. Radiography and radio-therapeutics . it willbe easy to trace thepath of the rays inrelation to a body in-terposed between the fnpiiQ fnVip Q-nrl fVi ^^^^ ^^^—Mackenzie Davidson cross-tliread localiser. () sensitive plate. One threaded needle is placed upon any particular part ofone of the photographic shadows of the foreign body, and the other needle upon a corresponding partin the second shadow. The pointwhere the threads cross and toucheach other will represent the positionof the part of the foreign bodychosen for location. A perpendicularis then dropped from the inter-section of t
. Radiography and radio-therapeutics . it willbe easy to trace thepath of the rays inrelation to a body in-terposed between the fnpiiQ fnVip Q-nrl fVi ^^^^ ^^^—Mackenzie Davidson cross-tliread localiser. () sensitive plate. One threaded needle is placed upon any particular part ofone of the photographic shadows of the foreign body, and the other needle upon a corresponding partin the second shadow. The pointwhere the threads cross and toucheach other will represent the positionof the part of the foreign bodychosen for location. A perpendicularis then dropped from the inter-section of the threads to the negativebelow, and a mark made where theperpendicular touches the distance of the spot thusmarked out from the cross wires ismeasured by a pair of operator is now in possession ofthe required measurements. If thedistances are 3 cm. and 1 cm., andthe depth from the crossing of thethreads to the plate 2| cm., then heknows that the foreign body hes at 2| cm. from the surface of the patients. Fig. 135.—Diagram to illustrate simple formulafor localising. (After Walsh.) 164 RADIOGKAPHY skin, at a distance of 3 cm. and 1 cm. from the cross wares, in a quadrantthat is easily determined by reference to the distinguishing mark placedthere when taking the double-exposure radiograph. Dawson Turner and others have pubhshed asimple formula for locahsing. Two radiographs aretaken on one plate by moving the tube a knowndistance. The distances are measured from tubeto plate (A), between the two positions of the tube(B), and between the two shadows on the photo-graphic plate (C). Let x equal the distance of theforeign body from the plate.
Size: 1520px × 1643px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, bookauthorknoxrobert18681928, bookcentury1900, bookdecade1910
