Exam #2 Summary
CT techs enter intructions into the system console
high voltage generator, gantry operations, pt table
Pencil beam
highly-collimated thin x-ray beam, used by HU in the first generation CT scanner, translate-rotate, tube rotates one degree
Miscentering
in either direction (x or y) out of field artifact, proper centering is imperative when using automatic exposure controls
Scout image
initial image acquired during a CT exam
6th generation scanners
spiral/helical, detector array
Rotating fan beam within a circular detector array
wide fan beam geometry, x-ray tube rotating in a circular path within a stationary, circular detector array, very short scan times, image reconstruction algorithm is at the detector opposed to the x-ray tube
3 major pieces of equipment
1) imaging system consisting of gantry and pt table 2) computer- processing the CT image data 3) operators console- controls the entire imaging process and displays the final image
Localizer scans
essential for every CT scan, used to determine the appropriate image center and DFOV
Cine
a way of view CT images in a movie-like format and is typically performed retrospectively, usually obtained by overlapping thin image set
Step and shoot scanning
axial scanning, x-ray tube rotates around the pt and acquires an image, table then moves a little further into the gantry, the x-ray tube rotates again the pt and acquiring another image, also called axial or conventional scanning
Misregistration
causued by pt breathing,
Spiral helical geometry
continuous rotation scanners, data acquistion collected in volumes rather than individual slices, based on slip ring technology
pitch
defined as table distance traveled in one 360° gantry rotation divided by beam collimation
Z-axis (axial plane)
divides the body into superior and inferior parts
Y-axis (coronal plane)
divides the pt body into anterior and posterior sections
X-axis (sagittal plane)
divides the pt lying on the table into right and left sides
Rotating fan beam outside a nutating detector ring
fan beam geometry, rotates outside of the detector ring, detector ring tilts during data collection, currently not manufactured
Second generation scanner
fan beam or multiple pencil beam, only takes around 20 seconds to 3.5 minutes per scan, translate-rotate, increased number of detectors,
Third generation scanner
fan beam, 360 degree rotation, curved detector array, continuously rotation fan beam scanning
7th generation scanners
flat-panel digital detectors, MDCT
Fan beam
introduced in 2nd generation scanner, narrow fan-like shape of about 10 degrees, 2nd generation scanners had a row of about 30 detectors, translate-rotate, shortened scan time around 20 seconds, 2nd generation scanners 10 times faster than 1st
Beam geometry
pencil beam, fan beam, cone beam
First generation scanners
pencil beam, translate rotate, 2 detectors were used, complete exam took 5 minutes, once pass was complete tube would rotate 1 degree, 180 degree rotation around pt
operator console controls
pitch, scan field of view, display field of view, annotation, scout, region of interest, window width, window level
cone beam geometry
produces multiple slices per revolution of the x-ray tube and detectors, requires algorithms to reconstruct images, utilized in scanners capable of imaging 16 or greater slices per 360 degree rotation
categorization of CT equipment
scanning geometry, scanning motion, and number of detectors
Cone beam
third generation scanner, 800+ detectors, commonly used today,
Fourth generation scanner
two types of beam geometries rotation fan beam within a circular detector array and rotating fan beam outside a nutating detector ring, rotate-stationary
Fifth generation scanners
ultra-fast scanner, EBCT, developed for the heart and circulation, goal is to produce high resolution images, curved detector