HSMI 1211 Introduction to Medical Imaging PDF

HSMI 1211 Introduction to Medical Imaging Image Display & Appreciation Learning Outcomes By the end of the session, the student shall be able to: 1. Outline image display. 2. Define image quality. 3. Discuss image quality in terms of contrast, density, and...

HSMI 1211 Introduction to Medical Imaging Image Display & Appreciation Learning Outcomes By the end of the session, the student shall be able to: 1. Outline image display. 2. Define image quality. 3. Discuss image quality in terms of contrast, density, and resolution. 4. Outline the factors that influence image quality. 5. Define Image Quality Criteria (IQC). 6. Outline some general IQC applicable to projection radiography. Image Display Image display enables the clinicians to: assess the radiographic images. determine the information contained in those images. Image display can be done in two methods based on the type of radiographic images. Hard-copy film → x-ray viewer/illuminator / viewing box Soft-copy images → monitors X-ray viewer / X-ray illuminator A housing with a light transmissive front panel and a means to hold the film in place for viewing. Contain at least a fluorescent lamp. Controls are available to adjust the intensity of the light. To view analog radiographic images (readily recorded on radiographic film) and also for printed digital images. Comes in many sizes. Maybe specific for certain usages: Dedicated Mammographic Illuminator Display monitors Requires a dedicated Image manipulation is computer system and monitor. possible. Modalities that display images Brightness on monitors are: Blackness of image Computed radiography Change anatomical perspectives Digital radiography Add text Magnetic Resonance Imaging Image reversal (black to white) (MRI) Measure distance Computed Tomography (CT) Save images Ultrasound Digital mammography Fluoroscopy Viewing Conditions: Affect the viewing perceptions and experience Hardcopy Viewing Softcopy Viewing Brightness of the transmitted Ambient of light of the light from the illuminator viewing room. should conform to standard. Type of display monitor. Ambient of light in the room Knowledge on the while viewing images. Too high appropriate window will hinder the viewer from settings for images. appreciating small structures. Illuminator that uses more than one light bulb. Glare from another section of the illuminator for multiple film viewing in a box. Image Appreciation Radiographic images must be assessed to ensure they are of diagnostic value. Diagnostic image: An image that fulfils certain requirements that can help the clinician to derive a diagnosis. Image Quality Image Quality Criteria Radiographic Density, Contrast, and Resolution X-ray penetration Image Quality Definition: The overall characteristic of a medical image that determines which objects and structures within a body are visible. Objective of imaging: To visualise the various anatomical structures and any signs of pathology if they are present. Image Quality Characteristics Image Quality Characteristics Image Quality Criteria Refers to the conditions or requirements that should be present in an image that would qualify the image as diagnostically acceptable. How? A systematic approach to justify whether a radiograph/image could be termed acceptable in terms of diagnostic quality, technique and free from artefacts. Image Quality Criteria (Image Critique) Identification Structural definition Radiographic density Fulfillment of ordered Radiation protection and examination collimation Distortion Required anatomy Artifacts Anatomical markers Image receptor system Resolution Image Quality Criteria (Image Critique) Image Quality Criteria (Image Critique) Image Quality Criteria – Radiographic Image Quality Radiographic Resolution Ability to accurately image an object. Also known as detail, sharpness, definition and resolving power. A system with better resolution indicates the smallest object that can be imaged using the said technology. Example: Resolving power of 11 lp/mm gives better detail than 9 lp/mm. Radiographic Contrast The differentiation between tissues presented by the different shades of grey adjacent to each other in an image. These different shades represent: Different tissue characteristics (different density, atomic number and thickness) Different attenuation characteristics. Radiographic contrast - Types Radiographic Contrast The controlling factor for contrast is the energy of the beam (kV). High energy: more penetration of x-rays, less absorption, resulting in low contrast image. Low energy: more absorption by bone, minimal absorption by soft tissue, distinct black and white → high contrast. Radiographic Contrast Contrast can be influenced by radiographic density. Overexposed and underexposed will hinder the ability to appreciate contrast. Radiographic Density The blackness of an image. It should be optimum (not too bright or too dark). This can be altered by changing: Imaging parameters (for non-digital acquisition) Viewing parameters (for digital acquisition) Is related to the attenuation of radiation in matter. Areas of lesser attenuation give higher radiographic density. Radiographic density Other factors that affect radiographic density: Energy of the radiation beam: kV Intensity of the radiation: mAs Source-image- distance (SID) Means: affected by the amount of radiation reaching the image receptor. X-ray Penetration Another image quality attributed to the energy of the beam. Attenuation properties: high energy able to penetrate the body compared to a lower energy. Underpenetrated: Low kV Overpenetrated: High kV kV settings depend on the purpose of the examination. Radiographic Distortion The image of the organs in the image must be as close as possible to its actual size and shape. The divergence of the x-ray beam, the angulation of the beam or the positioning of the patient can cause distortion in the image representation. Distortion can be shown in either the elongation or foreshortening of the images.