Patent Number: 
Section: description

Reference is now made to FIG. 4 which is a schematic illustration of a small, SPECT system 100, dedicated to the nuclear imaging of the breast. Preferably, SPECT system 100 is positioned on a shaft 102 that rotates around breast 110, on an axis 104 perpendicular to the body. Rotation may be provided by a motor (not shown) or other device. In the embodiment illustrated, a patient lies prone on a table 106, facing down, and breast 110 protrudes through a hole 108 in the table, and is thus pulled down by gravity. Additionally or alternatively, the breast may be pulled out by a vacuum pump (not shown) or a radiolucent cup or other construction for extending the breast. Alternatively, the patient stands xe2x80x9con fourxe2x80x9don the examination table. A chest-wall area within a diameter D is of interest. Breast 110 a height H. Optionally, a radiolucent, protective cap 116 is put on breast 110, to protect it from contact with the moving detectors. In an embodiment of the invention, SPECT system 100 is a dual-camera SPECT system, comprising two gamma cameras 120, 180xc2x0 apart, and perpendicular to the table. Preferably, each of cameras 120 is mounted on a leg 111. Optionally, a sliding mechanism 109 on shaft 102 allows the distance, W, between legs 111 to be adjusted, depending on the diameter of the breast. In some embodiments of the invention, each camera 120 comprises a collimator 36, preferably of special design, as described below, and a detector 22. Preferably, collimator 36 and detector 22 are substantially equal in size, and have a length L, that is at least equal to breast height H. Optionally, collimator 36 has a design described below, with respect to FIGS. 5A and 5B. However, other collimator types may be used, for some aspects of the invention. Optionally, output from each camera is sent to a computer 114, which analyzes the results and produces cross-sectional views of the breast, including the region adjacent the chest wall. Reference is now made to FIG. 5A, which is a schematic illustration of collimator 36 for nuclear imaging of the breast and chest wall, in accordance with an embodiment of the present invention. Optionally, collimator 36 comprises septa 37 whose field of view diverge near the chest wall edge of the collimator. That is to say that septa 37 view toward the chest wall rather than perpendicular to the axis of the breast. Optionally, the direction of view changes gradually away from the chest wall such that the septa 38 farther from the wall have a direction of view perpendicular to the axis and to the face of the camera. In this manner, it is possible to obtain information from the region of the breast close to the chest wall. This information cannot be obtained with a perpendicular parallel-hole collimator, with rotation around the breast. In these embodiments, reconstruction is preferably by iterative (ART) methods, as known in the art, at least for regions near the chest wall. Reference is now made to FIG. 5B, which is a schematic illustration of the field of view with special diverging-hole collimator 36 for a SPECT system for nuclear imaging of the breast. SPECT analysis can be obtained for the area bounded by lines g, h, and i, wherein with conventional, parallel-hole collimator, only the rectangle bounded by the two parallel cameras could have been analyzed. However, the additional information is acquired in exchanged for a certain loss in spatial resolution and an increase in artifacts, for the portion of the collimator having diverging holes. In addition, data should be acquired over 360xc2x0 rotation. Reference is now made to FIGS. 6A and 6B which are schematic illustrations of a camera-based SPECT system, dedicated to the nuclear imaging of the breast and chest wall, wherein the camera may be tilted, in accordance with embodiments of the present invention. Optionally, camera-based SPECT system 200 comprises two cameras 220, 180xc2x0 apart. Optionally, each camera 220 comprises a parallel-hole collimator 16, with septa at a right angle to the collimator length, and a detector 22. Optionally, cameras 220 are mounted on pivots, or hinges 202, on legs 111, so that cameras 220 can be tilted so as to scan at various angles with respect to axis of the breast 104. Optionally, a sliding mechanism 109 on shaft 102 allows cameras 220 to be adjusted closer together or further apart. In some embodiments, a slot 113 on each of legs 111 allows cameras 220 to be moved up and down along axis 104. FIG. 6A illustrates the collimator field of view when parallel-hole cameras 220 are at 30xc2x0 with respect to axis 104. Data acquired using this configuration includes gamma events occurring within the breast, near the chest wall. Optionally, length L of cameras 220 is sufficiently long so that at a 30xc2x0 tilt, its projection covers the complete diameter of interest, D, at the base of breast 110. However, small or larger tilt angles may be used if required to cover the breast near the wall. Preferably, as small an angle as possible is used. In this manner, chest wall information is acquired with no loss in spatial resolution. However, a second rotational pass should be made for SPECT analysis of the breast itself, as shown in FIG. 6B. Alternatively, the gamma ray activity is calculated using only the angulated camera configuration. In some embodiments, length L of camera 220 is shorter than breast height H. When this happens, several rotational passes are made with cameras 220 parallel to breast axis 104, at different breast xe2x80x9cheightsxe2x80x9d, as mounting hinges 202 of cameras 220 are moved down slots 113 of legs 111. In exemplary embodiments of the invention, the length L of the camera is between 10 and 15 cm square and it is about 10-15 cm apart. Preferably, a size about 12 cm square is suitable. Although the embodiments that have been described with reference to a dual-camera SPECT systems, other camera-based SPECT systems are possible. For example, the SPECT systems may comprise single scintillation camera. Alternatively, three or four scintillation cameras, arranged around the axis of rotation, may be used in order to enhance the system sensitivity. In some embodiments of the invention, the camera-based SPECT system comprises at least one NaI(T1) crystal and an array of PMTs for position sensitivity. Alternatively, the camera-based SPECT system comprises at least one pixelated solid-state scintillation crystal, which is smaller and more suitable to the small and cramped circumstances. Alternatively, it may comprise a single position sensitive PMT. Reference is now made to FIG. 7 which is a schematic illustration of a small multidetector SPECT system 400, dedicated to the nuclear imaging of the breast, comprising one or more stationary circular rings of detectors 420, in accordance with an embodiment of the present invention. Optionally, multidetector SPECT detector system 400 has a diameter which is slightly larger than the diameter of interest at the chest wall, D. Optionally, the rings are mounted on a shaft 402 that allows travel up and down along axis 104, guided by a slot 413, and powered by a motor (not shown). Optionally, a diverging-hole collimator design is used to obtain information regarding the chest wall and the breast. Alternatively, an interchangeable collimator system is used, with a slanted, parallel-hole collimator and a right-angle, parallel-hole collimator, to obtain information regarding the chest wall and the breast. Preferably, solid state pixelated detectors, are used for the detectors in the rings. In an embodiment of the invention, the ring may be rotated by a small amount to increase resolution or may be dithered to improve image quality as described in the above referenced PCT application. Alternatively or additionally, sub-element axial motion or dithering may be provided. Alternatively, enough rings are provided to cover the entire length of the breast. A collimator having an inward diverging view is preferably used for the rings near the chest wall. The present invention has been described using non-limiting detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. Variations of embodiments described will occur to persons of the art. In addition, while preferred embodiments of the invention have been described as having certain groups of features, some preferred embodiments of the invention may include fewer of more of the features or other combinations of features. Furthermore, the terms xe2x80x9ccomprise,xe2x80x9d include,xe2x80x9d and xe2x80x9chavexe2x80x9d or their conjugates shall mean: xe2x80x9cincluding but not necessarily limited to.xe2x80x9d The scope of the invention is limited only by the following claims.