Introduction to medical imaging Flashcards
Define medical imaging
is the extraction of anatomical and physiological information and the interpretation of that information inorder to carry a prescribed treatment.
List the stages involved in the flow of information from the patient to the observer.
- Formation of an invisible x-ray image.
- Convertional of invisible X-ray image to visible image.
- viewing, perception and interpretation of the image.
Describe the formation of the invisible x-ray image.
- When the incident x-ray beam from the tube of uniform intensities passes through an anatomical part.
- The ray is attenuated differently as it passes through the body, the bones absorb the ray and there’s little attenuation in muscle tissues.
- when the ray exits the body, its no longer uniform but carries information , it displays the pattern of intensities that are used to form an image on a film.
- the secondary beam is called the invisible image.
List the methods of converting the invisible x-ray image into visible image.
- Employing the photographic effect of x-rays on a sheet of sensitive film.
- Employing the fluorescent effect of X-rays on sensitive film.
- Employing the process of photostimulated luminescence
4.Employing the fluoroscopy effect of x-rays
Employing the photographic effect of x-rays on sheet of sensitive film.
- X-ray beam hits a photographic film and is chemically processed, the degree of blackness on the film is dependant on the number of x-rays that has received.
- screens are called direct exposure films.
Employing the fluorescent effect of x-rays on sensitive film.
- When x-rays interact with fluorescent materials they emit visible light depending on the amount of x-rays they’ve received.
- the light produced by the fluorescent material maybe recorded permanently on photographic films that are placed in intimate contact with it.
Employing the fluoroscopy effect of x-rays.
- The image is viewed in real time.
Employing the process of photo stimulated luminescence
- The x-rays irradiates the panel of photostimulable phosphor,
- The x-rays are stored there in form of energy called photo stimulated luminescence complexes.
- the panel is then scanned with a fine laser beam which converts the energy to visible light.
- a photo-multiplier tube is used to convert the visible light to an electrical signal.
Characteristics of radiographic images.
- Noise
- Contrast
- Sharpness
- Resolution
Noise
- patterns on the radiograph that carries little or no information/ chaotic information.
differentiate real and mental images.
- real images are real physical existing images which are accessible to scientific measurement and subject study.
- mental images are mental pictures that we make within our minds.
relationship between signal-to-noise ratio and information on the radiograph.
- When the signal to noise ratio is high that means the radiograph will be of high quality and fedility
Contrast
- This is the difference in optical density between adjacent structures in a radiograph.
Sharpness
- refers to how blackening changes at the boundary between adjacent parts.
Microdensitometer
a device used to measure optical density.
Forms of unsharpness in radiography.
- Geometric unsharpness
Arises from the geometric effects of the x-ray beam. e.g focal spot, object film distance, ffd - Photographic unsharpness
Arises from the photographic effect of the image formation. - Motion unsharpness
arises from patient motion.
Resolution
Ability of the imaging system to demonstrate closely spaced structures as different entities on the radiograph.
spatial frequency.
its how often details repeat within a specific area.
The modulation transfer function (MTF)
describes how well the system transfers contrast from an object to the image.
MTF of unity
the image produces the exact variations in the object.
relationship between spatial frequency and MTF
they’re inverse proportional to each other.
