Author
Tianyu Ma
Other affiliations: University at Buffalo, University of Houston, Chinese Ministry of Education ...read more
Bio: Tianyu Ma is an academic researcher from Tsinghua University. The author has contributed to research in topics: Detector & Iterative reconstruction. The author has an hindex of 13, co-authored 147 publications receiving 756 citations. Previous affiliations of Tianyu Ma include University at Buffalo & University of Houston.
Papers published on a yearly basis
Papers
More filters
••
TL;DR: Full 3D U-net is superior to several existing denoising methods, including Gaussian filter, anatomical-guided non-local mean (NLM) filter, and MAP reconstruction with Quadratic prior and relative difference prior, in terms of superior image quality and trade-off between noise and bias.
Abstract: Reducing radiation dose is important for PET imaging. However, reducing injection doses causes increased image noise and low signal-to-noise ratio (SNR), subsequently affecting diagnostic and quantitative accuracies. Deep learning methods have shown a great potential to reduce the noise and improve the SNR in low dose PET data. In this work, we comprehensively investigated the quantitative accuracy of small lung nodules, in addition to visual image quality, using deep learning based denoising methods for oncological PET imaging. We applied and optimized an advanced deep learning method based on the U-net architecture to predict the standard dose PET image from 10% low-dose PET data. We also investigated the effect of different network architectures, image dimensions, labels and inputs for deep learning methods with respect to both noise reduction performance and quantitative accuracy. Normalized mean square error (NMSE), SNR, and standard uptake value (SUV) bias of different nodule regions of interest (ROIs) were used for evaluation. Our results showed that U-net and GAN are superior to CAE with smaller SUVmean and SUVmax bias at the expense of inferior SNR. A fully 3D U-net has optimal quantitative performance compared to 2D and 2.5D U-net with less than 15% SUVmean bias for all the ten patients. U-net outperforms Residual U-net (r-U-net) in general with smaller NMSE, higher SNR and lower SUVmax bias. Fully 3D U-net is superior to several existing denoising methods, including Gaussian filter, anatomical-guided non-local mean (NLM) filter, and MAP reconstruction with Quadratic prior and relative difference prior, in terms of superior image quality and trade-off between noise and bias. Furthermore, incorporating aligned CT images has the potential to further improve the quantitative accuracy in multi-channel U-net. We found the optimal architectures and parameters of deep learning based methods are different for absolute quantitative accuracy and visual image quality. Our quantitative results demonstrated that fully 3D U-net can both effectively reduce image noise and control bias even for sub-centimeter small lung nodules when generating standard dose PET using 10% low count down-sampled data.
87 citations
••
TL;DR: The results showed that LSO background adds concentric ring artifacts to the reconstructed image, and the simple subtraction method can effectively remove these artifacts-the effect of the correction was more visible when the object activity level was near or above the eMDTA.
Abstract: This work is part of a feasibility study to develop SPECT imaging capability on a lutetium oxyorthosilicate (LSO) based animal PET system. The SPECT acquisition was enabled by inserting a collimator assembly inside the detector ring and acquiring data in singles mode. The same LSO detectors were used for both PET and SPECT imaging. The intrinsic radioactivity of 176Lu in the LSO crystals, however, contaminates the SPECT data, and can generate image artifacts and introduce quantification error. The objectives of this study were to evaluate the effectiveness of a LSO background subtraction method, and to estimate the minimal detectable target activity (MDTA) of image object for SPECT imaging. For LSO background correction, the LSO contribution in an image study was estimated based on a pre-measured long LSO background scan and subtracted prior to the image reconstruction. The MDTA was estimated in two ways. The empirical MDTA (eMDTA) was estimated from screening the tomographic images at different activity levels. The calculated MDTA (cMDTA) was estimated from using a formula based on applying a modified Currie equation on an average projection dataset. Two simulated and two experimental phantoms with different object activity distributions and levels were used in this study. The results showed that LSO background adds concentric ring artifacts to the reconstructed image, and the simple subtraction method can effectively remove these artifacts—the effect of the correction was more visible when the object activity level was near or above the eMDTA. For the four phantoms studied, the cMDTA was consistently about five times of the corresponding eMDTA. In summary, we implemented a simple LSO background subtraction method and demonstrated its effectiveness. The projection-based calculation formula yielded MDTA results that closely correlate with that obtained empirically and may have predicative value for imaging applications.
46 citations
••
TL;DR: Respiratory motion can have a substantial impact on dynamic PET in the thorax and abdomen and the INTEX method using continuous external motion data substantially changed parameters in kinetic modeling.
Abstract: Existing respiratory motion-correction methods are applied only to static PET imaging. We have previously developed an event-by-event respiratory motion-correction method with correlations between internal organ motion and external respiratory signals (INTEX). This method is uniquely appropriate for dynamic imaging because it corrects motion for each time point. In this study, we applied INTEX to human dynamic PET studies with various tracers and investigated the impact on kinetic parameter estimation. Methods: The use of 3 tracers—a myocardial perfusion tracer, 82Rb (n = 7); a pancreatic β-cell tracer, 18F-FP(+)DTBZ (n = 4); and a tumor hypoxia tracer, 18F-fluoromisonidazole (18F-FMISO) (n = 1)—was investigated in a study of 12 human subjects. Both rest and stress studies were performed for 82Rb. The Anzai belt system was used to record respiratory motion. Three-dimensional internal organ motion in high temporal resolution was calculated by INTEX to guide event-by-event respiratory motion correction of target organs in each dynamic frame. Time–activity curves of regions of interest drawn based on end-expiration PET images were obtained. For 82Rb studies, K1 was obtained with a 1-tissue model using a left-ventricle input function. Rest–stress myocardial blood flow (MBF) and coronary flow reserve (CFR) were determined. For 18F-FP(+)DTBZ studies, the total volume of distribution was estimated with arterial input functions using the multilinear analysis 1 method. For the 18F-FMISO study, the net uptake rate Ki was obtained with a 2-tissue irreversible model using a left-ventricle input function. All parameters were compared with the values derived without motion correction. Results: With INTEX, K1 and MBF increased by 10% ± 12% and 15% ± 19%, respectively, for 82Rb stress studies. CFR increased by 19% ± 21%. For studies with motion amplitudes greater than 8 mm (n = 3), K1, MBF, and CFR increased by 20% ± 12%, 30% ± 20%, and 34% ± 23%, respectively. For 82Rb rest studies, INTEX had minimal effect on parameter estimation. The total volume of distribution of 18F-FP(+)DTBZ and Ki of 18F-FMISO increased by 17% ± 6% and 20%, respectively. Conclusion: Respiratory motion can have a substantial impact on dynamic PET in the thorax and abdomen. The INTEX method using continuous external motion data substantially changed parameters in kinetic modeling. More accurate estimation is expected with INTEX.
37 citations
••
TL;DR: A new method has been developed that requires only a uniform flood source to irradiate a crystal array without the need to locate the interaction positions, and calculates DOI functions based solely on the uniform probability distribution of interactions over DOI positions without knowledge or assumption of detector responses.
Abstract: The detection of depth-of-interaction (DOI) is a critical detector capability to improve the PET spatial resolution uniformity across the field-of-view and will significantly enhance, in particular, small bore system performance for brain, breast, and small animal imaging. One promising technique of DOI detection is to use dual-ended-scintillator readout that uses two photon sensors to detect scintillation light from both ends of a scintillator array and estimate DOI based on the ratio of signals (similar to Anger logic). This approach needs a careful DOI function calibration to establish accurate relationship between DOI and signal ratios, and to recalibrate if the detection condition is shifted due to the drift of sensor gain, bias variations, or degraded optical coupling, etc. However, the current calibration method that uses coincident events to locate interaction positions inside a single scintillator crystal has severe drawbacks, such as complicated setup, long and repetitive measurements, and being prone to errors from various possible misalignments among the source and detector components. This method is also not practically suitable to calibrate multiple DOI functions of a crystal array. To solve these problems, a new method has been developed that requires only a uniform flood source to irradiate a crystal array without the need to locate the interaction positions, and calculates DOI functions based solely on the uniform probability distribution of interactions over DOI positions without knowledge or assumption of detector responses. Simulation and experiment have been studied to validate the new method, and the results show that the new method, with a simple setup and one single measurement, can provide consistent and accurate DOI functions for the entire array of multiple scintillator crystals. This will enable an accurate, simple, and practical DOI function calibration for the PET detectors based on the design of dual-ended-scintillator readout. In addition, the new method can be generally applied to calibrating other types of detectors that use the similar dual-ended readout to acquire the radiation interaction position.
31 citations
••
TL;DR: A scatter and crosstalk correction method for (99m)Tc/(123)I dual-radionuclide imaging for a CZT-based dedicated cardiac SPECT system with pinhole collimators and is validated using Monte Carlo simulation, line source experiment, anthropomorphic torso phantom studies, and patient studies.
Abstract: The energy spectrum for a cadmium zinc telluride (CZT) detector has a low energy tail due to incomplete charge collection and intercrystal scattering. Due to these solid-state detector effects, scatter would be overestimated if the conventional triple-energy window (TEW) method is used for scatter and crosstalk corrections in CZT-based imaging systems. The objective of this work is to develop a scatter and crosstalk correction method for (99m)Tc/(123)I dual-radionuclide imaging for a CZT-based dedicated cardiac SPECT system with pinhole collimators (GE Discovery NM 530c/570c).
26 citations
Cited by
More filters
••
TL;DR: The key performance properties of SPECT detectors and survey developments in both scintillator and semiconductor detectors and their readouts are discussed with an eye toward some of the practical issues at least in part responsible for the continuing prevalence of the Anger Camera in the clinic.
Abstract: The development of radiation detectors capable of delivering spatial information about gamma-ray interactions was one of the key enabling technologies for nuclear medicine imaging and, eventually, single-photon emission computed tomography (SPECT). The continuous sodium iodide scintillator crystal coupled to an array of photomultiplier tubes, almost universally referred to as the Anger Camera after its inventor, has long been the dominant SPECT detector system. Nevertheless, many alternative materials and configurations have been investigated over the years. Technological advances as well as the emerging importance of specialized applications, such as cardiac and preclinical imaging, have spurred innovation such that alternatives to the Anger Camera are now part of commercial imaging systems. Increased computing power has made it practical to apply advanced signal processing and estimation schemes to make better use of the information contained in the detector signals. In this review we discuss the key performance properties of SPECT detectors and survey developments in both scintillator and semiconductor detectors and their readouts with an eye toward some of the practical issues at least in part responsible for the continuing prevalence of the Anger Camera in the clinic.
193 citations
••
11 Jan 2018-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, a review and discussion of the state of the art for all techniques using prompt-gamma detection to improve the quality assurance in hadrontherapy is presented.
Abstract: Secondary radiation emission induced by nuclear reactions is correlated to the path of ions in matter. Therefore, such penetrating radiation can be used for in vivo control of hadrontherapy treatments, for which the primary beam is absorbed inside the patient. Among secondary radiations, prompt-gamma rays were proposed for real-time verification of ion range. Such a verification is a desired condition to reduce uncertainties in treatment planning. For more than a decade, efforts have been undertaken worldwide to promote prompt-gamma-based devices to be used in clinical conditions. Dedicated cameras are necessary to overcome the challenges of a broad- and high-energy distribution, a large background, high instantaneous count rates, and compatibility constraints with patient irradiation. Several types of prompt-gamma imaging devices have been proposed, that are either physically-collimated or electronically collimated (Compton cameras). Clinical tests are now undergoing. Meanwhile, other methods than direct prompt-gamma imaging were proposed, that are based on specific counting using either time-of-flight or photon energy measurements. In the present article, we make a review and discuss the state of the art for all techniques using prompt-gamma detection to improve the quality assurance in hadrontherapy.
178 citations
••
TL;DR: This paper summarized the recent developments of deep learning-based methods in inter- and intra-modality image synthesis by listing and highlighting the proposed methods, study designs, and reported performances with related clinical applications on representative studies.
Abstract: This paper reviewed the deep learning-based studies for medical imaging synthesis and its clinical application. Specifically, we summarized the recent developments of deep learning-based methods in inter- and intra-modality image synthesis by listing and highlighting the proposed methods, study designs, and reported performances with related clinical applications on representative studies. The challenges among the reviewed studies were then summarized with discussion.
137 citations
••
TL;DR: A UAV-enabled IoE (Ue-IoE) solution is introduced by exploiting UAVs’s mobility, in which it is shown that Ue-ioE can greatly enhance the scalability, intelligence and diversity of IoE.
134 citations
••
TL;DR: Novel imaging combinations are being considered that would enable simultaneous, or at least concurrent, dual-modality imaging through combined PET/MR or PET/CT, and the development of these new integrated instruments creates new bewildering challenges for PET detection systems, which must satisfy several other critical requirements.
Abstract: Positron emission tomography (PET) is the most sensitive of all medical imaging modalities for quantitatively probing biologic processes at the molecular level. However, spatial resolution in PET is significantly inferior to that of other imaging modalities that can provide exquisite images of the anatomy, such as X-ray computed tomography (CT) or magnetic resonance (MR) imaging. It has been one of the outstanding challenges of the last decade to combine PET with these complementary imaging modalities in order to synergistically exploit the benefits of each modality and to enhance the role of PET in pre-clinical research as well as in clinical routine and research. The simple juxtaposition of tomographs around a common axial bed, such as with current PET/CT technology, is very successful in allowing sequential acquisition of PET and anatomical data. However, novel imaging combinations are being considered that would enable simultaneous, or at least concurrent, dual-modality imaging through combined PET/MR or PET/CT. The development of these new integrated instruments creates new bewildering challenges for PET detection systems, which, in addition to the ability to measure annihilation radiation in PET, must satisfy several other critical requirements.
124 citations