PubMed Health⌕ Search

Biomedical subjects

K Spitzer

Publications and source records attributed to K Spitzer.

At least 19 recordsLinked to original sources
PubMed2003

On the design of active contours for medical image segmentation. A Scheme for Classification and construction.

OBJECTIVES: To provide a comprehensive bottom-up categorization of model-based segmentation techniques that allows to select, implement, and apply well-suited active contour models for segmentation of medical images, where major challenges are the high variability in shape and appearance of objects, noise, artifacts, partial occlusions of objects, and the required reliability and correctness of results. METHODS: We consider the general purpose of segmentation, the dimension of images, the object representation within the model, image and contour influences, as well as the solution and the parameter selection of the model. Potentials and limits are characterized for all instances in each category providing essential information for the application of active contours to various purposes in medical image processing. Based on prolops surgery planning, we exemplify the use of the scheme to successfully design robust 3D-segmentation. RESULTS: The construction scheme allows to design robust segmentation methods, which, in particular, should avoid any gaps of dimension. Such gaps result from different image domains and value ranges with respect to the applied model domain and the dimension of relevant subsets for image influences, respectively. CONCLUSIONS: A general segmentation procedure with sufficient robustness for medical applications is still missing. It is shown that in almost every category, novel techniques are available to improve the initial snake model, which was introduced in 1987.

Diagnostic Imaging↗
PubMed2002

Image processing and enhancement provided by commercial dental software programs.

OBJECTIVES: To identify and analyse methods/algorithms for image processing provided by various commercial software programs used in direct digital dental imaging and to map them onto a standardized nomenclature. METHODS: Twelve programs presented at the 28th International Dental-Show, March, 2001, Cologne, Germany and the Emago advanced software were included in this study. An artificial test image, comprised of gray scale ramps, step wedges, fields with Gaussian-distributed noise, and salt and pepper noise, was synthesized and imported to all programs to classify algorithms for display; linear, non-linear and histogram-based point processing; pseudo-coloration; linear and non-linear spatial filtering; frequency domain filtering; measurements; image analysis; and annotations. RESULTS: The 13 programs were found to possess a great variety of image processing and enhancement facilities. All programs offer gray-scale image display with interactive brightness and contrast adjustment and gray-scale inversion as well as calibration and length measurements. While Emago enables arbitrary spatial filtering with user-defined masks up to 7x7 pixels in size, most programs sparsely include filters and tools for image analysis and comparison. Moreover, the naming and implementation of provided functions differ. Some functions inappropriately use standardized image processing terms to describe their operations. CONCLUSIONS: Image processing and enhancement functions are rarely incorporated in commercial software for direct digital imaging in dental radiology. Until now, comparison of software was limited by the arbitrary naming used in each system. Standardized terminology and increased functionality of image processing should be offered to the dental profession.

Algorithms↗
PubMed2001

Addendum: B-spline interpolation in medical image processing.

This paper analyzes B-spline interpolation techniques of degree 2, 4, and 5 with respect to all criteria that have been applied to evaluate various interpolation schemes in a recently published survey on image interpolation in medical imaging (Lehmann et al., 1999). It is shown that high-degree B-spline interpolation has superior Fourier properties, smallest interpolation error, and reasonable computing times. Therefore, high-degree B-splines are preferable interpolators for numerous applications in medical image processing, particularly if high precision is required. If no aliasing occurs, this result neither depends on the geometric transform applied for the tests nor the actual content of images.

Diagnostic Imaging↗
PubMed2000

Pharmacokinetic profile of a low-molecular weight heparin (reviparin) in pregnant patients. A prospective cohort study.

Anticoagulant therapy during pregnancy is problematic. Patients are frequently treated with long-term low-molecular weight heparin despite a lack of evidence for its effectiveness, and in the absence of validated dosing recommendations. The objectives of this investigation were to characterize the safety and pharmacokinetic behavior of a low-molecular weight heparin (reviparin) administered throughout pregnancy. Forty-two patients followed in a tertiary-care rheumatology clinic who received prophylactic doses of reviparin (4900 anti-Xa units subcutaneously once daily) were enrolled in this investigation. Anti-Xa heparin levels, weights, and gestational ages of the patients were obtained on up to four occasions distributed throughout their pregnancy. The achieved anti-Xa heparin levels were highly correlated with the patient's weight, irrespective of the gestational age. No toxicity other than injection site hematomas was observed. The achieved intensity of anticoagulation with reviparin varies during pregnancy in direct proportion to the patient's weight. This variability may mandate dose adjustment in response to changes in a patient's weight during pregnancy, particularly if low-molecular weight heparin is administered at therapeutic doses.

Abortion, Habitual↗
PubMed2000

Scale-independent shape analysis for quantitative cytology using mathematical morphology.

A system for automatic quantification of morphological changes of cell lines, proposed for cytotoxicity tests of biomaterials, is presented. Light-micrographs of cultured cells are segmented by adaptive thresholding within a local adaptive window. Connected cells in binarized micrographs are separated by a novel morphological multiscale method, treating cells in their size-specific scale and hence resulting in scale-independent separations. Significant shape descriptors correlating well with cell toxicity are extracted from single cells. Size and compactness distributions turned out to be reliable and useful parameters, providing an alternative to the common subjective grading of shape deformations by visual inspection. The system is evaluated for several standardized toxical reference substances and is now in use for clinical biocompatibility testing.

Cell Line↗
PubMed2000

WWW-based continuing medical education: how do general practitioners use it?

WWW-based Continuing Medical Education (CME) is assumed to have the potential to make up for shortcomings in traditional lifelong learning of General Practitioners (GPs). This is obvious for CME systems with accreditation and control of the individual GP's CME activities but seems less clear for non-controlled CME systems like in several European countries, e.g. Germany. This paper reports results from the evaluation of a German CME website by 59 GPs (internet experience of 20 months on average) during a 4-months period. GPs mainly learned at home after work, with 46% of the GPs visiting the website at least once per month. Self-study and information seeking accounted for 58% of the activities, while communication and interaction were used infrequently. 77% of the GPs judged less but detailed information on selected topics more important than being able to access many but broad contents. GPs mostly prefer established means of learning and communication. It is concluded that the GPs' self-directed individual learning mainly needs high-quality information and well-structured collections of existing relevant WWW resources. Communication, virtual community building and sophisticated interactivity are of little importance at present. WWW-based CME complements existing CME activities, especially regarding individual information seeking on focused problems.

Computer Literacy↗
PubMed1999

Survey: interpolation methods in medical image processing.

Image interpolation techniques often are required in medical imaging for image generation (e.g., discrete back projection for inverse Radon transform) and processing such as compression or resampling. Since the ideal interpolation function spatially is unlimited, several interpolation kernels of finite size have been introduced. This paper compares 1) truncated and windowed sinc; 2) nearest neighbor; 3) linear; 4) quadratic; 5) cubic B-spline; 6) cubic; g) Lagrange; and 7) Gaussian interpolation and approximation techniques with kernel sizes from 1 x 1 up to 8 x 8. The comparison is done by: 1) spatial and Fourier analyses; 2) computational complexity as well as runtime evaluations; and 3) qualitative and quantitative interpolation error determinations for particular interpolation tasks which were taken from common situations in medical image processing. For local and Fourier analyses, a standardized notation is introduced and fundamental properties of interpolators are derived. Successful methods should be direct current (DC)-constant and interpolators rather than DC-inconstant or approximators. Each method's parameters are tuned with respect to those properties. This results in three novel kernels, which are introduced in this paper and proven to be within the best choices for medical image interpolation: the 6 x 6 Blackman-Harris windowed sinc interpolator, and the C2-continuous cubic kernels with N = 6 and N = 8 supporting points. For quantitative error evaluations, a set of 50 direct digital X rays was used. They have been selected arbitrarily from clinical routine. In general, large kernel sizes were found to be superior to small interpolation masks. Except for truncated sinc interpolators, all kernels with N = 6 or larger sizes perform significantly better than N = 2 or N = 3 point methods (p << 0.005). However, the differences within the group of large-sized kernels were not significant. Summarizing the results, the cubic 6 x 6 interpolator with continuous second derivatives, as defined in (24), can be recommended for most common interpolation tasks. It appears to be the fastest six-point kernel to implement computationally. It provides eminent local and Fourier properties, is easy to implement, and has only small errors. The same characteristics apply to B-spline interpolation, but the 6 x 6 cubic avoids the intrinsic border effects produced by the B-spline technique. However, the goal of this study was not to determine an overall best method, but to present a comprehensive catalogue of methods in a uniform terminology, to define general properties and requirements of local techniques, and to enable the reader to select that method which is optimal for his specific application in medical imaging.

Diagnostic Imaging↗
PubMed1999

Post-Doc: satisfying the information needs of general practitioners in continuing medical education and daily practice.

The learning needs of General Practitioners (GPs) are not optimally covered by traditional ways of Continuing Medical Education (CME). The European-funded Post-Doc project sets up a model for a European internet-based infra-structure and learning environment to support GPs' individual CME activities, focusing on problems of daily work. It integrates education, information and communication for both daily work and learning at home. Based upon a user requirements analysis, the service includes multimedia training applications, selections of relevant information sources, a calendar of events, and communication facilities. The service is intended to fit in existing health care structures and accreditation systems. Because of different languages and user requirements in Post-Doc's regions each region builds an own website. The regional prototypes are built and evaluated in cooperation with small core user groups. This regional approach proved feasible and also influenced the network structure with regional demonstrator websites and one master website including central functionality.

Computer-Assisted Instruction↗
PubMed1998

Observer-independent registration of perspective projection prior to subtraction of in vivo radiographs.

OBJECTIVES: To prove that the model of perspective projection allows precise registration of intra-oral radiographs regardless of whether they have been acquired with or without individual adjustment aids and independent of the human observer or computer algorithm marking corresponding landmarks in the images and, based on in vivo radiographs, to introduce and evaluate a model-based registration method. METHODS: Five observers (three experts and two non-experts) were asked to define corresponding points in 24 pairs of in vivo dental radiographs from the same region of the same patient. The landmarks were used to fit the model of perspective projection applying the least squares method. Misplaced landmarks were detected and suppressed by analysing the quality of all subsets of landmarks with respect to the minimal residual (leaving one out method). In addition, local correlation was used to optimize the quality of registration as well as observer independence. RESULTS: Using six or more corresponding landmarks in both radiographs the correlation of the images registered was > 0.95 (S.D. < 0.063) irrespective of the observers' expertise. CONCLUSIONS: Perspective projection is a reliable model for sequentially acquired intra-oral radiographs. The co-ordinates of anatomical landmarks are useful for determining the parameters of perspective projection. Local correlation and leaving one out techniques improve the geometrical adjustment as well as observer independence. Registration is nearly independent of the actual position of the landmarks and hence independent of the observer. Our algorithm will also be useful for registration techniques based on automatically detected landmarks.

Humans↗
PubMed1998

Formalising and acquiring model-based hypertext in medicine: an integrative approach.

Combining a knowledge acquisition methodology with a powerful data model we present an approach to the acquisition, maintenance and browsing of scientific medical hypertext. The hypergraph-based data model supports the consistent treatment of cyclic data structures, the nesting of complex object and provides an elegant way of path declaration to represent time-dependent medical processes or large hypertext tours. It encourages a stepwise schema design and therefore supports a spiral-shaped acquisition process. We formally define view mechanisms on the basis of a rule-based query and modification language. The views enable a context-sensitive presentation of medical knowledge according to the informational needs of the physician. Our approach has been applied to the implementation of an authoring and tutoring environment for a computer-based hypermedia reference book for cerebrovascular diseases (NeuroN). During the acquisition process the expressive power and flexibility of the representational formats have been evaluated.

Artificial Intelligence↗
PubMed1997

Prednisone and aspirin in women with autoantibodies and unexplained recurrent fetal loss.

BACKGROUND: Recurrent fetal loss has been well described in women with antiphospholipid antibodies. Such women also often have other autoantibodies commonly found in patients with systemic lupus erythematosus. Treating them with prednisone and aspirin may reduce the risk of fetal loss. METHODS: We screened 773 nonpregnant women who had the unexplained loss of at least two fetuses for antinuclear, anti-DNA, antilymphocyte, and anticardiolipin antibodies and for the lupus anticoagulant. Of 385 women with at least one autoantibody, 202 who later became pregnant were randomly assigned in equal numbers to receive either prednisone (0.5 to 0.8 mg per kilogram of body weight per day) and aspirin (100 mg per day) or placebo for the duration of the pregnancy. The women were stratified according to age (18 to 34 years or 35 to 39 years) and the week of gestation at which the previous fetal losses had occurred (< or = 12 or > 12 weeks). The primary outcome measure was a successful pregnancy. RESULTS: Live infants were born to 66 women in the treatment group (65 percent) and 57 women in the placebo group (56 percent, P=0.19). More infants were born prematurely in the treatment group than in the placebo group (62 percent vs. 12 percent, P<0.001). The major side effects of therapy in the mothers were hypertension (treatment group, 13 percent; placebo group, 5 percent; P=0.05) and diabetes mellitus (15 percent and 5 percent, P=0.02). CONCLUSIONS: Treating women who have autoantibodies and recurrent fetal loss with prednisone and aspirin is not effective in promoting live birth, and it increases the risk of prematurity.

Abortion, Habitual↗
PubMed1992

Multimodal tests of cerebrovascular reactivity in migraine: a transcranial Doppler study.

Altered cerebral vasoreactivity (CVR) has been implicated in migraine. To test this hypothesis, we studied CVR as measured by transcranial Doppler ultrasound (TCD) in 11 migraineurs and 12 healthy controls of similar age. Mean flow velocities (MFV) in the middle cerebral artery (MCA) were recorded during a cognitive and two motor tasks. MFV in the posterior cerebral artery (PCA) were measured during photic stimulation and observation of complex images. The increase of MFV in the MCA during the cognitive task was greater in migraineurs than in controls (9.1% vs 5.0%; P = 0.06). The increase of MFV in both tests for PCA reactivity was significantly greater in migraineurs than in controls: 17.4% vs 9.9% for photic stimulation (P less than 0.05) and 20.3% vs 10.2% for observation of complex images (P less than 0.05). Owing to overlap of individual results, the discriminative value of both tests was unsatisfactory. The variability of flow velocities as measured by standard deviations of MFV was significantly greater in migraineurs than in controls during all tests of PCA vasoreactivity. Differences in CVR between migraineurs and normal controls may be detected by TCD testing, in particular in the PCA territory. For individual diagnostic purposes, CVR tests proved to be insufficient.

Adult↗
PubMed1992

[Vertebrobasilar ischemia. Value of Doppler ultrasound in the acute phase].

We prospectively studied patients with acute vertebrobasilar ischaemia to assess the value of Doppler ultrasound compared to cerebral angiography during initial evaluation. Doppler ultrasound was diagnostic in 11 of 14 patients (79%). Transcranial ultrasonic examination yielded important information in addition to extracranial findings in 8 of 11 patients. Depending on the underlying vascular pathology, Doppler ultrasound proved to be a useful screening instrument to support acute management of vertebrobasilar ischaemia. With regard to clinical symptoms and ultrasonic findings, practical consequences for diagnostic evaluation are proposed.

Blood Flow Velocity↗
PubMed1990

Transcranial Doppler evaluation of common and classic migraine. Part I. Ultrasonic features during the headache-free period.

To study vascular abnormalities in migraine, transcranial Doppler (TCD) was used for evaluation of 100 consecutive patients with either common or classic migraine during the headache-free period. We insonated the basal cerebral arteries and the internal carotid artery (ICA) in the neck. Particular ultrasonic features in migraineurs included intracranial elevations of mean flow velocity (MFV) above 3 standard deviations of normal values in 16%, probably reflecting increased vasotonus. Marked asymmetry of MFV in corresponding intracranial arteries was found in 12%, and could represent "asymmetrical" vascular tone. Characteristic vascular bruits of low frequency and sometimes harmonic quality were detected in 56%. When compared to TCD findings in 40 young controls, MFV were significantly higher in all intracranial arteries in migraineurs, but not in the cervical ICA. Marked differences were also found for incidence of MFV elevations and vascular bruits (p less than 0.0001). Vascular reactivity in response to eye closing as measured by flow changes in the posterior cerebral artery (visually evoked flow) was significantly greater in migraineurs than in controls (%MFV change, 14.1 +/- 5.4 vs 11.4 +/- 4.8; p = 0.004). TCD features did not discriminate common from classic migraine. Taken together, our results support the view of intracranial vascular abnormality in migraineurs reflecting, in particular, a narrower and more reactive arterial tree. The value of TCD in the differential diagnosis of "vascular headache" and in the study of migraine pathophysiology will have to be determined in the future.

Adult↗
PubMed1990

Transcranial Doppler evaluation of common and classic migraine. Part II. Ultrasonic features during attacks.

Transcranial Doppler (TCD) examinations were performed in 13 patients with common and 5 patients with classic migraine during attacks and compared to TCD findings during the headache-free period. Two distinct patterns of flow changes were detected to distinguish common from classic migraine on the basis of TCD findings. During attacks, patients with common migraine exhibited reduction of flow velocities associated with an increase of pulse wave amplitudes. Vascular bruits that were heard during the headache-free interval often disappeared. Opposite changes were found in attacks of classic migraine during the headache phase with increase of flow velocities, decrease of pulsatility and more prominent or newly appearing bruits. These findings were often diffuse and did not appear to correlate with side of headache or side of neurological aura. Uniform changes occurred in the cervical internal carotid artery and the basal cerebral arteries in either form of migraine. We propose that these changes represent caliber fluctuations of the large arteries, suggesting vasodilatation during attacks of common migraine and vasoconstriction during attacks of classic migraine. We do not intend to imply a casual role of these preliminary findings in migraine pathogenesis, but we suggest that TCD be used in combination with other methods to study vascular changes in migrainous disorders.

Acute Disease↗