Thorax 03: Principles of Medical Imaging Flashcards
Xray imaging
The use of xrays to visualize structures inside the body
How do air, fat, soft tissue, water, bone, and metals look in an x-ray?
Air: black Fat: dark gray Water and soft tissue: light gray Bone: white metals: very white
Why is the 2D nature of xray images problematic?
Overlapping structures will come off as more highly attenuated and be distorted. Different views can give different images completely
Contrast agents
Agents that allow for sharper visualization of structures in an xray
Barium Sulfate
An insoluble contrast agent that is nontoxic with high density; when mixed with air, prepares double-contrast slides. Used to see hollow organs
Double contrast
Air fills up the structure to provide greater details by the contrast
Iodine
A contrast agent that is injected into the blood with a high atomic mass and is excreted in the urine. It attenuates well. Used for angiograms
Computed Topography (CT) scans
A scan that takes a bunch of image slices and computationally combines them into a single image
Hounsfield numbers
An arbitrary set of numbers for CT scans depicting how densities seen relate to other tissues; goes from -1000 (air) to 3095 (compact bone)
What are some advantages of CT?
Quick, motion is not a problem, grayscale can be manipulated, excellent resolution, cheap
What are some drawbacks of CT?
Uses ionization radiation, some patients allergic to iodine contrast, Renal function must be evaluated
Magnetic Resonance Imaging (MRI)
Creating magnetic fields to picture structures and measure energy releases of the ions inside
Advantages of MRI
No contrast agent, better soft tissue contrast, versetile
What are some disadvantages of MRI
Long time, movement can be a problem, more expensive, images cannot be manipulated, no metal inside the body, noisy, narrower than CT, gadolinium contrast cannot be used in pregnant patients, patients with renal dysfunction have higher risk for NSF
T1-weighted MRI
Fluid is dark and fat is bright
