Lesion detection and quantification performance of the Tachyon-I time-of-flight PET scanner: phantom and human studies

Zhang, Xuezhu; Peng, Qiyu; Zhou, Jian; Huber, J.; Moses, W.W.; Qi, Jinyi

doi:10.1088/1361-6560/aab0f3

“…Two TOF resolutions (500 ps and 320 ps) and two DOI resolutions (10 mm and 4 mm) were simulated and compared with the non-TOF and no DOI scanners. The 500 ps TOF was commonly available in commercial PET scanners (Jakoby et al 2011) and 320 ps TOF has also been reported in recent published work (Peng et al 2015, Miller et al 2015, Zhang et al 2018a). The choice of DOI resolutions also covered the range that had been reported in the literature (Du et al 2018, Zhang et al 2013a, Zhang et al 2013b).…”

Section: Methodsmentioning

confidence: 89%

“…However, the image quality of PET is mainly limited by the number of coincidence photon pairs that are recorded in each PET scan due to low sensitivity and concerns regarding radiation dose. To overcome the limitation of current PET scanners and explore new applications of PET, we are building a 2-meter long PET scanner, called the EXPLORER (http://explorer.ucdavis.edu) that will dramatically improve the photon detection efficiency for long axial FOV (AFOV) scans (Badawi et al 2013, Cherry et al 2017, Badawi et al 2018, Zhang et al 2018b). In addition to the improved sensitivity, it can cover the entire human body and will provide total-body high temporal resolution dynamic PET scans for the first time (Zhang et al 2014a).…”

Section: Introductionmentioning

confidence: 99%

Theoretical study of the benefit of long axial field-of-view PET on region of interest quantification

Zhang

¹

,

Badawi

²

,

Cherry

³

et al. 2018

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The aim of this study is to evaluate the benefit of long axial field-of-view (AFOV) PET scanners on region of interest (ROI) quantification. We simulated a series of PET scanners with an AFOV ranging from 22 cm to 220 cm. A theoretical framework was used to predict the contrast recovery coefficient (CRC) and the variance of ROI quantification in penalized maximum likelihood (ML) image reconstruction, in which the resolution and noise tradeoff was controlled by a regularization parameter with a quadratic penalty function. The characterization was based on the converged penalized ML reconstruction with an accurate system model. We examined quantification of a 2 mm ROI and 10 mm ROI in a clinically relevant scan range of 110 cm. Multiple bed positions with 50% overlap were used for scanners with shorter AFOV to provide a relatively uniform sensitivity across the 110 cm axial range. A uniform water cylinder of 20 cm in diameter and 230 cm in length was chosen to model the attenuation and background activity. We computed the variance reduction factor at fixed resolution. Effects of different detector capabilities, including TOF (time-of-flight) resolution (320 ps, 500 ps, and non-TOF) and DOI (depth-of-interaction) resolution (4 mm, 10 mm, and no DOI), were evaluated. The results show that at a normal activity level (370 MBq), the 220 cm AFOV scanner offers a ∼17-fold variance reduction for the 2 mm ROI and ∼26-fold variance reduction for the 10 mm ROI (both measured at CRC = 0.5) over the 22 cm AFOV scanner when both using detectors with 500 ps TOF resolution no DOI capability. The variance reduction factors of trues-only are higher than those of including scatters and randoms. Combining 320 ps TOF and 4 mm DOI, the 220 cm long scanner offers a ∼45-fold variance reduction over the 22 cm long reference scanner (500 ps TOF, no DOI) for imaging 2 mm and 10 mm ROIs. The variance reduction factors are higher at a lower activity level due to lower random fraction. In conclusion, our study demonstrates that a long AFOV scanner can greatly improve the quantitative accuracy of PET imaging compared to current state-of-the-art clinical PET scanners.

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“…Several excellent review articles on the current state of the field focus mostly on iterative methods and on needed corrections to the data (attenuation, scatter, random events, detector efficiency, noncolinearity, patient motion, K). See Budinger et al (1978, Tomitani (1981), Budinger (1983), Kao (2008), Li et al (2015), Yu et al (2015), Li et al (2016), Cherry et al (2018), Zhang et al (2018), Zhang et al (2020), Tong et al (2010), Iriarte et al (2016), Gullberg et al (2010), Surti and Karp (2016), Zhang et al (2017Zhang et al ( ), pp. 2465Zhang et al ( -2485, Jones and Townsend (2017), see their section 6 on reconstruction algorithms), and Vandenberghe et al (2016).…”

Section: Relation Of Krnl3d and Krnl3d-tof To Previous Analytical Met...mentioning

confidence: 99%

A backprojection kernel (KRNL3D) for very-wide-aperture 3D tomography applied to PET with Multigrid for precise use of time-of-flight data

Miller

¹

2021

Phys. Med. Biol.

0

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In ‘KRNL3D’ we derive a kernel function K(y 1, y 2, φ) whose backprojections from all directions (θ, φ) in the spherical band ∣ φ ∣ < φ ¯ max on the celestial sphere, when integrated with respect to solid angle, yield ρ, the 3D Gaussian point response function (PRF) of radius 1. This K, when convolved against line integral data from an unknown density function f, yields an integral formula for the ‘mollification’ ff = ρ ∗ f, which is a slightly blurred version of f, and which stabilizes the mild ill-posedness. Applied to positron emission tomography that backprojection reconstruction occurs stochastically and one emission event at a time, after needed data corrections. We describe Octave (≈Matlab) codes to tabulate K and to test its use with a large aperture φ ¯ max = π / 3 or π/6. ‘KRNL3D- TOF’ truncates backprojection to a cylindrical patch about the TOF approximate location of each event. These ‘backplacements’ decrease the computational cost and limit noise and streaking in one region from contaminating the reconstruction in more distant regions. They also retain the ability to count emission events in an isolated blob despite very low event counts, a valuable feature for dynamic studies of metabolic processes. ‘Multigrid’ allows further reduction in the radius and lengths of the cylinders, thereby enabling even more precise use of the TOF information. This precision should be especially important as researchers decrease the TOF uncertainty in newer generation scanners. Finally, we discuss ‘further work’ that needs to be done. Our codes are being made freely available at https://github.com/keithmillerberkeley/PET-codes.

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“…Timeof-flight (TOF) PET scanners can enhance the diagnostic accuracy of reconstructed images by locating positron emissions and improving the signal-to-noise ratio (SNR) of PET data [6,7]. It has been verified that an improved image quality of PET scanner can be achieved with a detector design that is capable of measuring TOF information [8][9][10].…”

Section: Introductionmentioning

confidence: 99%

PET detectors with 127 ps CTR for the Tachyon-II time-of-flight PET scanner

Xie

¹

,

Zhang

²

,

Peng

³

et al. 2019

Nuclear Instruments and Methods in Physics Research Section A:

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The signal-to-noise ratio (SNR) of the reconstructed image of Positron Emission Tomography (PET) can be improved by the timing measurement. In this article, we designed, fabricated and tested 32 time-of-flight (TOF) detectors for the second generation of Tachyon TOF-PET scanners. The detector module consists of two arrays of 2 × 12 lutetium-yttrium oxyorthosilicate (LYSO) crystal cubes of 6 ×6× 6 mm 3 . The discrete crystals were coupled to the 6 mm silicon photomultipliers (SiPMs) with optical glue. All the SiPM were tested for dark current. To correct the errors in the timing measurements caused by time-walk, two compensation methods (logcorrection and linear-correction) based on the relationship between energy and timing information were purposed. As a comparison, the SiPM arrays coupled to 4 mm and 6 mm side crystal cube without optical glue were tested for coincidence timing resolution (CTR). The mean and standard deviations (SD) of dark current for the 1536 tested SiPMs were 12.72 +/− 1.70 μA at the bias voltage of 31.5 V and the temperature of 20 °C (±1 °C). CTR performance has increased by ~5% within a narrow energy window, and ~10% in a wide energy window by log-correction. The mean and SD of the CTR of 6 mm side crystal cube glue coupled was 126.9 +/− 3.6 ps for the 768 pairs of tested SiPMs. The detector is expected to provide a technical reference for the next generation of ultra-fast CTR commercial PET scanner using multilayer detectors.

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Lesion detection and quantification performance of the Tachyon-I time-of-flight PET scanner: phantom and human studies

Cited by 6 publications

References 48 publications

Theoretical study of the benefit of long axial field-of-view PET on region of interest quantification

Theoretical study of the benefit of long axial field-of-view PET on region of interest quantification

A backprojection kernel (KRNL3D) for very-wide-aperture 3D tomography applied to PET with Multigrid for precise use of time-of-flight data

PET detectors with 127 ps CTR for the Tachyon-II time-of-flight PET scanner

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