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. A method of ultrasound imaging, comprising:
transmitting a first ultrasound signal from a transmit transducer array into a target object;
receiving first echoes of the first ultrasound signal with a first transducer that is omnidirectional in an image plane and is located in a first acoustic window;
storing the first echoes in a computer memory;
receiving second echoes of the first ultrasound signal with a second transducer that is omnidirectional in the image plane and is located in a second acoustic window that does not overlap the first acoustic window;
storing the second echoes in the computer memory;
obtaining position information of the first and second transducers relative to the transmit transducer array;
retrieving the first echoes from the computer memory and constructing a first image of the target object from the retrieved first echoes and the position information of the first transducer;
retrieving the second echoes from the computer memory and constructing a second image of the target object from the retrieved second echoes and the position information of the second transducer; and
combining the first and second images to form a combined image.
2. The method of claim 1 , further comprising, prior to combining the first and second images, determining a displacement of the second image relative to the first image.
3. The method of claim 1 , further comprising applying a Wiener filter to the first and second images before combining the first and second images.
4. The method of claim 1 , further comprising applying a Wiener filter to the combined image.
5. The method of claim 1 , wherein the second transducer is at least one transducer element on the transmit transducer.
6. The method of claim 1 , wherein the second transducer is separate from the transmit transducer and the first transducer.
7. The method of claim 1 , wherein the target object is human tissue.
8. The method of claim 7 , wherein the first acoustic window is selected from the group consisting of a first parasternal intercostal space, a second parasternal intercostal space, a suprasternal notch, a substernal position, a subcostal window, an apical view, a first intercostal space adjacent the sternum, and a second intercostal space adjacent the sternum, and wherein the second acoustic window is selected from the same group.