MRI medical device markers utilizing fluorine-19

Details MRI medical device markers utilizing fluorine-19 MRI medical device markers utilizing fluorine-19

2000-12-22

2003-06-03

Lee, Kevin (Department: 3753)

Surgery

Diagnostic testing

Detecting nuclear, electromagnetic, or ultrasonic radiation

C600S435000, C606S200000

Reexamination Certificate

active

06574497

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to apparatus and methods for medical imaging, specifically to the use of passive markers for magnetic resonance imaging. In a particular, the invention relates to the use of fluorine-19 (
19
F) nuclei containing compounds as contrast agents and markers for medical devices used in interventional magnetic resonance angiography.
Currently, x-ray fluoroscopy is the preferred imaging modality for cardiovascular interventional procedures. No other method, at this time, has the temporal or spatial resolution of fluoroscopy. As good as fluoroscopy is, however, it does have drawbacks. Catheterization is required in order to directly inject the high concentration of iodinated contrast agent required. Systemic administration of the contrast agent would require too high a dose of agent. Additionally, iodinated contrast agents are nephrotoxic with a real incidence of acute renal failure, particularly in patients with compromised renal function. Allergic reactivity also serves as a contraindication for certain patients. Visualization and tracking of devices under fluoroscopy is accomplished either by the device's inherent adsorption of x-rays, or by the placement of radiopaque markers. Fluoroscopy generates a compressed, two dimensional image of what are three dimensional structures. This requires multiple views to appraise complex vasculature. Moreover, fluoroscopy uses ionizing x-ray radiation with its attendant hazards. This is an issue for the patient during protracted or repeated interventions. It is a daily issue for the interventionalist who must also cope with the burden of personal dose monitoring and wearing lead shielding.
One imaging modality, which has the potential to supplant fluoroscopy, or perhaps replace it in the long term, is magnetic resonance imaging (MRI). MRI does not use ionizing radiation and does not require catheterization to image vasculature. MRI contrast agents, which are often necessary for best resolution, are much less nephrotoxic than iodinated fluoroscopy agents and are effective when administered intravenously.
One advantage of MRI is that different scanning planes and slice thicknesses can be selected without loss of resolution. This selection permits high quality transverse, coronal and sagittal images to be obtained directly. MRI has greater soft tissue contrast and tissue discrimination than computed tomography (CT) or other x-ray based imaging modalities, such as angiography. The reason for this being that in CT, the x-ray attenuation of tissues determines image contrast, whereas in MRI at least four separate variables can determine MRI signal intensity: (i) spin-lattice (longitudinal) relaxation time—T
1
, (ii) spin-spin (transverse) relaxation time—T
2
, (iii) proton density, and (iv) flow. MRI is presently used for diagnostic applications, but interventional magnetic resonance (iMR) angiography is an active area of research. For example, MRI guided balloon angioplasty has been performed to demonstrate feasibility. Similarly, stent placement in humans under MRI has also been demonstrated.
The technique of MRI encompasses the detection of certain atomic nuclei (those possessing magnetic dipole moments) utilizing magnetic fields and radio-frequency radiation. It is similar in some respects to x-ray computed tomography in providing a cross-sectional display of the body organ anatomy, only with excellent resolution of soft tissue detail. In its current use, the images constitute a distribution map of protons, and their properties, in organs and tissues. However, unlike x-ray computer tomography, MRI does not use ionizing radiation. The fundamental lack of any known hazard associated with the level of the magnetic and radio-frequency fields that are employed renders it possible to make repeated scans on vulnerable individuals. Additionally, any scan plane can readily be selected, including transverse, coronal, and sagittal sections. MRI is, therefore, a safe non-invasive technique for medical imaging.
The hydrogen atom, having a nucleus consisting of a single unpaired proton, has one of the strongest magnetic dipole moments of nuclei found in biological tissues. Since hydrogen occurs in both water and lipids, it is abundant in the human body. Therefore, MRI is most commonly used to produce images based upon the distribution density of protons and/or the relaxation times of protons in organs and tissues. Other nuclei having a net magnetic dipole moment also exhibit a nuclear magnetic resonance phenomenon which may be used in MRI applications. Such nuclei include carbon-13 (six protons and seven neutrons), fluorine-19 (9 protons and 10 neutrons), sodium-23 (11 protons and 12 neutrons), and phosphorus-31 (15 protons and 16 neutrons).
Fluoroscopy uses contrast agents to enhance the imaging of otherwise radiolucent tissues. Not surprisingly, fluoroscopic contrast agents work by x-ray absorption. Contrast agents also exist for MRI image enhancement. They work in a different manner, and typically shorten either the T
1
or T
2
proton relaxation times, giving rise to intensity enhancement in appropriately weighted images. The most popular MRI contrast materials are T
1
shortening agents and, in general, paramagnetic ions of elements with an atomic number of 21 to 29, 42 to 44 and 58 to 70 have been found effective as MRI contrasting agents. Such suitable ions include chromium(III), manganese(II), iron(III), iron (II), cobalt (II), nickel (II), copper (II), praseodymium(III), neodymium(III), samarium(
1
II) and ytterbium(III). Because of their very strong magnetic moments, gadolinium(III), terbium(III), dysprosium(III), holmium(III) and erbium(III) are preferred. Gadolinium(III) ions have been particularly preferred as MRI contrast agents.
In an MRI experiment, the nuclei under study in a sample (e.g. protons,
19
F, etc.) are irradiated with the appropriate radio-frequency (RF) energy in a controlled gradient magnetic field. These nuclei, as they relax, subsequently emit RF energy at a sharp resonance frequency. The resonance frequency of the nuclei depends on the applied magnetic field. In some cases, the concentration of nuclei to be measured is not sufficiently high to produce a detectable magnetic resonance signal. Signal sensitivity may be improved by administering higher concentrations of the target nuclei or by coupling the nuclei to a suitable “probe” which will concentrate in the body tissues of interest.
As noted above, iMR angiography is an active area of research. Device tracking and visualization under MRI is necessary for MRI guided interventions. Plastic devices show up poorly under MRI. The reason is that even though the majority of polymers contain hydrogen nuclei, the resonance signals from protons in polymers are broad and chemically shifted from protons in water from which the majority of the MRI signal is derived. Polymeric catheters, for example, show up as regions of little or no signal under MRI (signal voids). Hence, there is a need for markers to track and visualize interventional devices.
MRI markers are divided into two categories, active and passive. Active markers, as the name implies, participate in the radio frequency signal transmission or reception of the scanner. This includes markers that emit an RF signal, markers that receive an RF signal and convey it to the scanner via a connection, and markers that generate their own magnetic or electrical field by application of electrical currents. The term active implies some sort of electrical circuit is involved. Conversely, passive markers use no wires or circuitry and work by several mechanisms. One scheme is to distort the magnetic field of the scanner. Another is by enhancing or modifying the signal from protons in the vicinity. Still another is by containing nuclei with their own distinct signal that is different from water or fat. Passive markers have the advantage that they are simpler and, generally, have fewer parts. They require no connection to the scanner or additional circuitry. There also may be the per

Affiliated with

Also associated with

Rating

MRI medical device markers utilizing fluorine-19 does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with MRI medical device markers utilizing fluorine-19, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and MRI medical device markers utilizing fluorine-19 will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3119402