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ZigBee (IEEE 802.15.4) is a wireless mesh networking protocol low in cost, power, data rate, and complexity. To access Local Area Networks (LAN), 802.11b/g standard is used all over the world as Wi-Fi (Wireless Fidelity) standard. IEEE 802.15.4 Wireless Sensor Networks (WSNs) and IEEE 802.11b/g Wireless Local Area Networks (WLANs) are often collocated, causing a coexistence. The coexistence occurs because these networks share the same 2.4 GHz Industrial, Scientific, and Medical (ISM) band. A Simulation model has been introduced which completely reflects the ZigBee and WiFi coexistence. We have proposed frequency agility based interference avoidance algorithm. However, algorithm detects interference and adaptively switch nodes to safe channel for dynamically avoid WLAN interference with lower latency and energy consumption. The performance of ZigBee under WiFi is empirically evaluated in terms of the packet error rate (PER) and bit error rate (BER). The Simulation results using frequency agility algorithm demonstrate that the design guideline can efficiently mitigate the effect of WiFi interference and enhance the performance of ZigBee networks.

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Purpose: Region‐of‐interest (ROI) cone‐beam computed tomography (CBCT) can reduce dose to the patient. To provide data outside the ROI and overcome the truncation artifacts due to lack of data, we propose a new technique in which a material filter attenuates the beam except in a central ROI. DSA is used to subtract background bone and tissue as well as much of the ROI filter. Method and Materials: A ROI filter was made by making a 1 cm diameter aperture in 0.21 g/cm2 gadolinium screens. The ROI filter was fixed to the x‐ray tube assembly of a standard C‐arm gantry. Mask and contrast acquisitions were performed. Misregistration between the mask and contrast projections were corrected to reduce artifacts at the edge of the ROI. The intensities inside and outside the ROI were further equalized to adjust for the beam hardening effects of the filter outside the ROI. After corrections, reconstruction was performed with the acquisition system's software. Results: DSA‐ROI‐CBCT data were comparable to those obtained with standard DSA‐CBCT with registration and equalization each resulting in artifact reduction at the edge of the ROI. Data outside the ROI was noisier due to fewer photons. Since the x‐ray intensity in the periphery was reduced, the contrast‐to‐noise ratio of the iodinated vessels in the projections inside the ROI was approximately 40% higher than outside. The calculated integral dose reduction for the 12″ acquisition mode with the ROI filter was approximately 85% compared to a full‐field acquisition. Conclusion: By providing data outside the ROI, the new DSA‐ROI‐CBCT technique provides reconstructions inside the ROI comparable to standard DSA‐CBCT with minimal artifacts and significantly reduced integral dose compared to full‐field acquisition. This technique may be easily implemented in the clinical environment for DSA‐ROI‐CBCT reconstruction during ROI image‐guided interventions. (Support: NIH Grants R01‐NS43924, R01‐EB002873, Toshiba Medical Systems Corporation).