Dedicated Positron Emission Tomography Systems Research Articles

Development and Characterization of Modular Readout Design for Two-Panel Head-and-Neck Dedicated PET System Based on CZT Detectors.

Cadmium zinc telluride (CZT) detectors are suitable for various applications due to the good energy resolution and the simple pixilation to achieve high spatial resolution. Our group is developing a two-panel head and neck dedicated positron emission tomography system based on CZT detectors. Each panel will consist of 150 CZT crystals (4×4×0.5 cm3) covering an area of 20×15 cm2 in an edge-on configuration to achieve high detector efficiency at 511 keV. In this work, we present the design and development of a full data acquisition chain that enables a low noise and compact readout for each panel. The initial results of the readout circuit were quantified using a 1 kHz square wave test pulse. The pulse amplitude was chosen to generate approximately the same amount of charges as a 511 keV photon would provide in CZT. The best-case FWHM electronic noise at 511 keV was measured to be 0.69% ± 0.16% (3.52 ± 0.81 in keV units after conversion). The FWHM electronic noise at 511 keV for a complete DAQ chain was 4.33% ± 0.30% (22.13 ± 1.53 in keV units).

Positron Emission Tomography: alive and kicking after more than 65 years on stage

Positron emission tomography (PET) is the most diffuse method to image molecular processes within the human body. This paper is meant as a brief overview of the physics related to its imaging modality and of its numerous applications. Several references are provided where more details on the topic can be found. The first section describes the working principle of PET, the type of detectors used in a PET scanner, and the most important figures of merit to determine its performance, namely sensitivity, spatial resolution and time resolution, the latter revelant in particular for the so-called time-of-flight PET. The second section summarizes the evolution and trends for PET in clinical applications, focusing on hadrontherapy monitoring, total-body scanners, multimodal and dedicated PET systems, high spatial and temporal resolution detectors, and innovative PET radiopharmaceuticals.

Monitoring Proton Therapy Through in-Beam PET: An Experimental Phantom Study

In this paper, we investigate the use of a positron emission tomography (PET) system to monitor the proton therapy. The monitoring procedure is based on the comparison between the ${ \beta }+$ activity generated in the irradiated volume during the treatment, with the ${ \beta }+$ activity distribution obtained with Monte Carlo (MC) simulation. The dedicated PET system is a dual head detection system; each head is composed of nine scintillating LYSO crystal matrices read out independently with a custom modularized acquisition system. Our experimental data were acquired at the Cyclotron Centre Bronowice, Institute Nuclear Physics in Krakow, Poland, and were simulated with the FLUKA MC code. Homogeneous and heterogeneous plastic phantoms were irradiated with monoenergetic 130 MeV protons. The capabilities of our PET system to distinguish different irradiated materials were investigated, and the proton pencil-beams were used as probes. Our focus was to analyze the activity width and the total activity event number in several cases. Irradiations were performed using either single pencil-beams one at a time, or two pencil-beams during the same data taking. The comparison of 1-D activity profile for experimental data and MC simulation were always in good agreement showing that, the treatment quality assessment in proton therapy can be based on ${ \beta }+$ activity measurements.

First prototyping of a dedicated PET system with the hemisphere detector arrangement

A strong demand is expected for high-sensitivity, high-resolution and low-cost brain positron emission tomography (PET) imaging for early diagnosis of dementia, as well as for general neuroscience studies. Therefore, we have proposed novel geometries of a hemisphere detector arrangement for high-sensitivity brain imaging, in which an add-on detector at the chin position or neck position helps in sensitivity uniformity improvement. In this study, we developed the first prototype system for proof-of-concept using four-layer depth-of-interaction detectors, each of which consisted of 16 × 16 × 4 Zr-doped GSO crystals with dimensions of 2.8 × 2.8 × 7.5 mm3 and a high-sensitivity 64-channel flat-panel photomultiplier tube. We used 47 detectors to form a hemisphere detector with a hemisphere shape of 25 cm inner diameter and 50 cm outer diameter, and we used seven detectors for each of the add-on detectors. The total detector number of 54 was about one-fourth that of a typical whole-body PET scanner. The hemisphere detector for the prototype system was realized by multiple rings having different numbers of detectors and a cross-shaped top detector unit covering the top. Performance evaluation showed uniform spatial resolutions of 3–4 mm by the filtered back-projection method. Imaging tests of a hot-rod phantom done with an iterative method were able to resolve 2.2 mm rods. Peak sensitivity was measured as more than 10% at a region near the top of the head, which was achieved with the help of the top detector unit. In addition, using the prototype system, we performed the first FDG clinical test with a healthy volunteer. The results showed that the proposed geometries had high potential for realizing high-sensitivity, high-resolution, and low-cost brain PET imaging. As for the add-on detector position, it was shown that the neck position resulted in higher sensitivity and wider field of view (FOV) than the chin position because the add-on detector at the neck position can be placed continuously to the hemisphere detector and close to the FOV.

Current Status of Dedicated Breast PET Imaging

Positron emission tomography (PET) is a useful technique to visualize biologic processes within body. Techniques of PET imaging for breast cancer continue to evolve and have been improving the limitation of the spatial resolution of conventional whole body PET scanners. Currently, several types of dedicated breast PET system, including positron emission mammography and fully tomographic dedicated PET systems, have been developed. In this article, we review types and features of developed scanners, the results of clinical studies, and the potential future deployment of dedicated breast PET imaging. We also briefly review PET tracers that could be potential candidates for use in dedicated breast PET imaging.

First full-beam PET acquisitions in proton therapy with a modular dual-head dedicated system

During particle therapy irradiation, positron emitters with half-lives ranging from 2 to 20 min are generated from nuclear processes. The half-lives are such that it is possible either to detect the positron signal in the treatment room using an in-beam positron emission tomography (PET) system, right after the irradiation, or to quickly transfer the patient to a close PET/CT scanner. Since the activity distribution is spatially correlated with the dose, it is possible to use PET imaging as an indirect method to assure the quality of the dose delivery. In this work, we present a new dedicated PET system able to operate in-beam. The PET apparatus consists in two 10 cm × 10 cm detector heads. Each detector is composed of four scintillating matrices of 23 × 23 LYSO crystals. The crystal size is 1.9 mm × 1.9 mm × 16 mm. Each scintillation matrix is read out independently with a modularized acquisition system. The distance between the two opposing detector heads was set to 20 cm. The system has very low dead time per detector area and a 3 ns coincidence window, which is capable to sustain high single count rates and to keep the random counts relatively low. This allows a new full-beam monitoring modality that includes data acquisition also while the beam is on. The PET system was tested during the irradiation at the CATANA (INFN, Catania, Italy) cyclotron-based proton therapy facility. Four acquisitions with different doses and dose rates were analysed. In all cases the random to total coincidences ratio was equal or less than 25%. For each measurement we estimated the accuracy and precision of the activity range on a set of voxel lines within an irradiated PMMA phantom. Results show that the inclusion of data acquired during the irradiation, referred to as beam-on data, improves both the precision and accuracy of the range measurement with respect to data acquired only after irradiation. Beam-on data alone are enough to give precisions better than 1 mm when at least 5 Gy are delivered.

A Review on Recent Developments in Positron Emission Tomography Technology

Recent years have witnessed an increased use of in vivo imaging techniques in both medicine and biomedical research. Positron Emission Tomography (PET) is a functional in vivo imaging technique relying on the metabolism of molecules which are injected into the blood stream and have a high chemical affinity to a specific biological substrate. These substances are labelled with positron emitters resulting in gamma rays which can be recorded outside the body using coincidence detection. Radiation can be detected using a variety of solutions, in terms of transducers and system geometries, and combined to produce images using suitable image reconstruction algorithms. The applications of PET imaging (e.g. cancer, brain function, cardiac function and gene expression) are currently benefiting from technological developments leading to the proposal of new PET systems. These are more sensitive, dedicated to imaging specific organs or research animals and are becoming multimodal. These advances are fostering new uses of PET, for example in biology labs to study the onset, progression and therapy of disease or to image the female breast. New materials and equipment are also, being developed allowing combining PET with other imaging techniques, such as MRI. The purpose of this review is to illustrate the most important inventions patented in PET since 2006 in areas concerning data acquisition and processing for human and research use of PET. Finally the manuscript will present the authors views about forthcoming developments in PET. Keywords: PET, PET developments, multimodality imaging, time of flight PET, dedicated PET systems, Positron Emission Tomography, in vivo imaging techniques, chemical affinity, Time-of-Flight PET, MRI, radiopharmaceuticals, PET-CT systems, sequential acquisitions, simultaneous acquisitions, scintillation light, split-magnet solution

Development of a dedicated positron emission tomography system for the detection and biopsy of breast cancer

Dedicated positron emission mammography breast imaging systems have shown great promise for the detection of small, radiotracer-avid lesions. Our group (a collaboration consisting of West Virginia University, Jefferson Lab and the University of Washington) is extending this work by developing a positron emission mammography-tomography (PEM-PET) system for imaging and biopsy of breast lesions. The system will have four planar detector heads that will rotate about the breast to acquire multi-view data suitable for tomographic reconstruction. Each detector head will consist of a 96×72 array of 2×2×15 mm 3 LYSO detector elements (pitch=2.1 mm) mounted on a 3×4 array of 5×5 cm 2 flat panel position-sensitive photomultiplier tubes. PEM-PET is expected to have approximately two-millimeter resolution and possess the ability to guide the needle biopsy of suspicious lesions seen on the PET images. Initial tests of the scintillator arrays yielded excellent results. Pixel maps for all four scintillator arrays demonstrated that separation of the LYSO elements was very good; all of the LYSO array elements were observed, even in areas between individual PSPMTs. System energy resolution was measured to be 25% FWHM at 511 keV. Future work includes the use of field programmable gate arrays (FPGAs) to replace the current VME-based data acquisition system, a PSPMT gain normalization procedure to help improve response uniformity and energy resolution, and the addition of an x-ray source and detector to produce multi-modality PEM-PET-CT images of the breast.

Joint project of the international network of agencies for health technology assessment—Part 1: Survey results on diffusion, assessment, and clinical use of positron emission tomography

The International Network of Agencies for Health Technology Assessment (INAHTA) has been tracking activities associated with the clinical use of positron emission tomography (PET) in its members' healthcare systems since 1997 and published its first Joint Project report on PET in 1999. Part 1 of this Joint Project report presents survey results on diffusion, assessment activities, and policy for clinical use related to PET among INAHTA members since 1999. INAHTA members were surveyed in 2003-2004. Twenty-seven INAHTA agencies (69 percent response rate) from nineteen countries responded to the survey. Dedicated PET systems are the most universally installed systems to date. Mobile scanners and modified gamma cameras are used occasionally as lower cost alternatives, and interest in PET-computed tomography hybrid models is rising despite limited assessment of impact on service planning. PET was used and assessed most commonly for managing patients with cancer. All respondents reported having some form of public funding for clinical PET frequently linked to data collection for the purpose of gathering evidence to refine clinical use and guide resource allocation toward indications that maximize clinical and cost-effectiveness. The use of HTA within a continuous quality improvement framework can help optimize scarce resources for evaluation and use of high cost diagnostic technologies such as PET, particularly where potential clinical or cost-effectiveness is considerable but conclusive evidence is lacking.

Computer phantom study of brain PET glucose metabolism imaging using a rotating SPECT/PET camera

Positron emission tomography (PET) with [ 18 F] fluoro-deoxy-glucose (FDG) provides information about glucose metabolism and is used to measure tissue glucose kinetics in the brain. The recent interest in hybrid SPECT/PET systems emerged as a practical approach to reduce the high cost of purchasing a dedicated ring-detector PET system. We have implemented interpolation methods for processing the projection data that could potentially reduce artifacts when reconstructing a dynamic imaging sequence in a PET study from a dual-head rotating SPECT/PET system. The computer simulations predict that parameter estimates from the dedicated PET system will be superior to results using the rotating camera system. However, the rotating camera system using projection interpolation may approach the accuracy of the dedicated PET system if the data noise is below 20%.

The clinical impact of camera-based positron emission tomography imaging in patients with recurrent colorectal cancer.

F18-fluorodeoxyglucose (FDG)-positron emission tomography (PET) studies have clinical value in suspected recurrent or metastatic colorectal cancer cases. Because this modality is not accessible for many patients, a camera-based FDG (CB-FDG) coincidence imaging was suggested as an alternative. Although inferior in resolution to a dedicated PET system, it can make FDG studies available to more patients. We assessed the clinical value of CB-FDG in patients with recurrent colorectal cancer. The disease stage and treatment approach in 83 patients were twice determined by an oncologist and a surgeon, first based on the patient's records and blind to CB-FDG findings and then with the inclusion of FDG results in the decision-making analysis. On a lesion-based analysis, the sensitivity of CB-FDG was 95% and the specificity was 81% compared with 88% and 64%, respectively, for computed tomography. Adding FDG findings led to disease-stage alteration in 47 patients (57%), upstaging in 35 (42%), and downstaging in 12 (15%). FDG localized the tumor sites in 21 of 26 patients (81%) with suspected clinical recurrence and a negative conventional imaging workup. In 8 patients, FDG ruled out viable tumor tissue suggested by other modalities. The oncologist's suggested treatment approach was altered in 54% of the patients and the surgeon altered the decision on operability in 28%. CB-FDG assessment has clinical value for both staging and selecting treatment in patients with recurrent colorectal cancer and can be considered an alternative to an nonaccessible dedicated PET system.

Fused functional-anatomic images of metastatic cancer of cervix obtained by a combined gamma camera and an X-ray tube hybrid system with an illustrative case and review of the 18F-fluorodeoxyglucose literature

Background 18F-Fluorodeoxyglucose (FDG) assessments have provided clinically important information in cervical cancer. FDG studies can now be performed by both dedicated PET systems and by new-generation gamma cameras. Hybrid systems which consist of positron emission tomography (PET) or a gamma camera with X-ray for fusion of functional-anatomic data without changing the patient’s position are now available. Case A woman with newly diagnosed cervical cancer underwent preoperative FDG studies using a hybrid gamma camera. In addition to the known primary tumor, FDG detected heretofore unidentified metastatic disease at the liver, bone, and para-aortic lymph nodes: the treatment approach was consequently altered to chemo- and radiotherapy. The fused images provided precise localization of the lesions, guiding bone biopsy and radiation field planning. Conclusion When PET is unavailable, a modified gamma camera can provide clinically relevant data in patients with cervical cancer.

Impact of technology on the utilisation of positron emission tomography in lymphoma: current and future perspectives.

Positron emission tomography (PET) has now gained a place in the management of patients with cancer, including those with Hodgkin's disease and non-Hodgkin's lymphoma. Restaging studies and those addressing the monitoring of response to treatment are especially in focus. Most of the knowledge gained has been achieved with dedicated BGO-based PET technology, but there are a number of developments that will impact on the use of this metabolic imaging technique in the investigation of patients with lymphoma. The challenges ahead are determined by the need for high-quality whole-body imaging associated with increased patient throughput and the need to investigate the role of new labelled ligands. The latter are likely to yield new insights into tumour cell characterisation, tumour behaviour and tumour outcome assessment. The study of new radiolabelled ligands will impose further demands for rapid dynamic data acquisition and accurate tracer quantification. Current and future developments in PET technology range from the use of new detector materials to different detector geometries and data acquisition modes. The search for alternatives to BGO scintillation materials for PET has led to the development of PET instruments utilising new crystals such as LSO and GSO. The use of these new detectors and the increased sensitivity achieved with 3D data acquisitions represent the most significant current developments in the field. With the increasing demands imposed on the clinical utilisation of PET, issues such as study cost and patient throughput will emerge as significant future factors. As a consequence, low-cost units are being offered by the manufacturers through the utilisation of gamma camera-based SPET systems for PET coincidence imaging. Unfortunately, clinical studies in lymphoma and other cancers have already demonstrated the limitations of this technology, with 20% of lesions <15 mm in size escaping detection. On the other hand, the recent development of combined PET/CT devices attempts to address the lack of anatomical information inherent with PET images, taking advantage of further improvement in patient throughput and hence cost-effectiveness. Preliminary studies using this multimodality imaging approach have already demonstrated the potential of the technique. Although the potential exists, certain technical issues with PET/CT require refinement of the methodology. Such issues include organ movement (such as respiratory motion), which strongly influences the image fusion of a rapidly acquired CT scan with the slower acquisition of a PET dataset, and the derivation of CT-based attenuation coefficients in the presence of contrast agents or metallic implants. The application of the technology for radiotherapy planning also poses a number of associated challenges. Finally, the development of dedicated PET systems based on planar detector arrangements with new detector components has the potential to improve clinical throughput by over 100%, but clinical trials using such systems have still to be carried out in order to establish the associated whole-body image quality.

A survey of PET activity in Germany during 1999

Positron emission tomography (PET) is the most powerful molecular imaging technique currently available for clinical use. The aim of this study was to provide public health information on PET procedures carried out in Germany - a country with a very high number of PET installations. To this end, all facilities that in 1999 were running at least one dedicated PET system were contacted and requested to provide information in a questionnaire on the radiopharmaceuticals applied, the total number and age distribution of patients and volunteers examined, the main diagnostic applications and the range of administered activities. Based on the information provided by 48 of the 60 PET facilities in Germany, an annual frequency of about 0.34 PET procedures per 1,000 inhabitants was estimated, associated with an annual per capita effective dose of about 1.9 micro Sv. Averaged over all PET procedures, the mean effective dose to patients was 5.6 mSv. The age distribution of patients and volunteers was skewed markedly towards higher ages; only a very small fraction (<3%) of patients were children younger than 15 years while older patients, and especially those in the age group between 41 and 65 years, were overrepresented relative to the general population. In total, 28 different PET radiopharmaceuticals were used, with only half of these having been administered to more than 20 patients each. The most frequently applied radiotracer was the glucose analogue 2-[(18)F]fluoro-2-deoxy- D-glucose (FDG), which was utilised in more than 84% of all PET procedures. For this tracer, the median value for activities applied for examinations in the three-dimensional (3D) acquisition mode was only half of that used for two-dimensional (2D) measurements. Based on a statistical analysis of the distribution of mean FDG activities administered to patients in the 48 PET facilities who responded to our inquiry, diagnostic reference levels of 370 and 200 MBq are proposed for the 2D and the 3D mode, respectively.

Design and evaluation of an LSO PET detector for breast cancer imaging.

Functional imaging with positron emission tomography (PET) may be a promising technique in conjunction with x-ray mammography for breast cancer patient management. Conventional whole body PET scanners provide metabolic images of breast cancer patients with several shortcomings related to the general-purpose nature of these systems. In whole body scanners, the detectors are typically 20-30 cm away from the breast or axilla, reducing sensitivity, and these scanners have relatively large detector elements (> 4 mm), limiting spatial resolution. Dedicated PET systems for breast imaging aim to overcome these limitations and improve the overall diagnostic quality of the images by bringing the detectors closer to the area to be imaged, thereby improving sensitivity, and by using smaller detector elements to improve the spatial resolution. We have designed and developed a modular PET detector that is composed of a 9x9 array of 3x3x20 mm3 lutetium oxyorthosilicate (LSO) scintillator crystals coupled to an optical fiber taper, which in turn is coupled to a Hamamatsu R5900-C8 position-sensitive photomultiplier tube. These detectors can be tiled together without gaps to construct large area detector arrays to form a dedicated PET breast cancer imaging system. Two complete detector modules have been built and tested. All detector elements are clearly visualized upon flood irradiation of the module. The intrinsic spatial resolution (full-width at half-maximum) was measured to be 2.26 mm (range 1.8-2.6 mm). The average energy resolution was 19.5% (range 17%-24%) at 511 keV. The coincidence time resolution was measured to be 2.4 ns. The detector efficiency for 511 keV gamma rays was 53% using a 350 keV energy threshold. These promising results support the feasibility of developing a high resolution, high sensitivity dedicated PET scanner for breast cancer applications.

Positron emission tomography

The potential of the coincidence technique in positron imaging was recognized early on and pilot experiments were performed as early as the 1950s. In combination with the tomographic technique, it was possible in the late 1970s to demonstrate a new principle for medical diagnosis, positron emission tomography (PET). In more recent years PET has matured and has become an important clinical research tool, as well as a routine diagnostic modality. PET is a multidisciplinary undertaking. However, in this paper we mainly emphasize the contribution from nuclear physics, radionuclide production and detector development. New crystal materials with high density, high light output and short pulse length will, in the near future, improve the resolution and counting properties of PET instrumentation. The experience gained in the development of -detectors in nuclear and particle physics is applied to increase the solid angle and hence the sensitivity. Other factors must also be considered. There is interest in using positron-emitting nuclides with longer half-lives than those mainly associated with PET. Many of these long-lived nuclides, e.g. ( h) and ( h), emit high-energy gamma radiation in coincidence with the positron radiation, which will affect the detection and quantification abilities of PET. PET primarily yields functional and physiological information, and anatomical structures are sometimes difficult to identify. High-quality PET data usually have to be combined with an anatomical method like CT or MRI. The future will, besides highly sophisticated and dedicated PET systems for research, probably see clinically suited rotating gamma cameras integrated with CT or MR, which can efficiently be used both for SPECT and PET.