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Biomedical subjects

H J Llewellyn

Publications and source records attributed to H J Llewellyn.

17 recordsLinked to original sources
PubMed1994

Application of wavelet compression to digitized radiographs.

OBJECTIVE: Image data compression is an enabling technology for teleradiology and picture archive and communication systems. Compression decreases the time and cost of image transmission and the requirements for image storage. Wavelets, discovered in 1987, constitute a new compression technique that has been described in radiologic publications but, to our knowledge, no previous studies of its use have been reported. The purpose of this study was to demonstrate the application of wavelet-based compression technology to digitized radiographs. MATERIALS AND METHODS: Twelve radiographs with abnormal findings were digitized, compressed, and decompressed by using a new wavelet-based lossy compression algorithm. Images were compressed at ratios from 10:1 to 60:1. Seven board-certified radiologists reviewed images on a two-headed, high-resolution (2K x 2K) diagnostic workstation. Paired original and compressed/decompressed images were presented in random order. Reviewers adjusted contrast and magnification to judge whether image degradation was present, and if so, whether it was of diagnostic significance. Quantitative error measures were tabulated. RESULTS: Reviewers found no clinically relevant degradation below a compression ratio of 30:1. Skeletal radiographs appeared more sensitive to compression than did chest or abdominal radiographs, but the trend was not statistically significant. Quantitative error measures increased gradually with compression ratio. CONCLUSION: On the basis of subjective assessment of image quality and the computational efficiency of the algorithm, wavelet-base techniques appear promising for the compression of digitized radiographs. The results of this initial experience can be used to design appropriate observer performance studies.

Adult↗
PubMed1994

Detection of pooled secretions above endotracheal-tube cuffs: value of plain radiographs in sheep cadavers and patients.

OBJECTIVE: Mechanical ventilation is thought to increase the risk of nosocomial pneumonia by permitting leakage of bacteria-laden gastro-oropharyngeal secretions into the upper airways. The goal of this study was (a) to validate radiographic signs of pooled secretions above endotracheal-tube cuffs (supracuff liquid) in an animal model and (b) to determine whether suctionable pooled supracuff liquid can be identified on bedside radiographs of intubated patients. MATERIALS AND METHODS: Diagnostic criteria for supracuff liquid were initially validated by three radiologists interpreting 162 randomized radiographs made in an intubated sheep cadaver. The primary criteria included (a) replacement of the normal supracuff lucency with liquid opacity and (b) the formation of a sharp interface between the lucency of the upper edge of the cuff below and the liquid above. Graded infusions of 0, 3, 8, 13, and 23 ml of saline were made in triplicate into the space above the cuff, and radiographs were evaluated for the presence or absence of saline. The validated diagnostic criteria were used by two radiologists to estimate the frequency with which pooled liquid was seen on portable chest radiographs of 47 patients undergoing elective short-term postanesthetic mechanical ventilation. RESULTS: In the sheep-cadaver model, the diagnostic criteria for supracuff liquid allowed successful differentiation between no liquid, a small amount of liquid (3-8 ml), and a large amount of liquid (13-23 ml; c2, p < .0001). In a clinical study, radiographic signs of supracuff liquid were identified in 57% of 47 patients. In a small subset of patients (n = 18), the estimated liquid volume (mean +/- SEM) was calculated to be 7.8 +/- 1.1 ml (range = 2.1-18.4 ml). CONCLUSIONS: Radiography is a sensitive means of identifying small volumes of supracuff liquid above the inflated cuffs of endotracheal tubes. Potentially contaminating liquid pooled above the cuff of an endotracheal tube can be identified in about half of patients undergoing short-term mechanical ventilation. Our results suggest the suction of the supracuff space may be a reasonable prophylactic maneuver against nosocomial pneumonia. A much larger study is suggested to investigate the actual relation between pooled supracuff liquid and the development of nosocomial pneumonia.

Adult↗
PubMed1993

Chest "gestalt" and detectability of lung lesions.

Image perception in chest radiography is thought to occur on two levels, (a) a fast global response based on learned templates ("gestalt") and, (b) a slower systematic scan process. The relative importance of "gestalt" on the detection of nodular lung cancers was studied by disturbing the "gestalt" through rotation of the radiograph but not actually diminishing the image content available for viewing. Sixty chest radiographs (20 normals, 21 with subtle lung cancers, 19 with obvious lung cancers) were presented to three readers in normal and abnormal (rotated randomly in 90 degree increments) orientation for varying durations (0.25 s, 1 s, 4 s and unlimited viewing time). The results indicate that the detectability of obvious and subtle lung lesions was degraded by the disturbed "gestalt" for both short and long viewing times. The readers did not significantly increase their unlimited viewing time when faced with rotated images (4.4 +/- 3.4 s) as opposed to non-rotated images (4.0 +/- 3.2 s). We conclude that the detection of lung lesions relies heavily on the chest "gestalt" and that systematic scanning cannot fully compensate for an impaired global response due to a disturbed "gestalt."

Humans↗
PubMed1991

Mediastinal abnormalities: detection with storage phosphor digital radiography.

Conventional film radiography (FR) and six postprocessing algorithms of isodose storage phosphor digital radiography (SR) (0.2-mm X 10-bit pixel matrix) were compared in the evaluation of 40 mediastinal and 30 pulmonary lesions in 60 patients who underwent computed tomography of the chest. The six SR algorithms varied among each other in only one image parameter. One algorithm approximated conventional image characteristics. The other five algorithms were designed to optimize imaging of the mediastinum and tested the effects of gray-scale reversal, adjustment of optical density, a linear instead of a sigmoid gradation curve, and moderate edge enhancement of high and medium spatial frequencies. Performance was evaluated by calculating the average area under the receiver operating characteristic curve (Az) of 5,040 observations by six readers. Post-processing with high-frequency edge enhancement and density optimization for the mediastinum significantly improved performance of SR over FR in the detection of mediastinal lesions (Az = .80 +/- .02 vs .73 +/- .01, respectively). Gray-scale reversal significantly decreased performance (Az = .64 +/- .03). All SR algorithms that were postprocessed to optimize imaging of the mediastinum were significantly inferior to FR in the detection of pulmonary lesions.

Algorithms↗
PubMed1991

Interstitial lung disease: impact of postprocessing in digital storage phosphor imaging.

The ability to resolve the fine linear structures of interstitial lung disease is one measure of the limiting performance characteristics of an imaging system. Conventional screen-film radiography was compared with six algorithms of isodose storage phosphor digital radiography (0.2-mm x 10-bit pixel matrix) in the detection of interstitial lung abnormality documented by means of computed tomography in 40 patients with abnormalities and 25 healthy control subjects. Performance was evaluated with an analysis of variance (the Fisher paired comparison test; P less than .05) of the average receiver operating characteristic area of 2,730 observations by six readers. The moderately and the more markedly high-frequency edge-enhanced algorithms of storage phosphor digital radiographs were equivalent in performance to screen-film radiography. The default mode, low- and medium-frequency edge-enhanced algorithms, and gray scale reversed mode of storage phosphor digital radiography were inferior to screen-film radiography. The authors conclude that high-frequency edge-enhanced algorithms can perform as well as screen-film radiography in the detection of interstitial disease.

Algorithms↗
PubMed1991

Detection of bullous lung disease: conventional radiography vs digital storage phosphor radiography.

The detection of fine linear contours and altered aeration are requirements for the radiologic diagnosis of bullous lung disease and are severe measures of the spatial and contrast resolution of chest imaging systems. We compared plain film radiography with five postprocessing algorithms of storage phosphor digital radiography (2144 x 1744 x 10 bit matrix with 0.2-mm pixel size) in the detection of CT-proved bullous lung disease (35 patients and 25 normal control subjects). Receiver-operating-characteristic analysis of 2160 observations by six interpreters was done to evaluate the observers' performance. By analysis of variance (p less than .05), we found that the default digital algorithm and the three edge-enhancing algorithms of high and medium frequencies performed less well than plain films did, but the differences fell short of statistical significance. Gray-scale reversal was the only digital algorithm that performed significantly less well than plain films did. We conclude that any differences between digital algorithms and plain films in the detection of bullous lung disease were too small to be detected in this study. Any difference between the two methods in providing clinically important, diagnostic information is likely to be insignificant.

Algorithms↗
PubMed1990

Screening for asbestos-related pleural disease with digital storage phosphor radiography.

Digital storage phosphor radiography (SR) has a wide dynamic range and unique postprocessing capabilities that may improve the performance of screening studies for asbestos-related pleural disease compared with conventional film radiography (FR). In a group of 32 asbestos-exposed and nine control subjects with established pleural data, we compared the screening performance of FR and SR obtained with a single isoexposure, dual-energy technique (system resolution 0.2 mm, 10 bits). Performance was evaluated for 7320 observations by eight readers using a paired t test (P less than .02 with Bonferroni correction) of averaged receiver operating characteristic curve (ROC) areas (Az +/- standard error). We found that SR alone and SR supplemented by dual-energy soft-tissue and calcium images (SRde) were superior to FR in the overall detection of pleural abnormalities (Az = 0.90 +/- 0.01, 0.90 +/- 0.01, and 0.88 +/- 0.01, respectively). In the specific detection of pleural calcification, SRde was superior to FR (Az = 0.91 +/- 0.01 and 0.87 +/- 0.01, respectively; P less than 0.01). Analysis of variance indicated that SRde most closely reproduced an established pleural score based on the International Labor Organization (ILO) classification of the pneumoconioses (P less than 0.05, Scheffé's multiple comparison test). We conclude that isodose SR performs at least as well as FR in screening for asbestos-related pleural disease. SR supplemented by dual-energy images might improve the specific detection of pleural calcifications compared with FR.

Asbestosis↗
PubMed1990

Digital storage phosphor imaging versus conventional film radiography in CT-documented chest disease.

The advantages of imaging the chest with digital storage phosphor radiography (SR) may be nullified by its spatial resolution, which is lower than that of conventional film radiography (FR). To test the reader detection performance with the two modalities under clinical conditions, the authors compared 140-kVp isoexposure SR (system resolution: 0.2 mm, 10 bits) and FR images of a variety of chest abnormalities proved by computed tomography (CT) (157 patients, 244 abnormalities, 5,652 observations, six readers). In all tests, SR was as good as or better than FR (P less than .05). In overall detection, indicated by the average area of receiver operating characteristics, SR and FR were equivalent. SR was superior for mediastinal lesions and for pulmonary opacities greater than 2 cm in diameter. For all other types of pulmonary lesions and pleural abnormalities, SR and FR were equivalent. Currently available commercial SR systems can replace film radiographic systems in the detection of a wide variety of chest lesions. SR is likely to enable better visualization than FR in the detection of mediastinal and large pulmonary abnormalities.

Female↗
PubMed1989

Impact of postprocessing on the detection of simulated pulmonary nodules with digital radiography.

The authors compared the impact of five postprocessing algorithms on diagnostic performance in the detection of simulated pulmonary nodules on storage phosphor-based digital chest radiographs. Tissue equivalent paraffin nodules (0.5-2.5 cm diameter) were randomly positioned over the chest of a normal volunteer. Receiver operating characteristics (ROC) analysis of a total of 2500 observations by five readers indicated that the default unenhanced image having the appearance of a conventional chest radiograph (ROC area = 0.87 +/- 0.05) was as good as an image with moderate enhancement of medium frequencies (ROC area = 0.85 +/- 0.03), an image with reversed gray scale polarity (ROC area = 0.84 +/- 0.02), an image with reversed gray scale and moderate enhancement of medium frequencies (ROC area = 0.87 +/- 0.03), and an image with a linear rather than a sigmoid gradation curve and incorporating moderate enhancement of medium frequencies (ROC area = 0.87 +/- 0.03). The authors conclude that the specific algorithms they tested had no effect on the detection of pulmonary nodules.

Algorithms↗
PubMed1989

High frequency edge enhancement in the detection of fine pulmonary lines. Parity between storage phosphor digital images and conventional chest radiography.

Fine linear structures represent a severe test of the minimum spatial resolution that is needed for digital chest imaging. We studied the comparative observer performance of storage phosphor digital imaging (1760 X 2140 pixel matrix, 10 bits deep), and conventional radiography (Lanex medium screen, Ortho C film) in the detection of simulated fine pulmonary lines superimposed on the normal chest when exposure factors were identical (20mR skin entrance dose at 141 kVp). Receiver operating characteristics analysis of 2160 observations by six readers found that high frequency edge-enhanced digital images (ROC area: 0.78 +/- 0.06) performed better than unenhanced digital images (ROC area: 0.70 +/- 0.07) (P less than 0.01 for paired t-test), and that edge enhanced digital images performed on a par with conventional radiography (ROC area: 0.78 +/- 0.09). We conclude that for the detection of fine linear structures, storage phosphor digital images can perform on a par with higher resolution conventional chest radiographs when a high frequency edge-enhancement algorithm is employed.

Adult↗
PubMed1989

Improved control of image optical density with low-dose digital and conventional radiography in bedside imaging.

The technical and diagnostic performance of simultaneously acquired low-dose (44% of standard dose) storage-phosphor digital radiographs (system resolution = 0.2 mm, 10 bits) were compared with those of standard-dose conventional bedside radiographs of the chest in 32 patients. The mean optical density (OD) of the lungs (800 measurements) was closer to the ideal density with digital radiography (1.45 OD +/- 0.20 [standard deviation] vs 1.75 OD +/- 0.53) and was less often outside the usable range (2.5% vs 42.5%). Receiver operating characteristic analysis for detection of simulated nodules and monitoring devices (nine readers, 4,608 observations) showed that digital radiography was superior to conventional radiography (P less than .05) for four of the nine readers and equivalent to conventional radiography for five readers. The authors concluded that digital radiography produces more consistent and ideal image density and performs at least as well as conventional radiography under phantom test conditions.

Absorptiometry, Photon↗
PubMed1988

Lung lesions: correlation between viewing time and detection.

The influence of viewing time on the detectability of subtle and obvious lung cancers was studied. Frontal chest radiographs of 40 patients with subtle cancers, 40 patients with obvious cancers, and 40 healthy control subjects were shown to four observers for four different viewing times (0.25 second, 1 second, 4 seconds, and unlimited time). Receiver operating characteristic analysis was used to compare the detectability of lesions. Performance was degraded as viewing time decreased. The true-positive fractions for subtle and obvious cancers were 30% and 70% at 0.25 second and 74% and 98% at unlimited viewing time, respectively, for a given false-positive fraction of 20%. Thus, even with unlimited viewing time, the false-negative fraction for subtle cancers was 26%. The difference in detectability between subtle and obvious lung cancers was exaggerated at 1.0 second compared with 4 seconds and unlimited viewing time. The following conclusions were reached: (a) a substantial proportion of subtle lung lesions are missed, even with unlimited viewing time; (b) a large proportion of obvious lung cancers are detected with flash viewing; (c) the detectability of lesions decreases considerably as viewing time becomes less than 4 seconds; and (d) differences in detectability are exaggerated by short viewing times.

False Negative Reactions↗
PubMed1988

Subtle lung cancers: impact of edge enhancement and gray scale reversal on detection with digitized chest radiographs.

The authors studied the impact of edge enhancement and gray scale polarity reversal on the detection of subtle lung cancers. Three experienced readers reviewed 46 biopsy-proved subtle lung cancers and 46 normal controls on chest radiographs that had been digitized into a 1,024 X 1,536-pixel matrix 8 bits deep. Receiver-operating characteristics (ROC) analysis of 1,656 pooled observations indicated that performance was best with the unmodified images (ROC area = 0.83), degraded by moderate enhancement of medium frequencies (ROC area = 0.80), and markedly impaired by severe enhancement of low frequencies (ROC area = 0.69). Gray scale polarity reversal further degraded performance (unenhanced ROC area = 0.74; moderately enhanced ROC area = 0.76; severely enhanced ROC area = 0.76). The authors conclude that edge enhancement and gray scale polarity reversal can impair the detectability of subtle lung cancers on digitized radiographs of medium resolution.

Humans↗
PubMed1985

Treatment planning for colorectal cancer: radiation and surgical techniques and value of small-bowel films.

For colorectal cancer, the adjuvant radiation dose levels required to achieve a high incidence of local control closely parallel the radiation tolerance of small bowel (4500-5000 rad), and for patients with partially resected or unresected disease, the dose levels exceed tolerance (6000-7000 rad). Therefore, both the surgeon and the radiation oncologist should use techniques that localize tumor volumes and decrease the amount of small intestine within the irradiation field. Surgical options include pelvic reconstruction (reperitonealization, omental flaps, retroversion of uterus, etc.) and clip placement. Radiation options include the use of radiographs to define small bowel location and mobility combined with treatment techniques using multiple fields, bladder distention, shrinking or boost fields, and/or patient position changes (prone, decubitus, etc.). When both specialties interact in optimum fashion, local control can be increased with minimal risks to achieve a suitable therapeutic ratio.

Colonic Neoplasms↗
PubMed1980

The oblique view: an unnecessary component of the initial adult lumbar spine examination.

A retrospective study was undertaken to determine the diagnostic contribution of oblique views in 200 consecutive lumbar spine examinations done in adults. In four cases (two percent) there was a change in the radiographic interpretation when the oblique views were used for diagnosis. Considering the low diagnostic and therapeutic yield, as well as the gonadal radiation dose, the authors feel that the oblique view should not be a routine part of the initial lumbar spine examination in adults.

Adult↗
PubMed1978

Quality assessment and assurance in diagnostic imaging. Theoretical and practical considerations and a quality audit of the excretory urogram.

Concepts necessary to an understanding of the basics of quality assurance audits are presented. Included are specific examples that bridged theory and practice by applying the protocol to a real-life diagnostic imaging situation. This method meets the present requirements of the Joint Commission of the Accrediation of Hospitals.

Costs and Cost Analysis↗