BRIEF DESCRIPTION OF THE DRAWING
These and further features, aspects and advantages of the invention will be discussed more in detail hereinafter with reference to the disclosure of preferred embodiments of the invention, and in particular with reference to the appended Figures that illustrate:
FIG. 1, an overall arrangement of an apparatus of which the invention forms part;
FIG. 2, a first tessellation arrangement;
FIG. 3, a second tessellation arrangement;
FIG. 4, a circuit arrangement for non-destructive readout;
FIG. 5, a time-diagram of the various operations.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 illustrates an overall embodiment of an apparatus in which the invention is applied. Herein, a source 22 of irradiation, such as X-ray, is made to temporarily irradiate an object 26, such as a human person or a part thereof. The purpose of irradiation can be diagnostic, which will be considered to be the case here. In principle, other purposes are feasible, such as recognized by persons skilled in the art. The transmission pattern of the radiation is measured by a C-MOS array 28, and upon termination of the irradiation period, read out for use by a radiologist or other.
Now, the operation is started by a start command on control terminal 20. At this instant, a reset command will be given to measuring CMOS array 28 and to the combining or arithmetic means 30. Furthermore, the irradiation of object 26 will commence, and the irradiation will lead to charge accumulation in the cells of CMOS array 28. A subset of multiple distributed C-MOS cells across the array are targeted for contributing to the dose measurement. This contributing is effected by repeated non-destructive readout thereof to arithmetic means 30. The readout of array 28 is effected in relatively brief intervals wherein the irradiation can be paused if necessary. If necessary, a certain calibration factor can be applied for converting the reading acquired to an actual dose figure. The optimum dose can be found from the data read-out. For example, the readout subset of cells may exhibit a sufficient amount of image contrast. The necessary dose can be a function of the irradiated subject, such as being dependent on the body weight. In other situations, the average absolute dose would be determinative.
Now, if the right dose has been attained, a termination signal will appear on line 34. On the one hand, this will signal irradiation facility 22 to stop more or less immediately. On the other hand, this will signal evaluation device 32 to read out all CMOS for outputting the measured transmission image on line 36 for further usage. Generally, this will take appreciably more time than the reading of only the subset of cells.
As a different application of the above, the dose signal can be used as a trigger signal to activate the array as a whole for integrating the radiation dose received. To this effect, the feedback will reset all cells to zero, which can be effected in a very brief interval. The measuring of only a few cells for producing the trigger signal will nevertheless result in fast operation. Here, the intended dose should of course have a very low value.
FIG. 2 illustrate a first tessellation arrangement. Tessellation in this regard means that the cells actually used will form a substantially uniform two-dimensional pattern across the array. If necessary, some deviation from uniformity can be used. Anyway, at the edges of the array always some degree of non-uniformity will be present. This can be seen through comparing the left and right edges of the array: the left hand edge has relatively more dose sensing cells than the right hand edge. The uniformity should be targeted such that the combined dose sensing does not have discrepancies due to any non-uniformity. In fact, if non-uniformity were too large or too small, the algorithmic means that produces the trigger or dose signals could introduce or rather enhance non-uniformities.
Now, the advantage of such (quasi-)uniform distribution is that the outcome is largely independent of shifts in the position of the object. The device has an array of vertical drivers 50 that each will drive all cells of a line. For column read out 52, in this embodiment only each fifth cell is used for measuring, which will need specific addressing. This means that in this embodiment, accessing is only necessary for one fifth of all lines, which can be effected in a sequence that proceeds from top to bottom in the array. In consequence, the embodiment allows to speed up the read-out process by a factor of about five for generating only the dose and/or trigger signals.
FIG. 3 illustrates a second tessellation arrangement. Here likewise, only one fifth of the lines is addressed. The advantage of the arrangement is that each column has exactly one cell taken into account. This allows to effect the column readout in only a single one operation. In comparison with FIG. 2 this gives a further speed-up by a factor of five. Of course, in a practical case some further operations could be necessary. To attain the above effects, the measuring cells of the subset have some specific facilities that will be discussed hereinafter with reference to FIG. 4. Various other patterns for locating the dose-measuring cells are feasible.
FIG. 4 illustrates a circuit arrangement for non-destructive readout. The elementary set-up has the radiation measurement device proper 60, reset transistor 62 with control terminal RS, reference voltage terminal VREF 64, SF transistor 66, select gate 68 and output terminal 70. A more extended circuit has a second selection transistor 72 present for selecting the dose measurement cells. Persons skilled in the art will know to interconnect the various cells to realize the dose-sensing patterns of FIGS. 2 and 3. A still further circuit arrangement for hardwired control of generating the subset of cells has the control terminal SEL of transistor 68 adjacent to two different control conductors SEL and DS SEL, respectively. The conductors are arranged in a horizontal or vertical direction for selective hardwired interconnection to said control electrode of transistor 68. The interconnection can be done in one of more processing steps during manufacture. This allows to create two different groups of cooperating cells from the distributed C-MOS cells. A first group could generate the trigger signal, whereas the second group could create the dose-sensing signal. The outputs would appear on terminal 70, and the combining algorithm could have the appropriate form for each of the two usages. Two peripheral input circuits could have an appropriate arrangement for controlling the two subsets of cells and for routing the outputs in a manner to achieve the desired results.
FIG. 5 illustrates a time-diagram of the various operations. Vertical range 98 indicates the address range of all array cells. Arrow 102 indicates power on. Edge 104 of X-Ray trace 100 indicates the start of the irradiation. This start is detected by the trigger producing array cells that can for example be located along the edge of the array. Thereupon, line 106 indicates the global reset of all array cells, followed by the integration in all array cells. During irradiation, the amount of radiation received is monitored by the dose sensing subset of cells. Arrow 108 indicates the attainment of the target radiation, and the ensuing termination of the X-Ray radiation along trace 100. Sloped line 110 indicates the sequential read-out of all cells for evaluation of the measurement. Thereupon, a next measurement can be effected.
According to the invention, multiple options exist for trigger or dose control. Finally, there will always be some kind of algorithm that compares the sense information with some kind of set-point.
For a prototype for a dental product, it was found that the maximum statistical deviation from the average was about 2% for various different images under consideration. It was considered that such one-digit percentage variation was perfectly allowable. Furthermore, an important feature of the invention is that full-frame image information can become available at line speeds. Higher dose sensing resolution can be achieved through multiple line reads in the proposed approach.
Now, the present invention has hereabove been disclosed with reference to preferred embodiments thereof. Persons skilled in the art will recognize that numerous modifications and changes may be made thereto without exceeding the scope of the appended Claims. In consequence, the embodiments should be considered as being illustrative, and no restriction should be construed from those embodiments, other than as have been recited in the Claims.
Patent Application
20080001094
