Effective count rates for PET scanners with reduced and extended axial field of view

MacDonald, L.R.; Harrison, Robert L.; Alessio, Adam M.; Lewellen, T.K.; Kinahan, Paul E.

doi:10.1088/0031-9155/56/12/011

Cited by 30 publications

(28 citation statements)

References 16 publications

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“…However, the slow and relatively low-light-yield scintillator (bismuth germanate) necessitated the use of coarse axial septa to minimize scatter and counting rate problems, greatly reducing the possible sensitivity gain. There also has been a range of computer simulation studies designed to examine the effects of longer axial FOVs and the impact on scatter and random coincidences, as well as to determine the most effective way to distribute a fixed volume of scintillator material given this is a key determinant in the overall cost of a PET system (1,7,10,(13)(14)(15)(16)(17). The availability now of improved scintillation materials based on lutetium compounds, which have a more favorable combination of speed, light output, and stopping power, has made it feasible to develop fully 3-dimensional systems that can handle the higher counting rates and scatter fraction, and additionally provide time-of-flight information to further improve performance.…”

Section: Historymentioning

confidence: 99%

Total-Body PET: Maximizing Sensitivity to Create New Opportunities for Clinical Research and Patient Care

et al. 2017

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PET is widely considered the most sensitive technique available for noninvasively studying physiology, metabolism, and molecular pathways in the living human being. However, the utility of PET, being a photon-deficient modality, remains constrained by factors including low signal-to-noise ratio, long imaging times, and concerns about radiation dose. Two developments offer the potential to dramatically increase the effective sensitivity of PET. First by increasing the geometric coverage to encompass the entire body, sensitivity can be increased by a factor of about 40 for total-body imaging or a factor of about 4-5 for imaging a single organ such as the brain or heart. The world's first total-body PET/CT scanner is currently under construction to demonstrate how this step change in sensitivity affects the way PET is used both in clinical research and in patient care. Second, there is the future prospect of significant improvements in timing resolution that could lead to further effective sensitivity gains. When combined with total-body PET, this could produce overall sensitivity gains of more than 2 orders of magnitude compared with existing state-of-the-art systems. In this article, we discuss the benefits of increasing body coverage, describe our efforts to develop a first-generation total-body PET/CT scanner, discuss selected application areas for total-body PET, and project the impact of further improvements in time-of-flight PET.Key Words: instrumentation; molecular imaging; PET/CT; instrumentation; PET; total-body imaging J Nucl Med 2018; 59:3-12 DOI: 10.2967/jnumed.116.184028Al l nuclear medicine studies in humans are limited by the trade-offs between the number of detected decay events, imaging time, and absorbed dose. The number of detected events determines the signal-to-noise ratio (SNR) in the final image, but constraints on administered activity, as well as high random event rates and dead time that occur at high activities, currently prevent acquisition of high-SNR images in short times. This in turn limits the ability to perform high-resolution, dynamic imaging studies with tracer kinetic modeling, because short-time-frame datasets are always noisy. A further limitation is that although the tracer injection is systemic and radiotracer is present in the entire body, current imaging systems contain only a small portion of the body within the field of view (FOV). For applications in which the distribution of radiotracer in the entire body or multiple organ systems is of interest, this limitation leads to further inefficiencies and makes it difficult to acquire dynamic data from all the tissues of interest. If one takes whole-body PET scanning with 18 F-FDG as an example, the total efficiency with which pairs of coincidence photons that escape the body are detected is well under 1% even on today's best scanners. Simplistically, this number can be derived by considering that the average geometric sensitivity within the FOV of a typical clinical PET scanner is under 5% and that with an axial coverage of ...

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Section: Historymentioning

confidence: 99%

Total-Body PET: Maximizing Sensitivity to Create New Opportunities for Clinical Research and Patient Care

et al. 2017

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“…Several Monte Carlo simulation studies to evaluate longer AFOV scanners have focused mainly on the increased scanner sensitivity and noise equivalent counts (NEC) (Badawi et al, 2000, Eriksson et al, 2007, Hunter et al, 2009, MacDonald et al, 2011, Eriksson et al, 2011, Poon et al, 2012). In addition to simulation studies, there have also been prototype developments of two scanners with axial FOV that is much longer than that available commercially.…”

Section: Introductionmentioning

confidence: 99%

Impact of detector design on imaging performance of a long axial field-of-view, whole-body PET scanner

Surti

Karp

2015

Phys. Med. Biol.

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Current generation of commercial time-of-flight (TOF) PET scanners utilize 20–25 mm thick LSO or LYSO crystals and have an axial FOV (AFOV) in the range of 16–22 mm. Longer AFOV scanners would provide increased intrinsic sensitivity and require fewer bed positions for whole-body imaging. Recent simulation work has investigated the sensitivity gains that can be achieved with these long AFOV scanners, and has motivated new areas of investigation such as imaging with very low dose of injected activity as well as providing whole-body dynamic imaging capability in one bed position. In this simulation work we model a 72 cm long scanner and prioritize the detector design choices in terms of timing resolution, crystal size (spatial resolution), crystal thickness (detector sensitivity), and depth-of-interaction (DOI) measurement capability. The generated list data are reconstructed with a list-mode OSEM algorithm using a Gaussian TOF kernel that depends on the timing resolution and blob basis functions for regularization. We use lesion phantoms and clinically relevant metrics for lesion detectability and contrast measurement. The scan time was fixed at 10 minutes for imaging a 100 cm long object assuming a 50% overlap between adjacent bed positions. Results show that a 72 cm long scanner can provide a factor of ten reduction in injected activity compared to an identical 18 cm long scanner to get equivalent lesion detectability. While improved timing resolution leads to further gains, using 3 mm (as opposed to 4 mm) wide crystals does not show any significant benefits for lesion detectability. A detector providing 2-level DOI information with equal crystal thickness also does not show significant gains. Finally, a 15 mm thick crystal leads to lower lesion detectability than a 20 mm thick crystal when keeping all other detector parameters (crystal width, timing resolution, and DOI capability) the same. However, improved timing performance with 15 mm thick crystals can provide similar or better performance than that achieved by a detector using 20 mm thick crystals.

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“…High image quality is required for an accurate diagnosis (3). PET image quality is strongly dependent on scanner sensitivity (4), which in turn is associated with the length of the axial field of view (FOV) (4)(5)(6). A PET system with a longer axial FOV has a higher sensitivity because there are a large number of detectors ( Fig.…”

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confidence: 99%

Impact of Time-of-Flight PET/CT with a Large Axial Field of View for Reducing Whole-Body Acquisition Time

Akamatsu

Uba

Taniguchi

et al. 2014

Journal of Nuclear Medicine Technology

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The aim of this study was to evaluate the imaging performance of 39-and 52-ring time-of-flight (TOF) PET/CT scanners. We also assessed the potential of reducing the scanning time using a 52-ring TOF PET/CT scanner. Methods: PET/CT scanners with 39-and 52-ring lutetium oxyorthosilicate detectors were evaluated. The axial fields of view were 16.2 and 21.6 cm, respectively. We used a National Electrical Manufacturers Association International Electrotechnical Commission body phantom filled with an 18 F solution containing background activity of 5.31 and 2.65 kBq/mL for the studies. The sphere-to-background ratio was 4:1. The PET data were acquired for 10 min in 3-dimensional list mode and then reconstructed with both ordered-subsets reconstruction maximization and ordered-subsets reconstruction maximization plus point-spread function plus time-of-flight algorithms. PET images with different acquisition times were reconstructed (from 1 to 10 min). The image quality was physically assessed using the sensitivity, noise-equivalent counting rate, coefficient of variation of background activity, and relative recovery coefficient. Results: The total system sensitivities of the 39-and 52-ring scanners were 5.6 and 9.3 kcps/MBq, respectively. Compared with the 39-ring scanner, the noise-equivalent counting rate of the 52-ring scanner was 60% higher for both the high-activity and the low-activity models. The recovery coefficient was consistent, irrespective of the number of detector rings. The coefficient of variation of the 52-ring scanner using a 3-min acquisition time was equivalent to that of the 39-ring scanner using a 4-min acquisition time. Conclusion: The image quality of the 52-ring scanner is superior to that of the 39-ring scanner. The acquisition time per bed position of the 52-ring system can be reduced by about 25% without compromising image quality. In addition, the number of bed positions required is 25% lower for the 52-ring system. Finally, the examination time required for a whole-body PET scan is considered to be reduced by about 40% if the 52-ring scanner is used. PETi s a molecular imaging technique that provides metabolic information useful for patient care and for monitoring the pharmacokinetics of drugs (1,2). High image quality is required for an accurate diagnosis (3). PET image quality is strongly dependent on scanner sensitivity (4), which in turn is associated with the length of the axial field of view (FOV) (4-6). A PET system with a longer axial FOV has a higher sensitivity because there are a large number of detectors (Fig. 1). In addition, the number of bed positions can be reduced because of the large axial range for whole-body PET. PET scanners with a longer axial range can be used to reduce the patient dose, decrease the scanning time, or reduce the image noise while maintaining other constant image characteristics. To date, however, there has been no comparison of actual PET images acquired on systems having different axial FOVs.In this study, we evaluated the PET image quality of 39-and...

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Effective count rates for PET scanners with reduced and extended axial field of view

Cited by 30 publications

References 16 publications

Total-Body PET: Maximizing Sensitivity to Create New Opportunities for Clinical Research and Patient Care

Total-Body PET: Maximizing Sensitivity to Create New Opportunities for Clinical Research and Patient Care

Impact of detector design on imaging performance of a long axial field-of-view, whole-body PET scanner

Impact of Time-of-Flight PET/CT with a Large Axial Field of View for Reducing Whole-Body Acquisition Time

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