Flat-panel System Research Articles

Digital amorphous silicon flat-panel detector radiography at different exposure doses versus mammography film: possibility of radiation dose reduction in detecting rheumatologic bone defects

Radiographic examinations of the skeleton are the most commonly performed radiologic procedures, even outnumbering examinations of the chest. The imaging systems used in skeletal radiography must meet high standards in terms of contrast and spatial resolution to effectively visualize the high contrast between bone and soft tissue as well as fine bone structures. To determine the performance of amorphous silicon flat-panel detector radiography compared to mammography film in detecting rheumatologic bone defects at different exposure doses. The study enrolled 44 patients with known or presumed skeletal changes of the hand associated with inflammatory rheumatic diseases. Following a clinically indicated radiographic examination of the peripheral extremities using mammography film, a survey radiograph of one hand was taken in the posteroanterior (PA) view by digital radiography, at the same exposure dose and at a dose reduced to one quarter of the mammography film doses. Four independent radiologists scored the resultant images using the Sharp/van der Heijde and Ratingen scoring methods. The study received University of Cologne Ethics Committee and German Federal Radiation Protection Agency approval. Compared to mammography film, digital flat-panel detector radiography produced a significantly better image quality at identical uptake doses. A greater number of erosions were detected with the digital flat-panel detector than with mammography film at the same and at reduced doses. Although the spatial resolution of the digital flat-panel system used in this study was poorer than mammography film, this was compensated for by its wider dynamic range and improved contrast resolution, even at the reduced dose.

Physical image quality comparison of four types of digital detector for chest radiology

Image quality for similar exposure conditions has been compared for two computed radiography (CR) systems (needle-based and conventional storage phosphor) and two flat-panel (DR) systems from different manufacturers mainly devoted to chest radiology. Image quality was assessed with a contrast-detail object and acrylic material to simulate clinical conditions. Specific image evaluation software was used to measure the contrast and obtain an image quality figure. Phantom and detector incident air kerma were measured for all images. Image quality differences were significant, and in the range of 100-300 microGy (phantom incident air kerma) the needle-based CR system and one of the DR systems show similar image quality and they are quite superior when compared with the conventional CR system.

Radiation dose survey in a paediatric cardiac catheterisation laboratory equipped with flat-panel detectors

Flat-panel X-ray detectors for fluoroscopy represent a modern imaging equipment that is being implemented in paediatric cardiac catheterisation laboratories. Infants and children represent a group of patients with a high radiosensitivity. A survey of 273 (126 diagnostic and 147 therapeutic) paediatric catheterisations was performed to investigate the radiation doses delivered by the new X-ray system. Statistical parameters (75th, 50th and 25th percentiles) of dose-area product (DAP) and fluoroscopy time are reported for patients divided into six age groups: 0-30 d, >1-12 m, >1-3, >3-5, >5-10 and >10-15 y. For accurate risk estimation, effective dose (E) has been determined for all patients using the PCXMC software. For diagnostic procedures, the third quartile of E ranges from 11.3 mSv for newborns to 7 mSv for children of 10-15 y. Therapeutic procedures are more complex than diagnostic. Consequently, the third quartile of E is 22.6 mSv (0-30 d), 18.6 (>1-12 m), 13.3 (>1-3 y), 21.5 (>3-5 y), 17.8 (>5-10 y) and 34.1 mSv (>10-15 y). Dose conversion factors, which relate the DAP and E, have been estimated for each age group. The results of this study may serve as a first step in the optimisation process, in order to make full use of the dose reduction potential of flat-panel systems.

Design of a prototype tri-electrode ion-chamber for megavoltage X-ray imaging

High-energy (megavoltage) X-ray imaging is widely used in industry (e.g., aerospace, construction, material sciences) as well as in health care (radiation therapy). One of the fundamental problems with megavoltage imaging is poor contrast and spatial resolution in the detected images due to the dominance of Compton scattering at megavoltage X-ray energies. Therefore, although megavoltage X-rays can be used to image highly attenuating objects that cannot be imaged at kilovoltage energies, the former does not provide the high image quality that is associated with the latter. A high contrast and spatial resolution detector for high-energy X-ray fields called the kinestatic charge detector (KCD) is presented here. The KCD is a tri-electrode ion-chamber based on highly pressurized noble gas. The KCD operates in conjunction with a strip-collimated X-ray beam (for high scatter rejection) to scan across the imaging field. Its thick detector design and unique operating principle provides enhanced charge signal integration for high quality imaging (quantum efficiency ∼50%) despite the unfavorable implications of high-energy X-ray interactions on image quality. The proposed design for a large-field prototype KCD includes a cylindrical pressure chamber along with 576 signal-collecting electrodes capable of resolving at 2 mm −1. The collecting electrodes are routed out of the chamber through the flat end-cap, thereby optimizing the mechanical strength of the chamber. This article highlights the simplified design of the chamber using minimal components for simple assembly. In addition, fundamental imaging measurements and estimates of ion recombination that were performed on a proof-of-principle test chamber are presented. The imaging performance of the prototype KCD was found to be an order-of-magnitude greater than commercial phosphor screen based flat-panel systems, demonstrating the potential for high-quality megavoltage imaging for a variety of industrial applications.

Image Quality and Radiation Dose on Digital Chest Imaging: Comparison of Amorphous Silicon and Amorphous Selenium Flat-Panel Systems

The aim of this study was to compare the image quality and radiation dose in chest imaging using an amorphous silicon flat-panel detector system and an amorphous selenium flat-panel detector system. In addition, the low-contrast performance of both systems with standard and low radiation doses was compared. In two groups of 100 patients each, digital chest radiographs were acquired with either an amorphous silicon or an amorphous selenium flat-panel system. The effective dose of the examination was measured using thermoluminescent dosimeters placed in an anthropomorphic Rando phantom. The image quality of the digital chest radiographs was assessed by five experienced radiologists using the European Guidelines on Quality Criteria for Diagnostic Radiographic Images. In addition, a contrast-detail phantom study was set up to assess the low-contrast performance of both systems at different radiation dose levels. Differences between the two groups were tested for significance using the two-tailed Mann-Whitney test. The amorphous silicon flat-panel system allowed an important and significant reduction in effective dose in comparison with the amorphous selenium flat-panel system (p < 0.0001) for both the posteroanterior and lateral views. In addition, clinical image quality analysis showed that the dose reduction was not detrimental to image quality. Compared with the amorphous selenium flat-panel detector system, the amorphous silicon flat-panel detector system performed significantly better in the low-contrast phantom study, with phantom entrance dose values of up to 135 muGy. Chest radiographs can be acquired with a significantly lower patient radiation dose using an amorphous silicon flat-panel system than using an amorphous selenium flat-panel system, thereby producing images that are equal or even superior in quality to those of the amorphous selenium flat-panel detector system.

SU-FF-J-42: Cone Beam CT Based Treatment Planning

Purpose: To evaluate treatment planning based on cone beam CT (CBCT) using latest software on a LINAC 21IX CBCT imaging system. Method and Materials: An anthropomorphic chest phantom having bone, soft tissue, and lung components was used to create and evaluate treatment plans based on conventional CT and CBCT images. Conventional CT images of 2.5 mm slice thickness were taken with a GE discovery LS CT/PET system. CBCT images slices were also reconstructed from flat panel system on a Varian LINAC 21IX. Eclipse treatment planning system was used to compare treatment plans from the conventional CT and CBCT images. The AAA algorithm was used in the treatment planning system for inhomogeneity correction. Regions of interest around the bone, soft tissue, and lung in both CT and CBCT images using identical HU threshold values were drawn. Identical targets located in the lung were used in each treatment plan. Analysis of the treatment plans was performed by comparison of geometrical dimensions, total volumes and dose volume histograms of the target and regions of interest. Results: Geometric comparison of actual external spatial dimensions and others in lung and bone were found to be within 1 mm. Volumetric comparison of the regions of interest resulted in a 2.8% difference of the vertebrae, 3.3% of the right lung, and 3.7% of the total external volume. Dosimetric results show similar dose distributions. Dose volume histograms are also comparable. Conclusion: Results demonstrate that treatment planning based on CBCT is feasible. Plans created from CBCT images are comparable to plans created with conventional CT systems. Conflict of Interest: Partly funded by Prostate Cancer Foundation grant UW 133-HR30.

TU‐FF‐A4‐06: Variation in Dual‐Energy Chest Radiography Among Systems Using Identical Digital Flat Panel Detectors

Purpose: To study the variation of dual‐energy chest radiography systems by measuring Spectral Quality Factor (SQF) and subtracted‐image Noise Quality Factor (NQF) defined by Alvarez, Seibert, and Thompson (2004)1. SQF depends on the x‐ray energy spectrum and detector DQE. NQF is a measure of noise in the subtracted image, which depends on SQF and detected signal levels. Method and Materials: Stepwedges of aluminum and polycarbonate duplicating the original work and a 4.8 mm thick acrylic slab were radiographed in dual energy chest mode at 120 and 60 kVp using 15 systems (XQ/i, XR/d, and XR/dII; GE Medical Systems; Milwaukee, WI). Exposure levels of approximately 16, 24, 47, and 57 mR were measured free‐in‐air, corrected to the surface of the acrylic slab. SQF was calculated from effective linear attenuation coefficients, slopes of logarithm of pixel values behind each step relative to an uncovered area versus step thickness from raw images of each stepwedge at low and high energy. NQF was the slope of SNR2 in the soft‐tissue image of the smallest step of the polycarbonate stepwedge versus entrance exposure. Results: Alvarez, et al. compared three dual‐energy detector technologies, reporting results in relative terms, including variation of ±5% in SQF for an individual unit like ours. Our SQF was approximately 1.2×10−8 mm−2 ±14%. They reported NQF of 0.18 mR−1 estimated from Fig.10 using images subtracted by their own algorithm. Our NQF was approximately 0.16 mR−1 ±9% using images subtracted by the clinical system. Conclusions: SQF and NQF are useful indicators of dual energy system performance that can be determined in a practical setting with clinical systems. Values for our flat panel systems are in general agreement with previous reports.

High-performance n-channel 13.56MHz plasma-enhanced chemical vapor deposition nanocrystalline silicon thin-film transistors

Hydrogenated nanocrystalline silicon (nc-Si:H) films were directly deposited by using 13.56MHz plasma-enhanced chemical vapor deposition at a substrate temperature of 260°C with highly hydrogen (H2) diluted silane (SiH4) gases. The nc-Si:H film showed a high Raman crystalline volume fraction (XC∼85%) and low oxygen concentration (CO∼1.5×1017at.∕cm3). The formation of high-quality nc-Si:H is explained in terms of the effective roles of atomic hydrogen in the plasma. Top-gate staggered n-channel thin-film transistors (TFTs) adopting 90–100nm nc-Si:H channel and ∼300nm hydrogenated amorphous silicon oxide (a-SiOx) gate dielectric layers showed a field-effect mobility (μFE) of ∼150cm2∕Vs, a threshold voltage (VT) of ∼2V, a subthreshold slope (S) of ∼0.23V∕dec, and an on/off current ratio of more than 106. The TFT performance reported here offers promise for the total integration of peripheral electronics for active-matrix flat panel systems.

Patient Radiation Dose in Percutaneous Transluminal Coronary Angioplasty Using Various Types of Flat-panel Digital X-ray Systems

Patient Radiation Dose in Percutaneous Transluminal Coronary Angioplasty Using Various Types of Flat-panel Digital X-ray Systems

Comparison of a CCD and a flat-panel digital system in an Interventional Cardiology Laboratory

We evaluated the performances of angiographic units equipped with a flat-panel (FP) detector and image intensifier (II) charge-coupled device (CCD) in the Interventional Cardiology (IC) Department. Entrance dose rate and dose per image, along with the dose at the II level were measured using 2 mm copper sheets to simulate a patient. Image quality (IQ) was evaluated using a phantom. Doses increased with fluoroscopy level changing from low to high. FP presented higher doses than CCD. Periodic measurements showed differences of up to 35%. Low mode IQ did not significantly differ from normal and high mode for both systems. Low fluoroscopy mode was decided to be used routinely. Both X-ray systems performed within international recommendations for conventional systems with the exception of higher cine radiation doses and II dose rates, stressing the fact that more studies are required to investigate whether dose levels should be adjusted.

Image quality measurements and metrics in full field digital mammography: an overview

This paper gives an overview of test procedures developed to assess the performance of full field digital mammography systems. We make a distinction between tests of the individual components of the imaging chain and global system tests. Most tests are not yet fully standardised. Where possible, we illustrate the test methodologies on a selenium flat-panel system.

Comparison of a digital flat-panel versus screen–film, photofluorography and storage-phosphor systems by detection of simulated lung adenocarcinoma lesions using hard copy images

The purpose of this study was to compare hard copy images from a flat-panel detector digital radiography system with conventional radiography, photofluorographic radiography and storage phosphor radiography for the detection of simulated lung adenocarcinoma lesions and also for radiation dose. To test the diagnostic performance of these four systems, the authors used 15 types of lung adenocarcinoma phantom according to Noguchi's classification and an anthropomorphic chest phantom. The visual evaluation of tumour detectability by four radiologists and two general thoracic surgeons was examined with a five-level confidence scale. Lung doses were measured with glass dosemeters for the chest radiology systems under the conditions used by each hospital and centre. Our results indicated that flat-panel detector digital radiography and storage phosphor radiography are not necessarily superior to conventional radiography and photofluorographic radiography for detecting lung adenocarcinomas when only hard copy images are used, and this suggests a need to carefully optimize chest radiography.

Radiation Dose to Patients and Radiologists During Transcatheter Arterial Embolization: Comparison of a Digital Flat-Panel System and Conventional Unit

The objective of our study was to evaluate the exposure doses to patients and radiologists during transcatheter arterial embolization (TAE) for hepatocellular carcinoma (HCC) using a new angiographic unit with a digital flat-panel system. Doses were assessed for 24 procedures: 12 using a new unit with a digital flat-panel system and 12 using a conventional unit. Doses to patients' skin were evaluated with thermoluminescent dosimeters behind the left, middle, and right portions of the liver. The doses to the radiologists were measured by an electronic personal dosimeter placed on the chest outside a lead protector. The maximal skin doses to the patients and the dose equivalents, Hp(0.07), to the radiologists were compared between the two procedure groups with each angiographic unit. For procedures with the new unit, the mean maximal skin dose to the patients was 284 +/- 127 (SD) mGy (range, 130-467 mGy), and Hp(0.07) to the radiologists was 62.8 +/- 17.4 muSv. For procedures with the conventional unit, the maximal skin dose to the patients was 1,068 +/- 439 mGy (range, 510-1,882 mGy), and Hp(0.07) to the radiologists was 68.4 +/- 25.7 muSv. The maximal skin dose to the patients was significantly lower with the new unit than with the conventional unit (p < 0.0005). There was no significant difference in the Hp(0.07) to the radiologists between the two procedure groups. The new digital flat-panel system for angiographic imaging can reduce the radiation dose to patients' skin during TAE for HCC as compared with the conventional system.

Comparative evaluation of an II based and a flat panel based cardiovascular fluoroscopy system within a clinical environment

The image quality and dose parameters from a 2004 Siemens Axiom Artis dBC cardiac biplane with flat panel detector were evaluated and compared to similar parameters evaluated for a 1977 Toshiba DPF 2000A biplane cardiac unit with a conventional image intensifier. Image quality assessment was performed with the Westmead test object; using solid water as a patient equivalent absorber. The patient dose comparison of the two systems is based on dose area product meter readings for 1512 patient cases recorded over 6 months following installation of the Siemens flat panel digital unit. The image quality results indicate that: (a) high contrast resolution was better with the digital flat panel unit, (b) low contrast resolution is similar between systems, and (c) the threshold contrast of the flat panel system is the same or inferior to that of the image intensifier system. Input dose to the surface of the flat panel detector showed a strong dependence on field size, similar to the behaviour of image intensifier system. For the most common clinical procedure--Left Heart Study via Judkins--the average total dose area product reading was 64.0 Gy-cm2 against 67.7 Gy-cm2 for the digital and conventional units respectively (p = 0.27) indicating no significant difference in dose performance between the two x-ray machines.

Randomized study of the safety and clinical utility of rotational vs. standard coronary angiography using a flat-panel detector

The purpose of this study was to test the hypothesis that rotational angiography improves patient safety while maintaining diagnostic accuracy for patients undergoing coronary angiography. Despite advances in angiographic technique, patients remain at risk for complications of coronary angiography, including contrast-induced nephropathy and radiation exposure. Technology has been developed to perform coronary angiography with active rotation of the imaging system that may reduce the quantity of contrast and radiation to which the patient is exposed. Fifty patients undergoing diagnostic cardiac catheterization were randomized to either standard vs. rotational angiography of the coronary arteries using a prespecified protocol with a flat-panel single-plane imaging system. We measured the quantity of radiographic contrast utilized and radiation exposure. Using an intention-to-treat analysis, there was a 40% reduction (24 +/- 5 vs. 40 +/- 10 ml; P < 0.0001) in contrast utilization in the rotational group compared to the standard group. Neither radiation exposure (35 +/- 14 vs. 30 +/- 20 Gycm(2); P = 0.35), fluoroscopic time (44 +/- 33 vs. 44 +/- 40 sec; P = 0.99), nor procedure time (249 +/- 137 vs. 214 +/- 79 sec; P = 0.26) differed, although significant intraoperator variability was noted for both standard and rotational angiography. The radiation exposure using this flat-panel system is significantly lower than prior reports that used an image intensifier system. Rotational coronary angiography has the potential to improve patient safety by markedly reducing radiographic contrast exposure while maintaining comparable diagnostic accuracy, radiation exposure, and procedure time compared to standard coronary angiography.

SU‐FF‐I‐20: Improved Image Quality And Dose Efficiency with a Next‐Generation Interventional Cardiac Digital Flat Panel (DFP) System

Purpose: Cardiologists are treating smaller coronary vessels using stents with less metal content and smaller micro strut thicknesses designed to reduce in‐stent restenosis rates. We present the image quality and dose measurements of a next‐generation digital flat panel (DFP) cardiovascular angiography system optimized to meet the needs of these demanding interventional procedures. Specific improvements include a detector with higher DQE at fluoroscopic (73% at 1 μR) and record (79%) doses, optimized xray exposure factors based on a neural‐net patient thickness estimation, and an xray source with higher fluoro power and increased range of spectral filtration. Performance improvements are demonstrated in a controlled comparison with the most widely installed state‐of‐the art DFP system. Method and Materials: Measurements of image quality and dose were made using the standard cardiovascular benchmarking SCAI‐NEMA phantom on a state‐of‐the‐art Innova®2000 and the new DFP system. Low contrast iodine visibility and phantom entrance dose were measured for simulated medium and large patient sizes using 20 and 30 cm thicknesses of polymethlymethacrylate (PMMA), respectively. Other measurements included limiting resolution, dynamic range and moving guide wire visibility, using the standard 20 cm phantom configuration. Measurements were obtained using normal mode, 30 frames per second (fps) fluoroscopy over all fields of view. Results: The new DFP system demonstrated significant improvement (p&lt;=0.05) in low contrast iodine detectability, at equal or lower doses, and in moving wire visibility. Working thickness (dynamic range) was improved. Spatial resolution limits were comparable. Conclusions: The SCAI‐NEMA measurements strongly suggest that, compared to the current state‐of‐the‐art DFP system, the new interventional cardiovascular DFP system will provide better dose efficiency with a significant improvement in device and vessel visibility in a cardiac environment marked by anatomical motion. Images and data demonstrating stent visualization improvements will also be presented. Conflict of Interest: Authors are employees of a medical imaging equipment manufacturer.

SU‐DD‐A2‐03: Influence of Equipment Variables Upon Cardiac Radiation Levels

Purpose: The main goal is to demonstrate the effects of varying imaging equipment parameters have upon patient radiation dose in modern cardiac catheterization x‐ray systems. The parameters examined include: pulse rate, Field‐of‐View (FoV), patient thickness, fluoroscopy versus record mode, SID settings and ABC programs. Method and Materials: A Siemens flat panel Axion Artis FC cardiac unit was used. The patient was simulated by sheets of acrylic varying in thickness from 10 cm to 30 cm. The exposure rate was measured at the entrance surface of the acrylic with an ionization chamber. Results: The entrance exposure rate varied with the (FoV)N where −2 &lt;N&lt; −3. The exposure rate varied directly with pulse rate in both fluoroscopy and record mode; in comparison to continuous or 30 pps, 15 pps reduced the radiation levels by 50%. The plus mode increased radiation levels by 40–50% and the minus mode reduced the levels by 40–50%. One minute of record imaging is equivalent to about 10 minutes of fluoroscopy. For both modes, the radiation levels increase approximately as an exponential function of thickness with an HVL in acrylic of about 2.8 cm. Maximum exposure rates for large patients can be 10 – 20 R/min in fluoroscopy and over 100 R/min in record mode. Conclusions: Although typical cardiac catheterization radiation levels are available for image intensifier and cine film systems, these data provide information related to a modern flat panel and digital recording system. Data about the relative effects permit significant dose savings to be realized by judicious selection of settings. In comparison to older equipment without these modern features, utilization of all the dose reduction steps can result in a dose savings of over 90%. Conflict of Interest: Some free software upgrades to equipment were provided during evaluations; no other financial conflicts exist.

Reducing dose in urography while maintaining image quality—a comparison of storage phosphor plates and a flat-panel detector

The introduction of new flat-panel detector technology often forces us to accept too high dose levels as proposed by the manufacturers. We need a tool to compare the image quality of a new system with the accepted standard. The aim of this study was to obtain a comparable image quality for two systems-storage phosphor plates and a flat-panel system using intravenous urography (IVU) as a clinical model. The image quality figure was calculated using a contrast-detail phantom (CDRAD) for the two evaluated systems. This allowed us to set a dose for the flat-panel system that gave equivalent image quality to the storage phosphor plates. This reduced detector dose was used in an evaluation of clinical images to find out if the dose reduction from the phantom study indeed resulted in images of equal clinical image quality. The image quality was assessed using image criteria of the European guidelines for IVU with visual grading analysis. Equivalent image quality in image pairs was achieved at 30% of the dose. The CDRAD contrast-detail phantom makes it possible to find dose levels that give equal image quality using different imaging systems.

Development of high quantum efficiency, flat panel, thick detectors for megavoltage x-ray imaging: A novel direct-conversion design and its feasibility

Most electronic portal imaging devices (EPIDs) developed to date, including recently developed flat panel systems, have low x-ray absorption, i.e., low quantum efficiency (QE) of 2%-4% as compared to the theoretical limit of 100%. A significant increase of QE is desirable for applications such as a megavoltage cone-beam computed tomography (MVCT) and megavoltage fluoroscopy. However, the spatial resolution of an imaging system usually decreases significantly with an increase of QE. The key to the success in the design of a high QE detector is therefore to maintain the spatial resolution. Recently, we demonstrated theoretically that it is possible to design a portal imaging detector with both high QE and high resolution [see Pang and Rowlands, Med. Phys. 29, 2274 (2002)]. In this paper, we introduce such a novel design consisting of a large number of microstructured plates (made by, e.g., photolithographic patterning of evaporated or electroplated layers) packed together and aligned with the incident x rays. On each plate, microstrip charge collectors are focused toward the x-ray source to collect charges generated in the ionization medium (e.g., air or gas) surrounded by high-density materials that act as x-ray converters. The collected charges represent the x-ray image and can be read out by various means, including a two-dimensional (2-D) active readout matrix. The QE, spatial resolution, and sensitivity of the detector have been calculated. It has been shown that the new design will have a QE of more than an order of magnitude higher and a spatial resolution equivalent to that of flat panel systems currently used for portal imaging. The new design is also quantum noise limited down to very low doses (approximately 1-2 radiation pulses of the linear accelerator).

Quantitative coronary arteriography on digital flat-panel system.

On images acquired with a digital flat-panel (DFP) detector, known for its better image quality, the performance of a validated quantitative coronary arteriography (QCA) software, CAASII (Cardiovascular Angiography Analysis System or CAAS), and a DFP-dedicated QCA algorithm (flat-panel analysis software or FPAS) was compared in a phantom and a patient study. On phantom, FPAS performed with higher accuracy the quantification of the smallest tubes and the calibration of an empty catheter. The overall accuracy and precision for the quantification procedure was better for FPAS (0.07 +/- 0.04 mm) than for the CAAS (0.19 +/- 0.06 mm; P = 0.03 and P < 0.01, respectively). In the patient study, the main difference between the two algorithms was found in the small diameters: CAAS almost always gave higher values than FPAS for the minimal luminal diameter (P < 0.001) and could only give values up to 70% for diameter stenosis. In conclusion, the FPAS can be considered more appropriate for assessing severe stenoses on digital flat-panel images.