KEYWORDS: Positron emission tomography, Breast, Sensors, Monte Carlo methods, Imaging systems, Magnetic resonance imaging, Biopsy, Scanners, Chest, Breast imaging
This paper presents a new high-sensitivity PET geometry for high fidelity MRI-compatible PET breast imaging which can scan both breasts simultaneously and have: high sensitivity and resolution; compatibility with MR-breast imaged volume; complete visualization of both breasts, mediastinum and axilla; and a modular design. Whereas contemporary dedicated x-ray and molecular breast imaging devices only scan one breast at a time, this approach relies on an unconventional PET geometry, and is able to provide a PET field of view (FOV) larger than that from dedicated breast MRI. The system geometry is evaluated with GATE Monte Carlo simulations of intrinsic system parameters. Various sized lesions (4-6mm) having [6:1 to 4:1] lesion:background radioactivity ratios mimicking different biological uptake are simulated, strategically located throughout a volumetric anthropomorphic torso. Dedicated breast PET (dbPET) imaging is compared with contemporary clinical PET. The dbPET system sensitivity is >6X greater than for contemporary whole-body PET. The novel, non-conventional system geometry allows for simultaneous dual-breast imaging, along with full medial and axillary imaging. Iteratively reconstructed full-volumetric images illustrate sharper visualization of 4mm lower uptake [4:1] lesions throughout the FOV compared with clinical PET. Image overlap between dedicated breast PET and MRI FOVs is excellent. Simulation results indicate clear superiority over conventional, high-sensitivity whole-body PET systems, as well as improved sensitivity over single-breast dbPET systems. This proposed system potentially facilitates both early detection and diagnosis, especially by increasing specificity of MRI, as well as visualizing tissue heterogeneity, monitoring therapeutic efficacy, and detecting breast cancer recurrence throughout the entire mediastinum.
A new low profile gamma camera is being developed for use in a dual modality (x-ray transmission and gamma-ray
emission) tomosynthesis system. Compared to the system’s current gamma camera, the new camera has a larger field of
view (~20x25 cm) to better match the system’s x-ray detector (~23x29 cm), and is thinner (7.3 cm instead of 10.3 cm)
permitting easier camera positioning near the top surface of the breast. It contains a pixelated NaI(Tl) array with a crystal
pitch of 2.2 mm, which is optically coupled to a 4x5 array of Hamamatsu H8500C position sensitive photomultiplier
tubes (PSPMTs). The manufacturer-provided connector board of each PSPMT was replaced with a custom designed
board that a) reduces the 64 channel readout of the 8x8 electrode anode of the H8500C to 16 channels (8X and 8Y), b)
performs gain non-uniformity correction, and c) reduces the height of the PSPMT-base assembly, 37.7 mm to 27.87 mm.
The X and Y outputs of each module are connected in a lattice framework, and at two edges of this lattice, the X and Y
outputs (32Y by 40X) are coupled to an amplifier/output board whose signals are fed via shielded ribbon cables to
external ADCs. The camera uses parallel hole collimation. We describe the measured camera imaging performance,
including intrinsic and extrinsic spatial resolution, detection sensitivity, uniformity of response, energy resolution for
140 keV gamma rays, and geometric linearity.
Mark Williams, Guimin Zhang, Mitali More, Allen Goode, Stan Majewski, Randy Wojcik, Brian Kross, Vladimir Popov, Andrew Weisenberger, Martin Stanton, Walter Phillips, Alexander Stewart, Thomas McCauley, Tao Wu, Edward DiBella
We are developing a scanner for simultaneous acquisition of x-ray computed tomography (CT) and single photon emission tomography (SPECT) images of small animals such as mice and rats. The scanner uses a cone beam geometry for both the x- ray transmission and gamma emission projections by using an area x-ray detector and pinhole collimator, respectively. The CT and SPECT data set are overlaid to form a coregistered structural-functional 3D image. The CT system includes a single CCD-based x-ray detector and a microfocus x-ray source. The SPECT scanner utilizes tungsten pinhole collimators and arrays of CsI(Tl) scintillation detectors. We describe considerations and the early performance of a prototype scanner.
Breast cancer is the most common cancer of American women and is the leading cause of cancer-related death among women aged 15 - 54; however recent years have shown that early detection using x-ray mammography can lead to a high probability of cure. However, because of mammography's low positive predictive value, surgical or core biopsy is typically required for diagnosis. In addition, the low radiographic contrast of many nonpalpable breast masses, particularly among women with radiographically dense breasts, results in an overall rate of 10% to 25% for missed tumors. Nuclear imaging of the breast using single gamma emitters (scintimammography) such as 99mTc, or positron emitters such as F-18- fluorodeoxyglucose (FDG) for positron emission tomography (PET), can provide information on functional or metabolic tumor activity that is complementary to the structural information of x-ray mammography, thereby potentially reducing the number of unnecessary biopsies and missed cancers. This paper summarizes recent data on the efficacy of scintimammography using conventional gamma cameras, and describes the development of dedicated detectors for gamma emission breast imaging. The detectors use new, high density crystal scintillators and large area position sensitive photomultiplier tubes (PSPMTs). Detector design, imaging requirements, and preliminary measured imaging performance are discussed.
We report on the development of a high resolution radiation imaging system which is capable of detecting and imaging the coincident gamma and x-ray emissions of the radioisotope iodine 125 (125I). Iodine 125 is commonly available as a label to molecular biology probes. Iodine 125 decays via electron capture emitting a 35 keV gamma-ray with the prompt emission of several 27 - 32 keV x rays. A coincidence condition can be set to detect the 125I decays thus reducing background radiation contribution to the image. We are testing the use of arrays of CsI(Na) crystal scintillators coupled to position sensitive photomultiplier tubes for this application. Laboratory studies have thus far been done on mice using a prototype of our detector which is intended to be used to image gene expression in live mice to advance research in neurobiology.
We report on studies of a small field of view scintimammography camera based on a position sensitive PMT and a crystal scintillator array. A 5 inch R3292 Hamamatsu PMT was coupled to a variety of scintillators, including pixelized NaI(Tl), CsI(Na) and YAP. Laboratory and phantom studies were performed to compare performances of the above scintillator sensors with special emphasis on spatial resolution and scatter rejection. The results of Monte Carlo simulations for different pixel sizes are also presented.
Reverse Geometry X-radiography imaging uses a unique configuration of x-ray source, patient, and x-ray detector to produce high resolution images. With the current system, produced by Digiray, one can obtain a resolution of 16 lp/mm and a contrast sensitivity of 0.2%. Using a lead focusing grid with 100 keV x-rays at 1 mA a dose of less than 20 mR/sec was measured. Typical acquisition times are 1/16 sec for 256 line resolution to 8 sec for 2048 line resolution. An optimized multi-detector system under development should reduce the dose rate to far less than 1 mR/sec and allow the possibility for fast volume CT applications providing laminographic view of the patient. Also `mini-probe' detectors have been developed which may be used to produce in-vitro unobstructured views.
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