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PubMed1993

How do we collect data for surveillance of wound infection?

The surveillance of surgical wound infection (SWI) may be undertaken for a number of purposes which include evaluating changes in practice, studying the epidemiology of SWI and for assessing the quality of health care. Purchasers require this information from providers as an indicator of the quality of care. Surveillance of SWI can also have a role in audit, by setting standards and comparing observed practice with agreed standards. The level of SWI can be the standard, and the collection, analysis and interpretation of data (undertaken during surveillance) could be the means for measuring the standard. In a surveillance programme, data collection is often the most time consuming and difficult element and requires considerable planning. Initially, the data to be collected should be defined. This will be influenced by the purposes of surveillance, the ways the events (SWI) are defined, the data required to produce meaningful analyses and criteria used for identifying the patient. After the data has been defined, data collection methods should be chosen. The importance of assessing the accuracy and limitations of data collection methods in local settings is stressed. Only then is it possible to be sure that the data is a reliable basis on which to base decisions which promote the quality of health care.

Data Collection↗
PubMed1999

The epidemiology of Type 2 diabetes and its current measurement.

Type 2 diabetes is globally increasing in prevalence and is widely recognized as a major cause of morbidity and mortality, as well as being a burden to the health-care services. Planning for current and future diabetes services requires up-to-date prevalence information. The enumeration of Type 2 diabetes is, however, surprisingly difficult. Large numbers of people are undiagnosed, and those known cases have variable loci of care. Traditional techniques include cross-sectional diagnostic surveys, postal or house-to-house surveys and cohort surveys. All are time-consuming and expensive, and may potentially undercount. The use of multiple patient lists (e.g. hospital clinic data, general practitioner (GP) lists, prescribing information, etc.) can, however, increase accuracy and, if the data are computerized, may be rapid and inexpensive. A new and potentially exciting tool to utilize multiple lists in Type 2 diabetes prevalence assessment is known as 'capture-recapture'. In this, statistical models are used to estimate prevalence from the degree of overlap between lists. Capture-recapture is emerging as a valuable tool in the epidemiological assessment of Type 2 diabetes.

Animals↗
PubMed2004

Dosimetric uncertainties of three-dimensional dose reconstruction from two-dimensional data in a multi-institutional study.

Inconsistencies in the treatment planning process leading to dosimetric uncertainties may affect conclusions drawn from interinstitutional radiation oncology clinical trials. The purpose of this study was to assess the dosimetric uncertainties resulting from the process of reconstructing three-dimensional dose distributions from two-dimensional treatment plan information provided by participating institutions in a randomized clinical trial. This study was based on American College of Radiology Protocol #427, Locally Advanced Multi-Modality Protocol; a multi-institutional phase II randomized study involving radiation therapy for patients with inoperable non-small cell lung cancer. Several sources of dosimetric uncertainty were identified and analyzed, including image quality of hard-copy computed tomography (CT) images, slice spacing of CT scans, treatment position, interpretations of target volumes by radiation oncologists, the contouring of normal anatomic structures, and the use of common beam models for all dose calculations. Each source of uncertainty was investigated using a set of plans, with the ideal characteristics of digital images with 3-mm axial slice spacing and a flat couch, consisting of eight cases from Vanderbilt University Medical Center with electronically transferred CT data. The target volume DVH values were dependent on the additional uncertainty introduced by differences in delineation of the target volumes by the participating radiation oncologists. The DVH values for the lungs and heart were dependent on image quality and treatment position. Esophagus DVH values were not dependent on any of the sources of uncertainty. None of the structure DVH values were dependent on slice thickness or variations in the contouring of normal anatomic structures. Reconstruction of three-dimensional dose distributions from two-dimensional treatment plan information may be useful in cases for which digital CT data is not available or for historical data review. However, dosimetric accuracy will depend on image quality of the treatment planning CT data and consistency in the delineation of tumor volumes.

Body Burden↗
PubMed1989

Feasibility of studying subfertility using retrospective self reports.

During an investigation of possible reproductive effects of environmental agents, 261 male and 155 female workers were interviewed concerning subfertility at some time in the past: the time taken to conceive, for all births; and the occurrence of one or more fertile phases lasting for 6 months or more. When these two variables were compared, the quality of reporting was acceptable in 89.7% of instances, and data editing enabled accuracy to be improved. Reporting was more reliable with shorter duration of recall, and female workers' reports were somewhat more reliable than those of male workers. The distribution of time taken to conceive was similar for male workers to that observed in previously published prospective series, though with a higher estimate of subfertility when infertile phases were also considered. Comparison with published estimates of reduced fertility appeared to be reassuring. As predicted, the equivalent comparisons for female workers showed the presence of a strong selection effect.

Data Collection↗
PubMed1996

Algorithms for verbal autopsies: a validation study in Kenyan children.

The verbal autopsy (VA) questionnaire is a widely used method for collecting information on cause-specific mortality where the medical certification of deaths in childhood is incomplete. This paper discusses review by physicians and expert algorithms as approaches to ascribing cause of deaths from the VA questionnaire and proposes an alternative, data-derived approach. In this validation study, the relatives of 295 children who had died in hospital were interviewed using a VA questionnaire. The children were assigned causes of death using data-derived algorithms obtained under logistic regression and using expert algorithms. For most causes of death, the data-derived algorithms and expert algorithms yielded similar levels of diagnostic accuracy. However, a data-derived algorithm for malaria gave a sensitivity of 71% (95% Cl: 58-84%), which was significantly higher than the sensitivity of 47% obtained under an expert algorithm. The need for exploring this and other ways in which the VA technique can be improved are discussed. The implications of less-than-perfect sensitivity and specificity are explored using numerical examples. Misclassification bias should be taken into consideration when planning and evaluating epidemiological studies.

Algorithms↗
PubMed2005

por Variable-region typing by DNA probe hybridization is broadly applicable to epidemiologic studies of Neisseria gonorrhoeae.

The porin gene (porB) of Neisseria gonorrhoeae encodes the major outer membrane protein identified as PI or Por. To examine the utility of por variable-region (VR) typing, porB from 206 isolates was characterized by using oligonucleotide probes in a checkerboard hybridization assay that identifies the sequence types of five VRs of both PIA and PIB porB alleles. The strains represented temporally and geographically distinct isolates, isolates from a large cluster, epidemiologically linked partner isolates, and a collection of strains from disseminated gonococcal infections. By using rigorous epidemiologic criteria for transmission of infection between sex partners, por VR typing was more discriminatory than serovar typing in classifying isolates from both members of 43 epidemiologically linked pairs: 39 of 43 pairs were classified as coinciding by por VR typing compared to 43 of 43 by serovar determination (P = 0.058). porB sequence data confirmed the accuracy of the por VR method. Relationships between VR type and serovar typing monoclonal antibodies were observed for all six PIB and three of six PIA antibodies. por VR typing is a molecular tool that appears to have broad applicability. This method can be adapted to a wide range of technologies from simple hybridization to microarray and may allow for typing from noncultured clinical specimens.

Bacterial Typing Techniques↗
PubMed2005

High-spatial-resolution MR angiography of renal arteries with integrated parallel acquisitions: comparison with digital subtraction angiography and US.

PURPOSE: To retrospectively compare three-dimensional gadolinium-enhanced magnetic resonance (MR) angiography, performed with an integrated parallel acquisition technique for high isotropic spatial resolution, with selective digital subtraction angiography (DSA) and intravascular ultrasonography (US) for accuracy of diameter and area measurements in renal artery stenosis. MATERIALS AND METHODS: The study was approved by the institutional review board, and consent was obtained from all patients. Forty-five patients (17 women, 28 men; mean age, 62.2 years) were evaluated for suspected renal artery stenosis. Three-dimensional gadolinium-enhanced MR angiograms were acquired with isotropic spatial resolution of 0.8 x 0.8 x 0.9 mm in 23-second breath-hold with an integrated parallel acquisition technique. In-plane diameter of stenosis was measured along vessel axis, and perpendicular diameter and area of stenosis were assessed in cross sections orthogonal to vessel axis, on multiplanar reformations. Interobserver agreement between two radiologists in measurements of in-plane and perpendicular diameters of stenosis and perpendicular area of stenosis was assessed with mean percentage of difference. In a subset of patients, degree of stenosis at MR angiography was compared with that at DSA (n = 20) and intravascular US (n = 11) by using Bland-Altman plots and correlation analyses. RESULTS: Mean percentage of difference in stenosis measurement was reduced from 39.3% +/- 78.4 (standard deviation) with use of in-plane views to 12.6% +/- 9.5 with use of cross-sectional views (P < .05). Interobserver agreement for stenosis grading based on perpendicular area of stenosis was significantly better than that for stenosis grading based on in-plane diameter of stenosis (mean percentage of difference, 15.2% +/- 24.2 vs 54.9% +/- 186.9; P < .001). Measurements of perpendicular area of stenosis on MR angiograms correlated well with those on intravascular US images (r(2) = 0.90). CONCLUSION: Evaluation of cross-sectional images reconstructed from high-spatial-resolution three-dimensional gadolinium-enhanced MR renal angiographic data increases the accuracy of the technique and decreases interobserver variability.

Adult↗
PubMed2004

Endoscope motion compensation for laryngeal high-speed videoendoscopy.

The purpose of this study was to develop and evaluate a method for automatic endoscopic motion compensation (MC) specialized for laryngeal high-speed videoendoscopy (HSV) of sustained phonation. Specifically, the left-right and posterior-anterior endoscopic shifts were addressed. The method is based on the hypothesis that the difference between endoscopic and vocal fold dynamics is sufficient for accurate estimation of the endoscopic motion relative to the vocal folds. The research questions of particular interest were as follows: is MC of laryngeal HSV possible at the subpixel level, and what are the validity, reliability, and accuracy of the proposed MC method? First, the MC accuracy was assessed on simulated HSV data with exactly known motion trajectories. Then, the accuracy and reliability of MC were evaluated on real HSV data. Finally, the validity of MC was established by correlating objective to perceptual ratings. The method demonstrated subpixel accuracy and reliable performance when tested on both simulated and real data. Perceptual ratings of the endoscopic motion demonstrated high intrarater and interrater reliabilities. Perceptual and quantitative assessments of endoscopic motion were in agreement. The reported result is encouraging for resolving a persistent problem toward building better methods for visual and quantitative voice assessment.

Female↗
PubMed1996

The use of the 'binormal' model for parametric ROC analysis of quantitative diagnostic tests.

The binormal model is widely used for parametric receiver operating characteristic (ROC) analyses of data concerning the accuracy of medical diagnostic tests. Empirical evaluation of the performance of this model in the face of departures from binormality has been limited to interpretations of radiology-type examinations recorded on a rating scale. This paper extends the investigation to the performance of the model with biochemical and other tests recorded on an interval scale. In order to describe non-binormal pairs of distributions, a useful standardized graphical display is developed; this display also illustrates several features of ROC curves. We consider non-binormal pairs of distributions with or without a monotone likelihood ratio and show that by transformation of the underlying scale, one can make many such pairs resemble closely the binormal model. These findings justify Metz's use of the binormal model in the 'LABROC' software for ROC analyses of laboratory type data even when the raw data may 'look' decidedly non-Gaussian.

Diagnostic Imaging↗
PubMed1999

[The accuracy of the fine needle aspiration biopsy in 1250 thyroid nodules].

Between 1989 and 1998 a total of 1250 thyroid nodes underwent Fine Needle Aspiration Biopsy (FNAB). Of these 150 went on to surgery with subsequent histological examination which proved positive for malignant neoplasm in 35 nodes. The remaining 115 nodes presented benign lesions. The cytological diagnoses were preventatively broken down into three groups: a) benign; b) malignant; c) suspected malignancy. Group a) included 53 nodes; histology confirmed the diagnosis of a benign lesion in 50 of these nodes (True Negatives), while 3 proved malignant (False Negatives). The cytological diagnosis of malignancy was reached in 24 nodes (group b) and subsequent histology confirmed the malignancy in 18 cases (True Positives) while the remaining 6 nodes tested negative for neoplasm (False Positives). Group c) included those thyroid nodes which cytology classified as follicular neoplasms and for which histology was required to reach a diagnosis of malignancy or benignity; for this reason these cases were not used in the evaluation of diagnostic reliability. Of these 15 (20.5%) proved malignant and 58 (79.5%) benign (44 follicular adenomas and 14 micro-macrofollicular struma nodes). On the basis of the above data, the diagnostic accuracy of FNAB is 88.3%, sensitivity 85.7% and specificity 89.3%. These findings are substantially in agreement with the international literature which considers cytological testing highly reliable. In analyzing the cases which were not confirmed by histology, it was interesting to note that among the 4 false positives--defined as the "presence of atypical cells in a lymphocyte infiltration context"--a full three were thyroadenitis nodes for which the presence of atypical cells is quite common. The three false negative nodes, on the other hand, included two cysts for which cytology did not reveal neoplastic cells. The present experience suggests the following: 1) FNAB is still the most reliable technique for the diagnosis of thyroid neoplasms; 2) the presence of atypical cells in thyroid node lesions is not always indication of a malignancy; 3) cysts must be subject to careful follow-up since they can mask a malignant neoplasm.

Adolescent↗
PubMed2006

[Our experience with an image guided navigation system for accurate alignment in total hip replacement by minimally invasive posterolateral surgery].

PURPOSE OF THE STUDY: The aim of the study was to compare a radiographic position of the acetabular component with a position guided by the navigation system in final acetabular cup alignment. MATERIAL: Between May and October 2005, 15 patients underwent implantation of a cementless acetabular component from the posterolateral minimally invasive approach with the use of kinematic navigation. METHODS: The final acetabular cup alignment was determined from the data saved in the navigation system. The radiographic measurement of acetabular cup inclination was made from an anteroposterior projection of both hips on one image, and anteversion was determined by the Ackland method. RESULTS: The average values for inclination and anteversion shown on radiographs were 41.8 degrees (range, 35-51) and 19.8 degrees (range, 5-32), respectively. The average values of cup alignment recorded at implantation by the navigation system were 27.6 degrees (range, 22-35) for inclination and 24.3 degrees (range, 17-28) for anteversion. DISCUSSION: The acetabular cup alignment is considered optimal when inclination is 45 degrees and anteversion 15 degrees. This is more difficult to achieve in minimally invasive surgery due to a limited view of the operating field. This disadvantage can be overcome by using various navigation systems the function of which depends on the accuracy of recorded data. CONCLUSIONS: Because the data recorded by the system used in our study were not accurate, we do not consider the OrthoPilot navigation system to be an effective aid in minimally invasive posterolateral surgery.

Aged↗
PubMed2006

Prediction of estrogen receptor agonists and characterization of associated molecular descriptors by statistical learning methods.

Specific estrogen receptor (ER) agonists have been used for hormone replacement therapy, contraception, osteoporosis prevention, and prostate cancer treatment. Some ER agonists and partial-agonists induce cancer and endocrine function disruption. Methods for predicting ER agonists are useful for facilitating drug discovery and chemical safety evaluation. Structure-activity relationships and rule-based decision forest models have been derived for predicting ER binders at impressive accuracies of 87.1-97.6% for ER binders and 80.2-96.0% for ER non-binders. However, these are not designed for identifying ER agonists and they were developed from a subset of known ER binders. This work explored several statistical learning methods (support vector machines, k-nearest neighbor, probabilistic neural network and C4.5 decision tree) for predicting ER agonists from comprehensive set of known ER agonists and other compounds. The corresponding prediction systems were developed and tested by using 243 ER agonists and 463 ER non-agonists, respectively, which are significantly larger in number and structural diversity than those in previous studies. A feature selection method was used for selecting molecular descriptors responsible for distinguishing ER agonists from non-agonists, some of which are consistent with those used in other studies and the findings from X-ray crystallography data. The prediction accuracies of these methods are comparable to those of earlier studies despite the use of significantly more diverse range of compounds. SVM gives the best accuracy of 88.9% for ER agonists and 98.1% for non-agonists. Our study suggests that statistical learning methods such as SVM are potentially useful for facilitating the prediction of ER agonists and for characterizing the molecular descriptors associated with ER agonists.

Forecasting↗
PubMed2001

In vivo measurement of 3-D skeletal kinematics from sequences of biplane radiographs: application to knee kinematics.

Current noninvasive or minimally invasive methods for evaluating in vivo knee kinematics are inadequate for accurate determination of dynamic joint function due to limited accuracy and/or insufficient sampling rates. A three-dimensional (3-D) model-based method is presented to estimate skeletal motion of the knee from high-speed sequences of biplane radiographs. The method implicitly assumes that geometrical features cannot be detected reliably and an exact segmentation of bone edges is not always feasible. An existing biplane radiograph system was simulated as two separate single-plane radiograph systems. Position and orientation of the underlying bone was determined for each single-plane view by generating projections through a 3-D volumetric model (from computed tomography), and producing an image (digitally reconstructed radiograph) similar (based on texture information and rough edges of bone) to the two-dimensional radiographs. The absolute 3-D pose was determined using known imaging geometry of the biplane radiograph system and a 3-D line intersection method. Results were compared to data of known accuracy, obtained from a previously established bone-implanted marker method. Difference of controlled in vitro tests was on the order of 0.5 mm for translation and 1.4 degrees for rotation. A biplane radiograph sequence of a canine hindlimb during treadmill walking was used for in vivo testing, with differences on the order of 0.8 mm for translation and 2.5 degrees for rotation.

Animals↗
PubMed1991

Does color-flow imaging improve the accuracy of duplex carotid evaluation?

To determine whether color-flow imaging enhances the accuracy of noninvasive carotid evaluation, the results of carotid duplex examinations from two laboratories, one with color-flow and the other with standard duplex imaging were compared. The techniques used by both laboratories were identical. All studies were interpreted by one of the authors, using the same criteria. From October 1988 through December 1989, 307 internal carotid arteries were evaluated with both color-flow imaging and standard angiography; and 206 underwent routine duplex scanning and angiography. Perfect agreement between test and angiographic results was significantly better with color-flow (86.6%) than with conventional duplex scanning (79.6%), p = 0.034 (t test for independent samples). Significantly fewer vessels were over classified by one category with color-flow (8.5%) than with routine duplex scanning (16.5%), p = 0.006. However, no difference was found in the number under-classified by one category (4.5% vs 3.4%), p = 0.5. Although these data support the accuracy of both modalities, there appears to be a trend toward improved results with the newer method. We attribute this to more precise placement of the pulsed Doppler sample volume afforded by the color-flow image.

Angiography↗
PubMed2002

Modeling of gas absorption cross sections by use of principal-component-analysis model parameters.

Monitoring the amount of gaseous species in the atmosphere and exhaust gases by remote infrared spectroscopic methods calls for the use of a compilation of spectral data, which can be used to match spectra measured in a practical application. Model spectra are based on time-consuming line-by-line calculations of absorption cross sections in databases by use of temperature as input combined with path length and partial and total pressure. It is demonstrated that principal component analysis (PCA) can be used to compress the spectrum of absorption cross sections, which depend strongly on temperature, into a reduced representation of score values and loading vectors. The temperature range from 300 to 1000 K is studied. This range is divided into two subranges (300-650 K and 650-1000K), and separate PCA models are constructed for each. The relationship between the scores and the temperature values is highly nonlinear. It is shown, however, that because the score-temperature relationships are smooth and continuous, they can be modeled by polynomials of varying degrees. The accuracy of the data compression method is validated with line-by-line-calculated absorption data of carbon monoxide and water vapor. Relative deviations between the absorption cross sections reconstructed from the PCA model parameters and the line-by-line-calculated values are found to be smaller than 0.15% for cross sections exceeding 1.27 x 10(-21) cm(-1) atm(-1) (CO) and 0.20% for cross sections exceeding 4.03 x 10(-21) cm(-1) atm(-1) (H2O). The computing time is reduced by a factor of 10(4).

Journal Article↗
PubMedDate not supplied

Using localization data from image interpretations to improve estimates of performance accuracy.

A recently developed model uses the localization of abnormalities on images to improve statistical precision in measuring detection accuracy Az, the area below an observer's receiver operating characteristic (ROC) curve for ratings of sampled normal and abnormal cases. This study evaluated that improvement by investigating how much the standard error of estimated Az decreased when the statistical analysis included localization data. Comparisons of analyses with vs without localizations were made for: 1) the estimates of Az from observers' rating ROC curves for nodular lesions on clinical chest films and liver CT scans; 2) the probability of correct choices between paired samples of normal and abnormal cases (equivalent to Az); and 3) the sampling distributions of Az measured in Monte Carlo simulations of 2,000 independent rating experiments. Localization information considerably improved the precision of Az estimates, particularly when detection accuracy was low (Az approximately 0.60). These data provided roughly the same benefits in estimation precision as would two-to-fourfold increases in the sizes of both 1) the samples of positive and negative cases and 2) the observer samples used to estimate Az means.

Data Interpretation, Statistical↗
PubMed1994

Imaging of lymphoma with PET with 2-[F-18]-fluoro-2-deoxy-D-glucose: correlation with CT.

PURPOSE: To prospectively compare the accuracy of positron emission tomography (PET) with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) in imaging thoracicoabdominal lymphoma to that of computed tomography (CT). MATERIALS AND METHODS: Sixteen patients with lymphoma (11 with non-Hodgkin lymphoma [NHL] and five with Hodgkin disease) underwent FDG-PET and CT. Blinded, independent interpretations of PET and CT studies were followed by a direct comparison of the images. Measurement of tumor uptake of FDG was performed on positive PET studies. RESULTS: Fifty-four foci of abnormal uptake were detected with PET in 13 patients. Forty-nine corresponding sites of lymphadenopathy and/or masses were detected with CT. All sites of adenopathy seen at CT were detected at PET. Three patients with Hodgkin disease had negative findings at abdominal PET, CT, and subsequent staging laparotomy. FDG uptake was comparable for both the low- and intermediate-grade lymphomas. CONCLUSION: These preliminary data indicate excellent accuracy for FDG-PET imaging of thoracicoabdominal lymphoma. All grades of NHL were successfully imaged with FDG-PET. PET appears to be a useful method for imaging lymphoma.

Adolescent↗
PubMed2006

Cervical pedicle screw placement: feasibility and accuracy of two new insertion techniques based on morphometric data.

This morphometric and experimental study was designed to assess the dimensions and axes of the subaxial cervical pedicles and to compare the accuracy of two different techniques for subaxial cervical pedicle screw (CPS) placement using newly designed aiming devices. Transpedicular fixation is increasingly used for stabilizing the subaxial cervical spine. Development of the demanding technique is based on morphometric studies of the pedicle anatomy. Several surgical techniques have been developed and evaluated with respect to their feasibility and accuracy. The study was carried out on six conserved human cadavers (average age 85 years). Axes and dimensions of the pedicles C3-C7 (60 pedicles) were measured using multislice computed tomography (CT) images prior to surgery. Two groups consisting of 3 specimens and 30 pedicles each were established according to the screw placement technique. For surgical technique 1 (ST1) a para-articular mini-laminotomy was performed. Guidance of the drill through the pedicle with a handheld aiming device attached onto the medial aspect of the pedicle inside the spinal canal. Screw hole preparation monitored by lateral fluoroscopy. In surgical technique 2 (ST2) a more complex aiming device was used for screw holes drilling. It consists of a frame with a fully adjustable radiolucent arm for carrying the instruments necessary for placing the screws. The arm was angled according to the cervical pedicle axis as determined by the preoperative CT scans. Drilling was monitored by lateral fluoroscopy. In either technique 3.5 mm screws made of carbon fiber polyetheretherketone (CF-PEEK) were inserted. The use of the CF-PEEK screws allowed for precise postoperative CT-assessment since this material does not cause artifacts. Screw placement was qualified from ideal to unacceptable into four grades: I = screw centered in pedicle; IIa = perforation of pedicle wall less than one-fourth of the screw diameter; IIb = perforation more than one-fourth of the screw diameter without contact to neurovascular structures; III = screw more than one-fourth outside the pedicle with contact to neurovascular structures. Fifty-six pedicle screws could be evaluated according to the same CT protocol that was used preoperatively. Accuracy of pedicle screw placement did not reveal significant differences between techniques 1 and 2. A tendency towards less severe misplacements (grade III) was seen in ST2 (15% in ST2 vs. 23% in ST1) as well as a higher rate of screw positions graded IIa (62% in ST2 vs. 43% in ST1). C4 and C5 were identified to be the most critical vertebral levels with three malpositioned screws each. Because of the variability of cervical pedicles preoperative CT evaluation with multiplanar reconstructions of the pedicle anatomy is essential for transpedicular screw placement in the cervical spine. Cadaver studies remain mandatory to develop safer and technically less demanding procedures. A similar study is projected to further develop the technique of CPS fixation with regard to safety and clinical practicability.

Aged, 80 and over↗