A CT scan or computed tomography scan makes use of computer-processed combinations of many X-ray measurements taken from different angles to produce cross-sectional images of specific areas of a scanned object, allowing the user to see inside the object without cutting. The 1979 Nobel Prize in Physiology or Medicine was awarded jointly to Allan M. Cormack and Godfrey N. Hounsfield "for the development of computer assisted tomography."Digital geometry processing is used to further generate a three-dimensional volume of the inside of the object from a small series of two-dimensional radiographic images taken around a single axis of rotation. Medical imaging is the most common application of X-ray CT, its cross-sectional images are used for diagnostic and therapeutic purposes in various medical disciplines. The rest of this article discusses medical-imaging X-ray CT; the term "computed tomography" is used to refer to X-ray CT, because it is the most known form. But, many other types of CT exist, such as positron emission tomography and single-photon emission computed tomography.
X-ray tomography, a predecessor of CT, is one form of radiography, along with many other forms of tomographic and non-tomographic radiography. CT produces data that can be manipulated in order to demonstrate various bodily structures based on their ability to absorb the X-ray beam. Although the images generated were in the axial or transverse plane, perpendicular to the long axis of the body, modern scanners allow this volume of data to be reformatted in various planes or as volumetric representations of structures. Although most common in medicine, CT is used in other fields, such as nondestructive materials testing. Another example is archaeological uses such as imaging the contents of ceramics. Individuals responsible for performing CT exams are called radiographers or radiologic technologists. Use of CT has increased over the last two decades in many countries. An estimated 72 million scans were performed in the United States in 2007 and more than 80 million a year in 2015. One study estimated that as many as 0.4% of current cancers in the United States are due to CTs performed in the past and that this may increase to as high as 1.5 to 2% with 2007 rates of CT use.
Lower radiation doses are used in many areas, such as in the investigation of renal colic. Side effects from intravenous contrast used in some types of studies include the possibility of exacerbating kidney problems in the setting of pre-existing kidney disease. Since its introduction in the 1970s, CT has become an important tool in medical imaging to supplement X-rays and medical ultrasonography, it has more been used for preventive medicine or screening for disease, for example CT colonography for people with a high risk of colon cancer, or full-motion heart scans for people with high risk of heart disease. A number of institutions offer full-body scans for the general population although this practice goes against the advice and official position of many professional organizations in the field due to the radiation dose applied. CT scanning of the head is used to detect infarction, calcifications and bone trauma. Of the above, hypodense structures can indicate edema and infarction, hyperdense structures indicate calcifications and haemorrhage and bone trauma can be seen as disjunction in bone windows.
Tumors can be detected by the swelling and anatomical distortion they cause, or by surrounding edema. Ambulances equipped with small bore multi-slice CT scanners respond to cases involving stroke or head trauma. CT scanning of the head is used in CT-guided stereotactic surgery and radiosurgery for treatment of intracranial tumors, arteriovenous malformations, other surgically treatable conditions using a device known as the N-localizer. Magnetic resonance imaging of the head provides superior information as compared to CT scans when seeking information about headache to confirm a diagnosis of neoplasm, vascular disease, posterior cranial fossa lesions, cervicomedullary lesions, or intracranial pressure disorders, it does not carry the risks of exposing the patient to ionizing radiation. CT scans may be used to diagnose headache when neuroimaging is indicated and MRI is not available, or in emergency settings when hemorrhage, stroke, or traumatic brain injury are suspected. In emergency situations, when a head injury is minor as determined by a physician's evaluation and based on established guidelines, CT of the head should be avoided for adults and delayed pending clinical observation in the emergency department for children.
Contrast CT is the initial study of choice for neck masses in adults. CT of the thyroid plays an important role in the evaluation of thyroid cancer. CT scans incidentally find thyroid abnormalities, thereby becomes the first investigation modality. A CT scan can be used for detecting both acute and chronic changes in the lung parenchyma, the tissue of the lungs, it is relevant here because normal two-dimensional X-rays do not show such defects. A variety of techniques are used, depending on the suspected abnormality. For evaluation of chronic interstitial processes such as emphysema, fibrosis, thin sections with high spatial frequency reconstructions are used; this special technique is called high resolution CT that produces a
The D-17B computer was used in the Minuteman I NS-1OQ missile guidance system. The complete guidance system contained a D-17B computer, the associated stable platform, power supplies; the D-17B weighed 62 pounds, contained 1,521 transistors, 6,282 diodes, 1,116 capacitors, 504 resistors. These components were mounted on double copper-clad, gold-plated, glass fiber laminate circuit boards. There were 75 of these circuit boards and each one was coated with a flexible polyurethane compound for moisture and vibration protection; the high degree of reliability and ruggedness of the computer were driven by the strict requirements of the weapons system. High reliability was required of the D-17B, it controlled a key weapon. Reliability of the D-17B was achieved through the use of solid-state electronics and a simple design. Simpler DRL logic was used extensively. In the late 1950s and early 1960s, when the D-17B was designed, transistors lacked today's reliability. DTL provided, either gain or inversion.
Reliability was enhanced by the rotating-disk memory with non-destructive readout. In actual real-time situations, Minuteman missiles achieved a mean time between failures of over 5.5 years. The Soviets could use vacuum tubes in their guidance systems; the US planners had to choose either to develop solid state guidance systems or consider the additional cost and time delay of developing larger rockets. Minuteman I D-17B computer specifications Year: 1962 The D17B is a synchronous serial general-purpose digital computer. Manufacturer: Autonetics Division of North American Aviation Applications: Guidance and control of the Minuteman I ICBM. Programming and numerical system: Number system: Binary, fixed point, 2's complement Logic levels: 0 or False, 0V. Execution times: Add: 78 1/8 Multiply: 546 7/8 or 1,015 5/8 Divide: Clock channel: 345.6 Hz Addressing: Direct addressing of entire memory Two-address and three-address instructionsMemory: Word length: 24 plus 5 timing Type: Ferrous-oxide-coated NDRO disk Cycle time: 78 1/8 Capacity: 5,454 or 2,727 Input/output: Input lines: 48 digital Output lines: 28 digital 12 analog 3 pulse Program: 800 5-bit char/sInstruction word format: +--------+--------+------+--------+---------+--------+--------+ | TP | T24 21 | 20 | 19 13 | 12 8 | 7 1 | 0 | +--------+--------+------+--------+---------+--------+--------+ | Timing | OP | Flag | Next | Channel | Sector | Timing | | | | | Inst.
| | | | | | | | Sector | | | | +--------+--------+------+--------+---------+--------+--------+ Registers: Phase and voltage output registersArithmetic unit: Add: 78 µs Multiply: 1,016 µsConstruction: transistor-diode logic is used. Timing: Synchronous Operation: SequentialInput 48 digital lines 26 specialized incremental inputs -Medium- -Speed- Paper/Mylar Tape 600 chars/sec Keyboard Manual Typewriter Manual OUTPUT -Medium- -Speed- Printer Character 78.5–2,433 ms Phase - Voltage 28 digital lines 12 analog lines 13 pulse lines 25,600 word/s maximum I/O transfer rate Physical characteristics Dimensions: 20 in high, 29 in diameter, 5 in deep Power: 28 VDC at 25 A Circuits: DRL and DTL Weight: 62 pounds Construction: Double copper clad, gold plated, glass fiber laminate, flexible polyurethane-coated circuit boardsSoftware: Minimal delay coding using machine language Modular special-purpose subroutinesReliability: 5.5 years MTBF Checking features: Parity on fill and on character outputs Power, space and site preparation Power, computer: 0.25 kW Air conditioner: Closed system Volume, computer: 1.55 cu ft Weight, computer: 70 lb Designed to fit in cylindrical guidance package.
The word length for this computer Is 27 bits. The remaining 3 bits are synchronizing bits; the memory storage capability consists of a 6000 rpm magnetic disk with a storage capacity of 2985 words of which 2728 are addressable. The contents of memory include 20 cold-storage channels of 128 sectors each, a hot-storage channel of 128 sectors, four rapid access loops of 1, 4, 8, 16 words four 1-word arithmetic loops, a two 4-word input buffer input loops; the outputs that can be realized from the D-17B computer are binary, single character, phase register status and voltage outputs. Binary outputs are computer generated levels of − 1 available on the binary output lines. D-17B Instruction Repertoire Numeric Code Code Description ------------ ---- ----------- 00 20, s
Anne Shirley was an American actress. Beginning her career as a child actress under the stage name Dawn O'Day, she adopted the stage name of Anne Shirley, after playing the title character in the film adaptation of Anne of Green Gables in 1934,after which she achieved a successful career in supporting roles. Among her films is Stella Dallas, for which she was nominated for an Academy Award for Best Supporting Actress. Although Shirley left the acting profession in 1944, at the age of 26, she remained in Los Angeles, where she died at the age of 75. Born in New York City as a baby she began modeling, made her film debut with a featured role in 1922's Moonshine Valley. Shirley began acting at the age of five as the live action "Alice" in Walt Disney's pre-Mickey Mouse silent animated series "Alice in Cartoonland", she had a successful child star career in Pre-Code movies, appearing in such films as Liliom, Tom Mix's Riders of the Purple Sage, So Big, Three on a Match and Rasputin and the Empress.
In 1934 she starred as the character of Anne Shirley in Anne of Green Gables, took that character's name as her stage name. After adopting the name Anne Shirley, she starred in Steamboat'Round the Bend, Make Way for a Lady and Stella Dallas, for which she was nominated for the Academy Award for Best Supporting Actress. Roles were in such movies as Vigil in the Night, Anne of Windy Poplars, The Devil and Daniel Webster and Murder, My Sweet, her final film. Of Shirley's portrayal in Saturday's Children, The New York Times commented that she "endows the little wife with heroic integrity and strength of character." Shirley married actor John Payne on August 1937, in Montecito, California. They had former actress Julie Payne, her second husband was screenwriter Adrian Scott. When he was blacklisted and decided to move the family to Europe, at the last minute she wrote him a "Dear John" letter saying she'd rather stay behind and divorce him, her third husband was nephew of Marion Davies. They had a son named Daniel Lederer.
Shirley had a brief relationship with younger western star Rory Calhoun and another with French movie star Jean-Pierre Aumont. Shirley was cremated. For her contributions to the motion picture industry, she has a star on the Hollywood Walk of Fame at 7020 Hollywood Blvd. Anne Shirley on IMDb Anne Shirley at the AFI Catalog of Feature Films Anne Shirley at the Turner Classic Movies database Anne Shirley at AllMovie Anne Shirley at Find a Grave Anne Shirley at Virtual History