Sparse circular array methods, performance, and application to intravascular imaging

The performance of the sparsely filled, circular array geometry is evaluated as a potential means of providing a forward-looking, ultrasound guidance system compatible with existing, excimer laser angioplasty catheters. An evaluation of sparsely filled, circular arrays is performed using simulation and experiment. The two-dimensional nature of the array allows focusing both in elevation and azimuth, and therefore a three-dimensional volume can be imaged. The beam-forming algorithm is reviewed and a series of simulated point-spread functions are presented for different numbers of array elements. To test the theory, a low-frequency, 16-element model of the array was fabricated and evaluated at 1.25 MHz. This model array (16 times larger than an actual intravascular array) was used to demonstrate the 3-D focusing properties using strong specular reflectors in water. Construction methods used for the model array are discussed. Some speculation on future methods for incorporating the ultrasound array with the optical fibers of the laser angioplasty catheters is offered. >