Final Flashcards
What type of imaging has multiple source/detector arrays that make complete 360 degree rotations around the patient in the axial plane?
Modern CT scanners
What did Hounsfield and Mcleod invent in 1973?
CT
What makes the 2 dimensional image seen on axial data of the CT scanner?
Small Pixels
What unit is the reference for the depth of the CT slice (volume element)?
Voxel
The CT scanners can reformatt the image to sagittall, coronal, or 3D orientations. What is this referred as?
MPR = Multi Planar Reformatting
What’s the best quality visual image/orientation for the CT?
Axial (pixel)
What CT image (besides axial) can create a good quality image?
Isotropic Voxel
has the same depth, width, & height
What type of unit is used to describe the shade of grey that a tissue presents on the scan?
Hounsfield
What HU = 0?
Water
What HU = -1000?
Air
What HU = +400
Cancellous Bone
What HU = +700-2000
Cortical bone
What HU = +2500-3000
Metal
What is it called when emphasizing views of certain ranges in the HU scale (CT scan)?
Windowing
What tissue is at the low end of the HU scale?
Soft Tissue
What is emphasized at the higher value end of the HU scale?
Cortical and Medullary Bone
What do you call the part of the CT detector that cannot distinguish between different tissues?
Partial Volume Effect
What is the most common mechanical artifact in the CT scan?
Ring Artifact
What are 2 types of CT images that requires use of the 3D reformatting capacity of the scanner?
CT Colongraphy and Angiography
What’s the first step to creating an MRI image?
Strong magnetic field aligns the vector of spin of protons in the body
The strong magnetic field units range is ________.
0.3-3.0 Tesla
What “resonates” with the bodies protons, causing them to gain energy and precess (spin around their axis) at a higher energy?
A 2nd Radiofrequency
What happens when the 2nd radiofrequency is turned off?
The excess energy is emitted from each tissue according to its proton concentration
What characteristic of the tissue causes an MRI image?
Each tissue in the body has it’s own pattern of proton return to normal state
When the radiofrequency is turned off the proton energy is emitted from each tissue and converted into?
a visible image
Fat is the brightest in a T1 weighted image, therefore what are 3 examples of tissue signals (high vs. low signals)?
- Cord higher signal than CSF
- Medullary bone & Spinal cord are higher signal
- Water and cortical bone are lower signal
Water and edema have the brightest (high) signal in T2 weighted MRI images; therefore, what tissues will have high and what will have low signals?
- Nucleus pulposus and CSF is high
2. Medullary bone, spinal cord is low
What tissue is a low (dark) signal in both T1 & T2 MRI’s?
Cortical Bone
Does T1 or T2 have a better detailed image?
T1
What MRI system suppresses fat so that edematous tissue can be better evaluated?
STIR (Short Tau Inversion Recovery)
How do MRI differentiate structures (oppposed to density as used with the CT)?
High signal = bright
Low signal = dark
Intermediate = anywhere in between
Is it okay to have batteries or iron on/in a patient who needs an MRI?
NO
It’s important to be very still while taking a MRI; therefore, what type of patient cannot have a MRI?
Epileptic (Seizures), Reactive-PTSD
What are 4 MRI contraindications to implants of the cardiovascular system?
- Pacemaker
- Cardiac defibrillator
- Aneurysm clips
- Carotid artery vascular clamp
What are 6 random contraindications for MRI’s?
- Neurostimulator
- Insulin or infusion pump
- Implanted drug infusion devise
- Bone growth/fusion stimulator
- Cochlear, otologic, or ear implant
- Some Tatoos (high metallic content)
What imaging system uses x-rays?
CT
MRI uses what for visual imaging?
Radiofrequency and magnets
What imaging machine uses densities in tissues vs. signal intensity?
MRI - signal intensity
CT - densities
Does CT or MRI provide exemplary detail?
CT
What machine provides exemlary tissue differentiation?
MRI
What machine can be reformatted from axial data?
CT
What machine requires multiplanar image acquisition?
MRI
What machine is the fastest?
CT (MRI not so fast)
Can any machine take images on patients with metal or battery implants?
Yes, CT
What machine is best for unstable patients?
CT
What are other names for radionuclide imaging?
Scintigraphy and Bone scan
What do patients ingest or get injected for Scintigraphy?
Radioisotopes chelated to substances that are inert
What is the most common radioisotope used in bone scans?
Technetium 99
Technetium 99 is referred to as a _______ that acts characteristically in the body and will circulate to areas of high physiologic function.
Tracer
How can a Scintingraphy be useful (what does it identify)?
Areas of abnormally high or low metabolic activity in organs and bones
What are 3 types of scintigraphy?
- 2D
- SPECT (single photon emission tomography)
- Hybrid SPECT
What are “Hot Spots” in scintigraphy?
Areas of high metabolic activity
What are “cold spots” in scintigraphy?
Area lacking vascular supply (abcess or avascular necrosis)
What is unique about Hybrid SPECT?
It combines CT or MRI with scintigraphy to gain anatomic and physiological comparison
What are the 3 types of bone scans?
Whole body, Limited, Three-phase
What bone scan is used for systemic bone disorders (ie. metastasis, arthritis, etc.)?
Whole body (images the entire skeleton)
What bone scan is used for fractures (occult/stress)?
Limited (images a specific region)
What bone scan images flow, blood pool, delayed images and is used for infection (osteomyelitis vs. cellulitis)?
Three Phase
What patient population benefits from the 3-phase bone scan for detecting early infection?
diabetic patients
How much Technetium 99m-MDP has an effective dose of 3 mSv whole body?
20 mCi
What’s the half life, biological half life, and effective half life for Technetium-99m-MDP?
6 hour half life
24 hour biological half life
4.8 hour effective half life
Describe the effective half life of Technetium-99m-MDP?
It’s total half life is 6 hours; however, the isotope is decaying & the body has started to clear it throught the urinary system.
Are bone scans sensitive or specific for increased bone metabolism?
Highly sensitive (poorly specific)
What imaging uses sound waves to bounce of internal structures?
Ultrasonography
What information bounces off the internal structures that allows an image to be seen?
Echos
What causes the sound waves to “bounce back” to the ultrasound transducer?
Changes in tissue density (solid vs. cysts)
When using an Ultrasonography where is the Transducer placed?
On the skin over the area of interest
What’s placed between the skin and the Transducer in order to facilitate sound wave transmission from Transducer?
Ultrasonic gel
What is unique about Ultrasonography?
It’s a real time study (structures viewed under active or passive motion) and can orient the image that’s not orthogonal
Ultrasonography is dynamic and image quality is highly dependent on what/whom?
The technician
Does US use ionizing radiation?
NO
What are the strengths of US?
- Obstetric evals
- Internal organ eval
- Large joints
- Muscles, tendons, ligaments around joints
- Intaoperative application
What is identification is limited with US?
Spinal evaluation, perispinal structures, and measuring muscle volume
What does the film look like when the film has too much contrast?
Appears too White and Black (over-exposed)
How would you correct a film with too much contrast?
increase kVp by 15% and dividing mAs by 2
When a film has too little contrast (too grey overall, washed out, dull) how is it corrected?
lowering kVp, which will require mAs by 2x to correct density
What landmark can be checked for film density?
ID blocker
If the film is too dark what could be the cause?
Processor
How would the density be fixed if the film is too dark?
Decrease the mAs (Leave the kVp alone)
What would be the consequence of excessive mAs &/or kVp, high developer temperature, chemicals too strong?
Film appears overexposed
What happens if the prossesor chemicals were just changed or replenishment rate is too high?
The film appears overexposed
Bone pathology substantially reducing bone density does what to film image?
Overexposed appearance
Mis-measurement of the patient results in a wrong technique causing what?
Errors in density
