W2- CT, MRI, Nuclear Imaging Flashcards
PART 1: CT
PART 1: CT
What is a CT?
X-ray beam and detector within circular scanner that moves around the patient.
What is the difference between X-ray and CT scan?
CT is a series of cross-section slices that can be reconstructed in sagittal and coronal planes, as well as 3D. Series of X-ray (up to 1000 projections)
CT Indications. (6)
- Bone and soft tissue tumors
- Fx
- Intra-articular abnormalities
- Bone fragment detection
- Bone mineral analysis
- Neuroimaging
What is a limitation of CT scans?
Inability to distinguish small areas of different tissues.
Scanning Process
- ______ image (2D) taken to localize target structures.
- ______ slices taken continuously with multiple-detector rows. (Structures can be made into 3D images)
- Scout image
- Helical (spiraling)
Data Conversion
- ________ for each cubic millimeter.
- Converted from digital signals into matrix. (Each cell (pixel) assigned shade of gray)
- Matrix transformed into an image.
- Contrasts and window modifications.
Radiodensities
“Multiplanar Reconstruction: Images can be rotated in space on a computer screen.”
3D CT
“Contrast material allows visualization of structures that impinge on neurologic structures.”
CT Myelogram
What is a big advantage of CT over radiograph?
- Radiodensity free of superimposed tissues.
- Can see slices as compared to averages of tissue radiodensity.
With a CT, denser structures appear more ______.
-What is a voxel?
- white
- Voxel- Product of pixel and slice thickness. (Average density of different tissues represented from within the voxel)
With CT imaging, having a familiarity with cross-sectional anatomy is important. Viewers scroll through multiple images. What is an axial image?
Axial image is as if the patient were supine, viewer looking in caudocephalad direction.
What is an axial image?
What is a sagittal image?
What is a coronal image?
Axial Image = Patient were supine, viewer looking in caudocephalad direction.
Sagittal Image = View from left to right.
Coronal Image = View as if facing the patient.
When it comes to bone, what is CT helpful for?
- Subtle Fx
- Degenerative changes
- Serious trauma
- Spinal stenosis
- IV disc pathology (push onto CNS)
- Intra-articular loose bodies
- Osseous alignment in any place
When it comes to neuroimaging, what is CT helpful for?
- Acute Trauma
- SPECT
- PET
What are some benefits of CT? (3)
- Less expensive than MR.
- Less time than MR and US.
- Benefits over problems related to physical barriers with MRI.
What are some limitations of CT? (2)
- Given observation is based on radiodensity, tissues of similar radiodensity may not be distinguishable.
- Radiation exposure.
PART 2: MRI
PART 2: MRI
What is an MRI?
- Radiofrequency waves within a magnetic field interact with tissues.
- Relies on detection of remitted radiofrequency waves that are absorbed.
What planes do we view MRIs in? (3)
- axial
- sagittal
- coronal
- Do different structures have different signal intensities with MRIs?
- Can contrast be used with MRI?
- Yes
- Yes
What are some indications for MRI? (4)
-soft tissue trauma, internal joint derangement, tumors, subtle FX/stress Fx
How many gradient coils are there with an MRI?
-3, one for each orthogonal plane
What are some extra variants of MRI machines?
- Open scanners
- Upright scanners
How does an MRI scan work?
- MRI uses protons, which spin creating a small magnetic charge.
- When a magnetic field is introduced (MRI), protons align with the field.
- MRI tech introduces radiofrequency pulse, disrupting the proton and forces it into either 90 or 180 degree realignment.
- Once the pulse is turned off, it realigns with the magnetic field, releasing electromagnetic energy along the way.
- MRI detects energy and can differentiate tissues based on how quickly they release energy after pulse it turned off.
- T1 Weighted: Images measure energy from structures that give up energy ______ = _____.
- T2 Weighted: Images measure energy from structures that give up energy _______ = _____.
- T1 = quickly = fat
- T2 = slowly = water
- With T1 weighted images, they show good anatomical detail. Tissues with high ______ content appear darker.
- With T2 weighted images, they are good at recognizing inflammation. Tissues with high _____ appear darker.
- water
- fat
What is contrast MR good at looking at?
blood vessels: Magnetic Resonance Angiography (MRA) and MRI Arthrogram
What is an axial image?
What is a sagittal image?
What is a coronal image?
Axial Image = Patient were supine, viewer looking in caudocephalad direction.
Sagittal Image = View from left to right.
Coronal Image = View as if facing the patient.
- MR is sensitive to changes in what in bones?
- What diagnosis can this lead to?
- Bone marrow
- Can lead to Dx of bone tumor, stress Fx, and AVN
MR can be used for _____ staging, but is not as effective as bone scan for screening purposes.
-tumor staging
__________ = Arthrogram + MRI
-MR Arthrography
__________ = View spinal canal and subarachnoid space with high resolution MRI + strong T2 weighting
-MR Myelography
MR Limitations. (6)
- Imaging of bone
- Time for image
- High cost
- Contraindications (ferromagnetic metal)
- Hardware can cause distortion of image
- Physical limitations with procedure parameters (ability to stay still, claustrophobia)
PART 3: NUCLEAR IMAGING
PART 3: NUCLEAR IMAGING
What is nuclear imaging?
Produces images by detecting radiation from different parts of the body after a radioactive tracer material is administered.
- Is nuclear imaging used to target a body region or is it for the whole body?
- Is nuclear imaging used for a static image of viewing over a period of time?
- either
- either
What is the difference between nuclear medicine and “Nuclear Imaging”?
- Nuclear Medicine = Introduction of radioactive agents for treatment and Dx.
- Nuclear Imaging = Nuclear medicine, though indicates intent of Dx.
What is the general indication for nuclear imaging?
Testing function of tissues. (Dx by physiologic change (as opposed to structure)
How does nuclear imaging work? (4)
- Radionuclide (emits gamma rays) introduced.
- Absorbed differently by tissues based on metabolic activity.
- Gamma rays observed by special camera.
- Computer converts to digital image.
Methods
- Static?
- Whole body?
- Dynamic?
Static = single image of targeted body region. Whole-body = AP Dynamic = Timed sequence
What are (2) other forms of nuclear imaging and what are they?
Single Photon Emission Computed Tomography (SPECT)
- 3D (indications bone, cardiac perfusion, brain, liver)
- Can produce thin slices
Positron Emission Tomography (PET)
-biologic function of cells (indications for CNS studies, tumors)
Nuclear Imaging Indications. (3)
- Cancer: staging, observation, and testing response to therapeutic interventions (screening pts with a high risk for metastasis to bone)
- Detection of metabolic bone diseases and other osteopathies.
- Detection of other bone abnormalities.
MSK Indications. (7)
- HO
- Fx and Stress Fx
- Inflammation/Infection
- Complications of foreign hardware/prosthetic/medical device
- CRPS
- PFPS
- AVN
- What is Scintigraphy?
- What typically indicates increased uptake with this imaging.
- Nuclear imaging of skeleton.
- Black spots (hot spots) on image typically indicate increased uptake.
Nuclear imaging (scintigraphy) is a good functional image used for what?
- Confirm disease
- Identify extent of disease
What is a bone scan?
Imaging study of the skeleton.
With a bone scan, uptake depends on balance of osteoblastic and osteoclastic activity.
- Increased uptake = ________
- Decreased uptake = _________
- Increased uptake = osteoblastic
- Decreased uptake = osteoclastic
What are the 3 phases of bone scan?
1st Phase = flow study (immediate)
2nd phase = blood pool (30 minutes)
3rd phase = delayed (2-4hrs)
*See if tracers are being dispersed where they should and if they are collecting indicating altered function.
What is an advantage of nuclear imaging bone scan?
High sensitivity for changes in bone metabolism.
What are some disadvantages of nuclear imaging bone scan?
- Low specificity
- Poor anatomic detail
What are some contraindications to nuclear imaging?
- Pregnancy
- Currently breast-feeding
