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Biomedical subjects

E J Halpern

Publications and source records attributed to E J Halpern.

17 recordsLinked to original sources
PubMed1995

A test pattern for quality control of laser scanner and charge-coupled device film digitizers.

Although clinical images provide the ultimate test of diagnostic performance for a film digitizer, such images are not generally suitable for daily quality control (QC) purposes. However, a well-designed test pattern will provide a rapid, comprehensive, objective and reproducible assessment of image quality. This pattern should evaluate various parameters of image quality, including high contrast resolution, low contrast discrimination, linearity of gray scale, geometric distortion, and noise. Furthermore, the pattern should detect light leak and film slippage, two problems commonly associated with film digitizers. The test pattern described in this manuscript was designed to provide quantitative measures of performance for a film digitizer. As part of a regular QC routine for a laser scanner or charge-coupled device digitizer, this pattern provides a simple method to identify and quantify changes in digital image quality.

Artifacts↗
PubMed1995

Threshold selection for CT angiography shaded surface display of the renal arteries.

The purpose of this study was to define objective criteria to calculate a tissue segmentation threshold for shaded surface display (SSD) rendering of the renal arteries with computed tomography angiography. Contrast-enhanced spiral CT scans were obtained through the renal arteries of nine patients. Six sets of SSD images were rendered for each patient with lower threshold values ranging from 80 to 130 Hounsfield units (HU) by increments of 10 HU. Visceral organ enhancement was measured in the aorta, liver, spleen, pancreas, and kidney. The segmentation threshold for each patient was determined by evaluation of the SSD images alone as well as by comparison with conventional arteriograms. The ideal threshold, as shown by comparison with conventional arteriography, was better correlated with a threshold value selected by qualitative evaluation of SSD images alone (rs = .42), than with measured enhancement in visceral organs (rs = -.289 to .009). The degree of stenosis was overestimated in a single renal artery (1 of 18) because of an inappropriate threshold selected by evaluation of the SSD images alone. In comparison with a segmentation threshold calculated from measured enhancement of visceral organs, a segmentation threshold selected by qualitative evaluation of the resulting SSD images is more likely to approximate the ideal threshold. Given the subjective nature of such threshold selection, further evaluation is warranted to determine whether threshold selection may result in inaccurate grading of stenosis.

Adult↗
PubMed1995

Renal artery stenosis: should we study the main renal artery or segmental vessels?

PURPOSE: To compare the sonographic diagnosis of renal artery stenosis (RAS) with Doppler interrogation of the main renal artery versus Doppler ultrasonography of segmental vessels. MATERIALS AND METHODS: The main renal artery-to-aortic peak systolic velocity ratio (RAR) and early systolic acceleration in segmental arteries were obtained in 186 patients. Conventional arteriographic correlation was available for 42 kidneys in 21 patients. Paired receiver operating characteristic (ROC) analyses were performed to evaluate RAR and minimum, average, and maximum early systolic acceleration in these 42 kidneys. RESULTS: Minimum early systolic acceleration was a better test than RAR (P = .05). Minimum early systolic acceleration plus RAR resulted in improved sensitivity for detection of RAS, but this improvement was not significant (P = .16). CONCLUSION: Minimum early systolic acceleration is the ultrasonographic method of choice to screen for RAS. RAR may provide marginal improvement in sensitivity but is probably not warranted in most clinical situations.

Adult↗
PubMed1995

Superior hypogastric plexus block for chronic pelvic pain in the presence of endometriosis: CT techniques and results.

PURPOSE: To evaluate the use of superior hypogastric plexus block with computed tomographic (CT) guidance in patients with endometriosis and chronic pelvic pain. MATERIALS AND METHODS: Seven blocks were performed on an outpatient basis in five women with endometriosis and pelvic pain. In the first four patients, one or two 20-gauge, 15-cm needles were placed anterior to the spine at the common iliac bifurcation from a posterior approach. In the fifth patient, the block was performed from an anterior approach with a single needle. RESULTS: One procedure resulted in mild pain relief, three in considerable pain relief, one in complete midline pain relief with no change in the lateral pain, and one in complete pain relief. One procedure was terminated because anesthetic was injected into the peritoneal cavity. There were no other complications. CONCLUSION: CT-guided superior hypogastric plexus block is easily performed and can be used to assess whether chronic pelvic pain can be attenuated by blocking the superior hypogastric plexus.

Adult↗
PubMed1995

Normal renal artery spectral Doppler waveform: a closer look.

PURPOSE: To characterize the spectral Doppler tracing of the normal renal artery. MATERIALS AND METHODS: Doppler tracings were obtained from a phantom of a vessel with variable compliance and from the kidneys of 15 healthy volunteers. RESULTS: In the phantom, vascular compliance had the following effects on systolic flow velocity patterns: low compliance, little change in the sharp appearance of the systolic component of the transmitted pulse; mildly increased compliance, down-stream dampening of early systolic acceleration (ESA) with the appearance of a sharp early systolic transmitted peak and of a more rounded late systolic compliance peak; high compliance, delayed and diminished transmitted peak that eventually disappeared within the enlarging down-stream compliance peak. Healthy subjects with compliant vessels had greater ESA and more frequently visualized early systolic peaks in the renal hilum than in the renal sinus. CONCLUSION: Absence of a discrete early systolic peak is a normal finding in young patients, especially in the more distal interlobar arteries. Loss of the early systolic peak may be explained on the basis of vascular compliance.

Acceleration↗
PubMed1994

CT done 4-6 hr after CT arterial portography: value in detecting hepatic tumors and differentiating from other hepatic perfusion defects.

OBJECTIVE: Nontumorous perfusion defects occur during CT arterial portography (CTAP) as normal variants or in cirrhosis, focal fatty infiltration, and portal vein obstruction. The purpose of this study was to determine whether delayed CT 4-6 hr after CTAP improves sensitivity to hepatic tumors and differentiates them from other hepatic perfusion defects. SUBJECTS AND METHODS: CTAP was done at 1-cm increments on 26 patients for evaluation of hepatic tumors. Delayed CT scans were obtained 4-6 hr later in all patients. Two observers retrospectively reviewed the CT scans obtained during CTAP and recorded size, shape, and location of suspected hepatic tumors. Confidence levels were assigned for each tumor. The delayed CT scan was then interpreted in conjunction with the CT scans obtained during CTAP, and confidence levels were reassigned. Surgical correlation was obtained for all patients. In the 26 patients, 86 masses were found at surgery. The sensitivity and number of false-positives for both CTAP alone and CTAP combined with delayed CT were compared with a two-tailed Student t-test. Receiver-operating-characteristic analysis also was performed. RESULTS: CTAP detected 73 (85%) of the 86 hepatic masses. Delayed CT had no effect on the sensitivity of CTAP. However, adding delayed CT decreased the total number of false-positives by 11, a statistically significant difference (p < .05). Receiver-operating-characteristic analysis revealed a significantly greater (p < .05) area under the curve (Az index) of 0.927 +/- 0.025 for CTAP combined with delayed CT compared with 0.886 +/- 0.032 for CTAP alone. Delayed CT was most useful for larger (> 1 cm) wedge-shaped perfusion defects and least useful for smaller (< 1 cm) round defects. CONCLUSION: Delayed CT has no effect in detecting tumors but may be useful for differentiating tumors from other hepatic perfusion defects seen on CTAP. The greatest benefit of delayed CT is in evaluating regions obscured by large wedge-shaped perfusion defects on CT scans obtained during CTAP.

Colorectal Neoplasms↗
PubMed1994

Sonographic evaluation of fetal growth: growth rate variability as a function of the interval between examinations.

OBJECTIVE: Fetal growth rates determined on the basis of findings at two separate sonographic examinations can be used to detect growth abnormalities. This article determines the relationship between the length of the interval between examinations and the associated variability in measured fetal growth rates. MATERIALS AND METHODS: We analyzed 1479 fetal measurements of the biparietal diameter, average abdominal diameter, and femur length from 539 normal pregnancies. Mean growth rates were computed as functions of gestational age. The standard deviation of the growth rate was computed as a function of the interval between examinations. RESULTS: The standard deviation of fetal growth rates is relatively constant when the interval between examinations is 8-10 weeks or more, but increases substantially when the interval is fewer than 6 weeks. CONCLUSION: From a purely statistical point of view, the optimal interval for assessment of fetal growth rates is 8-10 weeks or more. Shorter intervals, however, usually are mandated by the clinical situation. Correction factors can be used to determine the standard deviations and associated confidence intervals for fetal growth measured over a period of fewer than 10 weeks.

Embryonic and Fetal Development↗
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↗