JP2813992B2 - Raw data compression device and decompression device in CT scanner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to raw data (RAW DA) in a CT scanner.
TA) A compression device and an expansion device.

[Prior Art] FIG. 12 shows a general configuration example of an X-ray CT scanner.

In this X-ray CT scanner 90, 91 is an X-ray tube, and 92 is an X-ray tube.
It is a line detector. These rotate as indicated by arrows in the figure, and perform X-ray irradiation at slightly different angles to obtain ionized charge data.

The ionized charge data is collected by a data collection device (DAS) 93, digitized, and transferred to a computer 94 as raw data X _{(V) C.}

Here, _V in the raw data X _{(V) C} is a view number and corresponds to an angle. C is a channel number, and corresponds to each of the multiple channels of the X-ray detector 92.

The computer 94 transmits the transferred raw data X _{(V) C}
Is stored in the storage device 95. Also, stored raw data X
_{(V) C} is taken out, image-formed by the image reconstruction device 96, and displayed on the display device 97.

[Problems to be Solved by the Invention] In the above-mentioned conventional X-ray CT scanner 90, every time ionization charge data is obtained by one X-ray irradiation, the DAS 93 converts it into raw data X _{(V) C} , Transfer to 94.

However, the interval of X-ray irradiation, becomes shorter than the transfer time required for one cycle of the raw data X _{(V) C,} it becomes impossible to transfer the raw data X _{(V) C} every X-ray irradiation problems is there.

For this reason, it is conceivable to use a transmission system with a high transfer rate or temporarily store the raw data on the DAS 93 side, but in any case, there is a problem that the equipment load is greatly increased.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a raw data compression apparatus for compressing raw data so that raw data can be sequentially transferred to a computer even in a transmission system with a low transfer rate. It is another object of the present invention to provide a decompression device that restores the compressed data to original raw data.

[Means for Solving the Problems] The raw data compression apparatus according to the present invention is arranged such that when the raw data in the CT scanner is X _{(V) C} (where V is the view number and C is the channel of the detector), D _{( V) C} = X _{(V) C-} X _{(V-1) C} A primary difference calculating means for calculating a primary difference D _{(V) C} , and a predetermined number of bits n smaller than the number m of bits for raw data. It is determined whether or not the above D _{(V) C} fits, and if it is determined that it fits, Y _{(V) C} = D _{(V) C} , and if it is determined that it does not fit, Y _{(V) C} = X _{( V) C} , a primary compressed data generating means for generating primary compressed data Y _{(V) C} , and E _{(V) C} = Y _{(V) C−} Y _{(V-1) C for} a secondary difference E _{(V) A} secondary difference calculating means for calculating _C ; determining whether or not the E _{(V) C} is within a predetermined number of bits k smaller than the number of bits n for the primary difference; Y _{(V) C} , Y where E _{(V) C} is calculated
_{When (V-1) C} is the primary difference D _{(V) C} , D _{(V-1) C} , respectively, Z _{(V) C} = E _{(V) C} , otherwise, Z _{(V) C} = Y _{(V) C} ,
The secondary compressed data creating means for creating a secondary compressed data Z _{(V) C,} secondary compression data Z _{(V) C} Do raw data, or the primary difference,
It is characterized in that it comprises a discrimination code generation means for generating a discrimination code for discriminating whether it is a secondary difference.

The decompression device according to the present invention further includes: a determination unit configured to determine whether the secondary compressed data Z _{(V) C} is raw data, a primary difference, or a secondary difference based on the determination code; _{X (V) C = Z (} V) C, when it is determined that the primary _{difference, X (V) C = X} (V-1) C + Z (V) when it is determined that _C secondary difference, X _{(V ) C} = 2X _{(V-1) C-} X _{(V-2) C} + Z _{(V) C} Raw data calculating means for calculating raw data X _{(V) C} It is assumed that.

[Operation] The raw data compression device of the present invention calculates a primary difference and a secondary difference between raw data of adjacent views.
If the primary difference and the secondary difference each fall within the predetermined number of bits, the primary difference or the secondary difference is used instead of the raw data.

Since the raw data of adjacent views are often approximated, the probability that the primary difference or the secondary difference is used is high.

However, since the primary difference and the secondary difference have a smaller number of bits than the raw data, this means that data compression has been performed.

Since the data thus compressed contains raw data, primary differences, and secondary differences, a discrimination code for discriminating them is added.

Then, if these are transferred from the DAS to the computer, even low data generated at short intervals can be transferred without any trouble in a transmission system with a low transfer rate.

On the other hand, in the decompression device of the present invention, based on the compressed data transmitted from the DAS side and the discrimination code thereof,
A predetermined operation is performed to decompress the compressed data.

Thus, this restores the original raw data so that processing such as image reconstruction can be performed.

[Example] Hereinafter, the present invention will be described in more detail based on an example shown in the drawings. It should be noted that the present invention is not limited by this.

FIG. 1 is a circuit diagram showing a raw data compression apparatus 1 according to one embodiment of the present invention, which is provided between an output side of a DAS 93 and a transmission line shown in FIG.

First, as an initial setting of the operation of the raw data compression device 1, a shift register 3 for delaying raw data by one view, a shift register 7 for delaying the primary difference by one view, The control circuit 15 clears the shift register 9 for delaying the flag A indicating whether the difference is the primary difference by one view.

Next, when the strobe signal is output from the DAS 93, the control circuit 15 controls the pipeline register 2 to
It receives the raw data X _{(V) C} input from 3 and inputs it to the shift register 3, the subtraction circuit 4, and the data selector 5.

Shift register 3 is raw data delayed by one view
Outputs X _{(V-1) C.}

Therefore, the subtraction circuit 4 uses the raw data of the current view.
X _{(V) C} and the row data X _{(V-1) C of the} previous view are subjected to a subtraction operation, a primary difference D _{(V) C} is calculated, and output to the data selector 5. Further, the subtraction circuit 4 determines whether or not the calculated primary difference D _{(V) C} falls within the number of bits n for the primary difference set smaller than the number of bits m for the raw data. If it is within the range, 0 is output as the flag A, and if it is not within the range, 1 is output as the flag A.

The data selector 5 is controlled by the flag A. When the flag A is 0, it outputs a primary difference D _{(V) C} , and when the flag A is 1, it outputs low data X _{(V) C.} The output of the data selector 5 is the primary compressed data Y _{(V) C.}

The flag A and the primary compressed data Y _{(V) C} are input to the pipeline register 6.

The pipeline register 6 inputs the flag A to the shift register 9, the OR circuit 10, and the pipeline register 12. Further, the pipeline register 6 inputs the primary compressed data Y _{(V) C} to the shift register 7, the subtraction circuit 8, and the data selector 11.

The shift register 7 outputs the primary compressed data Y _{(V-1) C} delayed by one view.

Therefore, the subtraction circuit 8 subtracts the primary compressed data Y _{(V) C} of the current view from the primary compressed data Y _{(V-1) C of the} previous view, and calculates a secondary difference E _{(V) C.} Then, the data is output to the data selector 11. The subtraction circuit 8 determines whether or not the calculated secondary difference E _{(V) C} falls within the number of bits k for the secondary difference that is set to be smaller than the number of bits n for the primary difference. Judgment is performed, and if it is within the range, 0 is output as the flag B, and if not, 1 is output as the flag B.

On the other hand, the shift register 9 outputs a flag A (hereinafter, referred to as a flag a) delayed by one view to the OR circuit 10 and the pipeline register 12.

The data selector 11 outputs the flag A and the flag a (the flag A of the previous view) input through the OR circuit 10,
Controlled by the flag B input from the subtraction circuit 8,
The secondary difference E _{(V) C} is output only when the output of the OR circuit 10 is 0 and the flag B is 0, and otherwise, the primary compressed data Y _{(V) C} is output. This data selector 11
Is the secondary compressed data Z _{(V) C} and is input to the pipeline register 12.

The pipeline register 12 stores a flag A and a flag a.
, The flag B, and the secondary compressed data Z _{(V) C} are input to the bit merge circuit 13.

As shown in FIG. 2, when the flag A is 1, the bit merge circuit 13 sets the first bit and the next bit to 1, and thereafter continues the m bits of the secondary compressed data Z _{(V) C.} On the other hand, when the flag A is 0 and the flag a is 1, the flag A is 0, the flag a is 0, and the flag B is 1
, The first bit is set to 1, the next bit is set to 0, and then n bits of the secondary compressed data Z _{(V) C} are continued. Further, when the flags A, a and B are all 0, the first bit is set to 0, and then the secondary compressed data
Continue for k bits of Z _{(V) C.}

In this way, the bit merge circuit 13 creates data to which the discrimination code (the leading bit and the leading and next bits) is added, and packs the data into p bits as shown in FIG. Output.

 The FIFO 14 sends data to the computer 94.

As described above, the raw data X _{(V) C} and the primary difference D
And _{(V) C,} although secondary difference E _{(V) data C} and are mixed is transferred to a computer, the majority is the primary difference D _{(V) C} or secondary difference E _{(V) C,} data Compression has been performed.

Therefore, even if X-ray irradiation is performed at short intervals, data can be transferred to a computer without any trouble using a transmission system with a low transfer rate.

FIGS. 4 to 7 specifically illustrate the process of compressing raw data. However, for simplicity, the X-ray detector 92
Is 5 and the views are also 1 to 5.

First, FIG. 4 illustrates the contents of the shift register 3. View 0 shows a cleared state. After view 1, raw data X _{(V) C} is included.

Next, FIG. 5 illustrates the contents of the shift register 7. These are the primary compressed data Y _{(V) C} , whose contents are mainly the primary difference D _{(V) C} , and the primary difference D _{(V) C}
Are mixed with raw data X _{(V) C in} a portion that does not fit into n bits. View 0 shows a cleared state. The value described below each value is the flag A.

Next, FIG. 6 shows the secondary compressed data Z _{(V) C} expressed in the same format as in FIGS. 4 and 5. Here, it is mainly the secondary difference E _{(V) C} , but the raw data X _{(V) C} and the primary difference
D _{(V) C} is mixed. The values described below each value are a flag A, a flag a, and a flag B in this order. The Δ mark of the flag B indicates that it may be 0 or 1 (the same result is obtained).

Next, the output signal generated by the bit merging circuit 13 based on the secondary compressed data Z _{(V) C} and the flags A, a, and B shown in FIGS. It is expressed in a format. The value described below each value is the first bit or the first bit and the next bit, and is a discrimination code.

It is preferable that the raw data compression device 1 be integrated into an IC.

When the computer 94 receives the data from the raw data compression device 1, the data is stored in the storage device 95. Since the data is compressed, it is not necessary to use a high-speed and large-capacity hard disk device.

The computer 94 extracts the compressed data stored in the storage device 95 when necessary, performs decompression processing, and restores the original raw data. FIG. 8 is a flowchart showing the operation of the decompression process.

That is, in step 81 of FIG. 8, the compressed data stored in the storage device 95 is sequentially extracted, and it is determined whether or not the leading bit is 1.

If the first bit is 1, the routine proceeds to step 82, where it is determined whether the next bit is 1.

If the next bit is 1, the process proceeds to step 83, and the subsequent m bits are set to low data. That is, X _{(V) C} = Z _{(V) C.}

On the other hand, if the next bit is 0 in step 82, the flow advances to step 82 to calculate raw data by the following equation.

X _{(V) C} = X _{(V-1) C} + Z _{(V) C} Further, if the first bit is 0 in step 81,
Proceeding to step 85, the raw data is calculated by the following equation.

X _{(V) C} = 2X _{(V-1) C} -X _{(V-2) C} + Z _{(V) C In} step 86, the above steps are performed until there is no more data.
Repeat steps 81-85.

As described above, the raw data X _{(V) C} is restored.

FIG. 9 shows that the original raw data is restored from the compressed data of FIG. 7 as described above.

In another embodiment, a discrimination code m | n, m | k, n | m, n | k, k as shown in FIG. 10 is used instead of a discrimination code for each data as shown in FIG. As shown in FIG. 11, | m and k | n are added at each boundary where the number of data bits changes.

Further, as still another embodiment, the raw data compression apparatus is not hard logic as in the above-described embodiment, and a DSP is used.
Alternatively, one constituted by a microprocessor can be used.

In the above-described embodiment, the decompression process is described as a function of the computer.

For the sake of simplicity, the description of error correction at the time of data transfer is omitted, but for example, a bit merge circuit
Needless to say, it is preferable to add an error correction code at 13 so that the computer 94 can correct data errors.

[Effects of the Invention] According to the raw data compression apparatus and the expansion apparatus 1 in the CT apparatus of the present invention, even if the interval of X-ray irradiation is shortened, the transmission system having a low transfer rate is used to transfer data from the DAS to the computer. Raw data can be sent sequentially.

Further, since there is no need to store a large amount of data, it is not necessary to use a special hard disk, bulk memory, or the like.

Therefore, it is possible to cope with the continuous rotation type CT scanner without increasing the cost.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a raw data compression apparatus according to an embodiment of the present invention, FIG. 2 is a conceptual diagram for explaining the operation of a bit merge circuit, and FIG. 3 is a structure of data output from the bit merge circuit. Fig. 4, Fig. 4 is an illustration of raw data, Fig. 5 is an illustration of primary compressed data, Fig. 6 is an illustration of secondary compressed data, Fig. 7 is an illustration of data output to a computer, 8 is a flowchart of the decompression process, FIG. 9 is an explanatory diagram showing that the raw data is restored, FIG. 10 is an explanatory diagram showing another example of the discrimination code, and FIG. 11 is a diagram showing the discrimination code of FIG. FIG. 12 and FIG. 12 are block diagrams showing a general configuration example of an X-ray CT scanner. (Explanation of reference numerals) 1... Raw data compression device 2, 6, 12... Pipeline register 3, 7, 9... Shift register 4, 8... Subtraction circuit 5, 11... Data selector 13. Circuit 14 FIFO 15 Control circuit 90 X-ray CT scanner 92 X-ray detector 93 DAS 94 Computer 95 Storage device.

Claims (2)

(57) [Claims] 1. The raw data in a CT scanner is X
_{(V) C} (where, V is the view number, C is a channel of the detector) when _{a, (a) D (V)} C = X (V) C -X (V-1) C by the primary difference D _{( V)} a primary difference calculating means for calculating _C ; and (b) determining whether or not the D _{(V) C} falls within a predetermined number n of bits smaller than the number m of bits for raw data, and determining that the D _{(V) C} falls within the predetermined number n. When it is determined that Y _{(V) C} = D _{(V) C} does not fit, primary compressed data creation means for creating primary compressed data Y _{(V) C} by Y _{(V) C} = X _{(V) C} (C) a secondary difference calculating means for calculating a secondary difference E _{(V) C} from E _{(V) C} = Y _{(V) C} -Y _{(V-1) C} ; and (d) a primary difference. of the number of bits smaller than n predetermined number of bits k is determined whether the E _{(V) C} falls, determines that fits, and, Y when the calculated the E _{(V) C
When (V) C} and Y _{(V-1) C} are the primary differences D _{(V) C} and D _{(V-1) C} , respectively, Z _{(V) C} = E _{(V) C} , Z _{(V) C} = Y _{(V) C} to create secondary compressed data Z _{(V) C} , and (e) whether the secondary compressed data Z _{(V) C} is raw data, A determination code generating means for generating a determination code for determining whether the difference is a primary difference or a secondary difference. (A) determining means for determining whether the secondary compressed data Z _{(V) C} is raw data, primary difference, or secondary difference based on the determination code of claim 1; When it is determined, X _{(V) C} = Z _{(V) C} When it is determined as a primary difference, when X _{(V) C} = X _{(V-1) C} + Z _{(V) C} When it is determined as a secondary difference, X _{(V) C} = 2X _{(V-1) C-} X _{(V-2) C} + Z _{(V) C} and raw data calculating means for calculating raw data X _{(V) C.} Low data decompression device for CT scanner.