Birk, M.

Dapp, R.

Kretzek, E.

Ruiter, N.V.

Zapf, M.

English

Ruiter, N. V.

KITopen

Institute for Data Processing and ElectronicsHermann-von-Helmholtz-Platz 176344 Eggenstein-Leopoldshafen, Germanywww.ipe.kit.eduEvaluation of phase aberration correction for a 3D USCTE. Kretzek, R. Dapp, M. Zapf, M. Birk, N.V. Ruiter Introduction3D ultrasound computer tomography (3D USCT) promises reproducible high-resolution images for early detection of breast tumors. A prototype for 3D USCT has been developed at KIT. It has an optimized aperture in form of a semi-ellipsoid to maximize the isotropy of the 3D point spread function (PSF). The prototype provides three different modalities (reflectivity, speed of sound, and attenuation), and high image quality using 2041 transducers within one recording step. In this setup, with a diameter of 26 cm and height of 17 cm, ultrasound can travel over long distances up to 52 cm. Phase aberrations (PA) due to speed of sound (SOS) variations inside the measuring object (water, different breast tissues) cause many pulses not to overlap in a distinct voxel at the coherent reflectivity reconstruction. Previous research [1] showed that image quality can be increased significantly performing a PA correction. This is done by calculating an average SOS with Bresenham's line algorithm [2] from a SOS volume of the measuring object in several resolutions as approximation. As no quantitative error assessment was done yet, a simulation based on ray tracing is used to quantify their image degradation caused by PA and the effects of the applied PA correction. This is done with the metrics: constrast, resolution and displacement.References[1]  N. V. Ruiter, R. Schnell, M. Zapf, and H. Gemmeke, “Phase Aberration Correction for 3D Ultrasound Computer Tomography Images,” in 2007 IEEE Ultrasonics Symposium Proceedings, 2007[2]  J. D. Foley, A. van Dam, et al, Computer Graphics: Principles and Practice, Addison-Wesley Publishing Company, 1996, 2nd Edition in C.ConclusionSeveral negative influences on image quality could be determined caused by PA for two SOS regions for contrast, position, and resolution. Performing PA correction significantly improve 3 3image quality of the simulation, already with a small SOS volume of 32 voxels. For SOS volumes from 64  voxels on, only a small increase of image quality could be observed. The PA correction was successfully validated with real experimental data see Figure 2. Furthermore the reconstruction should be performed with higher SOS volumes to reach high resolution images also largely differing SOS values.Figure 1. Simulation object (left) and schema of the A-scan generation (right).MethodsThe simulated object constains two regions with different SOS values, see Figure 1: The water with c =1500 m/s and the region wof a hemispherical approximated breast with c =1460-1520 m/s. A point scatterer represents a small cancerous lesion.b A-scan generation and reconstruction with SAFTThe simulation generates the pressure over time signals (A-scans) including the analytic determined PA due to SOS variations. The time-of-fight (TOF) of the ultrasound is determined with equation (1). The A-scan value at TOF is set and convoluted with a Sinc function to represent the pulse applied for image reconstruction (see Figure 1).n-0.1 -0.050 0.050.1-0.1-0.0500.050.1-0.18-0.16-0.14-0.12-0.1-0.08-0.06-0.04-0.02X in mY in mZ in m 0101p(t)ttp(t)tp(t)TOFTOFThe reconstruction of the reflectivity I(x) is done by a Synthetic Aperture Focusing Technique (SAFT) algorithm with equation (2):For reconstruction with phase aberration correction a more realistic average speed of sound value was evaluated. The travelled path through the SOS volume results by the harmonic mean of N visited SOS voxels and their local speed of sound values with equation (3):ResultsUsed image quality metrics:Contrast: maximum intensity at one voxel induced by from the point scatterer.Resolution: full width at half maximum (FWHM) of this contrast distribution.Displacement: Difference between position of the point scatterer and of the position of maximum intensity.nnnSOS simulation A-scan Sinc functionwithout correction with correctionFigure 2. Reconstruction of a thread inside gelantine phantom without (left) and with (right) phase aberration correction.radiusIep IprPoint scattererReceiver Emitter 01Z    XZ-layer: FWHM  = 0.37 mmYZ x 104-202-2020123YXZXYx 104x 104-1012-1012012XZ-layer: FWHM  = 0.38 mmXZPoint scatterer no. 23:Point scatterer no. 1:x 104x 104x 104 200 voxelYXZXY Z 200 voxel   XY-layer: FWHM  = 0.65 mmXYXY-layer: FWHM  = 0.52 mmXY051015051015051015024024024x 104x 104x 104 40 voxelx 104x 104x 104  XY-layer: FWHM  = 0.40 mmXY246-20246-20246051015051015 51015-20246x 105XY-layer, FWHM  = 0.58 mmXYx 104x 104x 104x 105x 105x 1051632486480961121280,150,30,450,60,750,91,051460 14701480 14901500 15101520SOS volume in voxel³ SOS in m/s0,9-1,050,75-0,90,6-0,750,45-0,60,3-0,450,15-0,30-0,15Contrast normalized to 1normalized to 1Average contrast of all point scatterer3248648096112128160,20,40,60,81460147014801490150015101520SOS volume in voxel³ SOS in m/sDisplacement in mm0,6-0,80,4-0,60,2-0,40-0,2in mmAverage displacement of all point scatterer 16 32 48 64 80 96112 1280,30,350,40,450,51460148015001520SOS volume in voxel³SOS in m/s0,45-0,50,4-0,450,35-0,40,3-0,35FWHM in mmin mmAverage FWHM of all point scatterer 40 voxelmax-15 max-10 max-5 max max+5 max+10 max+15 max+20  in voxel051015x 104max-10 max-5 max max+5 max+10 max+15 max+20  in voxel01234x 104max-20 max-15 max-10 max-5 max max+5 max+10 max+15 max+20  in voxelmax-15 max-10 max-5 max max+5 max+10 max+15 max+20  in voxel-1012x 104max-15 max-10 max-5 max max+5 max+10 max+15 max+20  in voxel051015x 104max-20 max-15 max-10 max-5 max max+5 max+10 max+15 max+20  in voxel-202x 104A-scansA-scansA-scansA-scansA-scansA-scansSOS  = 128³ voxel, C  = 1460 m/svolume Breast1-0.1 -0.050 0.050.1X in m-0.1-0.0500.050.1-0.16-0.14-0.12-0.1-0.08-0.06-0.04-0.02-0.18Y in mZ in m23PSF  = 100ZoomSOS  = 16³ voxel, C  = 1460 m/svolume BreastPSF with PA correction:PSF  = 100Zoom231-0.1 -0.050 0.050.1X  in m-0.1-0.0500.050.1-0.16-0.14-0.12-0.1-0.08-0.06-0.04-0.02-0.18Y in mZ in mPSF  = 100ZoomPSF without PA correction:C  = 1460 m/sbreast-0.16-0.14-0.12-0.1-0.08-0.06-0.04-0.02-0.18Z in m-0.1-0.0500.050.1Y in m-0.1 -0.050 0.050.1X in m231

Evaluation of phase aberration correction for a 3D USCT

https://publikationen.bibliothek.kit.edu/220094458/3816458

Evaluation of phase aberration correction for a 3D USCT

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