CsI Detector Research Articles

Automatic procedure for mass and charge identification of light isotopes detected in CsI(Tl) of the GARFIELD apparatus

Mass and charge identification of light charged particles detected with the 180 CsI(Tl) detectors of the GARFIELD apparatus is presented. A “tracking” method to automatically sample the Z and A ridges of “Fast–Slow” histograms is developed. An empirical analytic identification function is used to fit correlations between Fast and Slow, in order to determine, event by event, the atomic and mass numbers of the detected charged reaction products. A summary of the advantages of the proposed method with respect to “hand-based” procedures is reported.

Monitoring the energy variation of an electron linac using a Cerenkov detector

A new method to monitor the energy variation of a multi-energy electron linac by combining a Cerenkov detector and a CsI(Tl) detector is reported. The signals in the Cerenkov detector show an appreciable but different dependence on the energy of the electron linac from the traditional CsI(Tl) detector due to the particular response of the former to charged electrons with high velocity above threshold. The method is more convenient than the HVL (half-value layer) method which is commonly employed to calibrate the energy of an electron linac for real time monitoring. The preliminary validity of the method is verified in a dual-energy electron linac with 6 MeV and 3 MeV gears. Moreover, the method combining the Cerenkov detector and the CsI(Tl) detector is applicable to probe the X-ray spectrum hardened by the inspected material and may serve as a novel tool for material discrimination with effective atomic number in radiation imaging.

Charged particle identification by pulse shape discrimination with single-sided segmented silicon-pad detectors

A charged particle detector array consisting of 50 Si–CsI detector telescopes for study of heavy-ion reactions is under construction in BARC-TIFR Pelletron-LINAC facility. Single-sided segmented silicon-pad detectors of 300 μm thickness and 400 mm 2 total active area have been fabricated for this purpose and their design parameters along with static and dynamic characteristics are presented. A low-cost solution for implementing the pulse-shape-based particle discrimination technique with the silicon-pad detectors has been demonstrated through in-beam measurements and the results obtained are presented.

A CsI(T1) detector array used in the experiment of the proton-rich nucleus 17Ne

To investigate the configurations of the valence protons in Borromean nucleus 17Ne, a CsI(T1) detector array, which consists of 9 CsI crystals (26 × 26 × 20mm3) coupled with photodiodes, has been successfully used in the 17Ne experiment to measure the energy of protons. In order to find the optimal working conditions and get the best energy resolutions, several technologies (including various wrapping materials, wrapping and coupling methods) have been used. The testing results showed that the best energy resolution of the CsI(T1) is about 3.3% using the 241Am α-source. The primary testing results with the proton beam were also provided.

Probing nonstandard interactions with reactor neutrinos

New limits on the weak mixing angle and on the electron neutrino effective charge radius in the low energy regime, below 100 MeV, are obtained from a combined fit of all electron-(anti)neutrino electron elastic scattering measurements. We have included the recent TEXONO measurement with a CsI (Tl) detector. Only statistical error of this measurement has been taken into account. Weak mixing angle is found to be sin^2 theta_W = 0.255 +0.022 -0.023. The electron neutrino effective charge radius squared is bounded to be r^2 = (0.9 +0.9 -1.0) x 10^{-32} cm^2. The sensitivity of future low energy neutrino experiments to nonstandard interactions of neutrinos with quarks is also discussed.

Radiation surveillance using an unmanned aerial vehicle

Radiation surveillance equipment was mounted in a small unmanned aerial vehicle. The equipment consists of a commercial CsI detector for count rate measurement and a specially designed sampling unit for airborne radioactive particles. Field and flight tests were performed for the CsI detector in the area where 137Cs fallout from the Chernobyl accident is 23–45 kBq m −2. A 3-GBq 137Cs point source could be detected at the altitude of 50 m using a flight speed of 70 km h −1 and data acquisition interval of 1 s. Respective response for 192Ir point source is 1 GBq. During the flight, the detector reacts fast to ambient external dose rate rise of 0.1 μSv h −1, which gives for the activity concentration of 131I less than 1 kBq m −3. Operation of the sampler equipped with different type of filters was investigated using wind-tunnel experiments and field tests with the aid of radon progeny. Air flow rate through the sampler is 0.2–0.7 m 3 h −1 at a flight speed of 70 km h −1 depending on the filter type in question. The tests showed that the sampler is able to collect airborne radioactive particles. Minimum detectable concentration for transuranium nuclides, such as 239Pu, is of the order of 0.2 Bq m −3 or less when alpha spectrometry with no radiochemical sample processing is used for activity determination immediately after the flight. When a gamma-ray spectrometer is used, minimum detectable concentrations for several fission products such as 137Cs and 131I are of the order of 1 Bq m −3.

Light output tuning for the long-length CsI(Tl) scintillators

Control over the mirror reflectivity of scintillator surfaces which is exerted due to imparting a special kind of roughness on crystal surfaces is one of the most technologically relevant, and thus commonly applied techniques of the assigned light output distribution in the detectors. As regards long-sample detectors (the ratio of crystal height to its transverse cross-section varies from 6 to 12), the use of this technique does not guarantee the stable light yield distribution on account of, firstly, the difference in activator concentration over the extent of long sample and, secondly, the local gradient in the activator concentration. This work studies such factors against the example of CsI(Tl) detectors that influence the choice of the effective mirror reflectivity of crystal surfaces. Established were such optimum values of the activator concentration and maximum admissible gradients of Tl ions concentration at which the uniform treatment of the surface guarantees the homogeneity of the light yield within ±0.5%, the sample-to-sample spread not exceeding ±2.5%.

Small Size Integrated CsI(Tl) Spectrometer Efficiency and Properties Dependence on Temperature

Small-sized radiation scintillation detectors have been extensively developed for portable radiation survey systems, for a variety of applications. The CsI(Tl) capacity to discriminate the energy-lines of a gamma-radiation source makes these detectors suitable for personal detection and spectrometry. Additional advantages are their miniature electronics and operation at room temperature. However, it is essential to inspect their efficiency, sensitivity and stability under the practical range of the environmental conditions expected during operation. The aim of this research is to study the changes in the response of a CsI(Tl) detector, 22 mm in diameter and 25 mm long, in the full range of operation temperatures, from -20 to 60 degC . Results show that the photopeak efficiency for the Cs-137 gamma-line remains constant, even though the peak center channel is shifted as function of the detector temperature. The peak spectral resolution was also analyzed in the same temperature range and was found to be around 8%. Since the photopeak efficiency has been constant over the entire tested temperature range, the CsI(Tl) detector is a suitable spectrometry detector for environmental operations.

CsI-detector-based dual-exposure dual energy in chest radiography for lung nodule detection: results of an international multicenter trial

To assess both sensitivity and specificity of digital chest radiography alone and in conjunction with dual-exposure dual-energy chest radiography for the detection and classification of pulmonary nodules. One hundred patients with a total of 149 lung nodules (3-45 mm; median, 11 mm) confirmed by CT were included in this study. Dual-exposure dual-energy chest radiographies of each patient were obtained using a CsI detector system. Experienced board-certified chest radiologists from four different medical centers in Europe reviewed standard chest radiographs alone and in conjunction with dual-energy images blinded and in random order. The reviewers rated the probability of presence, calcification and malignancy of all lung nodules on a five-point rating scale. Lesions detected were identified by applying a specific coordinate system to enable precise verification by the study leader. A receiver-operating characteristic (ROC) analysis was performed. In addition to the 149 true-positive CT proven lesions, 236 false-positive lung nodules were described in digital chest radiographies in conjunction with dual-energy chest radiographies. The cumulative sensitivity of chest radiography in conjunction with dual energy was 43%, specificity was 55%. For digital radiography alone, sensitivity was 35% and specifity was 83%. For the dual energy system, positive predictive value was 58%, and negative predictive value was 66% compared to the digital radiography with a positive predictive value of 59% and a negative predictive value of 65%. Areas under the curve in a ROC analysis resulted in 0.631 (95% confidence interval =0.61 to 0.65) for radiography with dual energy and 0.602 (95% confidence interval =0.58 to 0.63) for digital radiography alone. This difference was not statistically significant. For the detection of lesion calcification or the determination of malignancy, ROC analysis also failed to show significant differences. CsI-based flat-panel dual-exposure dual-energy imaging added to standard chest radiography did not show statistically significant improvement for the detection of pulmonary nodules, nor the identification of calcifications, nor the determination of malignancy.

A low noise charge sensitive preamplifier with switch control feedback resistance

In this paper, the design and analysis of a new low noise charge sensitive preamplifier for silicon strip, Si(Li), CdZnTe and CsI detectors etc. with switch control feedback resistance were described, the entire system to be built using the CMOS transistors. The circuit configuration of the CSP proposed in this paper can be adopted to develop CMOS-based Application Specific Integrated Circuit further for Front End Electronics of read-out system of nuclear physics, particle physics and astrophysics research, etc. This work is an implemented design that we succeed after a simulation to obtain a rise time less than 3ns, the output resistance less than 94Ω and the linearity almost good.

Property measurement of the CsI(Tl) crystal prepared at IMP**Supported by Knowledge Innovation Project of Chinese Academy of Sciences (CKJCX2-SW-N18, CKJCX2-SW-N04)

Large-sized CsI(Tl) single crystals, ∼ ϕ100 mm × 350 mm, have been grown successfully, and this CsI(Tl) coupled with PD has been successfully utilized at RIBLL (the Radioactive Ion Beam Line in Lanzhou) to measure the energy of heavy ions as a stopping detector. The performances of CsI(Tl) detector coupled with PD and APD have been tested and compared, including the temperature dependence of scintillating light yield.

Monte Carlo investigations of megavoltage cone-beam CT using thick, segmented scintillating detectors for soft tissue visualization.

Megavoltage cone-beam computed tomography (MV CBCT) is a highly promising technique for providing volumetric patient position information in the radiation treatment room. Such information has the potential to greatly assist in registering the patient to the planned treatment position, helping to ensure accurate delivery of the high energy therapy beam to the tumor volume while sparing the surrounding normal tissues. Presently, CBCT systems using conventional MV active matrix flat-panel imagers (AMFPIs), which are commonly used in portal imaging, require a relatively large amount of dose to create images that are clinically useful. This is due to the fact that the phosphor screen detector employed in conventional MV AMFPIs utilizes only approximately 2% of the incident radiation (for a 6 MV x-ray spectrum). Fortunately, thick segmented scintillating detectors can overcome this limitation, and the first prototype imager has demonstrated highly promising performance for projection imaging at low doses. It is therefore of definite interest to examine the potential performance of such thick, segmented scintillating detectors for MV CBCT. In this study, Monte Carlo simulations of radiation energy deposition were used to examine reconstructed images of cylindrical CT contrast phantoms, embedded with tissue-equivalent objects. The phantoms were scanned at 6 MV using segmented detectors having various design parameters (i.e., detector thickness as well as scintillator and septal wall materials). Due to constraints imposed by the nature of this study, the size of the phantoms was limited to approximately 6 cm. For such phantoms, the simulation results suggest that a 40 mm thick, segmented CsI detector with low density septal walls can delineate electron density differences of approximately 2.3% and 1.3% at doses of 1.54 and 3.08 cGy, respectively. In addition, it was found that segmented detectors with greater thickness, higher density scintillator material, or lower density septal walls exhibit higher contrast-to-noise performance. Finally, the performance of various segmented detectors obtained at a relatively low dose (1.54 cGy) was compared with that of a phosphor screen similar to that employed in conventional MV AMFPIs. This comparison indicates that for a phosphor screen to achieve the same contrast-to-noise performance as the segmented detectors approximately 18 to 59 times more dose is required, depending on the configuration of the segmented detectors.

Prospective comparison of two gamma probes for intraoperative detection of 18F-FDG: in vitro assessment and clinical evaluation in differentiated thyroid cancer patients with iodine-negative recurrence

This study was aimed at evaluating the spatial resolution and sensitivity of two hand-held gamma probes. Radioguided surgery was tested in seven patients with iodine-negative differentiated thyroid cancer (DTC) recurrence using (18)F-FDG PET. Two gamma probes were evaluated: Clerad's GammaSup with a collimated CsI(Tl) scintillator and Novelec's Modelo2 with a BGO scintillator. Five measurement tests were performed following the NEMA guidelines (NU3-2004). Radioguided surgery was performed in patients with recurrent DTC and abnormal (18)F-FDG uptake on preoperative (18)F-FDG PET images. Patients were injected with rTSH 2 days before surgery. A mean activity of 211 MBq of (18)F-FDG was injected 60 min before surgery. In vivo and ex vivo counts were recorded for suspected tumours and normal tissue. Spatial resolution was higher with the CsI(Tl) than with the BGO detector: 20.2-40.6 mm vs 20.6-55.3 mm from 0 to 20 mm depth. Sensitivity in air and water and through side shielding was higher for BGO but the signal-to-noise ratio was 88 and 22 with the BGO compared to 131 and 76 with the CsI(Tl) at 10 and 30 mm depth. Median in vivo SNR (tumour/non-tumour ratio) was 1.8 with both the BGO and the CsI(Tl) detector, while ex vivo ratios of 2.3 and 2.1, respectively, were obtained. Radioguided surgery allowed detection of all of the tumours identified by (18)F-FDG PET images. This study demonstrated the feasibility of high-energy photon detection with a conventional scintillator equipped with a collimator. The CsI(TI) probe detected more true events from background than did the BGO detector during surgery.

Image quality of a pixellated GaAs X-ray detector

X-ray detection requires materials with large atomic numbers Z in order to absorb the radiation efficiently. In case of X-ray imaging, fluorescence is a limiting factor for the spatial resolution and contrast at energies above the k α threshold. Since both the energy and yield of the fluorescence of a given material increase with the atomic number, there is an optimum value of Z. GaAs, which can now be epitaxially grown as self-supported thick layers to fulfil the requirements for imaging (good homogeneity of the electronic properties) corresponds to this optimum. Image performances obtained with this material are evaluated in terms of line spread function and modulation transfer function, and a comparison with CsI is made. We evaluate the image contrast obtained for a given object contrast with GaAs and CsI detectors, in the photon energy range of medical applications. Finally, we discuss the minimum object size, which can be detected by these detectors in of mammography conditions. This demonstrates that an object of a given size can be detected using a GaAs detector with a dose at least 100 times lower than using a CsI detector.

Material optimization for X-ray imaging detectors

Materials with atomic number Z as high as possible are considered for solid state X-ray imaging detectors in order to absorb the radiation efficiently. However, the energy and yield of the fluorescence photons increase also with Z, so that the contrast and spatial resolution of an image decreases with Z. We show that the Z value which optimizes the absorption and the image contrast for a given spatial resolution corresponds to GaAs. Now that the GaAs material (thick epitaxial layer) necessary to make pixel detectors exists, we illustrate the improvements in image quality this material brings by comparing, in case of imaging made with small pixels (100 μm), the spatial resolution and contrast with that obtained using CdTe and CsI detectors. Using the Rose model which gives the signal-to-noise ratio corresponding to the minimum detectable contrast, we evaluate the minimum size of the object which can be detected in specific conditions with detectors made of GaAs, CdTe and CsI.

Effect of scatter and an antiscatter grid on the performance of a slot‐scanning digital mammography system

The use of a grid increases perceptibility of low contrast objects in mammography. Slot-scan mammography provides a more dose efficient reduction of the scattered radiation reaching the detector than obtained with an antiscatter grid in screen-film or flat-panel digital mammography. In this paper, the potential of using a grid in a slot-scan system to provide a further reduction of scattered radiation is investigated. The components of the digital signal: primary radiation, off-focus radiation, scattered radiation, and optical fluorescence glare in a CsI(Tl) detector were quantified. Based on these measurements, the primary and scatter transmission factors (Tp, Ts), scatter-to-primary ratio (SPR), signal-difference-to-noise ratio (SDNR), and the SDNR improvement factor (K(SDNR)) were obtained. Our results showed that the SPR ranged from 0.05 to 0.19 for breast thicknesses between 2 and 8 cm, respectively. The values of K(SDNR) ranged from 0.85 to 0.94. Because the slot-scanning system has an inherently low SPR, the increase in dose required when the grid is used outweighs the benefit of the small increase in SDNR. It is possible that greater benefit could be achieved by using a grid with a higher Tp, such as obtained using air-core technology.

Segmented crystalline scintillators: Empirical and theoretical investigation of a high quantum efficiency EPID based on an initial engineering prototype CsI(Tl) detector

Modern‐day radiotherapy relies on highly sophisticated forms of image guidance in order to implement increasingly conformal treatment plans and achieve precise dose delivery. One of the most important goals of such image guidance is to delineate the clinical target volume from surrounding normal tissue during patient setup and dose delivery, thereby avoiding dependence on surrogates such as bony landmarks. In order to achieve this goal, it is necessary to integrate highly efficient imaging technology, capable of resolving soft‐tissue contrast at very low doses, within the treatment setup. In this paper we report on the development of one such modality, which comprises a nonoptimized, prototype electronic portal imaging device (EPID) based on a thick, segmented crystalline CsI(Tl) detector incorporated into an indirect‐detection active matrix flat panel imager (AMFPI). The segmented detector consists of a matrix of optically isolated, crystalline CsI(Tl) elements spaced at pitch. The detector was coupled to an indirect detection‐based active matrix array having a pixel pitch of , with each detector element registered to array pixels. The performance of the prototype imager was evaluated under very low‐dose radiotherapy conditions and compared to that of a conventional megavoltage AMFPI based on a Lanex Fast‐B phosphor screen. Detailed quantitative measurements were performed in order to determine the x‐ray sensitivity, modulation transfer function, noise power spectrum, and detective quantum efficiency (DQE). In addition, images of a contrast‐detail phantom and an anthropomorphic head phantom were also acquired. The prototype imager exhibited approximately 22 times higher zero‐frequency DQE compared to that of the conventional AMFPI . The measured zero‐frequency DQE was found to be lower than theoretical upper limits calculated from Monte Carlo simulations, which were based solely on the x‐ray energy absorbed in the detector—indicating the presence of optical Swank noise. Moreover, due to the nonoptimized nature of this prototype, the spatial resolution was observed to be significantly lower than theoretical expectations. Nevertheless, due to its high quantum efficiency , the prototype imager exhibited significantly higher DQE than that of the conventional AMFPI across all spatial frequencies. In addition, the frequency‐dependent DQE was observed to be relatively invariant with respect to the amount of incident radiation, indicating x‐ray quantum limited behavior. Images of the contrast‐detail phantom and the head phantom obtained using the prototype system exhibit good visualization of relatively large, low‐contrast features, and appear significantly less noisy compared to similar images from a conventional AMFPI. Finally, Monte Carlo‐based theoretical calculations indicate that, with proper optimization, further, significant improvements in the DQE performance of such imagers could be achieved. It is strongly anticipated that the realization of optimized versions of such very high‐DQE EPIDs would enable megavoltage projection imaging at very low doses, and tomographic imaging from a “beam's eye view” at clinically acceptable doses.

A novel Calorimeter Telescope for identification of relativistic heavy-ion reaction channels

A novel Calorimeter Telescope (CATE) is employed in the fast beam Rare Isotope Investigations at GSI (RISING) γ -campaign with relativistic energies at the Fragment Separator (FRS) at GSI. CATE consists of nine modular Si – CsI ( Tl ) detector telescopes for position and Δ E - E res measurements. It registers the scattering angle and identifies the charge ( Z) and the mass ( A) of exotic heavy ions produced after secondary fragmentation or Coulomb excitation.

Initial study of quasi-monochromatic X-ray beam performance for X-ray computed mammotomography

We evaluate the feasibility, benefits, and operating parameters of a quasimonochromatic beam for a newly developed x-ray cone beam computed mammotomography application. The value of a near monochromatic x-ray source for fully 3D dedicated mammotomography is the expected improved ability to separate tissues with very small differences in attenuation coefficients while maintaining dose levels at or below that of existing dual view mammography. In previous studies, simulations for a range of tungsten tube potentials, K-edge filter materials, filter thicknesses, and a 12 cm uncompressed breast, with a digital flat-panel CsI(Tl) detector model, indicated that thick, rare earth filter materials may provide optimized image quality. Figures of merit computed included: lesion contrast under different filtering conditions; ratio of measured lesion contrast with and without filtering; and exposure efficiency (SNR/sup 2//exposure). Initial experiments are performed with a custom built x-ray mammotomography system, cerium foil filters, and plastic breast and lesion tissue-equivalent slabs. Simulation results showed that tube potentials of 50-70 kVp with filters of Z=57-63 yielded quasimonochromatic x-ray spectra with improved FOMs. Initial experimental measurements corroborate simulation results in that, relative trends and rank order of contrast ratios and exposure efficiency were in agreement. These studies show that this approach can be implemented practically with simple hardware and yield improved exposure efficiency versus the unfiltered or minimally filtered case.

MO-E-I-609-02: Imaging Properties of Cone Beam Breast CT- Effects of Detector Properties and Imaging Conditions

Purpose: To investigates the effects of detector properties and imaging conditions on the imaging properties of cone‐beam breast CT with both computer simulations and imaging experiments. Method and Materials: Cone beam breast CT was simulated with the breast analytically modeled as cylinder embedded spherical shape soft tissue masses and calcifications. X‐ray spectrum, breast attenuation, geometric magnification, focal spot blurring, x‐ray detection,detector blurring, image pixelization and digitization were all incorporated in computing the projection images.Quantum noise, system noise,detector blurring were also simulated and incorporated in the model. Image filtering and reconstruction were then performed using the Feldkamp algorithm. Simulation was performed for two flat‐panel detectors, one CsI based and the other a‐Se based. Images of phantoms and breast specimens were also obtained to demonstrate the ability of our experimental cone beam breast CT system to image the 3‐D structures of the breast with embedded cancers and calcifications. Results: Our simulation results shows that the a‐Se detector performs slightly better at 30 and 40 kVp's while the CsI detector performs better at 50 or higher kVp's. ImageSNRs are optimized at 50 and 60 kVp for the s‐Se and CsI detector, respectively. Phantom images obtained with our experimental system show that with higher dose and smaller pixel size, calcifications as small as could be resolved. Images of breast specimens show excellent separation between glandular and adipose tissues. The speculated nature of the tumor masses can be clearly seen in selected projection while ambiguous in other projections or in regular mammograms. It was also found that inclusion of surgical clips (used to indicate tumor location) had caused detrimental reconstruction artifacts. Acknowledgment: This work was supported in part by a research grant EB000117 from the NIBIB and a research grant CA104759 from the NCI.