Al Filter Research Articles

Spectral optimization for dedicated breast CT

The authors investigated the choice of spectra for the optimization of the dose-weighted contrast-to-noise ratio (CNRD) for a dedicated breast CT scanner. The objective is to provide the desired image quality level at minimal dose values. The CNRD was investigated as a function of energy or tube voltage and filtrations for various breast sizes and contrasts. The authors performed simulations of the pendant female breast as cylinders consisting of a homogeneous mixture of adipose and glandular tissue with diameters from 6 to 18 cm. The contrasts of adipose tissue, calcium hydroxyapatite, and iodine contrast agent relative to glandular tissue were analyzed using inserts of 9 mm in diameter. Simulations were conducted for monochromatic and polychromatic radiation with a 3 mm Al or a 0.3 mm Cu filter. Simulations and measurements on an experimental micro-CT scanner were performed for validation purposes with a 6 cm water-equivalent cylinder, with inserts representing a pure density difference of 10%, calcium hydroxyapatite, and iodine contrast agent. A breast tissue sample embedded in paraffin was investigated to confirm the simulation results. Optimal tube voltages were found to be in the range of 30-55 kV for breast CT imaging. For example, with 3 mm Al or 0.3 mm Cu filtration, optimal tube voltages were about 53 and 48 kV, respectively, for the contrast iodine/glandular tissue for all diameters. With 3 mm Al filtration, optimal tube voltages increased from 30 to 37 kV and from 30 to 47 kV for the contrast calcium hydroxyapatite/glandular tissue and adipose/glandular tissue, respectively. Tube power requirements were estimated and the change in tube current relative to 80 kV was found to be between 4 and 14 and between 11 and 214 with 3 mm Al filtration or 0.3 mm Cu filtration, respectively. These numbers show that realizing the low optimal tube voltages may not be feasible in most cases due to power requirements. Depending on the filtration, the authors assume that a compromise solution has to be found between the highest potential dose reduction and a solution working with available x-ray sources. In view of the tube power constraints, the authors recommend aiming for tube voltages in the range of 50 kV and higher.

Development of a digital panoramic X-ray imaging system of adaptive image layers for dental applications

Abstract As a continuation of our digital radiographic sensor R&D, we have developed a prototyped digital panoramic X-ray imaging system for dental applications. The imaging system consists of a slit-collimated X-ray generator with a 0.4 mm focal spot size and a 3.5 mm Al filtration, a linear-array typed CMOS imager with a 48×48 μm2 pixel size and a 128 (in the scan direction)×3072 (in the vertical direction) pixel format, a series of microstep motors for the precise motion control of the imaging system, and the designed sequences for the motion control and pixel readout required to make a specific plane of interest (POI) to be focused. With the several test phantoms we designed, we obtained useful digital panoramic X-ray images by moving the X-ray generator and the CMOS imager along a continuously sliding rotational center. In this study, we demonstrated that the prototype system can be applicable to any shaped POI or multi-POIs simultaneously to be focused, provided that adequate sequences for motion control and pixel readout are designed. We expect that the imaging system will be useful for our ongoing applications of dental panoramic radiography and nondestructive testing.

SU-GG-I-52: Kerma Area Product and Energy Incident on Patients in X-Ray Imaging

Purpose: To quantify the total x‐ray energy incident on a patient undergoing an x‐ray exposure using the Kerma Area Product. Method and Materials: Knowledge of the x‐ray beam spectrum permits the total energy in the x‐ray beam (mJ) and the corresponding Kerma Area Product (KAP, unit: Gy‐cm2) to be determined. For each x‐ray beam spectrum, conversion factors between the total energy incident on the patient and the KAP were determined (mJ/Gy‐cm2). We investigated mono‐energetic x‐ray beams and x‐ray spectra of interest in diagnostic x‐ray imaging. For the latter, we determined the importance of x‐ray tube voltage (kV), x‐ray beam filtration (mm Al), x‐ray tube anode angle (°), and voltage ripple (%). Results: Energy incident per unit KAP increases from 6.71 mJ per Gy‐cm2 for 30 keV photons to 43.5 mJ per Gy‐cm2 for 100 keV photons. For 3 mm Al filtration beams, increasing the x‐ray tube voltage from 50 kV to 100 kV increased the energy incident per unit KAP from 7.0 mJ per Gy‐cm2 18.5 mJ per Gy‐cm2. At 80 kV, increasing the x‐ray tube filtration from 1 to 5 mm Al increased the energy incident per unit KAP from 9.0 mJ per Gy‐cm2 17 mJ per Gy‐cm2. The x‐ray tube anode angle and voltage ripple had very little effect (< 20%) on energy incident per unit KAP conversion coefficients. Conclusion: Energy incident on the patient, determined from the Kerma Area Product, can be combined with absorbed fraction values to quantify energy imparted to patients.

Radiotherapy in Early-Stage Dupuytren’s Contracture

In early-stage Dupuytren's contracture, radiotherapy is applied to prevent disease progression. Long-term outcome and late toxicity of the treatment were evaluated in a retrospective analysis. Between 12/1982 and 02/2006, 135 patients (208 hands) were irradiated with orthovoltage (120 kV; 20 mA; 4-mm Al filter), in two courses with five daily fractions of 3.0 Gy to a total dose of 30 Gy; separated by a 6- to 8-week interval. The extent of disease was described according to a modified classification of Tubiana et al. Long-term outcome was analyzed at last follow-up between 02/2008 and 05/2008 with a median follow-up of 13 years (range, 2-25 years). Late treatment toxicity and objective reduction of symptoms as change in stage and numbers of nodules and cords were evaluated and used as evidence to assess treatment response. According to the individual stages, 123 cases (59%) remained stable, 20 (10%) improved, and 65 (31%) progressed. In stage N 87% and in stage N/I 70% remained stable or even regressed. In more advanced stages, the rate of disease progression increased to 62% (stage I) or 86% (stage II). 66% of the patients showed a long-term relief of symptoms (i.e., burning sensations, itching and scratching, pressure and tension). Radiotherapy did not increase the complication rate after surgery in case of disease progression and only minor late toxicity (skin atrophy, dry desquamation) could be observed in 32% of the patients. There was no evidence for a second malignancy induced by radiotherapy. After a mean follow-up of 13 years radiotherapy is effective in prevention of disease progression and improves patients' symptoms in early-stage Dupuytren's contracture (stage N, N/I). In case of disease progression after radiotherapy, a "salvage" operation is still feasible.

Photon-induced positron annihilation for standoff bomb detection

We describe an approach to detect improvised explosive devices (IEDs) by using photon-induced positron annihilation radiation (PIPAR). This system relies on back-scattered γ photons from the target and surrounding objects following exposure to high energy X-rays from a betatron. In this work we simulate the use of Bremsstrahlung source operating at 3.5 MeV, with a scintillation detector, working in PIPAR mode, in order to reduce noise produced by undesired back-scattering from the surrounding objects. In this paper, we describe the basic imaging method and preliminary results on simulating a suitable betatron source. Two types of X-ray filters copper (Cu) and aluminium (Al), have been used in the simulation to observe their differences in the deposited energy spectrum in the iron target. It was found that the use of iron target in conjunction with 2 mm Al filter is capable of detecting annihilation γ photons. An initiated experiment with an interlaced source also shows promise.

PMMA and FEP surface modifications induced with EUV pulses in two selected wavelength ranges

Surface modification of PMMA and FEP polymers using extreme ultraviolet (EUV) in two spectral ranges was investigated. A laser-plasma EUV source based on a double stream gas puff target equipped with an Au coated ellipsoidal collector was used for the experiment. The spectrum of the focused radiation from Kr plasma consisted of a narrow feature with a maximum at 10 nm and a long-wavelength tail up to 70 nm. Al and Zr filters were employed for the selection of radiation from these two spectral regions. The radiation fluences in the two cases were comparable. Polymer samples were mounted in the focal plane of the EUV collector and irradiated for 1–2 min with a 10 Hz repetition rate. Weak ablation accompanied by creation of micro- and nanostructures of different kinds was obtained in both cases. Significant differences in the surface structures after irradiation of PMMA and FEP in these two spectral regions were revealed.

Half-value layer measurement: simple process method using radiochromic film

Although the half-value layer (HVL) is one of the important parameters for QA and QC, constant monitoring has not been performed because the measurements using an ionization chamber (IC) are time-consuming and complicated. To solve these problems, the use of radiochromic film (GAFCHROMIC XR TYPE R: GAF-R) with step-shaped aluminum (Al) filters, referred to herein as the simple process method, has been developed. The measurement X-ray tube voltages were 120 kV, 100 kV, and 80 kV. The Al filter area, the full exposure area, and the unexposed area were set on the GAF-R so as to obtain correct data. The HVL was evaluated using the density attenuation ratio. The HVLs obtained using the GAF-R and an 1C dosimeter were compared. HVLs with X-ray tube voltages of 120 kV, 100 kV, and 80 kV using the GAF-R were 4.10 mm, 3.55 mm and 2.97 mm, respectively. The difference ratios of the HVLs using the GAF-R and the IC were 1.2%, 7.6%, and 10.0%, respectively. The HVL at 120 kV can be routinely and quickly measured using the simple process method. Therefore, an IC dosimeter is not needed for HVL measurements for QA and QC. However, the HVL measurements of low energy (100 kV and 80 kV) need attention.

SU‐FF‐I‐18: Organ Doses and Projection Angles in Cone Beam CT

Purpose: To calculate how organ doses varies with projection angle for two types of cone beam CT geometry. Method: We used the PCXMC software package to compute organ doses to patients. We modeled a typical x‐ray spectrum using 120 kV x‐ray tube voltage and 6 mm Al filtration. Two cone beam irradiation geometries were modeled: (a) a standard CT gantry; and (b) a C‐arm. Both systems made use of a detector with dimensions of 30 cm × 40 cm. For the CT gantry system, the source to isocenter distance was 57 cm, and the SID was 93 cm. For the C‐arm system, the source to isocenter distance was 78.5 cm, and the SID was 120 cm. Organ dose to the five most radiosensitive organs (breast, colon, lung, red bone marrow, and stomach) were obtained for each cone beam arrangement at 15 degree intervals as the x‐ray tube rotates through 360 degrees around the patient. Results: On average, patient doses using the C‐arm were ∼60% of those obtained using the CT gantry. Ratios of maximum to minimum doses as a function of x‐ray tube angle ranged from ∼2.3:1 for the lung to ∼31:1 for the stomach. For the breast, colon, and stomach the highest doses were obtained for AP projections, whereas for the lung and red bone marrow, PA projections resulted in the highest organ doses. In all cases, dose minima were obtained when the x‐ray beam entered the patient in a lateral orientation. Conclusions: The high maximum to minimum dose ratios for radiosensitive organs such as the stomach and breast indicate that modulation of the x‐ray tube current with projection angle could result in substantial dose reductions in cone beam CT.

MO‐D‐304A‐05: Optimal Material Selection of Primary Modulator for Scatter Correction Based On the K‐Edge Discontinuity

Purpose: To select an optimal material for the primary modulator in order to minimize its effect of beam hardening (BH). A measurement‐based scatter correction method that uses a checkerboard pattern of attenuating material (primary modulator) placed between the X‐ray source and the object has been developed and verified. In the practical implementation, BH is a limiting factor because the signal modulation depends on the object in the field of view (FOV). Methods: The transmission factor for different modulator materials (Be, Al, Cu, Ag, W, Ho, Er and Tm) was calculated for object thicknesses ranging from 0 to 30 cm equivalent water by using a simulated spectrum of our tabletop cone‐beam CT system at 120 kVp. We then generated scatter‐free projection images of a 30‐cm diameter water cylinder, with and without the modulator in place, and reconstructed CT slices after demodulation. Visibility of rings was compared for no noise, and with 2% added Gaussian noise. We also measured the transmission factors of 25 μm of Cu, W and Er for different combinations of Al (0–8 mm) and Cu (0–0.3 mm) filtration. Results: For a transmission factor of ∼0.9, simulations show that Er provides the least amount of variability as a function of added filtration (max variation&lt;1.8%). The ring artifacts in simulated reconstructions were significantly reduced when using the Er, particularly in the presence of noise. Measured variability of transmission factors were 2.5%, 1.0% and 8.6% for 25 μm of Cu, Er and W, respectively. Conclusions: An optimization of modulator material to minimize BH artifact was proposed and validated. The variation of the transmission factor as a function of X‐ray energy reaches a local minimum when the K‐edge of the modulator material is near the mean energy of the spectrum. Design and evaluation of an Erbium modulator is underway.

SU‐DD‐A3‐04: Monte Carlo Simulation of a MicroCT‐Based Small Animal Radiotherapy System

Purpose: A microCT‐based small‐animal‐radiotherapy system with a variable‐aperture collimator has been constructed, and a Monte Carlo model of this system has been developed. A series of Monte Carlo (MC) simulations were performed in order to calibrate the model against measured beam commissioning data. Method and Materials: The EGSnrc codes were used for MC simulation. The simulations included different source models, different apertures, and included or excluded the effect of the plastic cylindrical shell enclosing the CT bore. We considered sources including a circular x‐ray beam with spectra generated by Boone‐Fewell formula, and a simulated x‐ray tube with parameters fit to measured beam profile. The beam width was set to 2, 5, 10, and 20 mm. The depth dose in water and the beam profiles simulated with and without the CT bore were compared, and the calibration factor for the conversion from MC dose to the measured dose rate in water was computed. Results: The simulation showed that a model with 2.5 mm Al filtration matches the measured depth‐dose curves, with the mean error on all measurement points for 2.5 mm Al was 2.5%. The CT bore introduces a 6% attenuation but does not significantly affect the beam energy spectrum or depth‐dose characteristics. The low energy part of the spectrum from the x‐ray‐tube simulation varied substantially from that predicted by the Boone‐Fewell model. The conversion factor was found to be 7.7415×1018 particles/min. Conclusion: Models and parameters in the Monte Carlo planning system have been determined from the depth‐dose measurements and simulations. The observed effect of the CT bore suggested that the effect can be attributed to additional attenuation, which significantly simplifies the software complexity of the Monte Carlo planning system.

Changes in radiological protection and quality control in Spanish dental installations: 1996-2003

The European Union has established specific directives concerning radiological protection which are obligatory for member States. In addition, all Spanish dental clinics with radiological equipment are required to have an annual quality control check. To analyze the effect of new European legislation on dental radiological practice in Spain and to determine whether it has resulted in lower doses being administered to patients. A total of 10,171 official radiological quality control reports on Spanish dental clinics, covering 16 autonomous regions, were studied following the passing of Royal Decree 2071/1995 on quality criteria in radiodiagnostic installations. The reports, compiled by U.T.P.R Asigma S.A., a company authorised by the Nuclear Safety Council, cover the years 1996 to 2003, which has enabled us to monitor the evolution of radiological procedures in dental clinics over a seven year period. According to the reports for 2003, 77.3 % of clinics complied with EU requirements, using equipment of 70 kVp, 8 mA, 1.5 mm Al filters, with a collimator length of 20 cm. However, non-compliance was detected in approximately a third (30.8%) of the equipment inspected: alterations in the kilovoltage used, exposure time, performance of the tubing, dosage, linearity/intensity of current and acoustic-luminous signal 6.86%. The mean skin dose reached 3.11 mGy for patients who received an x-ray of an upper molar, representing a decrease of 18% over the seven years studied. there has obviously been a general improvement in the parameters studied, but only 77.3% of the installations complied fully with official EU regulations concerning dental radiological protection.

Ｉｍａｇｅ ｑｕａｌｉｔｙ ｆｉｇｕｒｅの閾値によるＣｏｍｐｕｔｅｄ Ｒａｄｉｏｇｒａｐｈｙでの適正線量の推定

We estimated the optimum dose for imaging with a computed radiography (CR) system at two different pixel sizes based on the area under curve (AUC) in receiver operating characteristic (ROC) analysis and image quality figure (IQF). Samples for ROC analysis were prepared as follows. Acryl beads, 2.0 mm in diameter, were placed on a 50.0 mm tough water phantom that was fitted with a 20.0 mm Al filter (SID 200 cm, tube voltage 80 kV). The dose level at which the film density of the screen-film system (SRO250/SRG) was 1.0+/-0.05 served as the reference dose (0.69microC/kg). Five samples were prepared by multiplying the reference dose by 1/4, 1/2, 1, 2, and 4. The samples for image quality evaluation on the basis of IQF were prepared under identical conditions. A contrast-detail (C-D) phantom was placed on a 50.0 mm tough water phantom and images were taken. The contrast threshold of these samples was determined by 10 film readers, the same as those for the ROC analysis. When the significance of differences in the AUC was tested by the paired t-test (two-sided) and the Jackknife method, significant differences were noted between the reference dose and the 1/4 or 4-times dose at the standard pixel size (0.175 mm) and smaller pixel size (0.0875 mm) size, while no significant difference was noted between the reference dose and the 1/2 or 2-times dose. In terms of IQF, no significant difference was noted between standard and smaller pixel sizes (paired t-test). The IQF data indicate that the dose level for imaging with CR can be reduced by about 30% from the reference dose.

TLD assessment of mouse dosimetry during microCT imaging

Advances in laboratory animal imaging have provided new resources for noninvasive biomedical research. Among these technologies is microcomputed tomography (microCT) which is widely used to obtain high resolution anatomic images of small animals. Because microCT utilizes ionizing radiation for image formation, radiation exposure during imaging is a concern. The objective of this study was to quantify the radiation dose delivered during a standard microCT scan. Radiation dose was measured using thermoluminescent dosimeters (TLDs), which were irradiated employing an 80 kVp x-ray source, with 0.5 mm A1 filtration and a total of 54 mA s for a full 360 deg rotation of the unit. The TLD data were validated using a 3.2 cm3 CT ion chamber probe. TLD results showed a single microCT scan air kerma of 78.0 +/- 5.0 mGy when using a poly(methylmethacrylate) (PMMA) anesthesia support module and an air kerma of 92.0 +/- 6.0 mGy without the use of the anesthesia module. The validation CT ion chamber study provided a measured radiation air kerma of 81.0 +/- 4.0 mGy and 97.0 +/- 5.0 mGy with and without the PMMA anesthesia module, respectively. Internal TLD analysis demonstrated an average mouse organ radiation absorbed dose of 76.0 +/- 5.0 mGy. The author's results have defined x-ray exposure for a routine microCT study which must be taken into consideration when performing serial molecular imaging studies involving the microCT imaging modality.

TH‐C‐332‐07: Dual Energy Contrast‐Enhanced Breast Computed Tomography: A Phantom Study

Purpose: To investigate lesion enhancement with iodinated contrast material using dual energy breast computed tomography (CT). Method and Materials: The dual energy cone‐beam breast CT system consisted of a flat panel detector and an x‐ray tube installed on an optical bench. The x‐ray tube voltage and x‐ray beam filtration were switched at 30 Hz between 50 kVp (2.0‐mm Al filter) and 120 kVp (2.0‐mm Al + 0.8‐mm Ag filtration). A cylindrical breast phantom was constructed from polymethylmethacrylate (PMMA) and filled with oil and shredded PMMA. Five known concentrations of iodine (0.5, 1, 2, 4, 8 mgI/ml) were embedded in the phantom. The images were reconstructed with a Feldkamp filtered‐back‐projection algorithm. Dual energy subtraction was used to eliminate the contrast of oil and PMMA to enhance iodine signals. Results: The low energy scan could not distinguish PMMA and iodine concentrations of 0.5 and 1 mgI/ml. The high energy image could not distinguish PMMA and iodine concentration of 8 mgI/ml. After subtracting the PMMA, all five concentrations of iodine could be clearly visualized on the dual energy CT image. The dual energy iodine signal (CTDE) and the iodine concentration (CI) were related by (R = 0.998 and SEE=15.26) Conclusion: Dual energy contrast‐enhanced breast CT can potentially improve lesion.

SU‐GG‐J‐70: Development of An Image‐Guided Conformal Small Animal Irradiation Platform

Purpose: To develop an image‐guided conformal small animal irradiation system for pre‐clinical studies. The initial dosimetric and imaging properties of the system have been characterized. Method and Materials: The system consists of a 225 kVp x‐ray tube (GE Isovolt, maximum power 3 kW, focal spot=0.4mm–3.0mm), and 20.5×20.5 cm amorphous silicon flat panel detector (512×512 pixels, 7 frames‐per‐second) mounted on a rotating gantry. The system can rotate 360°, at a maximum speed of 3 RPM. The source‐isocenter distance is 31 cm, and the source‐imager distance is 62 cm. Cone‐beam CT images are generated from projections over half or full rotation, and reconstructed using filtered‐back projection. A motorized stage allows translational movement of specimen. Initial dosimetric characterization of the system has been done using EBT Gafchromic film in a solid water phantom at 2 cm depth. The unit is free standing and self‐shielded. Results: The maximum dose rate achievable at isocenter is 4.5 Gy/min for 220 kVp unfiltered beam, and 2 Gy/min for 220 kVp beam with 0.5mm added Cu filtration (HVL = 1.0mm Cu). The maximum dose rate for 100 kVp is 2.5 Gy/min (unfiltered) and 1.5 Gy/min with 2mm added Al filtration (HVL = 3.1 mm Al). Cone‐beam CT images are generated with a resolution of 0.2×0.2×0.2 mm. Conclusion: Image‐guided conformal pre‐clinical irradiation systems will enable novel translational research in radiation oncology and radiobiology. The presented system has been demonstrated to provide the dose rate, mechanical stability and image‐guidance capabilities necessary to facilitate such research.

TH‐C‐332‐05: Quantification of Breast Density with Dual Energy Mammography

Purpose: To investigate a quantitative method for measuring breast density (the percentage of glandular breast tissue) with dual energy mammography using a dual exposure / dual kVp technique. Method and Materials: An analytical simulation model was developed to determine the mean glandular dose required to quantify breast density to within an accuracy of 1%. The simulation considered stochastic x‐ray and detector noise sources in a dual energy breast density image. The breast was modeled as a semicircle 10 cm in radius with homogenous equal thicknesses of adipose and glandular tissues. Monoenergetic beams were simulated with an ideal detector and polyenergetic spectra were simulated with an energy integrating detector modeled after an existing clinical system. A surrogate breast phantom was constructed to simulate a range of breast densities from 0 to 100%. The phantom was imaged using a full field digital mammography system at 25 kVp and 39 kVp with an additional 2 mm Al filter added to the high energy image. Dual energy images were generated with a non linear basis decomposition algorithm to yield image thickness maps of glandular and adipose tissue. Breast density was quantified using the dual energy images. Results: For a 4.2 cm breast of 50% density, optimal energies determined from simulation, for monoenergetic beams and an ideal detector, were 19 keV and 71 keV. For an energy integrating detector and polyenergetic spectra, optimal energies were 20 and 69 kVp. The estimated required dose for either technique was less than 0.1 mGy. For dual energy images, the known (K) and measured (M) breast densities were related by M = 1.007K − 0.006 (r = 0.999). RMS error for all densities was calculated to be less than 2% of the mean density. Conclusion: The results suggest that breast density can be accurately measured with dual energy mammography.

SU‐GG‐T‐549: Dosimetry of An X‐Ray Endocavitary Proctoscope Adapted for Use with the Axxent® Electronic Brachytherapy System

Purpose: To analyze the dose rate and uniformity at the aperture of an Electro‐Surgical Instrument (ESI). Proctoscope when used with an Axxent® Model S700 X‐ray Source. Method and Materials: The ESI proctoscope was originally designed for use with a Philips RT‐50 x‐ray contact therapy unit. Because these units are no longer supported, an alternative x‐ray source is being sought which allows for duplication of the Papillon technique for treating anal‐rectal lesions. A source holder was fabricated to position the Axxent model S700 X‐ray Source collinearly on axis within a lead‐lined proctoscope possessing a 24 mm inner diameter aperture. This mechanism allows the distance from the proctoscope aperture to the source to be adjusted from 1 to 10 cm and allows a filter to be placed at the distal end of the source to harden the beam and/or flatten the dose distribution. The dose rate was measured at the proctoscope aperture using a PTW 34013 Soft X‐ray Chamber set into the surface of a Gammex RMI 457 solid water phantom. GAFChromic EBT radiochromic film was used for profile measurements. Results: For operation at 50 kVp and 0.30 mA beam current with a 0.5 mm thick Al filter and source‐to‐aperture distance of 3.4 cm, the dose rate was 1.1 Gy per minute. Profile evaluation indicated a dose uniformity of 5%, 8% and 15% across 80%, 93% and 98% of the aperture diameter, respectively, without use of a flattening filter. Conclusion: Measurements of dose rate and uniformity at the aperture of a 24 mm diameter ESI proctoscope indicate that the Axxent S700 x‐ray source may be a suitable alternative to the Philips RT‐50 Endocavitary Unit for treatment of anal‐rectal lesions. Conflict of interest: Research sponsored by Xoft, Inc.

Applicability of MiniPal 4 compact EDXRF spectrometer for soil and sediment analysis

AbstractOptimum measurement parameters for analysis of soil and sediment samples with the compact MiniPal 4 (MP4)EDXRF spectrometer (PANalytical, Almelo, The Netherlands) were presented. The following elements were considered: K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As and Pb. Since the elements from low Z to medium Z region were covered, three measurement conditions (sequences) were defined. The following parameters were selected for measurement of the elements K, Ti, and V: voltage = 12 kV; current = 750 µA; filter material: Al_thin. Cr, Mn and Fe were measured at 20 kV; 300 µA with Al filter while for measurements of Ni, Cu, Zn, As, Pb, Rb, and Sr an Ag filter was selected and tube voltage and current were 30 kV and 300 µA. Each sequence was measured for 200 s and measurements were done in the air. MP4 spectrometer was characterized with acceptable precision, long‐term stability and satisfactory minimum detection limit for the analyses of soil and sediment materials. For the elements K, Mn, Fe, and Ti the precision of the analysis was better than 0.5% and for all the other elements better than 5%. Detection limits for sediment samples were 20 ppm for K, 6.1 ppm for Ti, 5.2 for Mn, 4 ppm for Fe, 4.2 ppm for As and less than 2 ppm for all the other elements. These values were significantly lower compared to typical concentrations of the same elements found in unpolluted soil and sediments. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Improvements in trace element detection in energy dispersive spectrometry using an X-ray filter (FEDS) and applications to petrological problems

Interaction of electron beam with the surface of a massive sample leads to the emission of characteristic X-rays, which can be collected by an energy-dispersive detector. However, an ED spectrum is marked by a low peak/background ratio, which implies a detection limit around 0.5 wt% for the most common mineral forming elements. In this paper spectra obtained by an EDS microprobe, performed filtering the X-rays striking the detector with a mechanical Al filter (FEDS), are presented. The resultant energy spectrum, processed with an opportune digital filter, allows to reach a detection limit ranging from 100 to tens ppm, depending on the atomic number of the excited element. Therefore, the acquisition of major (by conventional EDS analysis) and trace (by FEDS analysis) elements on the same area (with a resolution of few micrometers) is made possible applying and/or removing the mechanical filter. In this paper the FEDS procedure is described and a comparison among trace elements in certified NIST glass standards and in a metamorphic rock-forming garnet is presented.

Experimental study of beam hardening artifacts in photon counting breast computed tomography

We are implementing an X-ray breast Computed Tomography (CT) system on the gantry of a dedicated single photon emission tomography system for breast Tc-99 imaging. For the breast CT system we investigated the relevance of the beam hardening artifact. We studied the use of a single photon counting silicon pixel detector (0.3 mm thick, 256 × 256 pixel, 55 μ m pitch, bump-bonded to the Medipix2 photon counting readout chip) as detector unit in our X-ray CT system. We evaluated the beam hardening “cupping” artifact using homogeneous PMMA slabs and phantoms up to 14 cm in diameter, used as uncompressed breast tissue phantoms, imaged with a tungsten anode tube at 80 kVp with 4.2 mm Al filtration. For beam hardening evaluation we used a bimodal energy model. The CT data show a “cupping” artifact going from 4% (4-cm thick material) to 18% (14-cm thick material). This huge artifacts is influenced by the low detection efficiency and the charge sharing effect of the silicon pixel detector.