Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Reexamination Certificate
2000-12-14
2003-04-22
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
C250S363020, C250S363040
Reexamination Certificate
active
06552348
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to an apparatus and method for medical examination, in particular, a lutetium oxyorthosilicate (LSO) or light-output equivalent positron emitting tomography (PET) detector.
2. Description of Related Art
The American Cancer Society has predicted that there will be more than 181,000 new breast cancer cases and more than 40,000 deaths from breast cancer in the United States in 2000. [American Cancer Society, “Cancer Facts and Figures—1999,” American Cancer Society, Atlanta, Ga. (1999).] Breast cancer is also the second leading cause of cancer death in women. Currently, mammography and physical breast examination, provide the two most effective methods for screening potential breast cancer patients. Although mammography allows the detection of very small, non-palpable lesions, it has a limited diagnostic accuracy for detecting cancer and image interpretation is subject to considerable inter-observer and intra-observer variability. The incidence of positive biopsies performed after mammographic findings ranges from 9% to 65%, with most investigators reporting a 15 to 30% positive biopsy rate. The sensitivity of detection by mammography drops considerably in women with dense, fibrocystic breasts.
Microcalcifications, one of the classic signs of occult malignancies, have a low predictive value of only 11.5% for the presence of cancer. The predictive value of masses that are thought to definitely represent malignancies is about 74%, but masses thought to be possibly malignant turn out to be carcinoma in only 5.4% of the cases. [M. Moskovitz, “The predictive value of certain mammographic signs in screening for breast cancer,” Cancer, 51, 1007-1011 (1983)]. Also, several studies have reported substantial variability among radiologists in interpretation of mammographic examinations. [K. Kerlikowske, et al., “Variability and accuracy in mammographic interpretation using the American College of Radiology Breast Imaging Reporting and Data System,” J. Natl. Can. inst., 90, 1801-1809 (1998)]. Therefore, mammography is a useful screening tool for detecting cancer, but it is limited by a large number of false positive tests, which result in unnecessary biopsies. Mammography is also limited by a considerable number of false negative tests, which result in the missed diagnosis of cancer.
It is also possible to use radio-pharmaceutical and radio-nuclide imaging to detect cancers, such as [
18
F]fluoro-2-deoxy-D-glucose (FDG). FDG is a radioactive analog of glucose, which is phosphorylated and trapped within cells. After a patient receives a dose of FDG, she may be examined with a detector that senses the gamma rays produced by
18
F. Positron emission tomography (PET), using FDG as a tracer of tumor glucose metabolic activity, is an accurate non-invasive imaging technology which probes tissue and organ function rather than structure. [See U.S. Pat. No. 5,453,623 and U.S. Pat. No. 5,961,457]. The increased rate of glycolysis in neoplastic cells, independent of the oxygen concentration present, has been previously reported. [O. Warburg, “On the origins of cancer cells,” Science, Vol. 123, 309-314 (1956) and U.S. Pat. No. 5,969,358]. This information is fundamental to the utility of FDG for imaging human neoplasms.
Whole body PET scanners are used clinically to diagnose and to stage a wide variety of cancers. [C. K. Hoh, et al., “PET in oncology: will it replace the other modalities?” Sem. Nucl. Med., 27, 94-106 (1997)]. PET scanners detect breast cancer with sensitivities between 70 and 90% and with specificities of 84-97%. [N. Y. Tse, et al., “The application of Positron Emission Tomographic imaging with fluorodeoxyglucose to the evaluation of breast disease,” Ann Surg., 216, 27-34 (1992); O. E. Nieweg, et al., “Positron Emission Tomography of Glucose Metabolism in Breast Cancer: Potential for Tumor Detection, Staging, and Evaluation of Chemotherapy,” Ann. N. Y. A. Sci., 698, 423-448 (1993); and R. L. Wahl, et al., “Primary and Metastatic Breast Carcinoma: Initial Clinical Evaluation with PET with the Radiolabeled Glucose Analogue 2-[F-18]-Fluoro-2-deoxy-D-glucose,” Radiology, 179, 765-770 (1991)]. A high diagnostic accuracy of PET imaging for staging of axillary lymph node involvement has also been reported. [L. Adler, et al., “Axillary lymph node metastases: screening with F-18 2-deoxy-2fluoro-D-glucose (FDG) PET,” Radiology, 203, 323-327 (1997)]. The. lower than desired diagnostic accuracy reported for PET imaging is due to relatively poor accuracy for detecting tumors of less than 1 cm in size. [N. Avril, et al., “Metabolic characterization of breast tumors with positron emission tomography using F-18 fluorodeoxyglucose,” J Clin. Onc., 14, 1848-1857 (1996)].
Most PET imaging technology is currently based on scintillation detectors. Radiation detection begins by injecting isotopes with short half-lives into a patient's body. The isotopes are absorbed by target areas within the body, causing the isotope to emit positrons that are detected when they generate gamma rays. When in the human body, the positrons collide with electrons and the two annihilate each other, releasing gamma rays. The emitted rays move in opposite directions, leave the body and strke the array of radiation detectors. In the majority of commercial PET systems, a “block” design composed of a high-density, partially-segmented (for weighted light sharing) scintillation crystal (bismuth germanate) is coupled to four photomultiplier tubes (PMTs). [M E. Casey, et al., “A multicrystal two dimensional BGO detector system for positron emission tomography,” IEEE Trans. Nucl. Sci., 33, 460-463 (1986) and S. R. Cherry, et al., “A Comparison of PET Detector Modules Employing Rectangular and Round Photomultiplier Tubes,” IEEE Trans. Nucl. Sci., 42, 1064-1068 (1995) and U.S. Pat. No. 5,453,623]. In this design, the scintillation crystal is subdivided into semi-discrete crystals by incomplete cuts which are filled with reflecting material. The PMTs are not position-sensitive and rely on the different depths of the cuts in the scintillation crystal to yield a light distribution on the PMT's which varies linearly with interaction position across the detector. A problem with the block design of current PET systems is that the intrinsic spatial resolution and the spatial sampling of the block is determined by the size of the individual crystals. In order to improve the intrinsic spatial resolution the size of the crystals needs to be reduced. However, with the block design it becomes difficult to decode smaller crystals. Another problem inherent to the block design PET system is that it is fairly bulky, because of the large dimensions of most single channel PMTs.
More recently, high resolution, high sensitivity PET detectors have been constructed by directly coupling the scintillator material
4
to a compact, low-cost, position-sensitive PMT (PS-PMT). By coupling small discrete scintillator elements
4
directly onto the active area of the PS-PMT, one maximizes light transmission from the scintillator
4
to the PS-PMT. [J. J. Vaquero, et al., “Performance Characteristics of a Compact Position-Sensitive LSO Detector Module,” IEEE Trans. Nucl. Sci.,17, 967-978 (1998) and R. Pani, et al., “Multi-PSPMT scintillation camera,” IEEE Trans. Nucl. Sci., 46, 702708(1998) and U.S. Pat. No. 5,864,141]. However, these PS-PMT's have a significant inactive area at the edges. Using the direct coupling method and tiling many detectors together to form planar arrays, therefore, produces large gaps between the detector modules
20
because the effective or active area
10
of the PMT
8
does not span the full physical dimensions of the face of the tube (
FIG. 1
a
). This reduces system sensitivity and sampling and causes problems in the reconstruction of the data. Therefore, it is desirable to develop some sort of tapered light
Cherry Simon R.
Czernin Johannes
Doshi Niraj K.
Shao Yiping
Silverman Robert W.
Fulbright & Jaworski L.L.P.
Gagliardi Albert
Hannaher Constantine
Regents of the University of California
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