Ch. 1 (405) CT overview

Iterative Reconstruction Algorithms (create what)

concept from the early development of CT in an effort to overcome image noise and streak artifact of the filtered back projection algorithm Creates simulated projections that are true representations of the scanned object

Computer performs

image reconstruction process

Cardiac CT Imaging Method

imaging the beating heart without compromising spatial and contrast resolution and reducing motion artifacts

Innovations in CT are striving to accomplish acceptable image quality for diagnostic interpretation and techniques that

improve patient care while reducing radiation doses

the first patient was scanned by his machine in?

in 1972

The first CT scanners required the x-ray tube and detectors to move (called?)

in a straight line across the patient's head > Starting from left to right, rotate 1 degree, then move from to left; repeated for 180 degrees > Process termed translate-rotate-stop-rotate or scanning > This method of data acquisition proved problematic due to length of exam time

A goal of any ionizing radiation modality is to

provide maximum information while keeping the radiation dose minimized

The acronym of choice for use in articles pub- lished in the RSNA journal, Radiology, is:

В. СТ.

U.S. Food and Drug Administration approves electron beam CT (EBCT) scanner

• 1983:

Multislice CT (MSCT) introduced at RSNA meeting

• 1998:

Spectral CT Imaging (also known as?)

• Also known as dual-energy CT • Utilizes the x-ray tube's wide energy spectrum that reaches the detector in a way to optimize all structures within an imaged object

Godfrey Newbold Hounsfield

• Bom in 1919 in Nottinghamshire, England discovered that measurements of x-rays passing through an object from all directions could be formed into a three-dimensional image • His research resulted in the first clinically useful CT scanner for imaging the brain

Applications of Volume CT

• CT fluoroscopy • Three-dimensional imaging and visualization • CT angiography • CT endoscopy-virtual reality imaging • Cardiac CT imaging • CT screening

digital image processing Examples include the following:

• Image refomatting (sagittal or coronal images created from axial acquisitions) Image smoothing Edge enhancement • Gray-scale manipulation • Three-dimensional (3D) processing

When and who applied these reconstruction techniques to produce the world's first clinically useful CT scanner for imaging the brain

• In 1963, Hounsfield

early 1920s, the term was used to described imaging a specific layer or section of the body

"body section radiography"

Radiation dose studies were performed as early as

1973 and continue today

Dynamic spatial reconstructor (DSR) is installed for dynamic volume scanning (year?)

1975:

First report of practical spiral CT scanner was presented at the Radiological Society of North America (RSNA) meeting in Chicago

1989:

Which of the following applications of volume CT is based on volume formulation, classifica- tion, and image projection? A. CT fluoroscopy B. CT angiography C. 3D imaging D. CT endoscopy

3D imaging

The formation of CT images by a CT scanner involves three steps:

> Data acquisition > Image reconstruction > Image display, manipulation, storage, recording, and communication

• CT advancements that have made cardiac imaging possible with excellent image quality

> Electron beam (EBCT) scanners > Multislice (MSCT) scanners > Dual source (DSCT) scanners

Three CT technology advances had to occur to make CT fluoroscopy possible

> Fast, continuous scanning based of spiral/helical scanning principles > Fast image reconstruction made possible by hardware that allowed quick calculations and new imaging reconstruction algorithms > Continuous image display in cine mode of two to eight images per second

• Notable contributors that revolutionized CT

> Godfrey Newbold Hounsfield > Allan MacLeod Cormack

Major CT Technology Trends

> Iterative reconstruction (IR) algorithms > CT detector technologies Radiation dose optimization > Spectral CT imaging > Graphics processing unit (GPU) computing

Two categories of detectors

> Solid state detectors (scintillation) > Gas-ionization detectors

Transformation to a 3D image consists of three steps (in both surface and volume based techniques)

> Volume formation (stacking images to form volume with some preprocessing) > Classification (determining the tissue types within the slices) > Image projection

Images can be stored and recorded in some form of archive

> X-ray film (no longer used) Magnetic tapes/disks Optical storage media (disk, tape, and card)

The primary goal of spiral/helical CT scanning is to: A. improve the volume coverage speed performance. B. improve the diagnostic skills of the radiologist. C. make use of lower mA values. D. scan children who are difficult to handle.

A. improve the volume coverage speed performance.

Who developed the first clinically useful CT scanner?

B. Hounsfield

Allan MacLeod Cormack

Born in Johannesburg, South Africa in 1924 Studied nuclear physics at Cambridge University • Developed solutions to the mathematical problems that plagued early CT development

Which of the following is true? A. An analog computer is used to produce images in CT. B. Volume scanning involves scanning the body one slice at a time. C. Two essential components of a digital image processing system are the ADC and the DAC. D. Quality control is not so well established in СТ.

C. Two essential components of a digital image processing system are the ADC and the DAC.

Which of the following does not produce a transverse axial sectional image? A. computed tomography B. conventional tomography C. conventional radiography D. computerized axial tomography

C. conventional radiography

Which of the following is based on virtual real ity principles? A. CT fluoroscopy B. CT angiography C. 3D imaging D. CT endoscopy

CT endoscopy

• CT angiography is defined as

CT imaging of blood vessels opacified by contrast media

Who shared the Nobel Prize in Medicine and Physiology for his contribution to the develop- ment of CT? A. Kuhl B. Ledley C. Cormack D. Kalender

Cormack

4. Which company pioneered the development of the first useful CT scanner for imaging the head? A. General Electric Medical Systems B. Siemens C. Elscint D. EMI

D. EMI

Electronic image communication requires a standard protocol to facilitate networking among the sending and receiving computers This standard is known as

Digital Imaging and Communication in Medicine (DICOM) standard

Other MSCT Improvements

High-speed imaging Large bore gantry apertures Improved z-axis resolution • Dose modulation techniques • Cone beam image reconstruction algorithms Pitch Improved isotropic resolution of less than 0.4 mm

Who played a significant role in the develop- ment of spiral CT? A. Kalender B. Cormack C. Ledley D. Edwards

Kalender

Hounsfield's work revolutionized radiology and transformed the old terminology

No longer referred to as transverse axial tomography The term computed tomography (CT) is now accepted throughout the medical community

In the 1960s, image reconstruction from projections proved useful in medical applications such as

Nuclear medicine in 1963 Computed tomography (CT) in 1967

Quality Control

Performs quantitative and qualitative tests to perfect working condition • Quality control tests range from those performed by technologists to those The performed by physicists performing

Radiation Dose Schemes (applied during data acquisition)

Prepatient filtering technique (15%) New ultrafast ceramic detectors (25%) Automatic tube current modulation technique that adjusts mA based on patient characteristics (automatic tube current modulation technique)

Detector Technologies

Responsible for absorbing attenuated radiation then converting it into electrical signals that become digitized and are sent to the computer to create the CT image

Spiral/Helical CT Scanners: Volume Scanning

Technique of CT imaging in which a volume of tissue is scanned by moving the patient continuously through the gantry of the scanner while the x-ray tube and detectors rotate continuously for several rotations • Continuous motion of the x-ray beam and patient results in a spiral or helical path

• Digital image processing

The x-ray beam passes through the patient and falls onto special detectors that convet the x-ray photons into electrical signals (analog sig- nals) converted into numerical data (digital data) for input into digital computer. Digital image processing involves digital computer to process and manipulate digital the use of a images.

Image Reconstruction from Projections concept

Theoretically derived in 1917 when mathematician Radon proved two- or three- dimensional objects could be "built up" from several projections from different directions

• CT has been in areas other than medicine

To study internal log defects > In paleoanthropology > In oil exploration > For fat stock breeding For other animal investigations > At major airports for automated explosives delection

Basic steps to familiarize the technologist

Turn scanner's power on and perform quality testing Place patient in scanner opening (gantry) using appropriate positioning for protocol Set technical factors at the control console > Begin scanning with x-ray tube and detectors inside the gantry rotating around patient

One of the central goals in the development of the scanner is to achieve isotropic resolution, where the

Voxel is a perfect cube The impact of isotropic resolution on CT images has improved image quality in all three dimensions;

CT Screening

a controversial tool that is used primarily to detect diseases early in healthy individuals Potential uses include the following: > Cardiac screening > Lung cancer screening > Virtual colonoscopy > Whole body imaging

Newer generation CT scanners resolved the time issue by allowing the technologist to acquire

a volume of tissue (volume scanning) with continuous rotation of the x-ray tube and detectors (spiral/helical)

CT Endoscopy: Virtual Reality Imaging (Virtual endoscopy)

an application of virtual reality that creates computer-generated inner views of tubular structures

Electrical signals are converted into

digital data for the computer

Image Manipulation Also known as

digital image processing Images may be modified to make them more diagnostic and useful for the observer

CT Fluoroscopy

display of an image to be in real time with variable frame rates

Attenuated x-ray beam is measured by detectors that convert the attenuated data into

electrical signals

Digital reconstructed image is converted into

electrical signals in order to be viewed by the technologist on a monitor

Communication refers to the

electronic transmission of text data and images from the CT scanner to other devices

Dual source CT (DSCT) scanners (used in and also known as?)

feature two x-ray tubes and two detector array components • Used primarily in cardiac imaging • Provide improved temporal resolution compared to single source CT (SSCT) Also known as dual-energy CT because each x-ray tube operates at different energy levels

Volume visualization

involves the use of certain computer tools that changes how the CT image is displayed, thus providing the technologist- observer with additional information • These tools include but are not limited to the following: > Windowing > Interactive > Cine visualization

Multislice CT (MSCT) Scanners based on the use of

multidetector technology to scan four or more slices per revolution of the x-ray tube and detectors • Increasing the number of slices per revolution thus increases the volume coverage and reduces the exam time • Number of slices per revolution has been increasing at a steady pace in recent years

(PACS)

picture archiving and communications system uses this standard for the networking and communication of images

Computed tomography (CT) produces sharp, clear cross-sectional images of the human body by

reconstructing a large number of projections from different locations

image reconstruction algorithms

special mathematical techniques are applied to the data to produce an image

• Data acquisition refers to (what measures it)

the collection of x-ray transmission measurements from the patient • Special electronic detectors measure the attenuation of the X-ray beam as it passes through the patient

The term generation is used to refer

to the method of scanning

In 1935, the term was refined to

tomography, derived from the Greek word tomos meaning section

In 1937, the term used to refer to the imaging ability of cross- sectional images to be acquired

transverse axial tomography

Radiation Dose Optimization

• Keeps with the "as low as reasonably achievable" (ALARA) philosophy • Striving for dose reduction in patients while maintaining diagnostic quality images

Imaging Parameters Affecting CT Dose (6)

• Slice thickness • Noise • Resolution detector efficiency • Reconstruction algorithm • Collimation • Filtration

Three-Dimensional Imaging transforms what to what?

• Specialized algorithms that transform transaxial CT data into simulated 3D images