CT Imaging

What is the gantry?

Circular device that houses x-ray tube, DAS and detector array

What was CT formally called?

Computed Axial Tomography (CAT)

5th generation scanners are classified as what?

high speed CT scanners

Detectors function as _____ receptors.

image

The table moves in increments or ____ according to scan parameters.

index

A CT of CNS demonstrates:

infarctions, hemorrhage, disk herniations, fractures and tumors

Tissue with less density than water is assigned a _____ CT number.

negative

Data acquisition determines the _____ prior to initiating the scan.

parameters

Window width:

range of CT numbers used to map signals into shades of gray. Determines the number of gray levels displayed in the image.

Dense residual barium can cause artifact similar to metallic objects. These artifacts are called _____ artifacts or _______ appearance

streaking sunburst

In conventional X-ray, Radiation passes through the patient and produces an image of the body part with body structures _________.

superimposed

In Computed Tomography, Tightly collimated x-ray beam is directed through patient from many different angles, resulting in an image that represents a cross section of the area scanned & eliminates _________.

superimposition

CT exposure comes from the continuous rotation which results in a ______ radiation dose gradient within the patient

symmetric

6th generation scanners improve _____ resolution and _____ patient dose.

temporal reduce

Most CT systems require ____ or _____ preventive maintenance

weekly or biweekly

A _____ number is assigned to each signal

whole

MSHCT

Multi Slice Helical CT

The 2nd generation scanners gantry rotates __ degrees between each translation

10

Current technology detector arrays allow up to ___ rows or channels

320

In a 3rd generation scanner there are ___ detectors arranged in a ______detector array

750 curved

Maximum Intensity Projection (MIP):

Reconstructing the brightest pixels from a stack of image data into a 3D image

Interventional procedures include:

-Abscess drainage -Tissue biopsy -Cyst aspiration

Advantages of CT over conventional angiography:

-Arbitrary image can be reconstructed without exposing patient to more radiation or additional IV contrast -Overlying structures can be eliminated so only vascular anatomy is reconstructed -Does not require arterial puncture ~ only minimal postprocedureobservation

What are the 3 major system components?

-Computer -Gantry & Table -Operator Console

4 basic functions of the computer?

-Control data acquisition -Image reconstruction -Storage of image data -Image display

What is the purpose of contrast media?

-Distinguish normal anatomy from pathology -Make disease processes more visible

What are the controls on a power injector?

-Flow rate of injection -PSI (pounds per square inch) of pressure -Amount of contrast to be delivered -Time delays

Most commonly requested procedures:

-Head, chest and abdomen -Examination of choice for head trauma -One of the 1st exam performed for possible stroke or CVA •R/o hemorrhage

What is a phantom?

-Multisectionedand constructed from plastic cylinders -Each section filled with test objects designed to measure performance

Patient factors:

-Patient movement -Body size -Slice thickness

What are the two basic types of detectors

-Scintillation or solid state detectors -Ionization or gas detectors

3D images of internal structures can be used for:

-Surgical planning -CT angiography (CTA) -Radiation therapy planning -Virtual reality imaging

The operates console allows the operater to enter:

-Technique factors -Slice thickness -Table index -Reconstruction algorithm

Temporal resolution:

-ability of the CT system to freeze any motion of a scanned object -Shortest amount of time needed to acquire a complete data set (cardiac imaging)

What is the 3rd generations scan time?

0.35 to 10 seconds per slice

The 1st generation scanner has a linear tube movement with a __ degree rotation.

1

100 rem =

1 Sv

CTA study calls for an __ to __ gauge angiocathwith an injection of 4 to 7 mL/sec

18-20

__% barium mixture for abdomen/pelvis CT image

2

In a 6th generation scanner there are __ sets of detectors that are offset by ___ degrees.

2 90

What is the second generations scan time?

20 seconds per single slice

Routine, non-CTA exam calls for a ___ gauge angiocathwith an injection rate of 2 mL/sec

22

Apertures are normally __ inches wide.

28

What is the 1st generations scan time?

3-5 minutes per scan

The gantry can rotate forwards and backwards up to ___ degrees.

30

The 2nd generation scanner has __ detectors placed closely together in a _____ _____.

30 detector array

Shaded Surface Display (SSD):

A 3D image of the surface of a particular structure, different tissue types within image are separated using segmentation, a threshold value is set and then shading is applied.

What is a voxel?

Adding slice thickness to the pixel gives it dimension = volume element

CTDI 100 (Dose index):

Allows calculations along full length of chamber

CT Anigoraphy:

An application of spiral CT using 3 dimensional imaging techniques

The gray level assigned to each pixel corresponds to the ___ number for that pixel

CT

CT Definition: (Bontragers)

CT uses a complex computer and mechanical imaging system to provide sectional anatomic images in the axial, sagittal and coronal planes

Effective dose is determined by multiplying _____ by a region specific conversion factor

DLP

What is a bolus injection?

Delivered quickly providing better contrast enhancement of structures & better opacification of blood vessels

What is a matrix?

Digital image is an array of numbers arranged in a grid of rows and columns

Anatomy displayed is referred to as:

Display FOV

DLP stands for:

Dose Length Product

Hounsfield units/ CT numbers:

Each pixel within the matrix is assigned a number that is related to the linear attenuation coefficient of the tissue within each voxel

5th generation scanners are EBCT scanners which stands for?

Electron beam CT

The 2nd generation scanner has a ____ shaped beam?

Fan

A power injector does what?

Faster delivery of IV contrast with reduced scan times

Scanners are characterized by what?

Generation

Array processor:

Millions of mathematic operations needed to digitize and reconstruct raw data

MDCT

Multi Detector CT

CT Definition: (Merills)

Process of creating a cross-sectional tomographic plane of any part of the body

What is multiplanar reconstruction?

Reconstruct axial images into coronal, sagittal or oblique body planes without additional radiation to the patient

What does generation mean?

Reference to level of technologic advancement of tube and detector assembly

Image that appears on the monitor depends on the scan diameter, this is called:

Scan FOV

Effective dose is measured in ____ or rems.

Sieverts (Sv)

What is a pixel?

Single square or picture element within the matrix

Helical CT use ___ ring technology with ____ degree continuous rotation of tube detector.

Slip ring 360

In 1974 Robert S. Ledley created what?

The 1st full body scanner

_____ CT refers to scanners with 64, 128, 256 and 320 rows

Volume

_____ is used as a reference material because it is abundant in the body and and provides uniform density

Water

The image processing technique is called:

Windowing or gray level mapping

Construction:

a volume of 3 dimensional data from original 2 dimensional data

Contrast resolution:

ability to differentiate between small differences in density within the image

Effective dose involves where the dose is being ______.

absorbed

Cone geometry does what?

accommodates increased length of detectors

Rendering or shading:

adds depth perception to final image

Dynamic scanning is based on what principle?

after administration of contrast, different structures enhance @ different rates

The computer then compiles and calculates the data according to pre-selected _______

algorithms

Windowing or gray level mapping does what?

allows the contrast in the image to be altered by adjusting the window width and window level

What injection site is preferred for IV insertion?

antecubital fossa

The opening within the center of the gantry is called the _____.

aperture

Bone-soft tissue interface such as in the skull-brain is called _____ ______ artifact.

beam hardening

Early 1970s, CT was only capable of imaging the ____ and only produced _____ images

brain axial

5th generation scanners are used for _____ studies.

cardiac

Volume CT scanners have _____ geometry

cone

Segmentation:

cropping or editing the target objects from the reconstructed data

Each image or slice is displayed in a ________ format

cross-sectional

Spatial resolution:

degree of blur or the ability to see the difference between 2 objects that are close together

Multi detector CT increase in the number of _____ row, allowing for _____ slices to be taken in one rotation.

detector multiple

What is field of view (FOV)?

determines the amount of data to be displayed on the monitor, like a scout image

The value of the number is _____ proportional to the strength of the signal.

directly

Measurement of CT dose is performed with a circular CT dosimetry phantom with implanted thermoluminescent ________.

dosimeters

6th generation scanners are ___ energy source or two x-ray tubes.

dual

Measured transmitted values are converted into an _____ signal which is sent to the computer.

electrical

Goal of quality control?

ensure system is producing the best possible quality images with minimal radiation dose to patient

Exceeding the table weight limit can do what?

give an inaccurate index reading, damage the table motor, or break the table top

Each pixel within an image is assigned a level of ____

gray

A power injector is mandatory for ____ CT scanners

helical

The host computer has a _____ storage capacity.

limited

The data is assembled into a ________that forms the axial image on the computer monitor

matrix

The detectors ______ the transmitted x-ray values.

measure

Data acquisition:

method of scanning the patient

The reconstructed image is displayed on the _____.

monitor

Noise:

most common cause is quantum noise resulting from random variation in photon detection; affects contrast resolution

What are volume CT scanners?

multi-slice scanners with 64 detector rows

4th generation scanners are not used often because of the increased _____ dose.

patient

Patient dose for each examination must be part of patient's ______ _______.

permanent record

Tissue with a density larger than water is assigned a _____ CT number

positive

Multiplanar reconstruction is known as:

post- processing technique

CTDI W:

provides a weighted average of the center & peripheral contributions

A detector assembly (image receptor) measures the _____ exiting the patient and sends the information to the host computer

radiation

Detectors measure the amount of _____ transmitted through the body

radiation

4th generation scanners have a ______ only movement. This means the tube rotates around the patient with the detectors remaining in a fixed position.

rotate

A patient is scanned by an x-ray tube ____ around the body part being examined

rotating

Helical CT reduces what?

scan times

Dynamic Scanning:

scanning through an area rapidly

The 1st scan is called the:

scout scan

In the 3rd generation scanner the X-ray tube and detector array rotate ________ around patient

simultaneously

Single slice or helical CT uses ____ _____ technology.

slip ring

A CT of the body demonstrates:

soft tissue structures, metastatic lesions, aneurysms, abscesses and fluid collections

The scout scan (aka topogram or scanogram) is used for what?

used to plan sequence of axial scan

Single slice or helical CT scans a _______of tissue rather than a group of individual slices in a single breath hold

volume

Water is assigned what number?

zero

Volume Rendering (VR):

•Sums the contributions of each voxel along a line from the viewer's eye through data set •Displays a wide range of tissues accurately depicting anatomic relationships