AMBER: a scanning multiple-beam equalization system for chest radiography

Conventional chest radiography is limited by the small useful exposure range of radiographic film. The wide variation in absorption thickness of different parts of the chest results in areas of under- and over-exposure. An advanced multiple-beam equalization system, AMBER, controls local exposure delivered to the film. The system has a row of 20 modulators in front of the x-ray tube, each able to change the height of the local slit beam during scanning. Changes are made in response to measurements from a linear detector array in front of the film cassette. This array consists of 20 individually functioning detectors coupled through electronic feedback loops to the 20 modulators. A scan is obtained in 0.8 second with a local exposure time of approximately 50 msec. AMBER results in radiographs with significantly improved exposure of the mediastinum without overexposure of the lungs.     

Comparison of scanning equalization and conventional chest radiography

A clinical comparison study of scanning equalization radiography (SER) and conventional chest radiography was performed with the latest prototype SER system. Conventional chest radiography was performed at 120 kVp with Lanex regular screens (Eastman Kodak, Rochester, NY) and Kodak Ortho-G or Ortho-C film (Eastman Kodak). The 253 volunteer patients were examined with both techniques. The chest radiographs were interpreted by four radiologists. The study group was composed of 58 normal and 195 abnormal posteroanterior and lateral chest radiographs. In 31 cases there were two major radiologic diagnoses. The number of correct interpretations increased when the SER images were examined, compared with the conventional Ortho-G (chi 2 = 4.17, P less than .05) and conventional Ortho-C (chi 2 = 16.9, P less than .001) radiographs. The overall accuracy of disease detection improved for all radiologists with the SER system. There was no disease category in which the accuracy of interpretation decreased when the SER system was used. The SER system is a clinically reliable method of improving image quality and increasing diagnostic accuracy.     

Improved chest disease detection with scanning equalization radiography

The efficacy of chest disease detection with scanning equalization radiography (SER) was evaluated in a clinical study of 95 patients: 51 normals and 44 with abnormal chest radiographs. A conventional and an SER image of each patient were interpreted independently by four radiologists. The increased numbers of true positives (3%) and true negatives (9%) when the SER images were interpreted were statistically significant. There was also a reduced number of false positives (7%) with SER. This improved disease detection was noted by each of the radiologists and led to more frequent agreement (11%) of the correct interpretation among the radiologists.     

Exposure equalization radiography of the chest: clinical comparison of slit and raster scanning techniques

Exposure equalization radiography systems with scanning slit and raster geometries were constructed and tested with 75 patients. The scanning equalization radiography (SER) technique uses a detector, placed behind the patient, connected in a feedback loop to a microprocessor-controlled x-ray source. The detector monitors the transmitted radiation, and in turn the x-ray output is varied to equalize the radiographic film density over the entire image. The clinical evaluation of these systems included 25 posteroanterior (PA) chest radiographs by an SER slit-geometry system (5.0-sec scan time), 25 PA chest radiographs by an SER raster-geometry system with an 8.8-sec scan time, and 25 PA chest radiographs by an SER raster-geometry system with a 4.7-sec scan time. These SER radiographs were compared to conventional radiographs of the same patients by two radiologists. The observers noted that the SER slit radiographs had seriously overexposed areas in 80% of instances, and that any potential gains from this system were offset by the overexposure problems. The radiographs obtained by the SER raster technique with a 4.7-sec scan time showed more uniform and adequate exposure in 80% of instances and better visualization of normal anatomic detail in the lung (52%) and mediastinum (84%) than conventional radiographs. The radiographs obtained by the SER raster technique with an 8.8-sec scan time showed fewer peripheral lung markings in 15 of 25 cases, presumably due to motion. In all other respects, the images were similar in quality to the SER raster 4.7-sec radiographs.     

Improved pulmonary nodule detection with scanning equalization radiography

The potential for improved pulmonary nodule detection with scanning equalization radiography (SER) was evaluated by means of observer performance testing during the interpretation of posteroanterior conventional radiographs and SER images of an anthropomorphic chest phantom with simulated nodules. A test set of 200 conventional and 200 SER radiographs of phantoms containing either one nodule or none was interpreted by four radiologists attempting to detect a nodule and indicate a confidence value. Their ability to detect nodules positioned over the lung was slightly improved with SER compared with conventional radiography (sensitivity, .56 vs .70); for nodules over the mediastinum or diaphragmatic areas, it was much improved (sensitivity, .29 vs .64). The results were also analyzed with receiver-operating characteristic methods, which revealed a significant improvement in lesion detect-ability over the thicker body parts with SER images. The capability of equalized chest radiographs to provide improved lesion detectability suggests that SER may set a new standard for film-based chest radiography and have a large clinical application.     

Area beam equalization: optimization and performance of an automated prototype system for chest radiography

RATIONALE AND OBJECTIVES: To evaluate the feasibility and performance of an x-ray beam equalization system for chest radiography using anthropomorphic phantoms. MATERIALS AND METHODS: Area beam equalization involves the process of the initial unequalized image acquisition, attenuator thickness calculation, mask generation using a 16 x 16 piston array, and final equalized image acquisition. Chest radiographs of three different anthropomorphic phantoms were acquired with no beam equalization and equalization levels of 4.8, 11.3, and 21. Six radiologists evaluated the images by scoring them from 1-5 using 13 different criteria. The dose was calculated using the known attenuator material thickness and the mAs of the x-ray tube. RESULTS: The visibility of anatomic structures in the under-penetrated regions of the chest radiographs was shown to be significantly (P < .01) improved after beam equalization. An equalization level of 4.8 provided most of the improvements with moderate increases in patient dose and tube loading. Higher levels of beam equalization did not show much improvement in the visibility of anatomic structures in the under-penetrated regions. CONCLUSION: A moderate level of x-ray beam equalization in chest radiography is superior to both conventional radiographs and radiographs with high levels of beam equalization. X-ray beam equalization can significantly improve the visibility of anatomic structures in the under-penetrated regions while maintaining good image quality in the lung region.     

Scanning equalization radiography of the chest: assessment of image quality

An evaluation of the image quality of scanning equalization radiography (SER) of the chest was conducted with 60 volunteer patients. Posteroanterior chest radiographs by SER and conventional methods were compared by six radiologists to determine the adequacy and uniformity of the film exposure and the visualization of normal anatomic structures. The radiographs by the SER technique were deemed to be superior for visualization of most anatomic features. With SER there were no film artifacts from the scanning technique and there was only occasional blurring of some structures with a 4.7-sec scan time.     

A method to optimize the processing algorithm of a computed radiography system for chest radiography

A test methodology using an anthropomorphic-equivalent chest phantom is described for the optimization of the Agfa computed radiography "MUSICA" processing algorithm for chest radiography. The contrast-to-noise ratio (CNR) in the lung, heart and diaphragm regions of the phantom, and the "system modulation transfer function" (sMTF) in the lung region, were measured using test tools embedded in the phantom. Using these parameters the MUSICA processing algorithm was optimized with respect to low-contrast detectability and spatial resolution. Two optimum "MUSICA parameter sets" were derived respectively for maximizing the CNR and sMTF in each region of the phantom. Further work is required to find the relative importance of low-contrast detectability and spatial resolution in chest images, from which the definitive optimum MUSICA parameter set can then be derived. Prior to this further work, a compromised optimum MUSICA parameter set was applied to a range of clinical images. A group of experienced image evaluators scored these images alongside images produced from the same radiographs using the MUSICA parameter set in clinical use at the time. The compromised optimum MUSICA parameter set was shown to produce measurably better images.     

Multiple-beam equalization radiography in chest radiology. Image quality and radiation dose considerations

The large difference in transmission between the mediastinum and the part of the chest mainly containing lungs causes major problems in chest radiography. A system for advanced multiple beam equalization radiography has been evaluated. Evaluation of image quality has been performed both using standard phantoms and from clinical radiographs. Measurements of radiation dose burden to the patient have been made both in clinical examinations and using an anthropomorphic phantom. The image quality, in areas with low transmission, is substantially increased using the equalization system. In parts of the chest mainly containing lung tissue, conventional systems show an equal or slightly better image quality. The radiation dose burden to the patient is increased by 25 percent using the equalization system, as compared to a low-dose air-gap system. In our opinion, the slight increase in radiation dose burden is well motivated by the high overall quality of the radiographs produced.     

Advanced multiple-beam equalization radiography in chest radiology: a simulated nodule detection study

To evaluate the efficacy of AMBER, a multiple-beam equalization system for chest radiography, the authors performed a nodule detection study using an anthropomorphic chest phantom. AMBER and conventional images were compared. The images were read by four observers, and analysis was done by means of modified receiver-operating characteristic (ROC) curves (free ROC curves [FROC]). The results of the FROC analysis show a significant increase in the detectability of nodules (P less than .001) projected over the mediastinum with the use of AMBER. No significant difference between AMBER and conventional images was noted in detectability of nodules projected over the lung.     

A survey of digital chest radiography

The problems of chest radiography as they relate to digital systems are described, the current approaches to these problems are reviewed, and the utility of digital chest radiography is demonstrated.     

A phantom for dose-image quality optimization in chest radiography

Optimization in chest radiography requires evaluation of patient dose and image quality. This study is aimed at proposing a simple geometrical phantom that realistically simulates the important anatomical regions of the thorax. For this purpose, the standard LucAl chest phantom is modified by adding an "anthropomorphic" insert and image quality test plate. Different test objects are arranged on the plate in three important anatomical areas; lung, cardiac, and subdiaphragmal regions. The aim is to simultaneously find two types of image quality index, objective and subjective, which can be used to compare different images in order to select the better image. Two objective indices are proposed, areal contrast index DeltaC(a) and scatter fraction P(s) and two subjectively estimated, a low contrast visualization index P(low) and a high contrast visualization index P(high). To demonstrate the potential of this phantom method it was applied to an X-ray unit to find the optical film density that ensures optimal visualization in different anatomical areas. It was found for the X-ray system under investigation that the automatic exposure control could be set to produce an optical density of about 1.8 in the lung field. The reported method is easily implemented in any clinical situation where optimization of chest radiography is needed.