X-ray CT apparatus

Details X-ray CT apparatus X-ray CT apparatus

1999-10-25

2001-09-11

Kim, Robert H. (Department: 2882)

X-ray or gamma ray systems or devices

Specific application

Computerized tomography

C378S016000

Reexamination Certificate

active

06289075

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to X-ray CT apparatus for performing X-ray computerized tomography (X-ray CT) with contrast media injected to patients, in which a CT for acquiring images for a diagnostic purpose (hereinafter called “production CT”) is preceded by a pre-CT for a monitoring purpose which is carried out with low doses in order to determine the timing of starting the production CT. More particularly, the invention relates to a technique for carrying out the pre-CT in an appropriate radiographic mode.
(2) Description of the Related Art
An X-ray CT apparatus (X-ray computerized tomographic apparatus) used in a hospital or the like, as shown in
FIG. 1
, includes an X-ray tube
51
and a multi-channel X-ray detector
52
opposed to each other across a patient M placed on a top board
50
. While the X-ray tube
51
and X-ray detector
52
are revolved about the body axis of patient M, a fan beam FB is emitted from the X-ray tube
51
. Based on X-ray detection data outputted from the X-ray detector
52
, an image reconstruction process is carried out to acquire computed tomographic images (CT images).
The conventional apparatus may be used to perform an X-ray CT of an internal organ (e.g. the liver) of a patient with a contrast medium applied thereto. This is done in order to check presence and position of a tumor by fixation (i.e. coloring) of the contrast medium in a region of concern in the CT images acquired. However, in performing an X-ray CT with a contrast medium, it is necessary to start a radiographic process (production CT) when the contrast medium has fully spread to the region of concern such as the liver.
Thus, the conventional X-ray CT apparatus allows a pre-CT to be carried out with low doses for monitoring purposes before a production CT in order to check whether the contrast medium has spread to the region of concern. The production CT is started after confirming by the CT images acquired from the pre-CT that the contrast medium has fully spread to the region of concern.
Further, it is conventional practice to perform the pre-CT in a combination of intermittent and continuous radiographic processes in which an intermittent radiography is executed for a predetermined period, and then a continuous radiography is executed. Specifically, as shown in
FIG. 2
, spreading conditions of the contrast medium are checked from time to time by observing CT images acquired from the intermittent radiography at an initial stage where the contrast medium has not spread to the full. When the contrast medium is thought to have spread to some extent, spreading conditions of the contrast medium are checked continuously by means of CT images acquired from the continuous radiography. Exposure dose is reduced for the intermittent radiography.
However, the conventional X-ray CT apparatus has a drawback of sometimes failing to determine the timing of starting the production CT correctly. This is because the pre-CT performed in the combination of intermittent and continuous radiographic processes can be ill suited for checking the spreading conditions of the contrast medium. On such an occasion, it is impossible to determine the timing of starting the production CT correctly.
SUMMARY OF THE INVENTION
This invention has been made having regard to the state of the art noted above, and its object is to provide an X-ray CT apparatus which enables the timing of starting a production CT to be determined correctly at all times.
The above object is fulfilled, according to this invention, by an X-ray CT apparatus for performing a pre-CT which is a form of computerized tomography carried out with low doses beforehand in order to determine timing of starting a production CT which is a form of computerized tomography for acquiring images for use in diagnosis, the apparatus comprising:
an X-ray emitting device for emitting X rays toward a patient;
an X-ray detecting device for detecting X rays transmitted through the patient;
a revolving device for revolving the X-ray emitting device and the X-ray detecting device about the patient;
an image reconstructing device for reconstructing sectional images of the patient based on X-ray detection data received from the X-ray detecting device;
a pre-CT control device for controlling the X-ray emitting device according to a radiographic mode of the pre-CT;
a production CT control device for controlling the X-ray emitting device according to radiographic conditions of the production CT; and
a pre-CT radiographic mode setting device for selecting and setting, as the radiographic mode of the pre-CT, one of three radiographic modes, i.e. a continuous radiographic mode for performing only a continuous radiography by continuously emitting X rays in low doses, an intermittent radiographic mode for performing only an intermittent radiography by intermittently emitting X rays in low doses, and a combined intermittent and continuous radiographic mode for performing the intermittent radiography and the continuous radiography in combination.
In performing X-ray tomography with the X-ray CT apparatus having the above construction, a contrast medium is given to a patient to be radiographed, and the pre-CT radiographic mode setting device is operated to select and set a radiographic mode for the pre-CT suited to the purpose of radiography, from among the continuous radiographic mode, the intermittent radiographic mode and the combined intermittent and continuous radiographic mode. Subsequently, the pre-CT is executed in the selected radiographic mode with lower doses than for the production CT to acquire sectional images. The operator monitors a coloring state of the contrast medium in a region of concern appearing in the sectional images acquired. When the coloring state of the contrast medium is found appropriate, the pre-CT is stopped and the production CT is started.
Preferably, the X-ray CT apparatus according to this invention further comprises a delay time setting device for setting a delay time lasting from a point of time when a pre-CT starting instruction is given to a point of time for starting the pre-CT.
With the X-ray CT apparatus having the above construction, the pre-CT is deferred for the delay time set by the delay time setting device to last from the point of time when a pre-CT starting instruction is given. Only upon lapse of the delay time, the pre-CT is started. During the delay time for deferring the pre-CT, the operator checks for any leakage of the contrast medium injected.
A point of time for starting a pre-CT in an X-ray CT performed by using a contrast medium must be associated with a point of time for starting a contrast medium injection. Particularly, for a pre-CT in the combined intermittent and continuous radiographic mode, the timing of switching between intermittent radiography and continuous radiography must also be associated with the point of time for starting a contrast medium injection. With the X-ray CT apparatus according to this invention, a pre-CT is always started upon lapse of a selected delay time. Thus, the association between the point of time for starting the pre-CT and the point of time for starting the contrast medium injection is secured, whereby the pre-CT is always started at the right time. The association between the timing of switching from intermittent radiography to continuous radiography and the point of time for starting the contrast medium injection is also secured. Thus, a switch is made between intermittent radiography and continuous radiography always with appropriate timing. As a result, a time for starting a production CT is determined accurately.
Without the above delay time setting function, the pre-CT would be started after a start of contrast medium injection and the operator's checking for any leakage of the contrast medium injected. However, since variations would occur with the checking time, the associations could not be secured between the point of time for starting the pre-CT and the point of time for starting the contrast medium injection,

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