Ray Theory-Based Transcranial Phase Correction for Intracranial Imaging: A Phantom Study

Abstract

Ultrasonic imaging provides a non-invasive way to diagnose brain disease. However, due to imaging degradation effects from the phase-aberration and reverberation, it is still challenging to achieve an accurate transcranial imaging. The objective of this work is to improve the quality of transcranial imaging. To this end, a ray theory based transcranial phase correction method was proposed to correct the phase abberation induced by cranial bones. With the pre-knowledge of the shape and longitudinal velocity of the cranial bones, the corrected phases are derived by solving eikonal equation (ray-theory). The Ideal Synthetic Aperture Focusing Technique (I-SAFT) is applied for signal acquisitions in simulations and in-vitro phantom experiment with one-element transmitting and all-element receiving method. Dynamic focusing is achieved at each imaging position with I-SAFT and the transcranial imaging distortion is modified with the proposed phase correction method. Simulations and experiments show that the imaging distortion of target circular phantoms was corrected, and the imaging quality is improved after the phase correction. With the proposed method, the average error of the central position of target phantoms decreases from 1.98 mm to 0.21 mm, the eccentricity of fitted ellipse averagely decreases from 0.63 to 0.19, and the average maximum luminance contrast of phantoms improves from 37.36dB to 42.41dB. It is illustrated that the proposed ray-theory based phase correction method might be useful for intracranial imaging.

Refraction-Corrected Transcranial Ultrasound Imaging Through the Human Temporal Window Using a Single Probe

“…As a result, optimal focusing with the imaging transducer was limited to a region, at rather large depth (for the imaging transducer) close to the part of the skull in contact with the calibration transducer, and at lateral positions where the skull was sufficiently flat to enable close contact with the calibration transducer. Prior knowledge on the compressional sound speed or thickness of skull [53], [58], [76], [88], [89] and correction based on CT scans [53]- [55] are also impractical on-site as these parameters vary in person [23], [25], [29], [51], [52], [90], [93] and EMS are not always equipped with CT scanners.…”

“…More recently, approaches that model refraction through the true geometry and thickness of the skull have been proposed; however, the method requires estimates of the thickness and wave speed in the skull at multiple positions with dedicated ultrasound measurements prior to image reconstruction [50]- [52]. Another family of methods relies on a CT or MRI scan of the skull to determine its geometry and knowledge or assumption of wave speed in bone, prior to TUI [53]- [56].…”

Transcranial ultrasound simulations: A review

“…However, smarter homogeneous models can be used to improve computation time without losing too much accuracy. For example, Jiang et al 74 . showed that taking different averaged properties for the refraction computations and for the time‐of‐flight computations significantly improves the accuracy without increasing the computation time.…”

Accelerated 2-D Real-Time Refraction-Corrected Transcranial Ultrasound Imaging

“…Phase aberration correction was first proposed by modeling the temporal bone as an infinitesimally thin aberrating layer at the surface of the transducer (so called the near-field phase-screen aberration model) [24][25][26], but the correction obtained by this approach is limited (axially and laterally) to a certain region called the isoplanatic patch [3,[27][28][29][30]. Another approach is using either ultrasound measurements [31][32][33] or CT/MRI scans of the skull to obtain the true geometry and sound speed of the temporal bone prior to image reconstruction, and then correct phase aberration and refraction during image reconstruction [34][35][36][37]. Recently, we have shown the feasibility of single-sided two-dimensional transcranial ultrasound through the human temporal window using a single handheld commercial probe, where the position, true geometry and sound speed of the bone layer were estimated for an accurate correction of phase aberration and refraction [38,39].…”