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PubMed1984

Accuracy of tidal volume, lung volume, and flow measurements by inductance vest in COPD patients.

We analyzed the accuracy of the inductance vest in measuring several ventilatory parameters in five patients with chronic obstructive pulmonary disease (COPD). We assessed tidal volume (VT) accuracy at different respiratory frequencies in different lying body positions with different thoracic and abdominal contributions to breathing and the accuracy over a 4-h time span. Mean percent error was calculated without regard to direction of error. The mean error of vest VT estimation was 7.6% for all body positions studied and 5.6% for right and left lateral positions combined. Vest VT accuracy was unchanged after 4 h and with changes in thoracic and abdominal contributions to VT. The mean errors for inspiratory and expiratory times were 3.3 and 2.0%, respectively. Volume was differentiated to flow. For respiratory rates ranging from 12 to 30 breaths/min, the mean error of the vest and our differentiation circuit in duplicating peak flows measured at the mouth was 3.5%. The ability of the vest to estimate changes in end-expiratory position or functional residual capacity was not as good as with VT; the mean error was 30.7%. For estimation of VT, ventilatory timing, and airflow in COPD patients, the inductance vest performs well. For measurement of changes in lung volume, improvements in vest design need to be made.

Abdomen↗

PubMed2006

Accuracy Evaluation for Region Centroid-Based Registration of Fluorescent CLSM Imagery.

We present an accuracy evaluation of a semi-automatic registration technique for 3D volume reconstruction from fluorescent confocal laser scanning microscope (CLSM) imagery. The presented semi-automatic method is designed based on our observations that (a) an accurate point selection is much harder than an accurate region (segment) selection for a human, (b) a centroid selection of any region is less accurate by a human than by a computer, and (c) registration based on structural shape of a region rather than based on intensity-defined point is more robust to noise and to morphological deformation of features across stacks. We applied the method to image mosaicking and image alignment registration steps and evaluated its performance with 20 human subjects on CLSM images with stained blood vessels. Our experimental evaluation showed significant benefits of automation for 3D volume reconstruction in terms of achieved accuracy, consistency of results and performance time. In addition, the results indicate that the differences between registration accuracy obtained by experts and by novices disappear with the proposed semi-automatic registration technique while the absolute registration accuracy increases.

Journal Article↗

PubMed1999

Diagnostic accuracy in 2,351 patients undergoing appendicectomy for suspected acute appendicitis: A retrospective study 1986-1993.

AIMS: To investigate the pre-operative findings, accuracy, perforation rate and complication rate in 2,351 patients who underwent appendicectomy during 1986-1993. METHOD: The 2,351 records from patients who underwent surgery were analysed to determine whether the pre-operative investigations introduced can improve the diagnostic accuracy when analysed in total. RESULTS: The total diagnostic accuracy which was 70.9% in 1986 increased to a statistically significant figure of 87.1% in 1993. In female patients, the figure increased from 61.7 to 82.4% and in males from 82.0 to 91.2% during the studied period. The complication rate was in total 10.4% including a mortality of 0.21% (5 patients). CONCLUSION: We believe that with a combination of increased interest in patients with acute appendicitis, a wider use of active in-hospital observation, a more standardised pre-operative laboratory investigation and the use of ultrasonography, a high diagnostic accuracy could be reached without an increased rate of complications and perforations.

Acute Disease↗

PubMed1999

The relationship of imaging techniques to the accuracy of frameless stereotaxy.

OBJECTIVE: We analyzed the accuracy of a frameless stereotactic system using computed tomographic (CT) and magnetic resonance imaging (MRI) scans of different slice thickness and T(1) versus T(2) weighting of MRI. METHODS: An open skull with graphite pegs fixed to its base was used for all scans. CT scans were done with slice thicknesses of 1, 2 and 3 mm. MRI-visible markers were placed on top of pegs for T(1)-weighted and T(2)-weighted MRI scans, which were acquired at thicknesses of 1.5, 3 and 5 mm. For each scan, 3 separate registrations of a probe were performed; the distance between the actual probe location and that displayed on the registered image was noted. Each measurements was repeated 3 times for each registration. RESULTS: Greatest accuracy was achieved with 3-mm-slice CT scans; this was not improved by using thinner slices. T(1)-weighted 1.5-mm MRI scans were 23% less accurate and T(2)-weighted 3-mm scans 37% less accurate. CONCLUSIONS: Frameless stereotaxy should be done using CT scans when the greatest possible accuracy is desired. There appears to be no advantage to using slice thicknesses less than 3 mm. For most craniotomy applications, T(1)-weighted MRI using 3-mm slices provides sufficient accuracy. Lesions imaged only on T(2)-weighted MRI also can be approached with adequate precision using 3-mm scans.

Cephalometry↗

PubMed2006

Application accuracy of automatic registration in frameless stereotaxy.

OBJECTIVE: We compared the application accuracy of an infrared-based neuronavigation system when used with a novel automatic registration with its application accuracy when standard fiducial-based registration is performed. METHODS: The automatic referencing tool is based on markers that are integrated in the headrest holder we routinely use in our intraoperative magnetic resonance imaging (MRI) setting and can be detected by the navigation software automatically. For navigation targeting we used a Plexiglas phantom with 32 notched rods of different heights. The phantom was fixed in the head holder and multiple optimized gradient echo slices containing the clamp-integrated markers were acquired. After that we measured a T1 MPRAGE sequence with a slice thickness of 1.0 mm for navigation. The deepest points of the surface of the rods were defined as target points in image space. In three measurement series we referenced the phantom once with 4, once with 7 fiducials and twice automatically. In one series we performed only one automatic registration. The localization error was measured 3 times per rod and registration. RESULTS: The median localization errors for standard registration with 7 fiducials were between 1.2 and 3.05 mm. With 4 fiducials, medians were in the range from 1.87 to 2.21 mm. For the automatic registration we obtained median localization errors between 0.88 and 2.13 mm. In 6 of the 8 samples that were compared the automatic registration showed an application accuracy that was highly significantly better (p < 0.001 in most cases) than that of fiducial-based standard registration. CONCLUSION: The application accuracy found for automatic referencing is at least not worse than that for standard registration no matter whether 4 or 7 fiducial markers were used. Therefore, its use in the operating room is feasible. In combination with intraoperative MRI it may become a favorable alternative to standard fiducial-based registration especially when an intraoperative update of navigation data is necessary.

Automation↗

PubMed1992

An independent application accuracy evaluation of stereotactic frame systems.

The purpose of incorporating stereotactic methodology into neurosurgical procedures is to consistently achieve a high degree of accuracy and precision in localizing intracranial targets. Therefore, the limits of resolution for the therapeutic intervention itself are a function of the accuracy and precision inherent to the particular stereotactic frame system itself. The total clinically relevant error (application accuracy) comprises errors associated with each procedural step, including imaging, target selection, vector calculation and the mechanical errors of stereotactic frames. To evaluate these parameters, a systematic error analysis was carried out in the 4 most commonly used CT-compatible stereotactic devices: the Brown-Roberts-Wells, Cosman-Roberts-Wells, Kelly-Goerss Compass (modified Todd-Wells) and Leksell frames. Over 7,681 independent test measurements were made. The results suggest a potentially significant degree of error in application accuracy of all stereotactic instrumentation which is accentuated by imaging-associated error. These individual error values must be considered with every clinical use of stereotactic frames.

Humans↗

PubMed1992

Use of the speed accuracy trade-off to characterize information processing in schizophrenics and normals.

Subjects performed a signal discrimination task under four conditions: normal pace, accuracy, speed, and SATO (equal effort to speed and accuracy). Characteristically, schizophrenics demonstrated decreased accuracy, poorer compliance, increased total response time, and increased simple reaction time. Surprisingly, central processing time (decision time) was equivalent. Analysis of processing resource allocation identified significant group differences only under the SATO condition. Here, controls balanced attentional resources but patients worked almost exclusively for speed. Under conjoint performance conditions, patients apparently minimize categorical processing time at the expense of accuracy. These data are interesting as they identify specific circumstances under which schizophrenics manifest an attentional deficit.

Adult↗

PubMedDate not supplied

Fine needle aspiration biopsy for improving the diagnostic accuracy of cut needle biopsy of focal liver lesions.

OBJECTIVE: To determine the value of fine needle aspiration biopsy (FNAB) in comparison to cut needle biopsy (CNB) for the diagnosis of malignancy of focal liver lesions. STUDY DESIGN: A retrospective analysis was conducted on 68 FNAB and 49 CNB procedures performed on 62 patients with focal liver lesions. RESULTS: Cytology permitted a diagnosis of the lesion in 78% of cases. When punctures with insufficient material were excluded (11), the diagnostic accuracy of FNAB was 93%. For the 49 patients who underwent both procedures, FNAB and CNB had the same diagnostic accuracy, 78%, when considered separately and of 88% when considered in combination. Sensitivity, specificity and positive predictive value were similar for the 2 techniques. The negative predictive value was 64% for FNAB and CNB used separately and reached 78% when the 2 techniques were combined. There were no complications during the execution of FNAB and CNB. CONCLUSION: FNAB is an effective and safe method for the diagnosis of focal hepatic lesions, with diagnostic accuracy similar to that of CNB. When the 2 techniques are combined, the accuracy of the diagnosis of malignancy of focal liver lesions increases.

Adult↗

PubMedDate not supplied

High diagnostic accuracy of cytologic smears of central nervous system tumors. A 15-year experience based on 4,172 patients.

OBJECTIVE: To investigate the diagnostic accuracy and current role of intraoperative cytologic smears of central nervous system tumors. STUDY DESIGN: Retrospective analysis of 4,172 patients operated on during 1985-1999, with 3,541 intraoperative smears performed during open procedures and 631 during stereotactic biopsies. RESULTS: Complete correlation with the final diagnosis was achieved in a mean of 89.8% (range, 83-93.7% per year). Diagnostic accuracy increased to 95% on average (range, 91.5-96.7% per year) when cases of partial correlation, mainly due to grading deviations, were included. The most accurate intraoperative diagnoses were obtained in cases of meningioma (97.9%), metastasis (96.3%) and glioblastoma (95.7%). A significant reduction in diagnostic accuracy was observed in cases of oligodendroglioma (80.9%) and ependymoma (77.7%). Besides diagnosis and grading, smear cytology provided resection guidance in cases of well-delineated tumors. CONCLUSION: Intraoperative smears in neurosurgery are easy to obtain and inexpensive and have high diagnostic accuracy. In addition to stereotactic biopsy procedures, intraoperative smears permit reliable intraoperative guidance during lesion targeting and resection.

Biopsy↗

PubMedDate not supplied

FNAC of malignant lymphoma in an area with a high incidence of T-cell lymphoma. Correlation of accuracy of cytologic diagnosis with histologic subtype and immunophenotype.

OBJECTIVE: To analyze the usefulness of fine needle aspiration cytology on malignant lymphoma in an area with a high incidence of T-cell lymphoma and to correlate the accuracy of cytologic diagnosis with histologic subtype and immunophenotype. STUDY DESIGN: We retrospectively studied the usefulness of fine needle aspiration cytology in the diagnosis of 49 cases of nodal and extranodal non-Hodgkin's lymphoma (NHL) and seven cases of Hodgkin's disease in a total of 56 patients in whom subsequent excisional biopsy revealed lymphoid malignancy. Slides showing the results of cytologic investigation were reviewed together with the information on which histologic diagnosis was based. On the basis of pathologic variables, such as prognostic groups based on the Working Formulation, so-called grade, cell size based on the modified Rappaport classification, and--in cases of NHL--immunophenotype, the accuracy of original and reviewed cytologic diagnoses was compared. RESULTS: Of the 49 cases of NHL, 8 (16.3%) were inadequate for cytologic diagnosis, and malignant lymphoma was diagnosed or suspected in 36 (73.5%), excluding inadequate specimens; the diagnostic accuracy for NHL was 87.8%. In high grade cases, malignant lymphoma was more easily diagnosed or suspected than in those that were low or intermediate grade. The rate of inadequate cases was highest in the "mixed small and large cell" category, and cases that were "false negative" were either composed entirely of small cells or contained a small cell component. Cytologic diagnosis or suspicion of malignant lymphoma was easily obtained in the "large cell" category, followed by mixed small and large cell and "small cell." Aspirates from non-B-cell type were more frequently acellular than those of B-cell type; with regard to diagnostic accuracy, however, there was no noticeable difference between the two immunophenotypes. CONCLUSION: In many cases in the mixed small and large cell category or where the immunophenotype was non-B, the aspirate was inadequate, and no definitive diagnosis was possible. Many of our cases of T-cell lymphoma were mixed small and large cell, and in Korea, where the incidence of extranodal and T-cell lymphoma is high, the usefulness of FNAC for the initial diagnosis of malignant lymphoma is limited. For a definitive diagnosis, biopsy is required.

Biopsy, Needle↗

PubMed2004

A systematic review of the accuracy of ultrasound in the diagnosis of deep venous thrombosis in asymptomatic patients.

Evaluation of the accuracy of ultrasound has yielded heterogeneous results. Our objective was to summarize the evidence on the accuracy of ultrasound compared to venography in asymptomatic patients, taking into account the variation due to threshold differences. Searches of journal table of contents, computer databases (Medline, Embase, Biomed, Cochrane) and conference proceedings were performed. A study was eligible if it prospectively compared ultrasound to venography for the diagnosis of DVT in asymptomatic patients. Data of studies selected for inclusion were extracted independently by two authors. High quality studies with consecutive patient enrollment, blind evaluation of the two techniques, and absence of verification bias are summarized as Level 1, while those not fulfilling one or more of these criteria are considered Level 2. Original study authors were contacted to confirm accuracy and to provide missing data. A pooled estimate of the accuracy of ultrasound was obtained according to the method of Moses and coworkers. This method gives a summary diagnostic odds ratio (DOR). The DOR is a single indicator of test performance. It varies between 0 and infinity and exceeds 1, only when ultrasound is more often positive in patients with DVT relative to those without DVT. Higher DOR indicates better discriminatory test performance. Thirty one studies were rated as potentially unbiased and graded as Level 1. The mean prevalence of DVT as determined by venography was 22%. In Level 1 studies, the odds of positive ultrasound in proximal veins was 379 times higher (95% confidence limits 65, 2,200) and in distal veins 32 times higher (7.5, 135) among patients with DVT than those without. Our results suggest that, particularly for proximal veins, ultrasound is accurate for the diagnosis of DVT in asymptomatic postoperative orthopedic patients. More research is needed in other clinical settings.

Humans↗

PubMed1981

Quantitative detection of regional left ventricular contraction abnormalities by two-dimensional echocardiography. II. Accuracy in coronary artery disease.

The quantitative approaches to the assessment of regional left ventricular (LV) function described in the preceding paper were applied in a well-defined population of patients with coronary artery disease. Two groups were chosen by electrocardiographic and angiographic criteria: group 1 had infarction and regional wall motion abnormalities and group 2 had no infarction and normal wall motion. Sensitivity to detect wall motion defects, specificity to correctly categorize normal segments, and overall predictive accuracy were evaluated for each two-dimensional echocardiographic approach. In addition, the ability of each method to localize regional contraction defects properly was evaluated. Area methods yielded better predictive accuracy than linear methods (87-95% vs 76-84%). No significant differences in accuracy were noted between quadrant and octant approaches. The fixed external-axis system was superior to a floating one for localizing contraction defects. We conclude that an area-based method, using a fixed-axis system and either octant or quadrant image subdivision, provides the best combination of predictive accuracy in categorizing LV segments as normal or abnormal and the greatest ability to localize LV regional abnormalities.

Adult↗

PubMed1985

Accuracy of two ear oximeters at rest and during exercise in pulmonary patients.

The accuracy of 2 ear oximeters (Hewlett-Packard 47201A and Biox IIA) was evaluated at rest and during exercise in 116 pulmonary patients. Ear oximetry measurements were compared with arterial oxygen saturation (SaO2) measured from simultaneous arterial blood samples. When used according to the manufacturer's instructions for stabilization during exercise testing, both oximeters demonstrated comparable accuracy in estimating arterial blood SaO2 both at rest and during exercise in these patients (95% confidence limits, 2 SEE = +/- 4 to 5%). The oximeters were more accurate in measuring a change in SaO2 from a previous reading (95% confidence limits, 2 SEE = +/- 2.5 to 3.5%). COHgb levels greater than 4% and dark skin pigmentation appeared to decrease the accuracy of ear oximetry measurements. Within the limitations of accuracy, both ear oximeters may be useful for clinical exercise testing in pulmonary patients.

Arteries↗

PubMed2005

Accuracy of Zernike polynomials in characterizing optical aberrations and the corneal surface of the eye.

PURPOSE: Zernike polynomials have been successfully used for approximately 70 years in many different fields of optics. Nevertheless, there are some recent discussions regarding the precision and accuracy of these polynomials when applied to surfaces such as the human cornea. The main objective of this work was to investigate the absolute accuracy of Zernike polynomials of different orders when fitting several types of theoretical corneal and wave-front surface data. METHODS: A set of synthetic surfaces resembling several common corneal anomalies was sampled by using cylindrical coordinates to simulate the height output files of commercial videokeratography systems. The same surfaces were used to compute the optical path difference (wave-front [WF] error), by using a simple ray-tracing procedure. Corneal surface and WF error was fit by using a least-squares algorithm and Zernike polynomials of different orders, varying from 1 to 36 OSA-VSIA convention terms. RESULTS: The root mean square error (RMSE) ranged-from the most symmetric corneal surface (spherical shape) through the most complex shape (after radial keratotomy [RK]) for both the optical path difference and the surface elevation for 1 through 36 Zernike terms-from 421.4 to 0.8 microm and 421.4 to 8.2 microm, respectively. The mean RMSE for the maximum Zernike terms for both surfaces was 4.5 microm. CONCLUSIONS: These results suggest that, for surfaces such as that present after RK, in keratoconus, or after keratoplasty, even more than 36 terms may be necessary to obtain minimum accuracy requirements. The author suggests that the number of Zernike polynomials should not be a global fixed conventional or generally accepted value but rather a number based on specific surface properties and desired accuracy.

Cornea↗

PubMed2003

Reliability, validity, and classification accuracy of a measure of DSM-IV diagnostic criteria for pathological gambling.

OBJECTIVE: The purpose of this study was to measure the reliability, validity, and classification accuracy of the DSM-IV diagnostic criteria for pathological gambling. METHOD: Participants in this study were drawn from two sources: 803 men and women from the general adult population of Minnesota and 259 men and women who were admitted to a gambling treatment program. A 19-item measure of the DSM-IV diagnostic criteria for pathological gambling was administered, along with other validity measures. RESULTS: The DSM-IV diagnostic criteria were found to be reliable and valid. With a standard cutoff score of 5, DSM-IV criteria yielded satisfactory classification accuracy results; however, a cutoff score of 4 made modest improvements in classification accuracy and, most important, reduced the rate of false negatives. CONCLUSIONS: The DSM-IV diagnostic criteria for pathological gambling, when operationalized into questions, demonstrated satisfactory reliability, validity, and classification accuracy, and a cutoff score of 4 improved diagnostic precision.

Adolescent↗

PubMed1981

Who should abstract medical records? A study of accuracy and cost.

The accuracy of patient record data depends not only on the quality of medical record keeping but also on the accuracy of the process of abstracting patient records to produce data suitable for analysis. This article reports results comparing record abstracts produced by four classes of abstracter: physicians, tumor registrars, nurses, and fourth-year medical students. The purpose of the comparison was to determine whether or not there were differences in accuracy among the four groups and, if accuracy was approximately equal, whether there were substantial differences among the costs of employing the four groups.

Abstracting and Indexing↗

PubMedDate not supplied

Enhancing and evaluating diagnostic accuracy.

Techniques that may enhance diagnostic accuracy in clinical settings were tested in the context of mammography. Statistical information about the relevant features among those visible in a mammogram and about their relative importances in the diagnosis of breast cancer was the basis of two decision aids for radiologists: a checklist that guides the radiologist in assigning a scale value to each significant feature of the images of a particular case, and a computer program that merges those scale values optimally to estimate a probability of malignancy. A test set of approximately 150 proven cases (including normals and benign and malignant lesions) was interpreted by six radiologists, first in their usual manner and later with the decision aids. The enhancing effect of these feature-analytic techniques was analyzed across subsets of cases that were restricted progressively to more and more difficult cases, where difficulty was defined in terms of the radiologists' judgements in the standard reading condition. Accuracy in both standard and enhanced conditions decreased regularly and substantially as case difficulty increased, but differentially, such that the enhancement effect grew regularly and substantially. For the most difficult case sets, the observed increases in accuracy translated into an increase of about 0.15 in sensitivity (true-positive proportion) for a selected specificity (true-negative proportion) of 0.85 or a similar increase in specificity for a selected sensitivity of 0.85. That measured accuracy can depend on case-set difficulty to different degrees for two diagnostic approaches has general implications for evaluation in clinical medicine. Comparative, as well as absolute, assessments of diagnostic performances--for example, of alternative imaging techniques--may be distorted by inadequate treatments of this experimental variable. Subset analysis, as defined and illustrated here, can be useful in alleviating the problem.

Breast Neoplasms↗

PubMedDate not supplied

The effect of disease-prevalence adjustments on the accuracy of a logistic prediction model.

The accuracy of a logistic prediction model is degraded when it is transported to populations with outcome prevalences different from that of the population used to derive the model. The resultant errors can have major clinical implications. Accordingly, the authors developed a logistic prediction model with respect to the noninvasive diagnosis of coronary disease based on 1,824 patients who underwent exercise testing and coronary angiography, varied the prevalence of disease in various "test" populations by random sampling of the original "derivation" population, and determined the accuracy of the logistic prediction model before and after the application of a mathematical algorithm designed to adjust only for these differences in prevalence. The accuracy of each prediction model was quantified in terms of receiver operating characteristic (ROC) curve area (discrimination) and chi-square goodness-of-fit (calibration). As the prevalence of the test population diverged from the prevalence of the derivation population, discrimination improved (ROC-curve areas increased from 0.82 +/- 0.02 to 0.87 +/- 0.03; p < 0.05), and calibration deteriorated (chi-square goodness-of-fit statistics increased from 9 to 154; p < 0.05). Following adjustment of the logistic intercept for differences in prevalence, discrimination was unchanged and calibration improved (maximum chi-square goodness-of-fit fell from 154 to 16). When the adjusted algorithm was applied to three geographically remote populations with prevalences that differed from that of the derivation population, calibration improved 87%, while discrimination fell by 1%. Thus, prevalence differences produce statistically significant and potentially clinically important errors in the accuracy of logistic prediction models. These errors can potentially be mitigated by use of a relatively simple mathematical correction algorithm.

Adult↗