Notes

EArly CT only scanned Heads
Water filled tank- reduce dynamic range of radiation reaching the detectors
80x80 pixels
0100 ACTA scanner- auto computerized transverse axial scanner - NO WATER TANK
Whole body scanner - 1974 Dentist Robert Ledley
CT first to privide digital or indirect imaging. Xray direct or analog
5 generations of CT dependant upon tube to detector configuration and scanning motion
FIRST GEN
Neurologic, Translation/rotation(1deg) princible, pencil beam
EMI scanner 80x80pixel
SECOND GEN
Narrow fan beam, translate/rotate(10deg) config, 3-52 detectors= Average 30 detectors. Image acquisition 10-20 seconds/slice. Reconstruction >5min.
THIRD GEN
Rotate/Rotate config.Moved 360 around pt, 256-1000 detectors, Curved detector array, 0.5-10sec/image, Reduced construction time. Wide fan beam. No more horizontal movement. DRAWBACKS: tube/detector must stay in synch at all times. Miscalibrations or malfunctions=ring artifacts -very common
FOURTH GEN
Rotation/Fixed config-AKA rotation only, Detectors fixed within scanner 600-4800, only tube moved around pt., increase pt dose and cost., Wide fan beam. Acquisition 1sec reconstruction realtime to 2 sec. 3rd & 4th gen developed at same time both principles still used today & image quality is almost the same. Single or multi slice. Single= 1 image/revolution=longer reath holds and scan time. Multi slice/channel= multiple images with each revolution. 4 slice to 64 slice. 64+ slice in development now not used for medicine. Rare to acquire 4+ slice/ revolution on routine studies. More slices you acquire-the shorter the tube life
FIFTH GEN aka. Ultra fast CT , EBCT
Electron beam config, 1284 detectors, wide fan beam, Acquisition 50ms, no X-ray tube= electron gun replaces it, capable of 640mA. Used in cardiac imaging.

System components of CT Suite
GANTRY- donut shape, houses xray tube, slip rings generators and detector array. Xray tube ~30in space, Slip rings- allow tube to rotate 360 in cordless power supply manner. High voltage gen- allows energy to be produced at high voltage. Detector array- like IR 2 types scintillation (crystals and ceramic) or Ionization (nobel gas)
TABLE/COUCH - Wood or low density carbon, moves with exam, 300-600lbs,
COMPUTER - Converts radiation into electrical energy , 4 purposes: data acquisition (DAS) image reconstruction image/data storage image display,
OPERATOR CONSOLE, Where tech controls CT scanner
AUTOMATIC INJECTOR - infuse large amounts of contrast at constant rate, 2 basic injector types- High and low pressure*. 4ml/s - 40ml/s,
CARDIAC MONITORS- cardiac and vascular patients coronary arteries, ejection fraction of heart, EBCT or new 64 slice CT Scanners.




TECHNICAL ASPECTS
Pixel- signle squares or picture elements
Voxel- product of the pixel area and slice thickness.
Matrix - made up or many pixels arranged in a grid of rows and colums
FOV - Determines amount of data to be acquired and displayed on the monitor
Hounsfield units - numbers that are assigned to pixels to help represent tissue being imaged
RAW data - measurements of xray transmissions prior to its conversion to elecrical signal

CT number range - 2000, air is -1000, bone +1000

Slide 46 techincalterms window width window level spatial resolution

Reconstruction - performed by the mainframe CT computer
process by which electrical signals are measured and transformed into an image

Reformatting - performed by tech using the workstation computer, process of changing axial imagees into coronal and sagittal

Axial scanning - table moves, stops, and image is taxing, used on routine heads. Not common for abdominal or thoracic due to extended breath hold.
Helical / spiral scannning - continually moving patient through radiaition field. compared to as a spring because of resemblancele. Very common performed with most CT scans because of shorter scan time breath hold
CT FLuoroscopy newly emerging tool, not comon to many hospitals commonly used for biopsies or abscess drain procedure very similar to traditional fluoroscopy as it displays realtime imaging
orthoginal at right angles to
axial is X axis - cartesian plane
CAT stood for computerd Axial tomography no longer in use as we are able to view images in all 3 planes as well as 3d
MOST IMAGES ARE PERFORMED IN AXIAL PLANE
Coronal plane is defined as the anatomical plane orthogonal to the transverse and saggital planes. Gantry tilt 30 cephalid and caudal there is limited coronal capabilities. X/Z plane --- used for sinuses and Facial bones non traumatic

Coronal exams: C T L spine, angiogram, sinuses, facial bones, orbits, Cardiac studies.

Sagittal imaging plane - anatomical plane oriented parallel to the median plane of the human body- It is orthogonal to the transverse and coronal planes. Constructed by use of axial images. Y/Z plane


3d imaging uses MPR to include axial coronal and saggital reconstructions. Surface rendering - shaded surface rendering, Volume rendering.
Commonly performed using Maximum intensity Projection MIP -- used for angiograms

Volume rendering is used for tissue and muscle, vessels, vitual colonoscopy cardiadc imaging

Dose: moderate to high radiation diagnostic technique