MEDICAL IMAGING - Introduction Flashcards
How does an X-Ray obtain an image?
Passing photons from a Tungsten target through the body to a recording plate aka plain film
How does a tissue that absorbs more radiation appear on an image?
Whiter Film! Bone = white Organs = dark Soft-tissue/water = medium white/intermediate density
How does the position of the patient influence the recorded image? Give an example
-Changes appearance of image Ex. Heart — In ANTEROPOSTERIOR VIEW, with the recording plate behind the patient, the heart appears bigger because the recording plate is further from the heart, which is near the anterior portion of the body — POSTEROANTERIOR VIEW is better KEY: structures further from the recording plate look abnormally large
What is Flouroscopy and what is is best used for
Real-time X-ray imaging
1) Provides continuous X-ray stream rather than one static shot
2) Angiography studies, fracture repair, orthopaedic surgery, barium contrast for GI studies
How many frames per second are used for 1)Peripheral Vascular and 2) Coronary Artery studies in Flouroscopy?
Peripheral = 2-3 frames/sec
Coronary A. = 15-30 frames/sec
Digital Subtraction Angiography
aka DS Angiography — used for seeing peripheral vascularization
1) Image taken
2) Tissues of interest are “substracted” (removed) from the image
3) Contrast is then injected into the artery and another image is taken
What is a major downside of DS Angiography? What are better, less invasive option?
Need to cut the artery in order to insert the comntract so blood gonna go ery-where
1) CTA (computed tomography angiography)
2) MRA (magnetic resonance angiography)
What is Current Multidetector Computed Tomography?
aka Computed Tomography
1) X-Rays move through the body in a helical fashion (body rotates, rays criss-cross)
2) Mathemattical algorithms are then used to construct a 3D image of the body from the compiled x-rays, viewed in either sggital, transverse or coronal planes
What are three benefits to Computed Tomography?
1) The gray-scale can be manipulated to enhance images
2) Can be viewed in multiple planes
3) Much better viewing capability than plain film (x-ray)
What is The Hounsfield Scale?
The measurement we use to assess computed tomography
What is Window Level and Window Width?
Window Level = the NUMBER on the scale set to middle grey
Window width = the RANGE of the grey scale mapped onto The Hunsfield Scale
What is the color on the scale when above or below the window width?
Above CT window width = Black
Below CT window width = White
What are narrow and wide window widths good for? What are the relative ranges for those tissues?
Wide window = good for bone
Narrow Window = good for soft tissue
Lung = 550 - 1600
Soft Tissue = 70 - 450
Bone = 570 - 3077
