Patent Number: 061817732
Section: claims

1. A radiation anti-scatter device comprising: a grid having a plurality of radiation absorbing elements,  a grid path comprising a start grid position at a first end of said path and a finish grid position at a second end of said path; and  a grid driver connected to said grid for moving said grid during an operating cycle from said start position to said finish grid position in a single unidirectional stroke at a variable speed along said path.  a grid having a plurality of radiation absorbing elements, and a grid driver connected to said grid for moving said grid in a single unidirectional stroke at a variable speed between a starting and an end position, wherein said variable speed comprises a velocity profile and wherein the velocity profile comprises a first velocity component V.sub.1 =K.sub.1 t for a first period and a second velocity component V.sub.2 =K.sub.2 t.sup.-m for a second period, where K.sub.1 and K.sub.2 are constants and m is greater than zero and equal to or less than one.  a source of penetrative radiation for emitting on command a radiation beam along a path;  a radiation detector positioned in the beam path for receiving said radiation, said detector comprising an array of radiation sensors aligned in a first direction; and  a movable radiation anti-scatter grid assembly positioned between said radiation source and said detector, said grid assembly comprising:  A. first accelerating said grid to a first velocity;  B. beginning asymptotically decelerating said grid from said first velocity toward a final velocity; and  C. causing said radiation exposure source to emit radiation only after the onset of step "B". 2. The radiation anti-scatter device according to claim 1, wherein said variable speed comprises a velocity profile having a decreasing velocity component. 3. The radiation anti-scatter device according to claim 2, wherein said velocity profile also comprises an increasing velocity component. 4. The radiation anti-scatter device according to claim 2 wherein the velocity profile comprises V=K.sub.2 t.sup.-m, where V is the grid velocity, K.sub.2 is a constant, t is time and m is an exponent having a value greater than 0. 5. A radiation anti-scatter device comprising: 6. A direct radiographic diagnostic imaging system comprising: 7. The system of claim 6 wherein said angle is 90 degrees. 8. The system of claim 7 wherein said grid traverses said detector in the first direction. 9. The system of claim 6 wherein said angle is an acute angle. 10. The system of claim 9 wherein said grid traverses said detector in a direction substantially perpendicular to said second direction. 11. The system of claim 6 wherein said velocity profile comprises V.sub.1 =K.sub.1 t for a first period and then V.sub.2 =K.sub.2 t.sup.-m for a second period, where V.sub.1 and V.sub.2 are velocity, K.sub.1 and K.sub.2 are constants, t is time, and m is an exponent having a value greater than 0. 12. The system of claim 8 further comprising a controller adapted to synchronize emission of said radiation beam with movement of said grid. 13. A method for reducing Moire patterns in a radiation detection system comprising a detector having an array of discreet sensors aligned along a first direction, a radiation exposure source, and an anti-scatter grid assembly located between said detector and said source, said method comprising traversing said grid across said detector once in a single unidirectional stroke with a variable velocity profile. 14. The method according to claim 13 wherein said velocity profile decreases asymptotically to zero. 15. A method for reducing Moire patterns in a radiation detection system comprising a detector having an array of discreet sensors aligned along a first direction, a radiation exposure source, and an anti-scatter grid assembly located between said detector and said source, said method comprising traversing said grid across said detector once in a single unidirectional stroke wherein the step of traversing said grid comprises: 16. The method according to claim 15 wherein said accelerating step comprises accelerating the grid at a velocity profile V.sub.1 =K.sub.1 t decelerating the grid at a velocity profile V.sub.2 =K.sub.2 t.sup.-m, where K.sub.1 and K.sub.2 are constants and m is greater than zero. 17. The method according to claim 16 wherein the accelerating step has a duration t.sub.1 of between about 0.001 and 0.5 seconds and the decelerating step has a duration t.sub.2 less than or equal to 2 seconds.