Oral Radiology - CT Basics

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Questions and Answers

What is a disadvantage of fourth-generation CT scanners?

They are unable to detect scatter radiation.

They require a lower acceptance angle for radiation.

They produce lower quality images.

Only 1/4th of detectors are in use at a single time. (correct)

How do incremental scanners acquire images?

Using a stationary detector that moves during exposure.

By keeping the patient stationary while the CT rotates.

By continuously rotating the x-ray tube around the patient.

With a stepping motion of the patient table for slice positioning. (correct)

What technological advancement eliminated the need for wired connections in helical CT imaging?

Magnetic resonance coupling.

Slip-ring technology. (correct)

Infrared wireless communication.

Digital signal processing.

What primary issue did Single-Slice CT (SSCT) encounter?

Excess stress on the x-ray tube due to heating. Signup and view all the answers

What does the 'z-axis' in Multi-Slice CT indicate?

The slice thickness direction. Signup and view all the answers

What is the significant feature of Multi-Detector CT (MDCT) scanners?

They typically utilize an array of 64 to 128 detector rows. Signup and view all the answers

What advantage does MSCT provide over SSCT?

Increased z-axis coverage to minimize rotations. Signup and view all the answers

How does the design of the fourth-generation CT scanner differ from third-generation scanners?

It has a circular array of fixed detectors. Signup and view all the answers

What is one major limitation of plain radiography compared to cross-sectional imaging?

Plain radiography cannot demonstrate soft tissue. Signup and view all the answers

What does CT technology primarily utilize to create images?

X-rays and computer processing. Signup and view all the answers

What distinguishes Multislice CT from conventional CT?

It can acquire multiple sections simultaneously. Signup and view all the answers

Which component of a CT scanner is responsible for controlling data acquisition?

Computer. Signup and view all the answers

What is a primary disadvantage of first-generation CT scanners?

It requires a linear movement of the x-ray tube. Signup and view all the answers

What scanning method is utilized in fifth-generation CT scanners?

Steering of electrons magnetically. Signup and view all the answers

What advancement in CT imaging technology allows for higher spatial resolution?

Micro-CT. Signup and view all the answers

What is the primary purpose of collimating the beam before it enters the patient?

To minimize patient exposure Signup and view all the answers

What improvement did third-generation CT scanners provide over the second generation?

Higher number of detectors and larger fan beam. Signup and view all the answers

In a CT scanner, what purpose does the gantry serve?

To house the X-ray tube and detectors. Signup and view all the answers

Which generation of CT scanners was specifically designed for cardiac scanning?

Fifth generation. Signup and view all the answers

Which of the following detectors is known to produce light when exposed to ionizing radiation?

Scintillation Crystals Signup and view all the answers

What is the primary function of the rotation in a CT scanner?

To scan one section at a time. Signup and view all the answers

Which of the following is NOT a feature of MDCT technology?

It is capable of producing exclusively 2D images. Signup and view all the answers

What is a characteristic of Xenon Gas Ionization Chambers?

They cannot be used in rotate-rotate scanners Signup and view all the answers

What main technological feature do second-generation CT scanners utilize for image acquisition?

Narrow fan beam with multiple detectors. Signup and view all the answers

What was a limitation of the fifth-generation CT scanners?

They operate at low x-ray flux. Signup and view all the answers

Which generation of CT scanners used a pencil beam to acquire images?

First Generation Signup and view all the answers

What was one reason why the First Generation of CT scanners became obsolete?

They were too slow, taking about 5 minutes Signup and view all the answers

Which of the following statements correctly describes the imaging process in first-generation CT scanners?

The x-ray beam is collimated at the source. Signup and view all the answers

How did the introduction of larger arrays of detectors in third-generation CT scanners benefit imaging?

It improved resolution and decreased scatter radiation. Signup and view all the answers

Which detector type has largely replaced previous scintillation designs due to lower afterglow?

Silicon Photodiodes Signup and view all the answers

What scanning movement did the Third Generation of CT scanners implement?

Rotation-Rotation Signup and view all the answers

What is a notable feature of the Fourth Generation CT scanners?

Entire detector ring for remnant radiation Signup and view all the answers

What is a primary advantage of using Third Generation Multidetector Helical CT compared to single-slice scanners?

Less motion artifact Signup and view all the answers

Which of the following components is housed in the circular gantry of a CT scanner?

X-ray tube-head and detectors Signup and view all the answers

What effect does smaller pixel size have on image quality in CT scans?

Improves image resolution Signup and view all the answers

Which statement accurately describes a voxel in computed tomography?

The depth or volume of pixels Signup and view all the answers

What is a disadvantage of Third Generation Multidetector Helical CT scanners?

Higher radiation exposure Signup and view all the answers

How is the attenuation profile produced during a CT scan?

From the interaction of X-rays with tissue Signup and view all the answers

In CT imaging, what does a Hounsfield unit represent?

The level of absorption in tissue Signup and view all the answers

What feature helps to reduce motion artifacts in CT scans?

Quicker scan times Signup and view all the answers

What causes ring artifacts in CT imaging?

Miscalibration of detector elements Signup and view all the answers

Which type of artifact occurs due to a voxel representing tissues of differing densities?

Partial Volume Artifact Signup and view all the answers

How does Dual Energy CT (DECT) enhance imaging of blood vessels?

By selectively increasing the effects of iodine Signup and view all the answers

What advantage does Dual Energy CT provide for patients with kidney stones?

It helps detect the type of stone present Signup and view all the answers

What benefit does metal artifact reduction software (MARS) provide in Dual Energy CT scans?

It significantly improves image quality near metal objects Signup and view all the answers

Study Notes

Oral Radiology - Computed Tomography (CT)

CT scanners use X-rays to produce 3D images.
Unlike plain radiography, CT overcomes the superimposition problem in conventional radiography.
CT employs tomography and computer processing to generate 3D images from 2D images.
CT uses very sensitive crystal or gas detectors instead of radiographic film.
The X-ray tube rotates around the patient, scanning one section at a time.
Key components of a CT system include the computer, gantry, table, and operator's console.
The computer controls data acquisition, reconstructs images, stores image data, and displays images.
The gantry is a circular device housing the data acquisition system (DAS) which includes: the X-ray tube, detectors, filters, collimators, and ADC.
MDCT (multi-detector CT) scanners operate at high tube voltage and tube current using x-ray tubes with rotating anodes.
They operate in ranges, 80 to 140 kVp and 200-800 mA.
X-ray beam is collimated to a thin fan beam prior to entering the patient to minimize patient exposure and scattered radiation.
Detectors function as image receptors for remnant radiation converting the measurement into an electrical signal proportional to radiation intensity.
Two main detector types: Scintillation (solid state) and lonization (xenon gas).
Ceramic scintillators produce light when exposed to ionizing radiation, while Xenon gas ionization chambers are less efficient and unsuitable for rotate-rotate scanners.
The table is an automated device linked to the computer and gantry.
It moves in increments based on the technologist's scan program.
CT scanners have evolved through different generations characterized by differences in beam configuration (pencil beam, small fan beam, large fan beam, large fan beam), detectors (one, multiple), and scanning methodologies (translation-rotation, rotation-rotation, rotate-stationary).
First generation CT scanners utilized a pencil beam and a single detector.
Second generation used a small fan beam and multiple detectors.
Third generation incorporated a large fan beam and multiple detectors.
Fourth generation used an array of detectors fixed in a ring around the patient.

CT System Advantages

Detailed imaging of hard and soft tissues.
Excellent differentiation between normal and diseased.
Ability to perform thin slice imaging.
Less exposure time and less motion artifact.
Highly improved image quality compared to conventional tomography.
Improved speed due to helical or spiral scanning.
The ability to obtain both axial, coronal and sagittal cuts, as well as 3D images/reconstructions.

Types of CT Scanners

Helical or Spiral CT Scanners: The patient is moved continuously through the gantry while the X-ray source moves continuously around the patient in a circle.
Multislice (Multi-Detector) CT Scanners: These have multiple rows of detectors, resulting in significantly faster scanning time, enabling better images/reconstructions. Increased speed enables scanning to be performed without needing the patient to hold their breath for extended periods.

CT Scan Disadvantages

High patient dose than single-slice scanners
Equipment is expensive.
Facilities are not widely available.
Risks related to IV contrast agents.
Metallic objects can produce streaking/star artifacts.
Ring artifacts can be caused by miscalibration or failure of detector elements, or insufficient dose.
Partial volume artifacts result when a single voxel represents tissues of differing densities.
Beam hardening artifacts appear as dark streaks between two structures, such as compact bone, dental implants, and dental restorations.

Dual Energy CT

Dual Energy CT (DECT) uses both normal X-rays (standard) and a less powerful x-rays (secondary beam).
DECT provides various additional advantages such as detecting subtle differences in structures, allowing for better images/reconstructions of blood vessels and assisting diagnoses of medical conditions like kidney stones.

Image Processing

Matrix: An array of numbers arranged in rows and columns.
Pixel: A single square or picture element within the matrix (defines the resolution of the image).
Voxel: The volume (depth/thickness of a pixel) represented on the image.

CT Numbers

Each voxel is assigned Hounsfield Units (HU) between -1000 and +1000.
This assignment is based on tissue absorption and forms the image's gray scale.
Air has a value of -1000 (blackest areas on the image/contrast).
Water has a value of 0.
Bone has a value of +1000 (whitest areas on the image/contrast).

Image Manipulation

In image manipulation, the Window level (WL) and Window Width (WW) are adjusted to highlight specific types of tissues or to accentuate subtle differences.
These modifications allow radiologists to see and differentiate various tissue types and structures.

Indications of CT

Intracranial disease
Bony fractures
Developmental anomalies
Sinuses
Oroantral fistula
Cysts (e.g., follicular cyst maxilla)
Benign tumours
Malignant tumours
Infection (sequestrum)
Salivary gland lesions.

Preoperative Assessment of Bone

CT is used in preoperative assessments to determine the height and thickness of the alveolar bone to guide implant placement.

CT Guided Biopsy

CT is employed in guiding biopsies through imaging techniques.
This approach facilitates accurate sample acquisition and improved diagnosis accuracy.

Advantages

Superior resolution
Detail in hard and soft tissue
The speed due to helical/spiral scanning means the image reconstruction can be performed much faster.

Disadvantages

More expensive
High dose radiation
Risks associated with IV contrast agents

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Description

This quiz covers the fundamental aspects of computed tomography (CT) in oral radiology. It explores how CT scanners utilize X-rays to create detailed 3D images, the key components of a CT system, and the technological advancements that differentiate CT from conventional radiography.