JP5405548B2 - PET equipment - Google Patents

Description

  The present invention relates to a PET apparatus that performs scanning in consideration of attenuation of a positron nuclide-labeled drug.

  A PET (Positron Emission Tomography) device is a device that measures the location of radioactivity. A subject to which a drug labeled with a positron emitting nuclide is administered is scanned in the whole body in the body axis direction, γ rays emitted from the subject are detected, and an image in the subject is reconstructed from the detection result (for example, , See "Patent Document 1").

The state and function of a specific organ or tissue can be reconstructed as an image by a PET device by labeling a drug having a property of selectively gathering in a specific organ or tissue with a positron emitting nuclide and administering it to a subject. it can. Positron-emitting nuclides include ¹⁸ F (half-life: 110 minutes), ¹⁵ O (half-life: 2 minutes), ¹¹ C (half-life: 20 minutes), ¹³ N (half-life: 10 minutes), and the like. Drugs labeled with this positron emitting nuclide are water, glucose, amino acids and the like.

  In order to scan the whole body of the subject, the bed on which the subject is placed and the detector for detecting radiation are relatively moved. A count of radiation from the collection location where the detector is located can be counted. The relative movement between the bed and the detector includes step movement and continuous movement. The step movement is a moving method in which the detector is sequentially moved to a collection position and is kept stationary for a common time at each collection position. Continuous movement is a method of moving without stopping at a constant moving speed from the start to the end of scanning. In any of the scanning methods, a certain time is required from the start of scanning of the subject to the end of all the imaging ranges, and the position where the radiation is collected is different every elapsed time.

  By the way, since the positron-emitting nuclide-labeled drug emits radiation when the nuclide decays, the radiation emission amount attenuates with the passage of time. Therefore, even if radiation emitted from the same amount of positron emitting nuclide-labeled drug is detected, the count of radiation per hour differs at the beginning and end of the period.

  Therefore, since it takes a certain amount of time to scan the whole body of the subject, the same amount of positron emitting nuclide-labeled drugs collected at the collection position scanned first and the collection position scanned after a predetermined time have passed. Even if they are different, the radiation counts obtained from both sides are different and appear different on the image.

  In order to reduce the influence of the attenuation of the positron-emitting nuclide-labeled drug, the PET apparatus has conventionally corrected the influence of the attenuation of the positron-emitting nuclide-labeled drug by image processing using software. That is, in the actual scan, the influence of the attenuation of the positron-emitting nuclide-labeled drug remains, but the data is processed after that to artificially reduce the influence of the attenuation of the positron-emitting nuclide-labeled drug. .

  Attenuation correction by this image processing is easily influenced by the algorithm, and depending on the correction location, it may be affected by correction more than the attenuation of the positron-emitting nuclide-labeled drug. The effect of attenuation cannot be reduced well, and the image is deteriorated. Further, as the algorithm for attenuation correction by image processing becomes more complicated, the load on the image processing is increased and the image processing takes a long time.

JP 2006-90752 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a PET apparatus capable of capturing a high-quality image by reducing the influence of attenuation of a positron nuclide-labeled drug by a scanning method. It is in.

To solve the above problems, a first aspect of the PET apparatus according to the present invention, a bed for supporting the patient a drug labeled with port Jitoron emitting radionuclides are administered, the gamma rays emitted from the positron a detector to be detected, the moving mechanism for relatively moving said detector and the object, the detector controls the moving mechanism so as to sequentially reach each collection position of the subject, before serial scan control unit for sequentially adjusting the radiation detection time for each of the respective collection position according to the relationship between the attenuation and the respective collecting locations over time of positron, the subject within the detection result of the detector And a reconstruction processing unit for reconstructing the image.

The scan control unit may adjust the radiation detection time for each collection position that has arrived to a time that compensates for the number of radiation detection counts that have decreased according to the decay of the positron-emitting nuclide over time.

  The scan control unit controls the moving mechanism so that the subject and the detector sequentially reach each collection position of the subject by relative step movement, and is stationary at each reached collection position. The radiation detection time at the reached collection position may be adjusted by increasing the time according to the decay of the positron emitting nuclide over time.

  According to the present invention, it is possible to reduce the processing burden of correcting the influence of the decay of the positron-emitting nuclide-labeled drug over time by image processing, to save or shorten the time required for image processing, and to improve the image quality by image processing. There is no deterioration.

It is a block diagram which shows the structure of the PET apparatus which concerns on 1st and 2nd embodiment. It is a schematic diagram which shows the table which prescribes | regulates the operation | movement of the relative movement of the detector and bed based on 1st Embodiment. It is a flowchart which shows operation | movement of the PET apparatus which scans according to the table which prescribes | regulates the operation | movement of the relative movement of the detector and bed based on 1st Embodiment. It is a block diagram which shows the detailed structure of the control part which concerns on 1st Embodiment. It is a schematic diagram which shows the imaging condition input screen which concerns on 1st Embodiment. It is a flowchart which shows the preparation operation | movement of the table which prescribes | regulates the operation | movement of the relative movement of the detector and bed of the PET apparatus concerning 1st Embodiment. It is a graph which shows the scanning aspect by the PET apparatus which concerns on 1st Embodiment. It is a block diagram which shows the detailed structure of the control part of the PET apparatus which concerns on 2nd Embodiment. It is a schematic diagram which shows the table which prescribes | regulates the operation | movement of the relative movement of the detector and bed based on 2nd Embodiment. It is a flowchart which shows operation | movement of the PET apparatus which scans according to the table which prescribes | regulates the operation | movement of the relative movement of the detector and bed based on 2nd Embodiment. It is a schematic diagram which shows the imaging condition input screen which concerns on 2nd Embodiment. It is a flowchart which shows the preparation operation | movement of the table of PET apparatus concerning 2nd Embodiment. It is a graph which shows the scanning aspect by the PET apparatus which concerns on 2nd Embodiment.

  Hereinafter, preferred embodiments of the PET apparatus according to the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing the configuration of the PET apparatus according to the present embodiment.

  The PET apparatus 1 according to this embodiment includes a gantry 2, a bed 3, and a console 4. The gantry 2 detects radiation emitted from within the subject. A subject is placed on the bed 3. The console 4 is set with shooting conditions, and controls the gantry 2 and the bed 3 according to the shooting conditions. Further, the console 4 reconstructs an image in the subject from the radiation detected by the gantry 2.

  The gantry 2 has an opening through which a subject placed on the bed 3 can be inserted. The gantry 2 includes a detector 21. The detector 21 is arranged in a multi-ring shape along the opening so as to surround the opening, and the multi-ring shape is arranged in multiple layers along the axis of the opening. The detector 21 detects the incidence of radiation within the range of the arrangement width along the opening axis.

  This multi-ring detector 21 detects two γ-rays in the opposite direction of 180 ° emitted when positrons emitted from positron nuclides are combined with nearby free electrons and annihilated. The incident direction of γ rays is determined by regarding the γ rays incident on the detector 21 at the same timing as two γ rays in the opposite direction of 180 °, and counted as γ rays in that direction.

  The detector 21 is a so-called gamma camera, and includes a scintillator and a photomultiplier tube (PMT). A scintillator composed of BGO (bismuth germanate) emits light when a gamma ray collides and outputs light having a peak at 420 nm. The photomultiplier tube outputs an electrical signal by photoelectric conversion when it receives light output from the scintillator.

  The gantry 2 and the bed 3 move relatively. The PET device 1 is provided with a moving mechanism 5 that moves either the gantry 2 or the bed 3 in the direction of the subject axis. The moving mechanism 5 moves the gantry 2 or the bed 3 in the direction of the subject body axis. The gantry 2 and the bed 3 move relative to each other.

  When the gantry 2 and the bed 3 move relatively, that is, when the subject and the bed 3 move relatively, the detector 21 is positioned around each radiation detection point set on the subject. . And the radiation radiated | emitted from the radiation detection location in the range of the arrangement width of the detector 21 injects into the detector 21, and is detected.

  The console 4 includes an input device 41, a control unit 42, a data collection unit 43, a reconstruction processing unit 44, and a display device 45. The input device 41 and the display device 45 are directly or indirectly electrically connected so that signal input / output with the control unit 42 is possible. The control unit 42 is directly or indirectly electrically connected to the moving mechanism 5 so that signal input / output is possible. The data collection unit 43 is directly or indirectly electrically connected so that a detection signal from the detector 21 can be input. The reconstruction processing unit 44 is electrically connected directly or indirectly so that the data collected by the data collection unit 43 can be input. The display device 45 is directly or electrically connected so that the image data reconstructed by the reconstruction processing unit 44 can be input.

  The data collection unit 43 collects projection data by counting the γ rays detected by the detector 21. The data collection unit 43 counts γ rays in the same incident direction in the same memory, and collects the incident direction and the counting result of γ rays from that direction as projection data.

  The reconstruction processing unit 44 reconstructs an image in the subject from the projection data. The reconstruction processing unit 44 is configured by a circuit that performs, for example, a convolution back porosimetry method.

  The control unit 42 sets a collection position for collecting radiation at various locations on the subject P, and scans for controlling the relative movement between the gantry 2 and the bed 3 so that a desired count number of γ rays can be obtained from the collection position. It is a control means. That is, the relative movement between the detector 21 and the subject is controlled. The desired count is a number that ignores the decay of radiation over time of the positron emitting nuclide labeled agent.

  The control unit 42 displays an input screen for inputting photographing conditions on a display device 45 such as an LCD display or a CRT display, and receives an operation signal representing the photographing conditions from the input device 41 such as a keyboard or a mouse. Then, a table representing how the gantry 2 and the bed 3 are moved relative to each other is generated according to the received photographing conditions, and the drive of the moving mechanism 5 is controlled according to this table.

  FIG. 2 is a schematic diagram illustrating a table Ta that defines the relative movement operation between the detector 21 and the bed 3 according to the first embodiment. In the present embodiment, the control unit 42 moves the detector 21 and the bed 3 step by step. The step movement is a movement in which the whole body of the subject P is divided into a plurality of collection positions and the detector 21 is stopped at each collection position for a predetermined time.

  The control unit 42 creates a table Ta that defines the rest time at each position of the subject P. Then, the subject P is moved step by step to each position, and the radiation detection time at the radiation detection point is applied for the rest time specified in the table Ta.

In the table Ta, a collection position number N representing a collection position and a stationary time ST _N are stored in association with each other. The collection position number N is given to each collection position in the order in which the detector 21 detects radiation. Rest time ST _N represents the time for stationary and a detector 21 and the bed 3 at the collection position represented by the collected position number N.

For example, the collection position number still time ST ₁ corresponds to 1 is stored and corresponds to the collection position number 2 rest time ST ₂ generates a stored table Ta, the control unit 42, the collection position number 1 detector 21 in the collection position represented is the moving mechanism 5 to move the detector 21 and the bed 3 so as to come, the movement mechanism and a detector 21 and the bed 3 by ST ₁ in its acquisition positions so as to still 5 is controlled as the radiation detection time. When the still time ST ₁ has elapsed, the control unit 42 moves the detector 21 and the bed 3 to a moving mechanism 5 as the detector 21 comes to collect position represented by the collection position number 2, its collection position in to control the moving mechanism 5 so as to still a detector 21 and the bed 3 by ST ₂ and radiation detection time.

  FIG. 3 is a flowchart showing the operation of the PET apparatus 1 that scans according to the table Ta.

  When the scan start is input (S01), the PET apparatus 1 starts the scan. When a button assigned with a scan start operation arranged in the input device 41 is pressed, a press signal of the button is input to the control unit 42. The control unit 42 starts scanning control when a button pressing signal to which a scan start operation is assigned is input.

  First, the control unit 42 initializes the collection position number N to “1” (S02). By first reducing the collection position number N, a collection point where radiation is detected is determined first. Further, the control unit 42 initializes the timer PT to “0” (S03). The timer PT is a counter value for measuring a stationary time, and indicates a time period during which radiation is detected while the detector 21 and the bed 3 are stationary.

Next, the control unit 42 reads the still time ST _N corresponding to the collection position number N from the table Ta (S04). Initially, since the collection position number N is initialized to “1”, the stationary time ST ₁ stored in the table Ta corresponding to the collection position number ₁ is read.

Reading the rest time ST _N, the control unit 42 causes the relative movement to the collection position corresponding to the detector 21 and the bed 3 in the collecting position number N (S05). The control unit 42 outputs a drive signal to the moving mechanism 5. The moving mechanism 5 is driven while the drive signal is output, and the detector 21 and the bed 3 are relatively moved accordingly. The relative movement between the detector 21 and the bed 3 is detected by the moving mechanism 5. The moving mechanism 5 includes an encoder that detects the rotation amount of the motor, and outputs the detected value to the control unit 42. The control unit 42 uses the value input from the moving mechanism 5 as a result of the relative movement between the detector 21 and the bed 3, and as a result of the relative movement between the detector 21 and the bed 3, the detector 21 It is determined whether the collection position represented by the collection position number N has been reached. When it is determined that the collection position represented by the collection position number N has been reached, the output of the drive signal is stopped. That is, it is stopped.

  When the detector 21 and the bed 3 are relatively moved to the collection position corresponding to the collection position number N, the control unit 42 starts counting up the timer PT (S06). That is, the detection time of the radiation emitted from the collection position corresponding to the collection position number N is counted.

  While stationary at the collection position corresponding to the collection position number N, the detector 21 detects radiation from this collection position, the data collection unit 43 collects projection data, and the reconstruction processing unit 44 reconstructs the image. A configuration process is performed (S07). Note that the image reconstruction by the reconstruction processing unit 44 may not be in real time.

Control unit 42, each time to count up the timer PT, it is determined whether the timer PT is a read still time ST _N or (S08). By this determination, the detection time of the radiation emitted whether satisfying ST _N is determined from the collected position represented by the collected position number N.

As a result of the determination, if PT ≧ ST _{N is} not satisfied (S08, NO), the timer PT continues to be incremented (S06), and radiation detection, projection data collection, and reconstruction processing are continued (S07). On the other hand, if PT ≧ ST _{N as} a result of the determination (S08, Yes), the detector 21 and the bed 3 so that the detection time of radiation emitted from the collection position represented by the collection position number N satisfies ST _N. And the next acquisition position is scanned.

  In the next collection position scan, the control unit 42 first sets the collection position number N to N + 1 (S09), counts up to the collection position number N representing the collection position to be scanned next, and sets the next collection position. Stipulate. Then, it is searched whether or not this new collection position number N exists in the table Ta (S10).

If a new collection position number N exists in the table Ta (S10, Yes), a timer is used to scan the collection position corresponding to the new collection position number N, for example, the collection position number 2 next to the collection position number 1. PT is initialized to 0 (S03), the stationary time (ST _N ) corresponding to the new collection position number N is read (S04), and the detector 21 is moved to the collection position corresponding to the new collection position number N ( S05), until the timer PT is greater than or equal to ST _N (S08, Yes), the count-up timer PT (S06), performs radiation detecting (S07). That is, the time from the detector 21 reaches the collecting position corresponding to the new collection position number N to satisfy ST _N, detects the radiation from the collecting position corresponding to the new collection position number N.

  If the new collection position number N does not exist in the table Ta (S10, No), all the collection positions have been scanned, and the operation of the PET apparatus 1 is terminated.

  FIG. 4 is a block diagram illustrating a detailed configuration of the control unit 42 according to the first embodiment that generates the table Ta and controls the relative movement between the detector 21 and the bed 3 according to the table Ta.

  The control unit 42 includes a display control unit 421, a stationary time table storage unit 422, an attenuation rate calculation unit 423, a half-life table 424, a time adjustment unit 425, and a movement controller 426. The display control unit 421 is a configuration for setting imaging conditions, and the stationary time table storage unit 422, the attenuation rate calculation unit 423, the half-life table 424, and the time adjustment unit 425 are configured to generate a table Ta. The movement controller 426 is configured to control the movement mechanism 5 according to the table Ta.

  The display control unit 421 displays an imaging condition input screen for generating the table Ta on the display device 45. The form of the shooting condition input screen is stored in advance.

  FIG. 5 is a schematic diagram showing an imaging condition input screen. In this imaging condition input screen, as the imaging conditions, the type of positron-emitting nuclide-labeled drug to be used, the number of images of the subject P to be divided, that is, the number PN of collection positions, and provisional radiation detection at each collection position Time DT is input.

  The type of positron emitting nuclide-labeled drug is displayed so as to be selectable from a pull-down menu. The positron-emitting nuclide-labeled drugs displayed in this pull-down menu are those stored in the half-life table 424.

  In the half-life table 424, the types of various positron-emitting nuclide-labeled drugs and the values representing the half-life H of the positron-emitting nuclide-labeled drugs represented by the types are stored in advance as a pair.

  In addition, when there is no positron emitting nuclide labeled drug used in the pull-down menu, it is possible to input the type of positron emitting nuclide labeled drug used and its half-life H. The inputted kind of positron nuclide emitting nuclide labeled drug and its half-life H are stored in the half-life table 424.

The stationary time table storage unit 422 stores the generated table Ta. When creating the table Ta of the collection position number N, the collection position numbers N-1, N-2,. Therefore, only the collection position number N assigned to each collection position according to the number of collection positions input on the imaging condition input screen is stored in the stationary time table storage unit 422. A stationary time ST _N is created and stored in order. For example, when “8” is input as the number of collection positions, collection position numbers N = 1 to N = 8 are stored.

The attenuation rate calculating means 423 calculates the attenuation rate R of the positron-emitting nuclide-labeled drug over time when the detector 21 reaches each collection position. The decay rate R represents the proportion of positron emitting nuclides that emit radiation with respect to the initial stage. This decay rate R is calculated by the elapsed time _TN and the half-life H of the positron-emitting nuclide-labeled drug used. The beginning of the elapsed time _TN is the time when the scan of the subject P starts, and when the radiation detection from the collection position corresponding to the collection position number 1 where the radiation detection is first performed starts. The end of the elapsed time _TN is when the detector 21 reaches the collection position corresponding to the collection position number N.

The elapsed time T _N is a cumulative value of the stationary time ST _N at each of the other collection positions scanned before the collection position. The elapsed time T _N at the collection position corresponding to the collection position number N is the stationary time ST _N-1 , ST _N-2 at each collection position corresponding to the collection position numbers N-1, N-2,. ,... Is a time obtained by adding all of.

That is, the attenuation rate calculation means 423 calculates the elapsed time _TN by the following calculation formula.

However, ST _{0 is set} to “0”, and the elapsed time T ₁ for the collection position corresponding to the collection position number 1 to be scanned _first is “0”.

  The half life H is read from the half life table 424. The attenuation rate calculating means 423 reads the half-life H corresponding to the type of positron-emitting nuclide-labeled drug input on the imaging condition input screen from the half-life table 424.

  The attenuation rate calculation means 423 calculates the attenuation rate R when the Nth collection position is reached by the following calculation formula.

The time adjustment means 425 calculates a radiation detection time at the Nth collection position, that is, a stationary time ST _N for keeping the relative movement between the detector 21 and the bed 3 stationary at the collection position corresponding to the collection position number N. . The rest time ST _N, the attenuation factor a R obtained, is calculated by the provisional radiation detection time DT entered in imaging condition input screen.

The time adjustment unit 425 calculates the stationary time ST _N by the following calculation formula.

According to this calculation formula, the attenuation rate R = 1 and the stationary time ST ₁ = DT at the collection position corresponding to the collection position number 1 where the scan is first performed.

The rest time ST _N according to this calculation formula is that the same amount of positron-emitting nuclide-labeled drug is collected at the collection position where radiation was first detected and the collection position corresponding to the collection position number N, and If there is no attenuation of the radiation, it is time to obtain a count equal to the count of radiation that will be incident on the detector 21 at the collection position corresponding to the collection position number N.

The amount of radiation released per unit time from the positron-emitting nuclide-labeled drug is such that the same amount of positron-emitting nuclide-labeled drug is collected at the collection position where the radiation was first detected and the collection position corresponding to the collection position number N. In addition, when the detector 21 reaches the collection position corresponding to the collection position number N, the ratio decreases to the rate of the attenuation rate R. The time adjusting means 425 calculates a rest time ST _N that compensates for the decrease in the count due to the radiation attenuation of the positron emitting nuclide-labeled drug by the radiation detection time.

For example, in the collecting position corresponding to the collection position number 1, the attenuation factor R is "1", the rest time ST ₁ at the collection position is an input radiation detection time DT. If the input radiation detection time DT is the same time as the half-life H, the radiation detection time DT is stopped at the collection position corresponding to the collection position number 1 and the detector 21 is placed at the collection position corresponding to the collection position number 2. There elapsed time T ₂ are when they reach has a DT. Therefore, the radiation emission per unit time of the same amount of the positron-emitting nuclide-labeled drug at the collection position corresponding to the collection position number 2 is halved. If the same amount of positron-emitting nuclide-labeled drugs are gathered at the collection positions corresponding to collection position number 1 and collection position number 2, the counts indicating the state and function of the collection position should be the same. the rest time ST ₂ as radiation detection time is increased to twice twice the ST ₁ in.

The movement controller 426 reads the table Ta stored in the stationary time table storage unit 422, controls the moving mechanism 5 according to the table Ta, and performs step movement of the detector 21 and the bed 3 and stationary time ST at each collection position. _N is controlled. When the movement controller 426 moves the detector 21 to the collection position corresponding to the collection position number N, the movement controller 426 detects only the stationary time ST _N stored in a pair with the collection position number N with reference to the table Ta. The vessel 21 and the bed 3 are stopped. When the rest time ST _N has elapsed, so that the detector 21 comes to collect the position corresponding to the collection position number N + 1, thereby moving the detector 21 and the bed 3. That is, the operation shown in FIG. 3 is controlled.

  FIG. 6 is a flowchart showing an operation of creating the table Ta of the PET apparatus according to the first embodiment.

  First, the display control unit 421 displays an imaging condition input screen (S20). In the PET apparatus 1, the operator inputs the types of positron-emitting various labeled drugs using the input device 41 (S21), and inputs the number of collection positions PN and the provisional radiation detection time DT at the collection positions. (S22). When these photographing conditions are input, each natural number from 1 to the value of the collection position number PN is assigned and stored as the collection position number N in the table Ta stored in the stationary time table storage unit 422.

The attenuation rate calculating means 423 initializes the collection position number N to N = 1 (S23) and initializes the elapsed time T _N to T _N = 0 (S24). The paired half-life H is read from the half-life table 424 (S25). The initialization is for calculating the attenuation rate R of the collection position number 1.

When the collection position number N is initialized, the elapsed time _TN is initialized, and the half-life H is read, the attenuation rate R when the elapsed time _TN has elapsed is calculated using these parameters (S26). In calculating the attenuation rate R, the attenuation rate R is calculated by applying these parameters to the attenuation rate R = exp (− (ln 2 / half-life H) * elapsed time T _N ). In calculating the first attenuation rate R after the collection position number N and the elapsed time _TN are initialized, that is, calculating the attenuation rate R at the collection position corresponding to the collection position number 1, the attenuation rate R = 1. Become.

When the attenuation rate R at the collection position corresponding to the collection position number N is calculated, the time adjustment unit 425 calculates the rest time ST _N by subtracting the input provisional radiation detection time DT by the attenuation rate R ( S27). Since the attenuation rate R corresponding to the collection position number 1 is “1”, the stationary time ST ₁ becomes the input radiation detection time DT.

When the stationary time ST _N is calculated, the time adjusting unit 425 stores the collection position number N stored in the table Ta and the stationary time ST _N in association with each other in the stationary time table storage unit 422 (S28). Thereby, the stationary time STN at the collection position corresponding to the collection position number _N is set.

Next, the collection position number N is set to N + 1 (S29), and it is determined whether the collection position number N> the collection position number PN (S30). That is, it is determined whether the still time ST _N is set for all the collection position.

And collecting the position number N> collection position number PN (S30, Yes), the rest time ST _N is for all the collection position to end the operation of creating the set because the table Ta.

On the other hand, the collection position number N> collection position number PN Otherwise (S30, No), processing for calculating the rest time ST _N of the collection position corresponding to the new collection position number N.

In the process of calculating the stationary time ST _N for the collection position corresponding to the new collection position number N, the elapsed time T _{N is set} to T _N = T _N−2 + ST _N−1 (S31), and the attenuation rate R from the calculation of (S26), to give the calculation of the rest time ST _N corresponding to the new collection position number N obtained by subtracting the radiation detection time DT interim in the new damping rate R (S27), collects position number N> collection S26 to S30 are performed up to the determination (S30) as to whether the number of positions is PN.

If the collection position number PN, for example 3, after the rest time calculation of ST ₁ for collecting position corresponding to the collection position number 1 is not a N> PN. Therefore, N = N + 1 to the collection position number N = 2 by, calculates the rest time ST ₂ for collecting the position number 2. At this time, depending on T _N = T _N−2 + ST _N−1 (N = 2), T ₀ = 0 and ST ₁ = DT. Therefore, after calculating the attenuation rate R with T ₂ = DT to calculate the stationary time ST _2. Further, in the calculation of the rest time ST ₃ the collection position number _3, depending on the _{T N = T N-2 +} ST N-1 (N = 3), since it is T 1 = _DT, the attenuation factor as T 3 = DT + ST ₂ calculates the rest time ST ₃ on calculating the R.

FIG. 7 is a graph showing a scan mode by the PET apparatus 1 according to the first embodiment. The vertical axis represents the attenuation rate R, and the horizontal axis represents the collection position number N and the elapsed time _TN .

As shown in FIG. 7, according to this PET apparatus 1, the integral value L _N of the attenuation rate R when reaching the collection position corresponding to each collection position number N and the stationary time ST _N at the collection position is , The rest time ST _N is adjusted so that they are all equal. Then, the influence of decrease in damping rate R is offset by increasing the rest time ST _N, when the same amount of positron labeled drug are gathered, the scan results are not related to time lag of the scan Can be obtained.

(Second Embodiment)
Next, the PET apparatus 1 according to the second embodiment will be described. The PET apparatus 1 continuously performs the relative movement between the detector 21 and the bed 3 while changing the speed every predetermined time interval IT, and does not stop halfway. Moreover, to calculate the attenuation rate R at predetermined time intervals IT, attenuation rate R is continue to the moving speed V _N passing through each collection position for each to be decreased, increasing the time required to pass through each collection position Let the radiation detection time increase. Each collection position referred to in the present embodiment refers to a range that passes in a time shorter than the predetermined time interval IT.

  FIG. 8 is a block diagram showing a detailed configuration of the control unit 42 of the PET apparatus 1 according to the second embodiment. The control unit 42 controls relative movement between the detector 21 and the bed 3 by changing the speed. The control unit 42 includes a display control unit 421, a speed table storage unit 427, an attenuation rate calculation unit 423, a half-life table 424, a speed adjustment unit 428, and a movement controller 426. The speed table storage unit 427 stores a table Tb describing a speed adjustment sequence. The attenuation rate calculation means 423 and the speed adjustment means 428 create a table Tb describing the speed adjustment sequence.

FIG. 9 is a schematic diagram showing a table Tb that defines the relative movement operation between the detector 21 and the bed 3 according to the second embodiment. In the table Tb, a predetermined time interval number N and a moving speed _N are stored in association with each other. The predetermined time interval number N is given for each time interval at which the speed is changed. The moving speed _N represents the relative moving speed between the detector 21 and the bed 3 at the time intervals in the order represented by the predetermined time interval number N.

For example, when the table Tb in which the moving speed V ₁ is stored corresponding to the predetermined time interval number 1 and the moving speed V ₂ is stored corresponding to the predetermined time interval number 2 is generated, the control unit 42 makes the predetermined time interval during the time represented by number 1, and controls the moving mechanism 5 so as to relatively moving the detector 21 and the bed 3 at the moving speed V _1, during the time represented by the predetermined time interval number 2, the moving speed controls movement mechanism 5 so as to relatively moving the detector 21 and the bed 3 in V _2, adjust the radiation detection time at each collection position detector 21 passes.

The movement controller 426 reads the table Tb stored in the speed table storage unit 427, controls the movement mechanism 5 according to the table Tb, and controls the speed of relative movement between the detector 21 and the bed 3. When the time corresponding to the predetermined time interval number N is reached, the movement controller 426 refers to the table Tb and decelerates the detector 21 and the bed 3 so as to relatively move at the movement speed _N.

  FIG. 10 is a flowchart showing the operation of the PET apparatus 1 that scans according to the table Tb.

  When the scan start is input (S41), the PET apparatus 1 starts the scan. When a button assigned with a scan start operation arranged in the input device 41 is pressed, a press signal of the button is input to the control unit 42. The movement controller 426 starts control for scanning when a push signal of a button to which a scan start operation is assigned is input.

  The movement controller 426 first initializes the predetermined time interval number N to “1” (S42). Further, the movement controller 426 initializes the timer PT to “0” (S43). The timer PT is a counter value for measuring a predetermined time interval.

Next, the movement controller 426 reads the movement speed V _N corresponding to the predetermined time interval number N from the table Tb (S44). Initially, since the predetermined time interval number N is initialized to “1”, the moving speed V ₁ stored in the table Tb corresponding to the predetermined time interval number ₁ is read.

When the moving speed _VN is read, the timer PT starts counting up (S45). At the same time, the movement controller 426, thereby relatively moving the detector 21 and the bed 3 at a moving speed _{V N} (S46). During a predetermined time interval corresponding to the predetermined time interval number N, the detector 21 detects radiation from this collection position, the data collection unit 43 collects projection data, and the reconstruction processing unit 44 performs image reconstruction processing. Is performed (S047).

Each time the movement controller 426 counts up the timer PT, it determines whether the timer PT is equal to or greater than the predetermined time interval IT (S48). As a result of the determination, if PT ≧ IT is not satisfied (S48, NO), the timer PT continues to be counted up and the moving speed _VN is maintained. That is, S46 to S48 are repeated. On the other hand, if PT ≧ IT as a result of the determination (S48, Yes), the next collection position that passes at a predetermined time interval is scanned at the next movement speed V _{N + 1} .

  In the next acquisition position scan, the movement controller 426 first sets the predetermined time interval number N to N + 1 (S49), and searches whether this new predetermined time interval number N exists in the table Tb (S50).

If a new predetermined time interval number N exists in the table Tb (S50, Yes), the timer PT is initialized to 0 (S43), and the moving speed V _N corresponding to the new predetermined time interval number _N is read (S44). Until the timer PT becomes equal to or higher than IT _N (S48, Yes), the relative movement is performed at the moving speed V _N (S47), and the radiation at the new collection position that passes at predetermined time intervals is detected (S47).

  If the new predetermined time interval number N does not exist in the table Tb (S50, No), all the collection positions have been scanned, and the operation of the PET apparatus 1 is terminated.

The display control unit 421 displays an imaging condition input screen for generating the table Tb on the display device 45. FIG. 11 is a schematic diagram showing an imaging condition input screen. In the imaging condition input screen, as an imaging condition, and the type of positron labeled agent used, the predetermined time interval for varying the moving speed V _N, the moving speed TV interim inputted.

The attenuation rate calculating means 423 calculates the attenuation rate R of the positron-emitting nuclide-labeled drug over time when the predetermined time interval represented by the predetermined time interval number N is reached. The beginning of the elapsed time _{TN is} the start of scanning of the subject P. The end of the elapsed time _TN is when the predetermined time interval corresponding to the predetermined time interval number N has started. The calculation formula of the attenuation rate R is the same as that in (Expression 2).

The speed adjusting means 428 calculates a moving speed V _N at which the detector 21 and the bed 3 move relative to each other at a radiation detection time at each collection position, that is, a time interval corresponding to a predetermined time interval number N. This moving speed V _N is calculated from the obtained attenuation rate R and the provisional moving speed TV input on the photographing condition input screen.

The speed adjusting means 428 calculates the moving speed V _N by the following calculation formula.

According to this calculation formula, at the first predetermined time interval IT, the attenuation rate R = 1 and the moving speed V ₁ = TV.

The moving speed V _N according to this calculation formula is that the same amount of positron-emitting nuclide-labeled drug is collected at the collection position where the radiation is first detected and the collection position where the radiation passes within the time corresponding to the predetermined time interval number N, and If there was no radiation attenuation of the positron emitting nuclide-labeled drug, a count equal to the count of radiation that would be incident on the detector 21 at the collection position passing within the time corresponding to the predetermined time interval number N is obtained. It is time for.

The speed adjusting unit 428, supplemented by the radiation detection time by adjusting the moving speed V _N which passes through the collecting position a reduction in the count due to the attenuation of the radiation of the positron-emitting nuclide labeled agent, the moving velocity V _N therefor is calculated The

For example, at the collection position that passes within the predetermined time interval IT corresponding to the predetermined time interval number 1, the attenuation rate R is “1”, and the movement speed V ₁ at the collection position is the input movement speed TV. is there. When the predetermined time interval IT is to be a half-life H the same time, IT is elapsed as the elapsed time T ₂ are when the detector 21 reaches the collecting position through a predetermined time interval in IT corresponding to the predetermined time interval number 2 doing. Therefore, the radiation emission per unit time of the same amount of the positron-emitting nuclide-labeled drug at the collection position passing within the predetermined time interval IT corresponding to the predetermined time interval number 2 is halved. If the same amount of positron-emitting nuclide-labeled drug is collected at each collection position passing within the predetermined time interval IT corresponding to the predetermined time interval number 1 and the predetermined time interval number 2, a count indicating the state and function of the collection position Should be the same number, and during the predetermined time interval IT corresponding to the predetermined time interval number 2, the radiation passes through the collection position passing within the predetermined time interval IT corresponding to the predetermined time interval number 2 in twice the time. to increase the detection time is doubled, the moving speed V ₂ to the half of the TV.

  FIG. 12 is a flowchart showing the creation operation of the table Tb of the PET apparatus according to the second embodiment.

  First, the display control unit 421 displays an imaging condition input screen (S60). The operator inputs the types of positron-emitting various labeled drugs using the input device 41 (S61), and inputs the time interval IT for changing the speed and the provisional moving speed TV (S62).

The attenuation rate calculating means 423 initializes the predetermined time interval number N to N = 1 (S63) and initializes the elapsed time T _N to T _N = 0 (S64). The half-life H paired with is read from the half-life table 424 (S65).

When the predetermined time interval number N is initialized, the elapsed time _TN is initialized, and the half-life H is read, the attenuation rate R when the elapsed time _TN has elapsed is calculated using these parameters (S66). In calculating the attenuation rate R, the attenuation rate R is calculated by applying these parameters to the attenuation rate R = exp (− (ln 2 / half-life H) * elapsed time T _N ).

When the attenuation rate R at the predetermined time interval IT corresponding to the predetermined time interval number N is calculated, the speed adjusting unit 428 calculates the moving speed V _N by multiplying the input temporary moving speed TV by the attenuation rate R. (S67).

After calculating the moving speed V _N , the speed adjusting unit 428 stores the predetermined time interval number N stored in the table Tb and the moving speed V _N in association with each other in the speed table storage unit 427 (S68). Thereby, the moving speed V _N at the collection position that passes within the time of the predetermined time interval IT corresponding to the predetermined time interval number _N is set.

Next, the predetermined time interval number N is set to N + 1 (S69), and the range S in which scanning is completed is calculated by S = S + V _N × IT (S70). Then, it is determined whether or not S ≧ total imaging range AS (S71). That is, it is determined whether the moving speed V _N is set for all the collection positions.

If S ≧ total imaging range AS (S71, Yes), the movement speed V _N is set for all the collection positions, and the table Tb creation operation is terminated.

On the other hand, if S ≧ total imaging range AS is not satisfied (S71, No), a process of calculating the moving speed V _N for the collection position passing within the predetermined time interval IT corresponding to the new predetermined time interval number N is performed.

In the process of calculating the moving speed V _N for the collection position corresponding to the new predetermined time interval number N, the elapsed time T _{N is set} to T _N = (N−1) × IT (S71), and S66 to S71. I do.

Assuming that the entire shooting range AS passes at three predetermined time intervals IT, S ≧ total shooting range AS is not obtained after the calculation of the moving speed V _N corresponding to the predetermined time interval number 1. Therefore, the predetermined time interval number N = 2 is set by N = N + 1, and the moving speed V _N is calculated for the predetermined time interval number 2. At this time, depending on T _N = (N−1) × IT (N = 2), the moving speed V ₂ is calculated after calculating the attenuation rate R with T ₂ = IT. Furthermore, (in the calculation of the moving velocity V ₃ for a given time interval number 3 calculates a moving speed V ₃ in terms of calculating the attenuation rate R as T 3 _{= 2} × IT.

FIG. 13 is a graph showing a scan mode by the PET apparatus 1 according to the second embodiment. The vertical axis represents the moving velocity V _N and damping rate R, the horizontal axis represents the predetermined time interval number N.

As shown in FIG. 13, according to the PET apparatus 1, the attenuation rate R when the predetermined time interval IT corresponding to each predetermined time interval number N is reached and the moving speed V _N at the predetermined time interval IT are calculated. The moving speed V _N is adjusted so that the integral values L _N are all equal. Then, the influence of the decrease in the attenuation rate R is offset by decreasing the moving speed V _N and increasing the radiation detection time. When the same amount of positron-emitting nuclide-labeled drugs are gathered, the time shift of the scan It is possible to obtain a scan result unrelated to.

Thus, in the PET apparatus 1 of each embodiment, the stationary time ST _N and the moving speed V _N of the detector 21 at each collection position are calculated according to the decay of the positron emitting nuclide-labeled drug over time, and the calculation result Accordingly, the detector 21 and the bed 3 are moved relative to each other. As a result, the detector 21 increases the radiation detection time at each collection position according to the decay of the positron emitting nuclide-labeled drug over time. Therefore, the count of radiation that has decreased due to the influence of attenuation is canceled out by the scanning method, and the processing load for correcting the influence of attenuation due to the passage of time of the positron-emitting nuclide-labeled drug by image processing is reduced, which is required by image processing. Time can be saved or reduced, and image quality is not deteriorated by image processing.

DESCRIPTION OF SYMBOLS 1 PET apparatus 2 Gantry 21 Detector 3 Bed 4 Console 41 Input device 42 Control part 421 Display control part 422 Rest time table memory | storage part 423 Attenuation rate calculation means 424 Half-life table 425 Time adjustment means 426 Movement controller 427 Speed table memory | storage part 428 Speed adjustment means 43 Data collection unit 44 Reconfiguration processing unit 5 Movement mechanism

Claims (6)

A bed on which a subject to which a drug labeled with a positron emitting nuclide is administered is placed;
A detector for detecting gamma rays emitted from positron emitting nuclides;
A moving mechanism for relatively moving the object and the detector;
Controls the moving mechanism so as to successively reach the detector at each collection position of the subject, the radiation detection time in accordance with the relationship between the attenuation and the respective collecting locations over time before Symbol positron A scan controller that sequentially adjusts for each collection position ;
A reconstruction processing unit for reconstructing an image in the subject from the detection result of the detector;
Providing
PET apparatus characterized by this. The scan control unit
Adjusting the radiation detection time for each collection position that has arrived to a time that compensates for the detection count of radiation that has decreased in accordance with the decay of the positron emitting nuclide over time,
PET apparatus according to claim 1, wherein the. The scan control unit
The moving mechanism is controlled so that the subject and the detector sequentially reach each collection position of the subject by relative step movement, and the quiescent time at each reached collection position is determined as the positron emission nuclide. Adjusting the radiation detection time at the reached collection position by increasing in accordance with the decay over time of
PET apparatus according to claim 1, wherein the. The scan control unit
Including time adjustment means for calculating, for each collection position, the rest time corresponding to the decay of the positron emitting nuclide-labeled drug over time,
PET apparatus according to claim 3, characterized in. The time adjusting means is
Memorize provisional radiation detection time,
The time when the provisional radiation detection time is increased according to the decay rate based on each elapsed time from the start of radiation detection to the collection position where radiation is first detected until the detector reaches each collection position. Calculating the rest time at each collection position;
The PET apparatus according to claim 4. The time adjusting means is
The integrated value of the provisional radiation detection time and the attenuation rate at the start of radiation detection for the collection position where radiation is first detected is equal to the integral value of the stationary time and the attenuation rate at each collection position. Calculating the rest time for each collection position;
The PET apparatus according to claim 5.

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