X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
2000-04-18
2002-07-30
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C382S130000, C382S132000, C382S282000
Reexamination Certificate
active
06426994
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an image processing method. The invention concerns notably an image processing method for producing one or more processed images in which changes in an object to be imaged are clearly reproduced. An image processing method of this kind is used particularly in angiography. During angiography images are formed of the blood vessels of a patient to be examined. To this end, a contrast agent is applied to the vascular system of the patient to be examined. First the arteries in the part of the body of the patient to be examined are filled with the contrast agent which later also reaches the veins. The type of contrast agent may differ, in dependence on the technique used to image the blood vessels; however, the contrast agent ensures in any case that the blood vessels are suitably detected by means of the relevant technique. The blood vessels of the patient to be examined can be imaged by means of magnetic resonance techniques utilizing a contrast agent in the form of a substance which produces a magnetic resonance signal which is stronger than that produced by the surrounding tissue. Such a technique for magnetic resonance imaging of the blood vessels of the patient to be examined is also referred to as magnetic resonance (MR) angiography. The blood vessels of the patient to be examined can also be imaged in X-ray images, the contrast agent then having an X-ray absorption which is higher than that of the surrounding tissue.
2. Description of Related Art
The article
Time-resolved contrast enhanced
3
D MR Angiography
by F. R. Korosec et al in MRM 36 (1996), pp. 345-351, describes a specific MR angiography method.
According to the known MR angiography method, successive magnetic resonance images are formed of a part of the vascular system of the patient to be examined. The magnetic resonance (MR) signals originating from the contents of the blood vessels are acquired during the passage of the blood with the contrast agent through the blood vessels. MR signals are acquired notably while the arteries in the relevant part of the vascular system have already been filled with the contrast agent but the contrast agent has not yet reached the veins. An arterial magnetic resonance image which shows the arteries filled with the contrast agent is derived from such MR signals. After some time, when the contrast agent has also reached-the veins and has not yet disappeared from the arteries, MR signals are acquired again. A venous magnetic resonance image which shows only the veins filled with the contrast agent is derived from the latter MR signals. Subsequently, a subtraction image is formed by subtracting the venous magnetic resonance image from the arterial magnetic resonance image. The subtraction image does offer useful information as regards the passage of blood with the contrast agent through the vascular system of the patient. However, the known MR angiography method cannot be used very well when a more recent, so-called “blood-pool” contrast agent is used. Such a contemporary contrast agent remains in the vascular system for a comparatively long period of time, for example from 10 seconds to as long as one minute, so that it takes a long time for the contrast agent to disappear from the arteries. More specifically, such a contemporary contrast agent remains in the vascular system so long that, when the contrast medium reaches the veins, a considerable concentration of contrast agent is still present in the artery whereto the contrast agent has been administered. When the known MR angiography method is used in conjunction with a contemporary contrast agent, therefore, it is necessary to postpone the acquisition of the MR signals for the venous magnetic resonance image for a long period of time after the administration of the contrast agent.
Citation of a reference herein, or throughout this specification, is not to construed as an admission that such reference is prior art to the Applicant's invention of the invention subsequently claimed.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method for imaging a dynamic process, such as the passage of blood with the contrast agent through the vascular system of the patient to be examined, more accurately and faster than the known MR angiography method. It is notably an object of the invention to provide an MR angiography method in which the passage of blood through the vascular system requires less time than in the known MR angiography method.
This object is achieved by means of an image processing method according to the invention wherein
a succession of two or more low-resolution images is acquired,
a series of one or more successive mask images is derived from the low resolution images,
a high-resolution image is acquired,
at least one of the mask images is applied to the high-resolution image as a bandpass filter in order to derive a filtered high-resolution image from the high-resolution image.
The one or more low-resolution images contain image information with a comparatively low spatial resolution. This means that the smallest detail that is faithfully reproduced in the low-resolution images is comparatively large. For example, the low-resolution images contain 64×64 or 128×128 pixels for a field of view having a diameter of from 20 to 40 cm. For the same field of view the high-resolution image contains 512×512 or even 1024×1024 pixels. The low-resolution images are successively acquired, so that the image information in the successive low-resolution images differs as a function of the changes occurring in the imaged object during the dynamic process, for example the progress of the contrast agent in the blood vessels of the patient to be examined.
The one or more mask images relate to variations of the spatial low-resolution image information of one or more successive phases of a dynamic process being studied by means of the image processing method according to the invention. For example, the successive mask images represent respective differences between successive low-resolution images. It is alternatively possible to derive the individual mask images from the low-resolution images in such a manner that such a mask image represents a cumulation of successive differences. For successive mask images the cumulation has then always been continued up to and including another phase of the dynamic process. Such a dynamic process is notably the passage of blood with the contrast agent through the vascular system of the patient to be examined. The phases of the dynamic process concern parts of the dynamic process which take place within finite time intervals. Such a time interval may be short or long, depending on the rate at which changes occur during the dynamic process. For example, in the case of the passage of blood through the vascular system of the patient the individual phases have a duration of approximately 10 seconds. The filling of the arteries with the contrast agent notably takes approximately from 10 to 40 seconds. The high-resolution image relates to the same (part of the) object as the low-resolution images, but the high-resolution image contains inter alia more image information with a much higher spatial resolution. This means that the high-resolution image faithfully reproduces details which are much smaller than the smallest details faithfully reproduced in the low-resolution images. For example, the spatial resolution of the low-resolution images is from five to ten times less than the spatial resolution of the high-resolution images. The one or more mask images are applied to the high-resolution image as a bandpass filter in order to select image information from the high-resolution image on the basis of the brightness values in the relevant mask image. For example, such a mask image is used as a bandpass filter by selecting from the high-resolution image those parts for which the relevant mask image has brightness values in a predetermined range in positions corresponding to positions
Kao Chih-Cheng Glen
Kim Robert H.
Koninklijke Philips Electronics , N.V.
Vodopia John
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