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At least 73 records · Page 4Linked to original sources
PubMed2000

Factors influencing the application accuracy of neuronavigation systems.

OBJECTIVE: The overall accuracy of neuronavigation systems may be influenced by (1) the technical accuracy, (2) the registration process, (3) voxel size and/or distortion of image data and (4) intraoperative events. The aim of this study was to test the influence of the registration and imaging modality on the accuracy. METHODS: A plexiglas phantom with 32 rods was taken for navigation targeting. Sixteen fiducials were attached to the surface of the phantom forming two different attachment patterns (clustered vs. diffusely scattered). This model was scanned by MRI and CT (1-mm slices). Registration was performed using different numbers and attachment patterns of the fiducials. Using CT or MRI, the localization error was measured in image space as the Euclidean distance between targets defined in image space and those detected in the physical space. Accuracy was measured with two commercial systems, the Zeiss MKM and the StealthStation. RESULTS: The mean localization error varied between 1.59 +/- 0.29 mm (MKM, 8 scattered fiducials, CT scanning) and 3.86 +/- 2.19 mm (MKM, 4 clustered fiducials, MRI). The worst localization error was 9.5 mm (MKM). In case of an optimal registration, the 95th percentile for the localization error was 2.2 (MKM) and 2.75 mm (StealthStation). The imaging modality has only minor influence on the localization error, with CT increasing accuracy minimally. Both the fiducial number and the attachment pattern critically influence the localization error: 8 fiducials and a generalized attachment pattern increase the accuracy significantly. No correlation between the calculated registration accuracy and the measured localization accuracy was found. CONCLUSION: The application accuracy of different neuronavigation systems critically depends on the registration. The calculated registration accuracy provided by the system does not correspond to the localization error found in reality. The accuracy of frameless neuronavigation systems is comparable to that of classical frame-based stereotactic devices.

Magnetic Resonance Imaging↗
PubMed1995

Diagnostic accuracy and short-term surgical outcomes in cases of suspected acute appendicitis.

OBJECTIVE: To test the hypothesis that, with modern diagnostic methods and antibiotics, more conservative use of surgery in cases of suspected appendicitis would not result in increased rates of short-term complications in confirmed cases. DESIGN: Population-based observational study using administrative data. SETTING: All Ontario hospitals in which primary appendectomy was performed from Apr. 1, 1981, to Mar. 31, 1992. PATIENTS: All 126,815 patients admitted to hospital for a primary appendectomy during the study period. OUTCOME MEASURES: Diagnostic accuracy rate (acute appendicitis as the primary diagnosis), perforation rate, in-hospital death rate and length of stay. RESULTS: The diagnostic accuracy rate among the male patients was stable throughout the decade; among the female patients it rose significantly, from 71.7% in 1981 to 75.3% in 1991 (p < 0.01). The perforation rates increased significantly among both the female and male patients (p < 0.01), whereas the mean length of stay decreased (p < 0.05). Despite sex-related differences in the accuracy rates, the male and female patients had similar in-hospital death rates and mean lengths of stay. The institutional diagnostic accuracy rates, as determined from data for 1989-90 to 1991-92, ranged from 50.0% to 96.7%. Multivariate analyses of 27,189 confirmed cases of appendicitis at 175 hospitals revealed that perforation was a strong predictor of in-hospital death (odds ratio [OR] 2.46, 95% confidence interval [CI] 1.24 to 4.88), but comorbidity was the strongest predictor (OR 11.50, 95% CI 5.96 to 22.10). For each 10% increase in the diagnostic accuracy rate, the perforation rate increased 14% (OR 1.14, 95% CI 1.10 to 1.19), but the accuracy rate was not significantly related to the in-hospital death rate or the length of stay. CONCLUSION: A higher diagnostic accuracy rate is associated with more perforated appendixes. Although perforation itself leads to adverse outcomes, a higher accuracy rate does not. This suggests that hospitals with higher accuracy rates incur more perforations, but, with close observation, timely laparotomy and the use of modern antibiotics, these patients have favourable outcomes. This contrasts with adverse effects of perforation among patients at high risk for perforation (especially very young children and elderly people) in centres at all accuracy levels. The variation in hospitals' diagnostic accuracy rates suggests that some proportion of appendectomies could be safely avoided.

Abdominal Pain↗
PubMed1996

[Accuracy of measurement and overestimation of CO2 of two capnometers intended for potential use in emergency medicine].

UNLABELLED: Capnometry, the noninvasive measurement of end-expiratory CO2 concentration (cCO2, vol%) or calculation of its respective partial pressure (pCO2; mmHg) is an established method. However, for prehospital settings, capnometry is still used very restrictively, mainly owing to the respective devices used. The prerequisite for their use is sufficient accuracy (+/-2 mmHg) and easy handling. Two special capnometers (STAT CAP. Nellcor: mainstream, semiquantitative estimation; Capnocheck 8200, BCI: sidestream, quantitative measurement, numeric display), developed recently for potential use in emergency medicine, are said to fit these criteria. Therefore, the objective of the present investigation was to assess the accuracy and precision of both devices, comparing methods under standardized in vitro (reference gases) and in vivo (intubated and ventilated patients) conditions. METHODS: Both devices ("STAT CAP": pCO2 range, light bars; "Capnocheck 8200") were evaluated regarding the accuracy of pCO2 (Capnocheck) and the precision of the CO2 range (STAT CAP). Tests were performed with four dry gas mixtures (STPD) of defined composition and during ventilation of 20 intubated patients (BTPS). All measurements were compared with the alveolar gas monitor "AGM 1304" (Brüel & Kjaer, Denmark) as a reference method with a proven +/- 1 mmHg accuracy of pCO2 measurement. RESULTS: The "Capnocheck" (BCI) presented an accuracy of the pregiven pCO2 of 0.7-1.4 mmHg (dry gas mixtures, STPD) and an overestimation of 0.2 +/- 4.1 mmHg (BTPS) during ventilation with pure oxygen; inaccuracy during ventilation with 70% N2O in O2 proved to be + 1.2 +/- 1.7 mmHg (BTPS). Nellcor's "STAT CAP" failed to reach the target value in 10% of analyses, as shown by the respective segment bar of the display. CONCLUSION: Evaluation of the accuracy of capnometers must focus on the necessary pH2O correction and the possible effects exercised by O2 (and N2O) as well as the possible dependence on barometric pressure (if pCO2, mmHg, is the desired value). The "Capnocheck" showed an accuracy of more than 2 mmHg in dry gas mixtures as well as in humidified air. Concerning the practical use during constant artificial ventilation, the digital display and accuracy of the sidestream capnometer allow for reliable conclusions on patients' ventilation and circulation (CO2 elimination). The 90% accuracy of the segment bar display of Nellcor's "STAT CAP", per se covering only a rather broad range of 20 mmHg, obviously does not provide more than a rough overview. Therefore, the STAT CAP cannot be recommended for prehospital capnometry in the field. However, both the accuracy of the BCI capnometer (Capnocheck) and its numeric display and easy handling strongly recommend this device also for clinical use.

Blood Gas Analysis↗
PubMed1995

Maintaining accuracy in stereotactic radiosurgery.

PURPOSE: To provide the manufacture's specification for the base phantom of a commercially available stereotactic radiosurgery system so that its accuracy can be confirmed, and to describe a calibration device that allows the accuracy of the base phantom to be verified quickly and on a routine basis. Modifications to the target pointer system that make matching the pointer tips easier and less likely to damage the pointer tips are also described. METHODS AND MATERIALS: In stereotactic radiosurgery, spatial accuracy is the key factor for successful dose delivery. With some commercially available systems, this accuracy depends on the accuracy of the base phantom coordinate system, how closely the tip of the target pointer can be matched to the tip of the base phantom pointer, and how accurately the coordinates set on the isocentric subsystem match those set on the base phantom. Two major problems, usually overlooked when evaluating system accuracy are, first, the base phantom, which establishes the stereotactic coordinate system, is assumed to be completely accurate. This is a dangerous assumption because the base phantom is used frequently for routine patient treatments and for standard quality assurance tests. To exacerbate the problem, no independent device is provided with stereotactic systems to check the accuracy of the base phantom. Second, the accuracy of the isocenter coordinates set on the head support stand depends upon how closely the target pointer and the base phantom pointer can be aligned. The hardware provided with the system is difficult to use and easily leads to damage of the pointer tips. RESULTS: In this work, we provide the manufacturer's specifications for a popular stereotactic system, describe a device that can be used to check quickly and easily the accuracy of the base phantom, and describe a modification to the transfer pointer system that allows the pointer tips to be more easily aligned with reduced possibility of damage to the pointer tips. CONCLUSION: The methods and apparatus described in this paper should be useful to anyone using a base phantom for testing radiosurgery accuracy.

Equipment Design↗
PubMed2006

A computer simulation analysis of the accuracy of partial genome sequencing and restriction fragment analysis in the reconstruction of phylogenetic relationships.

Partial genome sequencing (PGS) and restriction fragment analysis (RFA) are used frequently in molecular epidemiologic investigations. The relative accuracy of PGS and RFA in phylogenetic reconstruction has not been assessed. In this study, 32 model phylogenetic trees with 16 extant lineages were generated, for which DNA sequences were simulated under varying conditions of genome length, nucleotide substitution rate, and between-site substitution rate variation. Genotyping using PGS and RFA was simulated. The effect of tree structure (stemminess, imbalance, lineage variation) on the accuracy of phylogenetic reconstruction (topological and branch length similarity) was evaluated. Overall, PGS was more accurate than RFA. The accuracy of PGS increased with increasing sequence length. The accuracy of RFA increased with the number of restriction enzymes used. In fragment size comparison, the Dice and Nei-Li algorithms differed little, with both more accurate than the Fragment Size Distribution algorithm. For RFA, higher tree stemminess and longer genome length were associated with higher topological accuracy, whereas lower tree stemminess and lower substitution rates were associated with higher branch length accuracy. For PGS, lower tree imbalance was associated with higher topological accuracy, whereas lower tree stemminess, higher substitution rate, and lower between-site substitution rate variation were associated with higher branch length accuracy. RFA had higher topological accuracy than PGS only for the shortest sequence length (200 bps) at a low substitution rate, high tree stemminess, and long genome length. PGS had equal or higher accuracy in branch length reconstruction than RFA under all conditions investigated. Thus, partial genome sequencing is recommended over restriction fragment analysis for conditions within the parameter space examined.

Computational Biology↗
PubMedDate not supplied

Geometric accuracy of three-dimensional molecular overlays.

This study examines the dependence of molecular alignment accuracy on a variety of factors including the choice of molecular template, alignment method, conformational flexibility, and type of protein target. We used eight test systems for which X-ray data on 145 ligand-protein complexes were available. The use of X-ray structures allowed an unambiguous assignment of bioactive overlays for each compound set. The alignment accuracy depended on multiple factors and ranged from 6% for flexible overlays to 73% for X-ray rigid overlays, when the conformation of the template ligand came from X-ray structures. The dependence of the overlay accuracy on the choice of templates and molecules to be aligned was found to be the most significant factor in six and seven of the eight ligand-protein complex data sets, respectively. While finding little preference for the overlay method, we observed that the introduction of molecule flexibility resulted in a decrease of overlay accuracy in 50% of the cases. We derived rules to maximize the accuracy of alignment, leading to a more than 2-fold improvement in accuracy (from 19% to 48%). The rules also allowed the identification of compounds with a low (<5%) chance to be correctly aligned. Last, the accuracy of the alignment derived without any utilization of X-ray conformers varied from <1% for the human immunodeficiency virus data set to 53% for the trypsin data set. We found that the accuracy was directly proportional to the product of the overlay accuracy from the templates in their bioactive conformations and the chance of obtaining the correct bioactive conformation of the templates. This study generates a much needed benchmark for the expectations of molecular alignment accuracy and shows appropriate usages and best practices to maximize hypothesis generation success.

Models, Molecular↗
PubMed1997

Diagnostic accuracy of a rural live video telepathology system.

Accuracy of diagnoses rendered using a live video telepathology network was assessed for permanent sections of surgical pathology specimens. To determine accuracy, telepathology diagnoses were compared with those obtained by directly viewing the glass slide using a standard microscope. A total of 294 cases were read via both telepathology and glass slide by attending pathologists at a tertiary care medical center. Overall accuracy was defined as exact concordance between diagnoses. Clinically insignificant differences in diagnoses were excluded to determine clinically significant accuracy. For the 285 cases with complete data, the overall accuracy for telepathology was 0.912 (95% confidence interval [CI], 0.872-0.941), whereas the overall accuracy for glass slide readings was 0.968 (95% CI, 0.939-0.985). This difference is statistically significant (p = 0.009). When focusing on clinically significant discrepancies, where the difference in diagnosis might affect therapeutic decisions, the video accuracy was only slightly less than the glass slide accuracy (0.965 [95% CI, 0.934-0.982] vs. 0.982 [95% CI, 0.957-0.994], respectively), but this difference is not statistically significant (p = 0.302). Most of the cases with clinically significant differences involved lesions with inherently high interobserver variation. Certainty of diagnosis did not differ between video and glass slide readings (p = 0.911), but there was an association between certainty of diagnosis and diagnostic accuracy for video (p = 0.003 for clinically significant accuracies). Based on these findings, we recommend when using this telepathology system that only preliminary diagnoses should be given in the following situations: for diagnostic areas with known high interobserver variability; when the consultant has any degree of uncertainty about the presence or absence of the lesion in question; and when there is insufficient experience using telepathology as a diagnostic medium.

Crohn Disease↗
PubMed2003

An analysis of the accuracy of the CyberKnife: a robotic frameless stereotactic radiosurgical system.

OBJECTIVE: The use of stereotactic radiosurgical systems to treat intracranial and extracranial tumors and other lesions requires a high degree of accuracy in target identification and localization. The purpose of this study was to evaluate the total system accuracy of the CyberKnife (Accuray, Inc., Sunnyvale, CA), a frameless, image-guided, stereotactic radiosurgery system. METHODS: Clinically relevant accuracy or application accuracy of the CyberKnife radiosurgery system is based on 1) the beam delivery accuracy, which combines the robot and the camera image tracking system, and 2) target localization accuracy, which combines computed tomographic (CT) imaging and treatment planning. Clinically relevant accuracy can be measured by delivering a radiation dose to phantoms, in which the target is defined on a set of CT images using all components of the CyberKnife system, including the treatment planning software, the robot, the camera tracking system, and the linear accelerator. Clinically relevant accuracy was measured in head phantoms loaded with packs of radiochromic film. The accuracy measured is the displacement of the dose contours from the treatment plan to that measured in the radiosurgically exposed phantom. RESULTS: Measurements of mean errors of the second-generation CyberKnife system at Stanford University Medical Center, installed in 2001, ranged from 0.7 mm for a CT slice thickness of 0.625 mm to 1.97 mm for a CT slice thickness of 3.75 mm. CONCLUSION: The frameless, image-guided, second-generation CyberKnife radiosurgery system has a clinically relevant accuracy of 1.1 +/- 0.3 mm when CT slice thicknesses of 1.25 mm are used. CyberKnife precision is comparable to published localization errors in current frame-based radiosurgical systems.

Artifacts↗
PubMed2001

Accuracy requirements for image-guided spinal pedicle screw placement.

STUDY DESIGN: Accuracy requirement analysis for image-guided pedicle screw placement. OBJECTIVES: To derive theoretical accuracy requirements for image-guided spinal pedicle screw placement. SUMMARY OF BACKGROUND DATA: Underlying causes of inaccuracy in image-guided surgical systems and methods for quantifying this inaccuracy have been studied. However, accuracy requirements for specific spinal surgical procedures have not been delineated. In particular, the accuracy requirements for image-guided spinal pedicle screw placement have not been previously reported. METHODS: A geometric model was developed relating spinal pedicle anatomy to accuracy requirements for image-guided surgery. This model was used to derive error tolerances for pedicle screw placement when using clinically relevant screw diameters in the cervical (3.5 mm), thoracic (5.0 mm), and thoracolumbar spine (6.5 mm). The error tolerances were represented as the permissible rotational and translational deviations from the ideal screw trajectory that would avoid pedicle wall perforation. The relevant dimensions of the pedicle model were extracted from existing morphometric data. RESULTS: As anticipated, accuracy requirements were greatest at spinal levels where the relevant screw diameter approximated the dimensions of the pedicle. These requirements were highest for T5, followed in descending order by T4, T7, T6, T3, T12, L1, T8, T11, C4, L2, C3, T10, C5, T2, T9, C6, L3, C2, T1, C7, L4, and L5. Maximum permissible translational/rotational error tolerances ranged from 0.0 mm/0.0 degrees at T5 to 3.8 mm/12.7 degrees at L5. CONCLUSIONS: These results, obtained by mathematical analysis, demonstrate that extremely high accuracy is necessary to place pedicle screws at certain levels of the spine without perforating the pedicle wall. These accuracy requirements exceed the accuracy of current image-guided surgical systems, based on clinical utility errors reported in the literature. In actual use, however, these systems have been shown to improve the accuracy of pedicle screw placement. This dichotomy indicates that other factors, such as the surgeon's visual and tactile feedback, may be operative.

Biomechanical Phenomena↗
PubMed2006

Effect of written instructions on accuracy of self-reporting medication regimen in glaucoma patients.

PURPOSE: Our purpose was to evaluate the accuracy of self-reporting of the prescribed medication regimen in a glaucoma population, identify contributing factors, and assess the effect of written instructions. METHODS AND MATERIALS: All patients at an urban resident glaucoma clinic were offered participation in this prospective, case-controlled study. Two trained interviewers administered a confidential questionnaire consisting of six questions regarding the name and dosage of ophthalmic medications, education level, ability to read, and age. A verbatim response for each question was recorded on the questionnaire. At the end of the visit, patients were given a written chart describing their ophthalmic medications, frequency, and dosage. At their next scheduled visit, the same questionnaire was repeated. The patients' responses from both visits were compared with the regimen they were prescribed and with each other. This information was used to determine the accuracy of reporting medications. RESULTS: A total of 193 patients were enrolled in the study over a 10-month period; 164 patients completed both phases (85% completion rate). The study population consisted of 85 women and 79 men with a mean age of 68.40+/-11.6 years. Eighty-four patients had attained less than 12th grade education and 80 had completed high school. At the first visit, 66 patients (40%) showed less than 100% accuracy. Forty-nine of 84 (58%) patients who had not completed high school education showed less than 100% accuracy with a mean score of 65% (P=0.001), whereas 17 of 80 (21%) of patients who had completed high school showed less than 100% accuracy with a mean score of 87% (P=0.001). After written instruction, the accuracy of reporting improved by 23.36+/-30.8 percentile points in patients without completion of high school education and improved by 8.46+/-21.7 percentile points in patients who had completed high school (P<0.001). The mean number of ophthalmic medications prescribed was 2.10+/-0.93 (range 1 to 4). Patients on one medication had 100% accuracy in reporting 82% of the time, whereas those with four medications had 100% accuracy 21% of the time. Gender, age, and race of the patient were not correlated with the accuracy of self-reporting (P>0.05). CONCLUSION: The education level of the patient and the number of medications showed direct correlation with patients' ability to report medications accurately. Patients showed improvement in accuracy of reporting medications when given written instructions about their regimen, regardless of their level of education or number of medications.

Adult↗
PubMed2004

The use of "overall accuracy" to evaluate the validity of screening or diagnostic tests.

OBJECTIVE: Evaluations of screening or diagnostic tests sometimes incorporate measures of overall accuracy, diagnostic accuracy, or test efficiency. These terms refer to a single summary measurement calculated from 2 x 2 contingency tables that is the overall probability that a patient will be correctly classified by a screening or diagnostic test. We assessed the value of overall accuracy in studies of test validity, a topic that has not received adequate emphasis in the clinical literature. DESIGN: Guided by previous reports, we summarize the issues concerning the use of overall accuracy. To document its use in contemporary studies, a search was performed for test evaluation studies published in the clinical literature from 2000 to 2002 in which overall accuracy derived from a 2 x 2 contingency table was reported. MEASUREMENTS AND MAIN RESULTS: Overall accuracy is the weighted average of a test's sensitivity and specificity, where sensitivity is weighted by prevalence and specificity is weighted by the complement of prevalence. Overall accuracy becomes particularly problematic as a measure of validity as 1) the difference between sensitivity and specificity increases and/or 2) the prevalence deviates away from 50%. Both situations lead to an increasing deviation between overall accuracy and either sensitivity or specificity. A summary of results from published studies (N = 25) illustrated that the prevalence-dependent nature of overall accuracy has potentially negative consequences that can lead to a distorted impression of the validity of a screening or diagnostic test. CONCLUSIONS: Despite the intuitive appeal of overall accuracy as a single measure of test validity, its dependence on prevalence renders it inferior to the careful and balanced consideration of sensitivity and specificity.

Diagnostic Techniques and Procedures↗
PubMed2001

Accuracy evaluation of surface-based registration methods in a computer navigation system for hip surgery performed through a posterolateral approach.

OBJECTIVE: Many computer navigation systems have recently been developed for brain surgery, and the use of such systems in orthopedic surgery is increasing. Intraoperative registration of preoperative images is one of the most important steps in controlling the overall accuracy of computer navigation systems. Various parameters, such as CT-scan slice thickness, reconstruction pitch, intraoperative data sampling area, and data sampling volume, may affect the accuracy of registration. The purpose of this study was to evaluate the effect of the aforementioned parameters on the accuracy of registration for hip surgery performed through a posterolateral approach, and to find a clinically suitable trade-off between accuracy and surgical invasiveness. MATERIALS AND METHODS: One cadaveric pelvis and one cadaveric femur were used for this study. Four alumina ceramic balls with a diameter of 28 mm and within 1 micrometer of sphericity were attached to the pelvis, and three similar balls attached to the femur, to determine relative position. CT-scan images of the pelvis and femur were obtained with a helical scanner. Three sets of slice thickness and slice pitch were chosen for data acquisition, and two additional sets of reconstructed data were made. Bone contours were extracted by cutting out the surrounding substrate at a given CT number threshold, and surface models of the bone were made from the resultant data. The positions of the pelvis and femur were tracked by LED markers attached to the bone using an optical three-dimensional position sensor (OPTOTRAK). Registration of the computer models to the real objects was performed by measuring the position of a certain number of surface points on each object with an OPTOTRAK pen-probe. RESULTS AND CONCLUSION: Slice thickness and reconstruction pitch affected the accuracy of registration. As the sampling area was expanded from the periarticular area to the distant peripheral area, accuracy increased slightly. Accuracy did not increase when the whole area was used, but in fact decreased, especially in the femur. The positive effect of increasing the number of sampling points was saturated at 30 points when the surface of the periarticular area was sampled. The following trade-off between accuracy and invasiveness, in terms of various parameters of preoperative and intraoperative data, is proposed as clinically optimal: perform the CT scan with 3-mm slice thickness and 1-mm reconstruction pitch, and sample the periarticular area with 30 sampling points. With these parameters, the accuracy of registration was 1.2 mm and 0.9 degrees of bias with 0.7 mm and 0.3 degrees of RMS in the pelvis, and 1.4 mm and 0.6 degrees of bias with 1.3 mm and 0.3 degrees of RMS in the femur.

Cadaver↗
PubMed1993

Exploring the limits of precision and accuracy of protein structures determined by nuclear magnetic resonance spectroscopy.

The effects of the number, precision and accuracy of interproton distance restraints, of direct refinement against nuclear Overhauser enhancement (NOE) intensities and of the description of the non-bonded contacts on the precision and accuracy of a nuclear magnetic resonance (NMR) protein structure determination have been investigated. The model system employed is the 56 residue immunoglobulin G binding domain of streptococcal protein G. This choice was based on the availability of a very high resolution NMR structure (atomic root-mean-square distribution of the ensemble of 60 calculated structures about the mean co-ordinate positions of 0.25 A for the backbone atoms, 0.65 A for all atoms and 0.39 A for all atoms excluding disordered surface side-chains). The experimental NMR data set for this structure determination comprised a total of 1058 experimental restraints of which 854 were approximate interproton distance restraints corresponding to all the structurally useful NOEs observable for this protein. The calculations presented in this paper reveal the following. (1) The number of interproton distance restraints constitutes the single most important determinant of both precision and accuracy. The ensemble precision and accuracy improves significantly as the number of interproton distance restraints is increased to an average of approximately 15 per residue, of which approximately 60% involve unique proton pairs; subsequent additions of interproton distance restraints, however, lead to less dramatic improvements as information redundancy sets in. (2) The ratio of ensemble precision to ensemble accuracy (which ranges from 0.5 to 0.7 for the backbone atoms) is approximately independent both of the number, precision and accuracy of the interproton distance restraints, and of whether the structures are refined against interproton distance restraints or directly against NOE intensities. (3) In an ensemble of structures generated from a large number of loose approximate interproton distance restraints (an average of approximately 15 restraints per residue with approximately 60% involving unique proton pairs), the interproton distance vectors corresponding to the restraints are very well defined with approximately 80% of vectors between unique proton pairs having a standard deviation of < or = 0.1 A. (4) The accuracy of the mean co-ordinates of an ensemble of structures is significantly higher than the average accuracy of the individual structures comprising the ensemble. For an average ensemble precision of > or = 0.6 A, the dependence of the accuracy of the mean co-ordinates on ensemble precision is approximately linear.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding Sites↗
PubMed1999

A method for assessing the accuracy of intersubject registration of the human brain using anatomic landmarks.

Several groups have developed methods for registering an individual's 3D MRI by deforming a standard template. This achievement leads to many possibilities for segmentation and morphology that will impact nuclear medical research in areas such as activation and receptor studies. Accordingly, there is a need for methods that can assess the accuracy of intersubject registration. We have developed a method based on a set of 128 anatomic landmarks per hemisphere, both cortical and subcortical, that allows assessment of both global and local transformation accuracy. We applied our method to compare the accuracy of two standard methods of intersubject registration, AIR 3.0 with fifth-order polynomial warping and the Talairach stereotaxic transformation (Talairach and Tournoux, 1988). SPGR MRI's (256 x 256 x 160) of six normal subjects (age 18-24 years) were derformed to match a standard template volume. To assess registration accuracy the landmarks were located on both the template volume and the transformed volumes by an experienced neuroanatomist. The resulting list of coordinates was analyzed graphically and by ANOVA to compare the accuracy of the two methods and the results of the manual analysis. ANOVA performed over all 128 landmarks showed that the Woods method was more accurate than Talairach (left hemisphere F = 2.8, P < 0.001 and right hemisphere F =2.4, P < 0.006). The Woods method provided a better brain surface transformation than did Talairach (F = 18.0, P < 0.0001), but as expected there was a smaller difference for subcortical structures and both had an accuracy <1 mm for the majority of subcortical landmarks. Overall, both the Woods and Talairach method located about 70% of landmarks with an error of 3 mm or less. More striking differences were noted for landmark accuracy </=1 mm, where the Woods method located about 40% and Talairach about 23%. These results demonstrate that this anatomically based assessment method can help evaluate new methods of intersubject registration and should be a helpful tool in appreciating regional differences in accuracy. Consistent with expectation, we confirmed that the Woods nonlinear registration method was more accurate than Talairach. Landmark-based anatomic analyses of intersubject registration accuracy offer opportunities to explore the relationship among structure, function and architectonic boundaries in the human brain.

Adolescent↗
PubMed2000

Preoperative staging of rectal cancer with MRI: accuracy and clinical usefulness.

BACKGROUND: Preoperative staging is essential for planning of optimal therapy for patients with rectal cancer. Recently, magnetic resonance imaging (MRI) is used frequently because of its benefits of clear pelvic image are better than other diagnostic methods. The purpose of this study was to determine accuracy rates and clinical usefulness of MRI in preoperative staging of rectal cancer. METHODS: Between February, 1997, and December, 1999, 217 patients with histologically proven rectal cancer were staged preoperatively and had surgical resections performed. MRI criteria for depth of invasion was determined by the degree of disruption of the rectal wall. Metastatic perirectal lymph nodes were considered to be present if they showed heterogenous texture, irregular margin, and enlargement (>10 mm). RESULTS: The accuracy of the MRI for determining depth of invasion was 176/217 (81%) and regional lymph node invasion was 110/217 (63%). In the T stage, accuracy rate of T1 was 3/4 (75%), T2 was 20/37 (54%), T3 was 141/162 (87%), and T4 was 12/14 (86%), respectively. The specificity of lymph node invasion was 45/110 (41%) and the sensitivity was 91/107 (85%). The accuracy rate of regional lymph node involvement was 136/217 (63%). T1 and T2 were overstaged in 1/4 (25%) and 17/37 (46%), respectively, and T3 was understaged in 15/162 (9.2%). The accuracy rate to detect metastatic lateral pelvic lymph node was 4/14 (29%) after lateral pelvic lymph node dissection was done in 14 patients under MRI. The accuracy rate in assessing levator ani muscle tumor involvement was 8/11 (72%). CONCLUSIONS: MRI showed a good, comparable accuracy rate for determining depth of tumor invasion, compared with transrectal ultrasonography, which still has a low accuracy rate for detecting metastatic lymph node. MRI with endorectal coil may increase the accuracy rate of T1 and T2 lesions. In addition, clear sagittal and coronal sectional pelvic images can give a lot of information about adjacent organ invasion or any invasion of levator ani muscle. MRI can be useful for choosing an appropriate extent of lymph node dissection and type of surgery.

Adult↗
PubMedDate not supplied

Lower accuracy of TI-201 SPECT in women is not improved by size-based normal databases or Wiener filtering.

BACKGROUND: We have shown that the diagnostic accuracy of quantitative single photon emission computed tomography (SPECT) thallium 201 myocardial perfusion imaging is lower in women than in men and that much of the difference can be explained by the smaller size of the left ventricle in women. Therefore attempts at improving the accuracy of myocardial perfusion imaging in women should focus on the problem of lower accuracy in patients with small chamber size. We evaluated two strategies for this: size- and gender-based normal databases and inverse filtering with the Wiener filter. METHODS AND RESULTS: We identified 618 patients undergoing exercise SPECT TI-201 who either had a low pre-test probability of coronary artery disease or had catheterization-documented disease. Their images were analyzed on the basis of gender and chamber size: both gender and size- and gender-based normal databases were created. The studies were analyzed quantitatively, and the accuracy was evaluated by use of the area under the receiver operating characteristic (ROC) curve. Chamber size was significantly lower in women (size index 69+/-22 women vs 96+/-28 men; P < .0001). The accuracy of myocardial perfusion imaging was lower in women compared with men (ROC area: 0.92+/-0.01 men vs 0.85+/-0.03 women; P = .03), and there was an even greater difference in accuracy between patients with large versus small chamber size (ROC area: 0.94+/-0.01 large vs 0.81+/-0.03 small; P < .001). There was no improvement in the diagnostic accuracy either in women or in patients with small chamber size when a size- and gender-based normal database, Wiener filter, or the Wiener filter with a size- and gender-based normal database was used. CONCLUSION: The left ventricular chamber size in women is smaller than that in men. There is a significant difference in the accuracy of quantitative SPECT TI-201 between men and women and an even greater difference between patients with large versus small chamber size. Neither size- and gender-based databases nor Wiener filtering significantly improves accuracy in women or in patients with small chamber size.

Aged↗
PubMed2004

Accuracy of radiographic and radiostereometric wear measurement of different hip prostheses: an experimental study.

BACKGROUND: In vivo measurement of wear in the ball and socket articulation of total hip arthroplasties is of interest in the evaluation of both existing and new implants. Controversy reigns regarding the accuracy of different radiological measurement techniques and in particular how accuracy has been assessed. MATERIAL AND METHODS: We assessed the accuracy of 2 radiostereometric (RSA) techniques for wear measurement and 3 standard radiographic techniques, namely Imagika (image analyzing software), Imagika corrected for head center displacement, and the Charnley Duo method. 5 custom-made adjustable phantoms with different prosthetic components were used. RESULTS: In 20 measurements of all 5 phantoms at 3 levels of simulated wear (0.2 mm, 1.0 mm and 1.5 mm), the mean measurement error of the digital RSA examinations was 0.010 mm (accuracy 0.42). The corresponding error values for the three radiographic techniques were 0.19 (accuracy 1.3) for Charnley Duo, 0.13 (accuracy 1.3) for Imagika corrected, and 1.021 (accuracy 2.99) for Imagika. Measurement error decreased from 0.011 mm with ordinary RSA to 0.004 with RSA digital measurement. Head size, direction of wear in relation to the cup or type of prosthetic component did not influence the measurement error. The results of Charnley Duo and Imagika corrected were similar but the latter had an inexplicable systematic error in measuring one of the phantoms. Imagika had the worst results due to its inability to compensate for the out-of-head center effect. Alumina heads were difficult to analyze with all methods. INTERPRETATION: By using the ISO standard for assessing accuracy, RSA can be expected to measure wear with an accuracy of about 0.4 mm irrespective of prosthetic component studied or direction of wear, whereas the best technique, in our study, based on standard radiographs can be accurate to about 1.3 mm.

Arthroplasty, Replacement, Hip↗
PubMed1997

Spinal range of motion. Accuracy and sources of error with inclinometric measurement.

STUDY DESIGN: A quantitative construct assessing accuracy and component analysis of sources of error rather than reliability coefficients was tested prospectively in human performance measurements of lumbar spine motion using a cohort of healthy individuals. OBJECTIVES: To evaluate the accuracy of lumbar spine sagittal motion measurements using a computerized inclinometer, which involved progressive analysis of sources of error to identify the most problematic sub-components of the measurement process and device. SUMMARY OF BACKGROUND DATA: Many previous studies have described the reliability of inclinometric lumbar motion measurement techniques, but with inconsistent analysis about sources of error to explain identified variability. Similar deficiencies exist in identifying sources of error leading to variability for other human performance measurements (e.g., strength, endurance. lifting capacity, etc.). Yet, range of motion has important clinical applications in monitoring progress and assessing temporary and/or permanent impairment. This makes it especially important for clinicians to be able to recognize and correct factors that limit accurate measurements affecting clinical utility. METHODS: A computerized inclinometer was used for measuring the sagittal lumbar mobility of 38 healthy individuals after bench testing the device itself for device error. The human performance test conditions were: 1) initial test on study participants by untrained test administrators with no control of human performance or procedural variables, 2) identical tests by procedurally trained test administrators controlling human performance variability by monitoring and controlling total motion, and 3) test by procedurally trained test administrators without controlling for human performance variability. RESULTS: The accuracy of the methodology progressively was degraded by the various sources of error. Device error was negligible relative to error associated with the test process itself. Lack of test administrator training and the magnitude of the measured quantity were the major factors in test degradation. Combined (gross) lumbar flexion was the most accurate measure (worst case > 95% accuracy for overall test conditions), whereas pelvic extension was the least accurate (worst case > 36%). CONCLUSIONS: Clinical utility of lumbar spine sagittal motion measurement is highly sensitive to test administrator training to bridge pitfalls to measurement accuracy (bony landmarks, "rocking" of inclinometer on sacrum, etc.). Magnitude of the measurement is another important accuracy factor because absolute error tends to remain relatively constant. Device accuracy is usually an insignificant component of overall test accuracy. Analysis of human performance measurements, such as spinal range of motion, may be facilitated by physics-based assessment of accuracy and procedural error in providing more sophisticated analysis than is customarily accessible through reliability coefficients. Previous studies often failed to recognize correctable procedural errors, rarely addressed them, and almost never quantitated them.

Adult↗