P1 Flashcards by Trisha Labadlabad

Is the process of creating a cross-sectional
tomographic plane of any part of the body.

CT-SCAN

How well did you know this?

Not at all

Perfectly

The term “tomography” is derived from the Greek word “____”, meaning “____’’.

tomos, section

How well did you know this?

Not at all

Perfectly

refers to the old scanners that is only capable of displaying Axial Scans

CAT scan

How well did you know this?

Not at all

Perfectly

refers to the ability to define small objects.

Spatial Resolution

How well did you know this?

Not at all

Perfectly

refers to the ability of the system to differentiate small objects with
similar densities.

Low Contrast Resolution

How well did you know this?

Not at all

Perfectly

refers to the speed on which the data can be acquired. Increase in temporal resolution can decrease/eliminate artifacts

Temporal Resolution

How well did you know this?

Not at all

Perfectly

The mathematical principles of CT were first developed by ___ in ____.

Radon, 1917

How well did you know this?

Not at all

Perfectly

CT-scan was first demonstrated by ___ on ___

Godfrey Houndsfield, 1970

How well did you know this?

Not at all

Perfectly

developed the mathematics used to reconstruct images

Allan Cormak

How well did you know this?

Not at all

Perfectly

Allan Cormak (developed the mathematics
used to reconstruct images) and Godfrey
Houndsfield received the nobel prize award
on ____

1982

How well did you know this?

Not at all

Perfectly

•Beam: Pencil-like x-ray beam
•EMI labs
•Detectors: One
•Tube-detector movements: Translate-rotate
•Number of slices per rotation: One
•Scan duration: 5 minutes

1ST GENERATION CT scanners

How well did you know this?

Not at all

Perfectly

▪ Were also translate and rotate type.
▪ Fan beam
▪ Mutiple detector array
▪ 30 seconds imaging time
▪ Uses the bow tie filter to equalize the radiation intensity reaching the
detector

2nd Generation CT-scan

How well did you know this?

Not at all

Perfectly

a CT imaging system consists of a finely collimated x-ray beam and a single detector, both of which move synchronously in a translate and rotate fashion. Each sweep of the source detector assembly results in a projection, which represents the attenuation pattern of the patient profile

1ST GENERATION CT scanners

How well did you know this?

Not at all

Perfectly

operated in the translate and rotate mode with a multiple detector array intercepting a fan-shaped x-ray beam.

Second-generation computed tomography
imaging systems

How well did you know this?

Not at all

Perfectly

▪rotate-only units, third generation imaging systems can now produce an image in less than 100 ms.
▪uses a curvilinear detector array and a fan beam
▪The curvilinear detector array produces a constant source-to-detector path length
▪seconds scanning time.
▪Still widely used today.

3rd Generation CT-scan

How well did you know this?

Not at all

Perfectly

operate in the rotate-only mode with a fan x-ray beam and a multiple detector array revolving concentrically around the patient

Third-generation computed tomography imaging systems

How well did you know this?

Not at all

Perfectly

▪Incorporates a rotate and stationary configuration
▪Radiation detection is accomplished through a fixed circular array of detectors
▪May contain as many as 4000 individual detectors.
▪Fan shape beam
▪Free of ring artifact

4th Generation CT-scan

How well did you know this?

Not at all

Perfectly

operate with a rotating x-ray source and stationary detectors

Fourth-generation computed tomography imaging systems

How well did you know this?

Not at all

Perfectly

▪Also known as Electron-Beam CT (EBCT)
▪Was pioneered for cardiac imaging
▪No moving parts in the gantry

5th Generation CT-scan

How well did you know this?

Not at all

Perfectly

▪ Also known as the “Helical CT scanner”
• Data collection: Data is collected without pausing
• Speed: Helical CT scanners are faster than other CT scans
• Cost: These scanners are less expensive to produce and purchase

6th Generation CT-scan

How well did you know this?

Not at all

Perfectly

▪ Multi-spiral CT makes use of multiple detector arrays to make use of a wider portion of the x-ray fan beam d
▪ Section thickness in multi-slice CT is determined by detector width rather than by collimation thickness, using data
acquisition.
▪ This technology makes better use of the x-ray tube output and decreases heat loading for a given coverage range.
▪ Was introduced in 1998

7th Generation CT-scan

How well did you know this?

Not at all

Perfectly

CT Scan Modes

Step And Shoot
HELICAL (SPIRAL SCANNING)
Multi Detector Row scanning

How well did you know this?

Not at all

Perfectly

-the x-ray tube rotated 360° around the patient to acquire data for a single slice

-the motion of the x-ray tube was halted while the patient was advanced on the CT table to the location appropriate to collect
data for the next slice

Step And Shoot

How well did you know this?

Not at all

Perfectly

▪ When the examination begins, the x-ray tube rotates continuously. While the x-ray tube is rotating, the couch moves the patient through the plane of the rotating x-ray beam. Continuous data acquisition.

HELICAL (SPIRAL SCANNING)

How well did you know this?

Not at all

Perfectly

▪ This technology was expanded on in 1992 when scanners were introduced that contained two rows of detectors, capturing data for two slices per gantry rotation. Multiple slices per rotation

Multi detector row scaning

- refers to the thickness of a cross sectional slice

Z axis

- Rows and colums of pixels that makes up the whole image. -512 x 512 is the most common

Matrix

- the degree to which a beam’s energy is reduced.

Beam Attenuation

- the amount of xray photons absorbed/scattered per unit thickness

Linear Attenuation Coefficient

quantifies the degree that a structure attenuates an x-ray beam

Density

CT numbers or Density Value

Houndsfield Units

- is an artifact that occurs when multiple tissues with different densities occupy the same voxel

Volume Averaging

-composed of low and high intensity beams -causes artifacts due to scattered radiation -filtering with a substance such as Teflon or aluminum eliminates the photons with weaker energies, thus reducing patient dose and improves image quality

Polychromatic X-rays

-all the thousands of bits of data acquired with each scan. -These are the data that is waiting to be processed in order to create the “Image Data”

RAW data

-the process of converting Raw data to Image Data

Reconstruction

-processed Raw Data

Image Data

-then ring shape part of the CT-scan that houses components necessary to produce and detect Xrays.

The Gantry

-permits the gantry frame to rotate continuously making helical scanning possible

Slip Rings

-located within the gantry -prevents fluctuating temperatures within the gantry.

Cooling System

-CT-tubes made of tungsten anode, has a higher intensity beam. Higher heat capacity.

Xray Source

-improves image quality and reduces patient dose

Filtration

-restricts the x-ray beam to a specific area -decreases scattered radiation, improves image quality and reduces patient dose

Collimator

2 types of collimators

Source Collimator Pre detector Collimator

-affects the patients dose and determines how the dose is distributed across the slice thickness.

Source Collimator

-ensures the beam coming from the patient is the exact width and prevents scatter radiation reading.

Pre Detector Collimator

-collects the information regarding the degree to which each anatomic structure is attenuated by the beam

Detectors

-absorption rate of 60% to 87% -less expensive -still being manufactured but has become obsolete -due to its design prevents them for MDCT

Xenon Gas Detectors

-uses crystals that fluoreces when struck with and xray photon

Solid State Crystal Detectors/Scintillation Detectors

- transforms light to energy

Photo iodide

-measures the number of photons that strikes the detector, converts the analog signal to digital (ADS - Analog to Digital Converter) and then sends it to the computer

DAS (Data Acquisition System)

- is a finite set of unambiguous steps performed in a sequence to solve a problem - they are a precise set of steps to be performed in a specific to solve a problem..

Algorithm

- a mathematical tool that allows for the efficient reconstruction

Fourier Transform

- Fourier Transform is developed by the 17th century mathematician ____

Baron Jean- Baptiste-Joseph Fourier.

-is a mathematical method of creating missing data

Interpolation

- portion of the computer that can be physically touched.

Hardware

- is the instructions that tell the computer what to do to do it.

Software

- essential component of the CT system. Determines the number of images the CT system can store.

Hard Disk

- interprets computer program instructions and sequences task - Brain of the CT system.

CPU (central processing unit)

- imprinted in the factory. Used to store frequently used instructions. Required to start up the system.

ROM (read only memory)

- includes instructions that are frequently changed. Data that are used to reconstruct images.

RAM (random access memory)

type of data storage device that reads date sequentially

SAM (sequential access memory)

- a computer storage device that can be written once, but read many timed (CD-R, DVD-r, DVD+R, rewritable disk)

WORM (write once read many)

- includes all measurements obtained from the detector array. Requires larger computer storage space than image data.

RAW DATA (Scan Data)

-are those which result once the computer has processed the raw data. One Houndsfield unit is assigned in every pixel

IMAGE DATA

- compiles the information from all of the attenuation profiles to create an image

Back Projection

- helps reduce the appearance of artifacts.

Filter Functions

- determines the area, within the gantry, from which the raw data are required. -determines the number of detector cells collecting data.

SFOV (Scan Field of View)

- also called zoom or target. Determines how much of the raw data is to be used to create and image. Affects the image quality by changing the pixel size

DFOV (Display Field of View)

-used in mammography ⚬ uses an area x-ray beam to produce multiple digital images. ⚬ form a three-dimensional data set from which any anatomical plane can be reconstructed. ⚬ even better image contrast

Digital Radiographic Tomosynthesis.

-also called axial tomography -plane of the image is parallel to the long axis of the body -results in sagittal and coronal images

Conventional tomography

-Trans-axial or transverse image -perpendicular to the long axis -Coronal and sagittal images can be reconstructed from the transverse image data set

Computed Tomography

In CT, the most common matrix size is

512

This speed is particularly important to reduce or eliminate artifacts that result from object motion, such as those commonly seen when imaging the heart

Temporal Resolution

The degree to which an X-ray beam is reduced by an object is referred to as

attenuation

If an x-ray passed into an object and is less attenuated, the shade will be _____.

black

If an x-ray will pass into a structure and there is more attenuation them the shade will be ____.

white

the quantity of matter per unit volume, specified in units of kilograms per cubic meter

Mass density

The amount of x-ray beam that is scattered or absorbed per unit thickness of the absorber is expressed by the ______, represented by the Greek letter μ

linear attenuation coefficient

In general, the attenuation coefficient _____ with increasing photon energy and ____ with increasing atomic number and density

decreases, increases

These units are also referred to as CT numbers or density values

Hounsfield Unit

The purpose of the ____ is to identify if there is something wrong with a particular organ

Hounsfield unit

Using the system of _____, a measurement of an unknown structure that appears on an image is taken and compared with measurements of known structures

Hounsfield units

CT can be broken down into three segments

Data acquisition Image reconstruction Image display

It houses many of the components necessary to produce and detect x-rays

Gantry

The range of aperture size of gantry is typically

70 to 90 cm

The degree of tilt varies among systems of gantry but _____ is usual

15 to 30 degree

Current systems use electromechanical devices called

Slip rings

___ use a brushlike apparatus to provide continous electrical power and electronic communication across a rotating surface

Slip rings

They permit the gantry frame to rotate continuously

Slip rings

Generator that are currently used in in CT

High frequency generators

The power capacity of generator is listed in

Kilowatts

_____ produce the xray photons that create the Xray image

X ray tubes

Are used to shape the xray beam

Compensating filters

Used to describe the entire collection of detectors included in a CT system

detector array

The space between the grid

Interspace material

refers to the ability with which the detector obtains photons that have passed through the patient

Capture Efficiency

•refers to the number of photons absorbed by the detector and is dependent on the physical properties of the detector face (e.g., thickness, material).

Absorption Efficiency

•Is the time required for the signal from the detector to return to zero after stimulation of the detector by x-ray radiation so that it is ready to detect another x-ray event

Response Time

•Is the ratio of the maximum signal measured to the minimum signal the detectors can measure.

Dynamic Range

is used because of its ability to remain stable under pressure.

Xenon gas

A xenon detector channel consists of ____ tungsten plates

three tungsten plates

The process of moving the table by a specified measure us most commonly called

incrementation

The degree to which a table can move horizontally is called the

Scannable range

is a method to study waves of many different sorts and also to solve several kinds of linear differential equations.

Fourier transform

is a mathematical method of estimating the value of an unknown function using the known value on either side of the function

interpolation

is a mathematical method of creating missing data

Interpolation

• is the simplest type and is frequently used in mathematics and science

Linear interpolation

• assumes that an unknown point falls along a straight line between two known points

Linear interpolation

are ancillary pieces of computer hardware designed to feed data into the computer or accept processed data from the computer.

Input and output devices

include monitor, laser camera, printer, and archiving equipment such as optical disks or magnetic tape

Output devices

The ___ is the component that interprets computer program instructions and sequences tasks.

CPU

It contains the microprocessor, the control unit, and the primary memory

CPU

In the past the CPU design frequently used for CT image reconstruction was the ____ also called as

array processor, vector processor

, this design was able to run mathematical operations on multiple data elements simultaneously

vector processor

refers to the computers internal memory

Primary storage

-is used to store data that are likely to be in active use. -is typically very fast

Primary memory

is very fast, but is also volatile, losing the stored data in the case of a power loss

RAM

The opposite of RAM is ____, which stores data that can only be accessed sequentially (like a cassette tape)

serial access memory (SAM)

• The reconstruction that is automatically produced during scanning

Prospective Reconstruction

• The same raw data may be used later to generate a new image

Retrospective Reconstruction

- displayed in the monitor

Pixel

- contains value acquired by the algorithm and it will be averaged to have one value to place it in front as a HU and this is the pixel

Voxel

The path that the x-ray beam takes from the tube to the detector is referred to as a ___.

ray

: the detector senses each arriving ray and measures how much of the beam has been attenuated.

Ray Sum

: a complete set of ray sums

View

: the system accounts for the attenuation properties of each ray sum and correlates it to the position of the ray.

Attenuation Profile

The process of applying a filter function to an attenuation profile is called

convolution

⚬ common type of image reconstruction in CT scan

Filtered back-projection

is also called calibration field of view.

Scan Field of view

P1 Flashcards

(129 cards)