Abstract:
A radiation camera system, comprising:  
     a freely positionable radiation camera;  
     a spatial coordinate determining system that determines the coordinates of the camera; and  
     a receiver which receives the spatial coordinate information and imaging information, generated by the camera and provides imaging information referenced to a coordinate system not fixed in the camera.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a divisional of U.S. application Ser. No. 09/378,871, filed on Aug. 23, 1999. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to hand-held gamma cameras and in particular to a hand-held gamma camera with a remotely readable spatial position measurement.  
         BACKGROUND OF THE INVENTION  
         [0003]    Generally, in nuclear imaging, a radioactive isotope is injected to, inhaled by or ingested by a patient. The isotope, provided as known as a radioactive-labeled pharmaceutical (radio-pharmaceutical) is chosen based on bio-kinetic properties that cause preferential uptake by different tissues. The gamma or beta photons emitted by the radio-pharmaceutical are detected by radiation detectors outside the body, giving its spatial uptake distribution within the body, with little trauma to the patient.  
           [0004]    [0004]FIG. 1 illustrates a general nuclear-imaging detector  10  comprising a NaI(Tl) scintillation crystal  12 . Generally, scintillation crystal  12 , of a diameter D 1 , is large enough to image a significant part of the human body (typically 40 cm). An array of photo-multiplier tubes (PMTs)  14  view scintillation crystal  12 , to give positional sensitivity. Each PMT  14  has an x and a y coordinate. When a photon is absorbed by scintillation crystal  12 , light is generated. A number of PMTs  14  receive the light and produce signals. The X and Y coordinates of the event are determined by the strength of the signals generated by each PMT. The energy of the event is proportional to the sum of the signals, called the Z signal. Only Z signals within a given range are counted.  
           [0005]    Size is a basic drawback of the multiple PMTs detector system. The basic limiting size of a PMT is too large for multiple PMTs to be fitted in a small camera. An alternative system using an NaI(Tl) scintillation crystal, backed by a single, position sensitive PMT, can be substantially smaller, but the field of view is small.  
           [0006]    Semiconductors with high atomic numbers and relatively high densities such as CdZnTe, CdTe, HgI 2 , InSb, Ge, GaAs, Si, PbCs, PbCs, PbS, or GaAlAs, have a high stopping power and can be used as gamma ray detectors with good photon detection efficiencies, good spatial resolution, and a relatively high photon-energy resolution. Solid state semiconductor gamma cameras generally comprise arrays of pixelated detector, hereinafter referred to as “pixelated detectors”. One type of pixelated detector is described in PCT publication WO 98/23974, the disclosure of which is incorporated herein by reference. FIG. 2 shows a typical construction of a pixelated detector  20  comprising a crystal  22  formed from a semiconductor material such as one of those noted above. A face  24  of crystal  22  has a large single cathode electrode  26 . An opposite face  28  of crystal  22  has an anode  30  comprising a rectangular array of identical small square anode pixels  32 . Typically, sizes of anode pixels  32  vary between 1 and 4 mm 2 , and the thickness of crystal  22 , between anode  30  and cathode  26  is on the order of millimeters to a centimeter. In operation, a voltage difference is applied between anode and cathode so that an electric field, hereinafter referred to as a “detector field”, is generated in crystal  22 . This field is typically on the order of a few kilovolts per centimeter.  
           [0007]    When a photon, having an energy typical of the energies of photons used in gamma cameras, is incident on crystal  22 , it generally loses all its energy in crystal  22  by ionization and produces pairs of mobile electrons and holes in a localized region of crystal  22 . As a result of the detector field, the holes drift to cathode  26  and the electrons drift to anode  30 , thereby inducing charges on anode pixels  32  and cathode  26 . The induced charges on anode pixels  32  are sensed and generally partially processed by appropriate electronic circuits located in a detector base  34  to which detector  20  is mounted. Signals from the induced charges on pixels  32  are used to determine the time at which a photon is detected, how much energy the detected photon deposited in the crystal and where in the crystal the photon interaction took place.  
           [0008]    An alternative solid-state detector system is described in U.S. Pat. No. 4,672,207 “Readout System for Multi-Crystal Gamma Cameras” by Derenzo. The detector system comprises an array of scintillation crystals arranged in N rows and M columns and adapted to be struck by gamma rays from a subject. A separate solid-state photodetector is optically coupled to each crystal. N+M amplifiers, connected to the photodetectors distinguish the particular row and column of an activated photodetector.  
           [0009]    Another alternative solid state system comprises a single scintillation crystal, optically coupled to multiple photodetectors, wherein each photodetectors has a specific x, and y coordinate.  
           [0010]    Generally, a collimator  16  is placed between scintillation crystal  12  or  22  and the tissue. Commonly, collimator  16  is honeycomb shaped, comprising a large number of holes separated by parallel lead septa. The purpose of collimator  16  is to intercept and eliminate gamma-ray photons that are not traveling in an accepted direction, parallel to the lead septa.  
           [0011]    Small gamma cameras that are hand-held are known. Generally, they are based on solid-state detectors such as a pixelated detector. Alternatively, they comprises a single NaI(Tl) scintillation crystal and a single, position sensitive PMT.  
           [0012]    Small cameras are especially useful for detecting beta radiation. Since beta rays are strongly absorbed by tissues, small cameras are able to reduce the distance between the radiation source and the camera, especially in the operating room.  
           [0013]    A specific problem with hand-held gamma cameras is spatial location of any suspected finding with respect to some known reference system, since the hand-held camera itself is not referenced to any coordinate system.  
           [0014]    New radio pharmaceuticals enhance the need for mini-cameras for both beta and gamma radiation. These radio pharmaceuticals are based on peptides, FABs (fraction of antibody) or MAB (monoclonal antibodies) which are especially designed to attach themselves to receptors usually found in specific cancerous cells.  
         SUMMARY OF THE INVENTION  
         [0015]    One aspect of some preferred embodiments of the present invention relates to providing a small radiation camera such as a gamma camera or beta camera with a preferably remotely readable spatial coordinate determining device that registers the coordinates of the camera, Preferably, the six orthogonal position and orientation coordinates. Preferably, the remote spatial coordinate device comprises two parts:  
           [0016]    1. a transmitter which is attached to the camera, for example at the tip of the handle, and which transmits 3-D coordinate information, preferably continuously, during operation; and  
           [0017]    2. a receiver at some remote location to the camera, for example on the ceiling, or near a data-acquisition computer, which receives the 3-D coordinate information sent by the transmitter.  
           [0018]    In some preferred embodiments of this aspect, the remote spatial coordinate device is an optical device. Alternatively, it is based on radio positioning. Alternatively, it is a GPS like device (together with some means for measuring angles). Alternatively, it is based on micro-waves. Alternatively coordinate determination is based on measurements of static, pulsed DC or AC magnetic fields. Alternatively, any remote spatial coordinate determining device known in the art. None of the above techniques or devices are new, per se, and therefore will not be discussed in detail herein. Many such devices are known in the art, and the present invention may utilize any suitable device.  
           [0019]    In some preferred embodiments of this aspect, the remotely readable spatial coordinate determining device is connected to a data-acquisition computer and a display screen, preferably by a cable, so that information acquired by the gamma camera is displayed on screen in real time, with the spatial coordinates of any lesion. Alternatively, signals related to the coordinate determination may be carried by the same cable. Alternatively, both data and coordinate information may be transmitted to the computer by radio or optical communication means as known in the art.  
           [0020]    In some preferred embodiments of this aspect, referencing between the coordinate system of the remotely readable spatial coordinate determining device and the patient is achieved by a second, stationary imaging system, such as an x-ray machine, a CAT scanner, an MRI machine, or any other imaging system as known in the art. Alternatively, the patient affected tissue may be marked with some visible, radioactive ink, which is imaged by the camera. In some preferred embodiments of the invention, a separate positioning system may be attached to the patient, so that the patient and the gamma camera are mutually referenced via the two positioning systems. Alternatively, the “stationary” reference for the transmitter may be attached (or referenced to) the patient.  
           [0021]    In a preferred embodiment of the invention, the nuclear imaging information is superimposed on the X-Ray, MRI, ultrasound or other image.  
           [0022]    In some preferred embodiments of this aspect, imaging a suspected finding from different viewing angles (with positions and orientations provided by the remotely readable spatial coordinate determining device) yields the three-dimensional location of a suspected lesion and allows its three dimensional reconstruction.  
           [0023]    An aspect of some preferred embodiments of the present invention relates to providing a small invasive radiation camera with a remote spatial positioning device which may be used during operation to aid a surgeon in the location of suspected lesions. Preferably, the gamma camera is covered with a disposable, sterile, radiolucent condom-like cover. Preferably, information acquired by the radiation camera (or a planar or 3D reconstruction) is displayed on screen in real time, in the surgical room showing the location of any suspected lesion with respect to the patient&#39;s coordinates and/or structure. In some preferred embodiments of the invention, the camera is placed against the tissue.  
           [0024]    Alternatively, a small gamma camera may image through the skin. Since the camera is small, it allows the physician to get closer to the lesion than with a large camera.  
           [0025]    One particular advantage of such a camera is that it can give an indication as to whether all of a cancerous growth has been removed. In particular, before the growth is removed, the growth is imaged. After removal, an additional image of the same area is taken to determine if any of the tissue that took up the radiopharmaceutical remains in the body and where it is situated.  
           [0026]    An aspect of some preferred embodiments of the present invention relates to providing a small radiation counter at the tip of the radiation camera (gamma or beta) as a coarse probe. Preferably, the radiation counter has a much higher efficiency than the spatially sensitive and energy sensitive detector of the camera. Therefore, the counter may lead the physician to areas that need close examination. This is especially helpful for beta cameras.  
           [0027]    An aspect of some preferred embodiments of the present invention relates to providing a small gamma camera that is not hand-held; rather it is attached to an arm that descends from a gantry near or above the surgery table. The coordinates of the camera are then determined as described above or by other means.  
           [0028]    As used herein, the term “freely positionable” means a device which can assume substantially any position and orientation. Such devices include hand held devices and devices mounted on articulated arms.  
           [0029]    There is thus provided, in accordance with a preferred embodiment of the invention, a radiation camera system, comprising;  
           [0030]    a radiation imager having a field of view and having a first radiation sensitivity; and  
           [0031]    a radiation detector having a sensitivity greater than that of the imager and facing in a same direction as a field of view of the camera.  
           [0032]    There is further provided, in accordance with a preferred embodiment of the invention, a method of nuclear imaging comprising:  
           [0033]    providing a radiation imager having a field of view and having a first radiation sensitivity and a radiation detector having a sensitivity greater than that of the imager and facing in a same direction as a field of view of the camera;  
           [0034]    determining a direction for the imager based on a radiation signal from the detector.  
           [0035]    Preferably, the method includes moving the imager toward a region to be imaged based on the strength and direction of radiation causing the detector radiation signal. Preferably, the direction is determined from a direction which gives a maximum radiation signal from the detector.  
           [0036]    There is further provided, in accordance with a preferred embodiment of the invention, a method of determining whether a lesion which has been tagged with a radionuclide, has been removed, comprising:  
           [0037]    acquiring a first nuclear image of an area including the cancerous lesion, prior to excision of the lesion;  
           [0038]    acquiring a second nuclear image of the area after excision of at least part of the lesion; and  
           [0039]    comparing the first and second lesions to each other.  
           [0040]    Preferably, the first and second radionuclide images are acquired during surgery. Preferably, the images are acquired using a camera situated within the surgical opening.  
           [0041]    Preferably, the method includes determining the coordinates of a camera taking said images and utilizing said determined coordinates in making said comparison. Preferably, the image is acquired with an imaging face of the camera contacting body tissue.  
           [0042]    There is further provided, in accordance with a preferred embodiment of the invention, a radiation camera system, comprising:  
           [0043]    a freely positionable radiation camera;  
           [0044]    a spatial coordinate determining system that determines the coordinates of the camera;  
           [0045]    a receiver which receives the spatial coordinate information and imaging information, generated by the camera and provides imaging information referenced to a coordinate system not fixed in the camera.  
           [0046]    Preferably, the system includes:  
           [0047]    an image source;  
           [0048]    image alignment circuitry that receives the imaging information and an image from the source and references the imaging information to the image from the source; and  
           [0049]    a display that displays a radiation image based on the imaging information and the image from the source.  
           [0050]    Preferably, the radiation image and the image from the source are displayed on a same coordinate system.  
           [0051]    In preferred embodiments of the invention the image from the source is a CT image, an MRI image or an ocular image.  
           [0052]    In a preferred embodiment of the invention, the image from the source is a previous radiation image of a same portion of the patient.  
           [0053]    In a preferred embodiment of the invention, the radiation camera a hand held camera.  
           [0054]    In a preferred embodiment of the invention, the spatial coordinate information is determined by the measurement of magnetic fields.  
           [0055]    In a preferred embodiment of the invention, the camera comprises sensors which measure electromagnetic fields generated by at least one fixed source to produce said spatial coordinate information. Preferably, the system includes a receiver to which said spatial coordinate information is transferred, wherein said information is transferred to said receiver by wireless means.  
           [0056]    In a preferred embodiment of the invention, the imaging information is transferred to a receiver from the camera by wireless means.  
           [0057]    In a preferred embodiment of the invention, the camera is a gamma camera. Alternatively, the camera is a beta camera.  
           [0058]    In a preferred embodiment of the invention, the camera is an Anger camera.  
           [0059]    In a preferred embodiment of the invention, the camera is a solid state camera.  
           [0060]    In a preferred embodiment of the invention, the system includes a radiation detector having a sensitivity greater than that of the camera facing in a same direction as a field of view of the camera.  
           [0061]    In a preferred embodiment of the invention, the spatial coordinate determining system includes a position sensor mounted on the camera.  
           [0062]    In a preferred embodiment of the invention, the coordinate system is fixed in space.  
           [0063]    In a preferred embodiment of the invention, the coordinate system is referenced to a patient. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0064]    The present invention will be more clearly understood from the following detailed description of the preferred embodiments of the invention and from the attached drawings, in which same number designations are maintained throughout the figures for each element and in which:  
         [0065]    [0065]FIG. 1 is a schematic illustration of a nuclear-imaging detector, comprising an NaI(Tl) scintillation crystal, as known in the art;  
         [0066]    [0066]FIG. 2 is a schematic illustration of a pixelated, solid-state scintillation detector, as known in the art;  
         [0067]    [0067]FIG. 3 is a schematic illustration of a small gamma camera with a remotely readable spatial coordinate determining device, in accordance with a preferred embodiment of the present invention;  
         [0068]    [0068]FIG. 4 is a schematic illustration of a diverging-hole collimator, for imaging of the field around the gamma camera, in accordance with a preferred embodiment of the present invention; and  
         [0069]    [0069]FIG. 5 is a schematic illustration of a hand-held gamma camera with a remotely readable spatial coordinate determining device, used in an operating room, in accordance with a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0070]    Reference is now made to FIG. 3 which is a schematic illustration of a small gamma camera  30  with a remote spatial positioning device, in accordance with a preferred embodiment of the present invention. Preferably, gamma camera  30  comprises:  
         [0071]    a scintillation detector  32  which detects photon radiation;  
         [0072]    a collimator  34 , which allows only gamma rays traveling in a certain direction to reach scintillation detector  32 , attached to the side of scintillation detector  32  facing the skin;  
         [0073]    a photon-position sensitive device  36 , attached to scintillation detector  23  on its other side;  
         [0074]    a rigid skeleton  38  which contains all the aforementioned parts;  
         [0075]    a handle  39 , attached to skeleton  38  for holding and manipulating gamma camera  30 ;  
         [0076]    a coordinate transmitter  42 , attached to rigid skeleton  38 , either directly, or via handle  39 ; and  
         [0077]    a remote receiver  44  not physically attached to gamma camera  30 , which receives the 3-D information sent by transmitter  42 .  
         [0078]    In some preferred embodiments of the present invention, gamma camera  30  is very small, and can be used in the open body of a patient, during surgery.  
         [0079]    Transmitter  42  and remote receiver  44  which together make up remotely readable spatial coordinate determining device  36  may be any such device, known in the art.  
         [0080]    Scintillation detector  32 , collimator  34  and photon-position sensitive device  36 , may be any scintillation detector, collimator and photon-position sensitive device, as known in the art. In some preferred embodiments, scintillation detector  32  and photon position sensitive device  36  are replaced by a pixelated solid-state detector. Alternatively, an NaI(Tl) or CsI(TI)scintillation crystal coupled to solid-state diodes is used. Alternatively, any solid state gamma camera known in the art (including those described in the above referenced prior art cameras) may be used. Alternatively, an NaI(Tl) or CsI(TI) scintillation crystal coupled to a position sensitive PMT is used. Alternatively, a wide-angle, diverging hole collimator, is used in order to provide a larger field of view to compensate for the small size of the gamma camera.  
         [0081]    Reference is now made to FIG. 4 which is a schematic illustration of diverging-hole collimator  34 , for imaging of the field around gamma camera  30 . Preferably, collimator  34  comprises a circumference  45 , a center  46 , varying-angle septa  47  and right-angle, parallel-hole septa  48 . Preferably, varying-angle septa  47  around circumference  45  begin with a very acute angle, perhaps even near 0°, for viewing the field adjacent to the gamma camera. Preferably, the angle of varying-angle septa  47  increases gradually, for example, in small steps, so that the first several rows of septa around the periphery are divergent, and the septa near and at the center are at right angle to the axis of the collimator. In this manner, as the gamma camera is moved across the tissue, it views both the tissue directly below it and, with lower resolution, the tissue around it.  
         [0082]    In some preferred embodiments of the present invention, gamma camera  30  comprises also a gamma counter or detector  50  (shown on FIG. 3) for example at the front of gamma camera  30 . Counter  50  serves as a coarse probe. Preferably, counter  50  has a much higher efficiency than the spatially sensitive and energy sensitive detector  32 . Therefore, counter  50  may lead the physician to areas that need close examination. Preferably counter  50  is provided with a limited field of view, within the field of view of camera  30 , so as to aid in determining the direction with improved resolution.  
         [0083]    Reference is now made to FIG. 5 which is a schematic illustration of a hand-held gamma camera  30  with a remotely readable spatial coordinate determining device  43 , in an operating room  60 , in accordance with a preferred embodiment of the present invention. Preferably, a patient  62  is lying on an operation table  64 . A stationary imaging system  66 , such as an x-ray machine, a CAT scanner or any imaging system as known in the art is used for referencing the coordinates of patient  62  with some known spatial coordinate system. Alternatively, radioactive markers on the patient are used for reference for camera  30 . The patient image is displayed on a monitor  44 , attached to a data acquisition computer  70 .  
         [0084]    Alternatively, a video image of the patient (or the area) may be used as an intermediary to match the nuclear image with CT or MR images from previous scans. Such matching is known in the art.  
         [0085]    Event position information from gamma camera  30  are also sent to data acquisition computer  70 . The coordinates of gamma camera  30  are sent via transmitter  42 , receiver  44  and/or a cable  71 . Therefore, images from gamma camera  30  can be superimposed on the patient&#39;s coordinate system, as displayed by stationary imaging system  66 . In this manner, it is possible to image objects that are difficult to image by stationary imaging system  66 , by getting very close to them with small, hand-held gamma camera  30 , without losing the spatial positioning information that stationary imaging system  66  yields. The small camera can also be placed against an organ, even a moving organ.  
         [0086]    Furthermore, since gamma camera  30  is easy to manipulate, it is possible to obtain images at different viewing angles, and in this manner, calculate the 3-D coordinate of a suspected lesion.  
         [0087]    In a preferred embodiment of the invention, a gamma camera can be used to provide an indication as to whether all of a cancerous growth (or other selectively absorbing tissue or lesion) has been removed. In particular, before the growth is removed, the growth is imaged. After removal, an additional image of the same area is taken to determine if any of the tissue that took up the radiopharmaceutical remains in the body and where it is situated. Since the position of the probe during acquisition of both images is known, the images can be matched to determine whether any of the tissue tagged with the radiopharmaceutical has not been removed. In particular, a side by side comparison may be made. Alternatively or additionally a two color overlay may be displayed, with one color representing before and the other after.  
         [0088]    The present invention has been described using non-limiting detailed descriptions of preferred 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. Furthermore, the terms “comprise,” include,” and “have” and their conjugates mean, when used herein: “including but not necessarily limited to.” The scope of the invention is limited only by the following claims: