What is Christensen's Physics of Diagnostic Radiology and Why You Should Read It
Download Book Christensen's Physics of Diagnostic Radiology 146
If you are a radiology professional or student who wants to learn more about the physics principles behind different imaging technologies, you might be interested in reading Christensen's Physics of Diagnostic Radiology. This book is a classic text that provides a clear understanding of the physics concepts essential to getting maximum diagnostic value from the full range of current and emerging imaging modalities.
download book christensen's physics of diagnostic radiology 146
In this article, we will give you an overview of what this book covers, what is diagnostic radiology, what is physics of diagnostic radiology, and how to download this book online in different formats. We will also answer some frequently asked questions about this topic at the end.
What is Diagnostic Radiology?
Diagnostic radiology is a branch of medicine that uses various forms of radiation to create images of the internal structures of the body for diagnosis and treatment purposes. Diagnostic radiologists are physicians who interpret these images and provide reports to other doctors who manage the patient's care.
Diagnostic radiology encompasses a wide range of imaging modalities, such as:
X-ray radiography: This is the most common and oldest form of diagnostic imaging that uses x-rays to produce images of bones, chest organs, abdomen organs, etc.
Fluoroscopy: This is a type of x-ray imaging that uses a continuous beam of x-rays to create real-time images of moving structures, such as the gastrointestinal tract, the heart, or the joints.
Computed tomography (CT): This is a type of x-ray imaging that uses a rotating x-ray tube and detectors to create cross-sectional images of the body, which can be reconstructed into three-dimensional images.
Ultrasound: This is a type of imaging that uses high-frequency sound waves to create images of soft tissues, such as the liver, kidneys, blood vessels, etc.
Magnetic resonance imaging (MRI): This is a type of imaging that uses a strong magnetic field and radio waves to create images of various tissues, such as the brain, spine, muscles, etc.
Nuclear medicine: This is a type of imaging that uses radioactive substances (called radiotracers) that are injected or ingested by the patient and emit gamma rays that are detected by a special camera (called a gamma camera) to create images of the distribution and function of organs, such as the thyroid, bones, heart, etc.
Diagnostic radiology has many applications in different fields of medicine, such as cardiology, neurology, oncology, orthopedics, gastroenterology, urology, etc. Diagnostic radiology can help diagnose various diseases and conditions, such as fractures, infections, tumors, strokes, aneurysms, etc. Diagnostic radiology can also help guide interventional procedures, such as biopsies, angioplasties, stent placements, etc.
What is Physics of Diagnostic Radiology?
Physics of diagnostic radiology is the study of the physical principles and phenomena that underlie the production and detection of radiation and its interaction with matter. Physics of diagnostic radiology is important for understanding how different imaging modalities work and how to optimize their performance and quality.
Physics of diagnostic radiology covers topics such as:
Radiation physics: This includes the nature and properties of radiation, such as x-rays and gamma rays, how they are produced by different sources, such as x-ray tubes and radioactive substances, how they interact with matter, such as absorption and scattering, and how they are measured and quantified, such as dose and exposure.
Image formation physics: This includes the principles and methods of creating images from radiation signals, such as luminescent screens and film characteristics for x-ray imaging, image reconstruction algorithms for CT imaging, transducer characteristics and modes for ultrasound imaging, and magnetic resonance phenomena and sequences for MRI imaging.
Image quality physics: This includes the factors and parameters that affect the quality and accuracy of images, such as resolution, contrast, noise, artifacts, etc., and how to evaluate and improve them using techniques such as filters, beam restrictors, grids, etc. for x-ray imaging; windowing and filtering for CT imaging; harmonics and Doppler for ultrasound imaging; and k-space sampling and coil design for MRI imaging.
Radiation protection physics: This includes the biological effects of radiation on living tissues, such as deterministic and stochastic effects; the principles and practices of radiation protection, such as ALARA (as low as reasonably achievable) principle; and the standards and regulations of radiation safety for patients and personnel.
Radiation physics is the branch of physics that deals with the production and interaction of radiation with matter. Radiation physics is essential for understanding how x-rays and gamma rays are generated and how they affect the tissues they pass through.
Radiation Production and Interaction
X-rays are electromagnetic waves with high energy and short wavelength. They can be produced by two methods: bremsstrahlung and characteristic radiation. Bremsstrahlung occurs when high-speed electrons are decelerated by the electric field of a target atom in an x-ray tube. Characteristic radiation occurs when an inner-shell electron of a target atom is ejected by a high-speed electron and a higher-shell electron fills the vacancy. The energy difference between the two shells is emitted as an x-ray photon.
Gamma rays are electromagnetic waves with higher energy and shorter wavelength than x-rays. They are produced by radioactive decay processes in unstable nuclei. There are three types of radioactive decay: alpha decay (emission of an alpha particle), beta decay (emission of an electron or positron), and gamma decay (emission of a gamma ray).
X-rays and gamma rays interact with matter in four main ways: photoelectric effect, Compton scattering, pair production, and coherent scattering. an x-ray or gamma ray photon transfers all its energy to an inner-shell electron of an atom and ejects it. The atom becomes ionized and a higher-shell electron fills the vacancy. The energy difference between the two shells is emitted as a characteristic x-ray photon. The photoelectric effect is more likely to occur with low-energy photons and high-atomic-number atoms. The photoelectric effect is responsible for the contrast in x-ray images, as different tissues have different attenuation coefficients.
Compton scattering occurs when an x-ray or gamma ray photon transfers part of its energy to an outer-shell electron of an atom and ejects it. The photon changes its direction and loses some of its energy. The atom becomes ionized and the ejected electron is called a recoil electron. Compton scattering is more likely to occur with moderate-energy photons and low-atomic-number atoms. Compton scattering is responsible for the scatter radiation that degrades the image quality and increases the radiation dose.
Pair production occurs when a high-energy photon (above 1.02 MeV) interacts with the electric field of a nucleus and creates an electron-positron pair. The photon disappears and the electron and positron move in opposite directions. The positron eventually collides with an electron and annihilates, producing two gamma ray photons of 0.51 MeV each. Pair production is more likely to occur with high-energy photons and high-atomic-number atoms. Pair production is not relevant for diagnostic radiology, but it is important for nuclear medicine and radiation therapy.
Coherent scattering occurs when a low-energy photon interacts with an atom and changes its direction without losing any energy. The atom does not become ionized and no secondary radiation is produced. Coherent scattering is more likely to occur with low-energy photons and low-atomic-number atoms. Coherent scattering does not contribute to image formation or radiation dose, but it can affect the spectral distribution of the radiation beam.
Image Formation Physics
Image formation physics is the branch of physics that deals with the principles and methods of creating images from radiation signals. Image formation physics is essential for understanding how different imaging modalities work and how to optimize their performance and quality.
Luminescent Screens and Film Characteristics
Luminescent screens are devices that convert x-ray photons into visible light photons. They are used in conjunction with x-ray film to form x-ray images. Luminescent screens reduce the exposure time and radiation dose required to produce an image, as they amplify the signal by a factor of 50 to 100.
Luminescent screens consist of a thin layer of phosphor crystals that emit light when stimulated by x-rays. The phosphor crystals are coated on a plastic or metal base and covered by a protective layer. The most common phosphor materials used in luminescent screens are calcium tungstate (CaWO4) and rare earth compounds (such as gadolinium oxysulfide Gd2O2S).
Luminescent screens have two main characteristics: conversion efficiency and resolution. Conversion efficiency is the ratio of light energy emitted by the screen to x-ray energy absorbed by the screen. It depends on the type and thickness of the phosphor material, as well as the energy of the x-rays. Higher conversion efficiency means higher image brightness and lower radiation dose, but it also means higher noise and lower contrast.
Resolution is the ability of the screen to preserve the spatial details of the image. It depends on the size and distribution of the phosphor crystals, as well as the thickness of the screen. Smaller and more uniform crystals mean higher resolution, but they also mean lower conversion efficiency and higher radiation dose.
X-ray film is a photographic film that records the image formed by luminescent screens. X-ray film consists of a transparent plastic base coated with one or more layers of emulsion that contain silver halide crystals (such as silver bromide AgBr). When exposed to light from luminescent screens, some of the silver halide crystals are converted into metallic silver grains, forming a latent image.
the film is to light exposure. It depends on the size and concentration of the silver halide crystals, as well as the type and thickness of the emulsion. Higher speed means lower exposure time and radiation dose, but it also means lower resolution and higher noise.
Contrast is the measure of how well the film differentiates between different levels of light exposure. It depends on the shape and distribution of the characteristic curve of the film, which relates the optical density (OD) of the film to the logarithm of the exposure (log E). Higher contrast means steeper curve and greater difference in OD for a given difference in log E, but it also means narrower dynamic range and higher risk of underexposure or overexposure.
X-ray film requires processing to develop the latent image into a visible image. Processing involves four steps: developing, fixing, washing, and drying. Developing is a chemical reaction that reduces the exposed silver halide crystals into metallic silver grains, forming a negative image. Fixing is a chemical reaction that removes the unexposed silver halide crystals, making the image permanent. Washing is a physical process that removes the residual chemicals from the film, preventing deterioration. Drying is a physical process that evaporates the water from the film, making it ready for viewing.
Fluoroscopy is a type of x-ray imaging that uses a continuous beam of x-rays to create real-time images of moving structures. Fluoroscopy is useful for examining dynamic processes, such as swallowing, breathing, or blood flow, as well as for guiding interventional procedures, such as catheterization, angioplasty, or biopsy.
Fluoroscopy works by using an x-ray tube and an image intensifier. The x-ray tube produces a continuous beam of x-rays that passes through the patient and reaches the image intensifier. The image intensifier converts the x-ray photons into visible light photons and amplifies them by a factor of 5000 to 10000. The image intensifier consists of three main components: an input phosphor screen, a photocathode, and an output phosphor screen.
The input phosphor screen is a luminescent screen that converts x-ray photons into visible light photons. The input phosphor screen is usually made of cesium iodide (CsI) crystals that emit blue-green light when stimulated by x-rays.
The photocathode is a thin layer of metal that converts visible light photons into electrons. The photocathode is usually made of antimony (Sb) or cesium (Cs) compounds that emit electrons when illuminated by light.
The output phosphor screen is another luminescent screen that converts electrons back into visible light photons. The output phosphor screen is usually made of zinc cadmium sulfide (ZnCdS) crystals that emit yellow-green light when bombarded by electrons.
the flow and speed of the electrons from the photocathode to the output phosphor screen. The electrostatic focusing system consists of a series of electrodes that create an electric field that focuses the electrons into a narrow beam. The accelerating anode is a high-voltage electrode that increases the kinetic energy of the electrons, making them hit the output phosphor screen with more force and brightness.
The image intensifier produces a bright and magnified image of the x-ray beam that can be viewed by a television monitor or a camera. The image intensifier has two main characteristics: conversion factor and resolution. Conversion factor is the ratio of light output to x-ray input. It depends on the type and thickness of the phosphor screens, the voltage of the accelerating anode, and the energy of the x-rays. Higher conversion factor means higher image brightness and lower radiation dose, but it also means higher noise and lower contrast.
Resolution is the ability of the image intensifier to preserve the spatial details of the image. It depends on the size and shape of the input and output phosphor screens, the quality of the electrostatic focusing system, and the distortion of the image. Higher resolution means sharper image, but it also means lower conversion factor and higher radiation dose.
Viewing and Recording The Fluoroscopic Image
The fluoroscopic image produced by the image intensifier can be viewed and recorded by different devices, such as a television monitor, a camera, or a digital radiography system.
A television monitor is a device that displays the fluoroscopic image on a screen using an electron beam that scans across a phosphor coating. The television monitor is connected to the image intensifier by a video camera tube or a charge-coupled device (CCD) that converts light into electrical signals. The television monitor has two main characteristics: brightness and resolution. Brightness is the measure of how well the monitor reproduces the light intensity of the image. Resolution is the measure of how well the monitor reproduces the spatial details of the image.
the measure of how fast the camera can record the image. Resolution is the measure of how well the camera reproduces the spatial details of the image.
A digital radiography system is a device that converts the fluoroscopic image into a digital format that can be stored, processed, and displayed on a computer. The digital radiography system is connected to the image intensifier by a flat-panel detector or a CCD that converts light into electrical signals. The digital radiography system has two main characteristics: dynamic range and resolution. Dynamic range is the measure of how well the system can capture the variations in light intensity of the image. Resolution is the measure of how well the system reproduces the spatial details of the image.
Digital radiography is a type of x-ray imaging that uses digital detectors to capture and process x-ray images. Digital radiography has many advantages over conventional film-based radiography, such as lower radiation dose, faster image acquisition, easier image manipulation, and better image quality.
Digital radiography can be classified into two categories: direct and indirect. Direct digital radiography uses detectors that directly convert x-ray photons into electrical signals, such as amorphous selenium (a-Se) or mercuric iodide (HgI2) detectors. Indirect digital radiography uses detectors that indirectly convert x-ray photons into electrical signals, such as scintillator-photodiode or scintillator-CCD detectors.
Digital radiography has two main characteristics: dynamic range and resolution. Dynamic range is the measure of how well the detector can capture the variations in x-ray intensity of the image. Resolution is the measure of how well the detector reproduces the spatial details of the image.
Computed Tomography Physics
Computed tomography (CT) is a type of x-ray imaging that uses a rotating x-ray tube and detectors to create cross-sectional images of the body, which can be reconstructed into three-dimensional images. CT is useful for imaging complex structures, such as the brain, spine, chest, abdomen, etc., as well as for detecting subtle lesions, such as tumors, hemorrhages, fractures, etc.
CT Scanners and Image Reconstruction
the x-ray detector array. The x-ray detector array consists of multiple detectors that measure the intensity of the x-rays that reach them. The gantry is a circular structure that rotates the x-ray tube and the detector array around the patient. The computer collects and processes the data from the detectors and reconstructs the images using mathematical algorithms.
CT scanners can be classified into different generations based on the configuration and movement of the x-ray tube and the detector array. The first generation CT scanners used a single detector and a pencil beam of x-rays that moved in a linear fashion across the patient. The second generation CT scanners used multiple detectors and a fan beam of x-rays that moved in a linear fashion across the patient. The third generation CT scanners used multiple detectors and a fan beam of x-rays that rotated continuously around the patient. The fourth generation CT scanners used multiple detectors and a fan beam of x-rays that rotated continuously around the patient, but the detectors were fixed in a circular ring. The fifth generation CT scanners used multiple detectors and an electron beam that scanned a stationary target ring to produce x-rays that rotated around the patient.
CT image reconstruction is the process of creating cross-sectional images from the data collected by the detectors. CT image reconstruction is based on the principle of computed tomography, which states that any cross-sectional image can be represented by a set of projections (or line inte