Patent Publication Number: US-2021177367-A1

Title: Systems and methods for imaging the thyroid

Description:
BACKGROUND 
     X-ray fluorescence (XRF) is the emission of characteristic X-rays from a material that has been excited by, for example, exposure to high-energy X-rays or gamma rays. An electron on an inner orbital of an atom may be ejected, leaving a vacancy on the inner orbital, if the atom is exposed to X-rays or gamma rays with photon energy greater than the ionization potential of the electron. When an electron on an outer orbital of the atom relaxes to fill the vacancy on the inner orbital, an X-ray (fluorescent X-ray or secondary X-ray) is emitted. The emitted X-ray has a photon energy equal the energy difference between the outer orbital and inner orbital electrons. 
     For a given atom, the number of possible relaxations is limited. As shown in  FIG. 1A , when an electron on the L orbital relaxes to fill a vacancy on the K orbital (L→K), the fluorescent X-ray is called Kα. The fluorescent X-ray from M→K relaxation is called Kβ. As shown in  FIG. 1B , the fluorescent X-ray from M→L relaxation is called Lα, and so on. 
     SUMMARY 
     Disclosed herein is a system comprising: a plurality of X-ray detectors; wherein the X-ray detectors are configured to be positioned at different locations relative to the thyroid of a person, and to capture images of the thyroid with characteristic X-rays of iodine. 
     According to an embodiment, the system further comprising a radiation source configured to irradiate the thyroid with radiation that causes iodine inside the thyroid to emit the characteristic X-rays. 
     According to an embodiment, each of the X-ray detectors comprises an array of pixels, and is configured to count numbers of photons of the characteristic X-rays incident on the pixels within a period of time. 
     According to an embodiment, each of the X-ray detectors may be configured to count the numbers of X-ray photons within a same period of time. 
     According to an embodiment, the pixels are configured to operate in parallel. 
     According to an embodiment, each of the pixels is configured to measure its dark current. 
     According to an embodiment, at least one of the X-ray detectors further comprises a collimator configured to limit fields of view of the pixels. 
     According to an embodiment, energies of particles of the radiation are in the range of 30-40 keV. 
     According to an embodiment, the radiation is X-ray or gamma ray. 
     According to an embodiment, at least one of the X-ray detectors comprises an X-ray absorption layer configured to generate an electrical signal responsive to photons of the characteristic X-rays incident thereon. 
     According to an embodiment, the X-ray absorption layer comprises silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. 
     According to an embodiment, the X-ray detectors do not comprise a scintillator. 
     According to an embodiment, the system further comprising a processor configured to determine a three-dimensional distribution of the iodine in the thyroid, based on the images 
     According to an embodiment, the iodine is not radioactive. 
     Disclosed herein is a method comprising: causing emission of characteristic X-rays of iodine inside the thyroid of a person; capturing images of the thyroid with the characteristic X-rays, using a plurality of X-ray detectors positioned at different locations relative to the thyroid; determining a three-dimensional distribution of the iodine in the thyroid based on the images. 
     According to an embodiment, causing emission of the characteristic X-rays comprises irradiating the thyroid with radiation that causes the emission of the characteristic X-rays. 
     According to an embodiment, the method further comprising introducing the iodine into the blood stream of the person. 
     According to an embodiment, capturing the images comprises counting numbers of photons of the characteristic X-rays within a period of time. 
     According to an embodiment, capturing the images comprises counting numbers of photons of the characteristic X-rays within a same period of time. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
         FIG. 1A  and  FIG. 1B  schematically show mechanisms of XRF. 
         FIG. 2  schematically shows a system, according to an embodiment. 
         FIG. 3  schematically shows a side view of the system of  FIG. 2 , according to an embodiment. 
         FIG. 4  schematically shows an X-ray detector of the system of  FIG. 2 , according to an embodiment. 
         FIG. 5  schematically shows a cross-sectional view of the X-ray detector, according to an embodiment. 
         FIG. 6  schematically shows that the system of  FIG. 2  may include a collimator  108 , according to an embodiment. 
         FIG. 7  shows a flowchart for a method, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  schematically shows a system  200 . The system  200  includes multiple X-ray detectors  102 , according to an embodiment. The X-ray detectors  102  are positioned at different locations relative to an object  104  (e.g., the thyroid of a person). For example, the X-ray detectors  102  may be arranged at different locations along a semicircle around the person&#39;s neck or along the length of the person&#39;s neck. The X-ray detectors  102  may be arranged at about the same distance or different distances from the object  104 . Other suitable arrangement of the X-ray detectors  102  may be possible. The X-ray detectors may be spaced equally or unequally apart in the angular direction. The positions of the X-ray detectors  102  are not necessarily fixed. For example, each of the X-ray detectors  102  may be movable towards and away from the object  104  or may be rotatable relative to the object  104 . 
       FIG. 3  schematically shows that the system  200  may include a radiation source  106 , according to an embodiment. The system  200  may include more than one radiation source. The radiation source  106  irradiates the object  104  with radiation that can cause a chemical element (e.g., iodine) to emit characteristic X-rays (e.g., by fluorescence). The chemical element may not be radioactive. The radiation from the radiation source  106  may be X-ray or gamma ray. The energies of the particles of the radiation may be in the range of 30-40 keV. The radiation source  106  may be movable or stationary relative to the object  104 . The X-ray detectors  102  form images of the object  104  with the characteristic X-rays, (e.g., by detecting the intensity distribution of the characteristic X-ray). The X-ray detectors  102  may be disposed at different locations around the object  104  where the X-ray detectors  102  do not receive the radiation from the radiation source  106  that is not scattered by the object  104 . As shown in  FIG. 3 , the X-ray detectors  102  may avoid those positions where they would receive radiation from the radiation source  106  that has passed through the object  104 . The X-ray detectors  102  may be movable or stationary relative to the object  104 . 
     The object  104  may be a person or a portion (e.g., the thyroid) of a person. In an example, non-radioactive iodine is introduced into the person. The person may be directed to orally take or be injected a substance containing non-radioactive iodine. The non-radioactive iodine is absorbed by the thyroid. When the radiation from the radiation source  106  is directed toward the thyroid, the non-radioactive iodine inside the thyroid is excited by the radiation and emit the characteristic X-rays of iodine. The characteristic X-rays of iodine may include the K lines, or the K lines and the L lines. The X-ray detectors  102  capture images of the thyroid with the characteristic X-rays of iodine. The X-ray detectors  102  may disregard X-rays with energies different from characteristic X-rays of iodine. Spatial (e.g., three-dimensional) distribution of the iodine in the thyroid may be determined from these images. For example, the system  200  may have a processor  130  configured to determine the three-dimensional distribution of iodine in the thyroid, based on these images. 
       FIG. 4  schematically shows one of the X-ray detectors  102 , according to an embodiment. The X-ray detector  102  has an array of pixels  150 . The array may be a rectangular array, a honeycomb array, a hexagonal array or any other suitable array. Each pixel  150  is configured to count numbers of photons of X-rays (e.g., the characteristic X-rays of iodine) incident on the pixels  150  within a period of time. The pixels  150  may be configured to operate in parallel. For example, when one pixel  150  measures an incident X-ray photon, another pixel  150  may be waiting for an X-ray photon to arrive. The pixels  150  may not have to be individually addressable. Each of the X-ray detectors  102  may be configured to count the numbers of X-ray photons within the same period of time. 
     Each pixel  150  may be able to measure its dark current, such as before or concurrently with receiving each X-ray photon. Each pixel  150  may be configured to deduct the contribution of the dark current from the energy of the X-ray photon incident thereon. 
       FIG. 5  schematically shows a cross-sectional view of the X-ray detector  102 , according to an embodiment. The X-ray detector  102  may include an X-ray absorption layer  110  configured to generate an electrical signals responsive to photons of the characteristic X-rays incident thereon. In an embodiment, the X-ray detector  102  does not comprise a scintillator. The X-ray absorption layer  110  may include a semiconductor material such as, silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. 
     The X-ray detector  102  may include an electronics layer  120  for processing or analyzing the electrical signals incident X-ray photons generate in the X-ray absorption layer  110 . The electronics layer  120  may be integrated with the absorption layer  110  into the same chip. Alternatively, the electronics layer  120  may be constructed on a separate semiconductor wafer different from the absorption layer  110  and bonded to the absorption layer  110 . Examples of the X-ray absorption layer  110  and the electronics layer  120  may be found in a PCT Application PCT/CN2015/075950, the disclosure of which is incorporated by reference in its entirety. 
       FIG. 6  schematically shows that the system  200  may include a collimator  108 , according to an embodiment. The collimator  108  may be positioned between the object  104  and the detectors  102 . The collimator  108  is configured to limit fields of view of the pixels  150  of the detectors  102 . For example, collimator  108  may allow only X-rays with certain angles of incidence to reach the pixels  150 . The range of angles of incidence may be &lt;=0.04 sr, or &lt;=0.01 sr. 
     The collimator  108  may be affixed on the detectors  102  or separated from the detectors  102 . There may be spacing between the collimator  108  and the detectors  102 . The collimator  108  may be movable or stationary relative to the detectors  102 . The system  200  may include more than one collimator  108 . 
       FIG. 7  shows a flowchart for a method, according to an embodiment. In optional procedure  705 , iodine is introduced into the blood stream of the person. The iodine may be not radioactive. In procedure  710 , emission of the characteristic X-rays of iodine inside the thyroid of a person is caused. For example, the emission of the characteristic X-rays may be a result of irradiating the thyroid with radiation that has sufficiently high energy. The radiation may be X-ray or gamma ray. In procedure  720 , images of the thyroid are captured with the characteristic X-rays, using the X-ray detectors  102  positioned at different locations relative to the thyroid. In procedure  730 , a three-dimensional distribution of the iodine in the thyroid is determined based on the images. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.