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