X-ray CT apparatus and tube current determination method

Patent metadata

Field	Value
Publication number	US-9254107-B2
Application number	US-201113820539-A
Country	US
Kind code	B2
Filing date	Sep 4, 2011
Priority date	Sep 7, 2010
Publication date	Feb 9, 2016
Grant date	Feb 9, 2016

Abstract

In order to provide a technique of obtaining an image having high diagnosability without degrading the operability in an X-ray CT apparatus that suppresses the amount of exposure of an object by controlling the amount of radiation by setting a target image SD and determining the imaging conditions (tube current) satisfying the target image SD, there is provided an X-ray CT apparatus that controls the amount of radiation according to the size of an object in consideration of the contrast by simply inputting one image quality level as a reference of the image quality level that the operator desires. The input image quality level is set as a target image SD when scanning an object having a standard size with a standard tube voltage.

First claim

The invention claimed is:

1. An X-ray CT apparatus including an X-ray tube that performs X-ray exposure while rotating around an object, an X-ray detector that is disposed opposite the X-ray tube with the object interposed therebetween and detects the amount of X-rays transmitted through the object, an image reconstruction unit configured to reconstruct a tomographic image of the object on the basis of the amount of X-rays detected by the X-ray detector, and a display unit configured to display the tomographic image, the apparatus comprising:
a receiving unit that receives an image noise standard deviation, which is satisfied when imaging is performed by a specific imaging conditions in which a standard object having a predetermined size is imaged with a specific tube voltage, as a standard image quality level;
a scan planning unit that calculates a target image quality level, which is a target image noise standard deviation, using the standard image quality level, calculates a scan tube current to achieve the target image quality level, and sets imaging conditions at the time of actual imaging using the scan tube current; and
a control unit that controls operations of the X-ray tube, the X-ray detector, and the image reconstruction unit according to the set imaging conditions.

2. The X-ray CT apparatus according to claim 1 ,
wherein the scan planning unit includes:
a contrast determination section that determines contrast at each slice position of the object at a tube voltage at the time of actual imaging;
a contrast ratio calculation section that calculates, as a contrast ratio, contrast at each slice position at the tube voltage at the time of actual imaging with respect to contrast in the specific imaging conditions; and
a target image quality level calculation section that calculates the target image quality level at each slice position using the contrast ratio at each slice position and the standard image quality level, and

the contrast is a CT value difference between a lesion and a surrounding tissue.

3. The X-ray CT apparatus according to claim 2 ,
wherein the scan planning unit further includes:
a scanogram imaging section that executes scanogram imaging and generates a scanogram age from obtained scanogram data; and
a cross-section model generation section that generates an object cross-section model, which is obtained by modeling a water-equivalent ellipse at each slice position of the object, from the scanogram data, and

the contrast determination section calculates a water-equivalent diameter at each slice position of the object from the object cross-section model and determines contrast at each slice position of the object on the basis of contrast variation characteristics specifying a relationship between contrast and a water-equivalent diameter at each tube voltage set in advance.

4. The X-ray CT apparatus according to claim 3 ,
wherein the contrast variation characteristics are created for each main component of a contrast agent, and
the contrast determination section selects a contrast characteristic according to a main component of a contrast agent used at the time of actual imaging, the contrast determination being performed on the basis of the contrast characteristic.

5. The X-ray CT apparatus according to claim 1 ,
wherein the specific tube voltage is a standard tube voltage set in advance in the X-ray CT apparatus.

6. The X-ray CT apparatus according to claim 5 ,
wherein the scan planning unit further includes a condition evaluation index calculation section that calculates, after calculation of the scan tube current, an average value of the scan tube current and the standard image quality level when the specific tube voltage is set as a tube voltage used at the time of actual imaging,
the display unit displays the average value and the standard image quality level, which are calculated by the condition evaluation index calculation section, as condition evaluation indices,
the receiving unit receives an approval or disapproval for the displayed condition evaluation indices, and
the scan planning unit sets imaging conditions at the time of actual imaging using the calculated scan tube current when the condition evaluation indices are approved through the receiving unit.

7. The X-ray CT apparatus according to claim 6 ,
wherein, when an instruction to disapprove the imaging conditions evaluation indices is received by the receiving unit, the condition evaluation index calculation section calculates the standard image quality level and the average value of the scan tube current, as condition evaluation indices of each tube voltage, for each of other tube voltages that can be set in the X-ray CT apparatus,
whenever condition evaluation indices of each tube voltage are calculated by the condition evaluation index calculation section, the display unit displays the calculated condition evaluation indices simultaneously so as to match the tube voltage,
the receiving unit receives a selection of a tube voltage, which is used in actual imaging, from tube voltages simultaneously displayed, and
the scan planning unit sets imaging conditions at the time of actual imaging using the selected tube voltage and condition evaluation indices matched with the tube voltage.

8. The X-ray CT apparatus according to claim 7 ,
wherein the receiving unit receives a change in the standard image quality level of the condition evaluation indices simultaneously displayed, and
when the change is received by the receiving unit, the condition evaluation index calculation section calculates the standard image quality level of each tube voltage on the basis of a value after the change.

9. The X-ray CT apparatus according to claim 1 ,
wherein information specifying a size of the standard object is input through the receiving unit by an operator.

10. The X-ray CT apparatus according to claim 9 ,
wherein the scan planning unit further includes:
a scanogram imaging section that executes scanogram imaging and generates a scanogram image from obtained scanogram data;
a cross-section model generation section that generates an object cross-section model, which is obtained by modeling a water-equivalent ellipse at each slice position of the object, from the scanogram data; and
a standard object size calculation section that calculates the size of the standard object,

the display unit displays the scanogram image,
the receiving unit receives an input of a line specifying the size of the standard object on the scanogram image, and
the standard object size calculation section calculates the size of the standard object from the water-equivalent ellipse of the object cross-section model corresponding to a position of the input line.

11. The X-ray CT apparatus according to claim 1 ,
wherein the specific tube voltage is a tube voltage set as an imaging condition of actual imaging.

12. A tube current determination method of determining a scan tube current used in imaging of an X-ray CT apparatus, the method comprising:
an image quality level receiving step of receiving an image noise standard deviation, which specific imaging conditions are within when imaging a standard object having a size set in advance with a specific tube voltage, as a standard image quality level;
a target image quality level calculation step of calculating a target image quality level, which is a target image noise standard deviation, using the standard image quality level; and
a tube current determination step of calculating a scan tube current to achieve the calculated target image quality level and determining a tube current, which is used in actual imaging, from the calculated

Assignees

• Sugaya Yoshiaki
• Goto Taiga
• Hirokawa Koichi
• Hitachi Medical Corp

Inventors

• Sugaya Yoshiaki
• Goto Taiga
• Hirokawa Koichi

Classifications

• A61B6/465

  adapted to display user selection data, e.g. graphical user interface, icons or menus · CPC title

• A61B6/405

  Source units specially adapted to modify characteristics of the beam during the data acquisition process (A61B6/4021, A61B6/4035 take precedence) · CPC title

• A61B6/545

  involving automatic set-up of acquisition parameters · CPC title

• A61B6/467

  characterised by special input means · CPC title

• A61B6/4035

  the source being combined with a filter or grating · CPC title