CT Exam #2

Using narrow window width when displaying the brain makes it difficult to differintiate between white and gray matter T or F

False

Quantization

Final step;brightness value of each pixel is assigned a number aka grey level

****Be able to describe windowing, window width and window level. Be able to calculate what shades will be white, black and gray. Be able to describe what happens to the image as window width and window level change.

Window width: contrast Window level: brightness

What is image data? (reconstructed data)

-convolved data that has had an image reconstruction algorithm applied to it (used to create the displayed image, additional filters can be applied to this data)

What is convolved data?

-filtered raw data, refined raw data

What is raw data?

-results of measurement/preprocessed scan data and are subjected to image reconstruction algorithm used by the scanner computer can be stored and retrieved as necessary

Paramters that can be changed retrospectively on a multi slice scanner -thickness -slice incrementation (helical data only) -mAs -reconstructive algorithm -kVp -image center -DFOV

-thickness -slice incrementation -reconstructive algorithm -image center -DFOV

In a single slice system, which of the following technical parameters may be adjusted retrospectively? 1. section width 2. section increment 3. reconstruction algorithm A. 2 only B. 1 and 2 only C. 1, 2 and 2

1 and 2 only

****Please know the different types of data.

1. measurement data (scan data)2. raw data (reformatted raw data)3. convolved/filtered raw data4. image data (reconstructed data)

Which of the following belongs to the class of analytical algorithms for computed tomography? I. back projection II. filtered back projection III. Fourier reconstruction

2 and 3

Which of the following window levels and window widths should be utilized to best demonstrate chest anatomy? Please choose all that apply. -400 ww, 40 wl -1500 ww, -500 wl -80 ww, 40 wl -1800 ww, 400 wl

400 ww, 40 wl 1500 ww, -500 wl

What window width should be used for tissue types with similar densities? * 0-50 HU * 50-500 HU * 500-2,000 HU * 2,000-2500 HU

50-500 HU

the info included during the 3D reconstruction of a CT scan is controlled by the A. algorithm B. window setting C. threshold D. gray scale map

A

If the window width setting is 350 and the window length is 50, which of the following occurs? A. computed tomography numbers greater then +200 appear white B. computed tomography numbers less then 200 appear gray C. computed tomography numbers between 0 and +200 appear black D. only those numbers between +200 and +100 appear gray

A.

What does the DFOV determine A. how much collected raw data is used to create the image B. whether the x-ray tube rotates 180 or 360 degrees C.. the number of detector acquiring data D. area within the gantry where raw data is acquired

A.

The first operation to which raw data is subjected is referred to as A. Convolution B. back-projection C. 3-D surface shading D. none of the above

A. convolution

Component of the DAS responsible for converting the electronic signal into digital form. This digital data are then transmitted to the system computer for image reconstruction

ADC

350 ww, 50 wl

Abdomens-soft tissue

What parameters must be consistent in the source images to create reformations?

All the source images must have an identical DFOV, image center, gantry tilt, and they must be contiguous.

What window width should be used for tissue types with similar densities? A. 0=50 HU B. 50-500 HU C. 500-2,000 HU D. 2,000-2,500 HU

B.

Which of the folloinwg technical factor adjustments may be employed to reduce step artifacts in a multiplanar reformat MPR CT image? 1. acquisition of an isotropic data set 2. overlapping section increment 3. increase in effective mAs A. 1 only B. 1 and 2 only C. 2 and 3 only D. 1, 2, and 3

B.

Which of the following determines the max number of gray shades to be dispalyed on the television monitor A. window level B. window width C. contrast control on the monitor D. historgram

B.

Which algorithm is also known as the 'summation method'?

Back projection

***Image magnification uses only image data and does not improve resolution; it simply makes the existing image larger. When is it helpful to magnify a CT image?

Because magnification uses only image data and not raw data, pixel size is not affected. A magnified image retains accuracy in all image measurements. When trying to display suspected abnormalities for measurement.

100 ww, 30 wl

Brain

Range of CT numbers is defined as the A. depth of the CT image B. window length C. window width D. window level

C

Which of the following generates sagittal, coronal, and paraxial images from transaxial slices? A. back projection B. filtered projection reconstruction C. multiplanar reconstruction D. radiation treatment computed tomography

C.

1500 ww, -600 wl

Chest-Lung

An additional algorithm is required to allow for the reconstruction of variable slice thicknesses and addresses the problems of increased volume coverage and speed of the patient table in scanners that have more than 4 slices or above and it is called _______________.

Cone beam reconstruction

Windowing refers to A. certain region of interest on an image B. reformatting axial slices to coronal, sagittal, and paraxial slices C. opening multiple windows on the display device D. gray scale manipulation CT numbers

D.

The basic problem of the back-projection algorithm is? A. classical star pattern in the image B. image is blurred C. image is not diagnostic D. All the above

D. All the above

Which of the following reduces the amount of data that makes up the image? A. image enhancement B. image restoration C. image analysis D. image compression

D. image compression

Which visualization techniques uses all the info in the axial data set to display internal structures? A, interactive cine B. MIP C. multiplanar reconstruction D. volume rendering

D. volume rendering

IN general, the thicker the original slice, the better the reformation image T or F

F

Image manipuation produces additional info and is more than the other original data file T or F

F

A smoothing filter accentuates the difference between the neighboring pixels to enhance spatial resolution. T or F

False

In general, to maintain the same spatial resolution in the reformatted image, thicker slices are desired. T or F

False

The window width controls the image brightness and the window level controls the image contrast T or F

False

True or False: image magnification is essentially the same as decreasing the DFOV.

False

Provide an example of an area of anatomy that is best imaged with a wide window width. What is an area that is best visualized by a narrow width?

For lung studies, wide window width is best for displaying all the various tissues and parenchyma. For brain studies, narrow window widths are best to make it possible to differentiate the white and gray matter of the brain.

**** Initially, Hounsfield had problems with the image reconstruction process he choose. Please describe his initial problem and what image reconstruction process is used to correct this problem.

Images were noisy. Filtered back projection??

Also called area processes or group processes

Local operations

What is the difference between the different types of image compression.

Lossless- on the whole means there is no loss of information Lossy- information is lost. Provides high compression ratios; irreversible

Images are created by selecting each voxel along a line form the viewers eye through the data set and selects only the brightest

MIP

Sampling

Measures the brightness of each pixel in the entire image

Images are created by selecting the voxel with the minimum value for the line of display

MiniP

Does changing the window setting change the raw data in CT?

No, windowing changes the contrast of an image not the raw data.

Most frequently used imaging processing technique

Point operations

What is the difference between prospective reconstruction and retrospective reconstruction?

Prospective reconstruction is reconstruction automatically produced during scanning. b. Retrospective reconstruction reuses raw data to generate new images.

The brightness value of each sampled pixel is assigned an integer. This is the final step in the digitizing process.

Quantization

Uses data to later generate a new image

Retrospective Reconstruction

The logical steps in digitizing an image are: scanning, sampling, quantization sampling and quantization scanning and quantization scanning, sampling, analog to digital conversion

Scanning, sampling, quantization

1800 ww, 400 wl

Spine-Bone window

An advantage of MPR is it enable visualization of specific structures in relation to surronding structures T or F

T

Scanning

Taking a pic and divide it into picture elements aka pixels - scanning results in a grid with rows and columns

What does a high standard deviation indicate?

The higher the standard deviation, the greater the variation among pixels within the region

Please explain the effect of the parameters matrix size, pixel size and bit depth on image appearance.

The larger the matrix size, the smaller the pixel size, therefore the better appearance of details.

What is the difference between reconstruction and reformation?

The term "reconstruction" is used when raw data are manipulated to create pixels that are then used to create an image. "Reformation" is used when image data are assembled to produce images in different planes, or to produce (3D) images.

In your own words, please provide an overview of the digital imaging and image reconstruction process.

The tube scans the patient acquiring data (data acquisition). X-rays are detected by the detectors after they have been attenuated by the patient. The signal from the detectors is amplified, so the electronic signals are forwarded to the ADC to be digitized. The data is now in digital format and is sent to the computer for reconstruction. Data is stored through PACS.

Convolution kernels can be applied only to raw data. T or F

True

Image magnification uses only image data and does not improve resolution; it simply makes the existing image larger.

True

Image smoothing is an example of a linear image manipulation technique. T or F

True

Pixel values that are higher than the range selected by window width will appear white. All the values that appear lower than the range selected will appear black. T or F

True

The new generation of multislice computed tomography scanners requires modified image reconstruction algorithms. T or F

True

Through the manipulation of computed tomography numbers of the various tissues, the picture can be changed to show soft tissues and dense structures such as bone. T or F

True

What is measurement data?

arises from the detectors -this data is subject to preprocessing to correct this data before the image reconstruction algorithm is applied

systematic accounts for the attenuation profiles of each ray sum and correlates it to the position of the ray

attenuation profile

In the image reconstruction process in CT, what happens to the views

attenuation profile is created for each view

During quantization, the value of the integer is determined by size of patient FOV matrix size attenuation values

attenuation values

What does an edge filter do?

accentuates the difference between neighboring pixels to enhance spatial resolution.

Image data are obtained:

after back projection

The mathematical manipulations required during the reconstruction of a CT image are accomplished using a(n): 1. algorithm 2. kernel 3. mathematical filter function

all 3

The window width and window length settings for a given examination of the abdomen are 400 and 0, respectively. Which of the following is true? -all structures between -200 and 200 will spread through the gray scale -all structures between -200 and 200 will be white -all structures between -200 and 200 will be black -only those structures above 400 will have different shades of gray

all structures between -200 and 200 will spread through the gray scale

Raw data in CT is: A. data from the detectors B. requires a vast amount of hard disk space C. subject to the image reconstruction process D. all the above

all the above

The process of converting data from the attenuation profile to a matrix is known as?

back projection

If the window width setting is 200 and the window length is 0, which of the following occurs? -computed tomography numbers greater than +100 appear white -computed tomography numbers less then 100 appear gray -computed tomography numbers between 0 and +200 appear black -only those numbers between +100 and +200 appear gray

computed tomography numbers greater than +100 appear white

What type of beam diverges from the x-ray tube to include the outer edges of the detectors?

cone beam

Which describes the beam that diverges from the x-ray tube to the outer edges of the detectors?

cone beam

The first operation to which raw data is subjected is referred to as:

convolution

To sharpen the image, a(n) ________________ process is applied to modify the frequency contents of the projection before back projection. convolution accuracy resolution noise

convolution

_________________ is a mathematical filtration used by the CT system to remove blurring artifact during the back projection method of image reconstruction.

convolution

Filtered back projection is also referred to as the ______________ _______________.

convolution method

What term describes the difference between stimulated raw data and measured projection raw data

correction term

What term describes the difference between the simulated raw data and measured projection raw data? model projection correction term algorithm

correction term

As window width increases, picture contrast:

decreases

Data from the computed tomography detectors are first sent to the _________ before going to the computer.

digitizers

Condition and boost the electronic signal that the detectors transmit in response to radiation absorption

electronic amplifiers

Which of the following algorithms is most commonly used in state of the art computed tomography scanners? iterative algorithms back projections filtered back projection fourier reconstruction

filtered back projection

this data is subject to convolution to correct the blur artifact from the back projection reconstruction process

filtered or convolved data

The primary goal (s) of iterative reconstruction is:(Please choose all that apply) *Improve image quality *reduce noise *artifact reduction *improved low contrast detectability *increase radiation dose

first 4

This technique can result in scaling and sizing of the images

geometrical operations

A common operation in this processing technique is Fourier domain processing

global operations

Window refers to -gray scale manipulation using CT #'s -opening multiple windows on the display device -reformatting axial slices to coronal, sagittal, and paraxial slices -outlining a region of interest

gray scale manipulation of CT #'s

***What is the purpose of changing the signal from analog to digital in CT?

he DAC changes the digital signal from the computer's memory back to an analog format so that the image can be displayed on the monitor

Ray

how much the x-ray beam takes from the tube to the detector

____________ data is the reconstructed data that has been projected back onto a matrix after convolution by an algorithm and displayed on a monitor as a gray scale CT image. A. matrix B. raw C. image

image

also called reconstructed data, are convolved data that have been projected into the image matrix to create CT

image data

Primary goals of iterative reconstruction is A. decrease scan time B. improve image quality C. reduce noise D. artifact reduction -cost efficient -improved low contrast detectability

improve image quality reduce noise artifact reduction improve low contrast detectability

What step in the typical IR process generates the initial CT image form an FBP algorithm? input IR loop modeling output

input

Each pixel in a digital image will be assigned one of these. (3)

integer, CT number, shade of grey

What term is known as a calculation process using a series of operations that are repeated several times? projection iterations model domain

iterations

Which reconstruction algorithm starts with an assumption and compares this assumption with measured values, makes corrections to bring the two into agreement and then repeats this process over and over until the assumed and the measured values are the same or within acceptable limits.

iterative algorithms

Which of the following refers to the relationship of computed tomography numbers to the linear attenuation coefficients of the object to be imaged? -attenuation ratio -linearity -reciprocity -uniformity

linearity

Which type of images compression results in no loss of information in the compressed image data?

lossless or reversible

A CT image is formed in part by projecting back all of the attenuation values recorded during data acquisition onto a: pixel voxel matrix detector

matrix

Can also be called scan data, this data set is preprocessing before the reconstruction algorithm is applied

measurement data

The new generation of multi-slice CT scanners (those with 16 and greate detector rows) require what

modified image reconstruction algorithms

Before the data is sent to the computers, they are sent where?

must be converted to digital form first. This is done by the analog-to-digital converters, or digitizers.

Which is not a factor that produces high standard deviation? mixed attenuation tissue within the region of interest a region of interest that includes a streak artifact no variation within the region of interest a region of interest that is not inside the margins of the object being measured

no variatoin within the region of interest

Which of the following does not have to be identical to reformat a CT study? -pitch -image center -DFOV -gantry tilt

pitch

A histogram in digital image processing is: plot of #'s of pixels as a function of the number of gray levels location operation spatial frequency filter windowing level

plot of number of pixels as a function of the number of grey levels

What is region-of-interest editing? *A form of volume rendering that is designed to look inside the lumen of a structure *Creating images by comparing the intensity of each voxel in the data set to some predetermined threshold *The process of selectively removing or isolating information from the data set *data set and selecting only the voxel with the highest value for inclusion in the displayed image.

process of selectively removing or isolating information from the data set

Process of using raw data to create an image is called image reconstruction. This construction is automatically produced

prospective reconstruction

Convolution kernels can only be applied only to _______________ data.

raw

this data is the result of preprocessed scan data and are subjected to the image reconstruction algorithm used by the scanner

raw data

Which is not true about image reformation? -raw data is used -may be 2D or 3D -used to better display relationships -generates images in different plane or

raw data is used

detector senses each arriving ray and measures how much beam has been attenuated

ray sum

when raw data is manipulated to create pixels that are used to create an image reconstruction or reformation

reconstruction

Which of the following is not a primary goal of iterative reconstruction algorithms? -reduce image noise with lower exposure technique -preserve spatial resolution at lower exposure techniques -reduce photon starvation artifacts -reduce artifacts by patient motion

reduce artifacts by patient motion

when the image is assembled to produce images in different planes or to produce 3D images

reformation

process of selectively removing or isolating information from the data set. The purpose is to better demonstrate the area

region of interest editing

Uses raw data to generate an image

retrospective reconstruction

measures the brightness of each pixel. Second steps in the digitizing process

sampling

Division of the image into small regions or pixels. The first step in digitizing the image.

scanning

Please know the three steps in digitization.

scanning sampling quantization

The process of selectively removing or isolating information from the 3D data set is referred to as

segmentation

Images are created by comparing intensity of each voxel in the data set to some predetermined threshold CT value

shades surface display

Please choose all that apply. What parameters can be changed retrospectively? *slice thickness *gantry tilt *spacing *reconstruction algorithm *DFOV *SFOV

slice thickness, spacing, reconstruction algorithm, DFOV

As matrix size increases, so do ____________________. spatial resolution temporal resolution contrast resolution none of the above

spatial resolution

Limitations presented by the filtered back projection algorithm include each of the following except: image noise artifact creation patient dose speed

speed

Window level should be set at a point that is roughly the same value as the average attenuation number of the tissue of interest T or F

t

the ____ the original slice, the better the reformatted image

thinner

What is the goal of using a thin slice for scanning and reconstruction and a thick slice for viewing and storing

to maintain the advantage of high resolution images but also create image files that are manageable and more easily viewed by the radiologist

What is the goal of using a thin slice for scanning and reconstruction and a thick slice for viewing and storing A. maintain the advantage of high resolution but also create images files that are manageable and more easily viewed by the radiologist B. create reformatted images that display better anatomical relationships C. generate images with isotropic pixels D. none of the above

to maintain the advantage of high resolution images but also create image files that are manageable and more easily viewed by the radiologist.

complete set of rays

view

Images are created by collecting and manipulating data along a line from the viewer's eye through the data set. The software

volume rendering

Images are created by summing the contributions from each of the voxels and each voxel is assigned an opacity value based on its hounsfield unit. No information is ignored or discarded, every voxel contributes to the image.

volume rendering

Higher CT numbers are usually assigned what color black white grey

white

Center of a range of CT #'s is called:

window level

Which of the following determines the maximum number of gray shades to be displayed on the television monitor? window level window width contrast controls on the monitor contrast modulation

window width

The most common image processing technique used in CT is____________________________.

windowing