Reliability of predicting image signal‐to‐noise ratio using noise equivalent count rate in PET imaging

Chang, Tingting; Chang, Guoqiang; Clark, John W.; Diab, Rami; Rohren, Eric M.; Mawlawi, Osama

doi:10.1118/1.4750053

Cited by 39 publications

(30 citation statements)

References 32 publications

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“…A major limitation of some of these studies using NEC to optimize PET system design is that improvements in image quality due to time-of-flight (TOF) and depth-of-interaction (DOI) information cannot be measured. In addition, NEC is known to have limitations in predicting the image SNR when using advanced 3D iterative reconstruction algorithms, which are now commonly used clinically (Chang et al 2012). TOF-PET has improved many components of the imaging process, leading to a significant improvement in the quality of clinical PET images (Karp et al 2008, Surti 2015), and it is expected that TOF gains will also translate to improved image quality in long-axial scanner designs.…”

Section: Introductionmentioning

confidence: 99%

Parallax error in long-axial field-of-view PET scanners—a simulation study

et al. 2016

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There is a growing interest in the design and construction of a PET scanner with a very long axial extent. One critical design challenge is the impact of the long axial extent on the scanner spatial resolution properties. In this work, we characterize the effect of parallax error in PET system designs having an axial FOV of 198 cm (total-body PET scanner) using fully-3D Monte Carlo simulations. Two different scintillation materials were studied: LSO and LaBr3. The crystal size in both cases was 4×4×20 mm3. Several different depth-of-interaction (DOI) encoding techniques were investigated to characterize the improvement in spatial resolution when using a DOI capable detector. To measure spatial resolution we simulated point sources in a warm background in the center of the imaging FOV, where the effects of axial parallax are largest, and at several positions radially offset from the center. Using a line-of-response based OSEM reconstruction algorithm we found that the axial resolution in an LSO scanner degrades from 4.8 mm to 5.7 mm (FWHM) at the center of the imaging FOV when extending the axial acceptance angle (α) from ±12° (corresponding to an axial FOV of 18 cm) to the maximum of ±67°—a similar result was obtained with LaBr3, in which the axial resolution degraded from 5.3 mm to 6.1 mm. For comparison we also measured the degradation due to radial parallax error in the transverse imaging FOV; the transverse resolution, averaging radial and tangential directions, of an LSO scanner was degraded from 4.9 mm to 7.7 mm, for a measurement at the center of the scanner compared to a measurement with a radial offset of 23 cm. Simulations of a DOI detector design improved the spatial resolution in all dimensions. The axial resolution in the LSO-based scanner, with α = ±67°, was improved from 5.7 mm to 5.0 mm by incorporating a two-layer DOI detector. These results characterize the maximum axial blurring for a fully open 2 m long PET scanner and demonstrate that large sensitivity gains are possible with a modest reduction in resolution when using current clinical detector technology with no DOI capability.

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Section: Introductionmentioning

confidence: 99%

Parallax error in long-axial field-of-view PET scanners—a simulation study

et al. 2016

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“…Second, besides the NEMA phantom (Fig. 1a), the NECR has also been derived based upon other phantoms and Monte-Carlo simulation tools [9,11,12]. To what extent these different NECR derivation methods are consistent with each other needs to be answered.…”

mentioning

confidence: 99%

The use of noise equivalent count rate and the NEMA phantom for PET image quality evaluation

Yang

Peng

2015

Physica Medica

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“…Additionally, while image SNR can be predicted by the NEC rate when using FBP reconstruction, studies suggest that this is not true when using 3D iterative reconstruction, particularly for those applications requiring high activity concentration. 30 The results obtained with the proposed method were compared in all cases against the results obtained using only double coincidences (e.g., discarding all multiple events) and against the case in which triple coincidences are equally weighted among their possible LORs (average method). Finally, as the goal of this work is to show the effect on image quality and overall scanner performance of adding triple events to the standard coincidences, attenuation, scatter, and random corrections were not applied in any case.…”

Section: D Performance Evaluationmentioning

confidence: 99%

Recovery and normalization of triple coincidences in PET

et al. 2015

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Purpose: Triple coincidences in positron emission tomography (PET) are events in which three γ-rays are detected simultaneously. These events, though potentially useful for enhancing the sensitivity of PET scanners, are discarded or processed without special consideration in current systems, because there is not a clear criterion for assigning them to a unique line-of-response (LOR). Methods proposed for recovering such events usually rely on the use of highly specialized detection systems, hampering general adoption, and/or are based on Compton-scatter kinematics and, consequently, are limited in accuracy by the energy resolution of standard PET detectors. In this work, the authors propose a simple and general solution for recovering triple coincidences, which does not require specialized detectors or additional energy resolution requirements. Methods: To recover triple coincidences, the authors' method distributes such events among their possible LORs using the relative proportions of double coincidences in these LORs. The authors show analytically that this assignment scheme represents the maximum-likelihood solution for the triple-coincidence distribution problem. The PET component of a preclinical PET/CT scanner was adapted to enable the acquisition and processing of triple coincidences. Since the efficiencies for detecting double and triple events were found to be different throughout the scanner field-of-view, a normalization procedure specific for triple coincidences was also developed. The effect of including triple coincidences using their method was compared against the cases of equally weighting the triples among their possible LORs and discarding all the triple events. The authors used as figures of merit for this comparison sensitivity, noise-equivalent count (NEC) rates and image quality calculated as described in the NEMA NU-4 protocol for the assessment of preclinical PET scanners. Results: The addition of triple-coincidence events with the authors' method increased peak NEC rates of the scanner by 26.6% and 32% for mouse-and rat-sized objects, respectively. This increase in NEC-rate performance was also reflected in the image-quality metrics. Images reconstructed using double and triple coincidences recovered using their method had better signal-to-noise ratio than those obtained using only double coincidences, while preserving spatial resolution and contrast. Distribution of triple coincidences using an equal-weighting scheme increased apparent system sensitivity but degraded image quality. The performance boost provided by the inclusion of triple coincidences using their method allowed to reduce the acquisition time of standard imaging procedures by up to ∼25%. parameters like spatial resolution or contrast.

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Reliability of predicting image signal‐to‐noise ratio using noise equivalent count rate in PET imaging

Cited by 39 publications

References 32 publications

Parallax error in long-axial field-of-view PET scanners—a simulation study

Parallax error in long-axial field-of-view PET scanners—a simulation study

The use of noise equivalent count rate and the NEMA phantom for PET image quality evaluation

Recovery and normalization of triple coincidences in PET

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