WO2003076004A2 - Laser pointer device to localize site of radioactivity in the body - Google Patents

Abstract

A laser localizer may include a laser pointer on handle to be placed co-parallel against the surface of a detector head of a gamma camera and a mirror angled to direct the laser beam normal with respect to the detector head surface. The source of radiation may be a button containing Co-57 or other radioactive material placed under the mirror. When the image of the radioactive material in the laser localizer is superimposed on an image of a source of radioactive uptake in the patient on a system monitor, the laser beam will automatically point to the source within the body.

Description

LASER POINTER DEVICE TO LOCALIZE SITE OF RADIOACTIVITY IN THE BODY

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority to U.S. Provisional Patent Application Serial No. 60/362,673, filed on March 8, 2002, the disclosure of which is considered part of (and is incorporated by reference in) the disclosure of this application.

BACKGROUND [0002] Localization of gamma photon-emitting radioactive accumulations in the body is commonly performed by using a gamma camera to produce an image of the distribution of radioactivity in the body. It may be relatively easy to relate the source of radioactivity to surrounding structures if there are adjacent anatomical references, e.g., other radioactivity, but it is difficult to precisely localize single sources. This is particularly true when, for example, a surgeon wants to biopsy a specific site indicated by focal radioactive uptake. This is made even more difficult when the procedure is performed in the operating room under sterile conditions.

SUMMARY [0003] The invention permits the precise localization of a gamma emitting source of radioactivity in the body as viewed by a nuclear gamma camera or similar radioisotope imaging device. The radioactivity within the body is caused by a radioactive chemical having been administered by intravenous injection, orally, or by surgical implantation. Using a gamma camera or similar planar (2-D) imager plus a laser pointer that slides over the face of the camera, the operator can locate the source of radioactivity in the body from the location of the laser beam on the surface of the patient. This is accomplished by having a second, small point source of radioactivity located coaxially with respect to the laser beam so that both the radioactive source in the body and the radioactive point source on the laser pointing device can be observed on the monitor display of the gamma imager. When these images superimpose, the laser beam will automatically point to the source within the body.

[0004] The laser localizer may include a laser pointer on a handle adapted to be placed co-parallel against the surface of a detector head of the gamma camera and a mirror angled to direct the laser beam normal with respect to the detector head surface. The source of radiation may be a button containing cobalt-57 (Co-57) or other radioactive material such as technetium-99m (Tc-99m) positioned to be coaxial with the laser beam.

BRIEF DESCRIPTION OF THE DRAWINGS [0005] Figure 1 illustrates images of radioactive sources shown on a gamma camera monitor.

[0006] Figure 2 is a side view of a laser localizer in an operating position.

[0007] Figure 3 is a flowchart describing a real-time laser-guide localization technique.

[0008] Figure 4 is a perspective view of the laser localizer in use.

[0009] Figure 5 is a perspective view of a laser localizer according to an alternative implementation.

[0010] Figure 6 illustrates images of radioactive sources, including that from the laser localizer, on the gamma camera monitor. DETAILED DESCRIPTION [0011] In nuclear medicine imaging, very low-level radioactive chemicals (called radionuclides, radiopharmaceuticals, or radiotracers) are introduced into the body. The radioactive chemicals may, be introduced orally, intravenously, or by surgical implantation. The radioactive chemicals may be taken up by the organs in the body and then emit gamma rays the spatial distribution of which are measured by a gamma camera .

[0012] A gamma camera has one or more crystal detector (s), called scintillation crystal (s). These crystals detect the emitted gamma rays and convert the energy of the gamma ray into optical photons . The intensity and spatial location of these photons are then converted to electric signals, which are digitized and are reconstructed into an image by a computer. Other types of gamma cameras may have detectors that directly convert the gamma ray energy into an electric signal. Regardless of the method of conversion, the resulting image is viewed on a system monitor.

[0013] It may be difficult to translate the position on the system monitor to the location of a single source of radioactive uptake in the body. Reference sources may be used to relate the position of a source of radioactive uptake shown on the monitor to a position on the patient's body. For example, a calibrated radiation source may be placed on the skin, an image 105 of which shows up on the system monitor 100, as shown in Figure 1. The source of radioactive uptake 110, e.g., a sentinel lymph node, may be identified by its relative position to the injection site 115 and the calibrated source on the patient's skin.

[0014] In an embodiment, a laser localizer device is used to precisely localize sources of radioactive uptake in the patient. Figure 2 shows an exemplary laser localizer 200. The laser localizer may include a laser pointer 205 on a handle 210 and a mirror 215 angled to reflect a laser beam 220 from the laser pointer at a 90 degree angle to the plane of the handle. A source of radiation 225 is positioned under the mirror 215. The source of radiation may be, e.g., a removable button containing the cobalt-57 (Co-57) radioactive isotope. [0015] Figure 3 is a flowchart describing a real-time laser-guided localization operation 300 according to an embodiment. A radioactive material is introduced into the patient (block 305) . The patient is imaged with a gamma camera (block 310) , and a source of radioactive uptake is identified on the system monitor (block 315) . The laser localizer 200 is placed flat against the detector head 405 of the camera (block 320), which has a flat, two-dimensional surface 410, as shown in Figure 4. The laser pointer 205 may then be activated (block 325) . The laser pointer on the handle 210, and hence the laser beam exiting the laser source, are parallel to the plane of the detector head surface 410. The mirror 215 bends the laser beam so that it is normal to the detector head surface 410. A large, flat base 505 may also be provided on the laser localizer under the mirror to help keep the device flat and the laser beam perpendicular to the detector head surface 410, as shown in Figure 5. The laser beam illuminates a spot 250 on the patient's body 255 corresponding to the position of the radioactive button 225 on the detector head surface 410.

[0016] The radioactive button (Tc-99m is shown) appears as a hot spot 600 on the monitor, as shown in Figure 6. The operator slides the laser localizer over the surface of the detector until the image of the radioactive button 600 is superimposed over the image of the radioactive uptake source 605 shown on the system monitor (block 330) . Superimposition of the images as viewed on the monitor indicates that the laser beam is pointing directly at the site of radioactive uptake (block 335) , which may be beneath the surface of the skin or other tissue.

[0017] It may be desirable to mark the position of the source on the monitor itself because the intensity of the image of the radioactive material in the button may be much greater than that of the radioactive uptake source in the patient's body.

[0018] The localization technique may be used for a variety of imaging applications. For example, the laser localizer may be used to identify sentinel lymph nodes when screening for breast cancer. Sentinel node localization and skin marking can be performed outside of the operating room as long as the correct position of the patient is maintained. Alternatively, the node localization may be performed in the operating room. Furthermore, imaging immediately following surgical removal of the sentinel nodes can provide assurance that all nodes were removed.

[0019] The real-time laser-guided localization technique may be advantageous in instances when marking the patient's skin prior to surgery is impractical, e.g., when screening for colorectal cancer where the skin and tissue over the source of radioactive uptake needs to be moved or removed. [0020] In alternative implementations, other tracking technologies may be applied, which may eliminate the need for the radioactive button on the laser localizer. For example, a pressure-sensitive, radiation-transparent (at least to radiation of interest) tablet may be placed over the detector head surface and a tip placed under the mirror. The tablet may translate the position of the tip on the tablet, and hence on the detector head surface, to a position on the system monitor.

[0021] A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, blocks in the flowchart may be skipped or performed out of order and still produce desirable results. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. An apparatus comprising : a laser source to generate a laser beam; means for directing the laser beam at an angle normal to the surface of a detector head at a first location; and means for indicating on a monitor a second location corresponding to the first location on the detector head surface .

2. The apparatus of claim 1, wherein the means for directing the laser beam comprises a mirror.

3. The apparatus of claim 2, wherein the means for indicating comprises a radioactive material.

4. The apparatus of claim 3, wherein the radioactive material is placed under the mirror such that the radioactive material is between the mirror and the detector head surface when the apparatus is in an operating position.

5. The apparatus of claim 1, wherein the means for indicating comprises a pressure sensitive device.

6. The apparatus of claim 1, further comprising a handle connected to the laser source and adapted to be placed against the detector head surface.

7. The apparatus of claim 1, further comprising a base to maintain the laser beam at an angle normal to the detector head surface.

A method comprising: imaging a body with a gamma camera; identifying an image corresponding to a source of radioactive uptake in a body on a camera monitor; placing a localizer including an indicator on a detector head surface; positioning the indicator in the localizer on the detector head surface such that an image representative of the indicator is superimposed on the image of the source of radioactive uptake; and directing a laser beam at an angle normal to the detector head surface at the position of the radioactive material on the detector head surface.

9. The method of claim 8, wherein the indicator comprises a radioactive material.

10. The method of claim 8, wherein the laser beam directed at an angle normal to the detector head surface is directed to the source of radioactive uptake in the body when the image representative of the indicator is superimposed on the image of the source of radioactive uptake.

11. A laser localizer to localize a site of radioactivity in a body, the laser localizer comprising: a handle to be placed against a surface of a detector head; a laser pointer connected to the handle and oriented to generate a laser beam parallel to the detector head surface; a mirror in the path of the laser beam and tilted to direct the laser beam 90 degrees from the detector head surface; and a holder positioned under the mirror, the holder adapted to hold a radioactive material.

12. The laser localizer of claim 11, further comprising a base having a flat surface positioned under the mirror.