Computed Radiography Images Research Articles

SU‐FF‐I‐110: Measurement of X‐Ray Beam and Grid Misalignment in Portable Chest Radiography Using a 3D Test Object

Purpose: X‐ray beam to grid alignment is crucial for acquiring high‐quality portable chest radiographs. The purpose of this work was to measure x‐ray beam to grid alignment by imaging a custom alignment phantom during routine acquisition of portable chest images acquired using computed radiography (CR). A better understanding of typical beam alignment in the clinical practice is expected to be useful to specify the most appropriate grid ratio and to help foster better in‐room alignment. Materials and Methods: The disk‐shaped phantom was 5 cm in diameter and 1 cm tall. A 2 cm diameter ring of sixteen 2 mm tungsten balls was positioned at the entrance surface of the phantom and a 4 cm ring of twenty‐four balls was positioned at the exit surface. Computer analysis of the phantom on the CR image provided for measurement of the 3D spatial location of the x‐ray focal spot with respect to the image center. Results: Trial measurements using uniform exposure images demonstrated that the (x, y, z) location of the focal spot with respect to the image plane could be measured with error less than 2% of the x‐ray source to image distance. A preliminary clinical trial using 20 portable chest images demonstrated that misalignment of the x‐ray beam to the grid ranged from 0 to 14 cm (average = 6 cm) in the direction perpendicular to the gridlines. Conclusions: A phantom and image analysis application was developed to measure the x‐ray beam to grid misalignment for CR portable chest radiographs. Initial measurements showed that the precision is appropriate for this task. Preliminary clinical studies demonstrated a relatively wide variation in alignment in the clinical practice. The results of this work will be used to foster better alignment and to specify the most appropriate grid ratio for portable chest imaging.

TU‐C‐L100J‐05: A Practical Filmless Technique of Determining CT Beam Width

Purpose: To develop a filmless technique for the measurement of CT beam width for QA. Method and Materials: Images of pre‐patient collimated CT beams were acquired using Fuji computed radiography (CR) cassettes and direct‐exposure film (DF). CR cassettes were exposed using 80kV, 10mAs to avoid signal saturation. The DF was exposed at 80kV, 30mAs to achieve a proper optical density. The DF image was digitized then linearized. To achieve a proper signal range for CR, various plate‐reading protocols were evaluated. An IDL program was developed to automatically handle both the digitized film and a variety of CR image sizes. “Unprocessed” logarithmic CR data were linearized, which is critical to validate the FWHM. The program executes in an interactive fashion, whereby the user selects the beam to analyze. The program determines the background signal for subtraction then samples multiple cross‐beam profiles to form an averaged profile. The profile is smoothed and the FWHM is determined. Results: Under proper conditions of image acquisition, results show both DF and CR are appropriate techniques for beam width measurements. The CR technique demonstrated a high level of reproducibility with a coefficient of variation below 0.5%. Also, the CR results were within 0.3mm of specifications. Using various sizes of CR cassettes had a minimal effect on the results. However, if the properly exposed image is saturated due to an inappropriate CR plate reading protocol, the inaccuracy is substantial (>1mm). The technique worked well for annual tests of six GE scanners. Over a wide range of beam width configurations, all measurements were within 0.9mm of specifications. Conclusion: A technique for determination of CT beam width in a filmless environment was developed and tested. The results obtained using CR yield accurate measurements of CT beam profile width. The technique is effective, practical, and has proven to be robust.

Improvement of lung abnormality detection in computed radiography using multi-objective frequency processing: Evaluation by receiver operating characteristics (ROC) analysis

Computed radiography (CR) has been shown to have relatively low sensitivity for detection of pulmonary nodules. This poor sensitivity precludes its use as a screening modality despite the low cost, low dose and wide distribution of devices. The purpose of this study was to apply multi-objective frequency processing (MFP) to CR images and to evaluate its usefulness for diagnosing subtle lung abnormalities. Fifty CR images with simulated subtle lung abnormalities were obtained from 50 volunteers. Each image was processed with MFP. We cut chest images. The chest image was divided into two rights and left. A total of 200 half-chest images (100 MFP-processed images and 100 MFP-unprocessed images) were prepared. Five radiologists participated in this study. ROC analyses demonstrated that the detection rate of simulated subtle lung abnormalities on the CR images was significantly better with MFP (Az = 0.8508) than without MFP (Az = 0.7925). The CR images processed with MFP could be useful for diagnosing subtle lung abnormalities. In conclusion, MFP appears to be useful for increasing the sensitivity and specificity in the detection of pulmonary nodules, ground-glass opacity (GGO) and reticular shadow.

An observer study: comparison of computed radiography to electronic and film portal imaging

Introduction: Computed radiography (CR) is an imaging facility that does not require the use of hard copy film, digital images are obtained with a photostimulable phosphor plate, which replaces film, in a cassette. As the first UK radiotherapy site to trial CR, we are collecting data to assess the feasibility of using CR in radiotherapy treatment verification.Method: From 30 patients undergoing radical radiotherapy, 10 were consecutively accrued to three sites: pelvis, thorax and head and neck. Treatment verification images were taken using current protocols, but substituting standard imaging for CR images on one fraction. Four independent observers were used: two clinical oncologists and two therapy radiographers. Observers rated CR, electronic portal imaging (EPI) and enhanced contrast (EC) films of the three sites for both landmark visibility and ease of verification decision, using a numerical scoring system.Results: Ratings for visibility of landmarks and for verification decision were similar for CR and film/EPI images for most landmarks. However, CR images rated poorly compared to EC film in the head and neck region with landmarks such as thyroid cartilage and cricoid cartilage rating as ‘not clear’. CR images rated better than EPI images for both visibility and verification decision on the majority of landmarks in the pelvis region.Conclusion: Results gathered from a relatively small sample size have provided the following conclusion. The visibility of landmarks in CR images is comparable to that in film and EPI. Verification of treatment images based on CR is comparable to that of the current imaging media in the department.

A Study of Grid Artifacts Formation and Elimination in Computed Radiographic Images

Computed radiography (CR) has many advantages such as filmless operations, efficiency, and convenience. Furthermore, it is easier to integrate with the picture archiving and communication systems. Another important advantage is that CR images generally have a wider dynamic range than conventional screen film. Unfortunately, grid artifacts and moiré pattern artifacts may be present in CR images. These artifacts become a more serious problem when viewing CR images on a computer monitor when a clinic grade monitor is not available. Images produced using a grid with higher frequency or a Potter--Bucky grid (i.e., a moving grid, Bucky for short) can reduce occurrence but cannot guarantee elimination of these artifacts [CR & PACS (2000); Detrick F (2001), pp 7-8]. In this paper, the formation of the artifacts is studied. We show that the grid artifacts occur in a narrow band of frequency in the frequency domain. The frequency can be determined, accurately located, and thus removed from the frequency domain. When comparing the results obtained from the proposed method against the results obtained using previous computer methods, we show that our method can achieve better image quality.

Recognition and Prevention of Computed Radiography Image Artifacts

Initiated by complaints of image artifacts, a thorough visual and radiographic investigation of 197 Fuji, 35 Agfa, and 37 Kodak computed radiography (CR) cassettes with imaging plates (IPs) in clinical use at four radiology departments was performed. The investigation revealed that the physical deterioration of the cassettes and IPs was more extensive than previously believed. It appeared that many of the image artifacts were the direct result of premature wear of the cassettes and imaging plates. The results indicate that a quality control program for CR cassettes and IPs is essential and should include not only cleaning of the cassettes and imaging plates on a regular basis, but also visual and radiographic image inspection to limit the occurrence of image artifacts and to prolong the life cycle of the CR equipment.

Temporal subtraction in chest radiography: Automated assessment of registration accuracy

Radiologists routinely compare multiple chest radiographs acquired from the same patient over time to more completely understand changes in anatomy and pathology. While such comparisons are achieved conventionally through a side-by-side display of images, image registration techniques have been developed to combine information from two separate radiographic images through construction of a "temporal subtraction image." Although temporal subtraction images provide a powerful mechanism for the enhanced visualization of subtle change, errors in the clinical evaluation of these images may arise from misregistration artifacts that can mimic or obscure pathologic change. We have developed a computerized method for the automated assessment of registration accuracy as demonstrated in temporal subtraction images created from radiographic chest image pairs. The registration accuracy of 150 temporal subtraction images constructed from the computed radiography images of 72 patients was rated manually using a five-point scale ranging from "5-excellent" to "1-poor;" ratings of 3, 4, or 5 reflected clinically acceptable subtraction images, and ratings of 1 or 2 reflected clinically unacceptable images. Gray-level histogram-based features and texture measures are computed at multiple spatial scales within a "lung mask" region that encompasses both lungs in the temporal subtraction images. A subset of these features is merged through a linear discriminant classifier. With a leave-one-out-by-patient training/testing paradigm, the automated method attained an A(z) value of 0.92 in distinguishing between temporal subtraction images that demonstrated clinically acceptable and clinically unacceptable registration accuracy. A second linear discriminant classifier yielded an A(z) value of 0.82 based on a feature subset selected from an independent database of digitized film images. These methods are expected to advance the clinical utility of temporal subtraction images for chest radiography.

Evaluation of the diagnostic value of a computed radiography system by comparison of digital hard copy images with screen–film mammography: results of a prospective clinical trial

The purpose of the study was to determine prospectively the diagnostic value of a computed radiography (CR) system by comparing mammographic hard copy images with screen-film mammography (SFM). A series of 100 patients, who came for diagnostic investigation, underwent two-view SFM (Lorad M-IV Platinum) and digital mammography with a CR system (AGFA CR system). The images were obtained by double exposure, i.e. same view without removing compression of the corresponding breast. The CR images were processed with dedicated processing for mammography. Six radiologists read sets of SFM and CR images. The primary efficacy parameter was the overall diagnostic value. The secondary efficacy parameters were lesion conspicuity and lesion details (for masses and micro-calcifications), tissue visibility at chest wall and at skin line, axillary details, overall density and sharpness impression and the overall noise impression. These parameters were scored by a 7-point scoring system. "CR non-inferior to SFM" was concluded if the lower confidence interval bound exceeded 80%. The confidence interval for the overall diagnostic value was between 96.4% and 100%. Pooled analysis of the ten features for image quality comparison demonstrated for all but one feature (lesion details of the calcifications) CR non-inferiority to SFM.

Performance evaluation of a computed radiography imaging device using a typical “front side” and novel “dual side” readout storage phosphors

The Fourier-space modulation transfer function (MTF), normalized noise power spectrum (nNPS), and detective quantum efficiency (DQE) of a computed radiography (CR) x-ray imaging device were measured. Two different storage phosphor screens were used in conjunction with a single CR reader (Fuji, Clearview, CS). One of the storage phosphor plates (ST-BD) had a clear backing material which allowed "dual side read" of the latent image from both the "front" and "back" sides of the phosphor. The other phosphor plate had a light occluding backing material, limiting the readout to front side only (ST-VI). The standard RQA-5 beam quality was used. The MTF was measured using a 1 mm thick tungsten edge device. Compared to the ST-55BD phosphor, the ST-VI phosphor was found to have modestly higher MTF at all spatial frequencies. The nNPS(f) and DQE(f) were measured for nominal incident exposure levels ranging from 0.1 to 10 mR. The dual side read phosphor demonstrated superior DQE, especially at low spatial frequencies. At the frequency 0.5 cycles/mm, the DQE values for the 1 mR exposure were 0.36 and 0.21 for the ST-55BD and ST-VI phosphor plates, respectively. The differences between the spatial-frequency dependent DQE of the two plates can be attributed to the increased signal collection efficiency of the dual side read plates and differences in storage phosphor structure noise.

Enhanced Visualization Methods for Computed Radiography Images

This paper focuses on the application of two image enhancement techniques for the picture archiving and communications systems imaging diagnostic workstation applied to computed radiography (CR) and digital radiography images. The first method is a contrast enhancement technique based on a class of nonlinear intensity transformations described by analytic transfer functions derived from Hurter and Driffield characteristic curves. The second method employs antialiasing techniques preventing the formation of Moiré patterns on subsampled CR images containing antiscatter grid lines, designed to achieve a good balance between artifact suppression and resolution degradation. These techniques are likely to become standard features for all high-end medical imaging workstations in the near future, and thus, we are suggesting that more powerful descriptions of these types of processing should be included in the Digital Imaging and Communications in Medicine standard.

AEC set-up optimisation with computed radiography imaging

Phototimer set-up is a critical procedure for dose and image quality optimisation in computed radiography (CR) systems. While a conventional radiography automatic exposure control device (AEC) can be calibrated in order to gain a constant optical density on the film independent of beam quality and patient size, CR detectors present a high dynamic range which allows a much larger dose interval, but with different image quality levels. CR leads to a less frequent exam repetition, but may produce quite noisy images if the exposure level on the plate is not correct. The aim of this work is to evaluate the performance of a CR plate (Agfa MD40) in order to optimally calibrate an AEC device. The plate response has been characterised in terms of digital signal, exposure on the plate and signal-to-noise ratio for different beam qualities, in a patient of standard size.

Automated radiographic inspection of flexible risers: a feasibility study

Flexible risers are flexible pipes used to bring oil from oil wells deep underwater to the surface, where it can be processed by Floating Production, Storage and Offloading (FPSO) installations. Flexible risers consist of a number of layers of steel and polymer that have a complex structure and some layers are shielded by others, making non-destructive testing particularly difficult. This paper presents some experimental radiography of a sample flexible riser. Both single-wall and double-wall techniques were used with X-rays and gamma rays with both computed radiography imaging plates and an amorphous silicon flat-panel detector. The layer of the riser that is of particular interest is the pressure armour, which is the layer designed to withstand the infernal pressure. It is a layer that is particularly difficult to inspect, as it is shielded by a metallic layer on both sides. The resulting images were used to develop an image processing technique designed to detect separations in the pressure armour, which is also presented here. The technique is based on the use of the Hough transform to detect non-structural lines in the image. This technique has been tested on a defect simulated by image processing and an artificial defect introduced to the flexible riser sample. The technique was found to be successful in detecting the artificial defect in a set of images, with only 4% of misclassification, which were all false positive results.

Pilot study into optimisation of viewing conditions for electronically displayed images

The increased use of soft-copy reporting introduces new concerns over the effect of viewing conditions on the observer's ability to report images. Owing to their lower luminance, electronic display screens may be more susceptible to poor viewing conditions than conventional viewing boxes and there is the potential for images to be displayed in locations not optimised for viewing radiographs. In the present work, the effects of sub-optimal viewing conditions on the observer's performance for images on an electronic display device are investigated. A test object was used to produce a computed radiography image containing a wide range of grey levels. The image was scored under quasi-ideal and sub-optimal conditions and the effect of changing the viewing conditions on the observer's performance determined. Basic photometric quantities were used to characterise the viewing conditions and the degradation in observer performance related to these quantities. The presence of structured reflection had a significant effect on the observer's ability to discern low-contrast objects. The study demonstrates the need for adequate viewing conditions especially when images are displayed on low luminance devices in sub-optimal conditions.

Dose optimisation in computed radiography

After the installation of computed radiography (CR) systems in three hospitals in Luxembourg a patient dose survey was carried out for three radiographic examinations, thorax, pelvis and lumbar spine. It was found that the patient doses had changed in comparison with the patient doses measured for conventional radiography in the same three hospitals. A close collaboration between the manufacturers of the X-ray installations, the CR imaging systems and the medical physicists led to the discovery that the speed class with which each radiographic examination was to be performed, had been ignored, during installation of the digital imaging systems. A number of procedures were carried out in order to calibrate and program the X-ray installations in conjunction with the CR systems. Following this optimisation procedure, a new patient dose survey was carried out for the three radiographic examinations. It was found that patient doses for the three hospitals were reduced.

The physics of computed radiography: Measurements of pulse height spectra of photostimulable phosphor screens using prompt luminescence

Computed radiography (CR) is a digital technology that employs reusable photostimulable phosphor (PSP) imaging plates (IP) to acquire radiographic images. In CR, the x-ray attenuation pattern of the imaged object is temporarily stored as a latent charge image within the PSP. The latent image is optically readout as photostimulated luminescence (PSL) when the phosphor is subsequently stimulated using a scanning laser. The multiple stages necessary to create a CR image make it difficult to investigate either experimentally or theoretically. In order to examine the performance of the CR system at a fundamental level separate measurements of the processes involved are desirable. Here pulse height spectroscopy is used to study the prompt violet light emission or prompt luminescence (PL) from commercial PSP screens. Since the mechanism by which light escapes from the phosphor is identical for PL and PSL, observations and conclusions based on the pulse height spectra (PHS) of PL are relevant to the understanding of the behavior of the PSL light emission that outputs the radiographic image in CR. The PL PHS of screens of different thickness and optical properties were measured and compared with the PHS of conventional phosphors. A new method for calibration of the PHS in terms of the absolute number of optical photons per x-ray is introduced and compared to previously established methods.

Practical guidelines for radiographers to improve computed radiography image quality

Computed Radiography (CR) has become a major digital imaging modality in a modern radiological department. CR system changes workflow from the conventional way of using film/screen by employing photostimulable phosphor plate technology. This results in the changing perspectives of technical, artefacts and quality control issues in radiology departments. Guidelines for better image quality in digital medical enterprise include professional guidelines for users and the quality control programme specifically designed to serve the best quality of clinical images. Radiographers who understand technological shift of the CR from conventional method can employ optimization of CR images. Proper anatomic collimation and exposure techniques for each radiographic projection are crucial steps in producing quality digital images. Matching image processing with specific anatomy is also important factor that radiographers should realise. Successful shift from conventional to fully digitised radiology department requires skilful radiographers who utilise the technology and a successful quality control program from teamwork in the department.

Practical guidelines for radiographers to improve computed radiography image quality

Practical guidelines for radiographers to improve computed radiography image quality

Effectiveness of flexible noise control image processing for digital portal images using computed radiography

The purpose of this study was to evaluate the clinical efficacy of flexible noise control (FNC) image processing in off-line computed radiography (CR) portal images. An observer study was designed to compare FNC with multiobjective frequency processing (MFP) in images acquired using a CR portal imaging device (CRPID). The image processing of MFP and FNC used the same data and required no additional irradiation of patients, and all images were printed on 10-bit grey-level dry laser film. Four radiation technologists and one oncologist served as observers and evaluated 40 sets of images for three different treatment sites: brain, lung and pelvis. Six to 10 anatomical landmarks were selected from each treatment site. Each observer was asked to rate each landmark in terms of its clinical visibility and rate the ease of making the pertinent verification in the MFP- and FNC-processed images. In the ratings of the visibility of landmarks and for the verification of treatment ports, FNC-processed images were more visible than MFP-processed images except for several landmarks in the anteroposterior (AP) pelvis such as the pubic symphysis. The visibility of landmarks in FNC-processed images was comparable with that in MFP-processed images. The verification of treatment ports using the CRPID with FNC was generally achievable. In conclusion, this study suggests that FNC is effective for image processing of CR portal images.

SU-FF-I-58: Effects of Prepatient Filtration On Contrast, Scatter and Dose in CR Chest Exams: A Phantom Study

Purpose: To establish a convenient method for objective comparison of the consequences of exposure conditions and filtration on image quality and patient dose in adult and pediatric thoracic computed radiography (CR) examinations. Method and Materials: Computer simulation (MATLAB) was utilized for approximating the x-ray spectrum and its modification by pre-patient filtration, predicting the attenuation by the phantom, predicting pixel values in the CR image, calculating expected contrast-to-noise ratio (CNR), and estimating patient dose. CDRH LucAl Chest and Pediatric phantoms with the Al quality insert were imaged at 125 kVp with beam filters (Z=29, 57, 75) with a grid and 75 kVp with beam filters (Z=13, 29, 50) tabletop, respectively. Entrance Skin Exposure (ESE) and detector exposure were measured. Fuji FCR 5000 CR images were developed with L=4 in fixed EDR Mode. Pixel ROI and SD were extracted from DICOM images. Doses were estimated by calculating absorption of the attenuated spectra in water of 20 cm (adult) and 10 cm (pediatric) thickness. Scatter-to-primary ratios (SPR) were estimated for each case using beam blocks. Results: Filtration increased half-value layer (HVL) reducing ESE and contrast. Contrast-to-Noise Ratio (CNR) can increase, depending on Z and the thickness of the filter. The same CNR produced by the unfiltered beam using Automatic Exposure Control (AEC) can be accomplished at 23% lower ESE. Even with a lower ESE, higher HVL increases exposure-to-dose conversion, resulting in higher dose absorbed by the patient to produce the same receptor exposure. No filtered case had CNR superior to the unfiltered case at the same patient dose. SPR also increased with filtration. Conclusion: LucAl Chest and Pediatric phantoms provide standardized platforms for investigating effects of exposure conditions on image quality and patient dose in digital chest radiography. Filtration can provide identical CNR at lower ESE, but may also deliver higher patient dose.

SU-FF-T-224: The Use of Computed Radiography in Radiotherapy

Purpose: To investigate the feasibility of using Computed Radiography as a film replacement in a radiotherapy department. Method and Materials: A computed radiography (CR) system designed for radiotherapy has recently been introduced to the market. The CR system has separate imaging plates designed for KV imaging, low dose portal imaging (1–10mu) and high dose portal imaging (10–400mu). An evaluation of the possibility of using CR for all functions that are typically done with film in a radiotherapy department has been done. This included an evaluation of image quality of the CR system for portal imaging. It also included an evaluation of the CR system for various quality assurance issues such as gantry and collimator spoke shots, light to radiation congruence, and HDR source position accuracy. Results: The image quality provided by the CR images was determined by both Oncologists and therapists to be acceptable for use in conventional portal imaging. Images of a contrast resolution phantom were taken with CR, film and an ASi portal imager, and are similar for all three. Quality assurance tests typically done with film can be done with CR imaging techniques. The analysis of spoke shots is possible with the existing tools, but could be streamlined with the development of some analysis software. Similarly it is possible to evaluate the light field vs radiation field congruence with the existing tools in the CR system, but this could also be made easier with some further software development. Conclusion: Computed radiography can be used as a film replacement for imaging and QA in a clinical radiotherapy department. Conflict of Interest: This work has been supported by AGFA HealthCare.