Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-03-30
2003-09-30
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S436000, C600S433000, C600S458000
Reexamination Certificate
active
06628982
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to identifying landmarks which assist in visualizing internal structures during diagnostic and/or therapeutic procedures, including medical procedures.
BACKGROUND OF THE INVENTION
Targeting aids or landmarking devices have been employed in diagnostic imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRI)and ultrasound. These devices, commonly referred to as fiducial markers, generally occur as two types: internally occurring markers which are inherent in the subject's anatomy; and externally positionable imaging aids which can be permanently or temporarily affixed to the body under analysis. External fiducial markers have also been proposed for use and used in other imaging techniques such as positron emission tomography (PET) and single photon emission computed tomography (SPECT)as well as in imaging techniques such as MRI and CT. No effective internally positionable devices have been developed.
Imaging techniques such as PET and SPECT rely upon cellular uptake of suitable imaging solutions such as 2-(
18
F)-fluoro-2-deoxy-D-glucose (FDG) to provide accurate images of metabolically active tissue, including cancerous or abnormal tissue material. Malignant cells such as those found in cancerous tumor tissue, generally exhibit elevated energy requirements resulting in elevated levels of glucose consumption. By comparison, surrounding tissue is less metabolically active. Imaging techniques such as PET make use of this differential in cellular glucose uptake by employing radiopharmaceutically tagged uptake solutions to demonstrate areas of interest for imaging and analysis. Other PET techniques such as image amino acid transport, DNA synthesis, etc., as well as SPECT can, for example, image overexpression of receptors on tumors. While both methods allow distinction of tumor from normal tissues, there are instances in which PET and SPECT are difficult to use as a single scanning modality.
One drawback of such radiopharmaceutically assisted imaging techniques is that the visualized area of increased tracer accumulation is best localized in comparison to known anatomical references in order to be precisely characterized and located in the subject's body. In order to be visualized in a PET or SPECT scan, the anatomical element of interest must also be capable of sufficient uptake of radioactivity to provide a detectable emission. Thus, localization can be accomplished using PET or SPECT when a known anatomical landmark also exhibits increased radiotracer uptake relative to the surrounding imaged tissues. In such instances, the landmark can provide a reference against which the region under study can be located, analyzed and measured. This requirement becomes problematic in regions of greater anatomical variation, and in regions which have little radiotracer uptake on scan. Such regions provide few reference landmarks which have levels of increased cellular glucose or other tracer uptake.
This problem becomes more pronounced in situations where imaging data generated from PET or SPECT scans are to be integrated with imaging data derived from other methods such as,,i.e., MRI, CT, or ultrasound. As described in Wahl et al., “Anatometabolic Tumor Imaging: Fusion of FDG PET with CT or MRI to Localize Foci of Increased Activity,”
J. Nucl. Med
; 34(7); 1190-1197, (1993) “metabolic” data generated from PET studies of specific anatomical regions have been fused with imaging data generated by MRI and/or CT to visualize “hot spots” generated by abnormal cellular activity. Such data have been registered to anatomical images generated by MRI and/or CT. In Thornton et al., “A Head Immobilization System for Radiation Simulation, CT, MRI, and PET Imaging,”
Medical Dosimetry
; 16; 51-56, (1991), contour tubing is permanently mounted to immobilizing masks used in simulation planning and during radiation treatment for both central nervous system and cranial and facial tumors. A suitable positron emission material such as a fluorine-18 solution is inserted in the tubes to provide a positron emission from the known external source. The authors describe an external marker system that provides a reference system for imaging correlation.
In the process described in the Wahl et al. reference, external fiducial markers were placed during both anatomic (CT and MRI) and metabolic (PET) studies. These external fiducial markers, as well as inherent internal anatomical landmarks were used to reconstruct fused images from the various imaging studies. This permitted greater accuracy in localizing of structures of interest.
U.S. Pat. No. 4,884,566 to Mountz et al. is directed to an externally positioned apparatus for defining a plane of an image through a portion of the body. The device includes a frame onto which a plurality of channels can be mounted. A suitable imaging material can be contained in the channels to provide reference markers during scanning.
The methods and devices described in the Wahl and Thornton references present difficulties when employed to visualize regions where greater patient-to-patient anatomical variation is encountered. Such regions often lack internal landmarks or accurate correlation with the positioning of external fiducial markers. The device disclosed in Mountz has an effective use in imaging more confined and rigid regions like the cranium. However, external devices such as the Mountz device or that disclosed in Thornton are not designed for marking internal imaging regions such as the chest, abdomen or pelvis. In addition, external markers do not localize deep anatomy.
In three-dimensional radiation treatment planning, the ability to visualize targets and critical structures is crucial. These critical structures are organs which receive radiation dose but are not themselves targets for treatment. Examples of critical structures include, but are not limited to the optic chasm, esophagus, spinal cord, small and large bowels, rectum, kidneys, vaginal walls, etc. Knowledge of the location of critical structures, as well as the targeted tissue for treatment, permits more accurate targeting and precise administration of radiation dose and greater sparing of normal tissue radiation toxicity.
The problem can present in many situations, for example, when functional imaging is introduced into radiation treatment planning for thoracic cancers such as lung cancer. In such situations it is important to visualize critical structures such as the esophagus in a manner which will permit the radiation oncologist to locate and identify critical structures and to locate the target tissue to plan and administer therapeutic radiation dose in the most precise and accurate manner possible. Critical structures such as esophageal tissue are difficult to visualize in PET due to relatively low metabolic uptake of radiopharmaceutical marker by the esophagus, particularly in relation to the target tumor. Under such circumstances, metabolic emission imaging techniques such as PET or SPECT are of limited efficacy.
References such as Wahl et al. have proposed fusing data produced from metabolic imaging techniques with data generated from other imaging techniques. However, accurate visualization of certain critical structures or targets can be difficult even in multiple imaging systems. MRI is particularly sensitive to moving tissue. Even a reproducibly stationary-positioned patient will produce motion from breathing, heart rate or peristalsis which can create image displacement or edge blurring artifacts. MRI motion artifact correction techniques such as retrospective triggering and respiratory compensation as well as gradient motion compensation do not completely remove motion artifacts from an MRI image, (Brown et al. “MRI Imaging, Abbreviations, Definitions and Descriptions: A Review,”
Radioloay
(1999) 213(3): 647.) Deep anatomy fiducial markers can facilitate inclusion of MRI imaging in multi-imaging modality fusion by complementing existing MRI artifact correction techniques.
The sensitivity and specificity
Fisher Susan J.
Thomas Cherry T.
Wahl Richard L.
Dierker & Glassmeyer, P.C.
Lateef Marvin M.
Qaderi Runa Shah
The Regents of the University of Michigan
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