Imaging using a contrast agent

Details Imaging using a contrast agent Imaging using a contrast agent

1999-04-22

2001-04-17

Walberg, Teresa (Department: 3742)

Surgery

Diagnostic testing

Detecting nuclear, electromagnetic, or ultrasonic radiation

C250S302000, C424S009300, C600S420000

Reexamination Certificate

active

06219572

ABSTRACT:

BACKGROUND
This invention relates to imaging a region of a patient using a contrast agent.
Most methods of imaging can make use of a contrast agent of one kind or another. Typically, a contrast agent is injected into the vascular system of the patient, and circulates through the body in, say, around half a minute. An image taken of the patient then shows enhanced features relating to the contrast agent.
In the case of an X-ray image, a contrast agent such as iodine absorbs X-rays and injected iodinated compounds can be used to improve contrast in view of this.
In the case of magnetic resonance (MR) imaging, a contrast agent such gadolinium chelate affects the local magnetic field and thus the interaction between the tissue to be imaged (in particular the relaxation times of protons of water molecules) and the main magnetic field. This is because the molecules of the contrast agent, which are tumbling about, are paramagnetic.
A commonly used chelate is diethylenetriaminepentaacetic (DTPA). Another contrast agent is gadolinium (Gd) DOTA. Very small iron oxide particles are also used as a contrast agent in MR imaging.
For ultrasound, air in small bubble-like cells is used as a contrast agent.
It would be usual to take an image of a region of interest of the patient before the contrast agent was injected, and then another image after the contrast agent had circulated through the body. Features of interest could be highlighted by the second image.
In the case of angiography, the two images could be subtracted to image the blood flowing through vessels. This could be used to provide information on the functioning of various organs such as the liver, kidney and brain e.g. to ascertain if the blood brain barrier had sustained any damage from a tumour, which would be indicated by blood flow across that barrier.
The problem with MR and X-ray agents is that they are excreted relatively slowly, typically over periods of hours to a few days. This means that once an agent has been given, it is present throughout any subsequent rapidly repeated examination. Hence, where subtle changes are being studied by detecting the presence and absence of the agent, there is only one opportunity for making the observations. This is a particular drawback when studying perfusion (flow through capillaries delivering blood to tissues), because the amount of blood flowing is very small. The significance in the case of MR imaging is that only a small percentage, less than 5%, of tissue protons are intravascular.
SUMMARY
The invention provides a method of imaging a region of a patient using a contrast agent, which comprises the steps of acquiring image information before and after a contrast agent has been injected into the vascular system of the patient, injecting a liquid free of contrast agent through a catheter directly into the vascular system in the vicinity of the region being imaged, and acquiring image information after the liquid has been injected into the vicinity of the region being imaged and after the liquid has been replaced with blood containing the contrast agent.
The invention also provides apparatus for imaging a region of a patient using a contrast agent, comprising means for acquiring image information before and after a contrast agent has been injected into the vascular system of the patient, means for injecting a liquid free of contrast agent through a catheter directly into the vascular system in the vicinity of the region being imaged, and means for acquiring image information after the liquid has been injected into the vicinity of the region being imaged and after the liquid has been replaced with blood containing the contrast agent.
Following injection of the liquid, data can be obtained showing the status of the tissue in the presence of the liquid, and after a further period of time during which mixing of the injected liquid and the rest of the contents of the vascular system almost entirely eliminates the effect of the liquid, further data can be acquired. Image information obtained before and after the liquid introduction may be combined to achieve improved sensitivity especially in the case of small blood flows such as tissue perfusion, or may be compared if an interventional procedure has been carried out before the liquid is injected.
Advantageously, the step of injection of the liquid through the catheter is repeated to enable further image information with and without contrast agent to be acquired. This can be done as many times as is wished.
The catheter is advantageously provided with an expansible tip in order to block a vessel prior to injection of the liquid.
The liquid may be an injectable medium such as saline, or may be blood e.g. taken from the patient prior to the injection of the contrast agent.
The invention is applicable to any method of imaging in which a contrast agent is injected into the vascular system and is excreted relatively slowly, for example, MR imaging, X-ray imaging, ultrasound imaging, gamma ray (nuclear) imaging using injected radiopharmaceuticals, or optical imaging.


REFERENCES:
patent: 5906579 (2000-05-01), Vander Salm et al.
patent: 6033645 (2000-03-01), Unger et al.
patent: 6061587 (2000-05-01), Kucharczyk et al.
patent: WO 97/24064 (1997-07-01), None

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