CsI Flat Panel Detector Research Articles

Study of X-ray Beam Quality and Contrast-to-Noise Ratio of Lung Nodules in Chest FPD Radiography: Monte Carlo Simulation Using Chest Model Phantom

Contrast-to-noise ratio (CNR) of four X-ray beams (90 kV with 0.15-mm Cu filter, 90 kV with 0.2-mm Cu filter, 120 kV without filter and 120 kV with 0.2-mm Cu filter) in CsI-flat panel detector (FPD) radiography for lung cancer diagnosis was investigated using Monte Carlo simulation. Two billion photons were injected to the chest phantom model (width: 300 mm, length: 300 mm, thickness: 200 mm) with imitated lung nodules (10 mm diameter, CT value: +30 Hounsfield unit (HU), -375 HU, and -620 HU). Individual primary and secondary photon's process (absorption, scattering and penetration) in the phantom and CsI-detector was recorded by Monte Carlo simulation. CNR was calculated using primary and secondary absorbed photon's number in the CsI-detector. CNR of 90 kV X-ray beam with 0.15 mm and 0.2 mm Cu filters was higher to 120 kV X-ray beam because of higher primary object contrast and photon's contribution, and high photon's absorption to CsI. By Monte Carlo calculation, it was verified that 90 kV X-ray beam with 0.15 mm and 0.2 mm Cu filters yielded higher CNR to 120 kV X-ray beam.

Evaluation of Non-Uniform Image Quality Caused by Anode Heel Effect in Digital Radiography Using Mutual Information.

Anode heel effects are known to cause non-uniform image quality, but no method has been proposed to evaluate the non-uniform image quality caused by the heel effect. Therefore, the purpose of this study was to evaluate non-uniform image quality in digital radiographs using a novel circular step-wedge (CSW) phantom and normalized mutual information (nMI). All X-ray images were acquired from a digital radiography system equipped with a CsI flat panel detector. A new acrylic CSW phantom was imaged ten times at various kVp and mAs to evaluate overall and non-uniform image quality with nMI metrics. For comparisons, a conventional contrast-detail resolution phantom was imaged ten times at identical exposure parameters to evaluate overall image quality with visible ratio (VR) metrics, and the phantom was placed in different orientations to assess non-uniform image quality. In addition, heel effect correction (HEC) was executed to elucidate the impact of its effect on image quality. The results showed that both nMI and VR metrics significantly changed with kVp and mAs, and had a significant positive correlation. The positive correlation is suggestive that the nMI metrics have a similar performance to the VR metrics in assessing the overall image quality of digital radiographs. The nMI metrics significantly changed with orientations and also significantly increased after HEC in the anode direction. However, the VR metrics did not change significantly with orientations or with HEC. The results indicate that the nMI metrics were more sensitive than the VR metrics with regards to non-uniform image quality caused by the anode heel effect. In conclusion, the proposed nMI metrics with a CSW phantom outperformed the conventional VR metrics in detecting non-uniform image quality caused by the heel effect, and thus are suitable for quantitatively evaluating non-uniform image quality in digital radiographs with and without HEC.

Optimal Beam Quality in Chest Radiography Using CsI-flat Panel Detector for Detection of Pulmonary Nodules

Optimal beam quality for detection of pulmonary nodules in digital chest radiography using CsI-flat panel detector (FPD) was investigated in consideration of image quality and patient dose. The human chest phantom with inserted imitated nodules (diameter: 10 mm, CT value: +30 Hounsfield unit (HU), -375 HU, -620 HU) was used for the measurement of contrast-to-noise ratio (CNR) of imitated nodules by twenty beams arranged by five tube voltages and four filters. The CNR varies with X-ray tube voltage and added filter. CNR correlates weakly to the tube voltage, fairly to the effective energy in second-order polynomial and strongly to the quality index (effective energy divided X-ray tube voltage). In order to improve the CNR, the effective energy and the quality index are kept about 50 keV and more than 0.5, respectively, using an 80-100 kV beam with a copper filter. A 90 kV (2.5 mm Al inherent filtration) beam with a 0.15 mm copper filter and a 90 kV or 100 kV (2.5 mm Al inherent filtration) beam with a 0.2 mm copper filter are appropriate for chest radiography using CsI-FPD.

Scatter imaging during lung stereotactic body radiation therapy characterized with phantom studies

By collecting photons scattered out of the therapy beam, scatter imaging creates images of the treated volume. Two phantoms were used to assess the possible application of scatter imaging for markerless tracking of lung tumors during stereotactic body radiation therapy (SBRT) treatment. A scatter-imaging camera was assembled with a CsI flat-panel detector and a 5 mm diameter pinhole collimator. Scatter images were collected during the irradiation of phantoms with megavoltage photons. To assess scatter image quality, spherical phantom lung tumors of 2.1–2.8 cm diameters were placed inside a static, anthropomorphic phantom. To show the efficacy of the technique with a moving target (3 cm diameter), the position of a simulated tumor was tracked in scatter images during sinusoidal motion (15 mm amplitude, 0.25 Hz frequency) in a dynamic lung phantom in open-field, dynamic conformal arc (DCA), and volumetric modulated arc therapy (VMAT) deliveries. Anatomical features are identifiable on static phantom scatter images collected with 10 MU of delivered dose (2.1 cm diameter lung tumor contrast-to-noise ratio of 4.4). The contrast-to-noise ratio increases with tumor size and delivered dose. During dynamic motion, the position of the 3.0 cm diameter lung tumor was identified with a root-mean-square error of 0.8, 1.2, and 2.9 mm for open field (0.3 s frame integration), DCA (0.5 s), and VMAT (0.5 s), respectively. Based on phantom studies, scatter imaging is a potential technique for markerless lung tumor tracking during SBRT without additional imaging dose. Quality scatter images may be collected at low, clinically relevant doses (10 MU). Scatter images are capable of sub-millimeter tracking precision, but modulation decreases accuracy.

Evaluation of 90 kV Beam with 0.15 mm Cu Filter in Chest Radiography Using CsI-flat Panel Detector

To compare the visibility of anatomic structure in chest radiography acquired with different beam quality (120 kV beam and 90 kV beam with 0.15 mmCu) using CsI-flat panel detector. Pair image obtained by different beam quality of 100 person's chest radiographies which were taken periodical health examination were compared with the visibility of normal structures (pulmonary vessels) and abnormal opacities by two pulmonologists and four radiological technologists. Moreover, the spectrum of the two beam quality were calculated using Monte Carlo simulation. Dominant observers gave high score significantly (p<0.01) to the 90 kV beam's image in spite of 20% less dose. Monte Carlo simulation showed that 90 kV beam with 0.15 mmCu were much absorbed primary photon than 120 kV beam to CsI detector, and less absorbed secondary photon. The visibility of anatomic structure and abnormal opacities in FPD chest radiography was improved by using the 90 kV beam with 0.15 mmCu than traditional 120 kV beam's chest radiography.

OA099] Patient dose evaluation and optimization during hysterosalpingography using digital X_ray equipment

Introduction Hysterosalpingography (HSG) is the radiological examination of the uterus and fallopian tubes and is most primarily used to evaluate tubal patency in healthy patients of child bearing age with infertility. In light of ICRP (International Commission on Radiological Protection) recommendations and Italian Legislation concerning the protection of individuals against ionizing radiation risk related to medical exposure, the present work aimed at monitoring and optimizing the radiation dose imparted to patients undergoing this procedure. Materials and Methods A first survey was carried out in our radiology department, collecting data from 31 subjects during HSG, carried out using digital equipment (model Opera, Housing GMM, Italy, with over-couch tube, CsI flat panel detector Thales, model Pixium RAD 4343 with pixel size 148 μ m, Automatic Exposure Control). Data showed a wide variability, with the mean DAP (Dose Area Product) being higher than those reported by other authors [1] from other departments, suggesting need for optimization. After intervention (consisting in reducing the field size, the fluoroscopy time and the number of radiographs) a new group of 53 subjects was monitored, showing significant DAP reduction. ESAKs (Entrance Surface Air Kerma – free in air) – calculated by using normalized radiation output (previously assessed during quality controls), current*time product (recorded during HSG) and source-skin distance – were converted to dose to ovaries by using appropriate coefficients. Also ED (effective dose) was evaluated. Results Mean DAP decreased from 3348 to 634 mGy*cm2. The 75th percentile of the DAP distribution, 800 mGy*cm2, was adopted as Institutional Diagnostic Reference Level. Mean estimated dose to ovaries was about 0.8 mGy and mean effective dose was about 0.3 mSv. Conclusions Periodic review of the procedures, in light of both technological advances and clinical requests, is necessary in order to improve clinical practice with guaranteed patient safety.

TH-A-103-11: Breast Density Measurement with Cone-Beam CT and MRI: A Postmortem Study

Purpose: To investigate the feasibility of breast density quantification using a cone‐beam computed tomography (CBCT) and a magnetic resonance imaging (MRI) system with a postmortem study. Methods: Twenty pairs of postmortem breasts were imaged with a bench‐top CBCT system based on a CsI flat panel detector and an Aurora 1.5T dedicated Breast MRI system. The CT images were acquired at 50 kVp with a mean glandular dose (MGD) of approximately 3 mGy. A T1‐weighted gradient echo technique was used in MRI scans to maximize the contrast between the adipose and glandular tissues. Image processing procedures were implemented to segment the glandular tissue from adipose tissue. For CBCT images, standard histogram thresholdings based on visual assessment and automated segmentation based on a basic fuzzy c‐means (FCM) algorithm were used. For MRI images, FCM‐based clustering and the coherent local intensity clustering (CLIC) method, which estimated and removed the bias field, were used. Finally, the breast densities measured with the two systems were compared to the definitive tissue compositions obtained from chemical analysis. The linear correlation coefficient, Pearson r, was used to evaluate the two imaging modalities and the investigated image segmentation methods. Results: Both histogram thresholdings and FCM techniques used for CBCT images show excellent correlations with respect to the fibroglandular ratio (FGR) from chemical analysis, with r values of 0.964 and 0.980, respectively. The correlations of the MRI measurement were slightly worse than those from CBCT. The CLIC method successfully removed the intensity inhomogeneity induced by the bias field, and improved the r value from 0.864 to 0.915. Conclusion: CBCT can be used to accurately quantify the breast density with automated clustering algorithms. It is anticipated that CBCT may outperform breast MRI in breast density quantification due to high spatial resolution and the absence of the bias field.

TU‐G‐110‐03: Optimal Techniques for Dual Energy and Spectral Breast Computed Tomography with an Iodinated Contrast Agent

Purpose: To investigate the optimal techniques for dual energy and spectral breast computed tomography with an iodinated contrast agent.Methods: Simulations were performed for three CT systems. The first system was based on a CsI flat panel detector and used a dual kVp technique. The second and third systems were based on a CZT photon counting detector with energy resolution and single kVp technique. The first CZT system used a single threshold to separate photons from one acquisition into either low or high energy images. The second CZT system used multiple thresholds to separate photons from one acquisition into one of five energy images. Iodine images for the dual kVp system and the two energy CZT system were generated under the assumption that a linear three material decomposition contains glandular tissue, adipose tissue and iodine. For the second CZT system, iodine images were generated using an iterative likelihood maximization algorithm. Beam energies ranging from 40 to 140 kVp were simulated for all systems. A figure‐of‐merit (FOM), defined as the dual energy signal‐to‐noise ratio of contrast in the iodine image divided by the square root of mean glandular dose, was used to quantify imaging performance. Results: The highest FOM, normalized to 1.0, was seen with the two energy CZT system at a beam energy of 40 kVp. Performance from the five energy CZT system was highest at 46 kVp with an FOM value of 0.75. The FOM of the dual kVp was maximized at beam energies of 48 kVp and 140 kVp with a value of 0.28. Conclusion: The results of this study indicate that a CZT based CT system of either configuration could potentially produce images of significantly higher quality than that of a comparable flat panel based dual energy CT system.

SU‐C‐220‐02: A High Efficiency Grid System for Abdominal Radiography

Purpose: To improve scatter control in abdominal radiography.Methods: A crossed grid system was constructed and consists of a stationary low ratio, high strip density conventional grid (8:1, 60 lines/cm) positioned above and with its septa orthogonal to the septa of a novel high ratio, air interspace, coarse strip density scanning grid (15:1, 2.0 lines/cm). The latter has articulating grid slats; during an exposure the slats remain focused on the x‐ray focal spot. To suppress grid line artifacts, a trapezoidal x‐ray exposure was generated and coupled with the movement of the scanning grid. This effectively eliminates grid line artifacts for small grid movements. The grid DQE was measured for 4 grid configurations: the crossed grid system, the scanning grid alone, a stationary 15:1 conventional grid, and no grid. The measurements were made with standard CsI flat panel detector and a variety of acrylic thicknesses and x‐ray tube potentials.Results: In all cases the DQEgrid measured with the various grid systems was markedly better (130% to 580%) than that measured without a grid. The performance of the crossed grid system was 6% to 120% better than the conventional 15:1 grid. The scanning grid system performed 22% better (20 cm acrylic, 60 kVp) to 6% worse (40 cm acrylic, 120 kVp) than the crossed grid system. While subtle gridline artifacts are present in flat‐field images, the artifacts are invisible in images of anthropomorphic phantoms Conclusions: A high efficiency scanning grid system has been designed and constructed. The system requires only a short grid movement during an exposure to suppress grid line artifacts. It can be used with or without a crossed conventional low ratio grid. In either case, its dose efficiency in controlling scatter is markedly superior that of a high quality, high ratio conventional stationary grid.The authors are co‐owners of X‐Ray Imaging Innovations, which has developed this technology, and are co‐inventors of U.S. Patent 6,795,529, which covers this technology

TU-C-I-609-04: Optimization of Radiographic Imaging Using Simulated Radiography and Electronic Observers

Purpose: Software incorporating an anatomical radiograph simulator, effective dose calculator, and image quality analysis has been developed to determine the optimal balance between patient dose and image quality. Method and Materials: Radiograph simulation is divided into the primary and scattered portions of an x-ray interaction. A tomographic phantom, VIP-Man, is used to simulate the scattered portion using the ESGnrc Monte Carlo code. The primary portion is simulated using the projection ray-tracing method through the Visible Human CT data set. To produce a realistic radiograph, the software simulates quantum noise, blurring effects, lesions, detector absorption efficiency, and other imaging artifacts. The primary and scattered portions of the simulated radiograph are combined to form an image for simulated observer studies and image quality analysis. Absorbed doses in the VIP-Man phantom were also obtained from the Monte Carlo simulations. Once radiographs are produced, they are analyzed using several simulated observer filters including; non-prewhitening matched filter with eye, Hotelling, and channelized Hotelling. Using the VIP-Man phantom as a representative patient, a CsI flat panel detector and a small lesion in the left lung was examined as a test case. Energy was varied mono-energetically while fluence was varied. Approximately 2000 simulated images and 200,000 data files were analyzed. Results: Receiver Operator Characteristic (ROC) curves and the corresponding Area Under Curve (AUC) charts were developed for the 2000 simulated images. For the patient size considered, the energy at which the minimum effective dose required to obtain an AUC of 0.85 was determined to be 70 keV. Conclusion: Coupling an imaging simulator with a computerized simulated observer represents a new avenue for maintaining image quality while minimizing patient dose. Rescaling the VIP-Man phantom will extend the database of representative patients for a verity of imaging tasks.

A framework for optimising the radiographic technique in digital X-ray imaging

The transition to digital radiology has provided new opportunities for improved image quality, made possible by the superior detective quantum efficiency and post-processing capabilities of new imaging systems, and advanced imaging applications, made possible by rapid digital image acquisition. However, this transition has taken place largely without optimising the radiographic technique used to acquire the images. This paper proposes a framework for optimising the acquisition of digital X-ray images. The proposed approach is based on the signal and noise characteristics of the digital images and the applied exposure. Signal is defined, based on the clinical task involved in an imaging application, as the difference between the detector signal with and without a target present against a representative background. Noise is determined from the noise properties of uniformly acquired images of the background, taking into consideration the absorption properties of the detector. Incident exposure is estimated or otherwise measured free in air, and converted to dose. The main figure of merit (FOM) for optimisation is defined as the signal-difference-to-noise ratio (SdNR) squared per unit exposure or (more preferably) dose. This paper highlights three specific technique optimisation studies that used this approach to optimise the radiographic technique for digital chest and breast applications. In the first study, which was focused on chest radiography with a CsI flat-panel detector, a range of kV(p) (50-150) and filtration (Z = 13-82) were examined in terms of their associated FOM as well as soft tissue to bone contrast, a factor of importance in digital chest radiography. The results indicated that additive Cu filtration can improve image quality. A second study in digital mammography using a selenium direct flat-panel detector indicated improved SdNR per unit exposure with the use of a tungsten target and a rhodium filter than conventional molybdenum target/molybdenum filter techniques. Finally, a third study focusing on cone-beam computed tomography of the breast using a CsI flat-panel detector indicated that high Z filtration of a tungsten target X-ray beam can notably improve the signal and noise characteristics of the image. The general findings highlight the fact that the techniques that are conventionally assumed to be optimum may need to be revisited for digital radiography.