CT image production

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During an axial scan, the total amount of anatomical coverage per tube rotation is dependent on which of these variables? - The number of active detector rows2 - The thickness of active detector rows3 - - the pitch

- The number of active detector rows2 - The thickness of active detector rows3 -

During an axial scan, the total amount of anatomical coverage per tube rotation is dependent on which of these variables? 1 - The number of active detector rows2 - The thickness of active detector rows3 - The pitch

1 and 2 aka collimation

Common DFOV for c spine is

120 mm (12 cm)

KVP should never exceed

140

After performing a CT of the chest, an ROI placed in the air outside of the patient yields of an average CT number of -1,223. This error represents a problem with

Accuracy

What does undersampling cause

Alaising

Iterative reconstruction

Basically you can lower the dose and allegedly maintain imaging quality with advanced reconstruction

What artifact occurs when the x-ray beam passes through dense material like bone metal or contrast

Beam hardening

out of field artifacts is caused by patient

Being outside SFOV

Which algorithms increase spatial resolution?

Bone Lung

Dense materials such as _______ and _______attenuate _______

Bone Metal More

Consider a CT image that was initially displayed with a 300 window width and a 30 window level. DECREASING the window level from 30 to 0 will have what effect on the image?

Brighter

Reconstruction of raw data into image data occurs within which component of the CT system?

COmputer system

window width refers to the range of

CT numbers that will be expressed in the image as some shades of gray

Smoothing algorithms like standard are better for _________but not for _________

Contrast resolution Spatial resolution

What is the principle function of the data acquisition system (DAS) in CT?

Converts electrical signals into raw data

The purpose of the detector array in CT is to:

Converts photons to electrical signals

What data process is used to smooth or sharpen image data for better visualization of the desired anatomy?

Convolution

The physical dimensions of the matrix and pixels are determined by

DFOV

Compared to a pitch of 1, a pitch of 1.137 will have: Decrease scan time Decrease patient dose decrease spatial resolution

Decrease patient dose Decrease spatial resolution

What factors increase temporal resolution

Decrease rotation time Increase slice thickness Increase pitch

Increasing the window level of a CT image will result in:

Decreased brightness

What 6 factors increase spatial resolution?

Decreased detector size Decreased pitch increased rotation time Decreased DFOV Decreased slices Decreased noise Increased matrix size Bone algorithm

Using a larger reconstruction slice thickness results in which of the following?

Decreased image noise Decreased spatial resolution

As noise increases, contrast ___________

Decreases

Increasing mA and kVp _______noise and _________contrast

Decreases Increases

WIDER window width ________contrast and has a ____________ gray scale

Decreases Wider

increasing slice thickness _______total scan time which __________ temporal resolution

Decreases increases

Adjacent areas with significant density differences can cause an artifact called

Edge gradient

Alaising is caused by

Fast scans or increased pitch

High pitch results in a __________scan with ________resolution images

Faster Lower

If pitch is greater than one this results in

Faster scan speed Lower Dose Less spatial resolution

Window level is usually set similar to the

HU

The most common mode of scanning is

Helical

Spatial resolution is tested using QC and line pairs. The more line pairs the _________the spatial resolution

Higher

What uses an ROI and provides a frequency of HU for the area

Histogram analysis

Which of these quantitative analysis methods in CT can be used to identify the maximum Hounsfield value in an area of concern?

Histogram analysis

Other methods for improving temporal resolution

Image gating Half scan algorithms

What is the most important factor influencing contrast resolution

Image noise

Consider a PACS network in which imaging studies are distributed directly to specific reading stations and to the PACS archive server. What is the main advantage of this distribution system?

Images are duplicated in the PACS archive server and at the reading workstation If the archiver server goes down, images can still be sent to specific reading stations

What factors increase contrast resolution?

Increase technical factors Decrease patient size Increase thickness Lower standard deviation

Contrast is _________with thicker slices

Increased

During a routine CT scan of a pediatric chest, the radiologist requests that the technologist reconstruct the image data with 1.25 mm slices rather than 2.5 mm slices. One negative effect of this change will be:

Increased image noise

As window level _______the contrast gets _______

Increases Darker

Decreasing pixel size and FOV

Increases spatial resolution

What is the mostly likely cause of the blurry appearance of this coronal reformation of the abdomen?

It was reconstructed from a thick slice

During CT angiography, images may be reconstructed using only the greatest density encountered along each ray. This type of specialized CT image is called a(n):

MIP

Window level represents the

Midpoint of CT numbers that will be viewed

Motion artifact causes _________ of the patients anatomy

Misregistration

What do the numbers in a matrix represent

Number of pixels

Which of the following is used for long-term storage of digital image data?

PACS

Different tissues being averaged into one slice is

Partial volume averaging

Increasing DFOV decreases________but _________spatial resolution

Pixel size Increases

What portion of the patient can be visualized through the process of retrospective reconstruction?

Portions in the SFOV

A single "view" acquired during a CT scan is also called a

Projection

What puts specific numbers to observations seen on a CT (the exact size of an aneurysm)

Quantitative analysis

A measurement tool used in quantitive analysis to acquire various calculations for an area of interest

ROI

The process of assigning a specific level of edge-enhancement to the CT image data is controlled by mathematical filters called:

Reconstruction algorithms

Concerning personal health records, federal laws does NOT allow a patient to:

Remove their records

What cannot be changed retrospectively

SFOV Acquisition thickness

What type of 3D rendering just shows the surface?

Shade surface display

How does cone beam artifact affect the appearance of the CT image?

Shape distortion of anatomy

Select all parameters that CAN be changed retrospectively.

Slice interval Slice thickness Reconstruction algorithm DFOV Start and end

Bc MPR images are created in different planes the technologist must select new

Slice thickness and intervals

A detector array is arranged into rows called ________and having more of them makes the beam_____

Slices Wider

In MPR and reconstruction slice thickness affects

Spatial resolution Noise

What algorithm must be used with volume rendering to avoid noise

Standard (smoothing)

What does filtered back production remove

Star like artifacts

Retrospective reconstruction

Start and end locations Slice thickness and interval DFOV Reconstruction algorithm Window width and level

EMR is different than EHR bc it just involves patient information from

That certain doctors office

Uniform array

The detector rows are equal size

When using a CT scanner with non-uniform detector rows, which of the following statements is true:

The inner rows have the highest spatial resolution

1024 x 1024 matrix refers to

The number of pixels in a matrix

Acquisition thickness refers to:

The thickness of active detector rows

Changing the thickness of a voxel may also change

The tissue types in the voxel

Kvp should only be changed with the _______of patient

Thickness

Because of loss of information MPR reformats must be taken from ________slices

Thin

What quality control test evaluates the ability of the CT scanner to produce the same CT number for the same material regardless of where the ROI is placed?

Uniformity

When scanning a water phantom for quality control, you notice that an ROI in the center of the phantom reads 0 HU but an ROI on the edge of the phantom reads 4 HU. This is a problem with:

Uniformity

Digital process of projecting the entire data set

Volume rendering

Linearity

When the attenuation of an object increases so should the CT number

Numbers above the window width are _______and numbers below are ______

White Black

The gantry houses

X-ray tube detectors collimators high voltage generator ADC

Changing the slice thickness of an axial reconstruction changes the dimensions of the image data in what axis?

Z axis

Reconstruction algorithm (convolution)

an add sharpness to the images (bone and edge-enhancing kernels) or they can smooth the images for viewing soft tissues (standard kernels)

MPR reformats axial images to

be viewed in other planes (sagittal, coronal, obliques)

Unlike axial who acquires one section at a time, helical

captures one large spiral of data while the tube and table are in constant motion

Detectors are responsible for

collecting photons that have passed through the patient and converting them into a measurable electrical signal

A wide beam might cause a ______artifact

cone beam artifact

Increasing pitch ________ total scan time which _______ temporal resolution

decreases

Pitch only applies to helical scanning and is a ratio describing

distance the table moves during scanning compared to the beam width .

Kvp controls

energy of beam (quality) but also influences intensity

If a radiologist needs to know the ratio of fluid to blood in a cerebral lesion, what quantitative tool can help to estimate this ratio?

histogram analysis

MPR images are created from what kind of data

image data

What is interpolation

images must be viewed in axial sections (not a spiral), the computer must reconstruct the data into perfect planar slices from the volume of data

What affects noise the most?

kVP

DAS does 3 things

measures the transmitted radiation from the detectors converts electrical signal to a digital signal transmits the digital signal to the main computer

as voxel/slice thickness increases what happens

more anatomy is shown

Temporal resolution is the ability to see

moving parts

A higher standard deviation causes more _________

noise

mA is

quantity & intensity of beam and the exposure to the arrays

reconstruction images come from _______data and only come from _____plane but can use any_______

raw axial Algorithm

SFOV

refers to the entire area inside the scanner that is actually being scanned .

When a detector fails it causes a ________artifact

ring

Contrast resolution is the ability to

see parts with similar densities

Spatial resolution is the ability to

see small parts

The capacity of the machine to differentiate between objects of similar densities

sensitivity of the system

Prospective reconstruction

setting up reconstruction before the scan

Axial scanning is also called

slice by slice or step and shoot

voxel thickness equals

slice thickness

Smaller detector size results in better:

spatial resolution

Ejection fraction is the

the percentage of blood that is pumped out of the heart with each contraction (above 55 are good)

Convolution

the process through which scan data is mathematically filtered to better visualize specific tissue types.

The larger the matrix size

the smaller the pixels, the better spatial resolution

Viewing blood vessels and bone should be viewed using what slice thickness

thin

a uniform array can produce ______ slices and shows ________detail but has a ________dose

thin more higher

What else happens when pitch is increased

this results in a faster scan and less dose to the patient. Think of increased pitch as stretching out the spiral. More anatomy is scanned with each rotation of the tube. Less time is needed, and less dose is used. Unfortunately, the spatial resolution will decrease.

Which of these images is displayed with a widow width of 2500 and window level of 600

which image is most like the window level


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