[Numerical modeling of ultrasound thermotherapy]. / Numerische Modellierung der Ultraschall-Thermotherapie.

In ultrasound thermotherapy (USTT) high intensity focused ultrasound (HIFU) is used for noninvasive thermal treatment of human tissue deep inside the body. In this paper a FDTD-model is presented to simulate USTT. It combines nonlinear ultrasound propagation and broadband tissue attenuation together with the bio-heat transfer equation for calculation of temperature distribution in tissue. The temperature dependence of parameters is integrated in the complete model. Simulation results demonstrate the potentialities of this simulation tool to analyze and optimize thermotherapy.

Ease of use versus clinical effectiveness of restorative materials.

"Ease of use," as applied to dental materials and techniques, means different things to different people. Factors that may contribute to ease of use include a minimum number of application stages, easy application and shaping ability, quickness of use, lack of stick, and moisture sensitivity. Ease of use may also imply that a material or technique does not cause stress for the dentist and patient, is cost effective, is easy to learn, and should provide the operators with a sense of satisfaction with their work. Similarly, "clinical effectiveness" of the treatments prescribed for patients is not always capable of being accurately defined. Suggested factors that may contribute to clinical effectiveness include a lack of patient complaints with respect to longevity and/or cost, no secondary caries, and preservation of the remaining tooth structure during functional loading. Ease of use and clinical effectiveness are not necessarily related, but they must be combined for a technique to be successful. The achievement of this demands a partnership between clinicians, manufacturers, and patients.

Hemimethylation of DNA prevents chromatin expression.

The activity of hemimethylated herpes simplex virus thymidine kinase DNA and chromatin was analyzed by microinjection and thymidine incorporation into the DNA of thymidine kinase-negative Rat2 cells. Hemimethylated DNA was obtained by in vitro replication of single-stranded M13 DNA constructs and of chromatin produced by in vitro reconstitution of the DNA with purified chicken histone octamers. We found that methylation of either the coding or the noncoding DNA strand was sufficient to block expression of the hemimethylated chromatin. In contrast, the hemimethylated DNA was as active as the unmethylated control DNA after microinjection until chromatin formation occurred in the recipient cells. Microinjection of chromatin hemimethylated by bacterial Hae III methyltransferase excluded the possibility that inactivation was caused by symmetrical methylation of the injected molecules.

Helper activity for gene expression, a novel function of the SV40 enhancer.

In this investigation we demonstrate that the enhancer of SV40 possesses an additional function which is a 'helper activity' for a more efficient transfer of viral DNA from the cytoplasm into the nucleus. After DNA transfection into rat-2 cells, the rate of CAT gene expression linked to SV40 promoter/enhancer (pSV2CAT) was approximately 50 fold higher than linked to the tk promoter (pBLCAT2). After direct nuclear microinjection this difference was reduced to a factor of 10. However cytoplasmic injection of the same number of DNA molecules/cell showed again a 50 fold increase for the SV40 promoter/enhancer-CAT construct. This difference was not due to selective degradation of the pBLCAT2 DNA. The 'helper function' did not require the intact 72 bp sequence. In vitro synthesized enhancers lacking certain enhancer motifs (GT-I, TC-II and TC-I sequence) were still effective after cytoplasmic injection whereas an 8 bp deletion (representing a part of the AP-I motif) on the downstream side strongly reduced the helper function after cytoplasmic injection but not the classical transcriptional enhancement after direct nuclear transfer.