Design and preliminary tests of a family of adaptive waveforms to measure blood vessel diameter and wall thickness

In this article, we consider the adaptive design of waveforms to be used in vascular ultrasound. The advantage of these waveforms, when used with the proposed processing scheme, is that their application results in increased reflected energy, especially when compared with more conventional methods such as a short-gated sinusoid. This increase in reflected energy has potential to permit inferences to be made about wall thickness and vessel diameter from deeper vessels than possible with more traditional techniques. Here, the use of waveforms of the type A(t)e(j(kt/sup 2/)), 0/spl les/t/spl les/b, where A(t) is a specially designed envelope and k a sweep frequency, are proposed. Theorems are proved that describe how to choose an A(t) which results in either a maximum of reflected energy signal-to-noise ratio (SNR), or range resolution. The design of the waveform is adaptive in that both A(t) and k are derived in consideration of a specific blood vessel whose transfer function has been obtained experimentally. Numerical simulations illustrate the advantages of using these waveforms as well as the effects of the parameters. A simple experimental implementation of the methodology is presented on a brachial artery. The measurement of the impulse response of the artery is presented in this context. Results indicate that a processing gain in SNR over the instantaneous values obtained from the raw echo waveforms of 11 dB to 14 dB can be obtained via this methodology.