Hybrid Pixel-Waveform (HPWF) Enabled CdTe Detectors for Small Animal Gamma-Ray Imaging Applications

Gröll, A.; Kim, K.; Bhatia, Harsh; Zhang, J. C.; Wang, J. H.; Shen, Zhiqiang; Cai, Liang; Dutta, Joyita; Li, Q.; Meng, Ling Jian

doi:10.1109/tns.2016.2623807

Cited by 21 publications

(22 citation statements)

References 48 publications

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“…The sub-ns timing demonstrated here using the observed optical signal represents a dramatic improvement of the previously measured coincidence timing resolution of TlBr [Hitomi et al 2013]. It also is far better than the values of several nanoseconds obtained with other semiconductor-based detector systems as cadmium telluride (CdTe) or cadmium zinc telluride (CZT) that have been studied for PET [Abbaszadeh and Levin 2017, Groll et al 2016, Arino et al 2013, Mitchell et al 2008, Okada et al 2002]. It is worth noting that the approach used here likely would not work for CdTe or CZT, as the smaller band gap results in high optical absorption of these materials below about 830 nm.…”

Section: Discussionmentioning

confidence: 57%

Towards time-of-flight PET with a semiconductor detector

et al. 2018

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The feasibility of using Cerenkov light, generated by energetic electrons following 511 keV photon interactions in the semiconductor TlBr, to obtain fast timing information for positron emission tomography (PET) was evaluated. Due to its high refractive index, TlBr is a relatively good Cerenkov radiator and with its wide bandgap, has good optical transparency across most of the visible spectrum. Coupling an SiPM photodetector to a slab of TlBr (TlBr-SiPM) yielded a coincidence timing resolution of 620 ps FWHM between the TlBr-SiPM detector and a LFS reference detector. This value improved to 430 ps FWHM by applying a high pulse amplitude cut based on the TlBr-SiPM and reference detector signal amplitudes. These results are the best ever achieved with a semiconductor PET detector and already approach the performance required for time-of-flight. As TlBr has higher stopping power and better energy resolution than the conventional scintillation detectors currently used in PET scanners, a hybrid TlBr-SiPM detector with fast timing capability becomes an interesting option for further development.

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Section: Discussionmentioning

confidence: 57%

Towards time-of-flight PET with a semiconductor detector

et al. 2018

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“…We performed a point source experiment using a 10 μ Ci Na-22 point source (half life = 2.6 years) with a 250 μm diameter (Groll et al 2017). Note that although ideally a point source should be smaller than a virtual detector pixel size, this phantom is one of the smallest commercially available point source phantoms.…”

Section: Methodsmentioning

confidence: 99%

“…In our previous studies (Groll et al 2015, Groll et al 2016, Groll et al 2017), we have developed a hybrid pixel-waveform (HPWF) CZT/CdTe detector design that can offer an ultrahigh intrinsic spatial resolution with a detector pixel of 350 μm as shown in figure 1. In the prototype scanner, two detector panels and a rotating object, as shown in figure 1(a), are used to emulate the full-ring system.…”

Section: Introductionmentioning

confidence: 99%

“…Here, the optimal resolution of virtual detector was slightly higher than the half of real crystal size. Groll et al (Groll et al 2017) have exploited the same virtual detector sinogram rebinning using the ordered subsets expectation maximization (OSEM) algorithm and modeling the point spread function (PSF) to achieve a resolution of 30% higher than half of the actual crystal size.…”

Section: Introductionmentioning

confidence: 99%

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A novel depth-of-interaction rebinning strategy for ultrahigh resolution PET

et al. 2018

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Small animal positron emission tomography (PET) imaging often requires high resolution (∼few hundred microns) to enable accurate quantitation in small structures such as animal brains. Recently, we have developed a prototype ultrahigh resolution depth-of-interaction (DOI) PET system that uses CdZnTe detectors with a detector pixel size of 350 μm and eight DOI layers with a 250 μm depth resolution. Due to the large number of line-of-response (LOR) combinations of DOIs, the system matrix for reconstruction is 64 times larger than that without DOI. While a high resolution virtual ring geometry can be employed to simplify the system matrix and create a sinogram, the LORs in such a sinogram tend to be sparse and irregular, leading to potential degradation of the reconstructed image quality. In this paper, we propose a novel high resolution sinogram rebinning method in which a uniform sub-sampling DOI strategy is employed. However, even with the high resolution rebinning strategy, the reconstructed image tends to be very noisy due to insufficient photon counts in many high resolution sinogram pixels. To reduce noise effects, we developed a penalized maximum likelihood reconstruction framework with the Poisson log-likelihood and a non-convex total variation penalty. Here, an ordered subsets separable quadratic surrogate and alternating direction method of multipliers are utilized to solve the optimization. To evaluate the performance of the proposed sub-sampling method and the penalized maximum likelihood reconstruction technique, we perform simulations and preliminary point source experiments. By comparing the reconstructed images and profiles based on sinograms without DOI, with rebinned DOI and with sub-sampled DOI, we demonstrate that the proposed method with sub-sampled DOIs can significantly improve the image quality with lower dose and yield a high resolution of <300 μm.

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“…Since the low timing resolution requires an increased coincidence time window, a higher rate of random coincidences is recorded. Also, the relatively lower Z value requires a thicker detector and the fraction of photoelectric interactions is lower compared with inorganic scintillators such as LYSO …”

Section: Introductionmentioning

confidence: 99%

An edge‐readout, multilayer detector for positron emission tomography

Ruiz-Gonzalez

Furenlid

2018

Medical Physics

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Purpose We present a novel gamma-ray-detector design based on total internal reflection (TIR) of scintillation photons within a crystal that addresses many limitations of traditional PET detectors. Our approach has appealing features, including sub-millimeter lateral resolution, DOI positioning from layer thickness, and excellent energy resolution. The design places light sensors on the edges of a stack of scintillator slabs separated by small air gaps, and exploits the phenomenon that more than 80% of scintillation light emitted during a gamma-ray event reaches the edges of a thin crystal with polished faces due to TIR. Gamma-ray stopping power is achieved by stacking multiple layers, and DOI is determined by which layer the gamma ray interacts in. Method The concept of edge readouts of a thin slab was verified by Monte-Carlo simulation of scintillation-light transport. An LYSO crystal of dimensions 50.8 mm × 50.8 mm × 3.0 mm was modeled with 5 rectangular SiPMs placed along each edge face. The mean-detector-response functions (MDRFs) were calculated by simulating signals from 511 keV gamma-ray interactions in a grid of locations. Simulations were carried out to study the influence of choice of scintillator material and dimensions, gamma-ray photon energies, introduction of laser or mechanically-induced optical barriers (LIOBs, MIOBs), and refractive indices of optical-coupling media and SiPM windows. We also analyzed timing performance including influence of gamma-ray interaction position and presence of optical barriers. We also modeled and built a prototype detector, a 27.4 mm × 27.4 mm × 3.0 mm CsI(Tl) crystal with 4 SiPMs per edge in order to experimentally validate the results predicted by the simulations. The prototype detector used CsI(Tl) crystals from Proteus outfitted with 16 Hamamatsu model S13360-6050PE MPPCs read out by an AiT-16-channel readout. The MDRFs were measured by scanning the detector with a collimated beam of 662-keV photons from a 137Cs source. The spatial resolution was experimentally determined by imaging a tungsten slit that created a beam of 0.44 mm (FWHM) width normal to the detector surface. The energy resolution was evaluated by analyzing list-mode data from flood illumination by the 137Cs source. Result We find that in a block-detector-sized LYSO layer read out by 5 SiPMs per edge, illuminated by 511 keV photons, the average resolution is 1.49 mm (FWHM). With the introduction of optical barriers, average spatial resolution improves to 0.56 mm (FWHM). The DOI resolution is the layer thickness of 3.0 mm. We also find that optical-coupling media and SiPM-window materials have an impact on spatial resolution. The timing simulation with LYSO crystal yields a coincidence resolving time (CRT) of 200 – 400 ps, which is slightly position-dependent. And the introduction of optical barriers has minimum influence. The prototype CsI(Tl) detector, with a smaller area and fewer SiPMs, was measured to have central-area spatial resolutions of 0.70 mm and 0.39 mm without and with optical ba...

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Hybrid Pixel-Waveform (HPWF) Enabled CdTe Detectors for Small Animal Gamma-Ray Imaging Applications

Cited by 21 publications

References 48 publications

Towards time-of-flight PET with a semiconductor detector

Towards time-of-flight PET with a semiconductor detector

A novel depth-of-interaction rebinning strategy for ultrahigh resolution PET

An edge‐readout, multilayer detector for positron emission tomography

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