JP5897307B2 - Medical diagnostic imaging equipment - Google Patents

Description

  Embodiments described herein relate generally to a medical image diagnostic apparatus.

  The detector scintillator used in the medical image diagnostic apparatus is manufactured by finely dividing the detector in the manufacturing process, and a plurality of the scintillators are collected to constitute the detector. Therefore, it manufactures so that the characteristic of a scintillator may become as uniform as possible. However, this detector has a difference in sensitivity characteristics with respect to X-ray energy. This sensitivity characteristic causes low frequency ring artifacts on the reconstructed image. In order to improve this ring artifact, a technique has been used in which the detectors are rearranged so that the sensitivity characteristics are as uniform as possible.

  However, this method of rearranging the detectors is troublesome and time consuming, and has deteriorated the production efficiency.

  The objective is to reduce low frequency ring artifacts without reordering the detectors.

The medical diagnostic imaging apparatus according to this embodiment is generated from an X-ray tube that generates X-rays, a high-voltage generating unit that generates a high voltage for applying a high voltage to the X-ray tube, and the X-ray tube An X-ray detector having a plurality of X-ray detection elements for detecting the detected X-rays, and applying the first voltage generated by the high voltage generator to the X-ray tube, thereby detecting the plurality of X-rays By applying a first output value output from each element and a second voltage higher than the first voltage generated by the high voltage generator to the X-ray tube, the plurality of X-rays It gets the correction amount to reduce non-uniformity of output characteristics of the second X-ray detecting element specific to based rather of the plurality of output values outputted in each detection element, for correcting the output characteristic And a correction unit.

It is a figure which shows an example of the graph showing the sensitivity characteristic of the two-dimensional detector system which concerns on this Embodiment 1 and 2. FIG. It is a flowchart which shows the technical process which concerns on this Embodiment 1. FIG. It is a flowchart which shows the technical process which concerns on this Embodiment 2. FIG. 1 is a block diagram of a medical image diagnostic apparatus according to a first embodiment. It is a figure which shows typically the correction process with respect to the raw data which concerns on this Embodiment 1. FIG. It is a block diagram of the medical image diagnostic apparatus according to the second embodiment. It is a figure which shows typically about the averaging with respect to the data for every subdivision based on this Embodiment 2. FIG. It is a figure which shows typically the correction process with respect to the averaged data for every subdivision based on this Embodiment 2. FIG. It is a figure which shows typically the correction process with respect to the averaged data for every subdivision based on this Embodiment 2. FIG. It is a graph of the sensitivity characteristic in the two-dimensional detector system after correction | amendment which concerns on this Embodiment 2. FIG. It is a figure which shows the mode of the reduction of the artifact on the image which concerns on this Embodiment 1 and 2. FIG.

  The medical image diagnostic apparatus according to this embodiment will be described below with reference to the drawings. Hereinafter, although the medical image diagnostic apparatus will be described as a computer tomography apparatus, the present invention is not limited to this and can be widely applied to medical image diagnostic apparatuses using X-rays. In the following description, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

(Embodiment 1)
The first embodiment will be described with reference to FIGS. 1, 2, 4, and 5 along the flow of the flowchart of FIG.

  FIG. 4 is a diagram showing a configuration of the X-ray computed tomography apparatus 1 according to the first embodiment. As shown in FIG. 4, the X-ray computed tomography apparatus 1 includes a slip ring 2, a rotating frame 5, an X-ray tube 3, a gantry driving unit 4, a two-dimensional detector system 6, A data collection unit (DAS) 7, a contactless data transmission unit 8, a first calculation unit 9, a second calculation unit 19, a pre-processing unit 10, a high voltage generation unit 11, a host controller 12, A storage unit 13, a display unit 14, an input unit 15, a reconstruction unit 16, and a network communication unit 17.

  As shown in FIG. 4, the X-ray computed tomography apparatus 1 has a gantry. The gantry supports an annular or disk-shaped rotating frame 5 in a rotatable manner.

  The rotating frame 5 includes an X-ray tube 3 and a two-dimensional detector system 6 so as to face each other with a subject arranged on the top plate in the imaging region. Here, for explanation, the rotation axis of the rotary frame 5 is the Z axis, the imaging central axis connecting the focal point of the X-ray tube 3 and the center of the two-dimensional detector system 6 is the Y axis, and the axis orthogonal to the YZ plane is Defined as the X axis. During imaging, the subject is typically placed in the imaging area so that the body axis substantially coincides with the Z axis. This XYZ coordinate system constitutes a rotational coordinate system with the Z axis as the center of rotation.

  The X-ray tube 3 receives the application of a high voltage from the high voltage generator 11 and the supply of a filament current to generate X-rays.

  In the case of the multi-slice type, the two-dimensional detector system 6 has a plurality of arrays of detection elements having a plurality of channels in the channel direction (X axis) arranged in the slice direction (Z axis). In the case of the two-dimensional array type, the two-dimensional detector system 6 includes a plurality of X-ray detection elements that are densely distributed in both the channel direction (X axis) and the slice direction (Z axis).

  The high voltage generator 11 applies a high voltage to the X-ray tube 3 through the slip ring 2 in accordance with instruction information from the host controller 12.

  The host controller 12 includes a CPU (central processing unit) and a memory (not shown). The host controller 12 controls the operations of the high voltage generation unit 11 and the gantry driving unit 4 in accordance with instructions from the input unit 15. By controlling the high voltage generator 11, the rotating frame 5 continuously rotates at a constant angular velocity, and X-rays are generated from the X-ray tube 3 continuously or at every fixed angle.

  The gantry driving unit 4 can drive the top plate holding mechanism according to the control of the host controller 12. A data acquisition circuit (DAS) is connected to the two-dimensional detection system 6.

  The data collection unit 7 converts the current signal of each channel of the two-dimensional detector system 6 into a voltage, amplifies it, and converts it into a digital signal. Data (pure raw data) collected by the data collection unit 7 is sent to the calculation unit 9 via a non-contact type or slipping type non-contact data transmission unit 8 using light or magnetism.

  FIG. 2 is a flowchart showing the normal processing according to the first embodiment. The block diagram of FIG. 4 will be described below along the flow of this flowchart.

  The non-contact data transmission unit 8 sends the data (pure raw data) collected by the data collection unit 7 to the calculation unit 9.

  The first calculation unit 9 generates pure raw data collected by the data collection unit 7 when a high tube voltage is applied in the X-ray tube 3 and a low tube voltage relatively lower than the high voltage in the X-ray tube 3. A ratio with the pure raw data collected by the data collecting unit 7 when applied is calculated for each channel (S11). The calculated ratio is displayed on the display unit 14 as a graph, for example. An example of this graph is shown in FIG. 4 is a graph in which the horizontal axis is the channel number for each channel in the two-dimensional detector system 6 and the vertical axis is the ratio calculated in the first calculation unit 9. It can be seen from FIG. 1 that the sensitivity characteristics are different for each channel of the two-dimensional detector system 6. The pre-processing unit 10 performs pre-processing such as extreme signal intensity reduction or signal dropout correction mainly by the X-ray strong absorber by the metal part, and obtains raw data. This raw data is stored in the storage unit 13.

  For example, beam hardening correction is performed on the raw data (S12). Hereinafter, step S13 will be described in detail with reference to the block diagram of FIG. Note that the correction method is not limited to beam hardening, and other correction methods may be used.

For example, the second calculation unit 19 corrects the detector sensitivity on the raw data read from the storage unit 13 to, for example, a memory using, for example, the following equation. Hereinafter, the beam hardening correction will be described with reference to FIG.

Here, Raw _BHC (ch) is the raw data for each channel after correction, Raw _org (ch) is the raw data for each channel before correction, r is the coefficient, and BhcTbl [Raw _org (ch), ch] is , The correction amount for each channel when the correction table is used. That is, the correction value by the beam hardening correction determined by the output value of the raw data for each channel number and the channel number is shown. Further, E (ch) is a ratio for each channel calculated by the first calculator 9, and Scale is a predetermined constant.

Here, for the sake of explanation, an equation obtained by transforming Equation 1 is shown.

Here, a value obtained by adding the first term and the second term is obtained for each channel using a beam hardening correction table as shown on the right side of FIG. 5, and the correction value is obtained for each channel. This is added to the raw data output value. The addition processing of the first term and the second term is a conventional beam hardening correction method. The correction table in FIG. 5 has channel numbers on the horizontal axis and the output value of raw data for each channel number on the vertical axis. That is, if the output value of the channel number and the raw data in the channel number is determined, the coordinate point on the table is determined to be one, and the correction amount corresponding to the coordinate point is obtained one-on-one. Next, the second calculation unit 19 in FIG. 4 performs correction processing on the raw data using this correction table. The third term is obtained by multiplying the correction value for each channel determined using the correction table by a constant (Scale) and further multiplying the ratio calculated by the first calculation unit 9 for each channel. This third term is a term for reducing non-uniformity in the output characteristics of the detector. In order to reduce non-uniformity in detector output characteristics, the function BhcTbl [Raw _org (ch), ch] that represents the beam hardening correction amount for each channel is a function E (ch) that represents the output value related to the sensitivity for each channel. Multiplied by a constant Scale. In this multiplication, when the output value of the raw data (Raw _org (ch)) is high, a correction value having a small value is multiplied to suppress the output value. On the other hand, when the output value of the raw data (Raw _org (ch)) is low, a large correction value is multiplied to increase the output value. This reduces the non-uniformity of the sensitivity characteristics of the detector.

  Through the above processing, raw data that has undergone beam hardening correction is obtained from the second calculator 19. Thereafter, the corrected raw data is stored in the storage unit 13 or the like.

  The reconstruction unit 16 generates a plurality of data files (time-series data files) having different imaging times based on the data (raw data) corrected by the preprocessing unit 10.

  Although not shown in the drawing, the CPU executes a program stored in the memory when a command is input by operating the input unit 15 by a user such as a doctor or a technician. Alternatively, the CPU is installed in a program stored in the HDD (not shown), a program transferred from the network, received by the network communication unit 17 and installed in the HDD, or a drive for a recording medium (not shown). A program read from the storage medium and installed in the HDD is loaded into the memory and executed. Examples of the input unit 15 include a keyboard and a mouse that can be operated by an operator, and an input signal according to the operation is sent to the CPU. The input unit 15 is mainly composed of a main console and a system console.

  The network communication unit 17 performs communication control according to each rule. The network communication unit 17 has a function capable of connecting to a network through a telephone line.

(Embodiment 2)
Description of the same parts as those in the first embodiment will be omitted, and important parts different from those in the first embodiment will be described in detail along the flowchart of FIG. 3 and with reference to FIGS. 6 to 7D. In the second embodiment, unlike the first embodiment, the sensitivity ratio of the two-dimensional detector system 6 is averaged for each small section as shown in FIGS. 7A and 7B, and the average value for each small section is obtained. The raw data is corrected by using a plurality of different beam hardening correction tables according to the difference from the origin.

  FIG. 6 is a block diagram illustrating a configuration of the medical image diagnostic apparatus 1 according to the second embodiment. The difference from the block diagram (FIG. 4) showing the configuration of the medical image diagnostic apparatus 1 according to the first embodiment is only the difference between the presence / absence of the average value calculation unit 18 and the correction processing method in the second calculation unit 19. Hereinafter, the processing flow of the second embodiment will be described in detail with reference to the flowchart of FIG. 3 using FIGS. 7A and 7B.

  FIG. 7A is a diagram schematically illustrating averaging with respect to the sensitivity ratio for each small section according to the second embodiment. FIG. 7B is a diagram schematically illustrating a correction process using data in which the ratio of outputs of the two-dimensional detector system 6 is averaged.

  First, the non-contact data transmission unit 8 sends the data (pure raw data) collected by the data collection unit 7 to the first calculation unit 9.

  Next, in the first calculation unit 9, the pure raw data output value detected by the two-dimensional detector 6 when a high tube voltage is applied in the X-ray tube 3, and the low tube voltage in the X-ray tube 3. The ratio with the output value of the pure raw data detected by the two-dimensional detector 6 when applied is calculated (S21). The calculated ratio is output to the display unit 14 as a graph. An example of this graph is the graph shown on the left side of FIG. 7A. In this graph, the horizontal axis represents the channel number, and the vertical axis represents the ratio calculated for each channel in S21.

Next, the average value calculation unit 18 calculates an average value for each small section of the two-dimensional detector system 6. A number of channels are included in each subsection of the two-dimensional detector system 6. The average value calculation unit 18 calculates an average value for each small section using the ratio in each channel (S22). Next, beam hardening correction is performed as an example using the average value calculated in S22 for each channel (S23). Hereinafter, this beam hardening correction will be described. Note that the correction method is not limited to the beam hardening correction method, and may be another alternative correction method.

7B and 7C are diagrams conceptually showing the beam hardening correction according to the second embodiment. As shown in the left diagrams of FIGS. 7B and 7C, the beam hardening correction table is changed according to the difference from the value of 0 on the vertical axis with respect to the averaged ratio for each channel. Here, for the sake of explanation, an expression in which a value is substituted for the variable of Expression 1 is shown.

Equation 3 assumes that the channel number is 384, the raw data output value at channel number 384 is 10, and the value is substituted into a variable. In this case, as shown in FIG. 7B, if the channel number and the output value of the raw data of the channel number are determined, the correction amount is uniquely determined in the beam hardening table. By obtaining this correction amount for each channel number, the raw data output from the two-dimensional detector system 6 can be corrected. Further, for example, in the subsection shown a correction table T ₂ in FIG. 7C, to equalize the sensitivity characteristic of the two-dimensional detector system 6 gives generous amount of correction than the beam hardening table T _1. The diagram on the right side of FIG. 7C shows a beam hardening correction table for determining a correction amount uniquely determined by a channel number and an output value of raw data for each channel. Although FIG. 7C shows that there are two correction tables, two or more correction tables may exist.

  FIG. 7D is a graph showing sensitivity characteristics in the corrected two-dimensional detector system 6 according to the second embodiment. It can be seen that after the correction, the sensitivity of the two-dimensional detector system 6 is made more uniform than before the correction.

  FIG. 7E is a diagram illustrating a state of artifact reduction after correction according to the first and second embodiments. That is, FIG. 7E shows that the artifacts before and after the correction are reduced with respect to the image displayed on the display unit 14. Ring-shaped artifacts can be seen before correction, but ring-shaped artifacts are reduced after correction.

  Further, by using correction means for making uniform the output of each X-ray detection element as described in detail above, the correction process is executed on the raw data obtained through the subject, thereby eliminating artifacts. Data regarding the reduced projection image of the subject can be acquired.

  As described above, according to the present invention, the output for each detection element is made uniform by using correction means such as beam hardening correction for each detection element. By this equalization processing, it is possible to provide a medical image diagnostic apparatus that reduces ring artifacts without rearranging the detection elements.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... X-ray computed tomography apparatus, 2 ... Slip ring, 3 ... X-ray tube, 4 ... Mount drive part, 5 ... Rotating frame, 6 ... Two-dimensional detector system, 7 ... Data acquisition part (DAS), 8 ... non-contact data transmission unit, 9 ... first calculation unit, 10 ... pre-processing unit, 11 ... high voltage generation unit, 12 ... host controller, 13 ... storage unit, 14 ... display unit, 15 ... input unit, 16 ... Reconfiguration unit, 17 ... network communication unit, 18 ... average value calculation unit, 19 ... second calculation unit

Claims (10)

An X-ray tube that generates X-rays;
A high voltage generator for generating a high voltage for applying a high voltage to the X-ray tube;
An X-ray detector having a plurality of X-ray detection elements for detecting X-rays generated from the X-ray tube;
By applying the first voltage generated by the high voltage generation unit to the X-ray tube, the first output value output from each of the plurality of X-ray detection elements and the high voltage generation unit by applying a second voltage higher than said first voltage that is in the X-ray tube, based rather the the ratio of the second output value output in each of the plurality of X-ray detecting elements A correction unit for acquiring a correction amount for reducing non-uniformity of output characteristics of a plurality of X-ray detection elements, and correcting the output characteristics;
A medical image diagnostic apparatus comprising: The correction unit is
A first calculator that calculates a ratio of the first output value and the second output value for each of the plurality of X-ray detection elements;
A second calculation unit that calculates a correction amount for reducing the non-uniformity of the output characteristics for each of the plurality of X-ray detection elements using the calculated ratio;
The medical image diagnostic apparatus according to claim 1, comprising:   The medical image diagnostic apparatus according to claim 2, further comprising a display unit that displays an output distribution of the X-ray detector obtained based on the ratio calculated by the first calculation unit.   4. The medical image diagnostic apparatus according to claim 1, wherein the first voltage and the second voltage are tube voltages generated by the high voltage generation unit. 5. The correction unit is
The medical image diagnostic apparatus according to any one of claims 1 to 4, wherein a beam hardening correction is performed on each of output values of the plurality of X-ray detection elements, and a non-uniformity of the output characteristics is corrected. .   The correction unit performs beam hardening correction on each of the output values of the plurality of X-ray detection elements based on a correction table that defines a beam hardening correction value for each of the output values of the plurality of X-ray detection elements. The medical image diagnostic apparatus according to any one of claims 1 to 5. The correction table corresponds to output values of different X-ray detection elements,
The correction unit sets the output values of the plurality of X-ray detection elements based on the correction table corresponding to the output values of the X-ray detection elements, the first output value, and the second output value. The medical image diagnostic apparatus according to claim 6, wherein correction is performed. With respect to the X-ray detectors divided into a plurality of subsections adjacent to each other, an average value calculation for calculating an average value of output values of the plurality of X-ray detection elements belonging to the subsection for each of the plurality of subsections. Further comprising
The medical image diagnosis apparatus according to claim 1, wherein a beam hardening correction is performed on an average value of each of the subsections, and nonuniformity of the output characteristics is corrected.   The correction unit performs beam hardening correction on each of the output values of the plurality of X-ray detection elements based on a correction table that defines a beam hardening correction value for each of the output values of the plurality of X-ray detection elements. The medical image diagnostic apparatus according to claim 8. The correction table corresponds to the different average values,
The correction unit corrects each output value of the plurality of X-ray detection elements based on the correction table corresponding to the average value, the first output value, and the second output value. The medical image diagnostic apparatus described.

Images