110 MIDTERM

• Fluoroscopy is an imaging modality where the radiologist views a continuous image of the motion of internal structures while the x-ray tube is energized
• A spot film is a small static image on a small-format image receptor
• The two main areas of angiography are neuroradiology and vascular radiology, but they are now referred to as interventional radiology
• Angiography is for the visualization of vessels
• In fluoroscopy, the X-ray tube is usually under the patient couch
• In fluoroscopy, the image intensifier (or other image receptors) are set over the patient couch
• During fluoroscopy, the x-ray tube is operated at less than 5 mA
• The kVp of fluoroscopic imaging depends entirely on the section of the body that is being examined
• Automatic Brightness Control is a feature that allows the radiologist to select an image brightness level that is subsequently maintained automatically by varying the kVp, the mA, or sometimes both
• The principal advantage of image-intensified fluoroscopy over earlier types of fluoroscopy is increased image brightness
• Illumination levels are measured in units of lumen per square meter or lux
• Radiographs are visualized under illumination levels of 100 to 1000 lux; image-intensified fluoroscopy is performed at similar illumination levels
• The structures in the eye that are responsible for the sensation of vision are called rods and cones
• Light incident on the eye must first pass through the cornea, a transparent protective covering
• After passing through the cornea, light incident passes through the lens, where the light is focused onto the retina
• Between the cornea and the lens is the iris
• In the presence of bright lights, the iris contracts and allows only a small amount of light to enter
• In the presence of dim lights, the iris dilates and allows more light to enter
• When light arrives at the retina, it is detected by rods and cones
• The cones are concentrated at the center of the retina in an area called the fovea centralis
• The rods are most numerous on the periphery of the retina
• SENSITIVITY TO LIGHT

  Rods - more sensitive

  Cones - less sensitive
• THRESHOLD FOR VISION

  Rods - 2 lux

  Cones - 100 lux
• Cones are used primarily for daylight vision
• Daylight vision is also called photopic vision
• Rods are used for night vision
• Night vision is also called scotopic vision
• Cones perceive small objects much better than rods. This ability to perceive small detail is called visual acuity
• Cones are also much better at detecting differences in brightness levels. This property of vision is called contrast perception
• Cones perceive color, but rods are essentially colorblind
• The image intensifier raises illumination into the cone vision region, where visual acuity is greatest
• The brightness of the fluoroscopic image depends primarily on the anatomy, kVp and mA
• PREFERRED EXPOSURE FACTORS

  kVp - high

  mA - low
• THe glass or metal envelope provides structural support, but more importantly maintains a vacuum
• Rays that exit the patient interact with the input phosphor
• The input phosphor is cesium iodide (CsI)
• When an X-ray interacts with the input phosphor, its energy is converted into visible light
• The tightly packed cesium iodide crystals results in micro-light-pipes with little dispersion and improved spatial resolution
• After the input phosphor is the photocathode, which is bonded directly to the input phosphor with a thin, transparent adhesive layer
• The photocathode is a thin metal layer usually composed of cesium and antimony compounds that respond to photoemission