Scanner Generations + CT Components

Data Acquisition Concepts

What are the 2 elements of data acquisition?

beam geometry + components

What term(s) define the size, shape, motion and path of the x-ray beam?

beam geometry

What term(s) define the physical devices that shape and define the x-ray beam, measure transmission and convert information into digital data?

components

What term(s) define the portion of the beam that falls onto the detector? 

ray 

What term(s) define the collection of rays in 1 translation across an object?

view 

What term(s) define a linear movement of the tube and detector across the patient?

translation 

What term(s) define the electrical signal/the signature of attenuation generated by the detector? 

profile 

What term(s) define the collection of views transmitted for measurement?

data sample

What are the 3 primary types of data acquisition geometries?

parallel beam, fan beam, spiral/helical

What is another name for the parallel beam?

pencil/thin beam

What does the parallel beam consist of?

one tube + one detector

What does the fan beam consist of?

one tube + one row of detectors

What principle did both the 1st and 2nd generations scanners use?

translate-rotate

For the 1st generation scanner, how much did the tube and detector rotate per translation, and what was the total degree of rotation?

1 degree; 180 degrees

For the 2nd generation scanner, how much did the tube and detector rotate per translation, and what was the total degree of rotation?

5 degrees; 180 degrees 

Which generation of scanners marks the 1st of large historical advancements in CT technology? 

3rd generation 

What type of geometry did the 2nd, 3rd and 4th generation of scanners utilize? 

fan beam 

How were the detectors arranged in the 3rd generation scanner? 

curved-detector array; detectors were angled away from tube, allowing them to perform as a grid too 

How wide was the beam in the 3rd generation scanner?

30-40 degrees wide

What was the total degree of rotation for a 3rd generation scanner?

360 degree

What type of artifacts could be found in 3rd generation scanners due to the malfunction of a single detector?

rings

What does pre-patient collimation do?

determine slice thickness + decreases dose

What 2 beam geometries did the 4th generation scanner have?

rotating fan beam w/ circular detector array, rotating fan beam outside nutating detector ring

What type of principle did the 3rd generation employ?

rotate-rotate; continuous rotation

What type of principle did the 4th generation employ?

rotate-only

What was a downside to the 4th gen using a rotate-only principle?

overscanning

What type of scanners/geometry followed the 4th generation?

multi-slice; spiral/helical geometry

What type of technology made spiral/helical geometry possible?

slip rings

What is the 5th generation scanners also known as?

EBCT: electron beam CT

What was the EBCT intended for? 

high-speed scanning of heart + circulation, producing high-resolution images w/o motion artifacts

Did the EBCT involve any rotation of the tube and detectors?

nope! no mechanical motion

What did the EBCT replace a typical x-ray gun with?

electron beam gun

What does an electron beam gun do?

accelerated + focused + deflected electrons onto electromagnetic coil, directing them toward a tungsten target 

What were tungsten targets also known as?

target tracks

How many detectors did the first and second ring of a target track in the EBCT have?

864, 432

How many continuous images could the EBCT simultaneously capture with 4 target tracks?

4

How much faster does the EBCT obtain data compared to a conventional scanner?

10x

What type of scanner marked the 6th generation of CT scanners? 

DSCT: dual source CT 

What was a DSCT composed of?

2 sets of x-ray tubes and detectors

By how many degrees were the pairs of x-ray tubes and detectors in a DSCT offset to? 

90-95 degrees 

What were DSCT scanners meant to image?

cardiac imaging

What type of resolution could a DSCT scanner improve?

temporal

What type of geometry is used in the 7th generation of scanners?

cone-beam

What type of detectors are used in the 7th generation of scanners?

flat-panel digital

What type of array is used in the 7th generation of scanners? 

CsI scintillator w/ amorphous silicon thin-film transistor 

How was the spatial resolution of an image taken by a 7th generation scanner?

excellent

How was the contrast resolution of an image taken by a 7th generation scanner?

poor 

What can the 7th generation scanner be used for?

angiography or breast imaging

What technology aimed to render long, high-tension cables obsolete, instead using electromechanical devices with circular electrical-conducive rings + brushes?

slip ring

How does a slip ring transmit electrical energy? 

across rotating interface 

What 2 designs is the slip ring based off of?

disk (conductive ring) and cylinder (collection of conductive ring aligned on axis of rotation)

What is the most common type of slip ring?

low voltage

What are 3 advantages in using a slip ring?

continuous x-ray tube rotation, capacity for continuous acquisition protocols, elimination of start-stop process 

What type of x-ray tubes were present in the 1st and 2nd generation scanners?

fixed anode w/ oil-cooled x-ray tubes

What are rotating anode x-ray tubes made of?

RTM (rhenium, tungsten, molybdenum) alloy; may include graphite base

What could including a graphite base to a rotating anode x-ray tube do?

boost thermal capacity into high margins

What is the arget angle for a rotating anode x-ray tube?

12 degrees

What is the rotation speed of a rotating anode x-ray tube? 

3,600 - 10,000 rpm 

What is the working life of a rotating anode x-ray tube?

10,000 to 40,000 hours

What are 3 functions for the tube envelope in CT?

ensures vacuum, structural support of anode + cathode, high-voltage insulation

What is the tube envelope commonly made of?

metal

Name 3 reasons why metal is a good material for a tube envelope in CT.

prevent arcing (tungsten vaporization), higher tube currents, increased storage capacity

What is an all-metal disk of an anode made of? 

base = titanium, xirconium, molybdenum

What is a downside to an all-metal disk of an anode?

too heavy; cannot work with spiral/helical CT

What is the most common design for an anode in spiral/helical CT?

brazed graphite disk

What are the focal tracks of anodes in CT typically made of? 

rhenium + tungsten 

What is a chemical vapor deposition (CVD) graphite disk intended for?

spiral/helical CT x-ray tubes

What do the hub and stud of a rotor prevent?

heat transmission from disk to bearings

What unique solution did the stratton x-ray tube use to relieve issues on heat and cooling?

submerging the anode in oil

What is post patient collimation also known as?

pre detector collimation

How much does patient dose increase due to overscanning? 

5-30% 

What term describes scanning a patient outside the imaged range?

overscanning

What term describes when the beam is wider than the detector?

overbeaming

What type of collimation blocks the beam from excessively exposing tissue outside the area of interest along the z-axis? 

adaptive section collimation 

What directly cooled x-ray tube design was designed by Philips, with a spatial resolution of 0.5 mm? 

iMRC 800 x-ray tube 

What directly cooled x-ray tube was designed by Siemens, with a plane resolution of 0.4 mm voxel size

Vectors x-ray tube