Ct Physics 1

Question 1

First gen Ct scanners

Design

Source

Beam

Geometry

Answer 1

Design: single X-ray source and single X-ray detector cell to collect all data from single slice

Source and detector rigidly coupled
- beam: pencil beam translated across patient to obtain set of parallel projection measurement at one angle

Source / detector rotate slightly and a subsequent set measurements are obtained during a translation past patient

Process is repeated once for each projection angle until 180 projections , across a 24cm fov

Translation and rotation process, this geometry is referred to as a translate / rotate scanner or rectilinear pencil beam scanning

Question 2

First gen scanner

Name

Year

Time

Image looked?

Answer 2

• Emi mark I scanner (1972)
• earliest version: took 4-5 mins for a single scan and thus were restricted to some regions ( patient motion controlled)
• later version : used series of scans procedure time reduced some what by using two detector so that two parallel sections were acquired in one scan

Contrast resolution of internal structures was unprecedented , images had poor spatial

Resolution very poor

Question 3

Second generation scanner

Design

Source

Generation name?

Answer 3

Design: multiple detectors because X-ray source emits radiation over large angle, the efficiency of measuring projections was greatly

Source and array of detectors are translated as in first gen systems but since the beam measured by each detector is at slightly different angle with respect to object , each translation step generates multiple parallel ray projections

Multiple projections obtained during each transversal past the patient this scanner is significantly more efficient and faster than the first one.

This generation is translate / rotate scanner or rectilinear multiple pencil beam scanning

Question 4

Second generation scanner

Detectors

Early version

Later versions

First to allow type scans?

Answer 4

Adding detectors angularly displaced, several projections could be obtained in single translation

Early versions: 3 detectors each displaced by 1 percent , since each detector viewed the X-ray tube at different angle, a single transition produced 3 projection.

This system could rotate 3 degrees to the next projection rather than 1 degree making only 60 translations instead of 180 to acquire a complete section

Scan time as much as 3x

Later versions : up to 53 detectors . Fast enough ( tens of thousands of seconds) to permit acquisition during single breath hold.

First designs to permit scans of the trunk

Question 5

Third gen scanner

Improve

New design

Type movement

Type beam

How projections obtained

What motion is called

Answer 5

Pure rotational scanning motion could be used , then it would be possible to use high power, rotating anode X-ray tubes and thus improve scan speeds in thicker body parts

New design: larger array of detectors ( 300- 700 detectors ., usually arced shape

Slam bang translational motion was replaced with smooth rotational motion and higher output rotating motion and higher output rotating anode X-ray tubes

X-ray tube is collimated to wide X-ray beam( fan beam)

Directed toward an arc shaped row detectors

Tube and detector array rotate around patient

Different projections are obtained during rotation by pulsing X-ray source or by sampling the detectors at a very high rate

This motion is referred to as continuously rotating fan beam scanning

Question 6

In third gen scanners the apex is at the ?

Answer 6

Source

Question 7

Third gen scanners

Improvement

Sampling

Scan times

Answer 7

Improvement from detector and data acquisition technology detector array with enough , high spatial resolution cells allow ,measurement of a fan beam projection of entire patient cross section

Sampling considerations required scanning an additional arc of one fan angle beyond 180 degree , although most scanner rotate 360 degree for each scan

Current helical scanners are based on modifications of rotate- rotate designs

Scan times= few seconds or less and recent versions are capable of sub second scan times

Imaging process is significantly faster than 1st or 2nd generation systems

Question 8

Fourth generation scanner

Design

Source

Beam

Limitations

Answer 8

Design: also eliminated translate rotate motion. Circular array of fixed detectors

Source only rotates within a stationary ring of detectors

Larger fan beam

Shorter scanning time

Early versions: had some 600 detectors

Later versions: had up to 4,800

Limitations: less efficient use of detectors , less than 1/4 are used at any point during scanning

Only the X-ray generator and tube rotate at 360, thus shortening the scanning time even more

Question 9

3rd gen vs 4th gen

Answer 9

3rd gen- apex tube side

4th gen- apex detector side

Question 10

5th gen scanner

Design

Use

Scan time and number slices

Called

Answer 10

Design: X-ray tube is a large ring that circles patient, opposed to detector ring

Use: for cardiac tomographic imaging “ cine Ct”

X-rays produced = high energy electron beam

No moving parts to this scanner gantry

It is capable of 50 millisecond scan times and can produce 17 Ct slice/ second

Stationary/ stationary geometry

Question 11

X-ray tube

Housing?

Filament current?

Cathode vs anode

Melting point?

Answer 11

Vacuum accelerating electrons

Electron will travel faster

Filament alternating current

Thermal electrons

Cathode(-) filament plate with tiny slit

Connected to high voltage battery source

Target / anode (+) electrons collide with target

Produce X-ray

Must have high melting point ( tungsten)

Question 12

Cine Ct

Answer 12

No mechanical scanning motion

X-ray detector and tube anode are stationary

Anode, is very large semicircle ring that forms an arc around the patient scan circle

Source of X-rays is moved around the same path as fourth gen Ct scanner by steering an electron beam around the X-ray anode

Terms millisecond Ct, ultrafast ct and electron beam Ct have also been used , although latter can be confusing since the term suggests that the patient is exposed to an electron Beam

Question 13

Cine Ct system

Answer 13

Very fast scanner , data collection for 1 slice is 50-100 ms

Requires no mechanical motion to acquire data

Sweeps an intense electron beam across large stationary anode target which surrounds the patient

X-rays are emitted from the point where electrons strike target

X-rays transmitted through object are measured by stationary array of detectors

Cine Ct systems, have higher noise level and lower spatial resolution but are ideal for some clinical application cardiac imaging with and without the use of contrast agent , lung imaging , and pediatric studies

Question 14

Sixth generation scanner

Answer 14

1990, significant advancement in technology

Allowed 3D imaging with single breath hold

Question 15

Spiral helical 6 th gen ct scanner

Answer 15

Design: X-ray tube rotates as patient is moved smoothly into X-ray scan field

Simultaneous source rotation, table translation and data acquisition

Produces one continuous volume set data for entire region

Data for multiple slices from patient acquired at 1 sec/ slice

Question 16

Spiral/ helical vs axial scans

Answer 16

Spiral/ helical is same scan

Axial scan one slice at a time with small interscan delay

Question 17

Head scan done?

Answer 17

Axial

Question 18

Spiral/ helical scan the tube has a slight?

Answer 18

Angle

Question 19

Advantages of spiral Ct

Answer 19

Speed- patient movement continuous , shorter exam time entire abdomen or chest : 30 s (18h)

Improved detections :differences bh is standard Ct. small lesions fall out of plane each continuous slice

Improved contrast- image a region in short period . Contrast can be timed

Improved reconstruction and manipulation- volume data collected transverse data can be reconstructed in any plane strip away skin muscles , etc

Question 20

Contrast improved in Ct ( resolution) shows different ____

Answer 20

Greys

Question 21

Resolution

Answer 21

Ability of scanner to define small structures

High resolution- high bit depth

Low res- low bit depth

Question 22

Spiral/ helical Ct

Answer 22

Three technological developments

Slip ring technology gantry designs

Very high power day tubes

Interpolation algorithmns to handle projection data

Question 23

Interpolation

Answer 23

Takes volume of data and mathematically takes average of bit depth pixels if missing ones in between

Question 24

Slip ring technology

Answer 24

Alternative to cable system= slip ring

1989 kalender

Electromechanical devices: circular electrical conductive rings and brushes

Transmit electrical energy across moving transfer to a signal

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

Allow scan frame to rotate continuously with no need to stop between rotations to rewind system cables

Question 25

What goes to slip ring?

Answer 25

Fov

Question 26

Slip ring

Answer 26

Electromechanical device that allows the transmission of power and electrical signals from stationary to a rotating structure. Can be used in any electromechanical system that requires rotation while transmitting power or signals

Question 27

High power X-ray tube

Answer 27

Thermal load in Ct 1 and 2nd, stationary tube( low heat, slow scan) Oil cooling thermal system around tube, fast scans Scan time vs heat capacity increased by 5x Thermal depends on X-ray tube Tubes with much higher thermal capacities were required to withstand continuous operation over multiple rotations New design ; ceramic insulation , oil cooling of bearing, compact metal envelop Expected life of tube 10,000-40,000 hrs vs 1000 regular one

Question 28

Interpolation algorithmns

Answer 28

Kalender developed interpolation methods to generate methods to generate projections in a single plane Overlapping sections generated by math , not beam , improve z axis with no increase in dose Improved image quality

Question 29

Seventh generation Ct scan

Answer 29

New technology , single row had its limitations Design: multiple detector array Collimator spacing is wider and more of the X-ray that are produced by the tube are used in producing image data. Opening up the collimator in a single array scanner increases slice thickness , reducing spatial resolution in the slice thickness dimension With multiple detectors array scanner , slice thickness is determined by detector size not by collimator

Question 30

7th gen Ct scanner

Answer 30

Turbo charged spiral Up to 8 rows of detectors 4 rows, large volume of patient scanned 1 breath hold( thorax, abdomen , pelvis) at once Allows 1 mm sections thorough chest in 20 sec Improvement in details Problem with pace , stain on storage system

Question 31

7 th generations

Answer 31

Cone beam and multiple parallel row detectors Widened ( z direction) X-ray beam and detector array to acquire multiple (4-64 slices simulatanously) Advantage: reducing scan time/ increase z- resolution Disadvantage: less scatter rejection compared to single slice , very expensive

Question 32

Multiscanning

Answer 32

Relates to the technique of double or triple rotation of the tube and detectors around the same axial plane Provides double of triple the volume per slice, upon which the final image can be derived In practice each rotation produces its own of raw data bank Hence motion which may occur during one rotation can be averaged out from data of the remaining two rotations Multiscanning therefore reduces motion artifacts and consequently improves image quality

Question 33

Multiscanning ct

Answer 33

1998 all major manufactures introduced multislice Ct, simulatanous acquisition of four slices , providing great improvement 4 slice, not fast enough to avoid venous overlay assuming a cerebral circulation time less than 5 sec In 2000, 8 slice Ct were presented, followed by 16 slice in 2001 Most modern generation of msct is 64 slice per rotation, enabling a whole body cta with 1500 mm scan range in 22-25 sec Future announced 256 slices Complements: tubes and detector measurement systems , large influence on performance Development in software and computer capacity lead to processing and reconstruction in short time

Question 34

1st gen

Answer 34

Single X-ray tube. Pencil beam Single detector

Question 35

2 gen ct

Answer 35

Single X-ray tube Fan beam source Multiple detector

Question 36

3 rd gen scanner

Answer 36

Single X-ray tube Fan beam Many detectors

Question 37

4 th gen Ct

Answer 37

Single X-ray tube Fan beam Stationary ring of detectors

Question 38

6th gen Ct

Answer 38

3G/4g source 3G/4g source collimation 3G/4g detector source

Question 39

7th gen Ct

Answer 39

Single X-ray source Come beam source collimation Multiple array of detectors

Question 40

Ct scanner components

Answer 40

``` Ct radiographic table Ct filters Collimator Bore size Detectors Gantry/tube features Data acquisition system (das) Computer and array processor Consoles Tube heating monitors Archival methods ```

Question 41

Tube / generator

Answer 41

X-ray generator is based on three phase power to ensure efficient X-ray production . With the introduction of the slip ring technology the modern high frequency generator used in Ct scanners is small and compact Located inside gantry

Question 42

Kv ranges in Ct

Answer 42

80-140(speed photons travel)

Question 43

Ma range ct

Answer 43

100-400( the number of photons)

Question 44

Type beam modern Ct uses and type of anode?

Answer 44

Modern Ct use rotating anode Rotating anode uses large disk made tungsten , rhenium and molybdenum Heterogenous beam

Question 45

Spatial resolution requirement in Ct met by?

Answer 45

Large anode along with correct focal spot size

Question 46

Number filaments in cathode section?

Answer 46

2 filaments which activated when operator selects slice width Activated by slice thickness New design has improved heat generation and heat storage probs

Question 47

Types of interactions in Ct

Answer 47

Bremschlung and characteristic

Question 48

Ct first computer ? Date and location

Answer 48

1972 Atkins moreley hospital. Took 20 mins for head scan

Question 49

Analog

Answer 49

Computer that performs operations on continuous signal

Question 50

Digital

Answer 50

Computer in which discrete numbers are used to express data and instructions . Signal gets into binary numbers

Question 51

Ct CPU is ---- processor

Answer 51

Array processor

Question 52

Hardware

Answer 52

Physical device and or equipment of computer system

Question 53

Central processing unit( cpu)

Answer 53

Carries out instructions of a computer pprocessor reframe by performing basic arithmetic, logical, control and input/output operations

Question 54

Array processor

Answer 54

Central processing unit that implements an instruction set containing instructions that operate one dimensional arrays of data called vectors. The array processor must have flexibility , speed , power and expandability to accommodate the high acquisition , manipulation of data storage . Large array of parallel processors used today

Question 55

Vector

Answer 55

Instructions of one dimensional arrays of data

Question 56

Array processor reconstructs

Answer 56

Projected attenuation raw data into a Ct image

Question 57

Software

Answer 57

Operating data base communications to translators applications. In Ct there is pre processing , post processing and reconstruction

Question 58

Memory

Answer 58

Devices used to store info on computer . Ram, rom,

Question 59

Ram

Answer 59

Random access memory

Question 60

Rom

Answer 60

Read only memory . Gives basic instruction to start operations

Question 61

Output devices

Answer 61

Speakers, screens, printer

Question 62

Input devices

Answer 62

Keyboard, mouse, camera)

Question 63

Peripheral devices

Answer 63

Cell phones | Speakers

Question 64

Filtration

Answer 64

Located in tube window Placed there to absorb low energy photons that have no diagnostic quality and add patient dose X-ray beam stay heterogeneous

Question 65

Collimator

Answer 65

To restrict beam to area of interest and define slice thickeness which decreases patient dose and increases image quality Scatter radiation is undesirable adds noise to image

Question 66

Pre patient collimator

Answer 66

Placed in position that shapes the shape beam as it leaves Ct X-ray tube. This collimation reduces pt dose by allowing only those photons required by slice width

Question 67

Post patient collimation

Answer 67

Pre detectors which remove scatter radiation . Post patient collimation continues to provide definition of slice width

Question 68

Table

Answer 68

Moves vertically and longitudinally . Load capacity is 450lbs( 204kg)

Question 69

Gantry

Answer 69

Tube, detectors, slip rings, collimator, generator, das well all housed in gantry. It tilts from + 12 to + 30 degrees from vertical plane

Question 70

Couch

Answer 70

Moves horizontal and vertical . Patient coordinates x axis, z axis, y- axis

Question 71

X axis

Answer 71

Left to right

Question 72

Y axis

Answer 72

Anterior to posterior

Question 73

Z axis

Answer 73

Head to feet

Question 74

Laser optics

Answer 74

Positioning laser beam to center patient in gantry before scan

Question 75

Bore size

Answer 75

Gantry aperture usually 70cm

Question 76

Digital detector

Answer 76

X-ray sensors are used instead traditional film

Question 77

Detector efficiency

Answer 77

Aka capture efficiency - ability of detector to capture and absorb and convert X-ray photons into electrical signal

Question 78

Absorption efficiency

Answer 78

Quantity of X-ray photons absorbed by the detector and depends on physical density , atomic number, size and thickness of detector face

Question 79

Response time

Answer 79

Time it takes detector to detect X-ray photon then recover and detect another

Question 80

Ho do they work?

Answer 80

Xray photon must enter the chamber of detector ( captured) Collision of photon and detector material collide and results in an electromagnetic force great enough to measure light Electromagnetic event is amplified Amplified event is sent to data acquisition center Two types detectors, scintillation aka solid state detector and the gas ionization detector Solid state detector uses multiple detectors arranged in detector array module

Question 81

Detectors

Answer 81

Number and thickness of each slice acquired in single rotation determines the number of detectors arrays used To measure the incoming thick X-ray beam, beam thickness is divided by total number of slices acquired in single rotation. X-ray beam thickness= beam thickness ----------------- Slices acquired in one rotation X-ray beam thickness/ number of slices= slice thickness

Question 82

Data acquisition system

Answer 82

Electrical impulse is amplified and sent das to digitized by the analog to digital converter . The resulting digital data can then be used by the array processor to construct the Ct image( inside gantry)

Question 83

Archival methods

Answer 83

Data is stored in digital form. It preserves the dynamic range of images Stored in 2d pixels arrays Storage devices include magnetic tapes. Digital video tapes , optical disks, and optical tape. Also can be used for archiving Pace- picture archiving and communication system ( pacs) is medical imaging technology which provides economical storage of and convient access to images from multiple modalities

Question 84

Partial volume effect

Answer 84

When different density objects reside within vowel

Question 85

Partial volume artifact

Answer 85

Occurs when tissues widely different absorption are encompassed on the same Ct voxel producing a beam attenuation proportional to average value of these tissues Latest Ct machine reduced this

Question 86

Sampling

Answer 86

When detectors measure beam intensity on it

Question 87

Beam hardening

Answer 87

Artifact that occurs as streaks at bone edges adjacent to soft tissue . Seen most commonly in posterior fossa of brain

Question 88

Algorithmns

Answer 88

Defined set of instructions that lead to logical conclusion of tasks

Question 89

Field size

Answer 89

Scanning and display field field sizes. Large field- abdomen Small field- head

Question 90

Teleradiography

Answer 90

Transmission of radiological patient images such as X-rays , cts, and Mri from one location to another for purpose of sharing studies with other radiologist and physicians