Special Imaging Flashcards
What does CT stand for?
Computerized Tomography
What is CT (computerized tomography) also known as?
Computerized axial tomography (CAT)
What does a CT scan do?
Diagnostic imaging procedure that uses x-rays to present a cross-sectional image “slices” of the body
What are the cross sections reconstructed from?
Measurements of Attenuation coefficients (this calculates the ability of x-rays to pass through tissues)
What calculates the ability of x-rays to pass through tissues or being weakened or _____ by the tissues?
Attenuation coefficients
- Attenuated
CT is based on what fundamental principle?
The density of tissue that is passed by the x-ray beam is able to be measured from a calculation of the attentuation coefficients!
T/F: The emitter of x-rays rotates around the patient and the detector, placed in diametrically same sides.
FALSE
- The emitter of x-rays rotates around the patient and the detector, placed in diametrically OPPOSITE sides
T/F: Unlike x-ray radiography, detectors of the CT scanner do not produce an image
TRUE
CT scanners will measure the transmission of a thin beam, how thin is it?
1-10mm slices
The image of the certain section being imaged is taken from different angles, which allows the information to be viewed at a certain depth…. what depth is this? (i.e. 1-d, 2-d, 3-d)
3-dimension
T/F: CT scanning allows you to view body sections in all available planes and three dimensional imaging.
TRUE
What is each square in the image matrix called?
Pixel
What is the tiny elongated block of tissue known as?
Voxel
T/F: The size of the pixel was not determined by the computer program, but determined by the dimensions of the x-ray beam.
FALSE
- The size of pixel was determined by the computer program and NOT by the dimensions of x-ray beam
T/F: CT slice thickness is determined by computer programming and not the x-rays themselves.
TRUE
What are the units used in CT scans?
- Hounsfield units (HU)
- These are determined by the intensity of x-ray attenuation coefficient in tissues of different densities that can be a reliable measure of different compositions of body tissues
In HU, what are the measurements of Air, Fat, Water, Compact bone…
Air = -1000HU
Fat = -60 to -120 HU
Water = 0 HU
Compact Bone = + 1000 HU
Who pioneered the CT scan?
Sir Godfrey Hounsfield - Nobel Prize in 1979
Clinical application and indication for CT scanning?
- Head/Neck Pathology + paranasal sinuses
- CTA-CT angiography
- Chest and abdomen
- Imaging of acute trauma: fractures/dislocations
- CT is also used if MRI or other imaging is contraindicated
- Note: CT axial slices are modality of choice for investigating head trauma and cerebrovascular events (stroke)
Neck Ct+C is used in the diagnosis or what?
Lymphoma and Head/Neck Neoplasms
T/F: For cervical and other skeletal trauma CT imaging w/o contrast is the modality of choice especially if plain radiographs are unrewarding or require further special imaging.
TRUE
- ex. sagittal reconstruction of a cervical spine CT showing flexion teardrop fracture at C5
Correct ID of various radiographic densities referring to HU scale will help with accurate diagnosis and clinical management. If looking at a axial cut of a liver, what could one find?
Lipoma within the liver
What does MRI stand for?
Magnetic Resonance Imaging
T/F: Like CT an MRI helps look at the body within different planes.
TRUE
What two views are most helpful in an MRI?
Coronal, Sagittal
MRI uses what for imaging instead of radiation?
Detects magnetic changes in hydrogen atoms
T/F: Carbon is the most abundant in both water and fat.
FALSE
- Hydrogen is the most abundant
MRI uses two common sequences, what are they?
- T1 weighted image - fat is bright
- T2 weighted image - water is bright
Which weighted image is used for visualizing and appreciating normal anatomy?
T1
Which weighted image method is used for detecting disease process, since most pathologies lead to cell damage with inflammation and edema seen as bright or high signal intensity on __ and other fluid sensitive pulse sequences.
T2
What is based on imaging of protons?
MRI
T/F: In general Hydrogen atoms show strong (-) charge and spin at varied frequency along their own small EM field.
FALSE
- Hydrogen atoms show (+) charge
- and spin at CONSTANT frequency along their own small EM field.
T/F: When a strong magnet is applied N>S pole, protons line up along the stronger magnetic axis just like the needle of a compass.
TRUE
Which scan can be explained as the “Spinning Top” analogy?
MRI
- In the MRI scanner an external radio-frequency of the same frequency as the spinning protons is applied and the protons will then absorb this energy and become energized and being to resonate
- The external radiofrequency will then be “turned off” and the protons begin to decay or revert back to their original energy
- The decay frequency is then received as a radio wave and converted or digitized by the computer creating an image that depends on the number of protons in different tissues.
How an MRI works
What are loops of wire/thin conductive sheets on a cylindrical shell lying just inside the MRI scanner?
Gradients
What happens when a current is passed through these coils?
Secondary magnetic field is created
What is the primary function of gradients?
- It allows spatial encoding of the MR signal
- These are also critical for a wide range of physiologic techniques such as MR angiography, diffusion, and perfusion imaging
What are used to receive and transmit signal, from the patient in respect to an MRI?
Patient coils
_____ coils are the “antenna” of the MRI system. These coild can broadcast the RF signal to the patient and/or receive the returned signal.
Radiofrequency
T/F: MRI is far superior to any other imaging in detecting variations in soft tissue anatomic details.
TRUE
T/F: MRI is particularly helpful in detecting pathology of muscles, ligaments, soft tissues of the solid organs, bone marrow and the brain.
TRUE
