JPH03123538A - Low data compressing and expanding apparatus for ct scanner - Google Patents

Abstract

PURPOSE:To enable the transmitting of a low data to a computer gradually even in a transmission system of a low transmission rate by providing a judging code generating means to generate a judging code to judge whether a secondary compressed data is a low data, a primary difference or a secondary difference. CONSTITUTION:In the initialization of an action of a low data compression device 1, a shift register 3 for delaying a low data by 1 view minute, a shift register 7 for delaying a primary difference by 1 view minute and a shift regis ter 9 for delaying a flag A indicating whether a primary compressed data is a low data or a primary difference by 1 view minute are cleared with a control circuit 15. On the other hand, the shift register 9 outputs a flag A delayed by 1 view minute to an OR circuit 10 and a pipeline register 12. A bit merging circuit 13 sets an initial bit and the subsequent bit at 1 when the flag A is 1 and thereafter, it continues a secondary compressed data Z(v)c by m bits. This enables the transferring of a data to a computer without trouble even if an X ray irradiation is performed at a shorter interval.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to raw data (RAW data) in a CT scanner.
DATA) compression device and decompression device.

[Conventional technology] 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;
2 is an X-ray detector. These rotate as shown by the arrows in the figure and irradiate X-rays at slightly different angles to obtain ionization charge data.

Ionization charge data is collected by a data acquisition device (DAS) 93 and digitized into raw data X, v,.

The data is then transferred to the computer 94.

Here, V in the raw data x(V)c is a view number and corresponds to an angle. Further, C is a channel number, which corresponds to each of a large number of channels of the X-ray detector 92.

The computer 94 receives the transferred raw data X (
V) Store e in the storage device 95. Also, the stored raw data X[? , , is extracted, converted into an image by the image reconstruction device 96, and displayed on the display device 97.

[Problems to be Solved by the Invention] In the conventional X-ray CT scanner 90 described above, each time ionization charge data is obtained by one X-ray irradiation, the DAS 93 converts it into raw data Transferred to 94.

However, if the interval between X-ray irradiations becomes shorter than the time required to transfer one batch of raw data X(V)e, the raw data X(V) is transferred every time X-ray irradiation is performed. There is a problem that it becomes impossible to transfer.

For this reason, it is conceivable to use a transmission system with a high transfer rate or to temporarily store raw data on the DA993 side, but in either case, there is a problem that the load on equipment increases significantly.

SUMMARY OF THE INVENTION An object of the present invention is to provide a raw data compression device that compresses raw data so that raw data can be transferred to a computer one after another even in a transmission system with a low transfer rate. Another object of the present invention is to provide a decompression device that restores the compressed data to the original raw data.

[Means for Solving the Problems] The raw data compression device of the present invention compresses raw data in a CT scanner by X. , 6 (where ■ is the view number and C is the detector channel), then D(Ma11:X(Ma)
. -X(mar+1c) A first difference calculating means calculates the first difference D(Vlc), and determines whether the D(V)e falls within a predetermined number of bits n smaller than the number of bits m for raw data. , when it is determined that it will fit, Y (Vl e=”D H, 1, when it is determined that it does not fit, Y (Vl c−X (
Vl. , the primary compressed data Y. ) primary compressed data creation means for creating C; E (y) c= Y (Vl c-Y Iw-11t
a second-order difference calculation means for calculating a second-order difference Ef,)c, and determining whether E(1,.) falls within a predetermined number of bits k smaller than the number of bits n for the first-order difference; When determining that and calculating its E (V,.)
(11e+Y (V-o t is the first difference, respectively, 9..

When D(V-1)C, Z (V) c = E
[111e, in cases other than the above, Z (w) e =
Y fvl t, secondary compressed data creation means for creating secondary compressed data Z(w, t), and secondary compressed data Zl
v) Discrimination code generation means for generating a discrimination code for discriminating whether e is raw data, a first-order difference, or a second-order difference.

Further, the decompression device of the present invention determines whether secondary compressed data Z (V, t is raw data) by the above-mentioned discrimination code.

A determination means for determining whether it is an order difference or a second order difference, and when it is determined that it is raw data, X (Vlc = Z fil) When it is determined that it is a small first difference, it is X
e When it is determined that it is a second-order difference, X (V) a: 2 X (w-1) t
-na+Z (low data X (Vl
The configuration is characterized in that it includes a raw data calculation means for calculating c.

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

Since the raw data of adjacent views are often similar, there is a high probability that first-order differences or second-order differences will be used.

However, since these first and second differences have a smaller number of bits than the raw data, this means that data compression has been performed.

Data compressed in this way is called raw data.

Since there are both primary differences and secondary differences, a discrimination code is added to distinguish between them.

If these data are transferred from the DAS side to the computer side, even raw data generated at short intervals can be transferred without problems using 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 sent from the DAS side and its discrimination code,
A predetermined calculation is performed to decompress the compressed data.

Accordingly, the original raw data is restored and processing such as image reconstruction can be performed.

[Example] Hereinafter, the present invention will be described in more detail based on the example shown in the drawings. Note that this invention is not limited to this.

FIG. 1 shows a raw data compression device 1 according to an embodiment of the present invention.
This is a circuit diagram showing a circuit installed between the output side of the DAS 93 shown in FIG. 12 and a transmission line.

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

Next, when the strobe signal is output from the DAS 93, the control circuit 15 controls the pipeline register 2,
Raw data X manually generated from DAS93. , the shift register 3, the subtraction circuit 4, and the data selector 5
and enter it.

Shift register 3 outputs raw data X delayed by 1 vinyl.
. -1,, is output.

Therefore, in the subtraction circuit 4, the raw data X of the current view is
(Via and the raw data X.-Inc of the previous view are subtracted, the first difference D (V) c is calculated,
It is output to the data selector 5. Further, the subtraction circuit 4 is
The number of bits n for the primary difference is set smaller than the number m of bits for raw data.

It is determined whether the calculated first-order difference D (Vlc) has settled down, and if it has settled down, O is output as flag A, and if it has not settled down, 1 is outputted as flag A.

The data selector 5 is controlled by the flag A, and when the flag A is O, the first difference D(V). and flag A
When is 1, raw data X [vlc is output. The output of this data selector 5 is primary compressed data Y(V)g.

The flag A and the primary compressed data Y(V)a 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 vibe line register is the primary compressed data Y. , , are input to the shift register 7, the subtraction circuit 8, and the data selector 11.

The shift register 7 is the primary compressed data Y delayed by one view. -1, is output.

Therefore, in the subtraction circuit 8, the primary compressed data Y(r)c of the current view and the primary compressed data Y, w-
n. A subtraction operation is performed on E(V)C, and a second-order difference E(V)C is calculated and output to the data selector 11. Further, the subtraction circuit 8 applies the calculated second-order difference E(V) to the number of bits k for the second-order difference, which is set smaller than the number n of bits for the first-order difference. It is determined whether or not the value has settled down, and if it has, O is output as flag B, and if not, 1 is output as flag B.

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

The data selector 11 is controlled by flag A and flag a (previous view flag A) input via the OR circuit 10, and flag B input from the subtraction circuit 8, and the output of the OR circuit 10 is and the second-order difference E only when flag B is O. , , , , and otherwise output primary compressed data Y(V)e. The output of this data selector 11 is secondary compressed data Zfvlc, which is input to the pipeline register 12.

The pipeline register 12 contains flag A, flag a, flag B, and secondary compressed data Z. ,. input into the bit merge circuit 13.

As shown in FIG. 2, when flag 8 is 1, the bit merging circuit 13 sets the first bit and the next bit to 1, and then continues with m bits of secondary compressed data Z (yle. When flag A is 0 and flag a is 1, flag A is O, flag a is O, and flag B
When is 1, the first bit is set to 1, the next bit is set to O, and then n bits of secondary compressed data z[v, e are continued.

Further, when flag A, flag a, and flag B are all O, the first bit is O, and then the secondary compressed data Z. , C's bits are continued.

In this way, the bit merge circuit 13 creates data to which the discrimination code (the first bit and the first and next bits) is added, packs it into p bits at a time, and sends it to the FIF 014, as shown in FIG. Output.

PIFO 14 sends data to computer 94.

In the above manner, the raw data X. , the primary difference D(Vlc), and the secondary difference E(V)t are transferred to the computer, but most of the data is the primary difference D(Vlc) and the secondary difference E(V)t.
(Vlc or second-order difference E(V)e, and data compression is performed.

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

4 to 7 specifically illustrate the process of compressing raw data. However, for simplicity, the X-ray detector 92
The number of channels is 5, and the views are 1 to 5.

First, FIG. 4 shows an example of the contents of the shift register 3. View O shows a cleared state. View 1
From then on, raw data X (V) g is included.

Next, FIG. 5 shows an example of the contents of the shift register 7. These are the primary compressed data Y. .

However, the content is mainly the first-order difference D(V)t, which is the first-order difference. , raw data X1v)c is mixed in the portion where the data does not fit into n bits. In addition, view O
indicates a cleared state. Further, the value written in the lower number 5 of the multi-value is flag 8.

Next, FIG. 6 shows the secondary compressed data Z (w, t) expressed in the same format as in FIGS. 4 and 5. Here, it is mainly the secondary difference E (Vlc, but the raw data X ( V
l c and first difference. There is a mixture of lc and lc.

The values written at the bottom of the multivalue are flag A, flag a, and flag B in this order. The Δ mark of flag B indicates that it may be O or 1 (the same result will be obtained).

Next, FIG. 7 shows the secondary compressed data Z (Vl
The output signal created by the bit merge circuit 13 based on t, flag A, flag a, and flag B is expressed in the same format as FIG. 6.

The value written at the bottom of the multivalue 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 is implemented as an IC.

Now, on the computer 94 side, when data is received from the raw data compression device 1, it is stored in the storage device 95. Because the data is compressed, there is no need to use high-speed, large-capacity hard disk drives.

The computer 94 takes out the compressed data stored in the storage device 95 when necessary, decompresses it, and restores it to the original raw data.

FIG. 8 is a flowchart showing the operation of this expansion process.

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

If the first bit is 1, the process advances to step 82 and it is determined whether the next bit is 1 or not.

If the next bit is 1, the process advances to step 83 and the following m bits are made raw data. That is, X (Vl c
= Z fvl.

becomes.

On the other hand, if the next bit is 0 in step 82, the process proceeds to step 84, where raw data is calculated using the following equation.

X, v+ h= X (11-1) e+ Z (V
l cFurthermore, if the first bit is O in step 81, the process proceeds to step 85, and raw data is calculated using the following equation.

X tv) a=2 X (w-1)C X (V-2
1c +Z (VIt step 86 repeats steps 81 to 85 until there is no more data.

Through the above process, the raw data X(V, t) is restored.

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

As another example, instead of attaching a discrimination code to each piece of data as shown in FIG. 3, discrimination codes m1n, mlk, n1m, nlk, klm as shown in FIG.
.

One example is one in which kn is added at each boundary where the number of bits of data changes, as shown in FIG.

In yet another embodiment, the raw data compression device is not made of hard logic as in the above embodiments, but is implemented using a DSP.
Alternatively, it may be configured using a microprocessor.

Furthermore, in the above embodiments, decompression processing has been described as a computer function, but it may also be implemented using hard logic.

Note that for the sake of simplicity, we have omitted the explanation of error correction during data transfer, but for example, the bit merge circuit 1
It goes without saying that it is preferable to add an error correction code in Step 3 so that data errors can be corrected on the computer 94 side.

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

Furthermore, since there is no need to store large amounts of data, there is no need to use a special hard disk or bulk memory.

Therefore, it becomes possible to support continuous rotation type CT scanners without increasing costs.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a raw data compression device according to an embodiment of the present invention, Fig. 2 is a conceptual diagram for explaining the operation of the bit merging circuit, and Fig. 3 is the structure of data output from the bit merging circuit. 4 is an example of raw data, FIG. 5 is an example of primary compressed data, FIG. 6 is an example of secondary compressed data, FIG. 7 is an example of data output to a computer, Figure 8 is a flowchart of the decompression process, Figure 9 is an explanatory diagram showing how raw data is restored, Figure 10 is an explanatory diagram showing another example of the determination code, and Figure 11 is an illustration of the determination code in Figure 10. The diagram corresponding to FIG. 3 used and FIG. 12 are block diagrams showing a general configuration example of an X-ray CT scanner. (Explanation of symbols) 1..Raw data compression device 2.6.12..Pipeline register 3.7.9.
...Shift register 4.8...Subtraction circuit 5.11...Data selector 13...Bit merge circuit 14...FIFO 15...1 control circuit 90...X-ray CT scanner 92... ...X-ray detector 93...DAS 94...computer 95...storage device.

Claims (1)

[Claims] 1. Raw data in a CT scanner is X_(_V_)
＿C (where V is the view number and C is the detector channel)
When, (a) D_(_V_)_C=X_(_V_)_C-X_
First difference D_(_V_) due to (_V_-_1_)_C
(b) determining whether the D_(_V_)_C falls within a predetermined number of bits n smaller than the number of bits m for raw data, and when it is determined that it does; , Y_(_V_)_C=D_(_V_)_C When it is determined that the data does not fit, a primary compressed data creation means creates primary compressed data Y_(_V_)_C by Y_(_V_)_C=X_(_V_)_C; (c) E_(_V_)_C=Y_(_V_)_C-Y_
(_V_)_C to calculate a second-order difference E_(_V_)_C; (d) the E_(_V_)_C falls within a predetermined number of bits k smaller than the number of bits n for the first-order difference; Y_(_V_)_C, Y_(_V_-_1_
)_C are the first differences D_(_V_)_C, D_(
When _V_-_1_)_C, Z_(_V_)_
C=E_(_V_)_C In cases other than the above, Z_(_V_)_C=Y_(_V_)_C. Secondary compressed data creation means for creating secondary compressed data Z_(_V_)_C; Raw data in a CT scanner, comprising a discrimination code generation means for generating a discrimination code for discriminating whether compressed data Z_(_V_)_C is raw data, a first difference, or a second difference. Compression device. 2. (a) A determining means for determining whether the secondary compressed data Z_(_V_)_C is raw data, a primary difference, or a secondary difference using the determination code of claim 1; (b) When determining that the secondary compressed data Z_(_V_)_C is raw data; is, X_(_V_)_C=Z_(_V_)_C When it is determined to be a first-order difference,
_(_V_)_C When it is determined to be a quadratic difference, X_(_V_)_C=2X_(_V_-_1_)_C-
A raw data decompression device for a CT scanner, comprising raw data calculation means for calculating raw data X_(_V_)_C from X_(_V_-_2_)_2+Z_(_V_)_C.