure for this task using alowpassfilterinterpolation plus aDigitalConstantFractionDiscriminator (DCFD). We analyzed the best way to implement this algorithm on our dualheadPETsystem and how varying the quality of the acquired signal and electronic noise analytically affects timing resolution. Our detector uses two continuous LSO crystals with a position sensitive PMT. Six signals per detector are acquired using an analog electronics front-end and these signals are processed using an in-house digital acquisition board. The test bench developed simulates the electronics and digital algorithms using Matlab®. Results show that electronic noise and other undesired effects have a significant effect on the timing resolution of the system. Interpolated DCFD gives better results than non-interpolated DCFD. In high noise environments, differences are reduced. An optimum delay selection, based on the environment noise, improves timeresolution.

Online version

High-precision position estimation in PET using artificial neural networks

Research areas:
Authors:
Mateo, F.; Aliaga, R. J.; Ferrando, N.; Martínez, J. D.; Herrero, V.; Lerche, Ch. W.; Colom, R. J.; Monzó, J. M.; Sebastiá, A.; Gadea, R.
Year:
Type of Publication:
Journal:
Volume:
Number:
Pages:
Month:
2009
Article
Nucl. Instr. and Meth. Physics A
604
1-2
366–369
June
Keywords:
Positron emission tomography, Artificialneuralnetworks, Incidence positionestimation, Anger's logic, Multi-layer perceptron

 

Abstract:
Traditionally, the most popular technique to predict the impact position of gamma photons on a PET detector has been Anger’s logic. However, it introduces non linearities that compress the light distribution, reducing the useful field of view and the spatial resolution, especially at the edges of the scintillator crystal. In this work, we make use of neural networks to address a bias-corrected position estimation from real stimulus obtained from a 2D PET system setup. The preprocessing and data acquisition were performed by separate custom boards, especially designed for this application. The results show that neural networks yield a more uniform field of view while improving the systematic error and the spatial resolution. Therefore, they stand as a better performing and readily available alternative to classic positioning methods.

Online version

Maximum likelihood positioning for gamma-ray imaging detectors with depth of interaction measurement

Research areas:
Authors:
Lerche, Ch. W.; Ros, A.; Monzó, J. M.; Aliaga, R. J.; Ferrando, N.; Martínez, J. D.; Herrero, V.; Esteve, R.; Gadea, R.; Colom, R. J.; Toledo, J.; Mateo, F.; Sebastiá, A.; Sánchez, F.; Benlloch, J. M.
Year:
Type of Publication:
Journal:
Volume:
Number:
Pages:
Month:
2009
Article
Nucl. Instr. and Meth. Physics A
604
1-2
359–362
June

Keywords:

Depth of interaction, PET, Monolithic scintillation crystal, Maximumlikelihood


 

Abstract:

The center of gravity algorithm leads to strong artifacts for gamma-ray imaging detectors that are based on monolithic scintillation crystals and position sensitive photo-detectors. This is a consequence of using the centroids as position estimates. The fact that charge division circuits can also be used to compute the standard deviation of the scintillation light distribution opens a way out of this drawback. We studied the feasibility of maximum likelihood estimation for computing the true gamma-ray photo-conversion position from the centroids and the standard deviation of the light distribution. The method was evaluated on a test detector that consists of the position sensitive photomultiplier tube H8500 and a monolithic LSO crystal (View the MathML source). Spatial resolution was measured for the centroids and the maximum likelihood estimates. The results suggest that the maximum likelihood positioning is feasible and partially removes the strong artifacts of the center of gravity algorithm.

Online version

Cellular automaton-based position sensitive detector equalization

Research areas:
Authors:
Ferrando, Néstor; Herrero, V.; Cerdà, J.; Lerche, C. W.; Colom, R. J.; Gadea, R.; Martínez, J. D.; Monzó, J. M.; Mateo, F.; Sebastià, A.; Benlloch, J. M.
Year:
Type of Publication:
Journal:
Volume:
Number:
Pages:
Month:
2009
Article
Nucl. Instr. and Meth. in Physics A
604
1-2
211–214
June
Keywords:
Cellularautomaton, Discrete dynamical systems, Photomultiplier inhomogeneities, Energy filtering

 

Abstract:
Indirect positiondetectorsbased on scintillator crystals lack of spacial uniformity in their response. This happens due to crystal inhomogeneities and gain differences among the photomultiplier anodes. In order to solve this, PESIC, an integrated front-end for multianode photomultiplier based nuclear imaging devices was created. One of its main features is the digitally programmable gain adjustment for every photomultiplier output. On another front, cellularautomata have been proved to be a useful method for dynamic system modeling. In this paper, a cellularautomaton which emulates the behavior of the scintillator crystal, the photomultiplier and the front-end is introduced. Thanks to this model, an automatic energy-based calibration of the detector can be done by configuring the cellularautomaton with experimental data and making it evolve up to an stable state. This can be useful as a precalibration method of the detector.

Online version