Method and apparatus for correction of a discrete pixel image

#The present invention relates generally to the field of discrete pixel imaging systems, such as magnetic resonance imaging systems. More particularly, the invention relates to a technique for correcting or adjusting portions of image data to compensate for effects of image data filtration and expand to the field of view in such images.

#A variety of systems are known and presently in use for producing discrete pixel images. Such systems generally collect raw image data from a subject of interest over a desired imaging area, and convert the collected raw image data to data which can be used to reconstruct an image. In magnetic resonance imaging systems, for example, spins of gyromagnetic material in a subject of interest are altered and spatially encoded to produce emissions which are detected during a data acquisition phase of imaging. The sensed signals are filtered and further processed to produce digital data for each individual volume element or voxel in a desired slice of the subject. The voxel data is then processed to produce a corresponding set of discrete picture element or a pixel data which can be used to reconstruct a two-dimensional image. The resulting images may be used by radiologists, attending physicians, and clinicians to diagnose and treat physical conditions of patients. Similar processes are also employed outside the medical imaging field in an increasing number of applications.

#Features of interest, such as anatomical features, are imaged in magnetic resonance imaging systems by displaying the frequency content of received echo signals from the gyromagnetic material across a display area or image matrix. The position of the pixel data within the image is directly related to the frequency of the sensed signal. This correlation is generally known in the art as frequency encoding. The unique frequency for each position, i.e., the frequency encoding, is created by varying gradient magnetic fields produced by gradient coils in the imaging system. While the emissions from the subject are sensed in real time, the resulting time domain data must therefore be transformed to the frequency domain to assign to the data the proper location in the subject. This transformation is performed following band limit filtering on the raw image signals.

#FIG. 1 is a diagrammatical representation of a magnetic resonance imaging system including processing circuitry for filtering acquired image data in accordance with certain aspects of the present technique;

#FIG. 2 is a diagrammatical representation of exemplary steps in image data filtration, including correction for portions of a transition region in the data;

#FIG. 3 is an exemplary image created via the system of FIG. 1 and through the filtration of FIG. 2, illustrating an image slice through a subject over a field of view defined by frequency encoded data;

#Turning now to the drawings and referring first to FIG. 1, an exemplary imaging system is illustrated and designated by the reference numeral 10. In the embodiment of FIG. 1, imaging system 10 is a magnetic resonance imaging system including a scanner 12, image data acquisition and control circuitry 14, system control and processing circuitry 16, and an operator interface 18. Scanner 12, in turn, includes coil assemblies for selectively generating controlled magnetic fields used to select a portion of a subject of interest for imaging, as well as coils for exciting gyromagnetic materials in the subject and for sensing resulting emissions. In particular, scanner 12 includes a primary coil 20, which will typically include a superconducting magnet coupled to a cryogenic refrigeration system (not shown). Coil 20 generates a highly uniform magnetic field along a longitudinal axis of the scanner. A series of gradient coils 22 generate controllable gradient fields having desired orientations with respect to the subject of interest. In particular, as will appreciated by those skilled in the art, gradient coils 22 are capable of creating field for selecting an image slice, orienting the image slice, and frequency encoding gyromagnetic material within the slice to produce the desired image from frequency encoded data. One or more radio frequency transmitting and receiving coils 24 are provided for exciting the gyromagnetic material and for detecting emissions from the material during data acquisition phases of operation of the system. A patient table 26 is positioned within scanner 12 to support a subject 26, such as a human patient.

#In the embodiment illustrated in FIG. 1, operation of gradient coils 22 and transmitting/receiving coil 24 is controlled by image data acquisition and control circuitry 14. In general, circuitry 14 receives pulse sequence descriptions from control circuit 16, notably through interface circuitry 32. Such pulse sequence descriptions will generally include digitized data indicative of controlled pulses applied to coils 22 and 24 during excitation and data acquisition phases of imaging. Fields generated by the coils excite gyromagnetic material within the subject 28 to cause emissions from the material. Such emissions are detected by coil 24 and are transmitted to image data acquisition and control circuitry 14. Circuitry 14 then filters the detected signals as described more fully below, and transmits the filtered signals to control circuit 16 via interface circuitry 32. Power for operation of scanner 12 is provided by a power supply as indicated generally at reference numeral 30 in FIG. 1.

#In addition to interface circuitry 32, control circuit 16 includes examination pulse definition circuitry 34, image data process circuitry 36, memory circuitry 38, and interface circuitry 40 for communicating with operator interface 18. Examination pulse definition circuitry 34, which may generally be defined by appropriate code within one or more central processing units, signal processors or similar circuitry within image data processing circuitry 36. Circuitry 34 serves to define the digital pulse sequences to be executed by the coils of scanner 12 in accordance with pre-established examination protocols.