Midterm 2 - CT, MRI, Scintigraphy, Ultrasonography Flashcards
CT was invented by who (2) in what year?
Hounsfield and McLeod
1973
Modern scanners have multiple detector arrays that are stationary around what degree of the patient?
360 degrees: tube rotates around patient
The CT tube rotates around patient in the ___ plane
Axial
Helical CT scanners create a ______ acquisition of data
Spiral
Multi-slice scanners create data in thin slices, referred to as
Volumetric acquisition
This means 1) there are no gaps in acquisition of data and 2) when data is reformatted, the quality is as good as axial data.
What are small squares of CT data that make up the image we see on axial orientation scans?
Pixels — picture elements
What are comprised of pixel element PLUS depth of box?
Voxels — volume elements
What kind of scanner can produce isotopic voxel?
Helical CT
What is a voxel that has the same depth, width and height?
Isotopic voxel
In other words, the resolution of the data is the same no matter which plane you choose to see — the voxel and pixel elements have the same dimensions.
Reformatting allows views of data from:
Sagittal, coronal or 3-D
What are used to describe the shade of grey that a tissue presents on the scale on CT?
Hounsfield units (HU)
HU scale ranges from
-1000 to 3072 HU
Only ___ (#) HU can be assigned per pixel/voxel
1
HU translate to grey scale. +1000 is going to be [lighter/darker] -1000 [lighter/darker]
\+1000 = lighter e.g. bone -1000 = darker e.g. air
What is the process of emphasizing certain ranges in the HU scale? E.g. if we want to see more bone e.g. higher value end of the HU scale OR if we want to see more soft tissue
Windowing
Soft tissue windows allow better viewing of the low HU end of the scale: soft tissues.
Bone windows emphasize the higher value end of HU scale: cortical and medullary bone.
What is -1000 HU?
Air
What is 0 HU?
Water
What is +400 HU?
Cancellous bone
What is +700 to +2000 HU
Cortical bone
What is +2500 to +3000 HU
Metal
When the CT detector cannot distinguish between different tissues because they are in the same pixel, its called
Partial Volume Effect
Machine has to decide if it will make the Pixel black or white.
What technology uses a magnetic field?
MRI
In MRI, echo time (TE) and repetition time (TR) allow what?
Creation of sequences known as T1 and T2
In MRI, what is brightest for T1-weighted image? What is not bright?
Brightest: Fat
Not brightest: Water and fluid
Note: opposite is true for T2
In MRI, what the high signals/low signals in T2-weighted images
Bright = water & fluid
Not bright = fat
Basically, the less free protons, the lower signals
Compact tendon = low signal
A T-2 weighted sequence can be converted to a _____ sequence
FLAIR, Fluid Attenuated Inversion Recovery
What kind of image suppresses fat signal in MRI to make it appear black so that you can see tissue and fluid better?
STIR (short tau inversion recovery)
Overall, T1 vs T2 vs fluid sensitive studies (FLAIR, STIR) (what are they good for)
T1 = evaluate anatomy
T2 = find pathology
FLAIR, STIR good for pathology and edematous/watery tissues
Batteries e.g. cardiac pacemakers, insulin or infusion pumps; metals e.g. shrapnel from accidents or some high metallic tattoos; patients who can’t stay still because of seizures… these are contraindications for what procedure?
MRI
Looking at an MRI, the fat is bright. What weight of MRI is it?
T1
Looking at an MRI, water is bright. What weight of MRI is it?
T2 weighted
Between CT and MRI which one has less risk as far as radiation exposure?
MRI
How do CT and MRI refer to the tissue?
CT - density
MRI - signal intensity
CT is good at ___ while MRI is good at ___
CT - detail
MRI - tissue differentiation
what is faster: CT or MRI
CT
What procedure can be done on patients with metal or batteries: CT or MRI
CT
Is CT or MRI better for clinically unstable patients/
CT
Which one requires no reformatting: CT or MRI
MRI because it directly acquires multiplanar images
What type of imaging uses radioisotopes chelates to substances that are inert but processed by various tissues of the body?
Radionuclide Imaging AKA Scintigraphy
Technetium 99m is most common and used in bone scans
What does scintigraphy identify in organs and bones?
Physiological activity
Scintigraphy characterizes areas by
High or low metabolic activity
3 levels of scintigraphy scan comprehensiveness include:
Whole body = bony problems
Limited/pin-hole = fractures
3-phase = flow, blood pool, delayed images used for infections
Hot spot is an area of increased
Physiological activity
Cold spot is an area lacking
Vascular supply
20 m of Technetium-99m has an effective dose of 3 mSv in the whole body. What is the half life WITH body’s help in excretion by urinary system?
4.8 hour effective
Includes isotope decay + help from body
20 m of Technetium-99m has an effective dose of 3 mSv in the whole body. What is the half life WITHOUT body’s help in excretion by urinary system?
6 hour
Raw rate of decay, no help from body
20 m of Technetium-99m has an effective dose of 3 mSv in the whole body. What is the biological half-life??
24-hour
What imaging modality uses sound waves to create images?
Ultrasonography
When the sound waves bounce off internal structures, they create sound waves that bounce back which are called
Echoes
They come back to the source and are converted into images
How are images created in an ultrasonography scan?
Changes in tissue density cause sound waves to “bounce back” to the ultrasound transducer at differing rates which creates different images
What is the wand device called in ultrasonography?
Transducer
Ultrasound wave frequencies range
2-20 million Hz
What poisons ultrasound image?
Air
Metal
Strengths of Ultrasonography:
Internal organ evaluation Obstetrics Arteries, veins Joints MSK Cyst vs solid Cost effective
