RTE - CT SCAN COVERAGE

1. components

2. slice capability

3. technical specifications

4. data acquisition

5. scan geometry

what are the parts of a CT scanner?

1. gantry

2. table

3. xray table

4. detectors

5. collimators / filters

6. computer

7. display console

8. image storage units

what are the ct scan components? (8)

gantry

what houses the xray tube?

gantry

receives electronic commands from the operating console and transmit data to the computer for image production and analysis.

gantry

it includes 50-85 cm (20-34”) aperture for the patient

gantry

this can be angled up to 30 degrees; to permit positioning for partial coronal images.

gantry

lights are usually mounted, white halogen and low power red laser lights that are used for positioning,

X and Y

The _______ are defined within the gantry geometry.

the ________ is located inside the gantry

Digital Acquisition System

DAS means?

Table

This is made of carbon graphite fiber to decrease beam attenuation.

carbon graphite fiber

Patient table is made up of _______ to decrease beam attenuation

Table

it is capable of supporting the entire weight of the patient without sagging when fully extend

automatic indexing

patient couch should be of __________

patient table

it is capable of horizontal and vertical movement

patient table

capable of uninterrupted movement during spiral/helical acquisition (pitch)

xray tubes

these are high capacity tubes

high speed rotors

__________ are used in most tubes for the best heat dissipation

2-5 MHU

what is the MHU capacity designed specifically for CT anode capacity

30 exposures

may produce _______ per examinations.

detectors

should have high capture efficiency, high absorption efficiency and high conversion efficiency.

detectors

should have high stability, fast response time and a wide dynamic range

1. stability

2. response time

3. dynamic range

what are the 3 criterias for a CT system xray detectors?

Stability

the detector must be calibrated to meet quality control standards

Response Time

The speed with which rhe detector can react to reconginze an incoming photon and recover for the next input.

Dynamic Range

Is the ratio of the largest siganl that can be measured to the smallest.

preventive maintenance

calibration is part pf our _________?

• scintillation detectors

• gas or xenon gas-filled ionization chambers detector

what are the 2 classifications of detectors?

scintillation detectors

thsi detector is also called as solid state detectors

scintillation detectors

this detector requires power supply?

scintillation detectors

this detectpr was replaced by cadmium tungstate crystal-photodiode assemblies

scintillation detectors

________ are smaller and cheaper and do not require a power supply

90%

high x-ray detector efficiency approximately _____ of the xray incident on the detector are absorbed and contribute to the output signal.

Ionizing Radiation

The process of scintillation detectors: certain type of material will scintillate when irradiated, they emit a flash of light immediately in response to absorption of ___________.

gas filled detectors

filled with high pressure xenon gas (~30 atm)

free electrons

in gas filled detectors, ,when an xray photon enters, it ionizes the gass, releasing _________

electrical signal

The electrons are attracted to a positive electrode, creating an ________.

45%

gas filled detectors has approximately _______ overall total detection efficiency.

1. geometric efficiency

2. quantum efficiency

3. conversion efficiency

Three important factors contributing to detector efficiency

geometric efficiency

it refers to the area of the detectors sensitive to radiatipn as a fraction of the total exposed area.

quantum efficiency

refers to the fraction of incident xrays on the detector that are absorbed and contribute to the measured signal,

conversion efficiency

refers to the ability to accurately convert the absorbed xray signal into an electricl signal.

collimators

______ are with filters

collimators

reduces patient does by restricting the volume of the tissue irradiated.

collimators

it enhances image contrast by limiting scatter radiation

collimators

limits the area of the patient that intercepts the useful beam and thereby determines the slice thickness and patient dose.

collimators

used to shape xray beam size and width

1. pre-patient collimator (beam collimator)

2. post-patient collimator

2 types of patient collimators in CT scan

pre-patient collimator

it consist of several sections so that nearly parallel xray beam results

post-patient collimation

it is also called as detector collimation

post-patient collimator

it restricts the xray field viewed by the detector array

post-patient collimator

this collimation reduces the scatter radiation incident on the detectors and coupled with pre-patient collimator to define the slice thickness

bowtie filter

a beam-shaping intensity filter

bowtie filter

shapes the xray beam to match the patient’s anatomy, thereby reducing unnecessary radiation exposure to thinner body regions.

bowtie filter

it is positioned after the pre-patient collimator and before the x-ray beam reaches the patient

full bowtie filter

symmetrical thickness on both sides

full bowtie filter

designed for uniform body parts (e.g., head, abdomen)

full bowtie filter

reduces peripheral dose evenly

full bowtie filter

provides uniform image quality across the FOV

full bowtie filter

commonly used in ct scans

half bowtie filter

asymmetrical thickness (one side thicker)

half bowtie filter

designed for off center anatomy

half bowtie filter

used when anatomy does not occupy the full FOV

half bowtie filter

helps reduce dose to less-dense regions

half bowtie filter

commonly used in ct angiography and pediatric imaging.

computers

designed to control data acquisition, process and display and storage

computers

microprocessor and primary memory-the heart

Data Acquisition System

controls a variety of operations including:

• tube and detector collimation

• pixel size

• matrix size

• gantry angle

• tabletop entrance into the gantry aperture

• section increment movements of tabletop

• xray tube voltage and amperage

• scan speed and direction of detector signals

solid state detectors

xrays - light - electrical signal

gas detectors

ionization - electrical signal

CT COMPUTERS

the __________ processes the data using algorithms to create cross-sectional images.

display console

computer workstation where the technologist and radiologist view, manipulate and analyze reconstructed CT images.

CT Localizer Radiograph

often displayed as the first image if an examination

CT Localizer Radiograph

digital image acquisition that are created while the tube is stationary and table moves through the scan field.

CT Localizer Radiograph

these images allow the technologist to prescribe the location of cross selection slices

reverse display

available to reverse the image from left to right and or reverse the density display

Magnification

Refers to the apparent enlargement of structures on the CT image due to a reduced field of view during image reconstruction

Magnification

-mainly controlled by the Field of View (FOV) and matrix size

Three Dimensional Imaging

• Shows the anatomy in length, width, and depth, allowing structures to be viewed from different angles.

Three Dimensional Imaging

• Reconstructed images that provide volumetric visualization of anatomy using data from multiple axial slices.

Supression

Designed to suppress the information from surgical clips. Clip be outlined and then deleted from reconstruction data

Annotation

added to images for descriptions or anatomical labeling

Histograms

a graph that provides useful information regarding the radiograph

Image storage

refers to the saving, archiving, and retrieval of CT images and related data in digital systems for review, diagnosis, and long-term record keeping.

CT Scan Control

it refers to the system and interface used by the radiologic technologist to select, adjust, and initiate scanning parameters.

CT scan control

• It is the part of the CT system where the technologist ensures that the examination is safe, accurate, and optimized for image quality and patient dose.

operating console

It is used to put all the factors gained from the scanning.

• used by the CT scanner operator,

• used by the physician.

There are two different control consoles :

slice thickness

determines image detail

Pitch

controls table movement during helical scanning

operating console

The ________ is the control center of the CT scan.

Rotation Time

affects temporal resolution

slice

• represents a single cross-sectional image of the patient acquired during one rotation of the X-ray tube and detector system.

number of slices

The __________ indicates how many images can be acquired simultaneously in one gantry rotation, which is determined by the number of detector row.

more slices

________ = more anatomy covered per rotation

Reconstructed Slices

• These refer to the number of images that can be generated from the raw data using reconstruction algorithms.

z - axis coverage (Detector Configuration)

• This refers to the total anatomical thickness covered in one tube rotation.

Acquired slice

• This refers to the detector rows that physically capture data during one gantry rotation.

Acquired Slice

_________ = physical detector rows of the scanner.

• maximum mA

• The _______ indicates the highest tube current the system can deliver.