We cannot choose to ignore outcomes in the clinical assessment of diagnostic technologies.
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Decision Making↗
Biomedical subjects
C A Beam
Publications and source records attributed to C A Beam.
Analysis of clustered data in receiver operating characteristic studies.
Clustered data is not simply correlated data, but has its own unique aspects. In this paper, various methods for correlated receiver operating characteristic (ROC) curve data that have been extended specifically to clustered data are reviewed. For those methods that have not yet been extended, suggestions for their application to clustered ROC studies are provided. Various methods with respect to their ability to meet either of two objectives of the analysis of clustered ROC data are compared to consider a variety of ROC indices and their accessibility to researchers. The available statistical methods for clustered data vary in the range of indices that can be considered and in their accessibility to researchers. Parametric models permit all indices to be considered but, owing to computational complexity, are the least accessible of available methods. Nonparametric methods are much more accessible, but only permit estimation and inference about ROC curve area. The jackknife method is the most accessible and permits any index to be considered. Future development of methods for clustered ROC studies should consider the continuation ratio model, which will permit the application of widely available software for the analysis of mixed generalized linear models. Another area of development should be in the adoption of bootstrapping methods to clustered ROC data.
Bayes Theorem↗
Variability in the interpretation of screening mammograms by US radiologists. Findings from a national sample.
OBJECTIVE: To evaluate the effectiveness of screening mammography by estimating the variability in radiologists' ability to detect breast cancer within the US population of radiologists at mammography centers accredited by the American College of Radiology. METHODS: A two-way sample survey design was used as follows. Fifty mammography centers having an American College of Radiology-accredited unit were randomly sampled from across the United States. One hundred eight radiologists from these centers gave blinded interpretation to the same set of 79 randomly selected screening mammograms. The mammograms were from women who had been screened at a large screening center. Before their sampling, these women had been stratified by their breast disease status, established either by biopsy or by 2-year follow-up. Rates of biopsy recommendations were summarized by the mean, median, minimum, maximum, and range of sensitivity and specificity. Overall cancer detection ability was summarized by similar statistics for receiver operating characteristic curve areas. Ninety-five percent lower confidence bounds on the ranges in accuracy measures were established by boo-strapping. RESULTS: There is a range of at least 40% among US radiologists in their screening sensitivity. There is a range of at least 45% in the rates at which women without breast cancer are recommended for biopsy. As indicated by receiver operating characteristic curve areas, the ability of radiologists to detect cancer mammograms varies by as much as 11%. CONCLUSIONS: Our findings indicate that there is wide variability in the accuracy of mammogram interpretation in the population of US radiologists. Current accreditation programs that certify the technical quality of radiographic equipment and images but not the accuracy of the interpretation given to mammograms may not be sufficient to help mammography fully realize its potential to reduce breast cancer mortality.
Breast Diseases↗
Effect of human variability on independent double reading in screening mammography.
RATIONALE AND OBJECTIVES: To demonstrate the range of gains and losses that radiologists might experience from independent double reading in screening mammography. METHODS: From a national random sample of radiologists, the authors formed 131 pairs. For each radiologist, the authors analyzed the increase relative to his or her individual true-positive rate (TPR) or false-positive rate (FPR), number of additional cancers detected, and change to negative biopsy rate that would result from independent double reading after pairing. RESULTS: The average radiologist can expect an 8%-14% gain in TPR and a 4%-10% increase in FPR with pairing. For some radiologists, double reading increased the TPR with a small concomitant increase in FPR. Other radiologists, however, realized small gains in TPR with large increases in FPR. Adding the reading from a more experienced radiologist did not necessarily improve the TPR of a radiologist with less experience. CONCLUSION: Radiologists can form complementary and noncomplementary pairs for double reading. Use of this procedure must be decided on an individual basis.
Breast Neoplasms↗
Surrogates' predictions of seriously ill patients' resuscitation preferences.
BACKGROUND: Seriously or terminally ill patients are frequently incapacitated and unable to express their preferences regarding cardiopulmonary resuscitation (CPR). In this situation, family members or other surrogate decision makers are often asked whether they believe the patient would want to be resuscitated. We evaluated the concordance of patient CPR preferences and surrogate perceptions of the patient preferences in the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments (SUPPORT), a large, multicenter study of seriously ill hospitalized patients. METHODS: We compared patient preferences and surrogate perceptions in 1226 pairings in which both patient and surrogate responded to CPR decision questions. We also examined factors that might influence patient-surrogate concordance. RESULTS: Twenty-nine percent of patients with paired data did not want to be resuscitated; 26% of surrogates did not believe the patient they represented would want to be resuscitated. Within pairs, the overall exact agreement with respect to CPR decisions was 74%. For patients favoring CPR, only 16% of the surrogates misconstrued the patient's wishes. For patients who did not want to be resuscitated, however, 50% of the surrogates did not reflect the patient's wishes. If patients reported telling surrogates their CPR preference, concordance was significantly improved if the surrogate believed the patient did not want to be resuscitated and was significantly worsened if the surrogate believed the patient wanted CPR. This finding is likely an artifact of patients being more likely to report their preference to surrogates if that preference was not to be resuscitated. CONCLUSIONS: Surrogates' perceptions of patient CPR preferences are often inaccurate, particularly for those patients who do not want to be resuscitated. Methods to improve communication between patients and surrogates on CPR preferences should be developed and evaluated.
Adult↗
Random-effects models in the receiver operating characteristic curve-based assessment of the effectiveness of diagnostic imaging technology: concepts, approaches, and issues.
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Diagnostic Imaging↗
What are the issues in the double reading of mammograms?
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Female↗
Stratification in nonparametric ROC studies.
In many clinical experiments it is clear that external factors can affect the performance of diagnostic tests as these factors influence the distributions of separator variables. The authors investigate how stratification of cases and/or controls can be used in nonparametric received operating characteristic (ROC) studies, and develop statistical methods using stratification. The method can be used to simultaneously assess the ability of a diagnostic marker against several types of controls or cases. This allows a new method for the assessment of diagnostic tests.
Analysis of Variance↗
Magnetic resonance imaging of blood flow with a phase subtraction technique. In vitro and in vivo validation.
RATIONALE AND OBJECTIVES: One promising approach to flow quantification uses the velocity-dependent phase change of moving protons. A velocity-encoding phase subtraction technique was used to measure the velocity and flow rate of fluid flow in a phantom and blood flow in volunteers. METHODS: In a model, the authors measured constant flow velocities from 0.1 to 270.0 cm/second with an accuracy (95% confidence intervals) of +/- 12.5 cm/second. There was a linear relationship between the magnetic resonance imaging (MRI) measurement and the actual value (r2 = .99; P = .0001). RESULTS: Measuring mean pulsatile flow from 125 to 1,900 mL/minute, the accuracy of the MRI pulsatile flow measurements (95% confidence intervals) was +/- 70 mL/minute. There was a linear relationship between the MRI pulsatile flow measurement and the actual value (r2 = .99; P = .0001). In 10 normal volunteers, the authors tested the technique in vivo, quantitating flow rates in the pulmonary artery and the aorta. The average difference between the two measurements was 5%. In vivo carotid flow waveforms obtained with MRI agreed well with the shape of corresponding ultrasound Doppler waveforms. CONCLUSIONS: Velocity-encoding phase subtraction MRI bears potential clinical use for the evaluation of blood flow. Potential applications would be in the determination of arterial blood flow to parenchymal organs, the detection and quantification of intra- and extra-cardiac shunts, and the rapid determination of cardiac output and stroke volume.
Adult↗
1992 ARRS Executive Council Award. Detection of deep venous thrombosis: prospective comparison of MR imaging with contrast venography.
OBJECTIVE: Preliminary reports have described the use of MR imaging for the detection of deep venous thrombosis. However, no prospective study comparing MR imaging with contrast venography (the gold standard) has been reported. Accordingly, we performed a prospective, blinded study of the efficacy of MR imaging in 61 consecutive patients with clinically suspected deep venous thrombosis. In cases of disagreement, additional testing was performed to determine the diagnosis. SUBJECTS AND METHODS: From June 1991 to February 1992, 61 patients with clinically suspected deep venous thrombosis were examined with venography and MR imaging. The average time between studies was 3 hr. In 21 of the 61 patients, the final diagnosis was deep venous thrombosis. RESULTS: For detection of deep venous thrombosis in the pelvis, the sensitivity of MR imaging was 100% (9/9) with a 95% confidence interval of 72-100% and the specificity was 95% (52/55) with a 95% confidence interval of 85-99%. In the thigh, the sensitivity (16/16) and specificity (43/43) were both 100% with 95% confidence intervals of 83-100% and 93-100%, respectively. In the calf, the sensitivity was 87% (13/15) with a 95% confidence interval of 60-98% and the specificity was 97% (36/37) with a 95% confidence interval of 86-100%. CONCLUSION: We found no statistically significant difference between MR imaging and contrast venography in the detection of deep venous thrombosis. This result suggests that MR imaging is at least as sensitive and specific as contrast venography in the detection of deep venous thrombosis.
Female↗
Crypthecodinium and Tetrahymena: an exercise in comparative evolution.
Nucleotide sequences have been determined for the highly variable D2 region of the large rRNA molecule for over 60 strains of dinoflagellates. These strains were selected from a worldwide collection that represents all the known sibling species (compatibility groups, Mendelian species) in the sibling swarm referred to as Crypthecodinium cohnii. A phylogenetic tree has been constructed from an analysis of the variations in a length of about 180 bases, using PHYLOGEN string analysis programs. The Crypthecodinium tree is compared with the previously published but here augmented tree constructed upon the same rRNA region for the sibling species of a worldwide collection of ciliated protozoa related to the genus Tetrahymena. The first reported sequence of Lambornella clarki, the parasite of tree-hole mosquitoes, is included. The dinoflagellate species complex is much more homogeneous with respect to ribosomal variation. The mean number of differences among sequences from different Crypthecodinium species is about 7, in comparison with 22 differences among the ciliate species examined. Moreover, all the diversity in the dinoflagellates can be explained by base substitutions, whereas insertions and deletions are common in the ciliates. The dinoflagellates are also much more uniform with respect to nutritional and genetic economies. The two complexes differ also in the relationship between molecular variations and breeding compatibility. All tetrahymenine sibling species thus far examined are monomorphic in the D2 region, but several dinoflagellate species are polymorphic. Several different dinoflagellate species, moreover, have identical D2 regions. This kind of ribosomal identity of incompatible strains is found in these ciliates only in one tight cluster of species--Group C. The tetrahymenine swarm is apparently much older than the Crypthecodinium swarm, and the dinoflagellate species produce incompatible progeny species much more readily than do the ciliates, perhaps by the acquisition of mutations that potentiate incompatibility in sympatric populations.
Animals↗
Aortoiliac angioplasty: is there a need for other types of percutaneous intervention?
In a retrospective study, the authors compared results in 81 patients who underwent 117 percutaneous transluminal angioplasty (PTA) procedures in the iliac arteries and 21 patients who underwent iliac artery atherectomy. Both groups were similar with respect to symptoms and risk factors. The overall technical success rates were 97.4% for PTA and 100% for atherectomy. The initial clinical success was 92.8% for PTA and 100% for atherectomy. Complications requiring surgery occurred in four of 117 (3.4%) PTA and one of 21 (4.8%) atherectomy procedures. The 2-year patency rate for PTA was similar to that achieved with atherectomy in a smaller patient population. These results indicate that atherectomy does not offer any definite advantage over conventional PTA for the routine management of iliac lesions and make it difficult to justify the additional expense and complexity of this technique.
Angioplasty, Balloon↗
Threshold perception performance with computed and screen-film radiography: implications for chest radiography.
Images of a phantom obtained with computed radiography and standard screen-film imaging were compared to evaluate observer threshold perception performance with a modified contrast-detail technique. Optimum exposure necessary for performance with the imaging plate technique to match that with screen-film techniques was determined, as was comparative performance with variation in kilovoltages, plate type, spatial enhancement, and hard-copy interpolation method. It was found that computed radiography necessitates about 75%-100% more exposure than screen-film radiography to optimally match performance with Ortho-C film with Lanex regular or medium screens (Eastman Kodak, Rochester, NY) for detection of objects 0.05-2.0 cm in diameter. However, only minimal loss of detection performance (approximately 10% overall) was experienced if standard screen-film exposures were used with computed radiography. Little change in observer performance was found with variation in plate type, spatial enhancement, or method of hard-copy interpolation. However, perception performance with computed radiographic images was better at lower kilovoltages.
Humans↗
Gastrointestinal bleeding: treatment with gastrointestinal arterial embolization.
Retrospective analysis of 36 embolization procedures in 29 patients with gastrointestinal bleeding was undertaken, and the presence or absence of coagulopathy was identified as a major factor affecting embolization outcome. Embolization was successful in 18 of 29 (62%) patients and unsuccessful in 11 (38%). Eight of 11 failures (73%) occurred in patients with a coagulopathy, whereas three patients (27%) in whom embolization was successful also had a coagulopathy. Embolization was 2.9 times more likely to be unsuccessful (P = .0463) and death from bleeding after embolization was 9.6 times more likely to occur (P = .0065) in patients with a coagulopathy than in those without. Because embolization was successful in six of 14 (43%) coagulopathy patients, the authors advocate embolization in patients with gastrointestinal bleeding and coagulopathy, while all efforts to correct the coagulopathy would be made as early as possible.
Adolescent↗
Answering unanswered questions: proposal for a shared resource in clinical diagnostic radiology research.
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Humans↗
Strategies for improving power in diagnostic radiology research.
Research studies in diagnostic radiology often compare the diagnostic abilities of two imaging techniques. The "power" of such studies is the probability that they will detect a difference in abilities of a certain amount when, indeed, such a difference does exist. This article outlines several strategies that can be used to assess and improve the power of radiologic diagnostic studies. These strategies include selection of cases and controls, matching, use of one-tailed tests, selection of significance level, and choice of sample size.
Diagnostic Imaging↗
Evaluation of acute renal failure with magnetic resonance imaging using gradient-echo and Gd-DTPA.
Detection of acute renal failure (ARF) using fast-scan magnetic resonance imaging (MRI) with Gd-DTPA was studied in a dog model. ARF was produced in five dogs by infusion of norepinephrine (0.75 micrograms/kg/min) into the renal arteries for 40 minutes. MRI was performed 1 hour later and compared with baseline (pre-ARF) MRI. There was no significant difference in the ratios of signal intensity-vs.-time curves from 0 to 35 seconds after injection of Gd-DTPA. However, a difference between the outer and inner medulla was significant in the time period of 5 to 20 minutes after Gd-DTPA injection. These later signal intensity differences by fast-scan (gradient-echo) technique may be useful in the evaluation of ARF.
Acute Kidney Injury↗
Extravascular toxicity of two magnetic resonance contrast agents. Preliminary experience in the rat.
We compared the relative toxicities of standard concentrations of two magnetic resonance imaging (MRI) contrast agents, ionic gadolinium diethylenetriaminepentacetic acid (DTPA) and low-osmolar gadolinium-1, 4, 7 tris (carboxymethyl)-10-(2'-hydroxypropyl)-1, 4, 7, 10 tetra-azacyclododecane (HP-DO3A) with that of the conventional radiographic contrast medium meglumine diatrizoate, when extravasated into the deep dermal tissues of laboratory rats. Gadolinium-DTPA caused moderate necrosis, hemorrhage, and edema which was not statistically different than meglumine diatrizoate. In contrast, gadolinium HP-DO3A was significantly less toxic than meglumine diatrizoate. Additional experience will be needed in order to determine whether these laboratory results will be clinically relevant in humans.
Animals↗