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E J Halpern

Publications and source records attributed to E J Halpern.

46 records · Page 3Linked to original sources
PubMed1993

Calculation of tissue attenuation with a clinical ultrasound unit.

RATIONALE AND OBJECTIVES: Five alternative methods for estimating tissue attenuation with a clinical ultrasound unit were evaluated. METHODS: Two homogeneous tissue mimicking phantoms (with known attenuations of 0.25 and 0.54 db/cm/MHz) and 22 human placentas were scanned. Attenuation coefficients were computed by linear regression of 1) L(f), the log spectral difference; 2) Fav (d), the average spectral frequency; 3) log[P(d)], the logarithm of the spectral power; 4) Fav (d) x log[P(d)]; and 5) (Fav(d) + log[P(d)])/2. RESULTS: Each of these five heuristics provided accurate estimates for the relative attenuations of the two phantoms. For placental tissue, method 3 provided better regression fits than methods 1 and 2. Methods 4 and 5 provide the best regression fits (P < .01). CONCLUSIONS: The combination of both frequency and power information in methods 4 and 5 compensates, in part, for nonlinearities introduced by tissue heterogeneity. A parameter that combines both frequency and time domain information is likely to provide more reliable estimates of attenuation than power or frequency measurements alone.

Female↗
PubMed1992

Evaluation of teleradiology for interpretation of intravenous urograms.

The diagnostic yield of a commercial teleradiology/picture archiving and communication system (ATT-Philips Comm View T/PACS) was evaluated for 100 urograms. A single image from each examination was digitized (2048 x 1684 x 12-bit pixels) and transmitted from a satellite hospital over a T-1 line using the T/PACS system. The video display of each digitized image was reviewed independently by four radiologists. The same four radiologists reviewed the original film images at a different time without knowledge of their T/PACS interpretation. There was no statistically significant difference in the sensitivity for clinical findings between T/PACS (86%) and film (89%). The false positive rate, however, was significantly higher with T/PACS than with film (44 versus 32 false positive findings per 100 films). We conclude that T/PACS of the type studied here demonstrates sufficient sensitivity for the detection of clinically important urographic findings in the emergency setting. A final reading of the original films is still necessary, however, to assure appropriate specificity.

Contrast Media↗
PubMed1991

An improved phantom for quality control of laser scanner digitizers in picture archival and communications systems.

Various quality control (QC) procedures may be used to evaluate image quality for picture archival and communications (PACS) systems. A standard PACS QC protocol applied on a regular basis is desirable to ensure optimal diagnostic performance. We describe a QC phantom designed especially to test PACS systems that acquire images by digitizing x-ray films. The phantom is a sheet of x-ray film upon which a digital test pattern is printed. Multiple parameters of image quality are tested, including resolution, contrast, gray scale, geometric distortion, and noise. Individual test patterns are incorporated to detect specific artifacts of laser scanner digitizers. As part of a regular QC protocol, the phantom provides an objective measurement of change in digital image quality over time, as well as an objective means for comparison with other systems.

Lasers↗
PubMed1991

Quality assurance of picture archiving communication systems with laser film digitizers.

A comprehensive quality assurance (QA) program should be implemented for all teleradiology and picture archival and communications (PACS) systems. In this report, we summarize our QA experience with a teleradiology system that includes a laser digitizer for x-ray film. A key component required for the evaluation of laser film scanners is an appropriate test pattern; digitizers should be evaluated with enhanced test patterns specifically designed for this purpose. The phantom pattern should measure high-contrast resolution, low-contrast discrimination, gray scale linearity, geometric distortion, and noise. In addition, a uniformly exposed sheet of film (approximately 0.3 optical density) serves as a good phantom for testing screen nonuniformities of viewing station monitors. It is also suggested that clinical images should be included in a QA program. Finally, it is recommended that any discrepancies in the interpretation of teleradiology images should be monitored and investigated.

Lasers↗
PubMed1990

A quality-control phantom for digitization of radiographs.

Quality control is fundamental to the clinical application of digital radiography. A 14 x 17-in phantom radiograph was designed to test digital image quality by measurement of five parameters: high-contrast spatial resolution, low-contrast discrimination, linearity of gray-scale response, high-frequency noise, and geometric distortion. The phantom was used to evaluate the AT&T-Philips CommView picture archival and communications system (AT&T Bell Laboratories, West Long Branch, NJ; Philips Medical Systems, Shelton, CT). High-contrast resolution was found to be greater along the diagonal axis of the system than along either the horizontal or vertical axis. Problems with low-contrast discrimination and linearity of gray-scale response were identified. This phantom provides a simple tool for daily quality assurance testing and an objective standard for comparison of image quality between different digital radiography systems.

Quality Control↗
PubMed1990

Quadtree-based data compression of abdominal CT images.

An ROC study was performed to evaluate the effect of quadtree-based data compression on the diagnostic yield of CT images. Seventy images were selected from a series of consecutive abdominal/pelvic CT scans. Following the application of quadtree-based compression, all images were reviewed independently by three radiologists. The images were analyzed at six decreasing irreversible compression ratios (30.6:1 to 7.4:1), as well as after reversible compression (2.9:1). ROC curves reveal a gradual decrease in clinical accuracy with increasing compression ratios. At a compression ratio of 7.4:1, sensitivity for all major abnormalities was 99% with a specificity of 93%. As the compression ratio was increased to 30.6:1, sensitivity and specificity dropped to 75% and 83% respectively. Execution times for compression and decompression of the CT images with a PC-AT based digital radiography system varied from 24.7 to 18.5 seconds and from 16.2 to 5.1 seconds respectively, decreasing with higher levels of compression. We conclude that quadtree-based compression of abdominal CT images may have practical applications for a PC based digital radiography system.

Algorithms↗
PubMed1990

Application of region of interest definition to quadtree-based compression of CT images.

A quadtree-based data compression algorithm can provide different levels of compression within and outside of regions of interest (ROIs). The current study shows whether ROI compression can provide greater compression or diagnostic accuracy than uniform quadtree compression. In 75 single CT images from 75 consecutive abdominal examinations, 43 abnormalities were identified and surrounded by ROIs. Three radiologists interpreted the images following (1) 50:1 compression of the entire image; (2) ROI compression at five decreasing compression ratios (with 50:1 compression outside the ROI); and (3) reversible (lossless) compression of the entire image. Reversible compression (compression ratio 3:1) yielded a sensitivity of 96%. ROI compression of 15:1 was achieved with no loss of sensitivity; ROI compression of 28:1 yielded a sensitivity of 91% (not significantly different). At any given compression ratio, diagnostic sensitivity was greater with ROI compression than with uniform quadtree compression. For purposes of image archiving, quadtree-based ROI compression is superior to uniform compression of CT images.

Algorithms↗
PubMed1989

Evaluation of a quadtree-based compression algorithm with digitized urograms.

The effect of a quadtree-based data-compression algorithm on the diagnostic yield in digitized radiographs was studied for 100 urograms. Each image was digitized and reviewed at nine decreasing compression ratios ranging from 90:1 to 4.2:1, followed by a review of the uncompressed digital images. Four radiologists independently reviewed the digitized images and the original radiographs and agreed on a reference standard of 201 findings. Sensitivity, measured by the number of findings noted on the compressed digital images, decreased with increasing compression ratios at and above the 11:1 level. No loss of sensitivity was noted with a compression ratio of 4.2:1. Sensitivity decreased more precipitously for calcifications than for soft-tissue masses. Only a minimal loss of sensitivity for bilateral renal function was noted, even with high compression ratios. False-positive rates were unaffected by compression. The authors conclude that quadtree compression ratios of 11:1 and higher may result in loss of sensitivity in clinically relevant findings.

Algorithms↗
PubMedDate not supplied

The association of paracardial adenopathy with hepatic metastasis found on CT arterial portography.

BACKGROUND: The association of paracardial lymphadenopathy with hepatic metastases in patients undergoing computed tomographic arterial portography (CTAP) prior to possible resection of hepatic metastases is documented. METHODS: CTAP was performed on 45 patients with hepatic metastasis, including 30 with colorectal carcinoma, using 1 cm increments from the dome of the diaphragm through the liver. Two radiologists, blinded to the diagnosis and surgical results, reviewed all portograms and identified all paracardial lymph nodes larger than 8 cm. RESULTS: Enlarged paracardial lymph nodes were found in three of the 30 colorectal carcinoma patients and two of the remaining 15 patients. All three colorectal patients with paracardial lymphadenopathy demonstrated massive metastatic involvement of the anterior segment of the right hepatic lobe (segment 8: Couinaud nomenclature). Additional metastasis in the superior aspect of the liver was seen in two of these patients as well. Both patients without colorectal carcinoma with paracardial lymphadenopathy had metastasis involving the superior aspect of the liver. Paracardial lymphadenopathy was right-sided in all five patients and bilateral in one. By contrast, 48% (19 of 40) of patients without enlarged paracardial lymph nodes had metastasis in the anterior segment of the right lobe. CONCLUSIONS: This study suggests that paracardial lymphadenopathy is associated with metastatic disease to specific areas within the liver. This nodal involvement can be attributed to lymphatic drainage from the diaphragmatic surface of the liver.

Adult↗