Patent Application
20050041845
The present invention relates to medical imaging systems and in particular to an imaging system that sharpens portions of an image based on a determination of the underlying tissue type.
Diagnostic images of the lateral spine, for example, using dual energy x-ray, may be used to assess the presence of spinal fractures incident to osteoporosis and other bone diseases. A vertebra with upper and lower surfaces that are wedge shaped, concave, or compressed together may have experienced a fracture.
Often the edges of the vertebra are indistinct in the image. Sharpening filters, operating on the data underlying the image, may be used to highlight the edges of the vertebrae but will also highlight features in soft tissue around the bone such as the diaphragm, organs, ribs, abdominal gas, and other distracting tissue structures.
The present invention provides a method of sharpening only selected tissue types in a medical diagnostic image. In this way, for example, the bone image may be sharpened without generating distracting artifacts in the surrounding soft tissue. Alternatively, features in soft tissue may be sharpened without accentuating surrounding bone.
The invention is particularly suited to dual energy x-ray images which may automatically characterize image data based on tissue types, but the invention may also be applied to other imaging modalities where tissue type may be approximately identified. The user may manually adjust the regions automatically identified.
Referring now to
Control of the scanning motion and operation of the x-ray detector 18 and x-ray source 16 of the x-ray densitometer 10 is provided by a computer system 20 executing a stored control program stored in computer memory. The computer system 20 includes generally a screen 22, a cursor control device 24 (such as a mouse), and a keyboard 26 as are well understood in the art. An x-ray densitometer 10 as described above, and suitable for use with the present invention, is commercially available from General Electric Company of the United States under the trade name Prodigy.
Referring now also to
Referring to
The histogram 36 in this case will show multiple modes 38 and 38′ corresponding to different tissue types (e.g. bone and soft tissue). A threshold value 40 may be established separating the modes 38′ and 38, for example, by finding a local minima within an empirically established range and used to sort each pixel 32 of
According to the sorting with the threshold value 40, each pixel 32 of the image 30 is tagged in the memory of the computer system 20 with its tissue type to generate a bone pixel set 44 having attenuation caused principally by bone and a soft tissue pixel set 46 having attenuation caused principally by soft tissue. These sets may be optionally filtered using a spatial filtering system based on pixel location to provide that each of the bone pixel set 44 and soft tissue pixel set 46 define locally continuous regions uninterrupted by single pixels of the other tissue type. (?)
Generally, an x-ray densitometer 10 may only distinguish between two types of tissues, however more complex algorithms, for example, those which look at spatial locations of the pixels 32 in addition to attenuation values, may approximate divisions into greater numbers of tissue types as may be used by the present invention or may be used to refine the two tissue characterizations described. The present invention may also find use with other tissue identification techniques and may be used with single energy x-ray systems in which tissue types are deduced from single energy attenuation, for example, in a CT machine or standard x-ray system. While the tissue types of bone and soft tissue are used in this example, clearly other tissue types such as fat and non-fat tissue may be used.
Referring again to
In a preferred embodiment, this masked area 51 may be low-pass filtered to create a “soft mask” eliminating abrupt visual transitions in the final filtered image. For example, in a mask that provides a binary state of 1 for areas included by the mask and 0 for areas excluded by the mask, where the mask is applied by a simple multiplication of pixels of the underlying image times corresponding mask pixels, the mask is filtered to create a transition region at the interface between mask regions of 0 and 1, the transition region having fractional values, the lower the fractional value the less the contribution of the underlying image in the final masked image.
Referring now to
The high-pass filter 48 may be implemented in a number of ways well known to those of ordinary skill in the art including, for example, by taking a derivative of the unmasked area 52 of the image 30 or use of the Fourier transform, a truncation of low frequency data and a reverse Fourier transform of operating on the unmasked area 52 of the image 30. In a simple embodiment, a low-pass filtered image may be obtained using averaging techniques or the like and subtracted from the unmasked area 52 of the image 30 leaving high-pass filtered data 56.
The high-pass filtered data 56 is provided to a multiplier 58 which receives a weighting value x as will be described below. The product of the high-pass filtered data 56 and the weighting value x is provided to an adder 54.
The soft tissue pixel set 46 is provided directly to the adder 54.
The bone pixel set 44, prior to high-pass filtering, is also provided to multiplier 62 which receives a weighting value 1−x. The product of the high-pass filtered data 56 and the weighting value 1−x is provided to an adder 54.
The adder 54 provides an output 66 which provides new brightness values for pixels 32 to be displayed as an enhanced image on the screen 22 providing improved bone edge enhancement without enhancing features of the soft tissue.
Referring now also to
By changing the particular tissue selected in the unmasked area 52, other areas of the image can be accentuated or de-emphasized including regions including air or artifacts such as metal or the like. In addition, other filter strategies can be applied to the masked area 51, for example, the soft tissue may be further processed by low pass filtering to decrease its presence in the image or a high-pass filter to control or accentuate its presence in the image. The high-pass filtering may be applied to fat tissue when fat and non-fat tissue are analyzed.
It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.
