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At least 811 records · Page 45Linked to original sources
PubMed2006

Estimating 3D joint kinematics from video sequences of running and cutting maneuvers--assessing the accuracy of simple visual inspection.

Videos of sports injuries can potentially provide valuable information on non-contact ACL injuries. However, only the un-validated simple visual inspection approach has, so far, been used. Therefore, the purpose of this study was to test the accuracy and precision of researchers in estimating kinematics from video sequences of situations that typically lead to ACL injuries. We also tested if accuracy and precision could be improved through a training program. Using a routine surface marker based infrared, 240 Hz, 3D motion analysis system, we recorded running and cutting trials from three test subjects. Six observers were asked to provide estimates of kinematic variables from 27 video composites from one, two or three ordinary cameras, systematically varying viewing angles and time point of analysis. The observers thereafter went through a training program where 35 similar composites were analyzed, and feedback on the kinematics, as measured by the 3D motion analysis system, was provided on a group basis. Finally, the test was repeated to assess accuracy and precision. The mean error for knee flexion was -19 degrees, indicating a consistent underestimation. Hip flexion was underestimated by 7 degrees, but the standard deviation between the observers was 18 degrees on average, indicating poor consistency. Substantial errors were also found in the accuracy and precision of the other estimates. Only small group effects were seen from our training program. Based on these findings, results from studies using a simple visual inspection approach to describe joint motion must be interpreted with caution.

Adult↗
PubMed2006

Accuracy of high-resolution chromoendoscopy in prediction of histologic findings in diminutive lesions of the rectosigmoid.

BACKGROUND: The ability to differentiate adenomatous from nonadenomatous colonic polyps by using chromoendoscopy would obviate the need to remove hyperplastic lesions. The aim of this study was to define the accuracy of high-resolution chromoendoscopy for the determination of colonic polyp histology. METHODS: In 158 patients, 273 polyps (<5 mm) in the rectosigmoid were estimated for their histology. The endoscopists, in two steps, predicted the histopathology of each lesion on the basis of its surface characteristics by using high-resolution colonoscope without any staining and after indigo carmine dye according to the Kudo classification. RESULTS: The resected polyps included 48 adenomatous and 225 nonadenomatous polyps. When histologically confirmed hyperplastic polyps were compared with adenomatous polyps, the prediction of hyperplastic polyps based on endoscopic findings had a sensitivity of 93%, a specificity of 60%, and an overall accuracy of 81%. The corresponding sensitivity, specificity, and overall accuracy after indigo carmine dye were 94%, 64%, and 83%, respectively. CONCLUSIONS: The results suggest that the chromoendoscopy only marginally improves the determination between hyperplastic and adenomatous polyps when using high-resolution colonoscopes. The overall accuracy rate increased after dyeing, from 81% to 83%. The omission of histopathologic analysis cannot yet be achieved by chromoendoscopy.

Adenoma↗
PubMed2005

A retrospective biopsy study of the clinical diagnostic accuracy of common skin diseases by different specialties compared with dermatology.

BACKGROUND: With the recent trend for nondermatologists to treat dermatologic disorders, this retrospective biopsy study reviews the accuracy of the clinical diagnosis of physicians of different specialties performing surgical dermatologic procedures. OBJECTIVE: We assessed the diagnostic abilities of nondermatologist physicians who performed various types of skin biopsies and compared them with those of dermatologists. METHODS: The clinical diagnoses of family physicians, plastic, general, and orthopedic surgeons, and internists and pediatricians versus dermatologists were correlated with the histopathologic diagnoses. In total, 4451 cases were analyzed. RESULTS: Dermatologists diagnosed twice the number of neoplastic and cystic skin lesions correctly (75%) than nondermatologists (40%). The clinical diagnosis rendered by family practitioners matched the histopathologic diagnosis in only 26% of neoplastic and cystic skin lesions. Plastic surgeons, who performed the largest number of cutaneous surgical procedures among the nondermatologists, did better in the recognition of skin tumors than family physicians, but still had a diagnostic accuracy rate of only 45%. Inflammatory skin diseases were correctly diagnosed in 71% of the cases by dermatologists but in only 34% of the cases by nondermatologists. LIMITATIONS: A limitation of this retrospective, unblinded study is the use of the clinical data from the pathology requisition form as a surrogate for clinical diagnostic accuracy. CONCLUSIONS: The overall accuracy of the clinical diagnosis depends heavily on the clinicopathologic correlation. Without sufficient clinical data, the histopathologic diagnosis will be limited or restricted. This review concludes that without basic dermatology knowledge, clinicopathologic correlation is compromised.

Biopsy↗
PubMed2005

Evaluation of the accuracy of gadolinium-enhanced cardiovascular magnetic resonance in the diagnosis of cardiac sarcoidosis.

OBJECTIVES: This study analyzed the accuracy of gadolinium-enhanced cardiovascular magnetic resonance (CMR) for the diagnosis of cardiac sarcoidosis (CS). BACKGROUND: The diagnosis of CS was made according to the guidelines of the Japanese Ministry of Health and Welfare (1993); CMR has not been incorporated into the guidelines, and the diagnostic accuracy of CMR for the diagnosis of CS has not yet been evaluated. METHODS: We performed an analysis of 12-lead electrocardiograms (ECGs), 24-h ambulatory ECGs, echocardiograms, thallium scintigrams, and gadolinium-enhanced CMR studies in 58 biopsy-proven pulmonary sarcoidosis patients assessed for CS. The diagnostic accuracy of CMR for CS was determined using modified Japanese guidelines as the gold standard. RESULTS: The diagnosis of CS was made in 12 of 58 patients (21%); CMR revealed late gadolinium enhancement (LGE), mostly involving basal and lateral segments (73%), in 19 patients. In 8 of the 19 patients, scintigraphy was normal, while patchy LGE was present. The sensitivity and specificity of CMR were 100% (95% confidence interval, 78% to 100%) and 78% (95% confidence interval, 64% to 89%), and the positive and negative predictive values were 55% and 100%, respectively, with an overall accuracy of 83%. CONCLUSIONS: In patients with sarcoidosis, CMR is a useful diagnostic tool to determine cardiac involvement. New diagnostic guidelines should include CMR.

Adult↗
PubMed2004

Accuracy of dietary recall using the USDA five-step multiple-pass method in men: an observational validation study.

OBJECTIVE: This observational validation study was conducted under controlled conditions to test the accuracy of dietary recall in normal weight, overweight, and obese men using the USDA five-step multiple-pass method for dietary recall. DESIGN: Cross-sectional analysis of actual and recalled intake of food during 1 day. SUBJECTS/SETTING: Forty-two men ranging in age from 21 to 65 years and in body mass index from 21 to 39 kg/m(2) who lived in the metropolitan Washington DC area were studied. INTERVENTION: The subjects selected and consumed all meals and snacks, for 1 day, from a wide variety of foods provided at a human study facility. MAIN OUTCOME MEASURES: Actual and recalled energy, protein, carbohydrate, and fat intakes were determined by direct observation and by a 24-hour dietary recall, respectively. Dietary recall was determined via telephone administration of the USDA five-step multiple-pass method the following day. STATISTICAL ANALYSES PERFORMED: Analysis of variance and covariance tested the overall accuracy of recall and the effect of body mass index on dietary recall. Bland-Altman plots were used to assess bias in recall of food intake. RESULTS: In this population of men, there were no significant differences between actual and recalled intakes of energy (3,294+/-111 and 3,541+/-124 kcal/day), protein (117+/-5 and 126+/-5 g/day), carbohydrate (414+/-16 and 449+/-16 g/day), or fat (136+/-7 and 146+/-8 g/day), respectively. Accuracy of recall was not related to body mass index in that the obese men recalled food intake as accurately as the nonobese men. The energy intake of these men was significantly correlated (r=0.57, P<.05) with their estimated energy requirements. Significant interindividual variation in accuracy of recall was found. CONCLUSIONS: Under controlled conditions, the USDA five-step multiple-pass method can accurately assess intakes of energy, protein, carbohydrate, and fat in a population of men regardless of their body mass index. Researchers and clinical dietitians need to continue to examine factors that influence underreporting and overreporting of food intake by the multiple-pass 24-hour recall method.

Adult↗
PubMed2006

Dietary restraint and disinhibition do not affect accuracy of 24-hour recall in a multiethnic population.

Some psychological predictors of eating behaviors have been shown to affect usefulness of methods for dietary assessment. Therefore, this study was conducted to determine the association of dietary restraint and disinhibition with dietary recall accuracy for total energy, fat, carbohydrate, and protein. In a cross-sectional study, data were obtained from 79 male and 71 female non-Hispanic whites and African-American volunteers. Participants selected and consumed all foods for a 1-day period under observation and actual intake was determined. The following day, each participant completed a telephone 24-hour recall using the US Department of Agriculture Multiple-Pass method to obtain recalled intake. The Eating Inventory, which measures dietary restraint and disinhibition, was administered prior to eating any food in the study. Repeated measures analyses of variance were used to determine if dietary restraint or disinhibition were independent predictors of recall accuracy. The mean (+/-standard deviation) age and body mass index of the participants was 43+/-12 years and 29+/-5.5 (calculated as kg/m2), respectively. On average, men overreported intake of energy by 265 kcal and women by 250 kcal; both groups also overreported intake of protein, carbohydrate, and fat. When controlling for body mass index, sex, and race, restraint was a significant independent predictor of energy intake (P=0.004) and negatively correlated with energy intake (r=-0.23, P<0.001). Unlike intake of carbohydrate or protein, fat intake was significantly and negatively associated with dietary restraint (P<0.001; r=-0.3). Dietary restraint did not affect accuracy of recall of intake of energy, fat, carbohydrate, or protein, but was significantly associated with intake of energy and fat. Disinhibition was not related to intake or accuracy. Dietetics professionals should consider dietary restraint a possible reason for a lower than expected estimate of energy intake when using 24-hour recalls.

Adult↗
PubMed2004

Accuracy of selective sentinel lymphadenectomy after neoadjuvant chemotherapy: effect of clinical node status at presentation.

BACKGROUND: Both neoadjuvant chemotherapy and selective sentinel lymphadenectomy (SSL) are increasingly being used in treating primary breast cancer. It is important to determine whether SSL can be used after neoadjuvant chemotherapy and whether clinical node status at presentation affects accuracy of SSL. STUDY DESIGN: Between 1995 and 2003, 53 evaluable cases of invasive breast cancer were treated with neoadjuvant chemotherapy followed by SSL and completion axillary node dissection. The accuracy of SSL and the number of failed SSLs were assessed in the entire group and in the subset that were clinically node positive at presentation. RESULTS: The sensitivity of SSL was 96%, the negative predictive value was 96%, and the sentinel node identification rate was 94%. Of the 53 evaluable patients, 23 had clinically node-positive disease at presentation (43%) and the remainder were clinically node negative (57%). Of the successfully completed SSL, the status of the sentinel lymph node corresponded to that of overall axillary status in 49 of 50 patients (accuracy rate 98%). Two of the 23 patients with clinically node-positive disease at presentation had unsuccessful SSL. Of the remaining 21 patients with a clinically positive axilla before systemic therapy, a false-negative SSL result occurred in 1 patient (accuracy 95%, sensitivity 91%). CONCLUSIONS: Selective sentinel lymphadenectomy after neoadjuvant chemotherapy is both feasible and accurate. Although early reports found a lower performance of SSL after neoadjuvant chemotherapy, this study suggests reevaluation of the current practice of full axillary lymph node dissection in this setting, particularly in those patients who are clinically node negative at presentation.

Axilla↗
PubMed2005

The performance of tests of publication bias and other sample size effects in systematic reviews of diagnostic test accuracy was assessed.

BACKGROUND AND OBJECTIVE: Publication bias and other sample size effects are issues for meta-analyses of test accuracy, as for randomized trials. We investigate limitations of standard funnel plots and tests when applied to meta-analyses of test accuracy and look for improved methods. METHODS: Type I and type II error rates for existing and alternative tests of sample size effects were estimated and compared in simulated meta-analyses of test accuracy. RESULTS: Type I error rates for the Begg, Egger, and Macaskill tests are inflated for typical diagnostic odds ratios (DOR), when disease prevalence differs from 50% and when thresholds favor sensitivity over specificity or vice versa. Regression and correlation tests based on functions of effective sample size are valid, if occasionally conservative, tests for sample size effects. Empirical evidence suggests that they have adequate power to be useful tests. When DORs are heterogeneous, however, all tests of funnel plot asymmetry have low power. CONCLUSION: Existing tests that use standard errors of odds ratios are likely to be seriously misleading if applied to meta-analyses of test accuracy. The effective sample size funnel plot and associated regression test of asymmetry should be used to detect publication bias and other sample size related effects.

Diagnostic Errors↗
PubMed2006

New methods give better estimates of changes in diagnostic accuracy when prior information is provided.

OBJECTIVE: Whether tests such as imaging should be read with or without access to prior clinical information is controversial. Naïve comparisons may suggest that the provision of prior information improves test accuracy, whereas in fact the opposite may be true. This is because provision of clinical background may actually bias test readers to over- or underinterpret relevant test findings, and they may suboptimally integrate the previous and current evidence. We propose comparing the combined accuracy of prior information and a test read (i) with or (ii) without knowledge of prior information. Analysis methods include simple decision rules and logistic regression. STUDY DESIGN AND SETTING: A study of cancer detection in women presenting with breast symptoms, in whom ultrasound could be read with or without reviewing prior mammography. RESULTS: Naïve analysis gave an area under the receiver operating characteristics curve (AUC) for ultrasound read with mammography on view that was 4.6% higher (P < .01) than without mammography on view. Our approach, comparing the combined accuracy of mammography and ultrasound read i) with and ii) without knowledge of mammographic findings, showed much smaller differences. CONCLUSION: Our approach is more appropriate than naïve analyses. The particular choice of analytic method depends on the study size and the diagnostic accuracy of combinations of the prior information and the test reading.

Adult↗
PubMed2006

Recurrent events counted in evaluations of predictive accuracy.

OBJECTIVES: To describe an alternate approach for the calculation of sensitivity and specificity when analyzing the accuracy of screening tools, which can be used when standard calculations may be inappropriate. Sensitivity(ER) (ER denoting event rate) is the number of events correctly predicted, divided by the total number of events. Specificity(ER) is the amount of time that study participants are predicted to be event negative, divided by the total amount of participant observed time. Variance estimates for these statistics are constructed by bootstrap resampling, taking into account event dependence. METHODS: Standard and alternate approaches for calculating sensitivity and specificity were applied to hospital falls risk screening tool data. In this application, the outcome of interest was a recurrent event, there were multiple applications of the screening tool, delays in screening tool completion, and patients' follow-up durations were unequal. RESULTS: Application of sensitivity(ER) and specificity(ER) to this data not only provided a clearer description of the screening tool's overall accuracy, but also allowed examination of accuracy over time, accuracy in predicting specific event numbers, and evaluation of the added value that screening tool reapplications may have. CONCLUSION: Sensitivity(ER) and specificity(ER) provide a valuable approach to screening tool evaluation in the clinical setting.

Accidental Falls↗
PubMed2026

Clinical accuracy and short-term outcomes of intraoral photogrammetry for complete-arch implant rehabilitation: A retrospective multicentre study on 35 patients.

OBJECTIVES: To evaluate the clinical accuracy and short-term outcomes of complete-arch implant-supported fixed dental prostheses (ISFDPs) fabricated using an intraoral photogrammetry (IPG) based digital workflow in completely edentulous patients. METHODS: This multicenter retrospective clinical study included 35 patients rehabilitated with 52 complete-arch ISFDPs (10 FP1, 18 FP2 and 24 FP3 restorations) supported by 221 implants. All definitive prostheses were designed and fabricated using a fully digital workflow initiated by IPG acquisition with the Aoralscan Elite IPG&#xae; (SHINING 3D). The primary outcome was clinical accuracy, assessed at definitive prosthesis delivery through evaluation of passive fit using the Sheffield test and radiographic verification. Secondary outcomes included biologic and prosthetic complications, as well as implant and prosthesis survival rates during the follow-up. RESULTS: Passive fit was achieved in all definitive restorations (100%). Radiographic evaluation confirmed accurate marginal adaptation at the implant-prosthesis interface in all cases. No statistically significant differences in clinical accuracy were observed according to treated arch, number of supporting implants, or prosthetic design (P > .05). During a mean follow-up period of 12.1 &#xb1; 3.5 months, biologic and prosthetic complications were limited and generally minor. Implant survival was 99.5%, and prosthesis survival was 100%. CONCLUSIONS: Within the limitations of this retrospective clinical study, the IPG based workflow demonstrated high clinical accuracy and predictable short-term outcomes for complete-arch implant rehabilitation, consistently enabling passive fit and favorable prosthetic performance. CLINICAL RELEVANCE: IPG may represent a clinically reliable and predictable approach for complete-arch digital implant impression acquisition. The high rates of passive fit, together with the low incidence of biologic and prosthetic complications observed in this multicenter clinical study, support the use of IPG based workflows for the fabrication of complete-arch ISFDPs.

Humans↗
PubMed2004

Accuracy and stability of temperature probes for intracranial application.

Intracranial temperature measurement may play a pivotal role for prognosis and treatment of neurological and neurosurgical patients. For reliable clinical application, accurate temperature readings are therefore necessary. We present an independent in vitro study investigating the accuracy and stability of three temperature probes. Eight Neurovent-P Temp (RN), eight Licox temperature sensors (LT) and eight Neurotrend sensors (NT) were placed into a water bath. The temperature was increased in 3 degrees C increments from 30 to 42 degrees C before (accuracy test day 0) and after (accuracy test day 5) a long-term stability test run at 37 +/- 0.2 degrees C. The accuracy tests revealed deviations of <0.25, <0.2 and >0.4 degrees C for the RN, NT and LT probes, respectively, when compared to the reference measurement by a precision Pt100 temperature measuring instrument. All sensor types showed stable readings over the course of 120 h. The high variability of LT probes was due to a malfunctioning Licox monitor. Excluding these values reduced deviation below 0.21 degrees C the standard deviation at each temperature step was below +/-0.08 (RN, NT) and +/-0.12 (LT), laying within the range provided by the manufacturer (RN, NT: +/-0.1; LT: +/-0.2). In general, RN, NT and LT temperature measurement is reliable, but malfunctioning parts may lead to false interpretation of temperature readings. Therefore, validation of temperature probes to a reference temperature prior to clinical use is recommended.

Body Temperature↗
PubMed2005

Considerations in measuring cartilage thickness using MRI: factors influencing reproducibility and accuracy.

OBJECTIVE: The primary goal of this study was to describe and evaluate conditions that could influence the precision and accuracy of measuring in vivo cartilage thickness in the weight bearing regions of the knee from magnetic resonance imaging (MRI). DESIGN: Three-dimensional (3D) models of the femoral cartilage were created from segmented MR images. The weight bearing regions on femoral cartilage were selected for the portion of the tibiofemoral joint that sustains contact during walking. Six regions of interest (three on each condyle) were located on the femur. Average cartilage thickness was calculated over each region. The sensitivity of the precision of the measurements to observer variability was evaluated using intra- and inter-observer reproducibility tests of cartilage thickness measurements from the MRI-derived 3D models. In addition, the quantitative influence of a rule-based protocol for segmentation was evaluated using the inter-observer reproducibility protocol. Accuracy tests were conducted on porcine knees by comparing 3D models from MR images and laser scans across weight bearing and non-weight bearing regions. RESULTS: The precision was substantially better for the intra-observer tests (Coefficient of variation (CV) = 1-3%) than the inter-observer tests. Adding a rule-based protocol reduced variability in inter-observer tests substantially (CV = 6.6% vs 8.3%). Accuracy tests showed that the central and weight bearing regions on each condyle were more accurate than boundary and non-weight bearing regions. In addition, these results indicate that care should be taken when determining cartilage thickness of weight bearing regions with cartilage degenerations, since the thickness of thinner cartilage can be systematically overestimated in MR images. CONCLUSIONS: A rule-based approach can substantially increase inter-observer reproducibility when measuring cartilage thickness from multiple observers. This improvement in inter-observer reproducibility could be an important consideration for longitudinal studies of disease progression. In quantifying cartilage thickness, central and weight bearing regions on each condyle can provide more accurate measurement than boundary and non-weight bearing regions with average accuracy of +/-0.2-0.3 mm. An important finding of this study was that the weight bearing regions, which are usually of the greatest clinical interest, were measured most accurately by sagittal plane imaging.

Cartilage, Articular↗
PubMed2006

Kinematic patterns associated with accuracy of the drop punt kick in Australian Football.

Research into the kinematics of movement associated with the accuracy of the drop punt kick in Australian Football has been limited. The aim of this study was to examine pelvic and lower limb kinematics during the performance of a drop punt kick, in order to identify factors associated with accurate kicking performance. Ten professional Australian Football League (AFL) players performed 20 drop punt kicks towards a target situated 15m away, using their preferred leg. A three-dimensional motion analysis system was used to record the kicking motion from heel contact of the support limb through to ball contact. The subjects were divided into an accurate group (> or =50% accuracy; n=5) and an inaccurate group (<50% accuracy; n=5) based on target hit rate. Kinematic profiles for both kicking and support limbs were compared between the two groups. Results showed that the accurate group had significantly greater hip flexion in both limbs and greater knee flexion in the support limb throughout the kicking movement. The accurate group also had significantly greater anterior pelvic tilt at heel contact (accurate 20.8 degrees ; inaccurate 12.7 degrees ). These data show that kinematic differences in lower limb joint angles may be related to kicking accuracy.

Adult↗
PubMed2006

Magnetic resonance imaging accuracy for the diagnosis of superior labrum anterior-posterior lesions in the community setting: eighty-three arthroscopically confirmed cases.

Magnetic resonance imaging (MRI) has been shown in the literature to have high accuracy for the diagnosis of superior labrum anterior-to-posterior (SLAP) lesions. However, these studies have been performed at specialized institutions and have not been evaluated for community settings. Our hypothesis was that MRI diagnosis of SLAP lesions in the community setting is not as accurate as suggested by previous literature. The MRI reports for 83 consecutive surgically confirmed type II SLAP lesions were evaluated. The findings regarding the presence of SLAP lesions were documented from the community radiologists' MRI readings. Two blinded, fellowship-trained musculoskeletal radiologists evaluated these same 83 MRIs, as well as 17 MRIs with surgically confirmed normal superior labra. The musculoskeletal radiologists also used a visual analog scale to subjectively grade the quality of each MRI. MRIs were performed at 14 different centers and were read by 28 different community radiologists. There were 37 noncontrast MRIs and 46 MRI arthrograms. The community radiologists accurately identified 51% of the SLAP lesions. The sensitivities for the community radiologists were significantly better for the MRI arthrograms than for the noncontrast MRIs (P = .0002). For the two musculoskeletal radiologists, the sensitivities were 60% and 67.5%, and the specificities were 71% and 76.5%. The accuracies for the musculoskeletal radiologists were 62% and 69%. One of the musculoskeletal radiologists had significant correlation between the visual analog score and MRI diagnostic accuracy (P = .0006). The sensitivity for one of the musculoskeletal radiologists was significantly greater than the sensitivity for the community radiologists (P = .0063). The accuracies between the other musculoskeletal radiologist and the community radiologists were not significantly different (P = .0577). In this community setting, MRI was not accurate for the diagnosis of SLAP lesions. Musculoskeletal radiologists were more accurate than the community radiologists; however, the musculoskeletal radiologists were not as accurate as previous literature might predict.

Arthroscopy↗
PubMed2005

Inference of signaling and gene regulatory networks by steady-state perturbation experiments: structure and accuracy.

One of the fundamental problems of cell biology is the understanding of complex regulatory networks. Such networks are ubiquitous in cells and knowledge of their properties is essential for the understanding of cellular behavior. In earlier work (Kholodenko et al. (PNAS 99: 12841), it was shown how the structure of biological networks can be quantified from experimental measurements of steady-state concentrations of key intermediates as a result of perturbations using a simple algorithm called "unravelling". Here, we study the effect of experimental uncertainty on the accuracy of the inferred structure (i.e. whether interactions are excitatory or inhibitory) of the networks determined using the unravelling algorithm. We show that the accuracy of the network structure depends not only on the noise level but on the strength of the interactions within the network. In particular, both very small and very large values of the connection strengths lead to large uncertainty in the inferred network. We describe a powerful geometric tool for the intuitive understanding of the effect of experimental error on the qualitative accuracy of the inferred network. In addition, we show that the use of additional data beyond that needed to minimally constrain the network not only improves the accuracy of the inferred network, but also may allow the detection of situations in which the initial assumptions of unravelling with respect to the network and the perturbations have been violated. Our ideas are illustrated using the mitogen-activated protein kinase (MAPK) signaling network as an example.

Algorithms↗
PubMed2004

Gene expression profiling in mitochondrial disease: assessment of microarray accuracy by high-throughput Q-PCR.

Mitochondrial diseases are a heterogeneous array of disorders with a complex etiology. Use of microarrays as a tool to investigate complex human disease is increasingly common, however, a principle drawback of microarrays is their limited dynamic range, due to the poor quantification of weak signals. Although it is generally understood that low-intensity microarray 'spots' may be unreliable, there exists little documentation of their accuracy. Quantitative PCR (Q-PCR) is frequently used to validate microarray data, yet few Q-PCR validation studies have focused on the accuracy of low-intensity microarray signals. Hence, we have used Q-PCR to systematically assess microarray accuracy as a function of signal strength in a mouse model of mitochondrial disease, the superoxide dismutase 2 (SOD2) nullizygous mouse. We have focused on a unique category of data--spots with only one weak signal in a two-dye comparative hybridization--and show that such 'high-low' signal intensities are common for differentially expressed genes. This category of differential expression may be more important in mitochondrial disease in which there are often mosaic expression patterns due to the idiosyncratic distribution of mutant mtDNA in heteroplasmic individuals. Using RNA from the SOD2 mouse, we found that when spotted cDNA microarray data are filtered for quality (low variance between many technical replicates) and spot intensity (above a negative control threshold in both channels), there is an excellent quantitative concordance with Q-PCR (R2 = 0.94). The accuracy of gene expression ratios from low-intensity spots (R2 = 0.27) and 'high-low' spots (R2 = 0.32) is considerably lower. Our results should serve as guidelines for microarray interpretation and the selection of genes for validation in mitochondrial disorders.

Journal Article↗
PubMed2005

Cortical reconstruction using implicit surface evolution: accuracy and precision analysis.

Two different studies were conducted to assess the accuracy and precision of an algorithm developed for automatic reconstruction of the cerebral cortex from T1-weighted magnetic resonance (MR) brain images. Repeated scans of three different brains were used to quantify the precision of the algorithm, and manually selected landmarks on different sulcal regions throughout the cortex were used to analyze the accuracy of the three reconstructed surfaces: inner, central, and pial. We conclude that the algorithm can find these surfaces in a robust fashion and with subvoxel accuracy, typically with an accuracy of one third of a voxel, although this varies with brain region and cortical geometry. Parameters were adjusted on the basis of this analysis in order to improve the algorithm's overall performance.

Algorithms↗