Lawrence H Le | PubMed Health

PubMed2006

Identification and analysis of multimode guided waves in tibia cortical bone.

The hollow cylinder model filled with viscous-liquid is performed to simulate tibial bone shape in this paper. Short time Fourier transform (STFT) was applied to identify and analyze guided wave modes of a series of ultrasonic signals acquired at various transmitter-receiver positions for a fixed transmitter. Experimental results were compared with theoretical simulation. The high correlation values for group velocity were obtained between results of experiment and theory for L(0,2) (r=0.89, p<10(-5)), and L(0,3) (r=0.87, p<10(-5)). The experimental group velocities correlated strongly with cortical thickness (cortTh) for L(0,2) (r(2)=0.79, p<10(-5)) and L(0,3) (r(2)=0.74, p<10(-5)) at 0.5 MHz center frequency. The results showed that the STFT is an effective method to identify the propagating modes and derive dispersion information. The experimental results were in good agreement with theoretical predictions. This study suggests that the guided wave L(0,2) mode is a promising mode to assess change in cortical thickness.

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PubMed2003

Automatic quantitative low contrast analysis of digital chest phantom radiographs.

Up to the present, the majority of low contrast object evaluations performed on phantom images have been accomplished in a subjective fashion. This is mainly due to the time and effort required to manually measure each radiograph with a densitometer to obtain quantitative results. However, with the development of digital radiographic systems, it has become feasible to automate the detection and computation processes. In this work, a method that can automatically detect and compute the subject-to-noise ratio of the low contrast disks inside a geometric chest phantom is examined. This algorithm has the ability to locate the low contrast objects to an accuracy of less than one pixel, and provides results that are consistent with the understanding of subject-to-noise ratio. This algorithm should simplify the task of quantitative evaluation of contrast detail phantoms.

Algorithms↗