Sir Godfrey N. Hounsfield , DSc, the father of computed tomography, died on August 12, 2004 at the age of 84. He was awarded the Nobel Prize in Physiology or Medicine for 1979 along with Allan M. Cormack , a South African-born naturalized American physicist, for the “development of computer assisted tomography, a revolutionary radiological method, particularly for the investigation of diseases of the nervous system.”
Hounsfield’s name is immortalised in the Hounsfield units , a quantitative scale used to describe the brightness of tomograms ( radiodensity ). He left his money to fund engineering research and scholarships. He died in August 2004 at the age of 84 from a chronic and progressive lung disease, spending his last years in a nursing home. He was unmarried and unattached, and had no children.
Prototype CT Scanner Hounsfield built a prototype head scanner and tested it first on a preserved human brain , then on a fresh cow brain from a butcher shop, and later on himself. In September 1971 , CT scanning was introduced into medical practice with a successful scan on a cerebral cyst patient at Atkinson Morley's Hospital in Wimbledon, London , United Kingdom . In 1975 , Hounsfield built a whole-body scanner.
EARLY EXPERIMENTS In his initial experiments, Hounsfield used a gamma source rather than an x-ray tube, because the energy distribution of gamma radiation was more uniform It took nine days to acquire image data and 2 and a half hours to reconstruct the image. Once he replaced the gamma ray with an x-ray tube the scan time was reduced to 9 hours.
Tomography Tomography otherwise known as body section radiography, planigraphy, laminography or stratigraphy, is the process of using motion of the X-ray focal spot and image receptor (e.g. film) in generating radiographic images where object detail from only one plane or region remains in sharp focus
ZONOGRAPHY –ANGLE <10 DEG Zonography - a form of tomography where the tomographic angle is small, on the order of 10, resulting in a thick plane of focus. The technique is sometimes used to better delineate suspected pathology.
PANTOMOGRAPHY- Panorex Panoramic radiography for obtaining radiographs of the maxillary and mandibular dental arches and their associated structures.
AUTOTOMOGRAPHY A method of body-section radiography involving movement of the patient instead of the x-ray tube.
Instructional commands initiated by the technologist about pt. Specific imaging parameters, post processing & Archiving. Image Reconstruction Commands translated into machine language Timing/operation of table, gantry, high volt. Generator.These are electrical signals Digital to Analog (continuous, wave form) Attenuation Information In the form of tiny little electrical signals Amplified signals are sampled and then digitized by the analog-to-digital converter Image Creation
The raw data collected from measured attenuation information must be further processed (reconstructed) in the scanners array processor. Most CT systems today use a reconstruction method called filtered back projection .
In mathematics , computing , linguistics , and related disciplines, an algorithm is a finite list of well-defined instructions for accomplishing some task that, given an initial state, will proceed through a well-defined series of successive states, eventually terminating in an end-state.
EBCT To achieve shorter image acquisition times than conventional mechanical CT, especially for cardiac and pediatric imaging, Electron Beam CT (EBCT) was introduced in 1984 . EBCT provides image acquisition times down to 100msec that become possible with a non-mechanical movement of the X-ray source and a stationary detector array. For cardiac scanning, the heart is covered with prospectively ECG-triggered sequential scans. As EBCT is also restricted to single-slice acquisition for ECG-triggered scans examination times may still be beyond a single breath-hold. Typical scan times are 30 to 40 seconds for a 12cm volume.
Spiral/Helical scanners use slip ring technology to allow the tube to make continuous rotations around the patient while the patient simultaneously moves into the gantry so a volume of tissue may be scanned in one breath hold
Computerized tomographic angiography, also called CT angiography or CTA, is a test that combines the technology of a conventional CT scan with that of traditional angiography to create detailed images of the blood vessels in the body.
Based on a combination of spiral CT images and 3-D reconstruction techniques, virtual colonoscopy can detect most polyps of clinically significant size and differentiate between polyps and complex folds.
A dual-purpose imaging device, PET/CT is literally the combination of PET (positron emission tomography) and CT (computed tomography) imaging techniques within a single machine. The individual scans, which are taken virtually simultaneously, can be presented separately or as a single, overlapping, or "fused" image. The two techniques present different types of information about the human body: PET shows metabolic or chemical activity in the body; CT shows the body's anatomical structures. For example, a PET scan would highlight a tumor's increased glucose consumption, while a CT scan would reveal its physical mass.
Static detectors all round gantry (up to 4800 on a single ring)
Only tube rotates
Avoids ring artifact problems of 3rd generation scanners
Comparison Schematic illustration of different generations of X-ray CT scan geometries. Solid arrows indicate movements during data collection, dashed arrows indicate movement between sequences of data collection. The solid lines passing from the sources to the detectors are ray paths, and each set of solid lines from a single angular orientation constitutes a view. These illustrations show the source and detectors moving around a stationary object, as is the case with medical scanners. The motion is relative, however, and in many industrial scanners the object moves while the source and detectors are stationary. In all cases, the axis of rotation is the center of the circle. A . First-generation, translate-rotate pencil beam geometry. B . Second-generation, translate-rotate fan beam geometry. C . Third-generation, rotate-only geometry. D . Third-generation offset-mode geometry.