Image Formation Midterms CDR Lesson 1 PDF

# IMAGE FORMATION ## Introduction - The Invisible and Visible Image - Image Characteristics ## Learning Objectives By the end of this lecture the student will be able to: - Define the terms, image and identify its types and methods of viewing. - Identify the stages of image formation. - Differen...

# IMAGE FORMATION ## Introduction - The Invisible and Visible Image - Image Characteristics ## Learning Objectives By the end of this lecture the student will be able to: - Define the terms, image and identify its types and methods of viewing. - Identify the stages of image formation. - Differentiate between the invisible (latent) and visible image. - List and define the basic image characteristics. - Differentiate between density and contrast and state their relationship. ## References - John Ball & Tony Price; Chesney’s Radiographic Imaging ## Websites - http://www.e-radiography.net/ ## What is an Image? - The term image describe a recognizable pattern carrying information. - Other meaning: - An optical appearance. - A mental representation. - A form or semblance. - An idea or conception. ## Visual images are of two types - Real images: Those have real existence such as photographic or radiographic images. - Static (RADIOGRAPH OR PHOTOGRAPH - Dynamic (On a television screen). - Mental images: Pictures those generated within our minds. ## Medical imaging is essentially: - The extraction of anatomical and physiological information from the patient and the interpretation of these information for the purpose of diagnosing diseases. ## The flow of the information from the patient to the observer is through three stages: - The formation of the invisible image. - The conversion of the invisible image into a visible light image. - Interpretation of the visible image. ## Stage.1 The formation of the invisible image - During radiographic examination X-ray passes through the patient. - As x-rays penetrate through the body tissues it becomes modified each part of the beam is attenuated in a degree which depend on: - The tissue type. - The intensity of the beam. - Thickness of the tissue. ![Image of an x-ray beam interacting with body tissue] ## Image Formation Terms - **Primary Radiation** - The beam of photons, interacts with the pt’s body. - **Remnant Radiation** – The resulting beam that is able to exit from the patient. - **Scatter Radiation** - Radiation that interacts with matter & only continues in a different direction - not useful for image production. - **Attenuation** – Primary radiation that is changed (partially absorbed) as it travels through the pt. ![Diagram of the path and attenuation of the x-ray beam] ## Stage.1 The formation of the invisible image - During radiographic examination X-ray passes through the patient. - As x-rays penetrate through the body tissues it become modified each part of the beam is attenuated in a degree which depend on: - The tissue type. - The intensity of the beam. - Thickness of the tissue. - Film is the simplest image receptor, but it is usually coupled with intensifying screens, which help reduce the dose to the patient. - X-ray film responds to a range of wavelengths and is in fact far more sensitive to light than it is to x-rays. - After exposure to x-rays an invisible image known as the latent image is formed. ## Stage.2 The conversion of the invisible image into visible ### Types of Conversion - Using the photographic effect of x-rays on a sensitive sheet (x-ray film). - Using xeroradiographic effect process through exposing an electrically charged imaging plate. - Using the fluorescent effect of x-ray on a sensitive screen where the x-rays is converted into light when touches these screens. - Using the process of photon stimulated luminescence where a phosphor coated imaging plate is exposed to x-ray, the absorbed energy is stored in the phosphor layer until stimulated by laser photons to form the visible image. ## Why you see what you see... - The images have different levels of density – different shades of gray. - X-rays show different features of the body in various shades of gray. - The gray is darkest in those areas that do not absorb X-rays well – and allow it to pass through. - The images are lighter in dense areas (like bones) that absorb more of the X-rays. ## Stage.3 (Viewing) Interpretation of the visible image - The final image whether it be on a film sheet or on a television screen should be viewed under specific conditioned to evaluate its quality and then passes for diagnosis. ![Two x-ray images of a human torso] ## Stage.3 (Viewing) Interpretation of the visible image ### Types of viewing - Viewing by reflected light from a surface. - Examples( texts, illustrations in books etc). - Viewing by transmitted light. - Through a semitransparent layer (e.g. Radiographs). - Viewing by emitted light from fluorescent layer. - Examples( fluoroscopic image on the TV screen). ## Image characteristics - Noise - Contrast - Sharpness - Resolution ## Image characteristics ### Noise Real images consist of 2 components: - Meaningful pattern (Signal) - Chaotic pattern (Noise) The details of the structures is affected by noise. +Noise = - Details ## Image characteristics ### Signal to Noise Ratio (SNR) Under optimal condition the magnitude of signal is greater than the magnitude of the noise. - SNR is Saied to be high (More details). When the magnitude of nearest the magnitude of the noise. - SNR is Saied to be Low (Less details). ![Diagram illustrating high SNR and low SNR] ## Image characteristics ### Density and Contrast #### Density The amount of blackening "darkness" on the radiograph. #### Contrast The differences between the blacks to the whites. ![Diagram illustrates the concept of contrast] ## Image characteristics ### Contrast Changes ![Three x-ray images of a human torso illustrating different contrast levels] ## Image characteristics ### Sharpness Describe the blackening changes at the boundaries between adjacent parts. #### Element of Image Sharpness - **Recorded detail**: the sharpness of the lines of the image. - **Distortion**: the misrepresentation of the true size or shape of the image compared to the object. ## Image characteristics ### Sharpness (SHAPE DISTORTION – TERMS) ![Diagram illustrates true shape, elongated, and foreshortened shapes] ## Image characteristics ### Resolution The resolution of a system is its ability to demonstrate closely spaced structures in the subject as separate entities in the image. ![Image of a flower] ## Image characteristics ### Summary ![Diagram illustrating the relationship between image characteristics]