Lecture 11: Introduction To Imaging Flashcards
Advantages of X-ray?
- Quick
- Decent 2D images
Contrast agents used with X-rays and CT?
- Barium Sulfate
- Iodine compounds
Disadvantages of X-ray?
- Must take multiple angles
- Uses radiation
- Only 2D
- Distortion of image densities in certain angles
What are the two views used in X-ray?
- Anteroposterior (AP view)
- Posteriorantero (PA view)
What happens to images further away from recording plate?
They will appear larger.
If you want an image of a structure to be of normal scale, what should be done?
Use a view that places the recording plate closest to the image of interest.
Important when trying to observe if there is an enlargement of certain organs like the heart
Fluoroscopy is good for?
Real time imaging.
Uses a C-arm
How does computed topography (CT) work?
Using ionizing radiation, will take multiple images in a helical manner. These multiple views will be stacked using a computer, which creates a 3D image.
Advantages of CT?
- Quick (few seconds for whole body)
- Motion not as much a problem
- Gray scale can be manipulated on the viewing screen
- Resolution excellent for many areas
- Widely available and cheaper than MRI
Disadvantages of CT?
- Uses ionizing radiation
- Renal function must be evaluated if contrast used
- Some patients are allergic to iodine contrast.
How does MRI work?
- Magnets to create powerful static magnetic field, which will align hydrogen atoms.
- Pulse in radio waves to knock them out of alignment.
- Energy during re-alignment of atoms measured
Advantages of MR?
- No ionizing radiation
- Better soft tissue contrast than CT
- Extremely versatile: a variety of pulse sequences can be used for visualizing specific tissues and pathology
Disadvantages of MR?
- Longer time for sequences (many minutes)
- More expensive
- Images CANNOT be manipulated on the viewing screen like CT window; parameters must be set before each scan
- Gantry narrower than in CT; worse for claustrophobic patients
- Patient cannot have metal in body (i.e pacemakers)
- Gadolinium contrast cannot be used in pregnant women
- Patients with renal dysfunction have increased risk of NSF (nephrogenic systemic fibrosis)
- Noisy
Advantages of ultra sound?
- Relatively inexpensive
- Portable (good for emergent situations)
- Real-time images
- No radiation
- Good for visualizing motion (i.e. blood flow)
How does ultrasound work?
Uses “pulse-echo” sound wave energy. Transducer moving over skin emits pulses of sound waves into the body and then functions as a receiver that records the energy from the “echo” or reflection of sound waves from tissue interfaces within the body.
