Patent Publication Number: US-7587027-B2

Title: Method and apparatus for determining and displaying x-ray radiation by a radiographic device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. provisional patent application No. 60/871,785, filed on Dec. 23, 2006. 

   BACKGROUND 
   1. Technical Field 
   This disclosure generally relates to radiographic imaging systems and methods, and more particularly to methods and apparatus for determining and displaying x-ray radiation generated by radiographic devices 
   2. Description of the Related Art 
   The benefits of radiographic devices and procedures to detect and diagnose medical conditions are well documented in the art. A radiographic device typically includes an x-ray tube that is positioned near a patient and a media for capturing an x-ray image. The radiographic device may include various controls that affect the characteristics of the radiation generated by the x-ray tube. Primary among these are a voltage, or kV, control that affects how far the radiation penetrates the target, and a current, or mA, control that affects the number of photons produced by the tube that are ultimately directed toward the target area. Various types of image media are also known A fluoroscope, for example, uses a fluorescent screen to record the x-ray image. Unfortunately, as is also well known, overexposure to x-ray radiation may adversely affect one&#39;s health. Accordingly, practitioners attempt to limit or minimize exposure to x-ray radiation by using the lowest voltage and current settings necessary to capture the desired image. 
   The United States Food and Drug Administration (FDA) has developed regulations that limit the amount of x-ray radiation generated during radiograph procedures, thereby to protect patients from over exposure. Those regulations were recently amended to requite certain radiographic devices to display the x-ray radiation rate generated during a procedure and an accumulated radiation dosage generated over the course of a procedure. For example, under 21 CFR 1020.32, fluoroscopic equipment manufactured on or after Jun. 10, 2006 must display a current air kerma rate and a cumulative air kerma during and after operation of the x-ray tube. The displayed air kerma rate and cumulative air kerma values must not deviate from the actual values by more than 35%. The FDA defines “air kerma” as kerma in a given mass of air. The unit used to measure the quantity of air kerma is the Gray (Gy). For X-rays with energies less than 300 kiloelectronvolts (keV), 1 Gy=100 rad. In air, 1 Gy of absorbed dose is delivered by 114 roentgens (R) of exposure. “Kerma” is defined as the sum of the initial energies of all the charged particles liberated by uncharged ionizing particles in a material of given mass. 
   In view of the foregoing, it is desirable to provide an apparatus and method capable of determining and displaying both current and cumulative radiation output of a radiographic device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the disclosed methods and apparatuses, reference should be made to the embodiment illustrated in greater detail on the accompanying drawings, wherein: 
       FIG. 1  is a schematic diagram of a radiation display device according to the present disclosure; 
       FIG. 2  is an exemplary look-up table showing predicted radiation rates for given pairs of current and voltage values; 
       FIG. 3  is a block diagram of a method for determining and displaying radiation generating by a radiographic device; 
       FIG. 4  is an electrical schematic illustrating a current multi-switch used in the radiation device of  FIG. 1 ; and 
       FIG. 5  is an electrical schematic illustrating a voltage sensing circuit used in the radiation device of  FIG. 1   
   

   It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein. 
   DETAILED DESCRIPTION 
   This disclosure relates to methods and apparatus for determining and displaying x-ray radiation generated by a radiographic device. The exemplary methods may include storing in a memory a plurality of tables that correlate voltage and current values of an x-ray tube to a predicted radiation rate for a given radiographic device. Actual or approximate voltage and current values are then obtained from an operating x-ray tube. Based on these values, a predicted instant (or “dynamic”) radiation rate is selected from one of the stored tables and is displayed to the practitioner In addition, the method may approximate an accumulated radiation dose by measuring the time periods over which predicted radiation rates are generated and calculating a running total. Apparatus for conducting such methods is also disclosed. While fluoroscope methods and apparatus are described herein, it will be appreciated that this disclosure may be embodied in other types of radiographic methods and devices. 
     FIG. 1  illustrates exemplary apparatus  20  for determining and displaying radiation levels generated by a fluoroscope  10  The apparatus  20  receives feedback regarding the control settings, such as current and voltage, of the fluoroscope  10 . The fluoroscope  10  may have a multi-position switch  12 , in which each position of the switch is associated with a specific current setting In the exemplary embodiment illustrated in  FIG. 5 , the multi-switch  12  has five positions corresponding to five different current settings (such as 1, 1.5, 2, 2. 5, and 3 mA). The current level supplied to the fluoroscope tube may then be obtained by detecting or inferring the position of the multi-switch  12  In the illustrated embodiment five pairs of contacts  40   a - b ,  41   a - b ,  42   a - b ,  43   a - b , and  44   a - b  are provided to determine the position of the switch. Each contact pair is associated with an intended current setting, and therefore the position of the multi-switch  12  is used to infer the actual current level supplied to the fluoroscope tube. 
   The mechanism for determining switch position is generally referred to herein as a “current feedback circuit.” As used herein, a “current feedback circuit” encompasses any suitable method for directly sensing or approximating the current level supplied to the fluoroscope tube. The multi-switch  12  described above is one embodiment of a current sensing circuit that approximates or infers current level. Applicant has found that this approximation is sufficient to estimate radiation exposure within the 35% deviation currently allowed by the regulations. Alternatively, apparatus for directly sensing current level may be used (such as an analog/digital converter), which should be capable of generating more accurate results, if needed. 
   The fluoroscope  10  also includes a voltage control  14  for generating a voltage control setting. The apparatus  20  includes a voltage sensor  24  that directly measures the voltage of the voltage control signal and provides an analog voltage signal. As shown in  FIG. 5 , the voltage sensor  24  may be provided as a transformer  25  that directly measures the voltage level supplied to the fluoroscope tube An analog to digital converter  26  ( FIG. 1 ) may be provided to convert the analog voltage signal to a digital voltage signal. While the exemplary embodiment directly measures voltage level using the transformer  25 , it will be appreciated that other devices may be used to directly sense voltage level. Additionally, the voltage level may be inferred or approximated. As used herein, the term “voltage feedback circuit” encompasses circuits and/or devices that may directly measure voltage as well as those that infer or approximate the voltage level supplied to the fluoroscope tube. 
   A microprocessor  30  is provided for operating the apparatus  20 . The microprocessor  30  includes inputs for receiving the current and digital voltage signals. A plurality of look-up tables is stored in a memory  32  of the processor  30  The look-up tables may be generated based on empirical data obtained by operating the particular type of x-ray tube used in the fluoroscope  10  at various operating parameters. The x-ray tube may be the actual tube used in the device or a similar tube used in a test device. The empirical data provides a predicted radiation rate for a given combination of current and voltage signals of the tube. 
   One exemplary chart  40  for a particular x-ray tube is shown in  FIG. 2 , where voltage signals “kv” are provided along an x-axis of the table and current signals “ma” are provided along the y-axis of the table. The table is filled with predicted radiation levels, which in this case are measured in Rads/minute (R/min). It will be appreciated that the current and voltage signals, as well as the predicted radiation level, may be provided in any desirable units For example, the radiation levels may be provided in milliGrays per minute (mGy/min). The chart  40  was generated by operating the subject x-ray tube at select current/voltage settings and measuring radiation output. Radiation outputs at other current/voltage settings were interpolated from the select current/voltage settings. The interpolated radiation outputs were then validated by further testing. 
   While the exemplary embodiment uses look-up tables based on empirical data, it will be appreciated that other means may be used to estimate radiation output. Instead of generating tables, the mathematical relationships between current/voltage levels and radiation output may be integrated into the circuit board to provide a direct estimation of radiation output. For example, it is generally known that for a constant voltage level, radiation output will vary substantially directly proportionally to changes in the current level It is also known that for a constant current level, changes in voltage will cause the radiation output to vary according to the square of the ratio of the change in voltage level. These relationships generally hold true for voltage levels in the 50-90 kV range. Accordingly, a single radiation output and its associated current and voltage settings for a tube may be stored in memory and the known mathematical relationships between voltage/current settings and radiation output may be used to directly calculate an estimated radiation output for different current/voltage levels. 
   Based on the current and voltage signals, and with reference to the stored look-up tables, the microprocessor  30  will determine an instant or “dynamic” radiation rate for the fluoroscope  10 . 
   The microprocessor  30  may also determine a cumulative radiation dose in addition to the dynamic radiation rate. For example, the microprocessor  30  may include a sample loop circuit  34  that repeats after a set period of time “t” such as one second. Radiation that has accumulated during each time period “t” may then be approximated by multiplying the currently estimated radiation rate by the time period “t” to obtain a sample period accumulated radiation value. The sample loop is repeated for the duration of the x-lay tube operation to obtain subsequent sample period radiation values. The sample period radiation values are then aggregated to obtain a total accumulated radiation value that estimates the total radiation dosage administered during the radiographic procedure. 
   The exemplary apparatus also includes a back-up memory  50  for storing the dynamic radiation rate and the accumulated radiation value. The back-up memory  50  is preferably battery powered so that it may retain the stored values in the event of a power failure. 
   A display  60  is operatively coupled to the microprocessor  30  for displaying the dynamic radiation rate and the total accumulated radiation value. The display  50  may be provided as a LCD or other known output. The display  50  preferably shows the radiation units in addition to the numeric values for the radiation rates and accumulated radiation dosage determined by the microprocessor  30 . 
   A printer (not shown) may be operatively coupled to the microprocessor  30  for providing a hard copy of the radiation values determined during the radiograph procedure. Additionally, the apparatus  20  may include an interlock circuit that disables the radiographic device when the display  60  is disconnected 
   A method for determining and displaying radiation values is schematically illustrated in  FIG. 3  At block  100 , apparatus for deter mining and displaying radiation values is operatively coupled to a radiographic device, such as a fluoroscope A plurality of look-up tables is stored into a memory of the apparatus at block  102 . As noted above, the look-up tables may provide predicted radiation rates associated with measured current and voltage values. The predicted radiation rates may be based on empirical data. At blocks  104  and  106 , measured current and voltage values, respectively, are received via communication ports. A momentary radiation rate is determined and displayed based on the measured current and voltage values with reference to the stored look-up tables at block  108 . At block  110 , an accumulated radiation dosage is calculated and displayed. The accumulated radiation dosage may be approximated by running a sample loop that obtains the momentary radiation rate and repeating the sample loop after a known time interval. The radiation that accumulates during a given sample loop may be obtained by multiplying the momentary radiation rate by the time interval. The dosages for each sample loop conducted while the x-ray tube is operating are then aggregated to obtain a final accumulated radiation dosage. 
   While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.