Experimental Evaluation of a Portable Indirect Flat-Panel Detector for the Pediatric Chest: Comparison with Storage Phosphor Radiography at Different Exposures by Using a Chest Phantom

Evaluation of the image quality and dose reduction in digital radiography with an advanced spatial noise reduction algorithm in pediatric patients

OBJECTIVES

To evaluate whether the advanced spatial noise reduction (ASNR) algorithm installed in a digital radiography system generates acceptable images at a lower dose than a conventional denoising algorithm in pediatric patients.

METHODS

Nine sets of 30 images of pediatric patients, classified under three protocols and three age groups, were retrospectively selected. Different levels of low-dose image sets of these 270 images were generated by a noise simulation tool after validation testing using phantoms. Each image set was obtained with both the ASNR and conventional algorithm, and grouped randomly and blinded. Three experienced pediatric radiologists were asked to pick the "image with optimum dose" among images of different dose levels with an ALARA (as low as reasonably achievable) perspective. Dose reduction rates for each protocol and age group were calculated, and entrance skin exposure (ESE) was calculated using the values of kVp and mAs, assuming a standard body depth for each age group.

RESULTS

With the ASNR algorithm, estimated dose reduction rates were highest for abdominal radiographs (45.0%, 27.3%, and 24.3% in infants, children, and adolescents, respectively, p < 0.001). The mean dose reductions for all age groups in the abdominal, chest, and skull radiographs were 32.8%, 12.9%, and 23.2%, respectively (p < 0.001). Average of the calculated ESE was lower with the ASNR algorithm than with the conventional algorithm group (p < 0.001).

CONCLUSIONS

The ASNR algorithm facilitated optimization of image quality with a higher reduction in radiation dose than the conventional algorithm, making it more acceptable for use in pediatric patients.

KEY POINTS

•ASNR algorithm in DR system improves image quality via enhanced contrast and noise removal by estimating actual noise distribution based on a multi-scale noise covariance and frequency processing. •Noise simulation tool (NST) generating images of different dose levels can be used for evaluation of the optimum dose without unnecessary additional radiation exposure to pediatric patients. •Retrospective clinical study using NST showed that the ASNR algorithm enabled a higher reduction in radiation dose than the conventional algorithm in pediatric patients.

Characterization and validation of the thorax phantom Lungman for dose assessment in chest radiography optimization studies

This work concerns the validation of the Kyoto-Kagaku thorax anthropomorphic phantom Lungman for use in chest radiography optimization. The equivalence in terms of polymethyl methacrylate (PMMA) was established for the lung and mediastinum regions of the phantom. Patient chest examination data acquired under automatic exposure control were collated over a 2-year period for a standard x-ray room. Parameters surveyed included exposure index, air kerma area product, and exposure time, which were compared with Lungman values. Finally, a voxel model was developed by segmenting computed tomography images of the phantom and implemented in PENELOPE/penEasy Monte Carlo code to compare phantom tissue-equivalent materials with materials from ICRP Publication 89 in terms of organ dose. PMMA equivalence varied depending on tube voltage, from 9.5 to 10.0 cm and from 13.5 to 13.7 cm, for the lungs and mediastinum regions, respectively. For the survey, close agreement was found between the phantom and the patients' median values (deviations lay between 8% and 14%). Differences in lung doses, an important organ for optimization in chest radiography, were below 13% when comparing the use of phantom tissue-equivalent materials versus ICRP materials. The study confirms the value of the Lungman for chest optimization studies.

Detectability of simulated interstitial pneumonia on chest radiographs: comparison between irradiation side sampling indirect flat-panel detector and computed radiography

OBJECTIVE

To compare the detectability of simulated interstitial pneumonia on chest radiographs between an irradiation side sampling indirect flat-panel detector (ISS-FPD) and computed radiography (CR).

METHODS

Simulated interstitial pneumonia findings (ground-glass opacity, reticular opacity and honeycomb lung) were superimposed on an anthropomorphic chest phantom. Chest radiographs were acquired under three exposure levels (4.0, 3.2 and 2.0 mAs) with an ISS-FPD and with CR. 5 thoracic radiologists evaluated 72 images for the presence or absence of a lesion over each of 6 areas. A total of 1296 observations were analysed in a receiver-operating characteristic analysis. A jackknife method was used for the statistical analysis.

RESULTS

The areas under the curves (AUCs) for the detection of simulated honeycomb lung obtained with the ISS-FPD were significantly larger than those obtained with CR at all exposure conditions. For the detection of simulated ground-glass opacity and reticular opacity, there were no significant differences between the two systems. In addition, the AUCs for the detectability of simulated honeycomb lung obtained with the ISS-FPD at all exposure levels were significantly larger than those obtained with CR at 4 mAs.

CONCLUSION

The ISS-FPD was superior to CR for the detection of simulated honeycomb lung. Provided that the chosen model is representative of interstitial pneumonia, the use of an ISS-FPD might reduce a patient's exposure dose during the detection of interstitial pneumonia.

ADVANCES IN KNOWLEDGE

The ISS-FPD has shown its advantage compared with CR in the detection of honeycombing, one sign of interstitial pneumonia.

Digital radiography: optimization of image quality and dose using multi-frequency software

BACKGROUND

New developments in processing of digital radiographs (DR), including multi-frequency processing (MFP), allow optimization of image quality and radiation dose. This is particularly promising in children as they are believed to be more sensitive to ionizing radiation than adults.

OBJECTIVE

To examine whether the use of MFP software reduces the radiation dose without compromising quality at DR of the femur in 5-year-old-equivalent anthropomorphic and technical phantoms.

MATERIALS AND METHODS

A total of 110 images of an anthropomorphic phantom were imaged on a DR system (Canon DR with CXDI-50 C detector and MLT[S] software) and analyzed by three pediatric radiologists using Visual Grading Analysis. In addition, 3,500 images taken of a technical contrast-detail phantom (CDRAD 2.0) provide an objective image-quality assessment.

RESULTS

Optimal image-quality was maintained at a dose reduction of 61% with MLT(S) optimized images. Even for images of diagnostic quality, MLT(S) provided a dose reduction of 88% as compared to the reference image. Software impact on image quality was found significant for dose (mAs), dynamic range dark region and frequency band.

CONCLUSION

By optimizing image processing parameters, a significant dose reduction is possible without significant loss of image quality.

Novel, portable, cassette-sized, and wireless flat-panel digital radiography system: initial workflow results versus computed radiography

OBJECTIVE

The purpose of this article is to compare workflow efficiency between a conventional computed radiography (CR) system and a novel, portable, cassette-sized, and wireless flat-panel digital radiography (DR) system.

MATERIALS AND METHODS

Observational time-motion analyses were performed at one site at which CR and the new portable DR system are used concurrently. The workflow steps of both systems were identified and categorized to facilitate comparison. The times required for examination preparation, patient positioning, exposure, postacquisition processing, and the examination as a whole were recorded by a neutral observer. Timing differences between the CR and portable DR systems were compared, and all data were analyzed using commercially available statistical software. Nine general radiographic examination types were selected, with approximately 50 patients per examination type.

RESULTS

A total of 941 examinations (CR, n = 474; portable DR, n = 467) were timed in this study. Total examination time differences between CR and portable DR system (mean, 26.44 seconds; median 26.99 seconds) were found to be statistically significant (p < 0.001), with DR proving faster than CR. The single largest contributor to the time difference between CR and portable DR was postacquisition processing (mean, 26.58 seconds; median, 25.91 seconds), which was a composite of multiple individual steps, including cassette transport (CR only, mean, 13.22 seconds; median, 12.74 seconds), cassette readout (mean, 10.15 seconds; median, 10.4 seconds), and postprocessing (mean, 3.21 seconds; median, 3.11 seconds).

CONCLUSION

Overall radiographer time was significantly shorter when performing examination-related tasks with the novel, portable DR system than when performing comparable tasks with the CR system, a difference that appears to result largely from technology configuration.

Comparison of flat-panel digital to conventional film-screen radiography in detection of experimentally created lesions of the equine third metacarpal bone

Radiographic diagnosis of equine bone disease using digital radiography is prevalent in veterinary practice. However, the diagnostic quality of digital vs. conventional radiography has not been compared systematically. We hypothesized that digital radiography would be superior to film-screen radiography for detection of subtle lesions of the equine third metacarpal bone. Twenty-four third metacarpal bones were collected from horses euthanized for reasons other than orthopedic disease. Bones were dissected free of soft tissue and computed tomography was performed to ensure that no osseous abnormalities were present. Subtle osseous lesions were produced in the dorsal cortex of the third metacarpal bones, and the bones were radiographed in a soft tissue phantom using indirect digital and conventional radiography at standard exposures. Digital radiographs were printed onto film. Three Diplomates of the American College of Veterinary Radiology evaluated the radiographs for the presence or absence of a lesion. Receiver operator characteristic curves were constructed, and the area under these curves were compared to assess the ability of the digital and film-screen radiographic systems to detect lesions. The area under the ROC curves for film-screen and digital radiography were 0.87 and 0.90, respectively (P = 0.59). We concluded that the digital radiographic system was comparable to the film-screen system for detection of subtle lesions of the equine third metacarpal bone.

[Pediatric thoracic spine radiographs: Comparison of two scintillators]

PURPOSE

To compare image quality and radiation exposure from pediatric thoracic spine radiographs from two systems, one using a granular structure scintillator and another using a needle structure scintillator with 40% reduction of exposure.

PATIENTS AND METHODS

Randomized prospective study of 296 patients divided into 2 groups of 5 weight categories from 4 to 60 kg. Standard technique parameters are used for granular structure scintillators with dose reduction of 40% applied for needle structure scintillators based on results from a phantom study. Image quality based on detectability of 8 anatomical structures for both types of scintillators was assessed by 6 blinded radiologists. Exposure was expressed by DLP. Results underwent statistical analysis.

RESULTS

Overall, image quality was superior with corresponding dose reduction between 33-46% according to weight with needle structure scintillators. For the 4 lower weight categories, image quality was identical.

CONCLUSION

With image quality at least equal, new needle structure scintillator units allow a dose reduction of about 40%.

Advances in Digital Radiography: Physical Principles and System Overview

During the past two decades, digital radiography has supplanted screen-film radiography in many radiology departments. Today, manufacturers provide a variety of digital imaging solutions based on various detector and readout technologies. Digital detectors allow implementation of a fully digital picture archiving and communication system, in which images are stored digitally and are available anytime. Image distribution in hospitals can now be achieved electronically by means of web-based technology with no risk of losing images. Other advantages of digital radiography include higher patient throughput, increased dose efficiency, and the greater dynamic range of digital detectors with possible reduction of radiation exposure to the patient. The future of radiography will be digital, and it behooves radiologists to be familiar with the technical principles, image quality criteria, and radiation exposure issues associated with the various digital radiography systems that are currently available.

Depiction of low-contrast detail in digital radiography: comparison of powder- and needle-structured storage phosphor systems

PURPOSE

We sought to evaluate the low-contrast performance of a newly developed needle image plate/line scanner (NIP) computed radiography system in comparison with a standard powder image plate/flying-spot scanner (PIP) system.

MATERIALS AND METHODS

A total of 36 images of a CDRAD phantom, simulating low-contrast structures with different drill holes of different diameters, were obtained with both imaging systems using 9 different exposure variables. All images had window and level set to generate consistent density and contrast. In addition, multiscale contrast-dependent contrast amplification was applied to some of the images. All images obtained were printed and presented to a total of 10 observers (5 radiologists, 5 engineers/physicists), who were blinded to both the image plate and parameter setting used. The smallest detectable drill hole depth (= contrast) correctly identified was recorded for each diameter. The median values observed were calculated and tested for statistical differences between PIP and NIP using Student t test for matched pairs (level of significance P < or = 0.05).

RESULTS

At all but 2 settings of the variables, NIP images depicted significantly lower contrast levels (= lower depth of drill holes) compared with PIP images. The 2 settings also showed a trend towards better low contrast depiction with NIP. In no case was low contrast performance better using PIP images.

CONCLUSION

Images obtained with needle image plate/line scanner provide superior low contrast performance compared with the images obtained with powder image plate/flying-spot scanner.