- Nothing cut off — this is the reference
- The grid is level, centered to the central ray, the right way up, and used at its focal distance. Every primary ray runs down its own interspace, so nothing is cut off — a focused grid, properly positioned, exhibits no grid cutoff at all.
- An 8:1 grid accepts rays up to 7.1° off
- Grid ratio is the height of the strip divided by the width of the interspace. That single number sets how far a ray may deviate and still get down the channel — the taller and narrower the channel, the smaller the angle it accepts. It is why a high-ratio grid cleans up scatter better, and, in the same breath, why it cuts off more readily when you misalign it. Bushong states cleanup figures only for the ends of the range, so none is quoted here.
- Bucky factor 3× at 8:1 and 70 kVp
- A grid absorbs scatter, but it absorbs some primary radiation too, so the technique has to go up to put the same exposure on the receptor. The Bucky factor is how much — and it is also how much the patient dose goes up. It climbs with grid ratio, and it climbs with kVp, because higher kVp makes more scatter and that scatter has a harder time getting through. Raising the ratio therefore buys contrast and costs dose, which is the trade the exam asks you to reason about.