CT San Exam Practice

What is the name of the mathematical set of all defined instructions for accomplishing a task?

Algorithm

What is the principle called where an X-ray beam passes through tissue and is affected?

Attenuation

In what format are CT images displayed?

Cross sectional format

According to the lecture, what year is emphasized for the invention of CT?

1972

Which two generations of CT machines only ever rotated $180\text{ degrees}$ and back $180\text{ degrees}$?

First and second generation

Why did the first generation CT machine take a long time to process information?

It had to process the information off-site because there was no computer system built into the machine.

Why did it not make a difference whether patients could hold their breath during the earliest first-generation CT scans?

Because the only part of the body being scanned was the head.

What was the twofold purpose of every successive generation of CT machines?

To scan faster and get better images.

How do the detectors in a fourth-generation CT machine differ from earlier designs?

The detectors are stationary all the way around the machine while the X-ray tube rotates all the way around.

What are the defined attenuation parameters for bone, air, and water in CT scanning?

Bone is $+1000$, air is $-1000$, and water is $0$.

What scan is performed daily to ensure the CT machine is calibrated to the correct density parameters?

A phantom scan (placing a phantom in the machine)

What two elements always combine to help increase CT image resolution?

The number of detectors (more detectors) and the algorithm that is run.

A CT image/information is based on a principle of the x-ray beam going thru tissue and being affected, what is this called?

Attenuation

Tomo

to cut

Graphia

to display

Gustave Grossman “1934” was a pioneer in the development

of computed tomography (CT) technology, contributing to the advancement of X-ray imaging techniques that allow for detailed cross-sectional views of the body.

William Oldendorf “1960” was a key figure in the invention

of the first commercially available CT scanner in 1971, revolutionizing diagnostic imaging by enabling precise visualization of internal structures.

CT was invented in 1972 by

British engineer Godfrey Hounsfield of EMI Laboratories, England, and independently by South

African born physicist Allan Cormack of Tufts

University, Massachusetts

Tomographic Image

a picture of a slab of the patient’s anatomy

CT slice thickness is very

thin (1 to 10 mm) and is approximately uniform

Tomographic acquisition is the method

of obtaining cross-sectional images by using X-rays from multiple angles.

Second Generation CT Scan

utilizes two detectors and can produce images faster than the first generation, allowing for improved patient comfort and reduced scan time.

Third Generation CT Scan

uses a curved array of detectors and rotates around the patient, which allows for faster imaging and enhanced image quality.

CT 3rd Generation size and shape

fan-shaped beam 30-60 degrees

How many detectors were in the CT 3rd Generation?

288-700 detectors needed to read larger fan-shaped beam

Fourth Generation CT Scan

fixed detector ring source-rotation large fan beam

CT 4th Generation fan shape

same as 3rd generation

How many detectors are in the CT 4th Generation?

It typically has a fixed ring of detectors, usually fewer than in 3rd generation systems, generally around 200-400 detectors.

Cross-sectional Imaging

A section formed by a plane cutting thru an object, usually at right angles to an axis. Thus, allowing the visualization of 2 (TRUE) dimensions displayed on one image.

Algorithm

A step-by-step procedure used for calculations, data processing, or automated reasoning tasks in CT imaging.

The Next Generation is

Helical/ Spiral Scanning

Helical Simultaneous

translation, data acquisition & table movement and can obtain overlapping images (hundreds)

5th Generation “1990”

Spiral/ helical scanning, source of rotation, table translation, data acquisition

6th Gen Helical Multi-slice CT

Multi slice detectors, introduced 1998, allow acquisition of multiple slices in a single rotation.

As x-rays pass through the body they are ________ _ ________ at differing levels creating a matrix or profile of

x-ray beams of different strength.

absorbed or attenuated

Voxel

3D analog of a pixel

Pixel

2D picture element

The linear attenuation coefficient (μ) of each pixel is determined by

Composition of the voxel, thickness of the voxel, and quality of the radiation beam.

The numerical value stored in each pixel is a CT

number or

Hounsfield unit

CT scan subjects the human body to between _______ ______ times the radiation of a conventional x-ray, or around a year's worth of exposure to radiation from

both natural and artificial sources in the environment.

150 and 1,100

Cross Sectional Imaging CT

is a medical imaging technique that produces detailed images of the body's internal structures in slices. It combines X-ray technology and computer processing to create cross-sectional views of organs and tissues.

What x-ray modality was the precursor to CT?

Plain film x-ray

What devices allowed the processing of information that was gathered?

Computer systems and algorithms

What is the name of the mathematical set of well-defined

instructions for accomplishing a task?

algorithm

A CT image/information is based on a principle of the x-ray beam going thru tissue and being affected, what is this called?

attenuation

CT images are displayed in what format?

Digital slice format, typically displayed in cross-sectional images.

CT images are displayed in shades of?

gray

What allows the formation of 3D images?

Digital reconstruction algorithms that combine multiple 2D slices.

1st Generation CT

one x-ray source and one x-ray detector