WO2010001840A1 - X線ct装置 - Google Patents
X線ct装置 Download PDFInfo
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- WO2010001840A1 WO2010001840A1 PCT/JP2009/061818 JP2009061818W WO2010001840A1 WO 2010001840 A1 WO2010001840 A1 WO 2010001840A1 JP 2009061818 W JP2009061818 W JP 2009061818W WO 2010001840 A1 WO2010001840 A1 WO 2010001840A1
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- ray
- time resolution
- resolution rate
- imaging
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- 238000003384 imaging method Methods 0.000 claims abstract description 105
- 230000000737 periodic effect Effects 0.000 claims description 44
- 238000012545 processing Methods 0.000 claims description 12
- 238000001514 detection method Methods 0.000 claims description 2
- 238000007689 inspection Methods 0.000 abstract description 3
- 210000001835 viscera Anatomy 0.000 abstract 1
- 230000000747 cardiac effect Effects 0.000 description 38
- 238000002591 computed tomography Methods 0.000 description 31
- 238000000034 method Methods 0.000 description 20
- 230000002123 temporal effect Effects 0.000 description 13
- 238000010586 diagram Methods 0.000 description 12
- 238000005259 measurement Methods 0.000 description 10
- 206010006322 Breath holding Diseases 0.000 description 8
- 230000008859 change Effects 0.000 description 8
- 238000003745 diagnosis Methods 0.000 description 4
- 230000008602 contraction Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- 210000000056 organ Anatomy 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 230000001360 synchronised effect Effects 0.000 description 2
- 208000000418 Premature Cardiac Complexes Diseases 0.000 description 1
- 239000002872 contrast media Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000002526 effect on cardiovascular system Effects 0.000 description 1
- 230000036541 health Effects 0.000 description 1
- 210000004072 lung Anatomy 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000029058 respiratory gaseous exchange Effects 0.000 description 1
- 230000008685 targeting Effects 0.000 description 1
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
- A61B6/02—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
- A61B6/03—Computed tomography [CT]
- A61B6/032—Transmission computed tomography [CT]
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
- A61B6/54—Control of apparatus or devices for radiation diagnosis
- A61B6/541—Control of apparatus or devices for radiation diagnosis involving acquisition triggered by a physiological signal
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/316—Modalities, i.e. specific diagnostic methods
- A61B5/318—Heart-related electrical modalities, e.g. electrocardiography [ECG]
- A61B5/346—Analysis of electrocardiograms
- A61B5/349—Detecting specific parameters of the electrocardiograph cycle
- A61B5/352—Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
Definitions
- the present invention relates to an X-ray CT (Computed Tomography) apparatus, and more particularly to an X-ray CT apparatus for cardiovascular imaging.
- X-ray CT Computed Tomography
- a biosensor such as an electrocardiograph or a respiration sensor
- measurement by a device that converts physiological periodic motion into an electrical signal is performed.
- photographing and image reconstruction are performed using the obtained electrical signal.
- a reconstruction method targeting the heart is called an electrocardiographic synchronization reconstruction method.
- the electrical signals measured by the electrocardiograph are added to the imaging data and collected, and image reconstruction is performed based on the obtained electrocardiographic information, and a cardiac tomogram at an arbitrary cardiac phase is obtained.
- imaging data with different scans or views in the same cardiac time phase (hereinafter referred to as “division imaging data”) is collected from a plurality of heartbeats using an R wave of an electrocardiographic waveform as a reference. To do. It is possible to improve time resolution by reconstructing an image by combining the captured data thus collected.
- the time resolution varies because the collection pattern of the divided shooting data differs depending on the heart rate and the shooting conditions.
- the temporal resolution varies depending on the heart rate, scan speed, and bed movement speed. For example, as the bed moving speed is decreased, the number of pieces of divided photographing data that can be collected increases, so that the time resolution increases.
- the time resolution of the divided reconstruction is affected by the heart rate of the patient and the imaging conditions. In actual imaging, it is necessary to determine imaging conditions so that the image quality necessary for diagnosis can be obtained in consideration of the breath holding time and the exposure dose.
- first method for determining shooting conditions using the number of divided shooting data collected to create one image as an index.
- an optimal shooting condition is selected to collect the number of divided shooting data specified by the operator.
- the higher the number of divided image data to be collected the higher the time resolution can be obtained, but the exposure amount increases because the bed moving speed needs to be slowed down.
- the amount of exposure can be reduced because the bed moving speed can be set faster as the number of divided photographing data is reduced, but the time resolution is deteriorated.
- second method there is a method of determining shooting conditions using a bed moving speed as an index (hereinafter referred to as “second method”).
- shooting is performed at a couch moving speed designated by the operator, and image reconstruction is performed using collectable shooting data that can be collected.
- the slower the bed moving speed the higher the time resolution because more divided projection data can be collected.
- the faster the bed moving speed the less the divided projection data that can be collected and the lower the time resolution.
- the imaging conditions such as the number of divided imaging data or the bed moving speed must be adjusted according to the heart rate of the patient.
- the heart rate of the patient When the heart rate of the patient is large, that is, when the heart beat period is short, the time for which the heart is at rest is also shortened.
- the heart rate of the patient is small, that is, when the heart beat period is long, the time during which the heart is stationary also becomes long. Therefore, it is necessary to adjust the parameters to lower the time resolution and optimize the exposure dose.
- the operator Since the heart rate fluctuates under the influence of imaging conditions such as the patient's health condition and breath holding time, the operator must carefully adjust the imaging parameters according to the heart rate. This operation requires a great amount of labor for the operator, which complicates the photographing operation and deteriorates the inspection efficiency.
- the present invention has been made in view of the problems of the above-described divided reconstruction, and an object thereof is an X-ray CT capable of efficiently setting imaging conditions in imaging of a periodically moving organ such as the heart. Is to provide a device.
- the first invention is an X-ray source that irradiates X-rays, and an X-ray that is disposed facing the X-ray source with the subject interposed therebetween and detects an X-ray dose transmitted through the subject.
- a gantry that is equipped with a line detector, the X-ray source, and the X-ray detector, can rotate around the subject, a bed that can be moved by placing the subject, the X-ray source, and the X-ray detection
- An arbitrary phase of the periodic motion based on the X-ray dose data and the periodic motion data
- the control device for controlling the vessel, the gantry and the bed, the periodic motion measuring device for measuring the periodic motion of the subject
- An X-ray CT apparatus comprising: an image processing device that generates a reconstructed image of a subject in the computer; and a display device that displays the reconstructed image, wherein the period of the periodic motion is calculated from the data of the periodic motion And time resolution which is a ratio between the time resolution of the reconstructed image and the period
- the rate as an indicator, shooting condition calculating means for calculating a photographing condition
- an X-ray CT apparatus comprising: a.
- the first invention further comprises means for an operator to input the time resolution rate, and the imaging condition calculation means satisfies the time resolution rate input by the operator based on the data of the periodic motion. In this way, the shooting conditions may be calculated. In this way, by using the time resolution rate as an input value, the operator can set the shooting conditions using the time resolution rate that directly indicates good image quality as an index.
- the first invention further comprises means for dividing the range of the time resolution rate into a plurality, and displaying the shooting mode for each of the divided ranges of the time resolution rate on the display device, the shooting condition
- the calculation means may calculate the imaging condition so as to be within the range of the time resolution rate corresponding to the imaging mode selected by the operator based on the data of the periodic motion.
- the first invention calculates the variation of the time resolution rate based on the data of the periodic motion for a certain period measured by the periodic motion measuring device, and displays the calculated variation of the time resolution rate in the display Means for displaying on the apparatus may be further provided. As a result, it is possible to visually confirm a change in the time resolution rate that is expected when shooting is performed under the desired shooting conditions, and the operator can efficiently determine the shooting conditions.
- the first invention further includes means for displaying on the display device a rectangle for designating and inputting the time resolution rate, superimposed on a waveform indicating the data of the periodic motion measured by the periodic motion measuring device. It may be provided. By adjusting the position and width of the rectangle on the waveform in this way, it is possible to obtain a tomographic image with little motion artifacts with high accuracy and without depending on individual differences between subjects.
- the periodic motion is a heartbeat of a subject
- the imaging condition calculation means calculates imaging conditions based on a time from a T wave to an R wave in one cycle. May be. By using the time from the T wave to the R wave as a reference, it is possible to set shooting conditions linked to the heart rate, and to set shooting conditions with higher accuracy.
- the first invention may further comprise means for displaying a sample image corresponding to the time resolution rate on the display device. As a result, the operator can determine shooting conditions efficiently.
- an X-ray CT apparatus in which imaging conditions can be set efficiently in imaging of organs that periodically move, such as the heart.
- FIG. 21 Hardware configuration of X-ray CT system Flow chart showing cardiac image reconstruction processing Diagram showing an example of an electrocardiogram waveform Diagram explaining the subject's one heartbeat cycle and expected time resolution
- the figure which shows an example of the cardiac imaging condition setting screen 21 The figure which shows an example of the electrocardiogram synchronous image reconstruction method
- FIG. 1 is a hardware configuration diagram of an X-ray CT apparatus.
- the X-ray CT apparatus includes a scanner gantry 2, a bed 3, a display device 5, a periodic motion measuring device 6, an image processing device 7, a computer 12, an input device 13, and the like.
- the scanner gantry 2 includes an X-ray tube 1, an X-ray detector 4, a rotating disk 8, a collimator 9, a rotation driving device 10, a measurement control device 11, and the like.
- the X-ray tube 1 is an X-ray source and irradiates a subject with X-rays.
- the X-ray detector 4 detects X-rays emitted from the X-ray tube 1 and transmitted through the subject.
- the rotating disk 8 is rotated by the rotation driving device 10.
- the measurement control device 11 controls the rotary drive device 10, controls the X-ray intensity generated from the X-ray tube 1, and detects measurement data. Further, the measurement control device 11 receives a control command from the computer 12. The operator inputs various data to the computer 12 via the input device 13.
- the periodic motion measuring device 6 measures the periodic motion of the subject.
- the subject to be imaged is described as a heart, and the periodic motion measuring device 6 is described as an electrocardiograph.
- the present invention is not limited to these.
- the imaging target is the lung
- the periodic motion measuring device 6 may be a respirometer or the like.
- the image processing device 7 creates imaging data from the measurement data detected by the scanner gantry 2, and processes the imaging data into a CT image signal.
- the display device 5 displays a CT image, an imaging condition setting screen, and the like.
- FIG. 2 is a flowchart showing a heart image reconstruction process. As shown in FIG. 2, the X-ray CT apparatus collects electrocardiographic information using the periodic motion measuring apparatus 6 (S1).
- FIG. 3 is a diagram showing an example of an electrocardiogram waveform.
- the position of the R wave which makes it easy to identify the peak position, is usually used as the reference signal.
- the position of the P wave, Q wave, S wave, and T wave may be used as the reference signal.
- the time resolution rate is a ratio between the time resolution of the image created by the image processing device 7 and the heartbeat cycle calculated based on the data of the periodic motion measured by the periodic motion measuring device 6.
- the time resolution rate is handled as the input value. For example, (1) An image with 1 heartbeat cycle of 0.8 s and temporal resolution of 0.2 s and (2) An image with 1 heartbeat cycle of 1.0 s and temporal resolution of 0.2 s The image quality is inferior.
- an image with a heart rate cycle of 0.8 s and a time resolution rate of 20% and (2) an image with a heart rate cycle of 1.0 s and a time resolution rate of 20% have the same image quality. Obviously, as in the embodiment of the present invention, by using the time resolution rate as an input value, the operator can set shooting conditions using the time resolution rate that directly indicates the quality of the image as an index. it can.
- FIG. 4 is a diagram for explaining one heartbeat cycle and the expected time resolution of the subject.
- one heartbeat cycle of the subject is 1.0 s.
- the expected time resolution in the target examination is 0.2 s.
- FIG. 5 is a diagram showing an example of the cardiac imaging condition setting screen 21.
- the cardiac imaging condition setting screen 21 includes screen items such as an electrocardiogram display unit 22, a scan type display unit 23, a scan time display unit 24, a bed moving speed display unit 25, and a time resolution rate input unit 26.
- the electrocardiogram information collected in S1 is displayed on the electrocardiogram display unit 22, and the electrocardiogram information is updated at regular intervals.
- the scan type display unit 23, the scan time display unit 24, and the bed movement speed display unit 25 are boxes that display the calculation results of the computer 12, and the like.
- the time resolution rate input unit 26 is an input box.
- the time resolution rate input unit 26 may be a text box or a selection format such as a pull-down menu.
- the set values displayed in FIG. 5 are set values corresponding to the one heartbeat cycle and the expected time resolution of the subject shown in FIG.
- the electrocardiogram display unit 22 displays a waveform having a heart rate of “60 bpm”. That is, one heartbeat cycle of the subject is 1.0 s. Further, “20%” is input to the time resolution rate input unit 26 as described above with reference to FIG.
- the scan type display unit 23 displays “heart”, the scan time display unit 24 displays “0.5 s”, and the couch moving speed display unit 25 displays “10.0 mm / rot”.
- an average value of a plurality of heartbeats may be used as one heartbeat period used for calculation.
- the imaging condition calculation unit 12a calculates imaging conditions necessary for realizing the calculated time resolution. Typical parameters for adjusting the time resolution include a scan speed and a bed moving speed. The calculated shooting conditions are displayed on the display device 5 as shown in FIG.
- the relationship between time resolution and imaging conditions is determined depending on the specifications of the X-ray CT apparatus, imaging method, electrocardiographic synchronization reconstruction method, and the like. Therefore, for example, in accordance with the specifications of the X-ray CT apparatus, the imaging method, the electrocardiogram synchronization reconstruction method, etc., an imaging condition table in which the time resolution rate is associated with the imaging conditions is created in advance, and the measurement control apparatus 11 or the computer 12 may store the photographing condition table. Then, the imaging condition calculation unit 12a may acquire the imaging condition corresponding to the time resolution rate input in S2 from the imaging condition table.
- the X-ray CT apparatus images the heart according to the imaging conditions calculated in S3 (S4). At this time, the X-ray CT apparatus acquires imaging data and also acquires electrocardiographic information by the periodic motion measuring apparatus 6.
- the X-ray CT apparatus performs electrocardiogram synchronization image reconstruction using the imaging data and electrocardiogram information acquired in S4 (S5).
- FIG. 6 is a diagram showing an example of an electrocardiogram-synchronized image reconstruction method.
- a tomographic image of the relative position 80% of adjacent R waves is created.
- the image processing device 7 collects divided shooting data having different shooting angles at the same time phase from the shooting data shot during three heartbeats by the shooting angle required for reconstruction (about 180 degrees). .
- the shooting angle required for reconstruction about 180 degrees.
- the X-ray CT apparatus displays the ECG synchronized image reconstructed in S5 on the display apparatus 5 (S6). Then, the operator refers to the electrocardiogram synchronization image displayed on the display device 5 and performs diagnosis.
- the X-ray CT apparatus calculates the period of the periodic motion from the data of the periodic motion, and the ratio between the time resolution and the period of the reconstructed image generated by the image processing device 7.
- An imaging condition calculation unit 12a that calculates imaging conditions using a certain time resolution rate as an index is provided.
- the X-ray CT apparatus includes a means for an operator to input a time resolution rate as shown in FIG.
- the time resolution rate input (S2) shown in FIG. 2 may be divided into several ranges and the operator may select the divided range as a shooting mode.
- the time resolution rate is divided into ranges of 10 to 15%, 15 to 20%, and 20 to 25%, and the operator selects the divided range as a photographing mode.
- the shooting condition calculation means 12a of the computer 12 calculates the shooting conditions so that the time resolution rate of the shooting data is within the range of the time resolution rate of the selected shooting mode.
- the X-ray CT apparatus divides the range of the time resolution rate into a plurality, displays the imaging mode for each divided range of the time resolution rate on the display device 5, and the computer
- the twelve shooting condition calculation means 12a may calculate the shooting conditions so as to be within the range of the time resolution rate corresponding to the shooting mode selected by the operator based on the data of the periodic motion.
- the fluctuation of the heart rate during imaging occurs due to various factors such as breath holding and contrast medium administration, and affects the calculation of imaging conditions based on the time resolution rate. In order to suppress this influence, it is conceivable to perform a breath-holding exercise that simulates actual photographing before photographing, and to grasp the fluctuation tendency of the heart rate in advance. In this case, the imaging conditions are calculated using the average heart rate during breath holding practice as a parameter. However, when the heart rate fluctuates abruptly or when the imaging time is long, the optimal imaging condition may not be calculated even if the average heart rate is used.
- the imaging time takes a long time
- sudden cardiac motion such as extrasystole occurs, even if the average heart rate is calculated, it is not always possible to calculate correct imaging conditions.
- the operator may manually determine the shooting conditions. Therefore, in order for the operator to determine the photographing conditions efficiently, a fluctuation graph of the time resolution rate during the breath holding practice may be provided.
- FIG. 8 is a diagram showing an example of a cardiac imaging condition setting screen 21b that displays a fluctuation graph of a temporal resolution rate for a certain period.
- the cardiac imaging condition setting screen 21b includes screen items such as a temporal resolution rate variation graph display unit 28, a scan time input unit 24b, and a bed moving speed input unit 25b.
- the temporal resolution rate variation graph display unit 28 displays the heart rate during breath holding practice and the temporal change of the temporal resolution rate as a graph.
- the scan time input unit 24b and the bed movement speed input unit 25b are input boxes.
- the scan time input unit 24b and the bed movement speed input unit 25b may be a text box or a selection format such as a pull-down menu.
- the computer 12 calculates a time resolution rate when shooting is performed according to the input shooting conditions.
- the calculated time resolution rate is displayed on the display device 5. That is, the temporal resolution rate variation graph display unit 28 displays a temporal change in the temporal resolution rate (based on the temporal change in the heart rate) when photographing under the inputted photographing conditions. As a result, it is possible to visually confirm a change in the time resolution rate that is expected when shooting is performed under the desired shooting conditions, and the operator can efficiently determine the shooting conditions.
- the X-ray CT apparatus calculates the variation of the time resolution rate based on the periodic motion data measured by the periodic motion measurement device 6 for a certain period, and calculates the calculated time.
- the change in the resolution rate may be displayed on the display device 5.
- FIG. 9 is a diagram showing an example of the time resolution rate & reconstructed cardiac phase setting screen 31.
- the operator may set the time resolution rate and the position of the reconstructed cardiac phase using the screen shown in FIG.
- the time resolution rate & reconstructed cardiac time phase setting screen 31 has screen items such as a heart rate display unit 32, a reconstructed cardiac time phase display unit 34, and a time resolution rate display unit 35.
- a rectangle 33 is displayed so as to be superimposed on the waveform of an arbitrary one heartbeat.
- the width of the rectangle 33 indicates the time resolution rate, and the time resolution rate is adjusted by changing the width of the rectangle 33 using the input device 13 such as a mouse.
- the center position of the rectangle 33 indicates a reconstructed cardiac phase that is a cardiac phase in which reconstruction is performed.
- the reconstructed cardiac phase is adjusted by moving the position of the rectangle 33.
- the reconstructed cardiac phase display unit 34 and the time resolution rate display unit 35 values recalculated in accordance with the change of the rectangle 33 are displayed.
- the operator can move the rectangle 33 by, for example, aligning the displayed pointer with the vicinity of the center line of the rectangle 33 and performing a drag and drop operation.
- the operator for example, extends the rectangle 33 to the left and right by the same width from the center line by performing a drag and drop operation with the displayed pointer positioned near the left or right end of the rectangle 33. It can be narrowed.
- the computer 12 inputs the width of the designated rectangle 33 and the position of the center line. Further, the computer 12 calculates values to be displayed on the reconstructed cardiac time phase display unit 34 and the time resolution rate display unit 35 from the horizontal width of the input rectangle 33 and the position of the center line.
- the rectangle 33 is displayed so as to be superimposed on the electrocardiogram waveform, and by inputting the reconstructed cardiac time phase and the time resolution rate from the width and position of the rectangle 33, the imaging condition in consideration of the physiological information of the subject can be obtained.
- Decisions can be made. For example, it is known that the contraction movement of the heart starts with the P wave as the starting point, and by setting the time resolution rate and the reconstructed cardiac time phase so that the right side of the rectangle does not overlap the P wave, It is possible to remove the influence of the contraction motion on the reconstructed image.
- the X-ray CT apparatus displays a rectangle for designating and inputting a time resolution rate on the waveform indicating the data of the periodic motion measured by the periodic motion measuring device 6. 5 may be displayed.
- the value displayed on the reconstruction cardiac time phase display unit 34 and the time resolution rate display unit 35 is calculated from the width and position of the rectangle 33
- the input and output may be reversed. That is, numerical values are input to the reconstructed cardiac time phase display unit 34 and the temporal resolution rate display unit 35, the width and position of the rectangle 33 are calculated, and the rectangle 33 is displayed on the heart rate display unit 32 based on the calculated values. You may do it.
- the imaging conditions are set so that the time resolution rate specified by the operator can be obtained in one heartbeat cycle.
- the imaging conditions may be selected based on the time between the feature points of the electrocardiogram.
- the time from the T wave to the R wave may be used as the time between the feature points of the electrocardiogram.
- the operator designates the time from the T wave to the R wave and the desired time resolution rate, and the computer 12 sets the imaging conditions based on the time from the T wave to the R wave.
- the heart rate fluctuates it is generally known that the time from the R wave to the T wave does not change greatly, but changes from the T wave to the next R wave.
- the imaging condition calculation means 12a included in the computer 12 may calculate the imaging conditions based on the time from the T wave to the R wave in one cycle.
- FIG. 10 is a diagram showing an example of the cardiac imaging condition setting screen 21c. Note that the same screen items as those of the cardiac imaging condition setting screen 21 shown in FIG. As shown in FIG. 10, the cardiac imaging condition setting screen 21c includes an electrocardiogram display unit 22, a scan type display unit 23, a scan time display unit 24, a bed movement speed display unit 25, a time resolution rate input unit 26, and a sample image display unit. It has 29 screen items.
- the cardiac imaging condition setting screen 21c may display a sample image corresponding to the time resolution rate designated by the operator so that the operator can easily determine the time resolution rate.
- the image quality differs depending on the heart rate of the subject even with the same time resolution, so it is necessary to prepare as many sample images as the number of combinations of time resolution and heart rate. It was not right.
- it is only necessary to prepare a sample image based on the time resolution rate For example, when inputting the time resolution rate at 5% intervals, it is sufficient to prepare 20 sample images, which can be easily realized.
- the sample image displayed on the sample image display unit 29 is updated each time the operator changes the value of the time resolution rate input unit 26.
- the X-ray CT apparatus displays the sample image corresponding to the time resolution rate on the display device 5. Thereby, the operator can adjust the time resolution rate while confirming the image quality of the sample image.
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Abstract
Description
図1は、X線CT装置のハードウェア構成図である。X線CT装置は、スキャナガントリ2、寝台3、表示装置5、周期運動計測装置6、画像処理装置7、コンピュータ12、入力装置13等から構成される。
図2は、心臓画像の再構成処理を示すフローチャートである。図2に示すように、X線CT装置は、周期運動計測装置6を用いて、心電情報を収集する(S1)。
前述したX線CT装置の処理では、操作者が入力した時間分解能率に応じた撮影条件を算出する。しかし、実際の撮影では、選択可能な撮影条件は限定されており、厳密に期待する時間分解能率を実現する撮影条件を操作者に対して提案することは難しい。そこで、図2に示す時間分解能率の入力(S2)は、時間分解能率を幾つかの範囲に分割し、操作者は分割した範囲を撮影モードとして選択する方法を取ってもよい。
撮影中の心拍数の変動は、息止めや造影剤投与などの様々な要因に依って発生し、時間分解能率に基づいた撮影条件の算出に影響を与える。この影響を抑えるために、撮影前に実際の撮影を模擬した息止め練習を行い、心拍数の変動傾向を予め把握することが考えられる。この場合、息止め練習中の平均心拍数をパラメータとして、撮影条件を算出する。ただし、心拍数が急激に変動する場合や、撮影時間が長時間に及ぶ場合は、平均心拍数を使用しても最適な撮影条件が算出できない可能性がある。例えば撮影時間が長時間に及ぶ場合は、診断の重要性が高い身体部位で最も高い時間分解能が得られるように撮影条件を設定する必要がある。また期外収縮などの突発的な心運動が発生する場合は、平均心拍数を算出したとしても、正しい撮影条件を算出できるとは限らない。このような場合、操作者は撮影条件を手動にて決定しても良い。そこで、操作者が効率よく撮影条件を決定するために、息止め練習中の時間分解能率の変動グラフを提供しても良い。
図9は、時間分解能率&再構成心時相設定画面31の一例を示す図である。操作者は、図9に示す画面を用いて、時間分解能率と再構成心時相の位置を設定しても良い。図9に示すように、時間分解能率&再構成心時相設定画面31は、心拍表示部32、再構成心時相表示部34、時間分解能率表示部35等の画面項目を有する。心拍表示部32には、任意の1心拍の波形に重ねて、矩形33が表示される。矩形33の幅が時間分解能率を示しており、矩形33の幅をマウス等の入力装置13を用いて変更することによって時間分解能率を調整する。矩形33の中心位置が再構成を行う心時相である再構成心時相を示しており、矩形33の位置を移動することにより、再構成心時相を調整する。再構成心時相表示部34、時間分解能率表示部35には、矩形33の変化に応じて再計算された値が表示される。
これまでの説明では、1心拍周期において、操作者が指定した時間分解能率が得られるように撮影条件を設定したが、心電図の特徴点間の時間を基準に撮影条件を選択してもよい。例えば、心電図の特徴点間の時間としてT波からR波までの時間としても良い。この場合、操作者は、T波からR波までの時間および希望する時間分解能率を指定し、コンピュータ12は、T波からR波までの時間を基準として撮影条件を設定する。心拍数が変動する場合、一般的にR波からT波までの時間は大きく変わらず、T波から次のR波までの時間に変化することが知られている。つまり、T波からR波までの時間を基準とすることで、心拍数に連動した撮影条件の設定を行うことが可能となり、より精度良く撮影条件を設定することができる。このように、コンピュータ12が具備する撮影条件算出手段12aは、1周期中のT波からR波までの時間を基準として、撮影条件を算出するようにしても良い。
図10は、心臓撮影条件設定画面21cの一例を示す図である。尚、図5に示す心臓撮影条件設定画面21と同様の画面項目は、同様の番号を付して説明を省略する。図10に示すように、心臓撮影条件設定画面21cは、心電図表示部22、スキャンタイプ表示部23、スキャン時間表示部24、寝台移動速度表示部25、時間分解能率入力部26、サンプル画像表示部29等の画面項目を有する。
Claims (7)
- X線を照射するX線源と、被検体を挟んで前記X線源と対向して配置され被検体を透過したX線量を検出するX線検出器と、前記X線源及び前記X線検出器を搭載し、被検体の周囲を回転可能なガントリと、被検体を乗せて移動可能な寝台と、前記X線源、前記X線検出器、前記ガントリ及び前記寝台を制御する制御装置と、被検体の周期運動を計測する周期運動計測装置と、前記X線量のデータ及び前記周期運動のデータを基に、前記周期運動の任意の位相における被検体の再構成画像を生成する画像処理装置と、前記再構成画像を表示する表示装置と、を具備するX線CT装置であって、
前記周期運動のデータから前記周期運動の周期を算出し、前記再構成画像の時間分解能と前記周期との比である時間分解能率を指標として、撮影条件を算出する撮影条件算出手段、を備えることを特徴とするX線CT装置。 - 操作者が前記時間分解能率を入力する手段、を更に具備し、
前記撮影条件算出手段は、前記周期運動のデータを基に、操作者が入力した前記時間分解能率を満たすように撮影条件を算出することを特徴とする請求項1に記載のX線CT装置。 - 前記時間分解能率の範囲を複数に分割し、分割された前記時間分解能率の範囲ごとの撮影モードを前記表示装置に表示する手段、を更に具備し、
前記撮影条件算出手段は、前記周期運動のデータを基に、操作者が選択した前記撮影モードに対応する前記時間分解能率の範囲に納まるように撮影条件を算出することを特徴とする請求項1に記載のX線CT装置。 - 前記周期運動計測装置が計測した一定期間の前記周期運動のデータを基に、前記時間分解能率の変動を算出し、算出された前記時間分解能率の変動を前記表示装置に表示する手段、を更に具備することを特徴とする請求項1に記載のX線CT装置。
- 前記周期運動計測装置が計測した前記周期運動のデータを示す波形に重ねて、前記時間分解能率を指定入力するための矩形を前記表示装置に表示する手段、を更に具備することを特徴とする請求項1に記載のX線CT装置。
- 前記周期運動は、被検体の心拍動であって、
前記撮影条件算出手段は、1周期中のT波からR波までの時間を基準として、撮影条件を算出することを特徴とする請求項1に記載のX線CT装置。 - 前記時間分解能率に応じたサンプル画像を前記表示装置に表示する手段、を更に具備することを特徴とする請求項1に記載のX線CT装置。
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