Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-11-03
2002-06-18
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S410000, C600S421000, C600S380000, C324S307000, C324S322000
Reexamination Certificate
active
06408202
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to methods of magnetic resonance analysis and, in particular, to such methods for magnetic resonance imaging and spectroscopic analysis of intra thoracic anatomic structures, such as the aorta, from the esophagus of a patient. The invention is also related to a magnetic resonance analysis apparatus.
2. Description of the Prior Art
Current standard techniques for imaging the thoracic aorta include X-ray computed tomography (CT), standard magnetic resonance imaging (MRI) (e.g., body-coil MRI), transesophageal echocardiography (TEE), and contrast aortography. Each of these techniques suffers some important limitation in its ability to allow detailed mapping of the aortic wall and its anatomic and functional lesions.
Standard MRI and CT lack adequate resolution of the aortic wall for precise characterization of aortic atheromata in vivo, and are not able to provide measurements of focal variations in vessel wall compliance or distensibility (e.g., aortic wall tissue tagging information).
TEE allows real time imaging, but suffers from both an inability to image clearly that portion of the aortic wall which is directly against the esophagus due to the near field effect of ultrasound (e.g., portions of the thoracic aortic wall, particularly in the arch), and from an inability to register images to a fixed frame of reference, making precise mapping of aortic lesions problematic. Kasprzak, J. D., et al., Three-dimensional echocardiography of the thoracic aorta,
Eur. Heart. J.,
vol. 17, pp. 1584-92, 1996, discloses an attempt to circumvent this limitation using a technique to control movements of the probe while imaging in multiple planes with subsequent off-line 3-D image reconstruction. It is believed that the system is relatively cumbersome and not fully successful in obtaining “adequate” images in a select group of 21 patients.
Montgomery, D. H., et al., Natural history of severe atheromatous disease of the thoracic aorta: a transesophageal echocardiographic study,
J. Am. Coll. Cardiol.,
vol. 27, pp. 95-101, 1996, discloses an example of a sermi-quantitative atherosclerosis grading scheme which depends upon orthogonal views to estimate the three-dimensional characteristics of aortic lesions, but does not circumvent the inherent advantage of MR over ultrasound imaging at defining atheroma structure. See, for example, Martin, A. J., et al., Arterial imaging: comparison of high-resolution US and MR imaging with histologic correlation,
Radiographics,
vol. 17, pp. 189-202, 1997.
Contrast aortography, which is often considered to provide one of the best standards for aortic imaging, is actually a misnomer since none of the tissues which make up the aortic wall are visualized directly. Instead, only lesions which protrude into the lumen and focally displace the contrast agent can be “seen” as an absence of signal. Any inferences about the vessel wall depend upon a comparison of contrast displacement from the area of the lesion to the displacement around an adjacent “reference” segment of normal artery, which is often unavailable. See, for example, Thomas, A. C., et al., Potential errors in the estimation of coronary arterial stenosis from clinical arteriography with reference to the shape of the coronary arterial lumen,
Br. Heart J,
vol 55, pp. 144-150, 1993. It is believed that any statements about the thickness and stiffness of the vessel wall at the site of a contrast filling defect are purely conjectural.
For these reasons, some investigators prefer the term lumenography to describe standard contrast angiography in general (of which contrast aortography is a specific example). Libby, P., Lesion versus lumen,
Nature Medicine,
vol. 1, pp., 17, 18, 1995.
MRI has a distinct advantage over TEE in that tissue characterization is possible. See, for example, Toussaint, J. F., et al., Magnetic resonance images lipid, fibrous, calcified, hemorrhagic, and thrombotic components of human atherosclerosis in vivo,
Circulation,
vol. 94, pp. 932-38, 1996; and Correia, L. C. L., et al. By performing MRI using an intravascular receiver, higher resolution imaging can be achieved at the cost of invasiveness. See, for example, Ocali, O., et al.; Martin, A. J., et al.,
J Magn Reson Imaging,
vol. 8, pp. 226-34; Martin, A. J., et al.,
Radiographics,
vol. 17, pp. 189-202; and Atalar, E., et al.,
Magn Reson Med,
vol. 36, pp. 596-605.
Intravascular MR has overcome many of the limitations of CT and standard MRI at the cost of invasiveness. Martin, A. J., et al., High-resolution MR imaging of human arteries,
J. Magn. Resort. Imaging,
vol. 5, pp. 93-100, 1995, discloses an intra-aortic catheter coil which is employed to image the aortic wall in a pig model, although the coil is relatively large and requires ligation of the aorta.
Atalar, E., et al., High resolution intravascular MRI and MRS using a catheter receiver coil,
Magn. Reson. Med.,
vol. 36,pp. 596-605, 1996, discloses a 9 French (i.e., 3 mm outer diameter) catheter coil designed specifically for intravascular imaging. This validates the ability to quantitate atherosclerotic plaque burden and intraplaque composition against histopathology in cadaveric human aortae.
Although intravascular MRI is emerging as a valuable tool for studying aortic disease, in vivo human studies must await proper safety testing and regulatory approval.
There has been considerable interest on factors influencing atherosclerotic plaque stability. Plaque composition may predict plaque stability, and interventions that alter plaque composition may change the likelihood of plaque rupture and clinical events. Ferrari, E., et al., Atherosclerosis of the thoracic aorta and aortic debris as a marker of poor prognosis: benefit of oral anticoagulants,
J Am Coll Cardiol.,
vol. 33,pp. 1317-22, 1999, discloses that these hypotheses are supported by indirect evidence, although direct testing in vivo has not been possible.
The thoracic aorta represents a valuable window for the study of atherosclerotic plaque burden and vulnerability. See, for example, Fazio, G. P., et al.; Amarenco, P., et al., Atherosclerotic disease of the aortic arch and the risk of ischemic stroke,
N Engl J Med.,
vol 331,pp. 1474-79, 1994; Cohen, A., et al., Aortic plaque morphology and vascular events: a follow-up study in patients with ischemic stroke. FAPS Investigators. French Study of Aortic Plaques in Stroke,
Circulation,
vol. 96, pp. 3838-41, 1997; and Witteman, J. C., et al., Aortic calcified plaques and cardiovascular disease (the Framingham Study),
Am J Cardiol,
vol. 66, pp. 1060-64, 1990.
The prior art also shows that atherosclerotic disease of the thoracic aorta predicts cerebrovascular events, coronary disease/events, and death.
Without invading a vascular space, it is known to obtain similar information by receiving the signal from an adjacent body structure. The concept of placing a radio frequency (RF) receiver coil into a body cavity in order to image an adjacent structure by MR is disclosed by Narayan, P., et al., Transrectal probe for 1H and 31P MR spectroscopy of the prostate gland,
Magn. Reson. Med.,
vol. 11,pp. 209-20, 1989 (an endorectal RF receiver coil is employed to image the canine prostate); and by Schnall, M. D., et al., Prostate: MR imaging with an endorectal surface coil,
Radiology,
vol. 172, pp. 570-74, 1989 (an expandable endorectal RF receiver coil is employed to image the prostate in 15 humans having biopsy proven prostate carcinoma and two normal volunteers).
U.S. Pat. No. 5,348,010 discloses a rectal MRI receiving probe for use in imaging the prostate.
It is known to employ an endovaginal coil to image the vagina and adjacent structures. See, for example, Siegelman, E. S., et al., High-resolution MR imaging of the vagina,
Radiographics,
vol. 17,pp. 1183-1203, 1997.
U.S. Pat. No. 5,355,087 discloses the use of a probe in MRI or spectroscopy related to either the prostate or cervix. An RF receiving coil is inserted into the rectum or vagina in effecting these respective measure
Atalar Ergin
Lima Joao A. C.
Shunk Kendrick A.
Eckert Seamans Cherin & Mellott , LLC
Houser Kirk D.
Lateef Marvin M.
Qaderi Runa Shah
The Johns Hopkins University
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