Method and apparatus to produce ultrasonic images using multiple apertures
A combination of an ultrasonic scanner and an omnidirectional receive transducer for producing a two-dimensional image from received echoes is described. Two-dimensional images with different noise components can be constructed from the echoes received by additional transducers. These can be combined to produce images with better signal to noise ratios and lateral resolution. Also disclosed is a method based on information content to compensate for the different delays for different paths through intervening tissue is described. The disclosed techniques have broad application in medical imaging but are ideally suited to multi-aperture cardiac imaging using two or more intercostal spaces. Since lateral resolution is determined primarily by the aperture defined by the end elements, it is not necessary to fill the entire aperture with equally spaced elements. Multiple slices using these methods can be combined to form three-dimensional images.
1. An ultrasound imaging method comprising:
transmitting first ultrasonic energy into a target object to be imaged from a first transducer array positioned in a first acoustic window;
receiving first echoes of the first ultrasonic energy with a first single element of a second transducer array positioned in a second acoustic window;
obtaining first position information describing a first position of the first single element relative to the first transducer array by constructing x 1 and y 1 position data from a first time that the first echoes are received at the first transducer array and a second time that the first echoes are received at the second transducer array;
transmitting second ultrasonic energy into the target object to be imaged from the second transducer array positioned in the second acoustic window;
receiving second echoes of the second ultrasonic energy with a second single element of the first transducer array;
obtaining second position information describing a second position of the second single element relative to the second transducer array by constructing x 2 and y 2 position data of the second single element from a third time that the second echoes are received at the second transducer array and a fourth time that the second echoes are received at the first transducer array;
computing a z offset between the x 1 and y 1 position data and the x 2 and y 2 position data;
computing a minimum error squared error estimate of the first and second position information; and
adjusting a geometric delay created by a speed of sound difference on an echo return path to the first and second transducer arrays using the minimum error squared error estimate.
2. The method of claim 1 , further comprising: storing the first echoes in a computer memory before constructing the first image.
3. The method of claim 1 , wherein the target object is human tissue.
4. The method of claim 1 , wherein the first transducer array is separated from the second transducer array by a gap.
5. The method of claim 1 , wherein the first transducer array and the second transducer array are aligned with and configured to transmit ultrasonic energy in a common scan plane.
6. The method of claim 1 , wherein the first transducer array and the second transducer array are mounted in a rigid probe.
7. The method of claim 1 , wherein the first transducer array and the second transducer array are mounted in an adjustable, extendable hand held probe.
8. The method of claim 1 , wherein the first transducer array and the second transducer array are mounted in a fixture with articulated joints and sensors configured to measure relative positions of the first transducer array and the second transducer array.
9. The method of claim 1 , wherein the first ultrasound energy comprises a first sector scan.