IR

1. DISCOVERY- 1895,Wilhelm Röntgen (or Roentgen), working in a darkened laboratory in Würzburg, Germany- Fluorescence , x-rays; very first Nobel Prize for Physics in 1901

2. Conventional Radiography (CR, Plain Films)

-Images produced through the use of ionizing radiation, i.e., the production of x-rays, but without added contrast material like barium or iodine, are called conventional radiographs or, more often, plain films or x-rays

-source = x-ray machine; recorder = film, cassette, or photosensitive plate; processor = chemicals or digital reader

-combination of ionizing radiation and light striking a photosensitive surface produces a latent image that is subsequently processed to become visible

-PACS system: picture archiving communications and storage- images from all modalities can be stored and retrieved

-advantages- quick, inexpensive, easy to obtain

-disadvantages- reliance on ionizing radiation, limited range of densities; cancer potential

-common uses- cxr, abdominal films, initial skeletal system imaging for fractures or arthritis

-the five basic densities- air, fat, fluid or soft tissue, calcium, metal

-air: absorbs the least xrays and appears the blackest; decreased density, increased lucency

-fat: gray, somewhat blacker than soft tissue

-calcium: the most dense/ most opaque naturally occurring material eg bones, absorbs most xrays

-metal: usually absorbs all the xrays and appears the whitest

3. Computed Tomography (CT, CAT Scans)

-first introduced in the 1970s

-a gantry containing a rotating x-ray beam and multiple detectors in various arrays (which themselves are rotating continuously around the patient), along with sophisticated computer algorithms to process the data, a complete 3D set of images can be obtained

- CT image composed of pixels

-CT number from -1000 to +1000 Hounsfield units- after Godfrey Hounsfield; varies according to the density of tissue scanned and is a measure of how much xray beam is absorbed

-water = 0 hounsfield number; air = -1000; fat = ~-40 to -120; soft tissue = ~+20 to +100; bone = ~ +400 to +600; metal = ~+1000 or higher

-window = preselected range of Hounsfield numbers to best demonstrate the tissues being studied

-denser substances = higher CT numbers = increased attenuation = whiter appearance on CT

-post-processing allows for additional manipulation of the raw data to best demonstrate the abnormality without repeating a study or reexposing the patient

-three standard imaging planes in cross-sectional imaging: axial/ transverse, coronal, and sagittal

-axial/ transverse: divide body into upper and lower sections

-coronal/ frontal plane: divides the body into anterior and posterior sections

-sagittal plane: divides the body into right and left sections; midsagittal, parasagittal

-CT advantages: markedly expands the gray scale, markedly reduce any overlapping of structures that may obscure underlying pathology, patients with implantable devices contra to MRI can safely use CT, widely available

-CT disadvantages: utilizes ionizing radiation, expensive scanner, large space, sophisticated computer processing software

-CT is the cornerstone of cross-sectional imaging; can display any body part in any plane including 3D rendering in colour