Systems and methods for producing an image from a rotational intravascular ultrasound device

Abstract

The invention generally relates systems and methods to for producing an image from a rotational intravascular ultrasound device. A method can include alternately transmitting complementary Golay codes to a plurality of transducers in a intravascular ultrasound device; receiving echoes of the complementary codes from the transducers; performing pulse compression of the echoes that comprises weighting the received echoes and summing an odd number of weighted echoes, wherein a center echo is given a weighted value of 1.0 and weighted sums of its neighbors constitute complementary echoes of a Golay pair; and producing an image from the compressed echoes. A system can include a processor; and a plurality of beam modules coupled to the processor, each module comprising: a receiver for receiving a trigger signal from the processor; a complex programmable logic device programmed with a Golay code; a high voltage switching transmitter; and an ultrasound transducer.

Claims

1. A system for intravascular ultrasound (IVUS) imaging, the system comprising: a rotational IVUS catheter configured to be positioned within a vessel of a patient, the rotational IVUS catheter comprising a single ultrasound transducer configured to rotate about an axis to obtain an IVUS image of the vessel; and a processor in communication with the single ultrasound transducer, the processor configured to: alternately transmit a first code and a second code of a pair of complementary Golay codes to the single ultrasound transducer while the single ultrasound transducer is rotating about the axis within the vessel; receive, from the single ultrasound transducer, echo signals associated with the pair of complementary Golay codes, the received echo signals comprising a first echo signal, a second echo signal, and a third echo signal; perform pulse compression of the received echo signals, wherein the pulse compression comprises weighting the received echo signals and summing an odd number of weighted echo signals, wherein the second echo signal is associated with the second code, and wherein the first and the third echo signals neighboring the second echo signal are each associated with the first code; and produce the IVUS image from the compressed echo signals.

2. The system of claim 1, wherein the second echo signal comprises a weighted value of 1.0, and wherein the first and the third echo signals individually comprise a weighted value less than 1.0 such that a total weighted value of the first and the third echo signals is 1.0.

3. The system of claim 2, wherein the weighted values of the first and the third echo signals are equal.

4. The system of claim 1, wherein a bi-phase window is applied over the pair of complementary Golay codes.

5. The system of claim 4, wherein the bi-phase window is one of a bi-phase rectangular window, a bi-phase Hamming window, a bi-phase Hanning window, or a bi-phase Bartlett window.

6. The system of claim 1, wherein the processor is configured to compute a convolution of the received echo signals of the pair of complementary Golay codes.

7. The system of claim 1, wherein the processor is coupled to a display device and causes the IVU S image to be displayed.

8. The system of claim 1, wherein the pulse compression further comprises: summing the first echo signal, the second echo signal, and the third echo signal to generate a first scanline; and summing the second echo signal, the third echo signal, and a fourth echo signal to generate a second scanline, wherein the fourth echo signal is associated with the second code.

9. The system of claim 8, wherein: for the first scanline, the second echo signal is given a weighted value of 1.0 and the third echo signal is given a weighted value of less than 1.0, and for the second scanline, the second echo signal is given a weighted value of less than 1.0, and the third echo signal is given a weighted value of 1.0.

10. The system of claim 1, wherein the processor is configured to receive: the first echo signal at a first time; the second echo signal at a second time; and the third echo signal at a third time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a set of graphs showing the principle of side lobe cancellation using pair of Golay complementary sequences of length 8.

(2) FIG. 2 illustrate a system of the invention.

(3) FIG. 3 is a diagraph showing how methods of the invention are performed.

DETAILED DESCRIPTION

(4) The invention generally relates systems and methods to for producing an image from a rotational intravascular ultrasound (IVUS) device. Systems and methods of then invention are particularly useful for rotational IVUS. In a rotational IVUS catheter, a single transducer having a piezoelectric crystal is rapidly rotated (e.g., at approximately 1800 revolutions per minute) while the transducer is intermittently excited with an electrical pulse. The excitation pulse causes the transducer to vibrate, sending out a series of transmit pulses. The transmit pulses are sent at a frequency that allows time for receipt of echo signals. The sequence of transmit pulses interspersed with receipt signals provides the ultrasound data required to reconstruct a complete cross-sectional image of a vessel.

(5) The general design and construction of rotational IVUS catheters is shown, for example in Yock, U.S. Pat. Nos. 4,794,931, 5,000,185, and 5,313,949; Sieben et al., U.S. Pat. Nos. 5,243,988, and 5,353,798; Crowley et al., U.S. Pat. No. 4,951,677; Pomeranz, U.S. Pat. No. 5,095,911, Griffith et al., U.S. Pat. No. 4,841,977, Maroney et al., U.S. Pat. No. 5,373,849, Born et al., U.S. Pat. No. 5,176,141, Lancee et al., U.S. Pat. No. 5,240,003, Lancee et al., U.S. Pat. No. 5,375,602, Gardineer et at., U.S. Pat. No. 5,373,845, Seward et al., Mayo Clinic Proceedings 71(7):629-635 (1996), Packer et al., Cardiostim Conference 833 (1994), Ultrasound Cardioscopy, Eur. J.C.P.E. 4(2):193 (June 1994), Eberle et al., U.S. Pat. No. 5,453,575, Eberle et al., U.S. Pat. No. 5,368,037, Eberle et at., U.S. Pat. No. 5,183,048, Eberle et al., U.S. Pat. No. 5,167,233, Eberle et at., U.S. Pat. No. 4,917,097, Eberle et at., U.S. Pat. No. 5,135,486, and other references well known in the art relating to intraluminal ultrasound devices and modalities. The catheter will typically have proximal and distal regions, and will include an imaging tip located in the distal region. Such catheters have an ability to obtain echographic images of the area surrounding the imaging tip when located in a region of interest inside the body of a patient. The catheter, and its associated electronic circuitry, will also be capable of defining the position of the catheter axis with respect to each echographic data set obtained in the region of interest.

(6) Systems and methods of the invention use Golay codes. Use of Golay codes in ultrasound is described for example in U.S. Pat. Nos. 7,535,797; 6,958,042; 6,663,565; 6,638,227; 6,491,631; 6,375,618; 6,350,240; 6,312,384; 6,210,332; 6,186,949; and 6,146,328, the content of each of which is incorporated by reference herein in its entirety.

(7) Golay complementary sequences are pairs of binary codes, belonging to a bigger family of signals called complementary pairs, which consist of two codes of the same length N whose auto-correlation functions have side-lobes equal in magnitude but opposite in sign. Summing them up results in a composite auto-correlation function with a peak of 2N and zero side-lobes. FIG. 1 illustrates the principle of the side-lobe-canceling for a pair of signed of length equal to 8 bits each.

(8) There are essentially several algorithms for generating Golay pairs. Let the variables a.sub.i and b.sub.i(i=1, 2, . . . n) are the elements of two n-long complementary series equal either +1 or 1, [3],
A=a.sub.1, a.sub.2, . . . , a.sub.n;
B=b.sub.1, b.sub.2, . . . , b.sub.n. (1)

(9) The ordered pair (A;B) are Golay sequences of length n if and only if their associated polynomials
A(x)=a.sub.1+a.sub.2x+ . . . +a.sub.nx.sup.n-1,
B(x)=b.sub.1+b.sub.2x+ . . . +b.sub.nx.sup.n-1, (2)
satisfy the identity
A(x)A(x.sup.1)+B(x)B(x.sup.1)=2n (3)
in the Laurent polynomial ring Z[x, x.sup.1].

(10) Let their respectable auto-correlation functions NA and NB of the sequences A and B respectively be defined by

(11) $\begin{array}{cc}{N}_A\left(j\right)=\underset{iZ}{.Math.}{a}_i{a}_{i+j}{N}_B\left(j\right)=\underset{iZ}{.Math.}{b}_i{b}_{i+j}& \left(4\right)\end{array}$
where we set a.sub.k=0 if k.Math.(1 . . . n). Now condition (3) can be expressed by the sum N.sub.A+N.sub.B, and

(12) $\begin{array}{cc}{N}_A\left(j\right)+N_B\left(j\right)=\{\begin{array}{cc}2N,& j=0\\ 0,& j0\end{array}& \left(5\right)\end{array}$
The sum of both autocorrelation function is at j=0 and zeroing otherwise.

(13) The second, recursive method for constructing the Golay's sequences is presented below. Let the variables a(i) and b(i) be the elements (i=0, 1, 2, . . . 2.sup.n1) of two complementary sequences with elements +1 and 1 of length 2.sup.n
a.sub.0(i)=(i)
b.sub.0(i)=(i) (6)
a.sub.n(i)=a.sub.n-1(i)+b.sub.n-1(i2.sup.n-1)
b.sub.n(i)=a.sub.n-1(i)b.sub.n-1(i2.sup.n-1) (7)
where (i) is the Kronecker delta function.

(14) Equation (7) shows that in each step the new elements of the sequences are produced by concatenation of elements a.sub.n(i) and b.sub.n(i) of the length n.

(15) Example:

(16) Let n=1, then i takes values 0 and 1.
a.sub.1(0)=a.sub.0(0)+b.sub.0(1)=1;
b.sub.1(0)=a.sub.0(0)b.sub.0(1)=1;
a.sub.1(1)=a.sub.0(1)+b.sub.0(0)=1;
b.sub.1(1)=a.sub.0(1)b.sub.0(0)=1.

(17) As final results we obtain two complementary sequences of the length 2.sup.n:
a.sub.1={1, 1};
b.sub.1={1, 1}.
Once these operations are performed recursively for n=2, 3, 4 . . . the following complementary sequences are obtained:
a.sub.2={1, 1, 1, 1};
b.sub.2={1, 1, 1, 1}.
a.sub.3={1, 1, 1, 1, 1, 1, 1, 1};
b.sub.3={1, 1, 1, 1, 1, 1, 1, 1}.
a.sub.4={1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1};
b.sub.4={1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1}.
Similar method of generating the complementary code pairs, differing only in the applied mathematical formalism has been described by Mendieta and al. (Complementary sequence correlations with applications to reflectometry studies, Instrumentation and Development, 3, 6, 1996), the content of which is incorporated by reference herein in its entirety.

(18) FIGS. 2-3 illustrate systems and methods of the invention. The system includes a processor, and a plurality of beam modules coupled to the processor. Each module includes a receiver for receiving a trigger signal from the processor, a complex programmable logic device programmed with a Golay code, a high voltage switching transmitter, and an ultrasound transducer.

(19) The processor alternately transmits trigger signals to the beam modules, thereby causing the beam modules to alternately transmit complementary Golay codes. In the first instance of ultrasound transmission, odd transducers of the transducer array transmit ultrasound pulse signals corresponding to first code sequence (Golay code 1 (G1)). Even transducers the transducer array transmit ultrasound pulse signals corresponding to the second code sequence (Golay code 2 (G2)). Transmission of ultrasound pulse signals to a target object, such as a human body, and reception of reflected signals from the target object occur simultaneously. Switching between even transducers and odd transducers of the transducer array with respect to corresponding Golay codes in the first and second ultrasound transmissions reduces the grating lobes. The grating lobe is the peak of a beam pattern generated when the ultrasound signals is supplemented in an unwanted way.

(20) The processor receives echoes of the complementary codes. The processor performs pulse compression of the echoes that includes weighting the received echoes and summing an odd number of weighted echoes, in which a center echo is given a weighted value of 1.0 and weighted sums of its neighbors constitute complementary echoes of a Golay pair. For example, FIG. 3 shows that three beams are used for generating one composite Golay coded excitation scan line. The figure shows that each transmit signal is paired with a member of a Golay code. The system is set-up such that the pairs alternate (G1, G2, G1, G2, G1, G2 etc). Looking at the top three beams as an example. The first scan line is produced by summing one member of the pair from Golay code 2 and both members of the pair of Golay code 1. A member of the pair of Golay code 2 is the center line with the pairs of Golay code 1 adjacent to the member of the pair of Golay code 2. The weighting for the center beam (Golay code 2) is 1.0, while the weights for the neighboring beams (Goley code pair G1 and G1) are each 0.5. In this manner, the pair from Goley code 1 cancel each other, leaving only center line beam of the member of Goley code 2, thereby removing sidelobes for scanline 1 and eliminating motion artifacts for that scan line.

(21) The process is then repeated for each scan line and image is assembled from the scan lines. The processor is coupled to a display device and causes the image to be displayed.

INCORPORATION BY REFERENCE

(22) References and citations to other documents, such as patents, patent applications, patent publications, journals, books, papers, web contents, have been made throughout this disclosure. All such documents are hereby incorporated herein by reference in their entirety for all purposes.

EQUIVALENTS

(23) Various modifications of the invention and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the full contents of this document, including references to the scientific and patent literature cited herein. The subject matter herein contains important information, exemplification and guidance that can be adapted to the practice of this invention in its various embodiments and equivalents thereof.