CT Generations PDF

Generations of CT  Classification of computed tomography (CT) based upon: 1. arrangement of components and mechanical motion required to collect data. 2. type of beam that emerge from x-ray tube. 3. number of detectors. 4. time of image scan. 5. uses , advantages and disadvantages of generations....

Generations of CT  Classification of computed tomography (CT) based upon: 1. arrangement of components and mechanical motion required to collect data. 2. type of beam that emerge from x-ray tube. 3. number of detectors. 4. time of image scan. 5. uses , advantages and disadvantages of generations. 19/01/1442 Dr. Lubna Dr. Bager 3 1st CT Generation First Parallel beam, single detector, Translate-Rotate 19/01/1442 Dr. Lubna Dr. Bager 4 1st generation Scanner  Translate-rotate configuration.  After one translation the tube and detector rotate by 1 degree and translate again to collect readings from different direction.  This repeated for 180 degrees around the patient, this method of scanning is referred to as rectilinear pencil beam scanning (Fig). 19/01/1442 Dr. Lubna Dr. Bager 5 Beam Translation  Tube/detector translates left to right  Entire assembly rotates 1o to right  Tube/detector translates right to left X-ray Tube Detector 19/01/1442 Dr. Lubna Dr. Bager 6 1st generation Scanner Cont..  Tube produced a finely collimated beam or pencil beam.  Single or double detector were placed opposite the tube for radiation detection.  5 min to gather enough information for one slice.  Head imager only, not capable of body imaging. 19/01/1442 Dr. Lubna Dr. Bager 7 1st generation Scanner 19/01/1442 Dr. Lubna Dr. Bager 8 1st generation Scanner 19/01/1442 Dr. Lubna Dr. Bager 9 2nd generation scanner • Translate- rotate configuration. • After one translation tube and detector array rotate by larger increments and translate again. • This process is repeated for 180 degrees and is referred to as rectilinear multiple pencil beam scanning (Fig.). 19/01/1442 Dr. Lubna Dr. Bager 10 2nd generation scanner cont.. • Fan shaped beam. • Linear Detector array (about 30 detectors). • Multiple image projection per translation and the larger rotational increments and increased number of detectors result in shorter scan time. • 30 sec scan time. • In general, the time decrease is inversely proportional to the number of detectors. The more detectors, the shorter the total scan time. • Head and body imager. 19/01/1442 Dr. Lubna Dr. Bager 11 2nd Generation CT 10o  arc beam allowed 10 degree rotational increments  scan times reduced 19/01/1442 Dr. Lubna Dr. Bager 12 2nd CT Generation 19/01/1442 Dr. Lubna Dr. Bager 13 3rd generation scanner • Rotate – rotate configuration. • Fan shaped-beam. • This motion is referred to as continuously rotating fan beam scanning • Curvilinear detector array. • The curvilinear detector array provides constant distance between source and each detectors resulting in good image reconstruction. 19/01/1442 Dr. Lubna Dr. Bager 14 3rd generation scanner 19/01/1442 Dr. Lubna Dr. Bager 15 3rd Generation CT Patient 19/01/1442 Dr. Lubna Dr. Bager 16 3rd generation scanner Cont… • 1 sec. scan time. • Disadvantage: ring artifacts  If one detector fails, a ring artifact appears. 19/01/1442 Dr. Lubna Dr. Bager 17 3rd generation scanner 19/01/1442 Dr. Lubna Dr. Bager 18 4th generation scanner  Fourth generation was developed to suppress ring artifacts.  Rotate-stationary configuration.  Fan shaped beam.  Circular Detector array contain several thousand individual detectors (8000).  Patient dose may be somewhat higher with 4th generation because of inter space between detectors.  less than 1sec scan time. 19/01/1442 Dr. Lubna Dr. Bager 19 4th generation Scanner 19/01/1442 Dr. Lubna Dr. Bager 20 4th Generation (Non-spiral) CT  Tube rotates once around patient  Table stationary  data for one slice collected  Table increments one slice thickness  Repeat  Tube rotates opposite direction 19/01/1442 Dr. Lubna Dr. Bager 21 5th -Generation Scanner • High speed scanner, acquire scan data in milliseconds. • Two such scanners are the electron beam scanner (EBCT) and the dynamic spatial reconstruction (DSR) scanner. • DSR scanner is a highly specialized 5th -generation, high-speed scanner capable of producing dynamic three-dimensional (3D) images of volumes of the patient. 19/01/1442 Dr. Lubna Dr. Bager 22 5th -Generation Scanner - Cont • EBCT was first described by Douglas Boyd - 1980 • EBCT is applied first to cardiac imaging. • EBCT is based on electron beam technology and no x-ray tube is used. • Electron Beam CT has no moving parts. • stationary/stationary geometry 19/01/1442 Dr. Lubna Dr. Bager 23  The overall goal of the EBCT scanner is to produced high-resolution images of moving organs that are free of artifacts caused by motions.  The scanner performs this task well because its design enable it to acquire CT data 10 times faster than conventional CT scanners 19/01/1442 Dr. Lubna Dr. Bager 24 5th -Generation Scanner - Cont • EBCT has electron gun that generate electrons. • Theses electrons are accelerated, focused and deflected to strike 1 – 4 tungsten target rings in rapid sequence producing x-ray. • Collimators shape x-ray into a fan beam that pass through the patients to strike on stationary array of detectors 19/01/1442 Dr. Lubna Dr. Bager 25 5th -Generation Scanner - Cont • The detector array consist of two separate rings, which allows for either two image slices when one target ring is used or 8 images when all 4 target rings are used in sequence. • covering up to 8 cm of body tissues without moving the patient through the scanner. 19/01/1442 Dr. Lubna Dr. Bager 26 5th -Generation Scanner - Cont  This unique function, along with a real-time ECG cardiac triggering provides for capabilities for blood flow analysis and cine work.  The unit provides for critical diagnostic information when imaging cardiac, pediatric, trauma, and geriatric patients where acquisition speed is highly essential. 19/01/1442 Dr. Lubna Dr. Bager 27 Mode of Operation in EBCT  Single slice mode:  Is based on scanning one of the four tungsten target ring using collimation  Multislice mode:  Is based on scanning all four tungsten target rings using two detectors arrays to generate 2, 4, 6 or 8 scans with the patient immobilized 19/01/1442 Dr. Lubna Dr. Bager 28 Comparison between EBCT and conventional CT 1. The EBCT scanner is based on electron beam technology and no x-ray tube is used. 2. There is no mechanical motion of the components. 3. The acquisition geometry of the EBCT scanner is different compare with conventional CT. (stationary/stationary geometry) 4. EBCT acquire CT data 10 times faster than conventional CT scanners 19/01/1442 Dr. Lubna Dr. Bager 29 Clinical application of the EBCT Scanner  Left and right ventricular function  Valve motion  Cardiac wall thickening  Myocardial perfusion  Coronary arteries  pediatric studies  trauma studies 19/01/1442 Dr. Lubna Dr. Bager 30