. Radiography and radio-therapeutics . rays, tube along a horizontal bar which is marked with a millimetre scale, running both ways from acentral point at zero. The sensitive plate is placed underneath the patient,and protected in the usual way by black paper, or it may be placed in alight-tight cassette. Two wires are laid at right angles to each other on thephotographic envelope, and so placed that one of them runs in the samedirection as the horizontal bar which carries the tube above, and their pointof intersection lies beneath zero on the scale. The cross wires may befastened to a thin bo
. Radiography and radio-therapeutics . rays, tube along a horizontal bar which is marked with a millimetre scale, running both ways from acentral point at zero. The sensitive plate is placed underneath the patient,and protected in the usual way by black paper, or it may be placed in alight-tight cassette. Two wires are laid at right angles to each other on thephotographic envelope, and so placed that one of them runs in the samedirection as the horizontal bar which carries the tube above, and their pointof intersection lies beneath zero on the scale. The cross wires may befastened to a thin board or sheet of vulcanite, and retained in position overthe sensitive plate by drawing-pins, or they may be permanently fixed to aframe, upon which the plate is placed. The marks corresponding to the cross 1 The term central ray is somewhat misleading. It is obvious that no particularray can be exclusively employed. The term may be taken to signify the bundle of raysemerging from the centre of the focus spot upon the anti-cathode. 11. 162 RADIOGRAPHY wires should be painted with aniline ink or silver nitrate solution, so as toleave a mark on the body of the patient. In actual practice, if the cross wiresare thick enough to leave an impression upon the skin, the marking can berendered permanent by painting the lines on the skin immediately the patientrises from the table ; it is convenient to identify one of the corners of theplate by some opaque object, such as a small coin, with a corresponding signon the adjacent skin surface. Two equidistant points are marked off by clips,or any other method, at each side of zero on the horizontal scale bar, at decided on by the operator. The focus-tube is drawn up to one side-clip, and an exposure made. It is then pushed over to the other clip, and asecond exposure made of equal length. The distance from the centre point ofthe anode to the plate is then carefully measured. Accurate data have nowbeen obtained, from which the opera
Size: 1577px × 1585px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookidradiographyr, bookyear1919
