Physics: Ct 4

Front 1

What does a 3rd generation scanner look like

Back 1

Front 2

How does a 3rd generation scanner acquire data

Back 2

Diagram of the third-genera-
tion CT scanner, which acquires data by
rotating both the x-ray source with a wide
fan beam geometry and the detectors
around the patient. Hence, the geometry is
called rotate-rotate motion

Front 3

What is major difference between a 2nd and 3rd genereation scanner

Back 3

no more horizontal translation. Now it can scan and rotate around the patient instead of incrementally

Front 4

How many detectors did the 3rd generation scanner have

Back 4

300-700

Front 5

Did a 3rd generation scanner use a collimator

Back 5

yes which created divergent beams

Front 6

What does a 4th generation scanner look like

Back 6

Front 7

What is a major difference between 3rd and 4th generation scanners

Back 7

fourth-generation
CT scanner uses a stationary ring of de-
tectors positioned around the patient. Only the
x-ray source rotates with a wide fan beam geom-
etry, while the detectors are stationary. Hence,
the geometry is called rotate-stationary motion.

Front 8

did the detectors and source rotate in a 3rd genration scanner

Back 8

yes, (look at the picture)

Front 9

What is a major difference between 3rd and 4th generation scanners

Back 9

only the source rotates in 4th generation

Front 10

How many detectors did a 4th generation scanner have up to

Back 10

4800

Front 11

What was a major problem of scanners 4th deneration and before

Back 11

the z-axia (patient lenght) resolution

Thicker slices lead to partial volume averaging and thinner slices were limited by patient motion

Front 12

What was a reason why early scanners could just keep rotating

Back 12

cable

Front 13

What is a major benefit of helical CT

Back 13

you dont have to scan repeatedly along the z-axis

Front 14

What 3 advances were required to move from 4th generation CT to helical CT

Back 14

Three
technological developments were required: slip-
ring gantry designs, very high power x-ray tubes,
and interpolation algorithms to handle the non-
coplanar projection data

Front 15

What is a slip ring

Back 15

Slip rings are electromechanical devices consist-
ing of circular electrical conductive rings and
brushes that transmit electrical energy across a
moving interface

Front 16

What does a slip ring allow to happen

Back 16

All power and control signals
from the stationary parts of the scanner system
are communicated to the rotating frame through
the slip ring.

Front 17

What was a major advantage of slip ring over cable based CTs

Back 17

These sliding contactors allow the scan frame to
rotate continuously with no need to stop between
rotations to rewind system cables

Front 18

What was a problem that occured because of the increased speed that scans could be performed

Back 18

reduced interscan delay
increased the thermal demands on the x-ray tube;
hence, tubes with much higher thermal capacities
were required to withstand continuous operation
over multiple rotations

Front 19

How is the large heat capacity of modern x-ray tubes achieved

Back 19

The large heat capaci-
ties are achieved with thick graphite backing of
target disks, anode diameters of 200 mm or more,
improved high-temperature rotor bearings, and
metal housings with ceramic insulators

Front 20

What does a slip ring design look like

Back 20

Front 21

Why was an interpolation algorithm need for helical CT

Back 21

The problem with continuous tube and
table motion was that projections precessed in a
helical motion around the patient and did not lie
in a single plane. This meant that conventional
reconstruction algorithms could not work.

Front 22

What do the pitch values on helical CT typically range

Back 22

1-2

Front 23

What did helical CT virtually eliminate

Back 23

tissue misregistration 2/2 involuntary motion

Front 24

Was Z-axis resolution still a problem with single row multidector helical CT

Back 24

yes, Even though the z-axis resolution for helical CT
images far exceeds that of conventional CT im-
ages, the type of interpolation algorithm and the
pitch still affect the overall image quality. Also the patient had to breath so this was a limit.

Front 25

What is a principle difference between single row and multiple row scanners

Back 25

Front 26

What are examples of different models of multi-row detectors
(THESE ARE IN THE Z AXIS UNLIKE THE DETECTOR IMAGES SHOWN PREVIOUSLY)

Back 26

Front 27

What is a major advantage of multiple row detector designns

Back 27

the Z-axis resolution can be preserved

Front 28

What is an example of how a MDCT is better than a SDCT

Back 28

For example, if
a 10-mm collimation were divided into four
2.5-mm detectors, the same scan length could be
obtained in the same time but with a z-axis reso-
lution improved from 10 mm to 2.5 mm

Front 29

What are 2 types of Pitch

Back 29

beam pitch and detector pitch

Front 30

What is the formula of beam pitch

(used for MDCT and SDCT)

Back 30

beam pitch = T/W

T=table travel per gantry rotation
W=beam witdth

Front 31

What is the formula of detector pitch

(this is used for MDCT)

Back 31

detector pitch T/D

T=table travel per gantry rotation
D=detector witdth in mm

Front 32

What are the different type of pitch in MDCT

Back 32

Front 33

What does N stand for in the previous diagram

Back 33

Number of active detectors

Front 34

What is another formula for beam pitch

Back 34

beam pitch= detector pitch/N

Front 35

Why are there two different types of pitch

Back 35

some manufactures created the detector pitch and now everything is fucked

Front 36

Do some manufactures have many different size detectors through out the z-axis of there CT

Back 36

yes (Siemens)

Front 37

What is good way think about how the multidector size works

Back 37

if the detector is 1.25 then you can do 4x1.25 or 4x2.5 or 4x3.75 or 4x5 or 2x10.

4 (2 in last example) is talking about the number of slices for each rotation. The beam length will have to increase for each for example it will be 5 mm for 4x1.25 and 20mm for 2x10

Front 38

Example of available sections widths by vendor

Back 38

remember 4 refers to the number of slices along the z-axis obtained in a rotation and and the second number is the size of the slices. The beam with will be does numbers multiplied together.

Front 39

What is true isotropic spatial resolution

Back 39

cubic voxels, the image is equally sharp in any plane. This is true if a voxel is less than 1mm in any plane

Front 40

What is the problem with using a small focal spt

Back 40

The use of a small focal spot increases detail but
it concentrates heat onto a smaller portion of the anode therefore, more heat is
generated

Front 41

What determines the size of the focal spot

Back 41

The focal spot size of an x-ray tube is determined by the size of the filament and cathode which is determined by the manufacturer. Most x-ray tubes have more than one focal spot siz

Front 42

What happens to the focal spot size if the anode angle is decreased

Back 42

Decreasing the anode or target angle decreases the size of
the effective focal spot.

Front 43

What is the typical focal spot size on CT compared to plain film

Back 43

Generally, the anode angle of a conventional
radiography tube is between 12 and 17 degrees. CT tubes employ a target angle
approximately between 7 and 10 degrees

Front 44

How does anode angle influence heel effect

Back 44

s. The decreased anode or target angle
also helps eleviate some of the effects caused by the heel effect

Front 45

What is bigger CT focal spot size or plain film

Back 45

CT

Front 46

How does CT compensate for loss of resolution when using a larger focal spot

Back 46

. CT can
compensate any loss of resolution due the use of larger focal spot sizes by
employing resolution enhancement algorithms such as bone or sharp
algorithms, targeting techniques, and decreasing section thickness

Front 47

What are the collimators used in a CT

Back 47

s tube collimators, a set of prepatient collimators and post-patient or pre-detector collimators .

Front 48

Where are the tube or source collimators located

Back 48

the x-ray tube

Front 49

What do the tube or souce collimators do

Back 49

. The tube or
source collimators are located in the x-ray tube and determine the section
thickness that will be utilized for a particular CT scanning procedure.

Front 50

How does the collimator effect thickness of the x-ray beam

Back 50

When the
CT technologist selects a section thickness he or she is determining tube
collimation by narrowing or widening the beam

Front 51

What do the second set of collimators directly below the tube collimators (prepatient) do

Back 51

m. A second set of collimators
located directly below the tube collimators maintain the width of the beam as it
travels toward the patient

Front 52

Where are the post patient (predetector) collimators located

Back 52

A final set of collimators called post-patient or predetector collimators are located below the patient and above the detector

Front 53

What do the pre-detector collimators do

Back 53

The
primary responsibilities of this set of collimators are to insure proper beam width at the detector and reduce the number of scattered photons that may enter a detector

Front 54

What do the collimators and filters look like

Back 54

Front 55

What are the 2 types of filtration utilized by CT

Back 55

-mathematical filters

-Inherent tube
filtration and filters made of aluminum or Teflon are utilized in CT to shape the
beam intensity by filtering out low energy photons that contribute to the production of scatter

Front 56

What is a bow-tie filter

Back 56

Special filters called "bow-tie" filters absorb low energy
photons before reaching the patient

Front 57

Why is a bow-tie filter necessary

Back 57

X-ray beams are polychromatic in nature
which means an x-ray beam contains photons of many different energies.
Ideally, the x-ray beam should be monochromatic or composed of photons
having the same energ

Front 58

What is the basic principle of the detectors of CT

Back 58

collecting attenuated photon energy and converting it to electrical signal which will then be converted to digital signal for reconstruction

Front 59

What are the 2 types of detectors utilized by CT

Back 59

The
two types of detectors utilized in CT systems are scintillation or solid state and
xenon gas detectors.

Front 60

How does a scintillation detector work

Back 60

Scintillation detectors utilize a crystal that fluoresces when
struck by an x-ray photon which produces light energy. A photodiode is
attached to the scintillation portion of the detector. The photodiode transforms
the light energy into electrical or analog energy. The strength of the detector
signal is proportional to the number of attenuated photons that are successfully
converted to light energy and then to an electrical or analog signal.

Front 61

What are common scintillation crystals that are used

Back 61

successfully
converted to light energy and then to an electrical or analog signal. The most
frequently used scintillation crystals are made of Bismuth Germinate
(Bi4Ge3012) and Cadmium Tungstate (CdWO4). Earlier designs utilized
Sodium and Cesium Iodide as the light producing agent

Front 62

How does a scintillation detector work

Back 62