X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1999-07-28
2003-05-06
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
Reexamination Certificate
active
06560307
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to X-ray CT apparatus for enabling what is known as CT fluoroscopy.
(2) Description of the Related Art
With an X-ray CT apparatus of this type, an image reconstructing process can be carried out in a shorter time than an image reconstruction performed at a so-called off time. By using the image reconstructing process carried out in such a short time, numerous X-ray CT images may be picked up successively in real time and at a relatively fast rate such as 8 frames per second, for example. Thus, what is known as CT fluoroscopy is performed for observing X-ray CT images, which are sectional images, in the form of continuous dynamic images as in usual X-ray fluoroscopy. CT fluoroscopy, as it enables a real-time observation of continuous images, is used mainly in catheterization such as biopsy. Biopsy and the like usually take a relatively long time, i.e. from several tens of seconds to several minutes.
However, CT fluoroscopy cannot be performed continuously for a long time with a conventional X-ray CT apparatus capable of CT fluoroscopy. That is, with the conventional apparatus, while successively storing in memory all projection data acquired from CT fluoroscopy, an image is reconstructed each time projection data for predetermined angles enabling an image reconstruction has been collected, and such images are displayed successively. Thus, the time for continuously performing CT fluoroscopy is always limited by a storage capacity of memory for storing the projection data.
In time of CT fluoroscopy, numerous images are observed continuously. In practice, it often is the case that only several of those images are useful. In such a case, even though all the projection data collected are stored as with the conventional apparatus, only a small part of the data is reused (e.g. for reconstructing and observing images after CT fluoroscopy). This amounts to a wasteful consumption of memory.
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 uses memory efficiently to enable CT fluoroscopy to be performed continuously over an extended time, and allows projection data to be saved as necessary.
The above object is fulfilled, according to this invention, by an X-ray CT apparatus for enabling CT fluoroscopy comprising:
a scanning device including an X-ray tube and an X-ray detector for continuously repeating an X-ray scan to collect X-ray projection data from directions of varied angles;
a first storage having a storage capacity for storing projection data for angles necessary to reconstruct at least one image, the first storage storing, after the projection data for the angles is written therein, new projection data as written over the projection data written earliest;
a second storage having a storage capacity for storing projection data for angles necessary to reconstruct numerous images, the second storage successively storing projection data successively collected, without rewriting the projection data, until the storage capacity is exhausted;
an image reconstructing device for reconstructing an image from projection data for predetermined angles;
a control device for controlling storage of the projection data successively collected in a selected one of the first and second storages and transmission of the projection data to the image reconstructing device; and
a display device for displaying the image reconstructed by the image reconstructing device.
According to this invention, when a control is effected to store projection data successively collected in the first storage, the first storage stores the latest projection data for angles necessary to reconstruct at least one image. CT fluoroscopy may be performed by reconstructing images from this data at high speed, and displaying the latest X-ray CT images thereby successively acquired on the display device. In this case, since the first storage is constantly updated with a predetermined amount of latest projection data, CT fluoroscopy may be performed continuously over an extended time without a limitation by the storage capacity.
When a control is effected to store projection data successively collected in the second storage, the second storage, as does a storage in a conventional X-ray CT apparatus, successively stores, in the order of collection, the projection data successively collected until the second storage becomes full. The data collection therefore is limited by its capacity, but the data may be read again for image reconstruction to enable observation of selected images.
Thus, according to this invention, CT fluoroscopy may be performed continuously without a limitation of time, or, though limited in time, the projection data acquired for CT fluoroscopy may be saved for use in reproducing, with high image quality afterward, the images seen in time of CT fluoroscopy.
The above X-ray CT apparatus may further comprise a selection instructing device for instructing a selection of one of the first and second storages for storing the projection data collected, and transmission of the projection data to the image reconstructing device. The control device may perform controls, on instructions from the selection instructing device, to determine which of the first and second storages should be used for storing the projection data, and whether the projection data should be transmitted to the image reconstructing device.
This construction allows the operator to select and instruct which of the first and second storages the projection data should be stored in.
In the above X-ray CT apparatus, the control device may perform CT fluoroscopy by determining beforehand which of the first and second storages should be used for storing the projection data collected during the CT fluoroscopy. This selection may be instructed from the selection instructing device.
With this construction, a procedure of CT fluoroscopy not requiring the projection data to be saved may be carried out continuously without a limitation of time while storing and updating projection data only in the first storage. On the other hand, in a procedure of CT fluoroscopy requiring all the projection data to be saved, the projection data is successively stored, without overwriting, only in the second storage, thereby saving all the projection data collected in time of CT fluoroscopy, to enable a subsequent reproduction, with high image quality, of the images observed in time of CT fluoroscopy.
In the above X-ray CT apparatus, the control device may perform CT fluoroscopy while switching between the first and second storages for storing the projection data collected during the CT fluoroscopy.
With this construction, during CT fluoroscopy, projection data not to be saved may be stored in the first storage, while only projection data to be saved may be stored in the second storage. Thus, a continuous procedure of CT fluoroscopy may be performed for an extended time. In addition, among the projection data collected during one cycle of CT fluoroscopy, only necessary data may be saved for later use. In this way, the memory may be used efficiently.
In the above X-ray CT apparatus, the selection instructing device may be operable to instruct, during CT fluoroscopy, switching between the first and second storages for storing the projection data collected during the CT fluoroscopy. This switching of the storages may be effected as follows.
The control device is operable to store the projection data collected during CT fluoroscopy normally in the first storage, to switch storage of the projection data from the first storage to the second storage when an instruction is given from the selection instructing device to select the second storage for storing the projection data, and to switch storage of the projection data from the second storage to the first storage upon lapse of a predetermined time from the instruction.
With this construction, the operator may input a storage switching instruction at a po
Church Craig E.
Rader Fishman & Grauer
Shimadzu Corporation
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