- Email: [email protected]
Workshop summary
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 509 (2003) 355–360
Workshop summary M. Caria* Laboratoire de Biophysique M!edicale, Facult!e de M!edicine B.P. 38 28 Place Henry Dunant, 63001 Clermont Ferrand, France
Abstract This paper is my personal recollection of the IWORID2002 workshop. The aim is to provide an overview of the current state of the art in the field of imaging detectors, illustrated by examples from the Workshop materials. The current evolution in this field shows a clear tightening of the relationship between the various technological disciplines needed to conceive, design and produce imaging detectors. Indications are given that this trend towards stronger interdisciplinary connection will strengthen further in the future. r 2003 Elsevier B.V. All rights reserved. Keywords: Imaging; Medical imaging; Pixel detectors
1. Introduction The series of IWORID workshops is motivated by the need for well-balanced interaction between applied research in academics and industry. Its mission can be summarised as educational, i.e. promoting advances on material growth and characterisation of imaging detectors, their manufacturing, assembly, read-out hardware and software. The goal is to improve the vision and the coordination between research centres and universities, across disciplines, towards industry and end-users. In previous workshops, contributions in the fields of engineering, end-user needs, markets and funding agencies, overall technological vision and historical references, were a tiny minority or even fully absent. Considerable effort has been made to improve this situation for IWORID2002. It is
*Tel.: +33-0-47-3644-3991; fax: +33-0-47-333-9452. E-mail address: [email protected] (M. Caria).
recommended to continue and promote this effort in the future. After a general introduction, the paper will summarise some of the most challenging detector systems currently being developed. Separate sessions are dedicated to detector materials and engineering for final applications.
2. The attendance The attendance of our workshop has remarkably increased in the last years, as well as the number of contributed papers. The composition of the audience is also broadening. We have reached a balance with approximately equal numbers of participants with a physics or a technology background, with remarkable participation from the industry. The attendance of Eastern European Countries has also improved. Participation from the US, as well as from the Far East is still low, indicating
0168-9002/03/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-9002(03)01649-8
ARTICLE IN PRESS 356
M. Caria / Nuclear Instruments and Methods in Physics Research A 509 (2003) 355–360
Fig. 2. Universal curve representing fluctuation over time of Enthusiasm or Resources for a new technological development, as postulated by our honorary speaker Prof. Glenn Knoll of the University of Michigan.
Fig. 1. Attendance by country (a) and attendance by affiliation (b).
that worldwide communication about the IWORID workshop could still be improved. Fig. 1, by Arjen van Rijn, shows the attendance by country (left) and by affiliation (right).
An indication on how technological research develops, was nicely recorded by Prof. Glenn Knoll (the ‘‘Glenn Knoll Curve’’, Fig. 2): enthusiasm and resources for a new development will inflate or deflate in time, before they will finally reach a stable level adequate for success. Many labs in the world devote great resources to a new idea at first, but some time later enthusiasm for the idea rapidly decreases. The idea is taken up again at medium term by a less numerous, maybe more stubborn, community. Before development in a field can be considered established, the research effort and the resources dedicated, may undergo several such cycles of oscillating behaviour. Such a process may take more than 10 years before damping.
3. Detectors for radiation imaging: general trends Progress on detectors for radiation imaging requires adequate interactions between the following areas of activity: * * *
* *
Detector materials and related material science. Detector geometry and electrical solutions. Integrated front-end electronics and downstream electronic readout. Complete systems for final applications. Implementation and development of end-user needs.
The applications considered here, are (nonexhaustive list): Medical Imaging, Structural Biology, Space Applications, Charged Particle Detection, and Dosimetry.
4. CCDs, CMOS monolithic, and sandwich detectors Many attractive detector concepts for radiation imaging have been discussed during the workshop, and are listed here. A star indicates the degree of confidence (on an arbitrary scale) in the advancement in the field to accomplish adequate imaging detectors for end-users, i.e. the relevance of the technological questions to be answered: *
*
Charge Coupled Device (CCD) based detector systems. CMOS-based detectors that can be subdivided into:
ARTICLE IN PRESS M. Caria / Nuclear Instruments and Methods in Physics Research A 509 (2003) 355–360 *
*
*
Hybrid detectors, for which fast signal-processing (***), integrating electronics (**) and sensor materials (**) need intensive development, but for which the packaging (***) solutions are the most challenging. Monolithic detectors, for which integrated electronics (*) and materials (*) need further development, and for which the packaging solutions are less demanding. Systems of sandwiched passive and active detector components. For these, most of the development is done on the passive materials (***), with minor efforts in electronics (*) and engineering (*).
In what follows, we recall some of the most representative examples that are contributing to current progress. Considerations are made on the basis of technological status and availability to the end user. Detectors that are already implemented or are relatively close to their final system applications are: CCDs and CMOS monolithic systems. Sandwich detection systems can also be considered as mature and currently under use in final applications. 4.1. CCDs CCDs do not particularly suffer from engineering problems, their technology can be considered mature. Nor are they difficult to integrate in final systems. There exist numerous examples of daily use of this technology. An example of advances in CCD technology is the pn CCD detector.
357
by the availability of foundry design libraries and fabrication equipment. No conceptual limitations are present. Small area applications like the monitoring of particle beams are already in place. The main advantage is the large area application at a relatively low cost. The example of Active Pixel Sensors (APS), with their embedded preamplification step for each pixel, is the first step towards full integration of more complex functions integrated into the device. And, it opens the road to more complex applications like Medical Imaging. This application is, however, very demanding in terms of electronics functionality; there is still a long road. 4.3. Sandwich detector systems Rather than addressing full monolithic integration, there are successful projects with imaging devices made out of a sandwich of detectors like CCDs and scintillators. In this case the research is mainly focussed on properties of the scintillating material, like efficiency and response speed. Clinical and industrial devices are already equipped with such systems, for specific applications. The research focuses therefore on the performance required for specific applications rather than on the detector, the engineering or the electronics. Nearly 20 years were necessary to develop CT scanning with CCD and scintillators with superior contrast. The progress in CCDs coupled to scintillators for dental imaging applications, is also very promising. Gadolinium or BGO-based detectors are close to meeting their expectations.
4.2. Monolithic CMOS
5. CMOS hybrid detectors
Monolithic CMOS sensors seem to follow the same fruitful road. In certain areas they are still far from the end user and large scale industrialisation. The technique is challenging in terms of the electronic design although there are numerous examples of successful projects. It does not show particular material or engineering problems. The development of large-area devices (tens of square centimetres or more) still needs several more years. Currently, the limitations seem to be constituted
The situation is quite different in the case of CMOS hybrid detector systems. They can be subdivided into micro-strips and pixel detectors. The following holds for the different areas: 5.1. Micro-strip detectors Electronics (*) and sensor materials (*) do not constitute a relevant problem for these detector systems, while their engineering (***) is still
ARTICLE IN PRESS 358
M. Caria / Nuclear Instruments and Methods in Physics Research A 509 (2003) 355–360
challenging. In the case of micro-strips, the situation in terms of read-out integrated electronics is at a relatively mature stage for several applications. The geometry allows a relatively comfortable space to allocate for all the needed functions without being constrained by heat production. The sensor material still needs additional developments, especially where exotic alloys (e.g. GaAs) are used. Engineering the devices is still complex, given the high density and the tiny scale, in terms of overall design and assembling. 5.2. Pixel detectors For CMOS hybrid pixel detectors, electronics (**) and sensor material (**) constitute a relevant area of development, and engineering (***) is most challenging [1]. Among all systems described above, CMOS Pixel hybrid detectors still require the most development. Progress in electronics has been huge over the last five years, but there is still some way to go before reaching final applications. Constraints in terms of costs, functions, power consumption, and geometry, indicate that a few more years are needed. Related to that is also the choice of material. The low signal-to-noise ratio of the sensor material further constrains the design. Worst of all is the engineering problem. Flipchip bump bonding is the commonly used technique. Very few vendors have optimised this process for 200 mm wafers, and they have not yet reached large scale industrial processing. The versatility offered by developments in micro-electronic functionality and in the sensor material and geometry, make the CMOS hybrid very attractive, especially to boost new exciting developments. An example is constituted by threedimensional pixel implants. Characteristic of the choice of materials for the sensor wafer and the implants, as well as the manufacturing of the holes, the filling and the bonding are the many open questions that will only get a definite answer in two to four years from now. Another interesting geometry is the semiconductor drift chamber of the multi-anode type for which requirements in terms of material homogeneity are exceedingly high.
6. Detector materials Detector materials are an important component of the technological challenge discussed above. So many materials are possible that they deserve a brief dedicated session to illustrate the relevance of material optimisation research, before tackling the resolution of engineering problems related to the manufacturing of detectors from said materials. The first studies on germanium date back 30 years or more, and this material is still excellent for spectroscopic applications. Much development has been done by the company EG&G. Only recently do they feel comfortable with their high purity material and with the size of the crystals that can be fabricated. Pixel devices are being made now but of course they still need cooling to cryogenic temperatures. As stated above, sandwich detectors put emphasis on the development of new or better performing materials to satisfy application requirements. In the case of neutron detectors, no particular effort is made on the electronics, nor is it necessary for the engineering, but it is essential to have the highest possible efficiency on the neutron capture and conversion. For instance, LiBaF3 represents a promising material for development of storage imaging plates for imaging of slow neutrons. Special words must be reserved for two compound materials raising much expectation in the community: cadmium telluride and gallium-based compounds. CdTe and CdZnTe alloys are now made in series production, although only a few vendors are on the market. The results are encouraging, and for some applications, such as astrophysics and certain medical or material applications, the material is already mature enough. The relatively high cost remains an issue for several applications. Large monocrystalline ingots appear to be of adequate quality. Gallium and gallium arsenide type compounds are also attractive. The progress in this field has, however, slowed down remarkably in the last two years. This is a clear indicator of the difficult technological processing that is required to produce detector-grade material, which may be
ARTICLE IN PRESS M. Caria / Nuclear Instruments and Methods in Physics Research A 509 (2003) 355–360
performed only by very competent groups. It is remarkable that 3 in. epitaxial wafers can now be fabricated with large thickness. The manufacture of detectors from this material and the extension to a still larger area (4 in.) are the most eagerly awaited developments in this field. Looking at the historical perspective, and realising that developments on GaAs have been going on now for over 10 years, we can comfortably state that in the near future we will see a detector suitable for applications, in particular for medical imaging. The epitaxial GaAs material is more attractive and more elegant and seems to constrain the detector engineering less than the other intentionally (i.e. Cr-) doped Semi Insulating compounds. For those, cooling seems to be mandatory. Other exotic materials, like TlBr, are already studied for astrophysical applications, but are still at the start of their development cycle and we do not expect that their development time will be much shorter.
7. Engineering final detection systems A few considerations are due to the case of engineering. It is clear that looking back on the history of imaging detectors, a lesson has been learned that innovation on detectors must be coupled with an adequate engineering effort. Imaging detector developments that do not include an integrated effort to arrive at a commercially viable application are destined to remain little more than a conceptual design, reaching at best a proof of principle stage. In order to truly satisfy end-user applications, the community should mobilise all actors, considering detector engineering at the same level as micro-electronics, and the physics of detector materials and sensors. As there cannot be engineering without defining specifications, this approach shows that the interaction with the end user is essential and only an integrated strategy will pay over the long term. We have seen cases for which the interaction with industry has been not only an essential tool, but is mutually profitable.
359
The above statement gets even stronger supported by the clear gap between the density that can be reached by the integrated electronics functions and the density obtained by current interconnect technologies. This consideration should slow down the run to higher integration and smaller pixel sizes and bring more attention to the detector engineering and to yield problems.
8. The end user The end-user community has been represented in the series of workshops mostly in the fields of Medical Imaging, Industrial Analysis and Particles Imaging. It appears clearly that any given application has its specific needs. The requirements can be very different when, for example, going from PET scanning to Luggage Inspection. Where in medical applications it is essential to reduce the dose, in industry it may be much more relevant to reduce the costs. It is important to stress again the lesson we have learned, namely that end-users must interact closely with the engineering and the detector community. We have also learned that even if we limit ourselves to Medical Imaging, there is no universal detector system, leaving room for exciting research and developments ahead.
9. Conclusions Imaging detectors are a key to success in many scientific and industrial applications. Progress in this field will be boosted by this workshop, and without any doubt, at IWORID2002 dramatic progress has been demonstrated. A personal recollection cannot end without a personal contribution. I am pleased that IWORID2002 also gave me the opportunity to attain deeper knowledge of the Van Gogh affair. I now support the statement, based on solid scientific grounds, that Intermittent Porphyria disease, rather than Absinthe consumption, can be ascribed as responsible for his illness. Although Absinthe is no longer easy available and anyway not my favourite, I am pleased to have been cultivating with the other members of the
ARTICLE IN PRESS 360
M. Caria / Nuclear Instruments and Methods in Physics Research A 509 (2003) 355–360
International Advisory Committee our common culture for beverages containing a small volume fraction of ethanol.
and the entire Local Organizing Committee for their kind readiness, smiling efficiency and competence. Finally, I thank the Amsterdam canals for the inspiration they give when biking alone at night.
Acknowledgements I am indebted to David San Segundo Bello for providing me with the material to make this paper possible. I warmly thank Jan Visschers
References [1] M. Caria, Nucl. Instr. and Meth. A 447 (2000) 167.
Nuclear Instruments and Methods in Physics Research A 509 (2003) 355–360
Workshop summary M. Caria* Laboratoire de Biophysique M!edicale, Facult!e de M!edicine B.P. 38 28 Place Henry Dunant, 63001 Clermont Ferrand, France
Abstract This paper is my personal recollection of the IWORID2002 workshop. The aim is to provide an overview of the current state of the art in the field of imaging detectors, illustrated by examples from the Workshop materials. The current evolution in this field shows a clear tightening of the relationship between the various technological disciplines needed to conceive, design and produce imaging detectors. Indications are given that this trend towards stronger interdisciplinary connection will strengthen further in the future. r 2003 Elsevier B.V. All rights reserved. Keywords: Imaging; Medical imaging; Pixel detectors
1. Introduction The series of IWORID workshops is motivated by the need for well-balanced interaction between applied research in academics and industry. Its mission can be summarised as educational, i.e. promoting advances on material growth and characterisation of imaging detectors, their manufacturing, assembly, read-out hardware and software. The goal is to improve the vision and the coordination between research centres and universities, across disciplines, towards industry and end-users. In previous workshops, contributions in the fields of engineering, end-user needs, markets and funding agencies, overall technological vision and historical references, were a tiny minority or even fully absent. Considerable effort has been made to improve this situation for IWORID2002. It is
*Tel.: +33-0-47-3644-3991; fax: +33-0-47-333-9452. E-mail address: [email protected] (M. Caria).
recommended to continue and promote this effort in the future. After a general introduction, the paper will summarise some of the most challenging detector systems currently being developed. Separate sessions are dedicated to detector materials and engineering for final applications.
2. The attendance The attendance of our workshop has remarkably increased in the last years, as well as the number of contributed papers. The composition of the audience is also broadening. We have reached a balance with approximately equal numbers of participants with a physics or a technology background, with remarkable participation from the industry. The attendance of Eastern European Countries has also improved. Participation from the US, as well as from the Far East is still low, indicating
0168-9002/03/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-9002(03)01649-8
ARTICLE IN PRESS 356
M. Caria / Nuclear Instruments and Methods in Physics Research A 509 (2003) 355–360
Fig. 2. Universal curve representing fluctuation over time of Enthusiasm or Resources for a new technological development, as postulated by our honorary speaker Prof. Glenn Knoll of the University of Michigan.
Fig. 1. Attendance by country (a) and attendance by affiliation (b).
that worldwide communication about the IWORID workshop could still be improved. Fig. 1, by Arjen van Rijn, shows the attendance by country (left) and by affiliation (right).
An indication on how technological research develops, was nicely recorded by Prof. Glenn Knoll (the ‘‘Glenn Knoll Curve’’, Fig. 2): enthusiasm and resources for a new development will inflate or deflate in time, before they will finally reach a stable level adequate for success. Many labs in the world devote great resources to a new idea at first, but some time later enthusiasm for the idea rapidly decreases. The idea is taken up again at medium term by a less numerous, maybe more stubborn, community. Before development in a field can be considered established, the research effort and the resources dedicated, may undergo several such cycles of oscillating behaviour. Such a process may take more than 10 years before damping.
3. Detectors for radiation imaging: general trends Progress on detectors for radiation imaging requires adequate interactions between the following areas of activity: * * *
* *
Detector materials and related material science. Detector geometry and electrical solutions. Integrated front-end electronics and downstream electronic readout. Complete systems for final applications. Implementation and development of end-user needs.
The applications considered here, are (nonexhaustive list): Medical Imaging, Structural Biology, Space Applications, Charged Particle Detection, and Dosimetry.
4. CCDs, CMOS monolithic, and sandwich detectors Many attractive detector concepts for radiation imaging have been discussed during the workshop, and are listed here. A star indicates the degree of confidence (on an arbitrary scale) in the advancement in the field to accomplish adequate imaging detectors for end-users, i.e. the relevance of the technological questions to be answered: *
*
Charge Coupled Device (CCD) based detector systems. CMOS-based detectors that can be subdivided into:
ARTICLE IN PRESS M. Caria / Nuclear Instruments and Methods in Physics Research A 509 (2003) 355–360 *
*
*
Hybrid detectors, for which fast signal-processing (***), integrating electronics (**) and sensor materials (**) need intensive development, but for which the packaging (***) solutions are the most challenging. Monolithic detectors, for which integrated electronics (*) and materials (*) need further development, and for which the packaging solutions are less demanding. Systems of sandwiched passive and active detector components. For these, most of the development is done on the passive materials (***), with minor efforts in electronics (*) and engineering (*).
In what follows, we recall some of the most representative examples that are contributing to current progress. Considerations are made on the basis of technological status and availability to the end user. Detectors that are already implemented or are relatively close to their final system applications are: CCDs and CMOS monolithic systems. Sandwich detection systems can also be considered as mature and currently under use in final applications. 4.1. CCDs CCDs do not particularly suffer from engineering problems, their technology can be considered mature. Nor are they difficult to integrate in final systems. There exist numerous examples of daily use of this technology. An example of advances in CCD technology is the pn CCD detector.
357
by the availability of foundry design libraries and fabrication equipment. No conceptual limitations are present. Small area applications like the monitoring of particle beams are already in place. The main advantage is the large area application at a relatively low cost. The example of Active Pixel Sensors (APS), with their embedded preamplification step for each pixel, is the first step towards full integration of more complex functions integrated into the device. And, it opens the road to more complex applications like Medical Imaging. This application is, however, very demanding in terms of electronics functionality; there is still a long road. 4.3. Sandwich detector systems Rather than addressing full monolithic integration, there are successful projects with imaging devices made out of a sandwich of detectors like CCDs and scintillators. In this case the research is mainly focussed on properties of the scintillating material, like efficiency and response speed. Clinical and industrial devices are already equipped with such systems, for specific applications. The research focuses therefore on the performance required for specific applications rather than on the detector, the engineering or the electronics. Nearly 20 years were necessary to develop CT scanning with CCD and scintillators with superior contrast. The progress in CCDs coupled to scintillators for dental imaging applications, is also very promising. Gadolinium or BGO-based detectors are close to meeting their expectations.
4.2. Monolithic CMOS
5. CMOS hybrid detectors
Monolithic CMOS sensors seem to follow the same fruitful road. In certain areas they are still far from the end user and large scale industrialisation. The technique is challenging in terms of the electronic design although there are numerous examples of successful projects. It does not show particular material or engineering problems. The development of large-area devices (tens of square centimetres or more) still needs several more years. Currently, the limitations seem to be constituted
The situation is quite different in the case of CMOS hybrid detector systems. They can be subdivided into micro-strips and pixel detectors. The following holds for the different areas: 5.1. Micro-strip detectors Electronics (*) and sensor materials (*) do not constitute a relevant problem for these detector systems, while their engineering (***) is still
ARTICLE IN PRESS 358
M. Caria / Nuclear Instruments and Methods in Physics Research A 509 (2003) 355–360
challenging. In the case of micro-strips, the situation in terms of read-out integrated electronics is at a relatively mature stage for several applications. The geometry allows a relatively comfortable space to allocate for all the needed functions without being constrained by heat production. The sensor material still needs additional developments, especially where exotic alloys (e.g. GaAs) are used. Engineering the devices is still complex, given the high density and the tiny scale, in terms of overall design and assembling. 5.2. Pixel detectors For CMOS hybrid pixel detectors, electronics (**) and sensor material (**) constitute a relevant area of development, and engineering (***) is most challenging [1]. Among all systems described above, CMOS Pixel hybrid detectors still require the most development. Progress in electronics has been huge over the last five years, but there is still some way to go before reaching final applications. Constraints in terms of costs, functions, power consumption, and geometry, indicate that a few more years are needed. Related to that is also the choice of material. The low signal-to-noise ratio of the sensor material further constrains the design. Worst of all is the engineering problem. Flipchip bump bonding is the commonly used technique. Very few vendors have optimised this process for 200 mm wafers, and they have not yet reached large scale industrial processing. The versatility offered by developments in micro-electronic functionality and in the sensor material and geometry, make the CMOS hybrid very attractive, especially to boost new exciting developments. An example is constituted by threedimensional pixel implants. Characteristic of the choice of materials for the sensor wafer and the implants, as well as the manufacturing of the holes, the filling and the bonding are the many open questions that will only get a definite answer in two to four years from now. Another interesting geometry is the semiconductor drift chamber of the multi-anode type for which requirements in terms of material homogeneity are exceedingly high.
6. Detector materials Detector materials are an important component of the technological challenge discussed above. So many materials are possible that they deserve a brief dedicated session to illustrate the relevance of material optimisation research, before tackling the resolution of engineering problems related to the manufacturing of detectors from said materials. The first studies on germanium date back 30 years or more, and this material is still excellent for spectroscopic applications. Much development has been done by the company EG&G. Only recently do they feel comfortable with their high purity material and with the size of the crystals that can be fabricated. Pixel devices are being made now but of course they still need cooling to cryogenic temperatures. As stated above, sandwich detectors put emphasis on the development of new or better performing materials to satisfy application requirements. In the case of neutron detectors, no particular effort is made on the electronics, nor is it necessary for the engineering, but it is essential to have the highest possible efficiency on the neutron capture and conversion. For instance, LiBaF3 represents a promising material for development of storage imaging plates for imaging of slow neutrons. Special words must be reserved for two compound materials raising much expectation in the community: cadmium telluride and gallium-based compounds. CdTe and CdZnTe alloys are now made in series production, although only a few vendors are on the market. The results are encouraging, and for some applications, such as astrophysics and certain medical or material applications, the material is already mature enough. The relatively high cost remains an issue for several applications. Large monocrystalline ingots appear to be of adequate quality. Gallium and gallium arsenide type compounds are also attractive. The progress in this field has, however, slowed down remarkably in the last two years. This is a clear indicator of the difficult technological processing that is required to produce detector-grade material, which may be
ARTICLE IN PRESS M. Caria / Nuclear Instruments and Methods in Physics Research A 509 (2003) 355–360
performed only by very competent groups. It is remarkable that 3 in. epitaxial wafers can now be fabricated with large thickness. The manufacture of detectors from this material and the extension to a still larger area (4 in.) are the most eagerly awaited developments in this field. Looking at the historical perspective, and realising that developments on GaAs have been going on now for over 10 years, we can comfortably state that in the near future we will see a detector suitable for applications, in particular for medical imaging. The epitaxial GaAs material is more attractive and more elegant and seems to constrain the detector engineering less than the other intentionally (i.e. Cr-) doped Semi Insulating compounds. For those, cooling seems to be mandatory. Other exotic materials, like TlBr, are already studied for astrophysical applications, but are still at the start of their development cycle and we do not expect that their development time will be much shorter.
7. Engineering final detection systems A few considerations are due to the case of engineering. It is clear that looking back on the history of imaging detectors, a lesson has been learned that innovation on detectors must be coupled with an adequate engineering effort. Imaging detector developments that do not include an integrated effort to arrive at a commercially viable application are destined to remain little more than a conceptual design, reaching at best a proof of principle stage. In order to truly satisfy end-user applications, the community should mobilise all actors, considering detector engineering at the same level as micro-electronics, and the physics of detector materials and sensors. As there cannot be engineering without defining specifications, this approach shows that the interaction with the end user is essential and only an integrated strategy will pay over the long term. We have seen cases for which the interaction with industry has been not only an essential tool, but is mutually profitable.
359
The above statement gets even stronger supported by the clear gap between the density that can be reached by the integrated electronics functions and the density obtained by current interconnect technologies. This consideration should slow down the run to higher integration and smaller pixel sizes and bring more attention to the detector engineering and to yield problems.
8. The end user The end-user community has been represented in the series of workshops mostly in the fields of Medical Imaging, Industrial Analysis and Particles Imaging. It appears clearly that any given application has its specific needs. The requirements can be very different when, for example, going from PET scanning to Luggage Inspection. Where in medical applications it is essential to reduce the dose, in industry it may be much more relevant to reduce the costs. It is important to stress again the lesson we have learned, namely that end-users must interact closely with the engineering and the detector community. We have also learned that even if we limit ourselves to Medical Imaging, there is no universal detector system, leaving room for exciting research and developments ahead.
9. Conclusions Imaging detectors are a key to success in many scientific and industrial applications. Progress in this field will be boosted by this workshop, and without any doubt, at IWORID2002 dramatic progress has been demonstrated. A personal recollection cannot end without a personal contribution. I am pleased that IWORID2002 also gave me the opportunity to attain deeper knowledge of the Van Gogh affair. I now support the statement, based on solid scientific grounds, that Intermittent Porphyria disease, rather than Absinthe consumption, can be ascribed as responsible for his illness. Although Absinthe is no longer easy available and anyway not my favourite, I am pleased to have been cultivating with the other members of the
ARTICLE IN PRESS 360
M. Caria / Nuclear Instruments and Methods in Physics Research A 509 (2003) 355–360
International Advisory Committee our common culture for beverages containing a small volume fraction of ethanol.
and the entire Local Organizing Committee for their kind readiness, smiling efficiency and competence. Finally, I thank the Amsterdam canals for the inspiration they give when biking alone at night.
Acknowledgements I am indebted to David San Segundo Bello for providing me with the material to make this paper possible. I warmly thank Jan Visschers
References [1] M. Caria, Nucl. Instr. and Meth. A 447 (2000) 167.