A hybrid method for restoring the fidelity of ultrasound images of vessels

Distortions in ultrasound images of vessels can be significant even though these effects are negligible at larger scale imaging. System and propagation effects operate on a scale comparable to the dimensions of thin walls and features in longitudinal views. As a result , diagnostic inferences based on observed geometric features in the image such as lumen diameter and wall thickness may be in error. Also, these distortions can vary from imaging system to system as well as the settings and spatial locations within the same system. A hybrid approach combines measurements with wave models to reduce system and propagation effects on the image. First, a simulation model was developed that included reflections, reverberations , absorption and causal phase velocity dispersion as well as system transmit characteristics. Second, a sequence of measurement and modeling steps was used to extract data and incorporate it into correction and inverse filtering. The methodology was tested on a disk-shaped tissue mimicking phantom material and verified by independent physical measurements. Raw rf beamformed data was captured from a Terason 3000 ultrasound imaging system connected to a 5-12 MHz linear array. A tissue mimicking phantom in the shape of a disk was characterized by independent physical measurements. The thickness obtained from outer surface to outer surface (as is usually done in edge detection algorithms for vessel walls) from rf data gave a value of 1.00 cm or 5 % error compared to the corrected result of 0.987 cm, an error of 0.7%. Pulses from the top and bottom surfaces, originally .505 and .711 mm, were reduced by 83 % to 0.087 and .119 mm, respectively, after correction. Data from a more relevant thin walled tube of inner diameter 0.5mm provided an uncorrected value of 0.37 mm 26 %error and a corrected value of 0.493 mm (1.6 % error).A bovine bronchial airway, mounted in a tank filled with Krebs solution and subjected to doses of acetylcholine to simulate asthma li- e reactions, was observed to close down at higher doses. Early results showed that corrected images indicate the inner diameter was still open. A combination of correcting for propagation effects and inverse filtering has resulted in higher resolution images that are significantly more accurate representations of vessels and has provided ultrasound measured tissue parameters of absorption and sound speed for the vessel walls.