Contains reports on one research project.National Institutes of Health (Grant 5 P01 GM14940-05)National Institutes of Health (Grant NS08571

Hubelbank, M.

Tretiak, O. J.

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XI. COGNITIVE INFORMATION PROCESSINGAcademic and Research StaffProf. M. EdenProf. J. AllenProf. B. A. BlesserProf. T. S. HuangProf. F. F LeeProf. S. J. MasonProf. W. F. SchreiberProf. D. E. TroxelProf. I. T. YoungDr. R. R. ArcherR.J.B.R.J.A.AW.D.L.R.E.E.L.R.E.C.B.W.P.BochnerBowieBoyleBrennerEllis, Jr.FilipGoldsteinGrossmanHartmanA. HenckelsDr. G. H. GranlundDr. J. E. GreenDr. E G. GuttmannDr. K. R. InghamDr. J. I. MakhoulDr. D. M. OzonoffDr. D. SankowskyDr. O. J. TretiakF. X. CarrollGraduate StudentsM. HubelbankP. D. HenshawT. KitamuraJ. W. KlovstadG. P. MarstonG. G. MatisonG. PoonenN. RashidR. SingerD. G. SitlerD. A. FayDeborah A. FinkelC. L. FontaineC. C. HsiehE. R. JensenC. HehringD. E. RobinsonJ. M. SachsSandra A. SommersJ. S. VenturaA. A. SmithR. D. SolomonJ. H. StahlerW. W. StallingsW. D. StrattonK. P. WacksD. L. ShelanT. R. WillemainY. D. WillemsK. H. YungA. ARRAY TRANSDUCERS FOR MEDICAL USES OF ULTRASONICSt1. IntroductionUltrasonic systems of various types have been used in clinical practice for severalyears. Although with their aid the problem may be attacked in many different ways,with almost all of them an attempt is made either to take an internal measurement orto produce an image of soft tissue without the use of damaging radiation such as x raysor of internal probes. Essentially all systems depend on some form of reflectionof the ultrasonic signal. In the early designs it was assumed that the reflecting sur-faces were flat and perpendicular to the beam of ultrasonic energy. Such assumptionswere unacceptable, of course, so many of the newer systems use a technique called"compound scanning" which is somewhat more tolerant to the curvature of the surfacesthat are being examined. Compound scanning does not completely eliminate the prob-lems caused by surfaces that were not perpendicular to the axis of the ultrasonictransducer because it tends to only display surfaces that are tilted up to a few degrees.To overcome some of the limitations of previous systems, the approach describedThis work was supported principally by the National Institutes of Health (Grant5 P01 GM14940-05).tThis work was supported in part by the National Institutes of Health (Grant NS08571).QPR No. 101 235(XI. COGNITIVE INFORMATION PROCESSING)here makes use of an array of transducers that can not only be made tolerant totilted surfaces, but can also detect the angle of the tilt.2. TechniqueConsider the system shown in Fig. XI-1. Here a large plane transducer is drivenwith a pulse to generate a plane wave. This wave is reflected off the target and isreceived by the spherical receiver. If the target is of nonzero length and is not spher-ical, the energy reflected from it will be concentrated onto some limited area of thereceiver. We would then expect that it would be possible to determine the angle at whichthe target is tilted.AL (01 0)x3LTARGET11K- T/2TRANSMIT TER tRECEIVER COMPOSEDOF 2N+1 ELEMENTSFig. XI-1.A plane transmitter is pulsed toproduce a plane wave that is re-flected off a target of length L,tilted by an angle c. The reflectedenergy is measured at an angle 6by an element of a circular re-ceiver.Fig. XI-2.Reflected signal as a function of anglefor targets tilted from 0 to T/4 andL = k.As a test of the potential of this method of angle detection, a hypothetical two-dimensional situation was numerically evaluated. The target was assumed to be flatand of finite but small length, leading to the reflection pattern indicated by Eq. 1. (SeeFig. XI-2.) The receiver was assumed to be composed of a finite number of elements.Two tests were then made. In the first the correlation function was computed betweenthe signal received from a rotated target and the signal from a target parallel to thetransmitter, as indicated by Eq. 2. In the second test the autocorrelation function ofthe signal received from a tilted target was calculated by evaluating Eq. 3.QPR No. 101L][11236(XI. COGNITIVE INFORMATION PROCESSING)sin [ (sin + sin (-e)(AL(~, 6) = k (1)sin # + sin ((-O)where L is the length of the target, K includes all effects of attenuation andtarget absorption, ( is the angle at which the target is tilted, and 0 is the angleof the received signal. X is the wavelengthn=N 2c (0,) - A , ) AL ,0±r + 2)L n=-N(2'n=N n=NEc L 0, - 6 + n + 2)n=-N n=-Nn=N 2A (,e)= E AL AL ' +n)L n=-N(3)n=N n=NEA= AZ , AL  ' 0 +n=-N n=-NAs can be seen in Figs. XI-3 and XI-4, the 3-dB point corresponds to a 150 rotationof the received signal or a tilt of 7. 5' of the target. Thus there would appear to beno fundamental limitation at this level which would lead to the downfall of the entiresystem.To carry the evaluation a step further, and a little closer to reality, the receiverwas flattened out and focused. This was done in two dimensions as shown in Fig. XI-5.In such an implementation, the same transducer would be used for both transmitterand receiver. In transmit mode, all elements would be excited in parallel with ashort duration pulse. In receive mode, a delay would be introduced in the outputof each receiver element to equalize the total delay between the processor and thetarget. Effectively this means that the array produces a plane wave on transmit andis focused to some point during receive.The received signal is then correlated by multiplying the received and delayedsignals by the numerical value of the signal that would be received from a tiltedtarget. The resulting signals are then summed and sampled at the time correspondingQPR No. 101 237(, a7T/2-r/27/4OFig. XI-3. Sensitivity function for the con-figuration shown in Fig. XI-1using Eq. 3.Fig. XI-4. Sensitivity function for the config-uration shown in Fig. XI-1 usingEq. 2.S, 012(XI. COGNITIVE INFORMATION PROCESSING)INPUT YCOEFFICIENTI -OUTPUT--1~-TARGETL____ I __wIII- TRANSCEIVER COMPOSED OF 2N+1ELEMENTS CENTERED AT (0,0)Ai=AL (@, tan- 1di = MAX (02 +o- id)2) - 2 ( - i d) 2-N<i<NFig. XI-5. An array of elements is driven in parallel during transmit.During receive, the array is focused by the use of elec-trical delays and is made sensitive to a target at a specificangle (c).to the complete system time delay. The time sampling is done to improve the distanceresolution. This entire process is represented by Eq. 4.i=NLR, #,, L, , x O ( t ' x y ) = AL(i=-Nsin (Wsin )rL', i, x, y, = sin A L' (c tan-1 y -xid)t +h tx2 + (y -id) - xc /-1 YO - id. = tani xwhereQPR No. 101 239ox 32.25 A x 32.25 X35 X 355 X27.75 X 27.75X(a) (b)32.25X-3527.75 X(c)Fig. XI-6. Sensitivity functions for the arrays shown in Fig. XI-5. (a) Both target and receiver angleszero. (b) Only target tilted Tr/6. (c) Both target and receiver tilted at r/6. For L = L' = 4X,itc ft <n = 50, w = X, d = X, h(t) =0 otherwise.(XI. COGNITIVE INFORMATION PROCESSINGis the angle of target tilt that is being tested' is the actual angle at which the target is tiltedL is the assumed length of the targetL' is the actual length of the targetx and Yo are the x and y coordinates of the focal point of the arrayr L', i, x, (t) is the waveform received from a target at location x, y of length L'and tilted 4. The waveform is received at the i element of thearrayc is the velocity of soundW is the width of each receiver elementd is the distance between elements.Equation 1 was used as the directional function and a triangular waveform wasused as the system timpulse response. Figure XI-6 then shows the results of eval-uating Eqs. 4. Figures XI-6a and XI-6c shows the system response when the actualtarget angle and the assumed angle are the same. When the angles are differentas in Fig. XI-6b, the response is greatly reduced, as can be seen.3. ConclusionThe system that has been described here appears to be capable not only of detectinga target that is tilted with respect to the transmitter of an ultrasonic imaging systembut can even measure the angle at which the target is tilted. This capability should allowthe creation of an even more powerful system that could integrate all of the echoes froma large curved target into a display that would show all parts of the target rather thanonly those which are nearly parallel to the ultrasonic transducer.M. Hubelbank, O. J. TretiakQPR No. 101 241

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