Biomedical subjects

T Tolxdorff

Publications and source records attributed to T Tolxdorff.

24 records · Page 2Linked to original sources

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

Units of measure in clinical information systems.

The authors surveyed existing standard codes for units of measures, such as ISO 2955, ANSI X3.50, and Health Level 7's ISO+. Because these standards specify only the character representation of units, the authors developed a semantic model for units based on dimensional analysis. Through this model, conversion between units and calculations with dimensioned quantities become as simple as calculating with numbers. All atomic symbols for prefixes and units are defined in one small table. Huge permutated conversion tables are not required. This method is also simple enough to be widely implementable in today's information systems. To promote the application of the method the authors provide an open-source implementation of this method in JAVA. All existing code standards for units, however, are incomplete for practical use and require substantial changes to correct their many ambiguities. The authors therefore developed a code for units that is much more complete and free from ambiguities.

Mathematical Computing↗

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↗