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The accuracy of 'power' maps to display curvature data in corneal topography systems.

PURPOSE: To quantify the error introduced by videokeratographic corneal topography devices in using a paraxial formula to calculate power over the entire corneal surface, including areas removed from the central paraxial region where the formula is known to be invalid. METHODS: Corneal refractive power and two paraxial power approximations were computed as a function of distance from the apex for three theoretical surfaces, a sphere and two ellipsoids with 0.3 and 0.5 eccentricities. Color dioptric maps were then theoretically created. RESULTS: For the spherical surface, both curvature-based paraxial power approximations were uniform over the entire surface because curvature is constant. However, the corneal refractive power increased from center to periphery, demonstrating the known phenomenon of spherical aberration. For the ellipsoids, which have been shown to model the human cornea, curvature-based power approximations decreased from center to periphery because the curvature flattens peripherally. However, refractive power increased from center to periphery. The limits of the central paraxial region for these surfaces was shown to be approximately 2 mm in diameter for the paraxial power approximation used by videokeratographic devices to measure 8 mm in diameter. CONCLUSIONS: The direct correlation between corneal curvature and power with which clinicians are familiar is not valid in the peripheral regions measured by videokeratographic devices. Topographic devices measure curvature, which should not be interpreted as corneal power except in the central region. A recommendation to device manufacturers is to display "color curvature maps" instead of color dioptric maps, and to label the color bar with curvature values instead of power.

Cornea↗

Development of a primary health care information system in Ghana: lessons learned.

In Ghana, between January 1990 and September 1993, a series of steps were undertaken to review the existing vertical reporting procedures and to develop an integrated Health Management Information System (HMIS) for Primary Health Care (PHC). These steps included a situation analysis of the existing reporting systems; participatory design of tools for planning, data collection, feedback and reporting; field test and revision of the modified system; training of staff at all levels; development of tools for self-assessment and stimulation of routine feedback to lower levels and reporting of analysed indicators to higher levels. There were some notable achievements which included promotion of self-reliance, improved data relevance and accuracy, as well as strengthened supervision and support. However, it was difficult to identify the most appropriate institutional location for the HMIS; over-emphasis on process leads to reduced implementation; reporting was still given greater priority than analysis and use of data, and systems for collection and use were still cumbersome and time consuming. It is also difficult to prove that having better information really improves decision-making, or even coverage and quality of PHC service delivery. These issues, as well as lessons learned, are discussed in the paper.

Ghana↗

Indirect wrist MR arthrography: the effects of passive motion versus active exercise.

PURPOSE: In the wrist, to determine whether passive motion or active exercise yields a better indirect MR arthrographic effect following intravenous gadolinium administration. DESIGN AND PATIENTS: Twenty-six consecutive patients were studied by indirect wrist MR arthrography. In half active exercise and in half passive motion was performed. Four regions of interest were studied including the distal radioulnar joint, the radiocarpal joint, the midcarpal joint, and the triangular fibrocartilage. Ranges and means of signal intensity were calculated. Surgical follow-up was performed in 22 patients. RESULTS: The joint fluid intensity was greatest in the distal radioulnar joint. Fluid signal intensity was greater and more consistent in the passive motion group although the results did not achieve statistical significance. Imaging accuracy appeared similar in the two groups and was excellent for the triangular fibrocartilage (100%) and scapholunate ligaments (96%). CONCLUSION: Active exercise and passive motion yield similar degrees of wrist arthrographic effect, but the effect of passive motion is somewhat more consistent. Preliminary data show good accuracy for internal derangements.

Adolescent↗

New technologies in screening for breast cancer: a systematic review of their accuracy.

We systematically reviewed the literature on the accuracy of new technologies proposed for breast cancer screening. Four potential tests were identified (ultrasound, magnetic resonance imaging (MRI), full-field digital mammography (FFDM), and computer-aided detection (CAD)) for which primary studies met quality and applicability criteria and provided adequate data on test accuracy. These technologies have been assessed in cross-sectional studies of test accuracy where the new test is compared to mammography. Ultrasound, used as an adjunct to mammography in women with radiologically dense breasts, detects additional cancers and causes additional false positives. Magnetic resonance imaging may have a better sensitivity (but lower specificity) than mammography in selected high-risk women, but studies of this technology included small number of cancers. Computer-aided detection may enhance the sensitivity of mammography and warrants further evaluation in large prospective trials. One study of FFDM suggests that it may identify some cancers not identified on conventional mammography and may result in a lower recall rate. The evidence is currently insufficient to support the use of any of these new technologies in population screening, but would support further evaluation.

Breast Neoplasms↗

[Single nucleotide polymorphisms(SNPs)and SNP databases].

Along the rapid development of human genome sequencing project, the variation data of human DNA sequence has become more and more useful not only for studying the origin, evolution and the mechanisms of maintenance of genetic variability in human populations, but also for detection of genetic association in complex disease such as diabetes, obesity, hypertension, Alzheimer's disease, etc. In recent two years, the databases such as dbSNP, CGAP, HGBASE, JST and Go!Poly etc. to collect and exploit data of genomic polymorphisms mainly single nucleotide polymorphisms (SNPs) have been respectively established in the United States, European countries, Japan and China. This overview summarized the development and applications of those SNP databases and also discussed some issues regarding the potential improvement of accuracy of SNP data collected. China has one fifth population in the world. Therefore, development of the SNP database for Chinese populations is of importance in developing complete SNP databases of human genome and may also stimulate the further development of biomedical research and production in China.

Databases, Nucleic Acid↗

An implantable transducer for measuring tension in an anterior cruciate ligament graft.

The goal of this study was to develop a new implantable transducer for measuring anterior cruciate ligament (ACL) graft tension postoperatively in patients who have undergone ACL reconstructive surgery. A unique approach was taken of integrating the transducer into a femoral fixation device. To devise a practical in vivo calibration protocol for the fixation device transducer (FDT), several hypotheses were investigated: (1) The use of a cable versus the actual graft as the means for applying load to the FDT during calibration has no significant effect on the accuracy of the FDT tension measurements; (2) the number of flexion angles at which the device is calibrated has no significant effect on the accuracy of the FDT measurements; (3) the friction between the graft and femoral tunnel has no significant effect on measurement accuracy. To provide data for testing these hypotheses, the FDT was first calibrated with both a cable and a graft over the full range of flexion. Then graft tension was measured simultaneously with both the FDT on the femoral side and load cells, which were connected to the graft on the tibial side, as five cadaver knees were loaded externally. Measurements were made with both standard and overdrilled tunnels. The error in the FDT tension measurements was the difference between the graft tension measured by the FDT and the load cells. Results of the statistical analyses showed that neither the means of applying the calibration load, the number of flexion angles used for calibration, nor the tunnel size had a significant effect on the accuracy of the FDT. Thus a cable may be used instead of the graft to transmit loads to the FDT during calibration, thus simplifying the procedure. Accurate calibration requires data from just three flexion angles of 0, 45, and 90 deg and a curve fit to obtain a calibration curve over a continuous range of flexion within the limits of this angle group. Since friction did not adversely affect the measurement accuracy of the FDT, the femoral tunnel can be drilled to match the diameter of the graft and does not need to be overdrilled. Following these procedures, the error in measuring graft tension with the FDT averages less than 10 percent relative to a full-scale load of 257 N.

Aged↗

Experimental data checker: better information for organic chemists.

An experimental data checker has been developed that reads, analyses, and cross-correlates experimental information copied and pasted from authors' manuscripts, which will be useful for authors, referees, editors and readers of papers reporting new molecular information, and which makes possible a quantification of the accuracy of journals' data.

Journal Article↗

Determinants of long-term survival after major surgery and the adverse effect of postoperative complications.

OBJECTIVE: The objective of this study was to identify the determinants of 30-day postoperative mortality and long-term survival after major surgery as exemplified by 8 common operations. SUMMARY BACKGROUND DATA: The National Surgical Quality Improvement Program (NSQIP) database contains pre-, intra-, and 30-day postoperative data, prospectively collected in a standardized fashion by a dedicated nurse reviewer, on major surgery in the Veterans Administration (VA). The Beneficiary Identification and Records Locator Subsystem (BIRLS) is a VA file that depicts the vital status of U.S. veterans with 87% to 95% accuracy. METHODS: NSQIP data were merged with BIRLS to determine the vital status of 105,951 patients who underwent 8 types of operations performed between 1991 and 1999, providing an average follow up of 8 years. Logistic and Cox regression analyses were performed to identify the predictors of 30-day mortality and long-term survival, respectively. RESULTS: The most important determinant of decreased postoperative survival was the occurrence, within 30 days postoperatively, of any one of 22 types of complications collected in the NSQIP. Independent of preoperative patient risk, the occurrence of a 30-day complication in the total patient group reduced median patient survival by 69%. The adverse effect of a complication on patient survival was also influenced by the operation type and was sustained even when patients who did not survive for 30 days were excluded from the analyses. CONCLUSIONS: The occurrence of a 30-day postoperative complication is more important than preoperative patient risk and intraoperative factors in determining the survival after major surgery in the VA. Quality and process improvement in surgery should be directed toward the prevention of postoperative complications.

Databases as Topic↗

Collateral circulation in internal carotid artery occlusion. A study by duplex scan and magnetic resonance angiography.

BACKGROUND: Clinical effects of internal carotid artery (ICA) occlusion may range from the absolute absence of symptoms to lethal hemispheric stroke. In this paper symptoms of patients with ICA occlusion have been related to the development of collateral circulation, different types of developed collateral circulation have been assessed, and the degree of sensitivity and specificity of duplex scan has been appraised. METHODS: Forty-eight patients with ICA occlusion or subocclusion, 24 males and 24 females, aged between 50 and 83 years (67.7+/-7.15), underwent duplex scan and magnetic resonance (MR) angiography. Nineteen patients were completely asymptomatic, 20 patients showed permanent neurological symptoms and 9 patients had shown transient symptoms. RESULTS: Twelve patients (25%) did not show any collateral circulation, 29 patients (60%) showed collateral circulation through homolateral external carotid artery branches and 7 patients (15%) showed collateral circulation through other circuits. Of the 20 patients with permanent symptoms only 8 showed collateral circulation. On the contrary, all the 19 asymptomatic patients and the 9 patients with transient symptoms showed collateral circulation. Eventually, duplex scan showed 78% sensitivity, 100%, specificity and 83% diagnostic accuracy. CONCLUSIONS: Our data show: 1) a clear-cut prevalence of collateral circulation through homolateral external carotid artery branches with respect to other possible collateral circulation; 2) an inverse relationship between the development of collateral circulation and the appearance of permanent symptoms; 3) a good diagnostic accuracy of duplex scan in revealing collateral circulation in the case of ICA occlusion.

Aged↗

Diagnostic accuracy of simultaneous acquisition of transmission and emission data with technetium-99m transmission source on thallium-201 myocardial SPECT.

PURPOSE: This study evaluates not only the clinical usefulness but also the problems in attenuation correction for thallium-201 (Tl-201) myocardial SPECT by means of simultaneous transmission and emission data acquisition in the detection of coronary artery disease (CAD). METHODS: A three-detector SPECT system equipped with a Tc-99m line source and fan-beam collimators was used for simultaneous transmission and emission data acquisition for Tl-201 myocardial SPECT in 73 patients (18 patients for normal database and 55 patients for the evaluation of diagnostic accuracy). Attenuation-corrected (AC) images and non-attenuation-corrected (NC) images were reconstructed with an iterative maximum-likelihood estimation-corrected (ML-EM) algorithm. Both sets of images were reoriented into the short axis. Normal database polar maps were constructed from the AC and NC images for quantitative analysis. RESULTS: There was a significant difference in specificity between NC and AC images in the RCA territory and those in specificity and accuracy in the LCX territory. There was no significant difference in sensitivity found between NC and AC images in either territory, but sensitivity in both territories tended to decrease with attenuation correction. In the LAD territory, there were various changes in sensitivity and specificity observed with attenuation correction in cases with each quantitative criterion. CONCLUSIONS: Diagnostic performance of significant stenosis in the RCA and LCX territories quantitatively improved with attenuation correction because of an increase in specificity, but no significant improvement in diagnostic performance was obtained in the LAD territory with attenuation correction. We recommend combined interpretation of AC and NC images and careful evaluation of any SPECT image by means of transmission computed tomography.

Coronary Disease↗

Pharmacokinetic quantitation of naltrexone controlled release from a copolymer delivery system.

Naltrexone release rates from a controlled release delivery system have been quantitated over a time period greater than one month in the monkey. The method requires calibration of the pharmacokinetic parameters of each monkey utilizing an intravenous bolus dose and assay of unchanged naltrexone levels in plasma as a function of time after dosing. Also required are periodic plasma levels of unchanged naltrexone obtained subsequent to administration of the delivery system. Release rates are then calculated as well as the total amount released. Application of the methodology to a biodegradable copolymer naltrexone delivery system in three monkeys showed an initial release rate of 3-8% of the dose per day over the first 3-5 days followed by a slow, rather constant release rate of 1-3% per day from day 5 to the time of the last measurable plasma sample (36-43 days). Comparison of alternative calculation methods using both experimental and simulated plasma naltrexone data verified the accuracy of the release rate calculations. The sum of the calculated total amount of naltrexone released plus the assayed amount remaining in the delivery system after removal from the animal accounted for 91-94% of the administered dose in the two monkeys in which complete data were obtained.

Animals↗

Escherichia coli molecular genetic map (1500 kbp): update II.

The DNA sequence data for Escherichia coli deposited in the EMBL library (release 27), together with miscellaneous data obtained from several laboratories, have been localized on an updated and corrected version of the restriction map of the chromosome generated by Kohara et al. (1987) and modified by others. This second update adds a further 500 kbp, increasing the amount of the E. coli chromosome sequenced to about one third of the total: 1510 kbp of sequenced DNA is included in the present data base. The accuracy of the map is assessed, and allows us to propose a precise genetic map position for every sequenced gene. The location of rare-cutting sites such as AvrII, NotI and SfiI have also been included in the update in order to combine the data obtained from different sources into one single file. The distribution of palindromic sequences (to which most restriction sites belong) has been studied in coding sequences. There appears to be a significant counter-selection against several such sequences in E. coli coding sequences (but not in other organisms such as Saccharomyces cerevisiae), suggesting the existence of constraints on DNA structure in E. coli, perhaps indicative of a functional role for horizontal gene transfer, preserving coding sequences, in this type of bacteria.

Base Sequence↗

Algorithm for multi-curve-fitting with shared parameters and a possible application in evoked compound action potential measurements.

BACKGROUND: Experimental results are commonly fitted by determining parameter values of suitable mathematical expressions. In case a relation exists between different data sets, the accuracy of the parameters obtained can be increased by incorporating this relationship in the fitting process instead of fitting the recordings separately. METHODS: An algorithm to fit multiple measured curves simultaneously was developed. The method accounts for parameters that are shared by some curves. It can be applied to either linear or nonlinear equations. Simulated noisy "measurement results" were created to compare the introduced method to the "straight forward" way of fitting the curves separately. RESULTS: The analysis of the simulated measurements confirm, that the introduced method yields more accurate parameters compared to the ones gained by fitting the measurements separately. Therefore it needs more computer time. As an example, the new fitting algorithm is applied to the measurements of the evoked compound action potentials (ECAP) of the auditory nerve: This leads to promising ideas to reduce artefacts generated by the measuring process. CONCLUSION: The introduced fitting algorithm uses the relationship between multiple measurement results to increase the accuracy of the parameters. Its application in the field of ECAP measurements is promising and should be further investigated.

Action Potentials↗

Surgical audit: a review. Proceedings of an audit symposium.

The work of surgical departments involves varying proportions of investigation, diagnosis and treatment and the object of audit is to measure and monitor the outcome of this activity. It also serves as a secondary but important role in education, research and resource planning. The different methods of audit described in this symposium gave varying contributions to the definition of workload and outcome and to the education of the surgical staff. Irrespective of the audit system used, there is little doubt that weekly meetings specifically designed for the purpose are of prime importance, and the contributors used it in a variety of different ways. For Messrs. Eltringham and Espiner this meeting was seen much more as an educational exercise for the firm as a whole than a ritualistic method of collecting numerical information. Where other systems which rather more fastidiously collect numerical information are used, the weekly meeting becomes more important in ensuring the accuracy of the data collected. Some authors review the proforma on which the patient information is collected before it is entered into the computer, a point strongly made by Mr. Dunn and it does seem likely that as audit information is collected and challenged, then considerable efforts will have to be made to ensure the accuracy of the information being entered, for there is little point in defending an audit result by suggesting that the houseman who made the original entry did not do so very accurately. Many auditors used a lunch or coffee break as a convenient time to meet, but in some cases a lot of extra work was required for validation and if clinical audit is to represent a very accurate record of the work of a surgical department, this point requires careful consideration. If audit information is to be easily processed, then its means of collection is important.Most contributors used a single record card on which the information was recorded during the patient's stay and this record card can be designed to make entry into a computer system easy for a secretary.It is alos much easier to take records to a weekly meeting than 30 sets of patients' notes. In broad terms the audit systems discussed fell into 2 groups: those which used computers and those which did not. There is no doubt that the use of a computer helps in marshalling the information collected. Although a card system was very cheap and easy to use,it was very much difficult to retrieve information rapidly from it than from a computer based system.It seems that the use of computer entails the consumption of more time for entry and validation of data than a card based system, and there may be a temptation not to spend so much time on the educational aspects of audit. This problem can be overcome by holding regular meetings at which only results presented, perhaps firm by firm, in a hospital, so that discussions on policies relating to thromboembolic prophylaxis, the use of prophylactic antibiotics and similar topics can be discussed. Indeed if this kind of meeting does not take place, then it would seem that one of the principal objectives of audit is lost. For this meetings to take place a computer based system is almost certainly going to be essential. In setting up a clinical audit there is clearly a requirement for financial investment. This means first buy in a computer based system and several options are open to the prospective auditor. A simple desk top computer with a modified database system can be used but Messrs. Baird and Horrocks found it required a great deal of programming using a database programme that was already commercially available to obtain a workable system.Two or three commercial systems are now available using personal computers and it seems likely that in many hospitals this will be a popular choice. When introduced in Colchester General Hospital by Mr. Motson where such a facility had not existed in the past, computerisation has been well received and has achieved the desired result.As more hospitals develop their own sophisticated information systems, it may be possible to graft clinical audit information onto the hospital programmes in a way outlined by Mr. Marsland and Mrs. Tyndall. The advantage of this system is that there is often experienced help available for the design and implementation of the system and very powerful computers to use. The information yielded by audit needs to be kept in a confidential system. If this fails to occur,then the users of the system will cease to have confidence in it and the accuracy of the information put into the audit will lessen. As the whole object of audit is an attempt to collect accurate and detailed information about patients,then another prime objective could easily be lost. There is little doubt from the experiences presented in this review that audit is feasible.The benefits fall into two broad groups.Firstly by reviewing cases at regular weekly meeting evolving problems can be dealt with so there is an immediate benefit for that one patient and a useful learning experience for the staff.It is important not to lose sight of this in the wish to collect data on a computer.The second benefit is the ease of handling large amounts of information about patient activity. Only the Cambridge experience gave any longer term view and there was an impact on the complications of surgical treatment.It will be most important in the years to come, as audit systems are introduced, that their value is critically regarded because in order to establish and run clinical audit, a considerable amount of time will need to be devoted by everybody involved. The determination fo longer term response to surgical treatment in terms of graft patency,tumour recurrence and patient survival is not possible by any of the methods currently described. It is an undertaking of great importance and proportions and clearly has a bearing on clinical practice. Short term clinical audit will therefore be only one part of the evaluation of surgical care.

Computer Systems↗

Quantitative analysis of accuracy of an inertial/acoustic 6DOF tracking system in motion.

An increasing number of neuroscience experiments are using virtual reality to provide a more immersive and less artificial experimental environment. This is particularly useful to navigation and three-dimensional scene perception experiments. Such experiments require accurate real-time tracking of the observer's head in order to render the virtual scene. Here, we present data on the accuracy of a commonly used six degrees of freedom tracker (Intersense IS900) when it is moved in ways typical of virtual reality applications. We compared the reported location of the tracker with its location computed by an optical tracking method. When the tracker was stationary, the root mean square error in spatial accuracy was 0.64 mm. However, we found that errors increased over ten-fold (up to 17 mm) when the tracker moved at speeds common in virtual reality applications. We demonstrate that the errors we report here are predominantly due to inaccuracies of the IS900 system rather than the optical tracking against which it was compared.

Acceleration↗

Reflection and transmission pulse oximetry during compromised peripheral perfusion.

The performance of a reflection pulse oximeter and a transmission pulse oximeter was assessed during open-heart surgery when cardiac output, peripheral temperature, pulse pressure, and systolic pressure were low and vascular resistance was high. Before and after extracorporeal circulation (ECC) there was no difference in ability of the sensors to obtain readings and no difference in the accuracy of those readings. During partial ECC, especially after coronary artery bypass grafting, the reflection sensor gave readings earlier and at a lower pulse pressure. In addition, the transmission sensor failed to give any readings for 2 patients on partial ECC, for whom the reflection sensor did give readings. The accuracy of heart rate (HR) data was comparable for both sensors before ECC; however, during partial ECC, the reflection sensor tended to give values closer to the electrocardiographic HR. The accuracy of saturation data given by the reflection oximeter was comparable to that of the transmission oximeter. It is concluded that the accuracy of the saturation and HR data provided by the two methods of pulse oximetry are comparable, but that the reflection sensor is more likely to obtain readings under conditions of poorer peripheral circulation.

Adult↗

Soft tissue scanning for patient registration in image-guided surgery.

Prior to an image-guided surgical intervention, a correlation between the patient's data set and the surgical site is required. This study introduces a markerless registration method for cranio-maxillofacial surgery that is based on a high-resolution laser scan of the patient's skin surface. The Surgical Segment Navigator SSN++ rejects contaminated surface measurements in a way similar to the bluescreen technique. Acquisition of the spatial position and the corresponding surface color of each laser-scanned point facilitates this bluescreen method, removing points with a defined surface color, e.g., blue or green points. The accuracy of the laser-scan-based registration was measured via additional intraoral titanium-markers. These markers served only to check the accuracy of the markerless registration process. In twelve patients, the stability and accuracy of the data set alignment was evaluated for high-(300,000 surface points), medium-, and low-resolution (down to 3,750 surface points) laser scanning. The accuracy of the registration technique was best for high-resolution laser scanning (mean deviation 1.1 mm; maximum deviation 1.8 mm). Low-resolution laser scans revealed inaccuracies up to 6 mm.

Face↗