Biomedical subjects

T Tolxdorff

Publications and source records attributed to T Tolxdorff.

15 recordsLinked to original sources

PubMed1998

Implementing HL7: from the standard's specification to production application.

A C++ implementation of the HL7 health-care data interchange standard was developed by automatic methods applied to the authoritative specification of the standard. The reusable class library thus created presents an intuitive, flexible, and easy-to-use application programming interface to the HL7 protocol. This allows HL7 applications to be developed quickly while a high conformance to the standard is ensured.

Artificial Intelligence↗

PubMed1997

Knowledge-based system ADNEXPERT to assist the sonographic diagnosis of adnexal tumors.

ADNEXPERT is a knowledge-based system for the computer-assisted ultrasound diagnosis of adnexal tumors. In a case-based approach, ADNEXPERT used histopathologic and sonographic data from 2,290 adnexal tumors. After an ultrasound examination, the gynecologist interacts with the system. A maximum of 15 questions are posed; all but one question (age) relate to the sonographic findings. The help system gives online access to an ultrasound image library. Once the dialogue is complete, ADNEXPERT assesses the adnexal tumor pathology and makes a histological classification. A certainty factor (CF) model is used for knowledge representation. The CFs of the knowledge base are computed from the case database. During system evaluation, the accuracy of ADNEXPERT was tested by 69 new adnexal tumor cases, for which verified histopathological diagnoses were available. ADNEXPERT accurately assessed pathology in 49 cases (71%); in 10 cases (14%) correct indications to pathology were given; no diagnostic hints were attained in 2 cases (3%); and 8 cases (12%) were falsely diagnosed. Based on the positive results of the evaluation, ADNEXPERT will be tested under clinical conditions.

Adolescent↗

PubMed1995

[RADIOLIS. A radiologic instruction and training system for systematic evaluation of roentgen images exemplified by focal bone lesions].

RADIOLIS is an instructional software system for radiological training that guides the user through a systematic analysis of an image. The backbone of the analysis is a detailed and structured questionnaire which, as applied to our example, includes all relevant differential-diagnostic criteria for focal bone lesions. The variation range of the radiomorphologic characteristics in the questionnaire is introduced to the user with digitized X-ray images, making the simulation of an image analysis possible. In preparation, diverse teaching/learning methods reinforced by instructional psychology were incorporated during the system's development. At the core of the training system are an expandable image database and a database containing descriptions of image material formulated by radiology experts. The field of focal bone lesions, for instance, has already been integrated into RADIOLIS. A graphic user interface and an interactive dialogue enable both comfortable and simple use of the system and the user-specific structuring of the learning process.

Bone Neoplasms↗

PubMed1995

Differentiation of normal and pathologic brain structures in MRI using exact T1 and T2 values followed by a multidimensional cluster analysis.

A new method to differentiate and classify normal and pathologic brain tissue in Magnetic Resonance Imaging (MRI) is introduced. With a special pulse sequence, exact T1 and T2 values are simultaneously acquired, where the T2 values may show a biexponential decay behavior. The automatic segmentation of the tissue is based on a histogram analysis of the multidimensional parameters. The tissue-characterizing parameters are stored in a database, which serves as an objective classification of different tissues. A pilot study with 15 healthy volunteers and 100 patients showed a good differentiation between normal tissue like white and gray matter, cerebrospinal fluid, muscle, and fat, thereby revealing a biexponential decay behavior of fat. Pathologic tissue-like edema and meningioma could be classified with high accuracy, while glioblastoma or astrocytoma were difficult to classify because of their non-homogeneous structures.

Adipose Tissue↗

PubMed1995

Texture-based X-ray image segmentation by topological map.

The texture-based segmentation of x-ray images of focal bone lesions using topological maps is introduced. Texture characteristics are described by image-point correlation of feature images to feature vectors. For the segmentation, the topological map is labeled using an improved labeling strategy. Results of the technique are demonstrated on original and synthetic x-ray images and quantified with the aid of quality measures. In addition, a classifier-specific contribution analysis is applied for assessing the feature area.

Bone Diseases↗

PubMed1992

In vivo NMR T2 relaxation of experimental brain tumors in the cat: a multiparameter tissue characterization.

Experimental gliomas (F98) were inoculated in cat brain for the systematic study of their in vivo T2 relaxation time behavior. With a CPMG multi-echo imaging sequence, a train of 16 echoes was evaluated to obtain the transverse relaxation time and the magnetization M(0) at time t = 0. The magnetization decay curves were analyzed for biexponentiality. All tissues showed monoexponential T2, only that of the ventricular fluid and part of the vital tumor tissue were biexponential. Based on these NMR relaxation parameters the tissues were characterized, their correct assignment being assured by comparison with histological slices. T2 of normal grey and white matter was 74 +/- 6 and 72 +/- 6 msec, respectively. These two tissue types were distinguished through M(0) which for white matter was only 0.88 of the intensity of grey matter in full agreement with water content, determined from tissue specimens. At the time of maximal tumor growth and edema spread a tissue differentiation was possible in NMR relaxation parameter images. Separation of the three tissue groups of normal tissue, tumor and edema was based on T2 with T2(normal) < T2(tumor) < T2(edema). Using M(0) as a second parameter the differentiation was supported, in particular between white matter and tumor or edema. Animals were studied at 1-4 wk after tumor implantation to study tumor development. The magnetization M(0) of both tumor and peritumoral edema went through a maximum between the second and third week of tumor growth. T2 of edema was maximal at the same time with 133 +/- 4 msec, while the relaxation time of tumor continued to increase during the whole growth period, reaching values of 114 +/- 12 msec at the fourth week. Thus, a complete characterization of pathological tissues with NMR relaxometry must include a detailed study of the developmental changes of these tissues to assure correct experimental conditions for the goal of optimal contrast between normal and pathological regions in the NMR images.

Animals↗

PubMed1992

[New developments in the computer-assisted diagnosis of focal bone lesions].

Since the 1960s there have been numerous reports in the literature about computer-aided medical diagnosis and therapy. However, so far computer-aided diagnosis has not become important in the clinical routine or in the field of radiology. This paper describes the hitherto existing proposals for expert systems to evaluate focal bone lesions and presents a new concept. The basic ideas of this program are: (1) a PC-based interactive dialogue along on the basis of a defined questionnaire; (2) the use of certainty factors to handle uncertainty and vagueness in evaluating the different radiological findings and their correlation with diagnoses; (3) the link between visual information and the questionnaire. The aims of such expert systems are (a) a complete and systematic analysis of the films, (b) independency of association with previously diagnosed cases in reporting the films, (c) the procurement and use of radiological descriptive terms, and (d) aid in the radiological evaluation of focal bone lesions.

Bone Neoplasms↗

PubMed1990

Magnetic resonance imaging and regional biochemical analysis of experimental brain tumours in cats.

Multiexponential evaluation of in vivo multi-echo T2 measurements at 4.7T in cat brain with implanted tumour led to monoexponential results in all tissues. T2 of normal brain tissue, tumour and oedema was 67 ms, 10-100 ms and 90-180 ms, respectively. In the ventricles biexponential solutions were observed with T2 values and relative contributions of these two components differing for ipsi- and contralateral side. Best discrimination between tumour and oedema was achieved by the magnetization value M (O), and between oedema and normal brain tissue by T2. T2 values were compared with in vitro biochemical analyses for ATP, lactate, glucose, tissue electrolytes and water content. NMR parameters provide reliable predictions about the water content and metabolic state of oedema, but not of the tumour.

Adenosine Triphosphate↗

PubMed1990

A new segmentation algorithm for knowledge acquisition in tissue-characterizing magnetic resonance imaging.

Tissue-characterizing magnetic resonance imaging (MRI) is a new imaging method for differentiation and biochemical characterization of tissue based on multidimensional MR-parameter information. To support knowledge acquisition in tissue-characterizing MRI, a new segmentation algorithm has been developed by using clustering techniques. The visualization of the complex biochemical MR-parameter information is performed by extraction of regions with similar biochemical properties. The clustering algorithm leads to an easy and comfortable handling of the complex tissue-characteristic MR information and supports knowledge acquisition for knowledge-based tissue characterization.

Brain↗

PubMed1988

[Computerized sonographic imaging of tongue motility using pseudo-3 dimensional reconstruction].

A new method for analysis and documentation of tongue movements was used in 24 healthy volunteers. This method enables direct digitalization of the information obtained from sequences of B-Mode pictures. Besides of allowing to further digital evaluation of the findings, it offers the facility of "pseudo 3D"-reconstruction of the tongue movements occurring on swallowing. The method appears to be of particular value for therapy control in neurological and phoniatric patients.

Deglutition↗

PubMed1985

Identification and characterization of tissues by T2-selective whole-body proton NMR imaging.

T2-selective proton imaging at 10 MHz is based on a Carr-Purcell-Meiboom-Gill pulse sequence with at least 36 echoes and 2 tau greater than or equal to 6 ms employing the projection reconstruction technique. The transverse magnetization decay of the volume elements is multiexponential composed of up to three monoexponential T2 components. The T2 values are arranged in T2 histograms which are slice specific. T2 windows are defined in the T2 histogram and used for imaging and for selecting T2 values which are assigned to proton classes and tissues. Tissue characterization is based on the visualization of differences in T2 behavior. The T2 values are transformed into 256 gray levels or, by use of a red-green-blue lookup table, into a rainbow code. Two display techniques have been developed and implemented in the RWTH Aachen Magnetic Resonance Software System (RAMSES): (i) for nonselective T2 imaging with secondary T2 selection and encoding of molecular classes on the basis of T2 values; (ii) for T2-selective imaging by employing combined primary and secondary T2 selection and encoding particular tissues and variations therein. The tissues can be identified by selecting different classes of molecules, like water, lipids, and proteins, when shifting the primary T2 window on the T2 axis of the T2 histogram.

Adult↗

PubMed1984

Analysis of multiple T2 proton relaxation processes in human head and imaging on the basis of selective and assigned T2 values.

Two-dimensional T2-selective proton imaging of human head has been performed at 10 MHz employing Carr-Purcell-Gill-Meiboom pulse trains with echo separation of 6 and 12 msec. Using the information of 36 spin echoes and applying a recovery time of 2 sec the magnetization decay has been traced. The multi-exponential T2 relaxation curve of each pixel of the image has been deconvoluted into up to three mono-exponential functions which are defined by 1/T2,i and alpha i. The T2,i values are represented in a T2 histogram of the slice and then selected for generating images which relate to protons with specific T2. The alpha i values indicate the relative amounts of the T2-selected protons. Imaging on the basis of alpha i values increases the contrast of the image. The multiple T2-selective imaging technique leads to head images which show selectively cerebrospinal fluid, gray matter, different types of white matter, and nonassigned fast-relaxing proton classes.

Brain↗

PubMed1983

[Significance of the albumin content for axillary metastasis in breast cancer].

A very pronounced and significant difference in albumen concentration is seen in 337 breast cancer tissues compared with 94 histologically benign breast tissues. In cancer of the breast the mean albumen concentration is 8.4 mg/g tissue, whereas benign breast tissues show in 94% of the cases an albumen concentration of over 10 mg/g tissue, mean 16.4 mg/g. In breast cancer, 72% of the tissues have an albumen concentration up to 10 mg/g (cancers of low albumen content), whereas in 28% the albumen concentration lies over 10 mg/g (cancers of high albumen content). On analysing the axillary lymph node involvement in the two groups: low albumen and high albumen concentration, we find significantly more axillary metastases in the low-albumen than in the high-albumen cancer group. The difference is most pronounced when more then 3 lymph nodes are involved. This high lymph node involvement is found twice as often in the low-albumen than in the high-albumen group. It can be concluded that low-albumen breast cancers show a noticeably higher tendency to axillary lymph node metastases than do high-albumen cancers.

Adult↗

PubMed1983

[Relation of steroid hormone receptors to axillary lymph node metastasis in breast carcinoma].

In 337 patients with primary cancer of the breast, the oestrogen and progesterone receptor concentration was correlated to the metastasis of axillary lymph nodes taking into account the age of the patients and the size of the primary tumour. The frequency of axillary lymph node involvement increases significantly with size, although not quite steadily but rather stepwise within the T classification. Whereas the tumour diameter influences the receptor status only slightly, the age of the patients plays a major rôle in the oestrogen receptor concentration. In the age group up to 50 years the oestrogen receptor concentration is significantly lower than in the age group over 50 years. There is no comparable influence of age on progesterone receptor concentration. With all 337 breast cancers, no difference in axillary lymph node metastasis is found either between oestrogen receptor positive and oestrogen receptor negative cancers, or between progesterone receptor positive and progesterone receptor negative cancers. In the age group up to 50 years, if looked upon separately, the oestrogen receptor positive cancers do show significantly more often an axillary lymph node involvement, than do oestrogen receptor negative cancers. As this difference exists in the age group up to 50 years only, it is assumed that endogenous oestradiol favours the axillary spread in oestrogen receptor positive cancers. With oestrogen receptor negative cancers the axillary lymph node involvement increases from the younger to the older age group, explaining why in unselected series the oestrogen receptor negative cancers show a more unfavourable course.

Adult↗

PubMedDate not supplied

[Possible applications of a method for 3D reconstruction of CT image data. OP-planning, finishing of individual alloplastic implants for replacement of cranial and maxillofacial bone structures].

A method for the three-dimensional reconstruction of CT-image data permits manufacturing of natural size anatomical models thus enabling preoperative measurements of relevant parameters (length, areas, and volumes). The methods described allow for new perspectives in preoperative planning of dental implants, particularly for the maxillary problem area. The use of 3D image data for manufacturing individual alloplastic implants simplifies the exact reconstruction of symmetrical bone structures, which up to now was impossible to achieve with conventional methods. Applications in the fields of orthodontic surgery and in neurological surgery are suggested. Refinement of available techniques is possible by means of additional segmentation of soft tissues, and by implementation of more sophisticated software for better visualisation and smoothly shaped surfaces. Future applications may even include aesthetic surgery.

Adult↗