Quantitative sparse array vascular elastography visualizes the shear modulus distribution within vascular tissues, information that clinicans could use to reduce the number of strokes each year. However, the low transmit power sparse array (SA) imaging could hamper the clinical usefulness of the resulting elastograms. In this study, we evaluated the performance of modulus elastograms recovered from simulated and physical vessel phantoms with varying attenuation coefficients (0.6, 1.5, and 3.5 cm−1) and modulus contrasts (−12.04, −6.02, and −2.5 dB) using SA imaging relative to those obtained with conventional linear array (CLA) and plane-wave (PW) imaging techniques. Plaques were visible in all modulus elastograms, but those produced using SA and PW contained less artifacts. The modulus contrast-to-noise ratio decreased rapidly with increasing modulus contrast and attenuation coefficient, but more quickly when SA imaging was performed than for CLA or PW. The errors incurred varied from 10.9% to 24% (CLA), 1.8% to 12% (SA), and ≈4% (PW). Modulus elastograms produced with SA and PW imagings were not significantly different (p>0.05). Despite the low transmit power, SA imaging can produce useful modulus elastograms in superficial organs, such as the carotid artery.
Synthetic aperture (SA) ultrasound imaging provides accurate axial and lateral displacement estimates, however, the low transmit acoustic power of SA limits its clinical use. In this paper, we investigated the feasibility of using multi-element sub-aperture to improve acoustic power of SA imaging for carotid artery elastography. We used Field II to synthesize RF images with varying size sub-apertures, at different opening angles. Axial and lateral displacements were estimated by applying the 2D cross-correlation tracking algorithm to the synthesized RF images. Performance was assessed by computing root mean square error (RMSE) between the theoretical and estimated elastograms. A noticeable increase in power was observed for a configuration involving 3 -11 elements in the sub-aperture and an opening angle between 60°– 120°, respectively. More specifically, RMSE of axial and lateral displacements was less than 0.4% and 2%, respectively, and whereas in the case of radial and circumferential strain was less than 2% and 7%, respectively. These findings were encouraging enough to warrant further studies.
In this work, we explore the sensing applications of Surface Plasmon Resonance (SPR) enhanced
transmission of light through 1-D metal gratings on commonly available compact discs (CDs). We show that SPR
on CDs (CD-SPR) can be used to build a simple and compact angular displacement measurement system with submicro-
radian resolution. In addition we show that by controlling the azimuthal angle of the grating vector with
respect to incident k-vector, it is also possible to measure angular displacement in two planes which is not possible
with thin film SPR. The major advantage of this method is the compact form factor which will enable CD-SPR
based angular measurement systems to be integrated into other experimental setups with the least burden.