Supersampling Research Articles

SU-E-T-478: TomoTherapy® with 180 Beam Angles Per Rotation for Small Target Off-Axis Treatment

Purpose: Investigate the effect of increasing the number of beam angles per rotation to treat small off-axis targets with helical tomotherapy. Methods: TomoTherapy® gantry rotates continuously although radiation beam angles are discretized in the optimization. At each projection angle, the leaf open/close pattern is assumed unchanged. However, for small off-axis targets, the beam motion within a projection (7 degree) may require substantial portion of leaves to open/close for better target conformity. An off-axis (17 cm) target of 1 cm diameter in a cheese phantom was used in the planning study. The plans were optimized with 180 and 51 beam angles with source super sampling and the results were compared. The optimization constraints are the same for the two plans. Measurements were taken for a plan with four cylindrical targets of 1 cm diameter located at different radii from the central axis along a line in a cheese phantom. The plan was optimized and delivered with 180 beam angles on a Hi-Art® system. An EDR2 film was placed in the plane lined up with the four targets to measure the transverse dose distribution. Ion chamber point measurements were taken near three targets of the four. Results: Compared to the plan with 51 beam angles, the plan with 180 angles showed a 70% decrease of (D2-D98) for target dose uniformity, a 27% decrease of D100 for OAR avoidance and a 12% decrease of beam-on time. The film measurement showed good agreement between calculation and measurement. The point dose measurements showed agreement within a 1.6% difference. Conclusions: Delivery with 180 beam angles can improve the plan quality for small off- axis targets over 51 beam angles with source super sampling. Both target dose uniformity and OAR avoidance are improved. The plan with 180 beam angles was delivered and the measurements agreed with the calculation.

RAY TRACING RENDER MENGGUNAKAN FRAGMENT ANTI ALIASING

Rendering is generating surface and three-dimensional effects on an object displayed on a monitor screen. Ray tracing as a rendering method that traces ray for each image pixel has a drawback, that is, aliasing (jaggies effect). There are some methods for executing anti aliasing. One of those methods is OGSS (Ordered Grid Super Sampling). OGSS is able to perform aliasing well. However, this method requires more computation time since sampling of all pixels in the image will be increased. Fragment Anti Aliasing (FAA) is a new alternative method that can cope with the drawback. FAA will check the image when performing rendering to a scene. Jaggies effect is only happened at curve and gradient object. Therefore, only this part of object that will experience sampling magnification. After this sampling magnification and the pixel values are computed, then downsample is performed to retrieve the original pixel values. Experimental results show that the software can implement ray tracing well in order to form images, and it can implement FAA and OGSS technique to perform anti aliasing. In general, rendering using FAA is faster than using OGSS although there is some situation where the time effectiveness is equal. This is possible since the process of intersection searching on FAA needs additional time. Rendered images using FAA are relatively similar to those using OGSS.

高圧力科学におけるＩＴ 粉末Ｘ線回折像解析プログラムＰＩＰの進展

Recent progress in the software PIP is briefly summarized. New algorithms of the divided histogram method and the super sampling method have greatly improved the accuracy for two-dimensional image to one-dimensional profile conversion. The accuracy of peak positions in the one-dimensional pattern has been increased by optimizing their fitting region. Many other issues such as running with a TrueColor mode and porting to other platforms are also introduced.

Speech compression by speech recognition

A method of transmitting speech signals with reduced bandwith requirements. With this invention an original speech signal is first converted to a textual representation, and a facsimile of the original speech is determined from the textual representation. Then a minimum error turn is derived from the difference between the original speech signal and the facsimile of the original speech signal. The minimum error turn is then compressed, and it is this compressed minimum error turn, along with the textual representation, that is transmitted on the communications medium. At the receiving end, the textual representation and the difference representation are split through a demultiplexer. The textual representation is then passed through a synthesizer while the difference representation is passed through a mapper. The synthesizer along with synthesis parameter storage converts the textual representation into a digital representation of speech, while the mapper modifies the received difference representation by applying sub or super sampling corrections.