Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-04-16
2001-08-21
Casler, Brian L. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06278892
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of, and apparatus for use in, magnetic resonance angiography to detect, diagnose, and treat arterial diseases and injuries. Arterial diseases and injuries are common and often have severe consequences including death. Imaging arteries serves to detect and characterize arterial disease before these consequences occur.
A conventional method of arterial imaging includes inserting a catheter into the artery of interest (the artery under study) and injecting radiographic contrast, for example, an iodinated contrast, while taking radiographs of the artery. Radiographs are commonly referred to as X-rays. In this technique, the contrast remains in the arteries for a few seconds during which the arteries appear distinct from both the veins and background tissue in the radiographs.
Although a catheter-based contrast arteriography technique generally provides high quality arterial images, there is a risk of arterial injury or damage by the catheter and its insertion. There may be thrombosis, dissection, embolization, perforation or other injury to the artery itself. Furthermore, such a technique may result in a stroke, loss of a limb, infarction or other injury to the tissue supplied by the artery. In addition, hemorrhage at the catheter insertion or perforation sites may require blood transfusions. Moreover, kidney failure and brain injury may result from the toxic effects of the X-ray contrast.
More recent techniques of arterial imaging are based upon detecting the motion of the blood within the arteries and/or veins. These techniques involve employing magnetic resonance imaging (MRI) to image moving blood distinct from stationary background tissues. (See, e.g., Potchen, et al., eds., “Magnetic Resonance Angiography/Concepts and Applications”, Mosby, St. Louis, 1993; the text of which is incorporated herein by reference). Such techniques do not necessitate catheter insertion into the artery. These techniques are commonly known as 2D time-of-flight, 3D time-of-flight, MOTSA, magnitude contrast, phase contrast, and spin echo black blood imaging.
With pre-saturation pulses it is possible to primarily image blood flowing in one direction. Since arteries and veins generally flow in opposite directions, these pre-saturation pulses allow preferential visualization of the arteries or the veins. Because these techniques depend upon blood motion, the images are degraded in patients who have arterial diseases which decrease or disturb normal blood flow. Such types of arterial diseases that decrease or disturb normal blood flow include aneurysms, arterial stenoses, arterial occlusions, low cardiac output and others. The resulting lack of normal blood flow is particularly problematic because it is those patients with disturbed blood flow in whom it is most important to acquire good quality arterial images.
A related magnetic resonance imaging technique relies upon differences in the proton relaxation properties between blood and background tissues. (See, e.g., Marchal, et al., in Potchen, et al., eds., supra, pp. 305-322). This technique does not depend upon steady blood in-flow. Instead, this magnetic resonance imaging technique involves directly imaging the arteries after administering a paramagnetic contrast agent. Here, after administering the contrast agent, it is possible to image arteries directly based upon the blood relaxation properties. This technique overcomes many of the flow related problems associated with magnetic resonance imaging techniques which depend upon blood motion.
Several experts have performed magnetic resonance arterial imaging using intravenous injection of gadolinium chelates (paramagnetic contrast agents). These experts have reported their results and conclusions. In short, these results have been disappointing and, as a result, the use of gadolinium for imaging arteries has not been adopted or embraced as a viable arterial imaging technique. The images using this technique are difficult to interpret because the gadolinium tends to enhance both the arteries and the veins. Since the arteries and veins are closely intertwined, it is extremely difficult to adequately evaluate the arteries when the veins are visible. Further, the difficulty in interpretation is exacerbated as a result of contrast leakage into the background tissues.
As a result, there exists a need for an improved method of magnetic resonance angiography which provides an image of the arteries distinct from the veins and which overcomes the limitations of other techniques. Further, there exists a need for an apparatus which facilitates providing an image of the arteries distinct from the veins and which may be implemented in overcoming the limitations of other techniques.
SUMMARY OF THE INVENTION
In one aspect, the present invention is a method of imaging an artery in a patient using magnetic resonance imaging. The method includes administering magnetic resonance contrast agent to the patient prior to and/or during collection of image data. The contrast may be administered by intravenous infusion at a rate of infusion sufficient to provide a substantially elevated or maximum concentration of the contrast agent in the artery during collection of image data representative of a center of k-space.
In a preferred embodiment, the administration of the contrast agent includes temporally correlating a substantially elevated or maximum rate of infusion of the contrast agent with the collection of image data representative of the center of k-space. The rate of infusion and collection of image data are correlated in accordance with a delay time in a delivery system, a location of the artery and/or a physical condition of the patient.
In another preferred embodiment, the method according to this aspect of the invention further includes administering the contrast agent at a substantially elevated or maximum rate of infusion about 10 to about 30 seconds before collection of image data representative of the center of k-space. Where the contrast agent is paramagnetic, a maximum rate of infusion may be greater than 0.0015 Liters/Kg-sec
2
divided by the relaxivity.
Further, in another preferred embodiment, the method may include temporally correlating a period of a substantially elevated rate of infusion with the collection of image data representative of the center of k-space in accordance with a size of the artery so that the concentration of the contrast agent in the artery is substantially greater than veins adjacent to the artery during collection of image data representative of the center of k-space. In this preferred embodiment, the contrast agent may be administered at an infusion rate and for a period which provides a substantially elevated or maximum concentration of the magnetic resonance contrast agent in the artery during more than 50% of the period of collecting image data representative of the center of k-space. The contrast may also be administered to provide a substantially elevated or maximum concentration of the magnetic resonance contrast agent in the artery for a period of between about 50% to about 85% of the time of collecting image data representative of the center of k-space.
In one preferred embodiment, the step of administering the contrast agent to the patient further includes administering a paramagnetic contrast agent having a relaxivity. The paramagnetic contrast agent may be administered at a rate of infusion sufficient to provide a concentration of the paramagnetic contrast agent in the artery, during collection of image data representative of a center of k-space, of greater than 2.9/sec*relaxivity.
In another preferred embodiment, the techniques of this invention is implemented using a mechanical injector which is spring-loaded, pneumatic powered, or electrically powered. The mechanical injector may include a non-magnetic spring to pressurize the contrast agent for infusion into the patient. Further, the mechanical injector may be adapted to receive a vessel containing a gadolinium chelate.
In another aspect, the present inve
Casler Brian L.
Steinberg Neil
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