Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
1999-04-09
2003-10-21
Casler, Brian L. (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
Reexamination Certificate
active
06635030
ABSTRACT:
BACKGROUND OF THE INVENTION
One of the inventors herein is also the inventor of several prior patents related to the improved enhancement of a patient's organ undergoing a computed tomographic scan by controlling the injection of a contrast medium in accordance with a predicted enhancement. These patents include U.S. Pat. No. 5,583,902 and 5,687,208, the disclosures of which are incorporated herein by reference. Still other patents have been issued relating to contrast injectors and their use in order to obtain specific enhancement levels. These include U.S. Pat. Nos. 5,827,219; 5,840,026; 5,383,858; 5,662,612; 5,681,286; 5,456,676; and 5,300,031; the disclosures of which are incorporated herein by reference. Still other patents which have been issued and which relate to the field of contrast injectors and their use include U.S. Pat. Nos. 4,006,736; 5,868,710; 4,854,324; 4,210,138; 4,812,724; 5,865,744; 5,279,569; 5,865,805; 4,213,454; 4,695,271; 5,322,511; 5,269,762; and 5,851,184; the disclosures of which are also incorporated herein by reference.
While the use of contrast injectors for injecting a patient with a contrast agent in order to enhance a tissue or organ for CT scanning has been done for years, the first two patents mentioned above, i.e. the '
902
and the '
208
patents, represent one of if not the earliest attempt to scientifically solve the problem of computing an expected enhancement based upon a patient's physical parameters, assuming a given injection protocol. The inventors work in these prior patents was directed at solving this problem for a patient's organs, using complex differential equations and their solutions to help answer how a human body functions in processing the contrast agent, and then calculating a window of enhancement for which the threshold of desired enhancement is exceeded for a successful scan, assuming a typical injection protocol. As part of the '
208
patent, CT angiography was described and its special problems in obtaining high quality scans of blood vessels.
CT angiography (CTA) has been widely accepted, in some cases preferred over conventional angiography, to evaluate the anatomy of major blood vessels such as the aorta and pulmonary artery. In the prior art, the vessels are scanned using a thin-collimation spiral CT technique, while a bolus of contrast medium is injected at a high injection rate (3-5 mL/s) to achieve a high degree of vascular contrast enhancement. Typically, contrast medium is injected at a constant injection rate, i.e. a uniphasic injection protocol is used. This injection scheme results in a steadily rising vascular contrast enhancement profile with a single peak of enhancement occurring shortly after the completion of the injection, as shown by the data collected from a porcine experiment as shown in
FIG. 1
a
. Consequently, vascular enhancement tends to be non-uniform during image acquisition.
Uniform vascular enhancement through the entire period of image acquisition is highly desirable for the purpose of image processing and display, in which
3
D postprocessing is frequently based on a threshold CT attenuation value. In addition, it is expected that uniform enhancement would contribute to an optimized usage of contrast medium. In other words, for a given volume of contrast medium, a uniform contrast enhancement whose magnitude is lower than that of a peak enhancement generated by a uniphasic injection would provide a longer temporal window of adequate vascular enhancement than the uniphasic injection presently used in the prior art, thereby resulting in a longer optimal scanning interval. Alternately, it is expected that a smaller volume of contrast medium would be needed to provide a uniform vascular enhancement for the same scanning duration as that achieved by using a uniphasic injection protocol.
In addition to a uniphasic injection protocol, a biphasic injection protocol is sometimes used as well in the prior art. A typical biphasic injection protocol consists of two phases: a short rapid-injection phase, followed by a longer slow-injection phase. A biphasic injection protocol yields more prolonged enhancement than a uniphasic injection protocol, but it generates two enhancement peaks with a valley of enhancement in between. Data collected from another porcine experiment as shown in
FIG. 1
b
supports this conclusion. Each peak occurs shortly after the completion of each injection phase, as might be expected given the results from the first porcine experiment. Although the biphasic might be considered by one less sophisticated as a step in the right direction, it actually increases the complexity of the problem of first of all achieving a level of enhancement which reliably exceeds a threshold and then maintaining an enhancement level above that threshold for a time period that will be adequate to collect the image. As the prior art has little to teach with respect to solving this problem, other than the inventors own work which has not yet focussed on the injection protocol aspect of the problem, it would seem that unguided use of a biphasic injection protocol would perhaps increase the amount of contrast agent injected needed to reliably achieve a successful scan over that of a simple uniphasic injection protocol whose enhancement is easier to predict.
The present invention carries the inventor's prior work further by focussing on the injection protocol for CT angiography of the vascular system of a patient, and more particularly by computing an optimum solution of a specific contrast injection protocol for optimizing both the level of enhancement as well as the temporal duration of the enhancement, and an injector to achieve such injection protocol. A byproduct of this invention is as before, the ability to minimize the amount of contrast agent needed to be injected into a patient in order to reliably obtain a successful scan. This is important not only from a cost standpoint as the contrast agent can be expensive, but also from a health standpoint for the patient. The smaller the amount of contrast agent injected into a patient's body the less risk of harmful side effects.
More particularly, the inventors herein have succeeded in developing a contrast injector and a contrast injector protocol for implementation in the contrast injector which optimizes the use of the contrast agent to reliably achieve an enhancement in excess of a preselected threshold and to~maintain that “excess” level of enhancement for a temporal duration that is hear optimal given the amount of contrast agent used. The contrast injection protocol comprises a ramped, or multiphasic, or exponentially decaying, or steadily decreasing injection rate. An ideal solution is provided by the solution of differential equations describing a simplified compartment model in lieu of the more complex whole body model taught in one of the inventors prior patents mentioned above. This solution renders an exponentially decaying rate of injection having a particular decay coefficient. However, it is contemplated that in the real world, this exponentially decaying injection rate could be approximated by a linearly decay, or ramped decay, or even multi-step decay and yet yield acceptable results in accordance with the teachings of the present invention. Indeed, in the real world, something less than a true exponentially decaying injection rate must necessarily be the physical limit of a contrast injector, even the computer programmable one taught herein as part of the invention. Perhaps even more so as the computer programmable injector uses digital control which in actuality is a series of relatively small steps in changing the injection rate. Still another factor to consider and which also minimizes the precision that might be thought necessary is the varying physiological response between different patients to the injected contrast agent. As such, mathematical precision is not considered as a limit to the present invention.
The particular exponential decay coefficient calculated is proportional to t
Bae Kyongtae T.
Small James R.
Tran Huy Q.
B.H.B. LLC
Casler Brian L.
Lam Ann Y.
Thompson & Coburn LLP
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