or research; these include betatrons, linear accelerators (linacs), and synchrotrons. for gamma rays, radioactive sources such as 192ir, 60co, or 137cs are used. grid an anti-scatter grid may be placed between the patient and the detector to reduce the quantity of scattered x-rays that reach the detector. this improves the contrast resolution of the image, but also increases radiation exposure for the patient. detectors detectors can be divided into two major categories: imaging detectors (such as photographic plates and x-ray film (photographic film), now mostly replaced by various digitizing devices like image plates or flat panel detectors) and dose measurement devices (such as ionization chambers, geiger counters, and dosimeters used to measure the local radiation exposure, dose, and/or dose rate, for example, for verifying that radiation protection equipment and procedures are effective on an ongoing basis). side markers a radiopaque anatomical side marker is added to each image. for example, if the patient has their right hand x-rayed, the radiographer includes a radiopaque "r" marker within the field of the x-ray beam as an indicator of which hand has been imaged. if a physical marker is not included, the radiographer may add the correct side marker later as part of digital post-processing. image intensifiers and array detectors main article: x-ray image intensifier as an alternative to x-ray detectors, image intensifiers are analog devices that readily convert the acquired x-ray image into one visible on a video screen. this device is made of a vacuum tube with a wide input surface coated on the inside with caesium iodide (csi). when hit by x-rays material phosphors which causes the photocathode adjacent to it to emit electrons. these electron are then focus using electron lenses inside the intensifier to an output screen coated with phosphorescent materials. the image from the output can then be recorded via a camera and displayed. digital devices known as array detectors are becoming more common in fluoroscopy. these devices are made of discrete pixelated detectors known as thin-film transistors (tft) which can either work indirectly by using photo detectors that detect light emitted from a scintillator material such as csi, or directly by capturing the electrons produced when the x-rays hit the detector. direct detector do not tend to experience the blurring or spreading effect caused by phosphorescent scintillators of or film screens since the detectors are activated directly by x-ray photons. dual-energy dual-energy radiography is where images are acquired using two separate tube voltages. this is the standard method for bone densitometry. it is also used in ct pulmonary angiography to decrease the required dose of iodinated contrast. history further information: x-ray § history taking an x-ray image with early crookes tube apparatus, late 1800s radiography's origins and fluoroscopy's origins can both be traced to 8 november 1895, when german physics professor wilhelm conrad röntgen discovered the x-ray and noted that, while it could pass through human tissue, it could not pass through bone or metal. röntgen referred to the radiation as "x", to indicate that it was an unknown type of radiation. he received the first nobel prize in physics for his discovery. there are conflicting accounts of his discovery because röntgen had his lab notes burned after his death, but this is a likely reconstruction by his biographers: röntgen was investigating cathode rays using a fluorescent screen painted with barium platinocyanide and a crookes tube which he had wrapped in black cardboard to shield its fluorescent glow. he noticed a faint green glow from the screen, about 1 metre away. röntgen realized some invisible rays coming from the tube were passing through the cardboard to make the screen glow: they were passing through an opaque object to affect the film behind it. the first radiograph röntgen discovered x-rays' medical use when he made a picture of his wife's hand on a photographic plate formed due to x-rays. the photograph of his wife's hand was the first ever photograph of a human body part using x-rays. when she saw the picture, she said, "i have seen my death." the first use of x-rays under clinical conditions was by john hall-edwards in birmingham, england, on 11 january 1896, when he radiographed a needle stuck in the hand of an associate. on 14 february 1896, hall-edwards also became the first to use x-rays in a surgical operation. the united states saw its first medical x-ray obtained using a discharge tube of ivan pulyui's design. in january 1896, on reading of röntgen's discovery, frank austin of dartmouth college tested all of the discharge tubes in the physics laboratory and found that only the pulyui tube produced x-rays. this was a result of pulyui's inclusion of an oblique "target" of mica, used for holding samples of fluorescent material, within the tube. on 3 february 1896 gilman frost, professor of medicine at the college, and his brother edwin frost, professor of physics, exposed the wrist of eddie mccarthy, whom gilman had treated some weeks earlier for a fracture, to the x-rays and collected the resulting image of the broken bone on gelatin photographic plates obtained from howard langill, a local photographer also interested in röntgen's work. 1897 sciagraph (x-ray photograph) of pelophylax lessonae (then rana esculenta), from james green & james h. gardiner's "sciagraphs of british batrachians and reptiles" x-rays were put to diagnostic use very early; for example, alan archibald campbell-swinton opened a radiographic laboratory in the united kingdom in 1896, before the dangers of ionizing radiation were discovered. indeed, marie curie pushed for radiography to be used to treat wounded soldiers in world war i. initially, many kinds of staff conducted radiography in hospitals, including physicists, photographers, physicians, nurses, and engineers. the medical speciality of radiology grew up over many years around the new technology. when new diagnostic tests were developed, it was natural for the radiographers to be trained in and to adopt this new technology. radiographers now perform fluoroscopy, computed tomography, mammography, ultrasound, nuclear medicine and magnetic resonance imaging as well. although a nonspecialist dictionary might define radiography quite narrowly as "taking x-ray images", this has long been only part of the work of "x-ray departments", radiographers, and radiologists. initially, radiographs were known as roentgenograms, while skiagrapher (from the ancient greek words for "shadow" and "writer") was used until about 1918 to mean radiographer. the japanese term for the radiograph, rentogen (レントゲン), shares its etymology with the original english term.