title: Analysis and measurement of the modulation transfer function of harmonic shear wave induced phase encoding imaging.
abstract: Shear wave induced phase encoding (SWIPE) imaging generates ultrasound backscatter images of tissue-like elastic materials by using traveling shear waves to encode the lateral position of the scatters in the phase of the received echo. In contrast to conventional ultrasound B-scan imaging, SWIPE offers the potential advantages of image formation without beam focusing or steering from a single transducer element, lateral resolution independent of aperture size, and the potential to achieve relatively high lateral resolution with low frequency ultrasound. Here a Fourier series description of the phase modulated echo signal is developed, demonstrating that echo harmonics at multiples of the shear wave frequency reveal target k-space data at identical multiples of the shear wavenumber. Modulation transfer functions of SWIPE imaging systems are calculated for maximum shear wave acceleration and maximum shear constraints, and compared with a conventionally focused aperture. The relative signal-to-noise ratio of the SWIPE method versus a conventionally focused aperture is found through these calculations. Reconstructions of wire targets in a gelatin phantom using 1 and 3.5 MHz ultrasound and a cylindrical shear wave source are presented, generated from the fundamental and second harmonic of the shear wave modulation frequency, demonstrating weak dependence of lateral resolution with ultrasound frequency.
authors.affiliation: Department of Biomedical Engineering, University of Rochester, Rochester, New York 14627.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: McAleavey
mesh_terms: D000054:Acceleration; D000162:Acoustics; D000465:Algorithms; D003952:Diagnostic Imaging / Q000379:methods*; D054459:Elasticity Imaging Techniques; D004867:Equipment Design; D005583:Fourier Analysis; D005780:Gelatin; D010507:Periodicity; D019047:Phantoms, Imaging; D059629:Signal-To-Noise Ratio; D013016:Sound; D014465:Ultrasonics / Q000379:methods*
chemical_list: D005780:Gelatin