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Biomedical subjects

David Gur

Publications and source records attributed to David Gur.

At least 19 recordsLinked to original sources
PubMed2007

The prevalence effect in a laboratory environment: Changing the confidence ratings.

RATIONALE AND OBJECTIVES: We sought to assess whether or not prevalence levels affected the confidence ratings of readers during the interpretation of cases in a laboratory receiver operating characteristic-type observer performance study. MATERIALS AND METHODS: We reanalyzed a previously conducted observer performance study that included 14 readers and 5 different levels of prevalence. The previous study yielded the observation that in the laboratory we could not detect a "prevalence effect" in terms of differences in areas under the receiver operating characteristic curves. The detection ratings (for presence or absence) of lung nodules, interstitial disease, and pneumothorax for the five prevalence levels were compared, and a test for trend in averaged ratings as a function of abnormality prevalence was performed within a mixed-model setting that accounts for different sources of variability and correlations induced by the study design. RESULTS: The ratings of the cases in terms of confidence that the specific abnormality in question is present tend, on average, to be larger when actual disease prevalence is lower. The rate of the increase of the average confidence ratings with the decreasing prevalence of a specific abnormality is very similar for actually positive and actually negative cases for every considered abnormality. The observed trend in the changes of the average confidence ratings as a function of prevalence levels was statistically significant (p < 0.01). CONCLUSION: Expectations of disease prevalence in the case mix during a laboratory observer performance study may systematically affect the behavior of observers in terms of their actual confidence ratings.

Humans↗
PubMed2006

Prospective study of electrical impedance scanning for identifying young women at risk for breast cancer.

BACKGROUND: One way to improve the cost-benefit ratio for breast cancer screening in younger women is to identify those at high-risk of breast cancer and manage them in an optimal manner. The purpose of this study is to evaluate the sensitivity and specificity of Electrical Impedance Scanning (EIS) for identifying young women who are at risk for having breast cancer and should be followed with directed imaging technologies. METHODS: A prospective, observational, two-arm, multi-site clinical trial was performed on women aged 30-45 years. The 'Sensitivity Arm' included Clinical Breast Examinations (CBE) and EIS (T-Scan 2000ED) on 189 women prior to scheduled breast biopsy. The 'Specificity Arm' included 1361 asymptomatic women visiting clinics for routine annual well-woman examination. Sensitivity and specificity were determined. Relative probability for a woman with a positive EIS examination was computed and compared with other approaches commonly used to define 'high-risk' in this population. RESULTS: Fifty of 189 women in the Sensitivity arm had verified cancers, 19 of whom had positive EIS examination resulting in sensitivity of 38% (19/50). Of the 1361 women in the Specificity arm, 67 had positive EIS examination resulting in a specificity of 95% (1294/1361). The relative probability of a woman with a positive EIS examination was 7.68, which compares favorably with other established risk identifiers (e.g. two first-degree relatives with breast cancer or atypical ductal hyperplasia). CONCLUSION: EIS may have an important role as a screening tool for identifying young women that should be followed more closely with advanced imaging technologies for early detection of breast cancer.

Adult↗
PubMed2006

A multisite telemammography system for remote management of screening mammography: an assessment of technical, operational, and clinical issues.

OBJECTIVE: This paper describes a high-quality, multisite telemammography system to enable "almost real-time" remote patient management while the patient remains in the clinic. One goal is to reduce the number of women who would physically need to return to the clinic for additional imaging procedures (termed "recall") to supplement "routine" imaging of screening mammography. MATERIALS AND METHODS: Mammography films from current and prior (when available) examinations are digitized at three remote sites and transmitted along with other pertinent information across low-level communication systems to the central site. Images are automatically cropped, wavelet compressed, and encrypted prior to transmission to the central site. At the central site, radiologists review and rate examinations on a high-resolution workstation that displays the images, computer-assisted detection results, and the technologist's communication. Intersite communication is provided instantly via a messaging "chat" window. RESULTS: The technologists recommended additional procedures at 2.7 times the actual clinical recall rate for the same cases. Using the telemammography system during a series of "off-line" clinically simulated studies, radiologists recommended additional procedures at 1.3 times the actual clinical recall rate. Percent agreement and kappa between the study and actual clinical interpretations were 66.1% and 0.315, respectively. For every physical recall potentially avoided using the telemammography system, approximately one presumed "unnecessary" imaging procedure was recommended. CONCLUSION: Remote patient management can reduce the number of women recalled by as much as 50% without performing an unreasonable number of presumed "unnecessary" procedures.

Ambulatory Care Facilities↗
PubMed2006

Head-mounted versus remote eye tracking of radiologists searching for breast cancer: a comparison.

PURPOSE: We compared performance and visual search parameters of radiologists detecting masses on mammograms by using both a head-mounted (HDMT) and a remote (REM) eye tracker. MATERIALS AND METHODS: Five experienced radiologists read twice a case set of 20 one-view (medial-lateral oblique) mammograms, of which 12 contained a malignant mass and eight were lesion-free. For each observer, one trial used an HDMT eye-tracking system and the other used an REM system. Trials were separated on average by 2 months. Time to hit the location of the mass, dwell, and number of fixations in the location of the mass were measured. The same parameters were measured on a per-trial basis to determine whether there were memory effects from the previous trial. RESULTS: Dwell times in the location of true-positive, false-positive, and false-negative results were significantly shorter (P < .05) using the HDMT (median, 0.395 seconds) than REM (median, 0.482 seconds) systems, but the number of fixations in the location of the response was smaller using the REM system (median, 4.33 versus 5.0 for the HDMT). The observed differences did not seem to be caused by a memory effect. In addition, the relative lack of head mobility using the REM system caused observers to report neck strain. CONCLUSION: Overall, radiologists' visual search behavior was very similar using both types of eye-tracking device. However, because the REM system did not contain a magnetic head tracker, radiologists were allowed very limited head movements when using it, which made them uncomfortable during the experiment.

Breast Neoplasms↗
PubMed2006

The effect of image display size on observer performance an assessment of variance components.

RATIONALE AND OBJECTIVE: Our goal was to investigate the effect of the displayed image size on variance components during the performance of an observer performance study to detect masses on abdominal computed tomography (CT) examinations. MATERIALS AND METHODS: A previously performed receiver operating characteristic (ROC) study with eight observers to detect abdominal masses on 166 CT examinations was reanalyzed to assess variance components when comparing two similar modes with displayed image sizes varying by a factor of 2. Case, mode, and reader-related variance components were estimated for the group of eight observers and subsets of readers after excluding each of the participants. RESULTS: There was no significant difference in the average area under the ROC curves between the two modes using the two image sizes (P > .05). Reader and reader-by-case variability were substantially larger for the mode displaying enlarged images for the group and all subsets formed by excluding a single reader. Reader variability was affected by one observer who actually performed better with the enlarged images. CONCLUSION: Sequential viewing of enlarged CT images for the detection of abdominal masses did not improve performance and increased reader variability.

Abdominal Neoplasms↗
PubMed2006

A permutation test for comparing ROC curves in multireader studies a multi-reader ROC, permutation test.

RATIONALE AND OBJECTIVES: The aim of the study is to develop a permutation test to compare receiver operating characteristic (ROC) curves of two diagnostic modalities in a multireader paired design. MATERIALS AND METHODS: A statistical test for comparing two diagnostic modalities is developed based on all possible exchanges of the set of reader-ratings between the two modalities. An exact permutation test is formed by determining the frequency of the most extreme values of the statistic estimating the average difference in the areas under the ROC curves (AUCs). An asymptotic version of the test is constructed by obtaining the exact permutation variance and appealing to the asymptotic normality of the nonparametric estimator of the average difference in areas. Computer simulations were conducted to validate the type I error for small sample sizes. RESULTS: The new test provides a permutation approach for comparing ROC curves in a multireader paired-design setting in which effects of the readers are considered to be fixed. The type I error of the asymptotic test is close to the true value, even for samples as small as 20 normal and 20 abnormal cases. The test is designed to be sensitive to alternatives in which the AUCs of the two diagnostic modalities differ. CONCLUSIONS: The proposed test provides a powerful method for comparing two diagnostic modalities in a multireader paired-study design when the primary interest is to detect difference in average AUCs.

Analysis of Variance↗
PubMed2006

Reader variance in ROC studies--generalizability to reader population at high and low performance levels.

RATIONALE AND OBJECTIVES: To investigate the variability between discriminative performances of readers as a function of average performance levels during receiver operating characteristic (ROC) studies. MATERIALS AND METHODS: Four subsets of cases from previously ascertained ROC rating data by 12 observers when detecting interstitial disease and pneumothorax on posteroanterior chest films were selected for each abnormality and reanalyzed to assess changes in "reader" variance component. The subsets were selected based on a prestudy subjective assessment of the subtleness of depicted abnormality (positive cases) and the difficulty in determining its absence (negative cases). Reader variance component was estimated using a bootstrap approach for each subset and the results were used to assess a general relationship between variability and average performance level. RESULTS: The reader variance component decreased substantially (from 0.007704 to 0.000426), as expected, when the areas under the ROC curves (AUC) for detecting pneumothoraces increased from 84% to 97%. On the other hand, reader variance component increased substantially (from 0.000890 to 0.005181) when AUC for detecting interstitial disease increased from 59% to 87%. The large magnitude of and changes in the reader variance component resulted in a consistent nonmonotone relationship as a function of AUC when other related variance components were included in addition to the reader component. CONCLUSION: Among several factors affecting generalizability of ROC results to the population of readers, the reader variance component depended nonmonotonically on the average diagnostic performance and is lowest at both very high and very low levels of performance.

Clinical Competence↗
PubMed2006

Evaluation of lung MDCT nodule annotation across radiologists and methods.

RATIONALE AND OBJECTIVES: Integral to the mission of the National Institutes of Health-sponsored Lung Imaging Database Consortium is the accurate definition of the spatial location of pulmonary nodules. Because the majority of small lung nodules are not resected, a reference standard from histopathology is generally unavailable. Thus assessing the source of variability in defining the spatial location of lung nodules by expert radiologists using different software tools as an alternative form of truth is necessary. MATERIALS AND METHODS: The relative differences in performance of six radiologists each applying three annotation methods to the task of defining the spatial extent of 23 different lung nodules were evaluated. The variability of radiologists' spatial definitions for a nodule was measured using both volumes and probability maps (p-map). Results were analyzed using a linear mixed-effects model that included nested random effects. RESULTS: Across the combination of all nodules, volume and p-map model parameters were found to be significant at P < .05 for all methods, all radiologists, and all second-order interactions except one. The radiologist and methods variables accounted for 15% and 3.5% of the total p-map variance, respectively, and 40.4% and 31.1% of the total volume variance, respectively. CONCLUSION: Radiologists represent the major source of variance as compared with drawing tools independent of drawing metric used. Although the random noise component is larger for the p-map analysis than for volume estimation, the p-map analysis appears to have more power to detect differences in radiologist-method combinations. The standard deviation of the volume measurement task appears to be proportional to nodule volume.

Artificial Intelligence↗
PubMed2006

Computerized estimation of the lung volume removed during lung volume reduction surgery.

RATIONALE AND OBJECTIVES: This study was designed to develop an automated method for estimating lung volume removed during lung volume reduction surgery (LVRS) using computed tomography (CT). MATERIALS AND METHODS: The CT examinations of six patients who underwent bilateral LVRS were analyzed in this study. The resected lung tissue (right and left) was weighed during pathologic examination. An automated computer scheme was developed to estimate the lung volume removed using the CT voxel values and lung specimen weight. The computed fraction of lung volume removed was evaluated across a range of simulated surgical planes (ie, other than parallel to the CT image plane) and CT reconstruction kernels, and it was compared with the surgeons' postsurgical estimates. RESULTS: The computed fraction of the lung volume removed during LVRS was linearly correlated with the resected lung tissue weight (Pearson correlation = 0.697, P = .012). The computed fraction of lung volume removed ranged from 12.9% to 51.7% of the total lung volume. The surgeons' postsurgical estimates of lung volume removed ranged from 30% to 33%. The percent difference between the surgeons' estimates and the computed lung volume removed as a percentage of the surgeons' estimates ranged from -72.3% to 57.0% with mean absolute difference of 29.7% (+/-20.7). CONCLUSION: The preliminary findings of this study suggest that the proposed quantitative model should provide an objective measure of lung volume removed during LVRS that may be used to investigate the relationship between lung volume removed and outcome.

Absorptiometry, Photon↗
PubMed2006

A method to improve visual similarity of breast masses for an interactive computer-aided diagnosis environment.

The purpose of this study was to develop and test a method for selecting "visually similar" regions of interest depicting breast masses from a reference library to be used in an interactive computer-aided diagnosis (CAD) environment. A reference library including 1000 malignant mass regions and 2000 benign and CAD-generated false-positive regions was established. When a suspicious mass region is identified, the scheme segments the region and searches for similar regions from the reference library using a multifeature based k-nearest neighbor (KNN) algorithm. To improve selection of reference images, we added an interactive step. All actual masses in the reference library were subjectively rated on a scale from 1 to 9 as to their "visual margins speculations". When an observer identifies a suspected mass region during a case interpretation he/she first rates the margins and the computerized search is then limited only to regions rated as having similar levels of spiculation (within +/-1 scale difference). In an observer preference study including 85 test regions, two sets of the six "similar" reference regions selected by the KNN with and without the interactive step were displayed side by side with each test region. Four radiologists and five nonclinician observers selected the more appropriate ("similar") reference set in a two alternative forced choice preference experiment. All four radiologists and five nonclinician observers preferred the sets of regions selected by the interactive method with an average frequency of 76.8% and 74.6%, respectively. The overall preference for the interactive method was highly significant (p < 0.001). The study demonstrated that a simple interactive approach that includes subjectively perceived ratings of one feature alone namely, a rating of margin "spiculation," could substantially improve the selection of "visually similar" reference images.

Algorithms↗
PubMed2006

Multiview-based computer-aided detection scheme for breast masses.

In this study, we developed and tested a new multiview-based computer-aided detection (CAD) scheme that aims to maintain the same case-based sensitivity level as a single-image-based scheme while substantially increasing the number of masses being detected on both ipsilateral views. An image database of 450 four-view examinations (1800 images) was assembled. In this database, 250 cases depicted malignant masses, of which 236 masses were visible on both views and 14 masses were visible only on one view. First, we detected suspected mass regions depicted on each image in the database using a single-image-based CAD. For each identified region (with detection score > or = 0.55), we then identified a matching strip of interest on the ipsilateral view based on the projected distance to the nipple along the centerline. By lowering CAD operating threshold inside the matching strip, we searched for a region located inside the strip and paired it with the original region. A multifeature-based artificial neural network scored the likelihood of the paired "matched" regions representing true-positive masses. All single (unmatched) regions except for those either with very high detection scores (> or = 0.85) or those located near the chest wall that cannot be matched on the other view were discarded. The original single-image-based CAD scheme detected 186 masses (74.4% case-based sensitivity) and 593 false-positive regions. Of the 186 identified masses, 91 were detected on two views (48.9%) and 95 were detected only on one view (51.1%). Of the false-positive detections, 54 were paired on the ipsilateral view inside the corresponding matching strips and the remaining 485 were not, which represented 539 case-based false-positive detections (0.3 per image). Applying the multiview-based CAD scheme, the same case-based sensitivity was maintained while cueing 169 of 186 masses (90.9%) on both views and at the same time reducing the case-based false-positive detection rate by 23.7% (from 539 to 411). The study demonstrated that the new multiview-based CAD scheme could substantially increase the number of masses being cued on two ipsilateral views while reducing the case-based false-positive detection rate.

Algorithms↗
PubMed2006

Screening mammography: do women prefer a higher recall rate given the possibility of earlier detection of cancer?

PURPOSE: To prospectively survey women undergoing screening mammography to assess their attitudes toward and preference for the level of recall rates given the possibility that an increase in recall rates may result in earlier detection of cancer. MATERIALS AND METHODS: This HIPAA-compliant survey was performed with an institutional review board-approved protocol. Women who arrived for their routine screening mammographic examination from November 2004 to March 2005 were informed before they consented to participate. The distribution of responses for each survey question was summarized, and proportions for the entire group and different subgroups were computed. The z score statistic was used to assess significant differences between subgroups. RESULTS: Fifteen hundred seventy anonymized questionnaires were collected; 1171 (75%) were from women between 40 and 59 years of age. Of 1528 respondents, 1486 (97%) believed that a false-positive result would not deter them from continuing with regular screening, and most would have been willing to be recalled more often for either a noninvasive (86% [1308 of 1519 respondents]) or an invasive (82% [1248 of 1515 respondents]) procedure if it might increase the chance of detecting a cancer (if present) earlier. Compared with respondents undergoing their initial screening mammographic examination, women who had undergone at least one prior screening examination reported that they were more likely to continue with screening if they had received a previous false-positive result (P = .02). Women younger than 60 years and those previously recalled were more willing to be called back more often for a noninvasive or, when indicated, an invasive procedure (P < .05). CONCLUSION: A substantial fraction of women in this study would have preferred the inconvenience of and anxiety associated with a higher recall rate if it resulted in the possibility of detecting breast cancer earlier.

Adult↗
PubMed2006

CAD in screening mammography.

OBJECTIVE: The benefit and cost of computer-assisted detection (CAD) mammography screening remains a topic of great interest in breast imaging. Our purpose is to reflect on and interleave two articles in this issue of the AJR that highlight the difficulty in assessing the actual benefit of using CAD from either retrospective or prospective studies. CONCLUSION: This commentary describes the possible benefit and some of the issues associated with the clinical use of current CAD technology while emphasizing the expectation of and need for future improvements in CAD performance.

Breast Neoplasms↗
PubMed2005

A permutation test sensitive to differences in areas for comparing ROC curves from a paired design.

The area under the receiver operating characteristic (ROC) curve (AUC) is a widely accepted summary index of the overall performance of diagnostic procedures and the difference between AUCs is often used when comparing two diagnostic systems. We developed an exact non-parametric statistical procedure for comparing two ROC curves in paired design settings. The test which is based on all permutations of the subject specific rank ratings is formally a test for equality of ROC curves that is sensitive to the alternatives of AUC difference. The operating characteristics of the proposed test were evaluated using extensive simulations over a wide range of parameters. The proposed procedure can be easily implemented in experimental ROC data sets. For small samples and for underlying parameters that are common in experimental studies in diagnostic imaging the test possesses good operating characteristics and is more powerful than the conventional non-parametric procedure for AUC comparisons. We also derived an asymptotic version of the test which uses an exact estimate of the variance in the permutation space and provides a good approximation even when the sample sizes are small. This asymptotic procedure is a simple and precise approximation to the exact test and is useful for large sample sizes where the exact test may be computationally burdensome.

Biometry↗
PubMed2005

Electrical impedance scanning for the early detection of breast cancer in young women: preliminary results of a multicenter prospective clinical trial.

PURPOSE: To evaluate the feasibility and patient satisfaction with electrical impedance scanning (EIS) for early detection of breast cancer in young women. METHODS: Women undergoing screening clinical breast examination, imaging, or biopsy were eligible for EIS examination with T-Scan 2000ED (Mirabel Medical Systems, Austin, TX). Multiple logistic regression analysis evaluated the association between clinical variables and EIS performance. Patients completed a screening EIS satisfaction questionnaire (1 = least satisfied to 5 = most satisfied). RESULTS: Twenty-nine cancers were identified among 1,103 women. Sixty-six percent (19 of 29) of cancers were nonpalpable and 55% (16 of 29) were in women age < or = 50 years. EIS sensitivity and specificity in women younger than 40 years was 50% and 90%, respectively. Exogenous estrogen use (P < .001) and menopausal status (P = .007) correlated significantly with EIS performance. False-positive rates were increased in postmenopausal women and those taking exogenous hormones. No correlation was evident between EIS performance and family history, prior breast cancer, breast density, or palpability. EIS-positive women younger than age 40 were 4.5 times more likely to have breast carcinoma than were women randomly selected from the general population. Patients were highly satisfied with the comfort, speed, and reporting of EIS screening (mean score, 4.8). CONCLUSION: EIS seems promising for early detection of breast cancer, and identification of young women at increased risk for having the disease at time of screening. Positive EIS-associated breast cancer risk compares favorably with relative risks of conditions commonly used to justify early breast cancer screening. Patients are satisfied with a screening paradigm involving breast EIS.

Adult↗
PubMed2005

Trends in recall, biopsy, and positive biopsy rates for screening mammography in an academic practice.

PURPOSE: To retrospectively evaluate whether recall, biopsy, and positive biopsy rates for a group of radiologists who met requirements of Mammography Quality Standards Act of 1992 (MQSA) demonstrated any change over time during a 27-month period (nine consecutive calendar quarters). MATERIALS AND METHODS: Institutional review board approved study protocol, and informed consent was waived. All screening mammograms that had been interpreted by MQSA-qualified radiologists between January 1, 2001, and March 31, 2003, were reviewed. Group recall rates, biopsy rates, and detected cancer rates for nine calendar quarters were computed and attributed to performance date of original screening mammogram. Type of biopsy performed was classified as follows: stereotactic vacuum-assisted biopsy, ultrasonography (US)-guided core biopsy, US-guided fine-needle aspiration biopsy, surgical excision, and multiple biopsies. chi(2) Test for trend (two sided) and linear regression were used to assess trends over time for recall and biopsy rates, biopsy rates according to type of biopsy performed, and percentage of biopsy results positive for cancer. RESULTS: Group recall rate did not show a statistically significant trend during period studied (P = .59). Biopsy rates increased significantly from 13.02 to 20.12 per 1000 screening examinations (P < .001). A corresponding substantial decrease was seen in percentage of biopsies in which malignancy was found, although this trend was not statistically significant (P = .24). A significant increase (from 4.72 to 9.88 per 1000 screening examinations) was found in rate of stereotactic vacuum-assisted 11-gauge core biopsies performed (P < .001). CONCLUSION: Observed increase in biopsy rates reinforces the need to carefully select patients for biopsy to achieve efficient, efficacious, and cost-effective programs for early detection of breast cancers.

Biopsy↗