Technical Note: Quality assessment of virtual monochromatic spectral images on a dual energy CT scanner

PurposeTo assess the quality of images obtained on a dual energy computed tomography (CT) scanner.MethodsImage quality was assessed on a 64 detector-row fast kVp-switching dual energy CT scanner (Revolution GSI, GE Medical Systems). The Catphan phantom and a low contrast resolution phantom were employed. Acquisitions were performed at eight different radiation dose levels that ranged from 9 mGy to 32 mGy. Virtual monochromatic spectral images (VMI) were reconstructed in the 40–140 keV range using all available kernels and iterative reconstruction (IR) at four different blending levels. Modulation Transfer Function (MTF) curves, image noise, image contrast, noise power spectrum and contrast to noise ratio were assessed.ResultsIn-plane spatial resolution at the 10% of the MTF curve was 0.60 mm⁻¹. In-plane spatial resolution was not modified with VMI energy and IR blending level. Image noise was reduced from 16.6 at 9 mGy to 6.7 at 32 mGy, while peak frequency remained within 0.14 ± 0.01 mm⁻¹. Image noise was reduced from 14.3 at IR 10% to 11.5 at IR 50% at a constant peak frequency. The lowest image noise and maximum peak frequency were recorded at 70 keV.ConclusionsOur results have shown how objective image quality is varied when different levels of radiation dose and different settings in IR are applied. These results provide CT operators an in depth understanding of the imaging performance characteristics in dual energy CT.     

Design and development of a dedicated portable gamma camera system for intra-operative imaging

PurposeWe developed a high performance portable gamma camera platform dedicated to identification of sentinel lymph nodes (SLNs) and radio-guided surgery for cancer patients. In this work, we present the performance characteristics of SURGEOSIGHT-I, the first version of this platform that can intra-operatively provide high-resolution images of the surveyed areas.MethodsAt the heart of this camera, there is a 43 × 43 array of pixelated sodium-activated cesium iodide (CsI(Na)) scintillation crystal with 1 × 1 mm² pixel size and 5 mm thickness coupled to a Hamamatsu H8500 flat-panel multi-anode (64 channels) photomultiplier tube. The probe is equipped with a hexagonal parallel-hole lead collimator with 1.2 mm holes. The detector, collimator, and the associated front-end electronics are encapsulated in a common housing referred to as head.ResultsOur results show a count rate of ∼41 kcps for 20% count loss. The extrinsic energy resolution was measured as 20.6% at 140 keV. The spatial resolution and the sensitivity of the system on the collimator surface was measured as 2.2 mm and 142 cps/MBq, respectively. In addition, the integral and differential uniformity, after uniformity correction, in useful field-of-view (UFOV) were measured 4.5% and 4.6%, respectively.ConclusionsThis system can be used for a number of clinical applications including SLN biopsy and radiopharmaceutical-guided surgery.     

Comparative investigation of the detective quantum efficiency of direct and indirect conversion detector technologies in dedicated breast CT

PurposeTo investigate the dose saving potential of direct-converting CdTe photon-counting detector technology for dedicated breast CT.Materials and methodsWe analyzed the modulation transfer function (MTF), the noise power spectrum (NPS) and the detective quantum efficiency (DQE) of two detector technologies, suitable for breast CT (BCT): a flat-panel energy-integrating detector with a 70 μm and a 208 μm thick gadolinium oxysulfide (GOS) and a 150 μm thick cesium iodide (CsI) scintillator and a photon-counting detector with a 1000 μm thick CdTe sensor.ResultsThe measurements for GOS scintillator thicknesses of 70 μm and 208 μm delivered 10% pre-sampled MTF values of 6.6 mm⁻¹ and 3.2 mm⁻¹, and DQE(0) values of 23% and 61%. The 10% pre-sampled MTF value for the 150 μm thick CsI scintillator 6.9 mm⁻¹, and the DQE(0) value was 49%. The CdTe sensor reached a 10% pre-sampled MTF value of 8.5 mm⁻¹ and a DQE(0) value of 85%.ConclusionThe photon-counting CdTe detector technology allows for significant dose reduction compared to the energy-integrating scintillation detector technology used in BCT today. Our comparative evaluation indicates that a high potential dose saving may be possible for BCT by using CdTe detectors, without loss of spatial resolution.     

Probing the optical properties and luminescence mechanism of a UV‐emitting SrBPO5:Ce3+ phosphor

Ce‐doped (1 × 10^?5 to 3.0 mol%) SrBPO₅ phosphors were synthesized using a conventional solid‐state reaction route at 1273 K in an air atmosphere. Phase and morphology of the samples were studied from powder X‐ray diffraction (XRD) patterns and scanning electron microscope (SEM) micrographs, respectively. The band gap energies of the pure and Ce‐doped SrBPO₅ phosphors were calculated from the recorded diffuse reflectance spectra. Photoluminescence (PL) and Ce³⁺ lifetime were recorded at 300 and 77 K. Photoluminescence lifetime measurements revealed two‐lifetime values for Ce³⁺ at both 300 K (17 and 36 nsec) and 77 K (12 and 30 nsec), suggesting the presence of two different environments around Ce³⁺. Time‐resolved emission spectroscopy (TRES) studies confirmed the presence of Ce³⁺ in two different environments. In addition, SrBPO₅:Ce exhibited intense UV emission, signifying its possible use as an efficient sensitizer for solid‐state lighting applications. The effect of γ‐irradiation on PL was also determined. Thermally stimulated luminescence (TSL) glow curves of the γ‐irradiated phosphor, along with trap parameters, dose–response, and the possible TSL mechanism were also investigated. Positron annihilation lifetime spectroscopy was carried out to probe defects present in undoped and Ce‐doped SrBPO₅.     

Luminescence in Sr4Al14O25:Ce3+ aluminate phosphor

Cerium‐doped Sr₄Al₁₄O₂₅ phosphor is prepared using a single‐step combustion synthesis and its X‐ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) and thermoluminescence (TL) properties are characterized. XRD reveals the formation of the desired phase in the prepared sample. SEM micrographs of the prepared Sr₄Al₁₄O₂₅ phosphor show that the particle size is 10 µm. The prepared Sr₄Al₁₄O₂₅, along with Sr₄Al₁₄O₂₅:Ce_x (x = 0.5–5 mol%) shows a PL emission peak at 314 nm under UV excitation of 262 nm wavelength due to 5d → 4f transition. The phosphor is suitable for higher concentrations of Ce ions. The TL glow peak reveals three clearly visible distinct peaks at temperatures around 130, 231 and 336ºC. The three peaks are separated by deconvolution and kinetic parameters calculated using Chen's peak shape method. The calculation shows that the reaction follows second‐order kinetics with activation energy (E) values of 0.52, 0.81 and 1.12 eV, and frequency factor (s) values of 5.58 × 10⁵, 4.53 × 10⁷ and 4.57 × 10⁸ s^‐1 for the three individual peaks. Copyright © 2014 John Wiley & Sons, Ltd.     

Dose uncertainty and resolution of polymer gel dosimetry using an MRI guided radiation therapy system’s onboard 0.35 T scanner

Magnetic Resonance Imaging (MRI) scanners are widely used for 3D gel dosimeters readout. However, limited access to MRI scanners is a challenge in MRI-based gel dosimetry. Recent clinical implementation of MRI-guided radiation therapy machines provides potential opportunities for onboard gel dosimetry using its MRI subsystem. The objective of this study was to investigate the feasibility of gel dosimetry using ViewRay’s onboard 0.35 T MRI scanner. A BANG® polymer gel dosimeter was irradiated by three beams of 3 × 3 cm² field size. The T₂ relaxation rate (R₂) of the irradiated gel was measured using a Philips 1.5 T Ingenia MRI and a ViewRay 0.35 T onboard MRI and spin-echo pulse sequences. The number of signal averages (NSA) was set to 16 for the ViewRay acquisitions and one for the Philips 1.5 T MRI to achieve similar signal-to-noise ratios. The in-plane spatial resolution was 1.5 × 1.5 mm² and the slice thickness was 5 mm. The relative dose uncertainty was obtained using R₂ versus dose curves to compare the performance of dosimetry using the two different MRIs and field strengths. The dose uncertainty decreased from 12% at 2 Gy to 3.5% at 7.5 Gy at 1.5 T. The dose uncertainty decreased from 13% at 2 Gy to 4% at 7.5 Gy with NSA = 16 and 3 × 3 mm² pixel size, and from 10.5% at 2 Gy to 3.2% at 7.5 Gy with NSA = 16 and denoised R₂ maps (1.5 × 1.5 mm² pixel size) at 0.35 T. The mean of dose resolution was 0.4 Gy at 1.5 T while the mean of dose resolution was 0.8 Gy and 0.64 Gy at 0.35 T by downsampling and denoising the R2 map, respectively. Therefore, comparable dose uncertainty was achievable using the ViewRay’s onboard 0.35 T and Philips 1.5 T MRI scanners. 3D gel dosimetry using onboard low-field MRI scanner provides ViewRay users a 3D high resolution dosimetry option besides film and ionization chamber.     

Flow‐injection chemiluminescence determination of ofloxacin using the Ru(bpy)2(CIP)2+−Ce(IV) system and its application

This paper reports a flow‐injection chemiluminescence method for the determination of ofloxacin (OFLX) using the Ru(bpy)₂(CIP)²⁺–Ce(IV) system. Under the optimum conditions, the relative CL intensity was proportional to the concentration of OFLX in the range 3.0 × 10^–8–1.0 × 10^–5 mol/L and the detection limit was 4.2 × 10^–9 mol/L. The proposed method has been successfully applied to the determination of ofloxacin in pharmaceuticals and human urine. The chemiluminescence mechanism of the system is also discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Determination of oxytetracycline hydrochloride in milk and egg white samples using Ru(bipy)32+–Ce(SO4)2 chemiluminescence

A novel, rapid and sensitive chemiluminescence (CL) method for the determination of oxytetracycline hydrochloride (OTCH) is described in this paper. The presented method was based on the fact that OTCH could immensely enhance the CL of the reaction of cerium sulfate and tris(2,2‐bipyridyl) ruthenium (II) in acidic medium. Under optimal experimental conditions, CL intensity was favorably linear for OTCH in the range 5.0 × 10^?7 to 5.0 × 10^?5 g/ml, with a detection limit of 1.5 × 10^?7 g/ml (S/N = 3). The relative standard detection was 4.76% for 5.0 × 10^?6 g/ml (n = 11). This method was successfully applied to the analysis of OTCH in milk and egg white samples. According to the results of the kinetic curves for OTCH in the Ru(bipy)₃²⁺–Ce(SO₄)₂ CL system, together with CL and ultraviolet (UV)–visible spectra, the possible mechanism of the CL reaction is discussed briefly.     

Determination of pholcodine in syrups and human plasma using the chemiluminescence system of tris(1,10 phenanthroline)ruthenium(II) and acidic Ce(IV)

Pholcodine is an opiate derivative drug which is widely used in pediatric medicine. In this study, a chemiluminescence (CL) method is described that determines pholcodine in human plasma and syrup samples. This method is based on the fact that pholcodine can greatly enhance the weak CL emission of reaction between tris(1,10 phenanthroline)ruthenium(II), Ru(phen)₃²⁺, and acidic Ce(IV). The CL mechanism is described in detail using UV–vis light, fluorescence and CL spectra. Effects of chemical variables were investigated and under optimum conditions, CL intensity was proportional to the pholcodine concentration over the range 4.0 × 10^?8 to 8.0 × 10^?6 mol  L^?1. The limit of detection (LOD) (S/N = 3) was 2.5 × 10^?8 mol  L^?1. Percent of relative standard deviations (%RSD) for 3.0 × 10^?7 and 3.0 × 10^?6 mol  L^?1 of pholcodine was 2.9 and 4.0%, respectively. Effects of common ingredients were investigated and the method was applied successfully to the determination of pholcodine in syrup samples and human plasma.     

In-vivo dosimetry for field sizes down to 6 × 6 mm2 in shaped beam radiosurgery with microMOSFET

The aim of this study is to evaluate microMOSFET as in-vivo dosimeter in 6 MV shaped-beam radiosurgery for field sizes down to 6 × 6 mm². A homemade build-up cap was developed and its use with microMOSFET was evaluated down to 6 × 6 mm². The study with the homemade build-up cap was performed considering its influence on field size over-cover occurring at surface, achievement of the overall process of electronic equilibrium, dose deposition along beam axis and dose attenuation. An optimized calibration method has been validated using MOSFET in shaped-beam radiosurgery for field sizes from 98 × 98 down to 18 × 18 mm². The method was detailed in a previous study and validated in irregular field shapes series measurements performed on a head phantom. The optimized calibration method was applied to microMOSFET equipped with homemade build-up cap down to 6 × 6 mm². Using the same irregular field shapes, dose measurements were performed on head phantom. MicroMOSFET results were compared to previous MOSFET ones. Additional irregular field shapes down to 8.8 × 8.8 mm² were studied with microMOSFET. Isocenter dose attenuation due to the homemade build-up cap over the microMOSFET was near 2% irrespective of field size. Our results suggested that microMOSFET equipped with homemade build-up cap is suitable for in-vivo dosimetry in shaped-beam radiosurgery for field sizes down to 6 × 6 mm² and therefore that the required build-up cap dimensions to perform entrance in-vivo dosimetry in small-fields have to ensure only partial charge particle equilibrium.     

Dosimetric characterization of small fields using a plastic scintillator detector: A large multicenter study

PurposeIn modern radiation therapy accurate small fields dosimetry is a challenge and its standardization is fundamental to harmonize delivered dose in different institutions. This study presents a multicenter characterization of MLC-defined small field for Elekta and Varian linear accelerators. Measurements were performed using the Exradin W1 plastic scintillator detector.Materials and methodsThe project enrolled 24 Italian centers. Each center performed Tissue Phantom Ratio (TPR), in-plane and cross-plane dose profiles of 0.8 × 0.8 cm² field, and Output Factor (OF) measurements for square field sizes ranging from 0.8 to 10 cm. Set-up conditions were 10 cm depth in water phantom at SSD 90 cm. Measurements were performed using two twin Exradin W1 plastic scintillator detectors (PSD) correcting for the Cerenkov effect as proposed by the manufacturer.ResultsData analysis from 12 Varian and 12 Elekta centers was performed. Measurements of 7 centers were not included due to cable problems. TPR measurements showed standard deviations (SD) < 1%; SD < 0.4 mm for the profile penumbra was obtained, while FWHM measurements showed SD < 0.5 mm. OF measurements showed SD < 1.5% for field size greater than 2 × 2 cm². Median OFs values were in agreement with the recent bibliography.ConclusionsHigh degree of consistency was registered for all the considered parameters. This work confirmed the importance of multicenter dosimetric intercomparison. W1 PSD could be considered as a good candidate for small field measurements.     

Imaging performance of phase-contrast breast computed tomography with synchrotron radiation and a CdTe photon-counting detector

PurposeWithin the SYRMA-CT collaboration based at the ELETTRA synchrotron radiation (SR) facility the authors investigated the imaging performance of the phase-contrast computed tomography (CT) system dedicated to monochromatic in vivo 3D imaging of the female breast, for breast cancer diagnosis.MethodsTest objects were imaged at 38 keV using monochromatic SR and a high-resolution CdTe photon-counting detector. Signal and noise performance were evaluated using modulation transfer function (MTF) and noise power spectrum. The analysis was performed on the images obtained with the application of a phase retrieval algorithm as well as on those obtained without phase retrieval. The contrast to noise ratio (CNR) and the capability of detecting test microcalcification clusters and soft masses were investigated.ResultsFor a voxel size of (60 μm)³, images without phase retrieval showed higher spatial resolution (6.7 mm⁻¹ at 10% MTF) than corresponding images with phase retrieval (2.5 mm⁻¹). Phase retrieval produced a reduction of the noise level and an increase of the CNR by more than one order of magnitude, compared to raw phase-contrast images. Microcalcifications with a diameter down to 130 μm could be detected in both types of images.ConclusionsThe investigation on test objects indicates that breast CT with a monochromatic SR source is technically feasible in terms of spatial resolution, image noise and contrast, for in vivo 3D imaging with a dose comparable to that of two-view mammography. Images obtained with the phase retrieval algorithm showed the best performance in the trade-off between spatial resolution and image noise.     

Effects of Ce doping on the luminescent property of Ca3SiO4Cl2:Eu phosphor for green lighting

White light‐emitting diodes (LEDs) for green lighting are new solutions for energy saving and environmental protection. Ca₃SiO₄Cl₂:Ce,Eu is an efficient phosphor for white LEDs. Effective energy transfer from Ce³⁺ to Eu²⁺ occurs in Ca₃SiO₄Cl₂:Ce,Eu due to good spectrum overlap between the emission band of Ca₃SiO₄Cl₂:Ce and the excitation band of Ca₃SiO₄Cl₂:Eu, and hues vary systematically from blue to green at different Ce concentrations. A great improvement in the luminescent property of Ca₃SiO₄Cl₂:Eu has been observed on Ce³⁺ doping, which is attributed to energy transfer from Ce³⁺ to Eu²⁺ and an increase in the number of luminescent centers (Eu²⁺) on Ce doping. The optimal sample has a quantum efficiency of up to 75%, and can be an efficient green phosphor for white LEDs. Copyright © 2014 John Wiley & Sons, Ltd.     

Synchronous fluorescence determination of ferulic acid with Ce(IV) and sodium tripolyphosphate

In this study, a synchronous fluorescence detection method for ferulic acid (FA) is proposed based on a redox reaction between FA and Ce(IV) sulfate in dilute sulfuric acid medium at room temperature. It was found that FA could reduce Ce(IV) to Ce(III) in acidic medium, and sodium tripolyphosphate could further enhance the intrinsic fluorescence of the Ce(III) produced. The enhanced extent of synchronous fluorescence intensity was in proportion to the concentration of FA over the range 3.0 × 10^‐8 to 1.0 × 10^‐5 mol/L. The corresponding limit of determination (S/N = 3) was 1.3 × 10^‐8 mol/L. The proposed method was applied to the determination of sodium ferulate for injection sample with satisfactory results. Copyright © 2013 John Wiley & Sons, Ltd.     

Patient-specific respiratory models using dynamic 3D MRI: Preliminary volunteer results

Organ and tumour motion has a significant impact on the planning and delivery of radiotherapy treatment. At present imaging modality such as four-dimensional computer tomography (4DCT) cannot be used to measure the variability of motion between different respiratory cycles. To create reliable motion models, one needs to acquire volumetric data sets of the lungs with sufficient sampling of the breathing cycle. In this paper we investigate the use of highly parallel MRI to acquire such data. A 32 channel coil in conjunction with a balanced SSFP sequence and a SENSE factor of 6 were used to acquire volumetric data sets in five healthy volunteers. The acquisition was repeated for seven series of different breathing patterns. The data acquired was of sufficient spatial resolution (5 × 5 × 5 mm³) and image quality to carry out automated non-rigid registration. The acquisition rate (c.a. 2 volumes per second) allowed for a meaningful sampling of the different respiratory curves that were automatically obtained from the skin surface motion. This acquisition technique should provide images of high enough quality to create statistical respiratory models.     

Optimization of an ultra-fast silicon detector for proton and carbon beams using GEANT4 Monte Carlo toolkit

AimThe purpose of this study was to investigate the crosstalk effects between adjacent pixels in a thin silicon detector with 50 um thickness.BackgroundThere are some limitations in the applications of detectors in hadron therapy. So it is necessary to have a detector with concurrent excellent time and resolution. In this work, the GEANT4 toolkit was applied to estimate the best value for energy cutoff in the thin silicon detector in order to optimize the detector.Materials and MethodsGEANT4 toolkit was applied to simulate the transport and interactions of particles. Calculations were performed for a thin silicon detector (2 cm × 2 cm×0.005 cm) irradiated by proton and carbon ion beams. A two-dimensional array of silicon pixels in the x-y plane with 100 um × 100 um × 50 um dimensions build the whole detector. In the end, the ROOT package is used to interpret and analyze the resultsResultsIt is seen that by the presence of energy cutoff, pixels with small deposited energy are ignored. The best values for energy cutoff are 0.01 MeV and 0.7 MeV for proton and carbon ion beams, respectively. By applying these energy cutoff values, efficiency and purity values are maximized and also minimum output errors are achieved.ConclusionsThe results are reasonable, good and useful to optimize the geometry of future silicon detectors in order to be used as beam monitoring in hadron therapy applications.     

High resolution MR eye protocol optimization: Comparison between 3D-CISS, 3D-PSIF and 3D-VIBE sequences

PurposeThe purpose of this study was to compare selected MRI pulse sequences and to evaluate their utility for depicting specific anatomic regions in the eye.MethodsA High-Resolution (HR) 0.08 × 0.08 × 0.60 mm³ MRI protocol was developed on a 1.5-T clinical system and applied in the left eye of an albino rabbit, utilizing a small field of view surface coil. The comprehensive MRI protocol consisted of two 3D (T2/T1)w sequences (3D-PSIF and 3D-CISS), and one 3D T1w sequence (3D-VIBE). The T1w 3D-VIBE sequence was acquired, before and after intravenous injection of 0.2 mmol/kgr gadolinium-DTPA. Signal-to-Noise Ratios (SNR) and Contrast-to-Noise Ratios (CNR) amongst specific eye anatomical areas were calculated for each sequence. The presence of artifacts was rated subjectively utilizing a 5 point scale.Results3D-PSIF and 3D-CISS provide better delineation and visualization of the eye as compared with 3D-VIBE sequences. 3D-CISS images present the highest SNR and revealed better discrimination of the ocular surrounding tissues; its basic drawback though is related to ghost artifacts appearing in the anterior chamber and resulting in the lowest image quality. In post-contrast imaging, the T1w 3D-VIBE sequence provided the best overall image quality. Moreover, 3D (T2/T1)w sequences can provide good anatomic depiction of the eye segments. Agreement between the two independent readers was good.ConclusionsOptimization of a comprehensive MR eye imaging protocol is achieved. A higher SNR, a better spatial resolution and a reduction of the total scan time were obtained, thus making clinical MRI systems more reliable in eye imaging.     

Preparation of cross-linked carboxymethyl chitosan for repairing sciatic nerve injury in rats

A successful nerve regeneration process was achieved with nerve repair tubes made up of 1-ethyl-3(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) cross-linked carboxymethyl chitosan (CM-chitosan) with improved biodegradability. Chitosan has a very slow degradation rate, while the EDC cross-linked CM-chitosan tubes degraded to 30% of original weight during 8 weeks of incubation in lysozyme solution. In vitro cell culture indicated that the CM-chitosan films presented no cytotoxicity to Schwann cells. From in vivo studies using a 10 mm rat sciatic nerve defect model investigated by histomorphometry analysis, the average diameter of the fibers and the average thickness of myelin sheath in the CM-chitosan tubes were 3.7 ± 0.33 and 0.33 ± 0.04 μm, respectively, which demonstrated equivalence to nerve autografts (the current “gold” standard); furthermore, the average fiber density in the CM-chitosan tubes was 20.5 × 10³/mm², which was similar to that of autografts (21 × 10³/mm²) and significantly higher than that of common chitosan tubes (15.3 × 10³/mm²).     

Évaluation des paramètres et méthode de contrôle de qualité de la correction d’atténuation en tomographie par émission de positons

ObjectiveThe aim of this study is to evaluate the performance of the Computed Tomography based Attenuation Correction (CTAC) for Positron Emission Tomography (PET) data. Attenuation maps containing linear attenuation coefficients at 511 keV (LAC_511 keV) are calculated by trilinear conversion of Hounsfield Units (HU) obtained from CT slices after matrix size-reduction and gaussian filtering. Our work focusses on this trilinear conversion.Materials and methodsCT slices of an electron density phantom, composed of 17 cylindrical inserts made of different tissue-equivalent materials, were acquired using a Discovery ST4^® PET-CT. Data were processed with a customized version of CT quality control software, giving automatically the experimental conversion function: LAC_511 keV = f(HU). Furthermore, data from patient datasets were assessed using both smoothed CT slices and attenuation maps.ResultsLAC_511 keV extracted from phantom data are in good correlation with the expected theoretical values, except for the standard 10 mm diameter dense bone insert, where the obtained CTAC values are underestimated. Assuming a sample size issue, similar acquisitions were performed with a special 30 mm-diameter dense bone insert, confirming the underestimation as a consequence of the sample size. This effect, caused partly by a too smooth Gaussian filter of the CT images, could be limited by reducing the strength of the filter. Measurements from patients’ data showed the same underestimation of CAL_511 keV for high-density tissues.ConclusionWe assessed an underestimation of the CTAC obtained-values related to the sample size of the insert. A quality control was developed to this effect.