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PubMed2006

An effective method to verify line and point spread functions measured in computed tomography.

This study describes an effective method for verifying line spread function (LSF) and point spread function (PSF) measured in computed tomography (CT). The CT image of an assumed object function is known to be calculable using LSF or PSF based on a model for the spatial resolution in a linear imaging system. Therefore, the validities of LSF and PSF would be confirmed by comparing the computed images with the images obtained by scanning phantoms corresponding to the object function. Differences between computed and measured images will depend on the accuracy of the LSF and PSF used in the calculations. First, we measured LSF in our scanner, and derived the two-dimensional PSF in the scan plane from the LSE Second, we scanned the phantom including uniform cylindrical objects parallel to the long axis of a patient's body (z direction). Measured images of such a phantom were characterized according to the spatial resolution in the scan plane, and did not depend on the spatial resolution in the z direction. Third, images were calculated by two-dimensionally convolving the true object as a function of space with the PSF. As a result of comparing computed images with measured ones, good agreement was found and was demonstrated by image subtraction. As a criterion for evaluating quantitatively the overall differences of images, we defined the normalized standard deviation (SD) in the differences between computed and measured images. These normalized SDs were less than 5.0% (ranging from 1.3% to 4.8%) for three types of image reconstruction kernels and for various diameters of cylindrical objects, indicating the high accuracy of PSF and LSF that resulted in successful measurements. Further, we also obtained another LSF utilizing an inappropriate manner, and calculated the images as above. This time, the computed images did not agree with the measured ones. The normalized SDs were 6.0% or more (ranging from 6.0% to 13.8%), indicating the inaccuracy of the PSF and LSE We could verify LSFs and PSFs for three types of reconstruction kernels, and demonstrated differences between modulation transfer functions (MTFs) derived from validated LSFs and inaccurate LSFs. Our technique requires a simple phantom that is suitable for clinical scanning, and does not require a particular phantom containing some metals or specific fine structures, as required in methods previously used for measurements of spatial resolution. Therefore, the scanned image of the phantom will be reliable and of good quality, and this is used directly as a confident reference image for the verification. When one obtains LSF, PSF or MTF values, verification using our method is recommended. Further, when another method for the measurement of LSF and PSF is developed, it could be validated using our technique, as illustrated in the method proposed by Boone [Med. Phys. 28, 356-360 (2001)] and used in this paper.

Algorithms↗
PubMed1994

Screening for cognitive impairment in older individuals. Validation study of a computer-based test.

OBJECTIVE: This study examined the validity of a computer-based cognitive test that was recently designed to screen the elderly for cognitive impairment. DESIGN: Criterion-related validity was examined by comparing test scores of impaired patients and normal control subjects. Construct-related validity was computed through correlations between computer-based subtests and related conventional neuropsychological subtests. SETTING: University center for memory disorders. PARTICIPANTS: Fifty-two patients with mild cognitive impairment by strict clinical criteria and 50 unimpaired, age- and education-matched control subjects. Control subjects were rigorously screened by neurological, neuropsychological, imaging, and electrophysiological criteria to identify and exclude individuals with occult abnormalities. RESULTS: Using a cut-off total score of 126, this computer-based instrument had a sensitivity of 0.83 and a specificity of 0.96. Using a prevalence estimate of 10%, predictive values, positive and negative, were 0.70 and 0.96, respectively. Computer-based subtests correlated significantly with conventional neuropsychological tests measuring similar cognitive domains. Thirteen (17.8%) of 73 volunteers with normal medical histories were excluded from the control group, with unsuspected abnormalities on standard neuropsychological tests, electroencephalograms, or magnetic resonance imaging scans. CONCLUSIONS: Computer-based testing is a valid screening methodology for the detection of mild cognitive impairment in the elderly, although this particular test has important limitations. Broader applications of computer-based testing will require extensive population-based validation. Future studies should recognize that normal control subjects without a history of disease who are typically used in validation studies may have a high incidence of unsuspected abnormalities on neurodiagnostic studies.

Aged↗
PubMed1989

Ventricle-brain ratio, computed tomographic density, and brain area in 50 schizophrenics.

A sample of 50 DSM-III-diagnosed schizophrenics (mean age, 34 years) intentionally biased to contain a relatively high proportion of persistently unemployed persons was compared with a sample of 87 normal volunteers on three computed tomographic measures. These were lateral ventricle-brain ratio, regional brain computed tomographic density values, and brain slice area. Images were made with the same computed tomographic scanner and identical scan parameters. Computed tomographic data were assessed blindly using a computer-linked image array processor and electronic planimeter. Ventricle-brain ratios were significantly higher in schizophrenics, with 28% of the patient sample exceeding 2 SDs of the control mean. Brain area measures were not associated with an enlarged ventricle-brain ratio. Contrary to our prediction, ventricular enlargement was unassociated with most negative symptom ratings, but was correlated with the absence of positive symptoms. A history of abnormal delivery and the presence of left-handedness were significant predictors of an enlarged ventricle-brain ratio on multiple regression analysis. Schizophrenics had a significantly smaller brain slice area compared with normal controls, a finding not attributable to height differences between groups. Brain slice area was inversely correlated with computed tomographic brain density across all subjects. After correction of computed tomographic density values for area using a linear regression model, no significant regional density differences were detectable between normal controls and schizophrenics. Within normal controls there was a significant relationship between social class and brain slice area, but not ventricle-brain ratio.

Adult↗
PubMed1996

Reduced surface: an efficient way to compute molecular surfaces.

Because of their wide use in molecular modeling, methods to compute molecular surfaces have received a lot of interest in recent years. However, most of the proposed algorithms compute the analytical representation of only the solvent-accessible surface. There are a few programs that compute the analytical representation of the solvent-excluded surface, but they often have problems handling singular cases of self-intersecting surfaces and tend to fail on large molecules (more than 10,000 atoms). We describe here a program called MSMS, which is shown to be fast and reliable in computing molecular surfaces. It relies on the use of the reduced surface that is briefly defined here and from which the solvent-accessible and solvent-excluded surfaces are computed. The four algorithms composing MSMS are described and their complexity is analyzed. Special attention is given to the handling of self-intersecting parts of the solvent-excluded surface called singularities. The program has been compared with Connolly's program PQMS [M.L. Connolly (1993) Journal of Molecular Graphics, Vol. 11, pp. 139-141] on a set of 709 molecules taken from the Brookhaven Data Base. MSMS was able to compute topologically correct surfaces for each molecule in the set. Moreover, the actual time spent to compute surfaces is in agreement with the theoretical complexity of the program, which is shown to be O[n log(n)] for n atoms. On a Hewlett-Packard 9000/735 workstation, MSMS takes 0.73 s to produce a triangulated solvent-excluded surface for crambin (1 crn, 46 residues, 327 atoms, 4772 triangles), 4.6 s for thermolysin (3tln, 316 residues, 2437 atoms, 26462 triangles), and 104.53 s for glutamine synthetase (2gls, 5676 residues, 43632 atoms, 476665 triangles).

Chemistry, Physical↗
PubMed2000

Use of computer-assisted rescreening as an ancillary tool to subclassify AGUS cervical smears.

A substantial percentage of women with a diagnosis of atypical glandular cells of undetermined significance (AGUS) on cervical smears harbor a significant squamous or glandular, preneoplastic or neoplastic lesion on subsequent follow-up. Attempts to subclassify AGUS smears by conventional methods have had mixed results. To determine whether subclassification of AGUS cervical smears using computer-assisted rescreening based on the neural network would improve correlation with subsequent histologic follow-up, 91 cervical smears, conventionally diagnosed as AGUS without concomitant squamous lesions, were subjected to analysis by a computer-assisted automated screening system. Computer-generated images were evaluated by a cytotechnologist without the knowledge of the histologic outcomes. Prior to manual review, each case was classified as either within normal limits, no review required; or abnormal, review required. Based on the degree of abnormality, the latter category was further subclassified into either low probability or high probability of abnormality. The results of the computer-assisted reclassification were then compared with the histologic follow-up of all patients. Thirty-three cases (38.8%) had a significant lesion on histologic follow-up. The lesions included 4 CIN I, 7 CIN II/III, 12 endocervical adenocarcinomas (ACA), and 10 endometrial ACA. Based on computer-generated images, 65% of the smears that were triaged as high probability of abnormality, 11.5% that were triaged as low probability of abnormality, and 10.5% that were triaged as within normal limits had a significant lesion on subsequent follow-up. We conclude that computer-assisted rescreening aids in the triage of AGUS smears and that computer-assisted rescreening based on the neural network or other algorithms may be a useful ancillary tool for subclassifying AGUS cervical smears.

Adenocarcinoma↗
PubMed1989

Biomechanical properties of the proximal femur determined in vitro by single-energy quantitative computed tomography.

To assess the use of quantitative computed tomography as an in vivo predictor of fracture in the osteoporotic hip, we examined the in vitro relationship between single-energy quantitative computed tomography data, calibrated for scanner drift, and the mechanical properties of trabecular bone from the proximal femur. For 49 samples, the apparent density and ultimate strength were measured and their functional relationship to the computed tomography data determined. Apparent density demonstrated a moderate linear correlation to the computed tomography numbers (R2 = 0.60), and the ultimate strength was related through a power law (R2 = 0.83). In addition, for 8 intact femora, average computed tomographic data from the sub-capital region were moderately correlated to the ultimate fracture load applied under controlled in vitro conditions (R2 = 0.64). The average fracture energy for these femora was 43 J, a value more than an order of magnitude less than the energy available in a fall from standing height, suggesting that fall mechanics are a more important determinant of fracture risk than has been previously thought. The relationship between the energy absorbed to failure and the computed tomography data was best described by a power law (R2 = 0.90). Based on these results, it appears that quantitative computed tomography provides a potentially useful approach for the direct estimate of that component of fracture risk that can be attributed to a reduction in bone strength.

Aged↗
PubMed1986

Computed tomography of the abdomen and pelvis: documentation of tumor response and progression in disseminated prostate cancer.

Computed tomography of the abdomen and pelvis has been used to stage early prostatic cancer. We investigated its value in monitoring tumor response in more advanced disease. Serial computed tomography of the abdomen and pelvis was obtained along with multiple other staging tests prior to treatment and at 3- to 4-month intervals thereafter in 32 patients with stage D2 tumor treated initially with combination chemotherapy and with hormones at progression. Pretreatment lymphography with follow-up abdominal films was also performed. Initial computed tomography of the abdomen and pelvis showed evidence of node metastases in 35% of patients while lymphography was positive in 54%. Among 19 patients with tumor response and 25 with progression, the results of treatment were objectively documented by improvement or worsening, respectively, in a mean of 5.1 and 5.0 other staging tests, exclusive of computed tomography. Computed tomography of the abdomen and pelvis improved in 85% of responding patients examined. Progression was confirmed by worsening of computed tomography in 32%. Although lymphography was often abnormal prior to treatment, in our hands it was not useful in serial monitoring of tumor status. We conclude that serial computed tomography of the abdomen and pelvis, when initially positive, is a useful test to document objectively tumor response and progression in disseminated prostatic cancer.

Abdominal Neoplasms↗
PubMedDate not supplied

Encouraging underscreened women to have cervical cancer screening: the effectiveness of a computer strategy.

BACKGROUND: Computers that collect data from patients and provide both patients and practitioners with printed feedback on a range of health risks are a tool for assisting general practitioners with preventive care. This study assessed the impact of computer-generated printed feedback on cervical screening among women who were underscreened for cervical cancer. METHOD: Female attenders at two Australian general practices were randomly allocated to Experimental or Control groups. Women in both groups completed a health risk survey on a touch screen computer prior to their consultation. Those in the Experimental group received printed pages summarizing their results, including their eligibility for cervical screening and last Pap test, for themselves and their doctor. The number and proportion of underscreened women who had a Pap test in the 6 months after completing the computer survey, as determined by pathology records, were examined. RESULTS: Of the 679 participants, 139 were classified as underscreened on the basis of self-report (74 Experimental, 65 Control) and 272 on the basis of their pathology records (148 Experimental, 124 Control). Overall about one-third of women had a test in the 6-month period, and the differences between the groups were not significant for women overall (18-70 years) or for women 18-49 years. Among women 50-70 who were underscreened based on self-report, those receiving the printout were more likely to have a Pap test in the next 6 months (P < 0.05). This pattern was also evident, but did not reach statistical significance, for older women who were underscreened based on pathology records. CONCLUSIONS: We are unable to draw conclusions regarding the effectiveness of the computer system due to the modest proportions of women screened, the small numbers, and the fact that the computer survey may have created an intervention effect in the Control group. As the study suggests the computer system is acceptable to women and may be effective for encouraging screening among older women, further exploration of the system is desirable.

Adolescent↗
PubMed1985

"Neural" computation of decisions in optimization problems.

Highly-interconnected networks of nonlinear analog neurons are shown to be extremely effective in computing. The networks can rapidly provide a collectively-computed solution (a digital output) to a problem on the basis of analog input information. The problems to be solved must be formulated in terms of desired optima, often subject to constraints. The general principles involved in constructing networks to solve specific problems are discussed. Results of computer simulations of a network designed to solve a difficult but well-defined optimization problem--the Traveling-Salesman Problem--are presented and used to illustrate the computational power of the networks. Good solutions to this problem are collectively computed within an elapsed time of only a few neural time constants. The effectiveness of the computation involves both the nonlinear analog response of the neurons and the large connectivity among them. Dedicated networks of biological or microelectronic neurons could provide the computational capabilities described for a wide class of problems having combinatorial complexity. The power and speed naturally displayed by such collective networks may contribute to the effectiveness of biological information processing.

Animals↗
PubMed1989

The relationship of age, level of formal education, and duration of employment toward attitudes concerning the use of computers in the workplace.

The introduction of computer technology in the Canadian health care environment necessitates an adaptation by hospital employees in order to perform their jobs. One thousand twenty-two hospital staff were surveyed immediately following their initial orientation to computers. The survey identified attitudes toward change, and the use of computers in the workplace. Demographic data and job classifications of all respondents were tabulated. Hypotheses were tested regarding the relationships between age, formal education, and duration of employment, and attitudes toward computers and change. Results indicated a generally positive response toward the use of computers in the workplace and to change in general. However, statistically significant results were obtained indicating that age, level of education, and length of employment affect the degree of positive response to both computers and change. The results suggest that demographic variables such as age, level of education, and employment duration must be taken into consideration when planning for the implementation of computer systems in the health care setting.

Adult↗
PubMed1997

Computer-assisted interpretation of electromyograms of corpora cavernosa using fuzzy logic.

An electromyogram of the corpora cavernosa (CC-EMG) imparts information on the autonomic cavernous innervation and/or the cavernous smooth muscles. The CC-EMG is interpreted mainly by evaluation of signal patterns of higher activity. The time required for interpretation is reduced by the implementation of a computer-assisted diagnosis program with a Microsoft Windows user interface. The program offers four levels of diagnosis: on the first level, recordings can be edited; on the second and third levels, signal patterns can be searched or evaluated; and on the last level the final diagnosis is provided. The computer-assisted interpretation is based on digital measurement data. These data have been obtained through a 170.6-Hz sampling frequency and a quantization of 10 V/12 Bit of the amplified signal. The first task of this diagnosis program is to discover and extract signal patterns of higher activity from data stored on the hard disk of a personal computer (PC). For a mathematic description of these patterns the following features were defined: relative time position, relative reproducibility, part of normal phases, and part of whip phases. Syntactic pattern recognition was introduced to identify the characteristic signal forms. An evaluation of the patterns could be derived from these features using fuzzy logic. For a summary of the evaluated patterns the variable global normality was established. The global normality forms an important evaluation basis along with the global synchronism, which represents an investigator's first impression of a recording. The final diagnosis is completed using fuzzy logic. The program was tested by comparison of expert and computer diagnoses. A total of 30 records were independently evaluated by an expert team and the computer program. With reference to the four classified levels of diagnosis a correspondence of 70% could be found. Furthermore, the rate in each of the classified levels was higher than 50%. The discrimination between normal and abnormal evaluation was 80% for clinical routine. Our results show that a computer-assisted interpretation of the CC-EMG can be achieved using mathematically based software. Within the last 7 months this computer-assisted CC-EMG program proved to be of great help in routine diagnosis. Furthermore, it demonstrated results comparable with a blinded-expert interpretation. This approach should bring about dramatic improvements in the diagnosis of erectile dysfunction.

Electromyography↗
PubMed2000

Recursive implementations of temporal filters for image motion computation.

Efficient algorithms for image motion computation are important for computer vision applications and the modelling of biological vision systems. Intensity-based image motion computation proceeds in two stages: the convolution of linear spatiotemporal filter kernels with the image sequence, followed by the non-linear combination of the filter outputs. If the spatiotemporal extent of the filter kernels is large, then the convolution stage can be very intensive computationally. One effective means of reducing the storage required and computation involved in implementing the temporal convolutions is the introduction of recursive filtering. Non-recursive methods require the number of frames of the image sequence stored at any given time to be equal to the temporal extent of the slowest temporal filter. In contrast, recursive methods encode recent stimulus history implicitly in the values of a small number of variables updated through a series of feedback equations. Recursive filtering reduces the number of values stored in memory during convolution and the number of mathematical operations involved in computing the filters' outputs. This paper extends previous recursive implementations of gradient- and correlation-based motion analysis algorithms [Fleet DJ, Langley K (1995) IEEE PAMI 17: 61-67; Clifford CWG, Ibbotson MR, Langley K (1997) Vis Neurosci 14: 741-749], describing a recursive implementation of causal band-pass temporal filters suitable for use in energy- and phase-based algorithms for image motion computation. It is shown that the filters' temporal frequency tuning curves fit psychophysical estimates of the temporal properties of human visual filters.

Algorithms↗
PubMed2005

Sample size computations for PK/PD population models.

We describe an accurate, yet simple and fast sample size computation method for hypothesis testing in population PK/PD studies. We use a first order approximation to the nonlinear mixed effects model and chi-square distributed Wald statistic to compute the minimum sample size to achieve given degree of power in rejecting a null hypothesis in population PK/PD studies. The method is an extension of Rochon's sample size computation method for repeated measurement experiments. We compute sample sizes for PK and PK/PD models with different conditions, and use Monte Carlo simulation to show that the computed sample size retrieves the required power. We also show the effect of different sampling strategies, such as minimal, i.e., as many observations per individual as parameters in the model, and intensive on sample size. The proposed sample size computation method can produce estimates of minimum sample size to achieve the desired power in hypothesis testing in a greatly reduced time than currently available simulation-based methods. The method is rapid and efficient for sample size computation in population PK/PD study using nonlinear mixed effect models. The method is general and can accommodate any type of hierarchical models. Simulation results suggest that intensive sampling allows the reduction of the number of patients enrolled in a clinical study.

Algorithms↗
PubMed1976

Computer detection of premature ventricular complexes: a modified approach.

The accuracy of a data reduction system for arrhythmia detection in identifying premature ventricular complexes was evaluated in continuous tape records of 30 patients in a coronary care unit. Computer analysis was performed with a Honeywell 316 digital computer. Threshold values for dominant complexes were automatically determined and recognition of premature ventricular complexes was based on differences in QRS configuration, timing and T wave configuration from the dominant complexes. Verification of the computer accuracy in detecting premature ventricular complexes was made with visual beat by beat inspection using a two channel strip chart recorder with simultaneous recording of the electrocardiogram and computer signal. This procedure allowed for exact beat to beat correlation and, thus, absolute determination of false positive and false negative identification. From 0.5 to 6 continuous hours of monitoring per patient (average 3.5 hours) were analyzed for a total of 105 monitoring hours. The basic cardiac rhythms noted were normal sinus rhythm, sinue arrhythmia, sinus tachycardia, demand pacemaker rhythm, atrial fibrillation and atrioventricular (A-V) dissociation with junctional rhythm. Premature ventricular complexes were evident in 28 tapes (93 percent) including 12 (43% with multifocal premature ventricular complexes and 3 (11 percent) with ventricular tachycardia. The visual count of premature ventricular complexes totaled 7,921. Of these, 7,542 (95 percent) were properly classified by the computer. The total computer count was 8.717, representing a 13 percent false positive and 5 percent false negative identification rate. The false positive identifications of premature ventricular complexes occurred during periods of 10 seconds or more of continuous noise artifact and in the presence of atrial premature complexes conducted aberrantly. When these sections of tape were excluded, the computer had a less than 2 percent false negative and 3 percent false positive rate of identification of premature ventricular complexes.

Arrhythmias, Cardiac↗
PubMed1984

New directions in scientific computing: impact of advances in microprocessor architecture and system design.

The new generation of microcomputers has brought computing power previously restricted to mainframe and supermini computers within the reach of individual scientific laboratories. Microcomputers can now provide computing speeds rivaling mainframes and computational accuracies exceeding those available in most computer centers. Inexpensive memory makes possible the transfer to microcomputers of software packages developed for mainframes and tested by years of experience. Combinations of high level languages and assembler subroutines permit the efficient design of specialized applications programs. Microprocessor architecture is approaching that of superminis, with coprocessors providing major contributions to computing power. The combined result of these developments is a major and perhaps revolutionary increase in the computing power now available to scientists.

Computers↗
PubMed1989

Endosonography and computed tomography of esophageal carcinoma. Preoperative classification compared to the new (1987) TNM system.

Transesophageal endosonography and computed tomography were performed preoperatively in 74 patients with an esophageal carcinoma. The results were correlated with the histology of resected specimens according to the new (1987) TNM classification. Endosonography was superior to computed tomography in the evaluation of the depth of tumor infiltration, especially in the early stages and in nonresectable carcinoma (overall accuracy: endosonography 89%, computed tomography 59%). Endosonography was also more accurate than computed tomography in the assessment of regional lymph node metastases (overall accuracy: endosonography 80%, computed tomography 51%). The incidence of lymph node metastasis increased with the progression of the depth of tumor infiltration. The definitive exclusion factor for endosonography is severe stenosis, which cannot be passed with the instrument (26% of the cases). In these cases computed tomography was superior to endosonography in diagnosing celiac lymph node metastasis (overall accuracy: computed tomography 82%, endosonography 68%).

Adult↗
PubMed1977

Statistical comparison of power spectra: a computer program.

A general computer program, of interest to neurobiologists, for comparison of uncorrelated power spectra is presented. The program, ALPHAF, is written in Fortran V language and is easily compiled and executed in any computer with a Fortran software package. The purpose of the program is to read power spectral density (PSD) values into a computer from digital tape and then perform the following functions: (1) compute and report power; (2) compute and report averages of the computed power values over selected frequency bands and (3) compute and report statistical standardised normal distributions for a frequency spectrum of interest. The standardised normal distribution statistic is derived by using equation 7.20, page 250 of Random data: Analysis and measurement procedures (Bendat and Piersol, 1971).

Computers↗
PubMed1995

A comparison of computer-based and personal interviews for the gynecologic history update.

OBJECTIVE: To determine if patients would answer a computer-based interview in the same way as they would answer a personal interview. METHODS: Two hundred consecutive patients in a private practice setting were asked a set of eleven questions relating to their general and gynecologic health. The question set included issues appropriate to a routine, periodic gynecologic history update. Each subject was asked the same question set twice, once by a personal interview and once by a computer. This was done in a crossover fashion. One-half of the subjects were interviewed by a person first; the other half used the computer first. RESULTS: Statistical evaluation demonstrated that patient responses are equivalent. The two methods agreed overall in 96% of the responses. Analysis of the discordant responses showed that in some cases, the computer may be more effective than the personal interview in identifying risk factors. CONCLUSIONS: A computer-based questionnaire can generate responses that are equivalent to the responses to a traditional personal interview. In some cases, a computer may be more successful in eliciting risk factors. Further studies of the application of this technology for patient education and physician efficiency can now be carried out, knowing that subjects respond reproducibly to a computer interview format.

Adolescent↗