Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-06-09
2002-06-18
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S419000, C600S420000, C382S128000, C324S300000, C324S307000
Reexamination Certificate
active
06408201
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the art of locating a blood vessel lesion in a human subject, and more particularly, to an apparatus and method to efficiently identify a lesion over an entire patient's peripheral arterial vasculature and grade any identified stenosis using magnetic resonance imaging (MRI) technology.
Arteries are the blood vessels emanating from the heart that supply the necessary nutrients to the organs and tissues of the human body. A narrowing or constriction of an artery reduces the delivery of nutrients, such as oxygen to the recipient tissue and has profound effects on tissue function. In general, significant narrowing of an artery leads to compromised function of the organ in question, at best, and organ failure or death at worst. Stenosis or narrowing at any number of locations along the course of the arteries from the abdominal aorta through the calf can result in compromise of arterial blood flow to the distal lower extremities. The evaluation of the peripheral vessels is further complicated by the high incidence of tandem or synchronous lesions, any one of which could be the underlying cause for diminished arterial blood flow. Furthermore, the surgical decisions for potential bypass procedures to improve distal blood flow are greatly affected by the ability to assess the arteries in the foot. As a result, the successful imaging of the lower extremities (i.e. the peripheral run-off study) requires not only the accurate assessment of the presence and functional significance of a narrowing, but also the ability to evaluate the entire arterial course of the peripheral arterial tree from abdominal aorta to the foot. It is known that the flow in the vessel at the point of narrowing and immediately after the narrowing is characterized by rapid flow velocities and/or complex flow patterns. Quantitative flow data can readily aid in the diagnosis and management of patients and also help in the basic understanding of disease processes.
There are many techniques available for the assessment of the peripheral arteries that include traditional invasive catheter angiography and ultrasound. Because conventional x-ray angiography requires catheterization and the use of nephrotoxic iodinated contrast agents, it is reserved as the final option. Screening for peripheral arterial occlusive disease (PAOD) is typically performed using non-invasive methods such as ultrasound or plethysmography. However, neither of these techniques can provide angiographic illustration of the vessels and merely provides the assessment of individual segments of the intervening arterial anatomy. Both techniques are operator dependent and have confounding technical difficulties which make the imaging often tedious to perform. Moreover, neither technique can provide the comprehensive information required for surgical planning and traditional x-ray angiographic depiction is generally required as an adjunct for pre-operative management.
Magnetic resonance angiography (MRA) is an emerging method for the non-invasive assessment of arteries. Up to now, the application of MRA has been tailored to individual smaller vascular territories (40-50 cm fields of views). With the ability now to translate the table and imaging multiple overlapping fields-of-view, MRA can now be prescribed to image a much larger area such as necessary for evaluation of PAOD. The use of intravenously administered contrast agents for contrast-enhanced MRA, in particular, has enabled the depiction of 1-1.2 meters of arterial anatomy in less than 1 minute. MRA can also be performed using a number of methods. One technique, phase contrast (PC) MRA is a practical and clinically applicable technique for imaging blood flow. MRI utilizes radio frequency pulses and magnetic field gradients applied to a subject in a strong magnetic field to produce viewable images. When a substance containing nuclei with net nuclear magnetic moment, such as the protons in human tissue, is subjected to a uniform magnetic field (polarizing field B
0
), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field (assumed to be in the z-direction), but precess about the direction of this magnetic field at a characteristic frequency known as the Larmor frequency. If the substance, or tissue, is subjected to a time-varying magnetic field (excitation field B
1
) applied at a frequency equal to the Larmor frequency, the net aligned moment, or “longitudinal magnetization”, M
Z
, may be nutated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment M
t
. A signal is emitted by the excited spins after the excitation signal B
1
is terminated (as the excited spins decays to the ground state) and this signal may be received and processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (G
x
, G
y
and G
z
) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting MR signals are digitized and processed to reconstruct the image using one of many well-known reconstruction techniques.
Phase contrast MRA makes use of flow encoding gradient pulses which impart a velocity-dependent phase shift to the transverse magnetization of moving spins while leaving stationary spins unaffected (Moran P. R. A Flow Velocity Zeugmatographic Interlace for NMR Imaging in Humans. Magnetic Resonance Imaging 1982; 1: 197-203). Each phase contrast acquisition generates two images: a magnitude image that is proportional to the proton density of the object and may also be T
1
-weighted, and an image representing the phase of the object. The phase image produced has information only from the moving spins and the signal from stationary tissue is suppressed. Images representing both the average flow velocity over the entire cardiac cycle and at a series of individual points in the cycle have been generated using this technique. The phase contrast MR method produces phase images with intensities that represent the magnitude of the flow velocity and also the direction of flow. Therefore, such images may be used for both qualitative observation of blood flow and quantitative measurement. The practical application of phase contrast MR angiography and venography to the quantitative determination of flow velocity is therefore evident.
It would be advantageous to use magnetic resonance imaging technology to efficiently locate and identify a stenosis in a blood vessel along a patient's peripheral arterial vasculature and use this MR technology to grade the stenosis for follow up care. It would also be advantageous to use a contrast agent bolus injection to increase the image signal-to-noise ratio in the arterial vessels during the first passage of the contrast material to enhance the screening technique. However, to do so, a multi-station acquisition sequence must be used to scan the entire peripheral vasculature as the contrast bolus travels through the body. Previous attempts at using MR technology to improve the ability to detect and grade peripheral arterial stenoses have relied primarily on using a single anatomic scan to visualize the location of a stenotic vessel segment. In this method, it was desirable to achieve the highest spatial resolution possible by decreasing pixel size. In addition, in order to minimize flow-related artifacts such as intravoxel dephasing that can overestimate the degree of stenosis, the prior art employed first moment gradient nulling for flow compensation and short echo time (TE) parameters.
It would be desirable to improve on this prior art by accomplishing the converse. That is, to utilize the presence of flow-related artifacts to improve the detection of an arterial stenosis by sensitizing the image acquisition to intra-voxel flow dephasing effects, thereby exacerbating flow voids and increasing the conspicuity of arterial lesions in a quick screening scan. It would also be a
Foo Thomas K. F.
Ho Vincent B.
Della Penna, Esq. Michael A.
General Electric Company
Horton Esq. Carl B.
Lateef Marvin M.
Lin Jeoyuh
LandOfFree
Method and apparatus for efficient stenosis identification... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for efficient stenosis identification..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for efficient stenosis identification... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2936595