A comparative study on PET and SPECT image formation systems for a proper scanner choice in a considered PET center

In the last twenty years, the developed technology is being applied, making available better diagnoses and therapy to a variety of diseases. Since then the short-lived radionuclides were available only in the large physics research centers. The increasing clinical applications of radiopharmaceuticals have led to the rapid rise in the number of compact cyclotrons throughout the world. All medical cyclotrons currently available are suitable for sustaining programs for PET research and clinical application. To date, up to 122 medical cyclotrons have been established worldwide, and Brazil is about to install a new dedicated cyclotron (RDS111 from CTI), to its first PET Center, in Rio de Janeiro. Also the number of scanners in use in the world has increased, mainly those based on the positrons emission and annihilation. The better result gotten in the final contrast of the object imposes necessarily a comparative study and analysis of the image formation process, either in a system based on a Single Photon Emission Computerized Tomography (SPECT), as well as on Positron Emission Tomography (PET.) This comparative study should at least follow same increasing rates of the new devices with technological advances. That kind of study can be helpful on the decision of what type of scan should be the proper one, to a PET Center, on a specific region. Obviously, many other parameters are involved in that decision, and this discussion and analyses are the main subject of the present work. The objective is to make available a realistic comparative scenario, considering as many as possible the parameters involving. Many of the new devices have been introduced making great progresses. As an example, in the new PET scanners, the reduction of examination time, and the remarkable improvement on the diagnoses based on images. As a consequence, we have a broadening on the field of application, better performance, and making possible the precocious discovery of males. Presently multi-ring commercial PET scanners can operate in either two or three-dimensional acquisition modes. Some special features like the lead septa positioned between the rings of detectors are retractable allowing 3-D acquisition. In this mode the overall scanner sensitivity has a remarkable increasing compared with earlier scanners, in spite of an increase in both the scatter and random rate. Considering that all emission and transmission data are fed into the computers, and the coincidence events are stored as sinograms, it is also necessary to keep up with computational area. Just to give an idea on the complexity level, the software should be able to provide a full 2- D or 3-D reconstruction algorithm, based on filtered back projection, incorporating an attenuation correction procedure. This is necessary to characterize sinograms, which correspond to sets of two-dimensional projections of the tracer distribution. Software tools should also have the capability for image manipulation and ultimately using various bio-mathematical models. This way, the PET data could be transformed into information with physiological, pathological significance. In addition, a full determination of the quantitative information requires a kinetic model of the transport mechanism and of the physiological and biochemical processes in which each radiopharmaceutical participates. In a self-sustained project, like the PET Center project in Rio de Janeiro intend to be, the most important parameters to be considered in the equipment choice are the per capita income and acquisition and maintenance costs. However, these factors by itself cannot predict which the best equipment should be acquired and some inherent characteristic of the product as resolution, sensitivity, time of resolution, time of scan and others capabilities should be considered. Out of the comparative scenario regarding the relation cost-benefit, there are also some legal complies. Specifically connected to project of PET Center in Brazil, is the fact that the production of radioactive substances are monopoly of the federal government. As a consequence, and also considering that most PET radioisotopes are short-lived, the availability is restricted to this Southeastern region of Brazil. This region possesses technology to produce a large variety of radioisotopes/radiopharmaceuticals. That restriction also imposes another parameter related with regional disease that could be diagnosed by PET SPECT. Beyond the previous facts, the proper dealing with scanners requires many other capabilities. For instance, it is indispensable to understand all the internal equipment details, knowing the process of image formation and analyses in PET/SPECT. This knowledge should cover the radioactive source preparation, the bombarding in a cyclotron, and the distribution and injection of the radiopharmaceuticals. Also in this knowledge is included the positron emission and annihilation, the types of radiopharmaceutical syntheses, the types of crystals, the influence of the collimators in the final image, the identification of the interaction point, the formation principle of the plans and colors, the ways to introduce corrections, and to keep up with the new developments on the market. As mentioned before, this is part of PET Center project in Rio de Janeiro, and this study is still being carried out, and the objective here is to present the current status of the study. This way, it will be presented next just a specific part related to the PET and SPECT scanners and associated equipment. Once finished, we intend that being presented to this work, the technologist must be able to evaluate and define a proper scanner, by established criteria. Following should also be able to make the choice and develop a protocol for its use. As a result of the proposed procedures, is expected a positive impact on the reduction of general costs and better quality of life reflected by a better diagnosis e a proper therapy