This paper introduces into the essentials of computed tomography and gives a brief lead-in to Cardiac CT, which is the clinical application of computed tomography in cardiac imaging. At first, the usage of X-rays is explained and the resulting main task of a CT scanner: The reconstruction of a three-dimensional image from the X-ray shadows, that are captured by the digital radiation detector unit. This reconstruction problem is known as the inverse problem in mathematics, which was initially solved by Johann Radon. Transferred to the field of computed tomography, the inverse problem means the definition of a volume dataset by reconstruction algorithms like for instance the Fourier Transform, which is shortly introduced, as well as the filtered backprojection. The main issue of Cardiac CT is the steady movement of the heart and chest of an examined patient. To ensure high image quality the scanner is triggered by a concurrently recorded ECG. ECG Triggering can ensure that the scanner only captues
images during the phases of the heartbeat, where movement is minimal. One major application of Cardiac CT is non-invasive coronary angiography, which possibly could substitute invasive diagnostic surgeries like cardiac catheterization of non-emergency
patients.
Table of Contents
1. Introduction
2. Computed Tomography
2.1. X-rays (Roentgen rays)
2.2. Inverse Problem
3. Image Processing
3.1. Radon Transform
3.2. Fourier Transform
3.3. Filtered backprojection
4. Cardiac CT
4.1. ECG Triggering
4.2. Coronary CT Angiography
Objectives and Topics
This document aims to provide an overview of the technical foundations of computed tomography (CT) and its specific clinical application in cardiac imaging. The research focuses on the transition from basic X-ray generation and the mathematical inverse problem of reconstruction to specialized techniques like ECG triggering required to overcome cardiac motion artifacts.
- Technical fundamentals of X-ray generation and detection
- Mathematical principles of image reconstruction (Radon and Fourier Transforms)
- Techniques for filtered backprojection and convolution kernels
- Challenges of imaging moving structures, specifically the human heart
- Clinical application of non-invasive coronary CT angiography
Excerpt from the Book
4.1. ECG Triggering
In consequence of its steady movement, taking pictures of the heart with any diagnostic imaging device is problematic. Therefore, “motion artifacts can significantly affect cardiovascular CT images”[BS06, P. 19], which can be caused by the heartbeat itself or by breathing movement of the chest. Modern scanners working with “multidetector CT and electron beam CT techniques”[BS06, p. 19] provide the possibility to complete a scan within one single breath-hold, which minimizes the artifacts from respiration, but since the motion of the cardiac muscle is very complex and not directly controllable, the computer tomograph has to capture the images “preferably in the diastolic phase, when cardiac motion is minimal”[OFB+06, P. 76]. The very short scanning time can be reached by concurrent acquisition of multiple slices. Nowerdays computed tomography works with “up to 64 narrowly collimated slices.”[BS06, P. 123]
By simultaniously recording an ECG, the scanner can be triggered to only acquire data within a defined time period during this phase of the cardiac cycle. Though, due to the fact that no ECG rhythm is exactly constant, especially not the one of patients, suffering from a heart condition, determining the optimal time window is difficult. In practice, there are three different approaches to select the trigger moment. “The best image quality can be obtained in mid-diastolic phase”[OFB+06, P. 107], or in other words, in the middle of the time interval between two R-waves, which is defined as δRR = 50%. Alternatively “the end-systolic phase”[OFB+06, P. 107] starting at δRR = 30% was shown to be appropriate.
Summary of Chapters
1. Introduction: This chapter provides a brief history of CT technology, tracing its origins from Wilhelm Conrad Röntgen to modern diagnostic scanners.
2. Computed Tomography: It explains the physical mechanisms of X-ray production and defines the mathematical challenge of reconstructing 3D images from 2D projections.
3. Image Processing: This section details the mathematical algorithms, including Radon and Fourier Transforms, and the filtered backprojection technique used for image reconstruction.
4. Cardiac CT: This chapter discusses the specific challenges of imaging the heart and describes solutions such as ECG triggering and coronary angiography.
Keywords
Computed Tomography, Cardiac CT, X-rays, Inverse Problem, Radon Transform, Fourier Transform, Filtered Backprojection, ECG Triggering, Coronary Angiography, Hounsfield Units, Image Reconstruction, Medical Imaging, Diagnostic Technology, Convolution Kernels, Motion Artifacts.
Frequently Asked Questions
What is the primary focus of this paper?
The paper covers the essentials of computed tomography (CT) technology and its specialized implementation in cardiac imaging.
What are the central thematic areas?
The work discusses the physics of X-ray production, mathematical reconstruction algorithms, and clinical strategies to overcome motion artifacts in heart imaging.
What is the core research objective?
The goal is to explain how CT scanners function and how modern techniques enable non-invasive diagnosis of coronary conditions.
Which scientific methods are analyzed in the work?
The work analyzes the Radon Transform, the Fourier Transform, and the filtered backprojection method as mathematical foundations for image reconstruction.
What is covered in the main section?
The main section details X-ray generation, the mathematical "inverse problem," image processing algorithms, and the practical application of ECG-triggered Cardiac CT.
Which keywords best characterize this publication?
Key terms include Computed Tomography, Cardiac CT, Radon Transform, ECG Triggering, and Coronary Angiography.
Why is Cardiac CT more challenging than general CT?
Cardiac CT is challenged by the constant movement of the heart muscle, which requires high-speed acquisition and synchronization with the patient's heartbeat.
How does ECG triggering improve image quality?
ECG triggering allows the scanner to capture images only during the diastolic phase of the cardiac cycle, when heart movement is at its minimum.
- Arbeit zitieren
- B.Sc. Christian Brugger (Autor:in), 2011, The essentials of Computed Tomography and its application in cardiac imaging, München, GRIN Verlag, https://www.grin.com/document/176173
