Rong Zhou

Bio: Rong Zhou is an academic researcher from Tsinghua University. The author has contributed to research in topics: Detector & Scintillation. The author has an hindex of 4, co-authored 5 publications receiving 53 citations.

A SVD-Based Method to Assess the Uniqueness and Accuracy of SPECT Geometrical Calibration

Abstract: Geometrical calibration is critical to obtaining high resolution and artifact-free reconstructed image for SPECT and CT systems. Most published calibration methods use analytical approach to determine the uniqueness condition for a specific calibration problem, and the calibration accuracy is often evaluated through empirical studies. In this work, we present a general method to assess the characteristics of both the uniqueness and the quantitative accuracy of the calibration. The method uses a singular value decomposition (SVD) based approach to analyze the Jacobian matrix from a least-square cost function for the calibration. With this method, the uniqueness of the calibration can be identified by assessing the nonsingularity of the Jacobian matrix, and the estimation accuracy of the calibration parameters can be quantified by analyzing the SVD components. A direct application of this method is that the efficacy of a calibration configuration can be quantitatively evaluated by choosing a figure-of-merit, e.g., the minimum required number of projection samplings to achieve desired calibration accuracy. The proposed method was validated with a slit-slat SPECT system through numerical simulation studies and experimental measurements with point sources and an ultra-micro hot-rod phantom. The predicted calibration accuracy from the numerical studies was confirmed by the experimental point source calibrations at ~ 0.1nmm for both the center of rotation (COR) estimation of a rotation stage and the slit aperture position (SAP) estimation of a slit-slat collimator by an optimized system calibration protocol. The reconstructed images of a hot rod phantom showed satisfactory spatial resolution with a proper calibration and showed visible resolution degradation with artificially introduced 0.3 mm COR estimation error. The proposed method can be applied to other SPECT and CT imaging systems to analyze calibration method assessment and calibration protocol optimization.

A simple smart time-to-digital convertor based on vernier method for a high resolution LYSO MicroPET

Abstract: We proposed a new and low cost design of time-to-digital converter (TDC) based on Vernier method using only one FPGA EPF10K30ATI144-3 with 13 ns timing resolution performance Neither ECL (emitter-coupled logic) circuit nor high frequency clock was used in this design, which greatly reduced the complication and the power supply We used two oscillators with slightly different frequencies to measure small time interval All the time-to-digital converter functions were implemented on only one low-cost Altera FLEX II Family device Our preliminary results showed: 1) Vernier TDC had a less than 13 ns timing resolution that met the demand for coincidence measurement for LYSO MicroPET 2) No inacceptable degradation was observed in time resolution as of the number of the sliding jaw clock circulations was increased before coincidence 3) Vernier TDC accomplished on FPGA had good stability with temperature In a sum, we made a sufficient proof of high resolution and good stability of the proposed Vernier TDC design Now, we are planning to achieve higher time resolution and higher stability by high-performance FPGA using this smart Vernier TDC method And such simple design is being applied to our animal PET

A Fast Accuracy Crystal Identification Method Based on Fuzzy C-Means (FCM) Clustering Algorithm for MicroPET

Abstract: A high resolution detector is being developed for our small animal position emission tomography (MicroPET) The detector unit consist of 8x8 crystal blocks, coupled to four photomultiplier tubes (PMTs) Each scintillation event is mapped in a two dimensional (2-D) position through the relative ratio of the output signals of the PMTs Crystal Look-up table (CLT) used in ThuMicroPET scanner defines the matching relation between signal position of a detected event to a corresponding detector pixel location It has a direct impact on imaging quality and brings significant influence to the gantry overall performance However, the currently used method involves a lot of human interaction for CLT corrections, and cannot be implemented as a general process due to its complexity This paper introduces a fast accuracy method based on Fuzzy C-Means (FCM) Clustering Algorithm for crystal identification In the FCM, a cluster center and a fuzzy partition matrix of individual events in the 2-D position are defined By iteratively updating the cluster centers and the membership grades for each event, we can move the cluster center to the right location in a short time, based on minimizing objective function that represents the distance from any given events to a cluster center weighted by its membership grade The preliminary result shows that FCM can be used effectively in CLT construction, which significantly reduces the time, and brings excellent accuracy than we expected

A high resolution and high sensitivity small animal SPECT system based on H8500

Abstract: A compact multi-detector SPECT system for small animal (MicroSPECT) has been developed. The detector of MicroSPECT system is composed of a NaI scintillation crystal array and four H8500 flat panel position sensitive photon multiplier tubes(PS-PMT). The pixel size of the scintillation crystal array is 1.45 mmtimes1.45 mm and the total detection area is 103.75 mmtimes103.75 mm with 61times61 pixels. Four H8500 PS-PMTs are jointed together, coupling with the scintillation crystal array. Single pinhole and multi-pinhole collimators are used and special designed to satisfy the need of high spacial resolution or high sensitivity respectively. The DETECT2000 & MCNP Monte Carlo simulation programs were used for verifying the MicroSPECT system detector and pinhole collimator design. A high speed readout circuit was developed for the detectors. Each detector can achieve the counting rate at 300 k/s. The results show that the scintillation crystal array has an effective area of 55times55 pixels and that the joint parts of the PS-PMTs are still available for detection. We aim that the MicroSPECT system can achieve 1 mm spatial resolution or better.

Calibration of pinhole microSPECT system using line sources

Abstract: A method using line sources to calibrate a pinhole MicroSPECT system was proposed Projections' coordinates of "vitual" point sources were obtained by solving equations of centerlines, which were detected out of projection images of line sources by Radon transform Effect of depth of interaction that gamma photons rip into crystals was modeled when calculating the theoretical position of projection Several systems were simulated by Monte Carlo method and calibrated both by the proposed method and by using ideal point sources for comparison Calibration accuracy achieved by the proposed method is comparable to that by using ideal point sources

Development of an ultra-high resolution SPECT system with a CdTe semiconductor detector

Abstract: Objective The aim of this work was to evaluate an ultra-high spatial resolution SPECT system with a semiconductor detector and a high-resolution parallel-hole collimator or a pinhole collimator for small animal imaging.

Derivation of System Matrix From Simulation Data for an Animal SPECT With Slit-Slat Collimator

Abstract: We developed SPECT imaging capability on an animal PET system. Our goal was to provide animal PET users the SPECT capability at a low cost and facilitate potential PET/SPECT dual modality imaging applications. The SPECT function was enabled with a slit-slat collimator insert and by acquiring data in singles mode. The focus of this paper is to establish a method for deriving the system matrix for the SPECT system from Monte Carlo simulation. With the Monte Carlo package GATE, we simulated a uniform cylinder source which filled the SPECT field of view (FOV). To reduce the size of the original large and sparse system matrix, the detectors that were exposed to individual emission elements were selectively included for system matrix derivation and storage. The axial symmetry of the system was exploited so that only the base-axial volume was used for deriving system response. The system matrix derived was validated with point source measurements at known positions and implemented in an iterative reconstruction algorithm. The imaging performance of the system matrix was evaluated with experimental phantom studies. Reconstructed phantom images were artifact free and demonstrated expected spatial resolution. The method presented in this work is generally applicable to other SPECT imaging systems.

A 0.8 ps DNL Time-to-Digital Converter With 250 MHz Event Rate in 65 nm CMOS for Time-Mode-Based Modulator

Abstract: A time-to-digital converter (TDC) is proposed to re- place the multi-bit quantizer and the multi-bit feedback DAC of traditionalvoltage-mode modulator.Sincetime-modesystems process analog signals encoded in the time dimension rather than the voltage dimension, the proposed time-mode TDC makes the multi-bit ADC digital friendly and more suitable for nano- metrictechnologies.Apulse-width-modulator(PWM)convertsthe sampled-and-held voltage-sample to a digital pulse whose width is proportional to the voltage level of the sample. Then, the TDC gen- erates a digital code that corresponds to the pulse width. Simulta- neously, the TDC provides a time-quantized feedback pulse for the modulator, emulating the voltage-DAC in a conventional ADC.Linearity,jitteranddata-dependent-delayeffectsontheper- formance of the proposed architecture are analyzed. A chip proto- typeis fabricated in TI 65 nmdigitalCMOS process. THD of 67 dB is achieved which corresponds to a TDC's DNL of less than 0.8 ps without calibration. Measurements show that the -modulator achievesadynamicrangeof68dBandtheTDCconsumes5.66mW at 250 MHz event rate while occupying 0.006 mm .

A 0.8 ps DNL Time-to-Digital Converter With 250 MHz Event Rate in 65 nm CMOS for Time-Mode-Based $\Sigma \Delta$ Modulator

Abstract: A time-to-digital converter (TDC) is proposed to replace the multi-bit quantizer and the multi-bit feedback DAC of traditional voltage-mode ΣΔ modulator. Since time-mode systems process analog signals encoded in the time dimension rather than the voltage dimension, the proposed time-mode TDC makes the multi-bit ΣΔ ADC digital friendly and more suitable for nanometric technologies. A pulse-width-modulator (PWM) converts the sampled-and-held voltage-sample to a digital pulse whose width is proportional to the voltage level of the sample. Then, the TDC generates a digital code that corresponds to the pulse width. Simultaneously, the TDC provides a time-quantized feedback pulse for the ΣΔ modulator, emulating the voltage-DAC in a conventional ΣΔ ADC. Linearity, jitter and data-dependent-delay effects on the performance of the proposed architecture are analyzed. A chip prototype is fabricated in TI 65 nm digital CMOS process. THD of 67 dB is achieved which corresponds to a TDC's DNL of less than 0.8 ps without calibration. Measurements show that the ΣΔ-modulator achieves a dynamic range of 68 dB and the TDC consumes 5.66 mW at 250 MHz event rate while occupying 0.006 mm2.