Lecture 2: Intro To Medical Imaging Flashcards
What type of imaging uses photons that pass through the body to expose the recording plate?
X-rays
With x-rays, the greater the exposure, the ________ the density
Darker
With X-rays, the greater the absorption of the photons, the _______ the density
Lighter
How will organs, bones, soft tissue, and water appear on an x-ray?
Organs with air appear dark
Bones appear white
Soft tissues and water have intermediate density
What are 2 very important concepts to consider while examining an x-ray?
Plane of view
Orientation
The __________ view of a CXR shows magnification of the heart and mediastinum, so the ___________ view is preferred
Anteroposterior (AP)
Posteroanterior (PA)
What type of imaging uses a continuous stream of x-rays to view movement in real time?
Fluoroscopy
With fluoroscopy, the x-ray source is _______ the patient, and the data capture equipment are ______
[above/below?]
Below; above
What type of imaging uses x-ray images generated as the patient moves through a rotating x-ray tube while detectors on the opposite side collect the passing rays?
Computed tomography (CT)
[Multi-detector computed tomography]
With CT scans, mathematical algorithins are used to reconstruct _____ images of the body from the data collected.
Images in the ______ and _____ planes and renderings are reconstructed by computer from the serial slices
The gray-scale image can then be manipulated by the monitor
Axial
Sagittal; coronal
How is CT density measured?
Hounsfield scale
Density of water is 0
Density of air is ~1000
Compact bone is +3095
Soft tissues between -100 and 100
Why is it a potential problem with CT that the monitors only show 256 levels of gray?
Only a portion of the Hounsfield scale can be displayed; this window can be adjusted
A Hounsfield scale set to middle gray is referred to as the ______ ______; the range of gray scale mapped onto the Hounsfield scale is called the ______ ______
Window level; window width
CT numbers below the window with display as _______; CT numbers above the window width are _______
A _____ window width is good for imaging bone
A ______ window is better for soft tissue
Black; white
Wide
Narrow
What are some advantages to CT imaging in terms of time and motion?
Very quick (a few seconds for whole-body imaging)
Motion is not as much of a problem as things like simple x-ray
What are some advantages to CT in terms of ability to manipulate, degree of resolution, and availability?
Gray scale can be manipulated from viewing screen
Resolution excellent for many areas
Widely available and cheaper than MRI
What are some disadvantages to CT imaging in terms of patient risk?
Uses ionizing radiation
Renal function may be affected by contrast
Some patients are allergic to iodine contrast
What are the 2 most common contrast agents used in CT imaging?
Barium sulfate (administered orally or rectally)
Iodine compounds (administered IV)
What type of imaging relies on application of a strong magnetic field and pulse radio waves to knock nuclear spin of atoms out of alignment?
MRI (Magnetic Resonance Imaging)
What type of contrast agents are often used with MRI?
IV gadolinium
Oral agents (juice, H2O)
How does MRI technology generate an image?
When pulse waves knock nuclear spins out of alignment, atoms return to equilibrium and radiofrequency energy emitted is measured in a receiver coil to create images
Tissues have different relaxation times depending on water content and composition
Almost any tissue can be viewed by MRI by varying magnetic ________ and ________ strengths
Gradients; pulse
How would the items listed below appear on a T-1 weighted MRI image:
Tumor
Inflammation
Infection
Hemorrhage
Dark
How would the items listed below appear on a T-2 weighted image:
Increased water, as in edema Tumor Inflammation Infection Subdural collection
Bright
How would the items listed below appear on a T-1 weighted image:
Fat Subacute hemorrhage Melanin Protein-rich fluid Slowly flowing blood
Bright
How would the following appear on a T2-weighted MRI image:
Calcification
Fibrous tissue
Protein rich fluid
Dark
What are some advantages to MRI, especially as compared with CT, imaging?
No ionizing radiation
Better soft tissue contrast than CT
Extremely versatile: variety of pulse sequences can be used for visualizing specific tissues and pathology
What are some disadvantages to MRI imaging in terms of time, cost, and ability to manipulate images?
Longer time for sequences (many minutes)
More expensive
Images cannot be manipulated on the viewing screen like CT windows; parameters must be set before each scan
What are some disadvantages to MRI in terms of patient comfort and safety?
Gantry is narroer than CT - worse for claustrophobic patients
Gadolinium constrast risky for pregnant women or patients with renal dysfunction (risk of nephrogenic systemic fibrosis)
Noisy
How would bone appear on a CT soft tissue window vs. a T1 weighted MRI (both without contrast)?
White on CT
Dark on MRI
What are T2 weighted MRIs most useful for?
Detecting pathological process that have fluid accumulation (e.g., edema)
CSF will appear white
What imaging method measures physiological (functional) activity rather than anatomy and involves radioactive molecules attached to other compounds to form radiopharmaceuticals administered orally or IV designed to be taken up by specific cells?
Nuclear medicine
With nuclear medicine, what records the degree of radioactivity and what detects the pathology?
An external gamma camera
Pathology detected by identifying focal areas of various activity (hot spots/cold spots)
Nuclear medicine images can be superimposed on ____ or _____ images to combine functional and anatomical information
CT; MR
Where would you always expect to see spots on a nuclear medicine image?
In the kidneys and bladder, because this is how the contrast is excreted
What type of imaging is based on “pulse-echo” sound wave energy using a transducer that emits pulses of sound and functions as a receiver?
Ultrasound
What is the difference between high-frequency and low-frequency transducers in terms of what they visualize?
High-frequency visualize structures near the surface
Low-frequency have greater penetrating power but lower resolution; used for deeper structures
T/F: Ultrasound is a good method for visualizing air and tissues deep to bone
False
What type of ultrasound can visualize and measure blood flow?
Doppler ultrasound
What are some advantages to ultrasound technology?
Portable
Relatively inexpensive
No ionizing radiation
Good at capturing motion
What type of imaging is a form a fluoroscopy involving the rapid series of x-rays viewed in real time?
Digital Subtraction (DS) Angiography
[images taken before contrast injection is used to digitally “subtract” bones and other tissues from the view after contrast is administered]
What is the biggest disadvantage associated with DS Angiography?
It is an invasive procedure requiring access to arteries with some methods requiring use of an IV catheter for contrast injection
What is the difference between CT and MRI angiography?
CT angiography shows depth perspective because image can be manipulated
MRI angiography shows maximum intensity projection, and depth perspective can only be obtained by rotating the view
What type of imaging detects changes in blood oxygenation and flow?
Functional MRI (fMRI)
What is functional MRI (fMRI) often used for?
Producing activation maps of the brain; more active brain areas have increased blood flow
With functional MRI, hemoglobin is ____________ when oxygenated, but ____________ when deoxygenated; this difference leads to small differences in MR signal
Diamagnetic; paramagnetic
Where would you expect to see cortical activity on an fMRI in a person using their right hand?
Left postcentral gyrus (somatosensory)
Frontal lobe (primary motor)
