Low Photon Count Research Articles

Ultra-Fast Hybrid CPU–GPU Multiple Scatter Simulation for 3-D PET

Scatter correction is very important in 3-D PET reconstruction due to a large scatter contribution in measurements. Currently, one of the most popular methods is the so-called single scatter simulation (SSS), which considers single Compton scattering contributions from many randomly distributed scatter points. The SSS enables a fast calculation of scattering with a relatively high accuracy; however, the accuracy of SSS is dependent on the accuracy of tail fitting to find a correct scaling factor, which is often difficult in low photon count measurements. To overcome this drawback as well as to improve accuracy of scatter estimation by incorporating multiple scattering contribution, we propose a multiple scatter simulation (MSS) based on a simplified Monte Carlo (MC) simulation that considers photon migration and interactions due to photoelectric absorption and Compton scattering. Unlike the SSS, the MSS calculates a scaling factor by comparing simulated prompt data with the measured data in the whole volume, which enables a more robust estimation of a scaling factor. Even though the proposed MSS is based on MC, a significant acceleration of the computational time is possible by using a virtual detector array with a larger pitch by exploiting that the scatter distribution varies slowly in spatial domain. Furthermore, our MSS implementation is nicely fit to a parallel implementation using graphic processor unit (GPU). In particular, we exploit a hybrid CPU-GPU technique using the open multiprocessing and the compute unified device architecture, which results in 128.3times faster than using a single CPU. Overall, the computational time of MSS is 9.4s for a high-resolution research tomograph (HRRT) system. The performance of the proposed MSS is validated through actual experiments using an HRRT.

High speed, high fidelity detection of an atomic hyperfine qubit

Fast and efficient detection of the qubit state in trapped ion systems is critical for implementing quantum error correction and performing fundamental tests such as a loophole-free Bell test. In this work we present a simple qubit state detection protocol for a (171)Yb+ hyperfine atomic qubit trapped in a microfabricated surface trap, enabled by high collection efficiency of the scattered photons and low background photon count rate. We demonstrate average detection times of 10.5, 28.1, and 99.8 μs, corresponding to state detection fidelities of 99%, 99.856(8)%, and 99.915(7)%, respectively.

Denoising three-dimensional and colored images using a Bayesian multi-scale model for photon counts

X-ray images of distant stars and galaxies are typically registered by low photon counts at the pixel level, for which the Poisson distribution is a sensible model description. The resulting count data can be represented in a multi-scale framework, where the likelihood function factorizes in functions of relative intensity parameters corresponding to different levels from the whole frame down to the pixel level. In a Bayesian approach, a prior is assigned on these relative intensity parameters independently across levels and the image is reconstructed using the posterior mean of intensity parameter of each pixel. A novel prior which allows ties in the values of relative intensity parameters of neighboring regions has been recently shown to be very successful in finding structures in images. We extend this idea to reconstruct colored images from noisy data. The proposed method is completely data-driven, since all smoothing parameters are automatically estimated from the data without any additional user input. In the context of astronomical X-ray images, color represents the energy level of photons, which are also typically recorded by telescopes. The energy level can be considered as the third dimension of images. In a more general sense, the technique we develop applies to all three dimensional images, and can be used to process medical images as well.

Experimental results from Al/p-CdTe/Pt X-ray detectors

Recently, Al/CdTe/Pt detectors have been proposed for the development of high resolution X-ray spectrometers. Due to the low leakage currents, these detectors allow high electric fields and the pixellization of anodes with the possibility to realize single charge carrier sensing detectors. In this work, we report on the results of electrical and spectroscopic investigations on CdTe diode detectors with Al/CdTe/Pt electrode configuration (4.1×4.1×0.75 and 4.1×4.1×2mm3). The detectors are characterized by very low leakage currents in the reverse bias operation: 0.3nA at 25°C and 2.4pA at −25°C under a bias voltage of −1000V. The spectroscopic performance of the detectors at both low and high photon counting rates were also investigated with a focus on the minimization of time instability, generally termed as polarization, looking for the optimum bias voltage and temperature. Good time stability, during a long-term operation of 10h, was observed for both detectors at −25°C and by using an electric field of 5000V/cm. The 2mm thick detector exhibited good energy resolution of 6.1%, 2.5% and 2.0% (FWHM) at 22.1keV, 59.5 and 122.1keV, respectively. Performance enhancements were obtained by using digital pulse processing techniques, especially at high photon counting rates (300kcps). The 2mm thick detector, after a digital pulse shape correction (PSC), is characterized by similar performance to the thin detector ones, opening up to the use of thick CdTe detectors without excessive performance degradations. This work was carried out in the framework of the development of portable X-ray spectrometers for both laboratory research and medical applications.

Reducing Poisson noise and baseline drift in x-ray spectral images with bootstrap Poisson regression and robust nonparametric regression

X-ray spectral imaging provides quantitative imaging of trace elements in a biological sample with high sensitivity. We propose a novel algorithm to promote the signal-to-noise ratio (SNR) of x-ray spectral images that have low photon counts. Firstly, we estimate the image data area that belongs to the homogeneous parts through confidence interval testing. Then, we apply the Poisson regression through its maximum likelihood estimation on this area to estimate the true photon counts from the Poisson noise corrupted data. Unlike other denoising methods based on regression analysis, we use the bootstrap resampling method to ensure the accuracy of regression estimation. Finally, we use a robust local nonparametric regression method to estimate the baseline and subsequently subtract it from the x-ray spectral data to further improve the SNR of the data. Experiments on several real samples show that the proposed method performs better than some state-of-the-art approaches to ensure accuracy and precision for quantitative analysis of the different trace elements in a standard reference biological sample.

Evaluation of powder/granular Gd2O2S:Pr scintillator screens in single photon counting mode under 140 keV excitation

The aim of this paper is the evaluation of analternative, low cost solution for the gamma detector in planar imaging. Itis based on a powder scintillator, well established in X-ray imaging, andcould be further exploited in simultaneous bimodal imaging systems. For thispurpose, we have examined the performance of Gd2O2S:Pr powderscintillator, in the form of thick granular screens easily produced in thelaboratory by commercially available Gd2O2S:Pr powder. The screenwas coupled to a round position sensitive photomultiplier tube (R3292PSPMT). The system's evaluation was performed in photon counting mode under99mTc excitation. In all measurements, a general purpose hexagonalparallel collimator was used. Different samples of screens with coatingthickness varying from 0.1 g/cm2 to 1.2 g/cm2 were tested. The 0.6g/cm2 screen, corresponding to ∼ 2 mm actual thickness, was foundmost efficient under 140 keV irradiation. The system`s performance with theproposed screen is reported with the modulation transfer function. Moreoversensitivity, spatial and energy resolution as well as the uniformityresponse using phantoms were measured. The performance of the proposedscreen was compared with two CsI:Tl pixellated crystal arrays with 2 × 2 × 3 mm3 and 3 × 3 × 5 mm3pixel size. A spatial resolution,of 3 mm FWHM, for a 99mTc line source, was achieved at zero source tocollimator distance. In addition, the Gd2O2S:Pr screen showed aslower degradation of the spatial resolution with increasing source tocollimator distance e.g at 20 cm, the Gd2O2S:Pr screen showed aqspatial resolution of 8.4 mm while the spatial resolution of the pixellatedcrystals was 15 mm. Taking into account its easy production, its flexibilitydue to powder form, the very low cost and the good spatial resolutionproperties of the proposed alternative detector, powder scintillators couldpotentially be used for the construction of flexible detector geometries,such as ring type or gamma probes or as a low cost detector solution ineducational photon counting imaging applications, complementary to standardX-ray imaging.

Denoising of Magnetic Resonance and X-Ray Images Using Variance Stabilization and Patch Based Algorithms

Developments in Medical imaging systems which are providing the anatomical and physiological details of the patients made the diagnosis simple day by day. But every medical imaging modality suffers from some sort of noise. Noise in medical images will decrease the contrast in the image, due to this effect low contrast lesions may not be detected in the diagnostic phase. So the removal of noise from medical images is very important task. In this paper we are presenting the Denoising techniques developed for removing the poison noise from X-ray images due to low photon count and Rician noise from the MRI (magnetic resonance images). The Poisson and Rician noise are data dependent so they won’t follow the Gaussian distribution most of the times. In our algorithm we are converting the Poisson and Rician noise distribution into Gaussian distribution using variance stabilization technique and then we used the patch based algorithms for denoising the images. The performance of the algorithms was evaluated using various image quality metrics such as PSNR (Peak signal to noise ratio), UQI (Universal Quality Index), SSIM (Structural similarity index) etc. The results proved that the Anscombe transform, Freeman & Tukey transform with block matching 3D algorithm is giving a better result.

Wavefront phase retrieval with non-linear curvature sensors

Increasing interest in astronomical applications of non-linear curvature wavefront sensors for turbulence detection and correction makes it important to understand how best to handle the data they produce, particularly at low light levels. Algorithms for wavefront phase retrieval from a four-plane CWFS are developed and compared, with a view to their use for low-order phase compensation in instruments combining adaptive optics and Lucky Imaging. The convergence speed and quality of iterative algorithms is compared to their step-size, and techniques for phase retrieval at low photon counts are explored. Computer simulations show that at low light levels, preprocessing by convolution of the measured signal with a Gaussian function can reduce by an order of magnitude the photon flux required for accurate phase retrieval of low-order errors. This facilitates wavefront correction on large telescopes with very faint reference stars.

Direct measurement of mammographic X-ray spectra with a digital CdTe detection system.

In this work we present a detection system, based on a CdTe detector and an innovative digital pulse processing (DPP) system, for high-rate X-ray spectroscopy in mammography (1–30 keV). The DPP system performs a height and shape analysis of the detector pulses, sampled and digitized by a 14-bit, 100 MHz ADC. We show the results of the characterization of the detection system both at low and high photon counting rates by using monoenergetic X-ray sources and a nonclinical X-ray tube. The detection system exhibits excellent performance up to 830 kcps with an energy resolution of 4.5% FWHM at 22.1 keV. Direct measurements of clinical molybdenum X-ray spectra were carried out by using a pinhole collimator and a custom alignment device. A comparison with the attenuation curves and the half value layer values, obtained from the measured and simulated spectra, from an ionization chamber and from a solid state dosimeter, also shows the accuracy of the measurements. These results make the proposed detection system a very attractive tool for both laboratory research, calibration of dosimeters and advanced quality controls in mammography.

Methodological considerations for global analysis of cellular FLIM/FRET measurements

Global algorithms can improve the analysis of fluorescence energy transfer (FRET) measurement based on fluorescence lifetime microscopy. However, global analysis of FRET data is also susceptible to experimental artifacts. This work examines several common artifacts and suggests remedial experimental protocols. Specifically, we examined the accuracy of different methods for instrument response extraction and propose an adaptive method based on the mean lifetime of fluorescent proteins. We further examined the effects of image segmentation and a priori constraints on the accuracy of lifetime extraction. Methods to test the applicability of global analysis on cellular data are proposed and demonstrated. The accuracy of global fitting degrades with lower photon count. By systematically tracking the effect of the minimum photon count on lifetime and FRET prefactors when carrying out global analysis, we demonstrate a correction procedure to recover the correct FRET parameters, allowing us to obtain protein interaction information even in dim cellular regions with photon counts as low as 100 per decay curve.

Ultrafast fiber lasers for strong‐field physics experiments

AbstractThe recent demonstration of rare‐earth‐doped fiber lasers with a continuous‐wave output power approaching the 10‐kW level with diffraction‐limited beam quality proves that fiber lasers constitute a scalable solid‐state laser concept in terms of average power. In order to generate high peak power pulses from a fiber several fundamental limitations have to be overcome. This can be achieved by novel experimental strategies and fiber designs that offer an enormous potential towards ultrafast laser systems combining high average powers (> kW) and high peak power (> GW). In this paper the challenges, achievements and perspectives of ultrashort pulse generation and amplification in fibers are reviewed. This kind of laser system will have a tremendous impact on strong‐field physics experiments, such as the generation of coherent light by high‐harmonic generation. So far, applications in the interesting EUV spectral range suffer from the very low photon count leading to nonrelevant integration times with highly sophisticated detection schemes. High repetition rate high average power fiber lasers can potentially solve this issue. First demonstrations of high repetition‐rate strong‐field physics experiments using novel fiber laser systems will be discussed.

Single Molecule Fluorescence Image Patterns Linked to Dipole Orientation and Axial Position: Application to Myosin Cross-Bridges in Muscle Fibers

BackgroundPhotoactivatable fluorescent probes developed specifically for single molecule detection extend advantages of single molecule imaging to high probe density regions of cells and tissues. They perform in the native biomolecule environment and have been used to detect both probe position and orientation.Methods and FindingsFluorescence emission from a single photoactivated probe captured in an oil immersion, high numerical aperture objective, produces a spatial pattern on the detector that is a linear combination of 6 independent and distinct spatial basis patterns with weighting coefficients specifying emission dipole orientation. Basis patterns are tabulated for single photoactivated probes labeling myosin cross-bridges in a permeabilized muscle fiber undergoing total internal reflection illumination. Emitter proximity to the glass/aqueous interface at the coverslip implies the dipole near-field and dipole power normalization are significant affecters of the basis patterns. Other characteristics of the basis patterns are contributed by field polarization rotation with transmission through the microscope optics and refraction by the filter set. Pattern recognition utilized the generalized linear model, maximum likelihood fitting, for Poisson distributed uncertainties. This fitting method is more appropriate for treating low signal level photon counting data than χ2 minimization.ConclusionsResults indicate that emission dipole orientation is measurable from the intensity image except for the ambiguity under dipole inversion. The advantage over an alternative method comparing two measured polarized emission intensities using an analyzing polarizer is that information in the intensity spatial distribution provides more constraints on fitted parameters and a single image provides all the information needed. Axial distance dependence in the emission pattern is also exploited to measure relative probe position near focus. Single molecule images from axial scanning fitted simultaneously boost orientation and axial resolution in simulation.

Dipole Emitter Lateral Point Spread Function Communicates Orientation and Axial Position

Photoactivatable fluorescent probes developed specifically for single molecule detection extend advantages of single molecule imaging to high probe density regions of cells and tissues. They perform in the native biomolecule environment and have been used to detect both probe position and orientation. Native, high density, single molecule detection may have added significance if molecular crowding impacts biomolecule behavior as expected inside the cell. Fluorescence emission from a single photoactivated probe captured in an oil immersion, high numerical aperture objective, produces a spatial pattern on the detector that is a linear combination of 4 independent and distinct spatial basis patterns with weighting coefficients specifying emission dipole orientation. Basis patterns are tabulated for single photoactivated probes labeling myosin cross-bridges in a permeabilized muscle fiber undergoing total internal reflection (TIR) illumination. Emitter proximity to the glass/water interface at the coverslip implies the dipole near field and dipole power normalization are significant affecters of the basis patterns. Other characteristics of the basis patterns are contributed by field polarization rotation with transmission through the microscope optics. Pattern recognition utilizes the generalized linear model (GLM), maximum likelihood fitting, for Poisson distributed uncertainties. This fitting method is more appropriate for treating low signal level photon counting data than χ2 minimization. Results indicate that emission dipole orientation is measurable from the intensity image except for the ambiguity under dipole inversion. The advantage over an alternative method comparing two measured polarized emission intensities using an analyzing polarizer is that information in the intensity spatial distribution provides more constraints on fitted parameters and a single image provides all the information needed. Also, axial distance dependence in the emission pattern is exploited to measure relative probe position near focus. Supported by NIH NIAMS and NHLBI grants R01AR049277 and R01HL095572.

Photon event distribution sampling: an image formation technique for scanning microscopes that permits tracking of sub-diffraction particles with high spatial and temporal resolutions

In photon event distribution sampling, an image formation technique for scanning microscopes, the maximum likelihood position of origin of each detected photon is acquired as a data set rather than binning photons in pixels. Subsequently, an intensity-related probability density function describing the uncertainty associated with the photon position measurement is applied to each position and individual photon intensity distributions are summed to form an image. Compared to pixel-based images, photon event distribution sampling images exhibit increased signal-to-noise and comparable spatial resolution. Photon event distribution sampling is superior to pixel-based image formation in recognizing the presence of structured (non-random) photon distributions at low photon counts and permits use of non-raster scanning patterns. A photon event distribution sampling based method for localizing single particles derived from a multi-variate normal distribution is more precise than statistical (Gaussian) fitting to pixel-based images. Using the multi-variate normal distribution method, non-raster scanning and a typical confocal microscope, localizations with 8 nm precision were achieved at 10 ms sampling rates with acquisition of ~200 photons per frame. Single nanometre precision was obtained with a greater number of photons per frame. In summary, photon event distribution sampling provides an efficient way to form images when low numbers of photons are involved and permits particle tracking with confocal point-scanning microscopes with nanometre precision deep within specimens.

Structure of isolated biomolecules obtained from ultrashort x-ray pulses: exploiting thesymmetry of random orientations

Amongst the promised capabilities of fourth-generation x-ray sources currentlyunder construction is the ability to record diffraction patterns from individualbiological molecules. One version of such an experiment would involve directing astream of molecules into the x-ray beam and sequentially recording the scatteringfrom each molecule of a short, but intense, pulse of radiation. The pulses aresufficiently short that the diffraction pattern is that due to scattering from identicalmolecules ‘frozen’ in random orientations. Each diffraction pattern may be thoughtof as a section through the 3D reciprocal space of the molecule, of unknown,random, orientation. At least two algorithms have been proposed for finding therelative orientations from just the measured diffraction data. The ‘common-line’method, also employed in 3D electron microscopy, appears not best suited tothe very low mean photon count per diffraction pattern pixel expected in suchexperiments. A manifold embedding technique has been used to reconstruct the3D diffraction volume and hence the electron density of a small protein at thesignal level expected of the scattering of an x-ray free electron laser pulse from a500 kD biomolecule. In this paper, we propose an alternative algorithm whichraises the possibility of reconstructing the 3D diffraction volume of a moleculewithout determining the relative orientations of the individual diffraction patterns.We discuss why such an algorithm may provide a practical and computationallyconvenient method of extracting information from very weak diffraction patterns. Wesuggest also how such a method may be adapted to the problem of finding thevariations of a structure with time in a time-resolved pump–probe experiment.

Multiphoton time-domain fluorescence lifetime imaging microscopy: practical application to protein–protein interactions using global analysis

Förster resonance energy transfer (FRET) detected via fluorescence lifetime imaging microscopy (FLIM) and global analysis provide a way in which protein–protein interactions may be spatially localized and quantified within biological cells. The FRET efficiency and proportion of interacting molecules have been determined using bi-exponential fitting to time-domain FLIM data from a multiphoton time-correlated single-photon counting microscope system. The analysis has been made more robust to noise and significantly faster using global fitting, allowing higher spatial resolutions and/or lower acquisition times. Data have been simulated, as well as acquired from cell experiments, and the accuracy of a modified Levenberg–Marquardt fitting technique has been explored. Multi-image global analysis has been used to follow the epidermal growth factor-induced activation of Cdc42 in a short-image-interval time-lapse FLIM/FRET experiment. Our implementation offers practical analysis and time-resolved-image manipulation, which have been targeted towards providing fast execution, robustness to low photon counts, quantitative results and amenability to automation and batch processing.

Edge-Preserving Filtering of Images with Low Photon Counts

Edge-preserving filters such as local M-smoothers or bilateral filtering are usually designed for Gaussian noise. This paper investigates how these filters can be adapted in order to efficiently deal with Poissonian noise. In addition, the issue of photometry invariance is addressed by changing the way filter coefficients are normalized. The proposed normalization is additive, instead of being multiplicative, and leads to a strong connection with anisotropic diffusion. Experiments show that ensuring the photometry invariance leads to comparable denoising performances in terms of the root mean square error computed on the signal.

Spectrally resolved fluorescence lifetime imaging microscopy (SFLIM)—an appropriate method for imaging single molecules in living cells

Ever since the first examination of cellular structures, scientists have been fascinated by investigations of single cells. Over the last decade, many methods (e.g., capillary electrophoresis, electrochemical detection, mass spectroscopy, and optical spectroscopy) have been proposed for analyzing single cells [1]. Many of these methods are appropriate for in vitro experiments, which provide only a snapshot view of cells. However, some optical methods, like fluorescence spectroscopy, are also advanced enough for investigations of living cells. This is due to their simple application without the need for fixation or lysis of the respective cell. A variety of light microscopy techniques for imaging living cells, such as widefield excitation, confocal scanning and total internal reflection excitation, have been reviewed by D. J. Stephens and V. J. Allan [2]. The fluorescently labeled components required (e.g., proteins or DNA) can be added to the cell culture medium, from where they are taken up by the cells if the components are able to pass through the cell membrane. Alternatively, they can be directly injected into living cells via micropipets. Due to their toxicity, the concentration of the fluorescent dye should be as low as possible. This can be achieved by using single-molecule detection techniques that enable the measurement of low concentrations (approximately 10 M) of chromophores in homogeneous solutions and of individual immobilized molecules. In 2001, Sauer at al. established spectrally resolved fluorescence lifetime imaging microscopy (SFLIM) [3], which uses a standard confocal microscope set-up (Fig. 1a). For this technique, a pulsed laser diode with a wavelength of usually 635 nm and a repetition rate of 40–80 MHz is used. The laser beam is coupled into an oil immersion objective and focused onto the sample surface on a scanning table. Generally, the average excitation power is adjusted to 0.25–5 kW/cm. The fluorescence light emitted by the sample is collected by the same objective and focused onto a pinhole with a diameter of 50–100 μm. Fluorescence light passing through the pinhole is spectrally separated by a dichroic beam splitter and detected by two avalanche photodiodes. To generate fluorescence lifetime images, the signals from the two avalanche photodiodes are recorded by a timecorrelated single-photon counting interface card and the data are analyzed by applying a maximum likelihood estimator (MLE) algorithm, which is an appropriate method of determining monoexponential fluorescence lifetimes from low photon count statistics. Figures 1b–d show images of an untreated living cell (3T3 mouse fibroblast) in RPMI 1640 medium recorded by SFLIM [4]. The first image (Fig. 1b) shows the overall fluorescence intensity. The cell culture medium exhibits a constant background with a count rate of approximately 4 kHz, which is due to autofluorescence of the fetal calf serum (which is in the medium), whereas the cell itself shows lower autofluorescence. Some more intense signals occur in the cytoplasm arising from the Anal Bioanal Chem (2007) 387:37–40 DOI 10.1007/s00216-006-0762-1

Multiple-image radiography

Conventional radiography produces a single image of an object by measuring the attenuation of an x-ray beam passing through it. When imaging weakly absorbing tissues, x-ray attenuation may be a suboptimal signature of disease-related information. In this paper we describe a new phase-sensitive imaging method, called multiple-image radiography (MIR), which is an improvement on a prior technique called diffraction-enhanced imaging (DEI). This paper elaborates on our initial presentation of the idea in Wernick et al (2002 Proc. Int. Symp. Biomed. Imaging pp 129–32). MIR simultaneously produces several images from a set of measurements made with a single x-ray beam. Specifically, MIR yields three images depicting separately the effects of refraction, ultra-small-angle scatter and attenuation by the object. All three images have good contrast, in part because they are virtually immune from degradation due to scatter at higher angles. MIR also yields a very comprehensive object description, consisting of the angular intensity spectrum of a transmitted x-ray beam at every image pixel, within a narrow angular range. Our experiments are based on data acquired using a synchrotron light source; however, in preparation for more practical implementations using conventional x-ray sources, we develop and evaluate algorithms designed for Poisson noise, which is characteristic of photon-limited imaging. The results suggest that MIR is capable of operating at low photon count levels, therefore the method shows promise for use with conventional x-ray sources. The results also show that, in addition to producing new types of object descriptions, MIR produces substantially more accurate images than its predecessor, DEI. MIR results are shown in the form of planar images of a phantom and a biological specimen. A preliminary demonstration of the use of MIR for computed tomography is also presented.

Ultrafast spectroscopy studies on the mechanism of electron transfer and energy conversion in the isolated pseudo ginseng, water hyacinth and spinach chloroplasts

The spectroscopy characteristics and the fluorescence lifetime for the chloroplasts isolated from the pseudo ginseng, water hyacinth and spinach plant leaves have been studied by absorption spectra, low temperature steady-state fluorescence spectroscopy and single photon counting measurement under the same conditions and by the same methods. The similarity of the absorption spectra for the chloroplasts at room temperature suggests that different plants can efficiently absorb light of the same wavelength. The fluorescence decays in PS II measured at the natural QA state for the chloroplasts have been fitted by a three-exponential kinetic model. The three fluorescence lifetimes are 30, 274 and 805 ps for the pseudo ginseng chloroplast; 138, 521 and 1494 ps for the water hyacinth chloroplast; 197, 465 and 1459 ps for the spinach chloroplast, respectively. The slow lifetime fluorescence component is assigned to a collection of associated light harvesting Chl a/b proteins, the fast lifetime component to the reaction center of PS II and the middle lifetime component to the delay fluorescence of recombination of P+ 680 and Pheo-. The excitation energy conversion efficiency(η) in PS II RC is defined and calculated on the basis of the 20 ps electron transfer time constant model, 60%, 87% and 91% for the pseudo ginseng, water hyacinth and spinach chloroplasts, respectively. This interesting result is in unconformity with what is assumed to be 100% efficiency in PS II RC. Our result in this work stands in line with the 20 ps electron transfer time constant in PS II rather sound and the water hyacinth plant grows slower than the spinach plant does as envisaged on the efficiency. But, our results predict that those plants can perform highly efficient transfer of photo-excitation energy from the light-harvesting pigment system to the reaction center (closely to 100%). The conclusion contained in this paper reveals the plant growth characteristics expressed in the primary processes of photosynthesis and a relationship between a plant growing rate and its spectroscopy characteristics and fluorescence lifetimes, namely, the slower a plant grows, the less excitation energy conversation efficiency used might be anticipated.