Orthogonally reconfigurable integrated matrix acoustical array

Details Orthogonally reconfigurable integrated matrix acoustical array Orthogonally reconfigurable integrated matrix acoustical array

2001-10-02

2003-02-25

Lateef, Marvin M. (Department: 3737)

Surgery

Diagnostic testing

Detecting nuclear, electromagnetic, or ultrasonic radiation

C600S459000

Reexamination Certificate

active

06524254

ABSTRACT:

FIELD OF INVENTION
This invention relates to reconfigurable matrix acoustical arrays, and in particular to integrated matrix arrays configured for consolidating signal paths and orthogonally reconfigurable for operating orientation.
BACKGROUND OF THE INVENTION
Diagnostic ultrasound is an established and growing medical imaging modality. Currently one-dimensional ultrasound transducer arrays with up to 128 transducers are the standard in the industry. Separate coaxial cables are used to connect the transducers to the system electronics. Improved image quality requires the use of matrix (n by m) arrays with a thousand or more transducers. As transducer numbers increase and their dimensions grow smaller, limitations to present fabrication technologies arise. Cost, ergonomics, produce-ability and reliability are important issues. Signal loss due to the capacitance of the coax cables becomes a fundamental problem.
Medical ultrasound systems transmit a short pulse of ultrasound and receive echoes from structures within the body. The handheld probes are most often applied to the skin using a coupling gel. Specialty probes are available for endocavity, endoluminal and intraoperative scanning.
Almost all systems on the market today produce real-time, grayscale, B-scan images. Many systems include colorflow imaging.
Real-time images move as the operator moves the probe (or scanhead). Moving structures, such as the heart or a fetus, are shown on the video monitor.
Grayscale images depict the strength of echo signals from the body as shades of gray. Stronger signals generally are shown as bright white. Lower signals become gray and echo-free regions are black.
B-scans are cross-sectional or slice images.
Colorflow imaging adds a color overlay to the black and white image to depict blood flow.
Over the last 30 years, the major technical developments that have improved imaging or added diagnostic capability include:
Digital technology (late 70's to early 80's) provided image stability and improved signal processing;
Real-time imaging (late 70's to early 80's) provided quicker, easier imaging and functional information;
Electronically scanned linear arrays (late 70's to early 80's), including sequenced arrays and phased arrays, provided improved reliability;
Color-flow imaging (late-80's) opened up new cardiac and vascular applications;
Digital beamformers (early 90's) improved image quality;
Harmonic Imaging (late 90's) provided improved image quality particularly in difficult to image patients;
Coded-excitation Imaging (late 90's to present) permitted increased penetration allowing use of higher frequency ultrasound thereby improving image contrast;
Contrast agents (late 90's to present) offer improved functional information and better image quality.
3D (volumetric) imaging (late 90's to present) presents more easily interpreted images of surfaces such as the fetal face.
Referring to
FIG. 1
, there is illustrated a conventional linear transducer array ultrasound imaging system with probe shown in partial cross section, consisting of a system console [
1
], housing system electronics [
2
], to which can be connected the transducer probe assembly [
4
]. The probe assembly consists of the molded case [
5
] within which is housed an acoustic lens [
6
] over a 1 by 128 piezocomposite transducer array [
8
] with acoustical matching layers, an absorptive backing and structural support, and flexible printed circuit [
10
], connected to a 135 wire cable and mating connector for attaching to the system console. More details are provided below.
To form a typical sector (or wedge shaped) image, separate pulses are transmitted from each of the transducers of the array. The pulses are time-delayed with respect to each other so that the summation of the individual pulses is a maximum in the desired radial direction.
Upon reception, the echo signals received from structures within the body at each transducer are delayed with respect to each other to achieve a similar maximization along the same radial line. These signals are stored digitally.
To generate the next radial line in the image, the transmitter and receiver time delays are adjusted to change the direction of the maxima and the process is repeated. Images are thus built up line by line. Using digital storage (scan-conversion), they are converted to a conventional raster-scanned, gray-scale video image.
In general it is not required that the lines be contiguous, i.e. the selected line may come from one portion of the image on one pulse and a completely different portion of the image on the next pulse. The only requirement is that the image space is completely covered during the video image frame time. For example in a colorflow image overlayed on a grayscale image, the number of pulses allocated to the color portion may be several times that of the grayscale image.
When a pulse is transmitted by an array, transmitter time delays on each channel may also provide a focusing effect in addition to beam steering. On reception, the time delays may be adjusted in real time as the pulse propagates into the body. This, provides a focusing effect that tracks the pulse. The dynamic, or tracking focus, thus sweeps out from the probe at the velocity of sound. Almost all ultrasound systems use dynamic focusing which provides greatly improved resolution and image quality in the scanning plane.
Referring to
FIG. 2
, one-dimensional (1D, linear or 1×m) electronically scanned arrays are in widespread use today. Matrix arrays consisting of (n×m) transducers will be required in future systems to improve image quality. The various types of matrix arrays are the main topics of this discussion.
Referring to
FIG. 2A
, 1D arrays may have as many as 128 transducers and either be flat or curved. All such arrays on the market today are connected to the system electronics through a bundle of coaxial cables. Beamformers in the system electronics adjust the time delays between channels to provide electronic sector scanning and focusing. High performance systems typically use all 128 transducers in their beamformers. Lower performance systems may use as few as 16 of the 128 transducers at any instant. The scanning function is performed by switching transducers into the aperture on the leading edge of the scan and switching out transducers at the trailing edge. Use of a curved array as discussed in Erikson, K. R, “Curved Array of Sequenced Ultrasound Transducers”, U.S. Pat. No. 4,281,550, issued Aug. 4, 1981, produces a sector scan in these simpler, lower cost arrays.
Although one-dimensional arrays are almost universally accepted, these simple linear arrays have a basic limitation on image quality due to their fixed focus in the out-of-plane or elevation dimension. This leads to a slice thickness artifact. While the images appear to be infinitely thin slices, in fact they have finite thickness that changes along the depth dimension. This poor resolution can lead to many different artifacts. The most common is the filling-in of regions where echo levels are very low, with information from surrounding tissue.
Referring to
FIG. 2B
, 1.25D arrays typically use a (128×3) or (128×5) matrix. They are connected to the system electronics through a similar bundle of coax cables as the 1D array. The same beamformers are also used for scanning and dynamic focusing. As the pulse propagates into the body, only the center transducer is initially selected for receiving the reflected signals. By switching in additional transducers as the pulse propagates, the receiving aperture is enlarged and the receiver is weakly focused. Moderate improvements in image quality are obtained.
Referring to
FIG. 2C
, 1.5D arrays use a (128×n) matrix, with n typically an odd number, typically 5, 7 or 9. 1.5D arrays use dynamic focusing in the plane perpendicular to the scanning plane. This produces optimal resolution in all dimensions, further reducin

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