Ultrasound Plane Wave Doppler Quantification Using a Wall-Less Spinal Cord Representative Phantom

Spinal cord injuries are particularly impairing for patients, and can cause significant functional loss. Ultrasonic Doppler imaging is currently being studied as a clinical tool to link vascularization with injury severity. The sensitivity limitation may be improved by using a plane wave algorithm and should thus allow velocity estimation on small vessels with high blood velocities. This study quantifies the efficiency of both the conventional focused and the plane waves algorithms using wall-less phantoms with vessels of diameters close to what is observed in the spinal cord. The design of a wall-less flow phantom with small vessel diameters allowed us to compare the two Doppler sequences in conditions similar to those present in spinal cord imaging. This study focuses on seven vessel diameters ranging from 0.25 mm to 0.7 mm. The blood mimicking fluid flow was controlled using a pump ensuring a mean velocity of 10 cm/s. Using a Region Of Interest (ROI) centered on the maximum value pixel, the Signal-to-Noise Ratio (SNR), the diameter and velocities were calculated from the power Doppler images with both imaging processes. The algorithms' parameters were chosen to ensure the same Doppler sampling frequency, which allowed comparisons. The insonification angle was approximately 25° using a center frequency of 8.3 MHz. The SNR was 13 to 18 dB higher when using plane waves. The focused algorithm consistently overestimated the calculated diameter and underestimated the mean velocities. Higher SNR and more accurate diameters and velocities were obtained when using the plane wave imaging algorithm. This algorithm is therefore of particular interest in spinal cord vascularization measurements.