Image Guided Radiotherapy (IGRT) Comparison between Cone Beam CT and Ultrasound System for Prostate Cancer

Abstract

The spectrum and intensity are calculated for radiated pressure generated from turbulent flow by diffraction at the edge of a rigid half‐plane. The formulation relates the radiated spectrum to the local wavevector‐frequency spectral density of pressure near the edge in a plane bounding the flow and is based on the notion of a hydrodynamic pressure field driving a contiguous sound field. In the half‐plane extension, the pressure diffracted by the rigid surface vanishes, and the spectrum of the driving hydrodynamic pressure may be approximated accordingly. Results are obtained without explicit reference to fluctuating velocity when the (low Mach number)flow is regarded as confined to one side of the half plane and a model suitable for turbulent‐boundary‐layer wall pressure is used for the driving spectrum. Results are also obtained from a model suitable for pressure in the inertial subrange of homogeneous turbulence. From the wall‐pressure model, the frequency spectrum of radiated pressure, for ωδ/U⩾5 cosα, where U denotes flow speed, δ boundary‐layer thickness (large‐eddy scale), and α the angle of flow relative to the edge normal, is found to vary as ω−2, U 6, and for fixed radiating edge length, cos2α. The corresponding frequency‐integrated intensity varies as U 5 and cosα. Pertinence of results for a rigid surface to typical water‐loaded, flexible surfaces is suggested. Experimental results are interpreted on the basis of the formulation.