We have dissected the mouse H-2Kb gene promoter in order to define the sequences responsible for induction by tumour necrosis factor (TNF-az). An enhancer element (-187 to -158) composed of two imperfect direct palindromic repeats has been shown to be necessary and sufficient for TNF-a induction of a heterologous promoter. A multimer of either repeat is also responsive, while a single copy is not: this is the situation in the ,B2-microglobulin (j2-m) promoter which contains a single palindrome and does not respond to TNF-a. We had previously found that the two repeats can bind a factor named KBF1. We show here that in the uninduced state the transcription factor AP2 binds to the interpalindromic region, while in TNF-treated cells an NFxB-like activity is induced which displaces both KBF1 and AP2 and binds to the two palindromes. This strongly suggests that induction of an NFxB-like activity is responsible for TNF-ca stimulation of mouse MHC class I genes.

Using an aiming device may increase the lateral accuracy of navigated needle insertion.

Abstract-Respiratorymotion is a major source of reduced quality in positron emission tomography (PET). In order to minimize its effects, the use of respiratory synchronized acquisitions, leading to gated frames, has been suggested. Such frames, however, are of low signal-to-noise ratio (SNR) as they contain reduced statistics. Super-resolution (SR) techniques make use of the motion in a sequence of images in order to improve their quality. They aim at enhancing a low-resolution image belonging to a sequence of images representing different views of the same scene. In this work, a maximum a posteriori (MAP) super-resolution algorithm has been implemented and applied to respiratory gated PET images for motion compensation. An edge preserving Huber regularization term was used to ensure convergence. Motion fields were recovered using a B-spline based elastic registration algorithm. The performance of the SR algorithm was evaluated through the use of both simulated and clinical datasets by assessing image SNR, as well as the contrast, position and extent of the different lesions. Results were compared to summing the registered synchronized frames on both simulated and clinical datasets. The super-resolution image had higher SNR (by a factor of over 4 on average) and lesion contrast (by a factor of 2) than the single respiratory synchronized frame using the same reconstruction matrix size. In comparison to the motion corrected or the motion free images a similar SNR was obtained, while improvements of up to 20% in the recovered lesion size and contrast were measured. Finally, the recovered lesion locations on the SR images were systematically closer to the true simulated lesion positions. These observations concerning the SNR, lesion contrast and size were confirmed on two clinical datasets included in the study. In conclusion, the use of SR techniques applied to respiratory motion synchronized images lead to motion compensation combined with improved image SNR and contrast, without any increase in the overall acquisition times. Index Terms-Four-dimensional(4-D) positron emission tomography, respiratory motion, super-resolution.

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