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Biomedical subjects

N A Obuchowski

Publications and source records attributed to N A Obuchowski.

At least 19 recordsLinked to original sources
PubMed1998

Postoperative portable chest radiographs: optimum use in thoracic surgery.

PURPOSE: Daily portable chest radiographs are routinely ordered in many institutions after thoracic surgery. Our purpose was to assess the efficacy and cost of this practice and to determine the optimum use of postoperative x-ray studies. METHODS: A prospective review of all portable chest x-ray films after 100 consecutive elective thoracotomies (DRG 75) was conducted. Each x-ray study initiated a three-part survey. First, the surgeon listed whether the x-ray study was routine and the anticipated management had it not been available. The radiologist then interpreted and scored the x-ray study as follows: negative, expected findings; A, minor findings necessitating no intervention; B, minor findings necessitating intervention; or C, major findings necessitating intervention. Finally, the x-ray film and the interpretation were returned to the surgeon. Any interventions necessitated by the x-ray study were recorded. RESULTS: In 6 months, 99 patients underwent 82 pulmonary resections and 18 other major procedures. In the postoperative period, 769 portable chest x-ray studies were ordered, median five per patient (range 2 to 49). Of these, 731 (95%) were routine and 38 (5%), nonroutine. Severity scores were as follows: negative in 106 (13.8%), A in 558 (72.5%), B in 59 (7.7%), and C in 46 (6.0%). X-ray findings altered management in 43 of 769 studies (5.6%): in 33 routine (4.5%), in 10 nonroutine (26.3%), in 13 A (2.3%), in 22 B (37.3%), and in 8 C (17.4%). CONCLUSIONS: These results demonstrate that routine daily portable chest x-ray studies have a minimal impact on management. It is, in fact, nonroutine x-ray studies that more often alter management. Had routine portable chest x-ray studies, which cost $114 each in our institution, been limited to one immediately after the operation, only 133 such studies (100 routine and 33 nonroutine) would have been needed in the care of these patients. Elimination of 636 (82.7%) x-ray studies reduces the cost of care by $725 per patient ($286,000 annually). For major thoracic procedures, it is safe, efficacious, and cost effective to eliminate routine postoperative portable chest x-ray studies and order nonroutine portable studies only when clinically indicated.

Adult↗
PubMed1998

Right ventricular arrhythmia in the absence of arrhythmogenic dysplasia: MR imaging of myocardial abnormalities.

PURPOSE: To evaluate right ventricular abnormalities with magnetic resonance (MR) imaging in patients with arrhythmia but without arrhythmogenic dysplasia. MATERIALS AND METHODS: In 53 patients being evaluated for right ventricular arrhythmia and 15 control subjects, MR imaging was performed to evaluate fixed thinning, fatty replacement, or reduced systolic wall thickening or motion. A diagnosis of idiopathic right ventricular outflow tract tachycardia or indeterminate was assigned for each patient, and the severity of arrhythmia was categorized. RESULTS: Right ventricular abnormalities were revealed in 32 (60%) of the 53 patients: fixed thinning in 27 (84%), fatty replacement in eight (25%), and reduced wall thickening or motion in 31 (97%). Right ventricular abnormalities were found in 35 (76%) of 46 patients with idiopathic right ventricular outflow tract tachycardia and in seven (39%) of 18 patients with indeterminate diagnoses (P = .022). CONCLUSION: Mild right ventricular abnormalities are likely sources for arrhythmias, even in the absence of arrhythmogenic right ventricular dysplasia.

Adolescent↗
PubMed1997

Sample size determination for diagnostic accuracy studies involving binormal ROC curve indices.

Receiver operating characteristic (ROC) curves and their associated indices are valuable tools for the assessment of the accuracy of diagnostic tests. The area under the ROC curve is a popular summary measure of the accuracy of a test. The full area under the ROC curve, however, has been criticized because it gives equal weight to all false positive error rates. Alternative indices include the area under the ROC curve in a particular range of false positive rates ('partial' area) and the sensitivity of the test for a single fixed false positive rate (FPR). We present a unified approach for computing sample size for binormal ROC curves and their indices. Our method uses Taylor series expansions to derive approximate large-sample estimates of the variance and covariance of binormal ROC curve parameters. Several examples from diagnostic radiology illustrate the proposed method.

Diagnostic Tests, Routine↗
PubMed1997

Preliminary experience with double-phase SPECT using Tc-99m sestamibi in patients with hyperparathyroidism.

BACKGROUND: There is a continual search for a better imaging modality for parathyroid pathology. In recent years, Tc-99m sestamibi has been proposed as an alternative to T1-201 for parathyroid scintigraphy. The purpose of this study is to assess the usefulness of a double-phase Tc-99m sestamibi SPECT technique for parathyroid imaging. METHODS: Sixty-one consecutive patients with hyperparathyroidism were studied. Sixteen had previously undergone unsuccessful surgery for hyperparathyroidism. SPECT imaging of the neck and chest was performed at 15 minutes and again at 2 hours after 20-25 mCi of Tc-99m sestamibi was given intravenously. A positive scan was defined as a region of increased focal uptake that persisted on the delayed images. RESULTS: When compared with surgical findings, double-phase sestamibi SPECT correctly identified 55% (26/ 47) of the parathyroid adenomas in the previously unoperated group, and 91% (10/11) of the parathyroid adenomas in the reoperative group. Double-phase sestamibi SPECT was negative in 92% (109/118) of the normal parathyroid glands in the previously unoperated group, and in 88% (15/17) in the reoperative group. CONCLUSIONS: These preliminary data suggest that double-phase Tc-99m sestamibi SPECT is a promising procedure for the preoperative detection and localization of hyperfunctioning parathyroid tissue, especially in patients with recurrent or persistent postoperative hyperparathyroidism.

Adenoma↗
PubMed1997

Common carotid artery: variability of Doppler US velocity measurements.

PURPOSE: To determine if Doppler ultrasound (US) measurements of systolic velocity in the common carotid artery vary markedly with distance from the bifurcation. MATERIALS AND METHODS: Bilateral, insonation angle-corrected velocity was measured with US in the common carotid artery. Measurements were obtained 1, 2, 3, 4, and 5 cm from the carotid artery bifurcation in 20 volunteers (aged 25-43 years) with no history of neurologic or cardiovascular disease. RESULTS: Velocity in the common carotid artery increased with distance (toward the aorta) from the bifurcation (mean increase, 9 cm/sec for each centimeter of distance from the bifurcation, up to the 4-cm distance; P < .001). Velocity increased more rapidly in subjects who were younger (P < .001) and in those with a lower pulse rate (P = .001). CONCLUSION: The distance from the bifurcation at which common carotid artery velocity is measured should be standardized. This may increase the accuracy of the systolic velocity ratio for assessment of internal carotid artery stenosis and decrease some of the reported variability between different centers that perform US of the carotid artery.

Adult↗
PubMed1997

Assessment of the efficacy of noninvasive screening for patients with asymptomatic neck bruits.

BACKGROUND AND PURPOSE: Several recent clinical trials have shown that endarterectomy is efficacious in patients with asymptomatic carotid artery stenosis. The purpose of this study was to evaluate the effectiveness of various test strategies for screening and diagnosing carotid artery disease. METHODS: We constructed a model of the natural history of carotid artery disease using literature-based estimates of the prevalence and incidence of carotid artery stenosis and associated morbidity and mortality. Markov cohort simulation was used to estimate the mean quality-adjusted life years and monetary costs associated with various management strategies. RESULTS: Screening is cost-effective in the baseline model. Key parameters affecting the efficacy of screening are prevalence of operable lesions, benefit of surgery, surgical complication rates, quality of life with stroke, rate of stenosis progression, and excess morbidity and mortality. CONCLUSIONS: Asymptomatic patients with carotid bruits may benefit from screening if the prevalence rate is > or = 20%, the benefits and risks associated with surgery are similar to those observed in the Asymptomatic Carotid Atherosclerosis Study, and the quality of life with stroke is considerably lower than the quality of life without stroke. Ultrasound followed by three-dimensional time-of-flight MR angiography, if indicated, is a promising test strategy.

Carotid Stenosis↗
PubMed1997

Comparison of double-phase 99mTc-sestamibi with 123I-99mTc-sestamibi subtraction SPECT in hyperparathyroidism.

OBJECTIVE: Our purpose was to compare double-phase 99mTc-sestamibi single-photon emission computed tomography (SPECT) and simultaneous 123I-99mTc-sestamibi subtraction SPECT for preoperative localization of hyperfunctioning parathyroid tissue in patients with primary hyperparathyroidism. SUBJECTS AND METHODS: Fifteen patients with primary hyperparathyroidism underwent preoperative double-phase 99mTc-sestamibi SPECT and simultaneous 123I-99mTc-sestamibi subtraction SPECT imaging. At surgery, the location, weight, and histopathologic evaluation of all identified parathyroid glands were recorded. RESULTS: At surgery, 17 parathyroid adenomas and 37 normal parathyroid glands were identified. The sensitivity, specificity, and diagnostic accuracy for the detection of parathyroid adenomas were 88%, 97%, and 94%, respectively, for simultaneous 123I-99mTc-sestamibi subtraction SPECT and 53%, 86%, and 76%, respectively, for double-phase 99mTc-sestamibi SPECT. The differences in sensitivity and diagnostic accuracy were statistically significant (p = .031 and p = .016, respectively). CONCLUSION: Compared with double-phase 99mTc-sestamibi SPECT, simultaneous 123I-99mTc-sestamibi subtraction SPECT is a superior imaging study for the preoperative localization of hyperfunctioning parathyroid tissue.

Adenoma↗
PubMed1997

Nonparametric analysis of clustered ROC curve data.

Current methods for estimating the accuracy of diagnostic tests require independence of the test results in the sample. However, cases in which there are multiple test results from the same patient are quite common. In such cases, estimation and inference of the accuracy of diagnostic tests must account for intracluster correlation. In the present paper, the structural components method of DeLong, DeLong, and Clarke-Pearson (1988, Biometrics 44, 837-844) is extended to the estimation of the Receiver Operating Characteristics (ROC) curve area for clustered data, incorporating the concepts of design effect and effective sample size used by Rao and Scott (1992, Biometrics 48, 577-585) for clustered binary data. Results of a Monte Carlo simulation study indicate that the size of statistical tests that assume independence is inflated in the presence of intracluster correlation. The proposed method, on the other hand, appropriately handles a wide variety of intracluster correlations, e.g., correlations between true disease statuses and between test results. In addition, the method can be applied to both continuous and ordinal test results. A strategy for estimating sample size requirements for future studies using clustered data is discussed.

Angiography, Digital Subtraction↗
PubMed1997

Segmented three-dimensional echo-planar flow imaging of the cervical carotid arteries.

PURPOSE: To implement and assess the application of segmented three-dimensional echo-planar MR imaging time-of-flight flow sequences for studying the anatomy of the cervical carotid arteries at 1.5 T. METHODS: The 3-D echo-planar sequences were segmented along the in-plane phase-encoding direction. Echo train lengths (ETLs) of 3 and 5 and signal bandwidths of +/-25, +/-33, and +/-50 KHz were tested along with a conventional (ETL = 1) 3-D MR flow study in six healthy volunteers and in five patients with known arteriosclerotic disease involving the carotid bifurcation as confirmed by conventional angiography. The volunteer data were used to rank the techniques with respect to vessel dimension, vessel/background contrast, and quality by four trained neuroradiologists. For the patient studies, the percentage of stenoses was measured for all MR studies and compared against the conventional angiographic data using the criteria of the North American Symptomatic Carotid Endarterectomy Trial. RESULTS: Using Wilcoxon's test statistic and a significance level of .05, we found that the conventional MR flow examination was better than the segmented techniques and that the segmented techniques with ETL of 3 were superior to their counterparts with ETL of 5. For the ETL of 3 techniques, the high-bandwidth studies were inferior to their lower bandwidth counterparts; however, there was no significant difference between the performance of the medium- and low-bandwidth sequences. The patient data revealed that the segmented techniques consistently overestimated the severity of stenosis; however, in no instance did any of the segmented examinations erroneously indicate the presence of disease. CONCLUSIONS: The reduction in acquisition time and the zero false-positive rate we obtained suggest that segmented 3-D echo-planar MR flow techniques may be used as a screening/locating study for cervical carotid artery disease.

Adult↗
PubMed1996

Quantitative detection of outlet strut separations in Björk-Shiley convexo-concave mitral valves.

BACKGROUND: As of January 31, 1995, 564 outlet strut fractures (OSFs) of Björk-Shiley convexo-concave (BSCC) heart valves had been reported to the Shiley Heart Valve Research Center, of which approximately two thirds resulted in the death of the patient. Previous studies indicate that one leg of the outlet strut separates (single-leg separation, SLS) from the valve before the second leg breaks, which results in complete OSF. To identify those valves at risk of complete OSF, an in vivo radiographic imaging technique is being developed to evaluate the strut leg integrity. The goal of the present study was to develop an objective postprocessing technique to evaluate outlet strut leg integrity quantitatively in these cineradiographic images. METHODS AND RESULTS: Twenty-two sets (12 intact valves, 10 SLS valves) of cineangiographic images were obtained from individuals whose valve status was subsequently verified ex vivo. Several quantitative measures of SLS were evaluated to identify possible loss of metal or gaps in the SLS legs. Two of these measures, decrease in pixel intensity (DIPI) ratio and gap half-width, are diagnostic metrics of SLS: i.e., the maximum likelihood estimate of the area under the receiver operating characteristic curve was 0.892 (SD, 0.066) for a model based on DIPI ratio and 0.802 (SD, 0.093) for gap half-width. CONCLUSIONS: We have developed a postprocessing technique that can be used to objectively evaluate outlet strut integrity in cineradiographic images of BSCC heart valves. At an estimated specificity of 1.0, the estimated sensitivity of the objective review was comparable to that of a subjective expert review panel.

Analysis of Variance↗
PubMed1996

Intraoperative evaluation of renal cell carcinoma: a prospective study of the role of ultrasonography and histopathological frozen sections.

PURPOSE: Nephron sparing surgery is being performed increasingly for treatment of renal cell carcinoma, including in select patients with a normal contralateral kidney. The number of tumors in the involved kidney (single versus multiple) and presence or absence of perinephric fat involvement (pathological stage T1 to 2 versus T3A) are important prognostic factors. In a prospective study we evaluated the accuracy of intraoperative histopathological frozen section analysis of renal capsular biopsies for assessing local tumor stage, and the accuracy of intraoperative ultrasonography for assessing tumor focality. MATERIALS AND METHODS: Intraoperative frozen section biopsies and ultrasonography were compared with information obtained from preoperative computerized tomography (CT), intraoperative inspection of the kidney by the surgeon and permanent histopathological specimens. RESULTS: We evaluated 99 patients (102 kidneys) with localized sold renal masses undergoing either radical nephrectomy (48) or nephron sparing surgery (54). Final pathological analysis revealed 95 renal cell carcinomas (stage T3A in 24), 6 oncocytomas and 1 angiomyolipoma. Multiple tumors were detected in 18 of 102 kidneys overall. Frozen section analysis identified 87% of the stage T3A lesions with no false-positive results, compared to CT, which only identified 67%. Ultrasonography identified 14 of 18 multifocal tumors (78%) and was not more accurate than the combination of CT and intraoperative inspection. However, during nephron sparing surgery ultrasonography was useful to localize the intrarenal extent of tumors (17 cases). CONCLUSIONS: Our results clarify the role of intraoperative ultrasonography and frozen section analysis in patients undergoing nephron sparing surgery for renal cell carcinoma. Frozen section analysis may be useful in select patients with small peripheral tumors who are under consideration for elective nephron sparing surgery.

Carcinoma, Renal Cell↗
PubMed1996

Quantitative classification of breast tumors in digitized mammograms.

The goal of this study was to develop a technique to distinguish benign and malignant breast lesions in secondarily digitized mammograms. A set of 51 mammograms (two views/patient) containing lesions of known pathology were evaluated using six different morphological descriptors: circularity, mu R/sigma R (where mu R = mean radial distance of tumor boundary, sigma R = standard deviation); compactness, P2/A (where P = perimeter length of tumor boundary and A = area of the tumor); normalized moment classifier; fractal dimension; and a tumor boundary roughness (TBR) measurement (the number of angles in the tumor boundary with more than one boundary point divided by the total number of angles in the boundary). The lesion was segmented from the surrounding background using an adaptive region growing technique. Ninety-seven percent of the lesions were segmented using this approach. An ROC analysis was performed for each parameter and the results of this analysis were compared to each other and to those obtained from a subjective review by two board-certified radiologists who specialize in mammography. The results of the analysis indicate that all six parameters are diagnostic for malignancy with areas under their ROC curves ranging from 0.759 to 0.928. We observed a trend towards increased specificity at low false-negative rates (0.01 and 0.001) with the TBR measurement. Additionally, the diagnostic accuracy of a classification model based on this parameter was similar to that of the subjective reviewers.

Breast Diseases↗
PubMed1996

Acromial morphology: relation to sex, age, symmetry, and subacromial enthesophytes.

PURPOSE: To evaluate acromial shape in relation to age, sex, symmetry, and presence of subacromial enthesophytes. MATERIALS AND METHODS: Three hundred ninety-four cadaveric scapulas were reviewed. Specimens were categorized by sex and age (age range, 20-89 years). Acromial morphology was typed according to the Bigliani classification: type I, flat; type II, curved; and type III, hooked. The presence and degree of subacromial enthesopathy was recorded. Selective radiographic correlation was obtained. RESULTS: The relative percentages of acromial types I, II, and III were 22.8% (90 acromions), 68.5% (270 acromions), and 8.6% (34 acromions), respectively. There was a greater percentage of type III in men (10.2% [21 of 205] vs 6.9% [13 of 189] and type I in women (27.5% [52 of 189] vs 18.5% [38 of 205]). There was no relationship between acromial type and age (P = .667). Enthesophytes were most common in type III (20 [59%] of 34 acromions) versus type II (115 [42.6%] of 270 acromions) and type I (22 [24%] of 90 acromions). Acromial morphology was symmetric in 135 (70.7%) of 191 pairs of acromions and asymmetric in 56 pairs (29.3%). CONCLUSION: Acromial shape does not vary significantly with age. It does, however, differ between sexes. The relative percentages of the types differ from previously reported values. Acromial shape tends to be symmetric. A trend between acromial type and the presence of enthesophytes is observed.

Acromion↗
PubMed1996

Simple steps for improving multiple-reader studies in radiology.

Multiple-reader study designs have become popular in the radiology literature. We reviewed the major papers published in the American Journal of Roentgenology in the first 4 months of each of the years 1990 and 1995. The review was restricted to prospective studies of image interpretation. In the 1990 literature, we noted eight multiple-reader and 18 single-reader studies; in contrast, in the 1995 literature, we found 29 multiple-reader and eight single-reader studies. This trend reflects an increased awareness of the importance of multiple-reader studies. We examined the Results sections of the 29 multiple-reader studies from 1995 to assess the authors' motives for incorporating such a design. In 16 studies (55%), readers independently interpreted all images. However, the authors usually reported only the average interpretation of the readers; in only seven of the 29 studies (24%) did the authors describe differences among readers' interpretations. In 13 studies, interpretations were performed exclusively through "consensus reading." The method(s) used to achieve a consensus often were not explained. Only two of the 29 studies had more than three readers. In contrast, all of these studies included multiple patients. The average patient sample size was 45. Furthermore, differences observed among patients were routinely reported and/or depicted.

Bibliometrics↗
PubMed1996

Left ventricular outflow tract obstruction in hypertrophic cardiomyopathy: presurgical and postsurgical evaluation by computed tomography magnetic resonance imaging.

Along with hypertrophy of the left ventricle (LV), hypertrophic cardiomyopathy (HC) is characterized by LV outflow tract (LVOT) obstruction, partly from systolic anterior motion (SAM) of the anterior mitral leaflet; if obstruction is significant, excision of excess subaortic septal myocardium may be indicated. In this study, the ability of computed tomography magnetic resonance imaging (Cine MRI) to provide information about LVOT obstruction was assessed in a series of 37 HC cases undergoing evaluation, including echocardiography (0 to 14 days before), for possible septal myectomy; in 4 cases, Cine MRI was used postsurgically (5 to 25 months after). Blinded to echocardiography results, 3 reviewers analyzed by consensus the Cine-MRI LVOT-long-axis image-loops for SAM grade (none, mild, severe) and "aorta:LVOT signal ratio" (intensity in descending aorta/intensity in LVOT at maximum systolic-flow disturbance). Resting LVOT flow velocities were separately determined using Doppler analysis, permitting differentiation between insignificant (< 30 mm Hg) and significant (< or = 30 mm Hg) gradients. With echocardiography, significant resting obstruction was found in 62% of cases, including 92% treated surgically. A significant association between SAM grade and obstruction was found; all cases with a SAM grade of none had insignificant ([-] predictive value: 100%) and most with a severe grade had significant ([+] predictive value: 78%) obstruction. Signal ratio in the absence of a significant gradient was significantly lower than in its presence; a significant linear relationship between aorta:LVOT signal ratio and resting gradient was found: LVOT gradient = ([2.9] x [signal ratio]) + 22.8. SAM grade did not contribute significantly in obstruction categorization when signal ratio was known. In all cases studied after surgery, SAM grade had decreased from severe to insignificant levels and aorta:LVOT signal ratio had been significantly reduced. Insights into the dynamic nature of the LVOT in HC patients can be provided by Cine MRI, either during their evaluation for surgery or after their septal myectomy.

Cardiomyopathy, Hypertrophic↗
PubMed1996

Comparison of FDG-PET and sestamibi-SPECT in primary hyperparathyroidism.

UNLABELLED: Preoperative localization of hyperfunctioning parathyroid tissue in patients with primary hyperparathyroidism has been a longstanding diagnostic challenge. This study directly compared FDG-PET and sestamibi-SPECT for preoperative detection of abnormal parathyroid tissue. METHODS: Twenty-one consecutive patients with primary hyperparathyroidism were studied prospectively before surgical neck exploration. SPECT of the neck and chest was performed at 15 min and 2 hr after intravenous 99mTc-sestamibi. Regional body PET was performed 45 min after intravenous FDG. RESULTS: Surgery revealed 19 solitary parathyroid adenomas, 2 parathyroid adenomas in one patient; and 3 hyperplastic parathyroid glands in one patient, and 51 normal parathyroid glands. The diagnostic sensitivities for detection of parathyroid adenomas of 43% (9 of 21) for dual-phase sestamibi-SPECT and 86% (18 of 21) for FDG-PET were significantly different (p < 0.001). The difference in diagnostic specificities of 78% (40 of 51) for FDG-PET and 90% (46 of 51) for dual-phase sestamibi-SPECT approached statistical significance (p = 0.063). CONCLUSION: This study demonstrates that FDG-PET is more sensitive than sestamibi-SPECT in the preoperative localization of parathyroid adenomas in patients with primary hyperparathyroidism.

Adenoma↗
PubMed1995

Multireader receiver operating characteristic studies: a comparison of study designs.

RATIONALE AND OBJECTIVES: Traditionally, multireader receiver operating characteristic (ROC) studies have used a "paired-case, paired-reader" design. The statistical power of such a design for inferences about the relative accuracies of the tests was assessed and compared with alternative designs. METHODS: The noncentrality parameter of an F statistic was used to compute power as a function of the reader and patient sample sizes and the variability and correlation between readings. RESULTS: For a fixed-power and Type I error rate, the traditional design reduces the number of verified cases required. A hybrid design, in which each reader interprets a different sample of patients, reduces the number of readers, total readings, and reading required per reader. The drawback is a substantial increase in the number of verified cases. CONCLUSION: The ultimate choice of study design depends on the nature of the tests being compared, limiting resources, a priori knowledge of the magnitude of the correlations and variability and logistic complexity.

Analysis of Variance↗