Method and apparatus for virtual digital subtraction angiography

#The present invention relates generally to medical imaging systems and, more particularly, to a system that detects any change in relative position between a patient and the imaging device and corrects the image data for any such motion that occurs.

#Modern diagnostic medicine has benefited significantly from radiology. Radiation, such as x-rays, may be used to generate images of internal body structures. In general, radiation is emanated towards a patient's body and absorbed in varying amounts by tissues in the body. An x-ray image is then created based on the relative differences of detected radiation passing through the patients' body.

#Digital subtraction is a well known technique for visually enhancing differences between such images. For example, digital subtraction angiography (DSA) is used to visualize vasculature by comparing two or more images of the same blood vessels before and after injection of a contrast agent. Assuming that the only change between the pre-contrast image (or “mask”) and the contrast-containing image is related to the injection of the contrast agent, the “difference image” clearly outlines the vessels into which the contrast agent has flowed.

#FIG. 1 is a diagram of a surgical instrument navigation system in accordance with present invention;

#FIG. 2 is a diagram of a true and a distorted image that may be captured by the surgical navigation system;

#FIGS. 3A and 3B illustrates the projective transformation process employed by the surgical navigation system;

#FIG. 1 is a diagram of an exemplary surgical instrument navigation system. The primary component of the surgical instrument navigation system is a fluoroscopic imaging device 100. The fluoroscopic imaging device 100 generally includes a C-arm 103 attached to a mobile base 102 or fixed room system. An x-ray source 104 is located at one end of the C-arm 103 and an x-ray receiving section 105 is located at the other end of the C-arm 103. In addition, the fluoroscopic imaging device 100 includes a calibration and tracking target 106 attached to the x-ray receiving section 105. As will be further described below, the calibration and tracking target 106 further includes one or more radiation sensors 107, a plurality of tracking targets 109, and a plurality of calibration markers 111. While the following description is provided by reference to an x-ray imaging device, it is readily understood that other types on imaging devices, such as a computed tomography imaging device, a magnetic resonance imaging device or an ultra-sound device, are within the scope of the present invention. It is also readily understood that two-dimensional projection images or three-dimensional volumetric images are within the scope of the present invention.

#In operation, a patient 110 is positioned between the x-ray source 104 and the x-ray receiving section 105. In response to an operator's command input, x-rays emanating from source 104 pass through the patient area, including the patient 110 and the calibration and tracking target 106, and into the receiving section 105 of the imaging device. The receiving section 105 generates a two-dimensional image based on the intensities of the received x-rays. To do so, the receiving section 105 may be comprised an image intensifier that converts the x-rays to visible light and a charge coupled device (CCD) video camera that converts the visible light to digital images. Alternatively, the receiving section 105 may be a device that converts x-rays directly to digital images, thus potentially avoiding distortion introduced by first converting to visible light.

#Furthermore, the C-arm 103 is capable of rotating relative to the patient 110, thereby allowing images of the patient 110 to be taken from multiple directions. For example, the physician may rotate the C-arm 103 in the direction of arrows 108 or about the long axis of the patient 110. Each of these directions of movement involves rotation about a mechanical axis of the C-arm 103. In this example, the long axis of the patient 110 is aligned with the mechanical axis of the C-arm 103. In sum, the imaging device 100 is generally operable to capture one or more sets of image data representative of the patient 110.