Final Prep - Alternate Imaging Modalities Flashcards
The MRI image is obtained through the absorption and emission of energy of the __________ of the electromagnetic spectrum
radio frequency
Earth’s magnetic field is measrued as:
1G (Gauss) or 0.0001 T (Tesla)
Since the human body is mostly water (2 hydrogen atoms per molecule) the nuclei of the hydrogen atoms spin about a central axis within their own magnetic field. When placed in an MRI, what happens to the protons?
They line up in the direction of the scanner’s axis and then the MRI machine applies a RF pulse specific to hydrogen
Once the MRI applies the RF pulse, what happens to the gradient magnets?
They are rapidly turned on and off, altering the magnetic field. This pulse causes the protons to absorb the energy and spin in a different direction, creating resonance
When the RF pulse is turned off, what happens to the hydrogen protons?
They slowly return to natural alignment and release stored energy. This energy comes in the form of heat or radio frequency.
Define CAT scan
Computed Axial Tomography
CAT Scans work by:
using computer-generated x-ray measurements from different angles to produce tomographic images of the scanned object
During a CAT scan, a thin x-ray beam rotates around the area of the body, creating a _______ of internal structures
3D image
In its simplest form, CT imaging consists of what?
Finely collimated x-ray beam and a single detector, both moving together in a translate-rotate mode
Water is assigned an arbitrary HU value of:
0
Since water is “neutral” or 0 on an HU scale, tissue DENSER than water will have a ______ value and tissue LESS DENSE than water will have ______ values
positive, negative
Nuclear scintigraphy is the science of diagnosis by means of:
Radioisotopes
Nuclear scintigraphy is very effective in:
Isolating pathology and function of organs or tissue
______ imaging is often used in equine patients where other methods are difficult due to size
Nuclear scintigraphy
What are 4 disadvantages to using Nuclear Scintigraphy?
- Poor image resolution, provided minimal detail
- Radiation dose is high
- images are not usually disease specific
- Dificult to localize exact anatomical site of source of emission
Define PET scan
Positron emission tomography
Define SPECT scan
single positron emission tomography
PET scans work by:
Using nuclear medicine imaging to produce a 2D or 3D picture of functional/metabolic processes in the body
What areas are PET scans efficient for viewing?
Oncology, neurology, cardiology, pharmacology and muscular-skeletal imaging
What is a major disadvantage of PET scans
2-3 times the price of a CT
When scanning soft tissue, which test will produce higher detail? An MRI or a CT Scan
MRI
When scanning bony structures, which test will produce higher detail? MRI or CT?
CT
Which test causes more unecessary irradiatioin? MRI or CT
CT
From Mild to Marked, what level of radiation is produced by MRI? CT?
MRI - none
CT - moderate
Which test is quicker? MRI or CT. How long does each take?
MRI - 30-45 mins
CT - Under 5 mins
Define Half-Life:
The interval for a given number of nuclei (or their radioactivity) to decay to one-half of the original value
Define Millicuries (mCi)
The quantity identifier for the radiation emitted by the isotopes is the Curie.
Define Scintigraphy
Nuclear scintigraphy is the science of diagnosis by means of radioisotopes, the patient is injected with a radionuclide, and the nuclear medicine camera detects the emission of radioactivity from the patient
Define Osteoblastic activity
Indicates accelerated metabolism within the bones, which will result in an indication of higher radiation emitted “a hot spot”
Define Radioactive decay
The spontaneous transformation of an unstable atomic nucleus into a lighter one, in which radioation is released in the form of alpha particles, beta particles and gamma rays
Define Radioisotope
Atoms in an element tat have the same atomic number but different atomic mass - excess radioactivity
Define Radioactivity
emission of ionizing radiation or particles caused by spontaneous decay of a nuclei
Define Technetium or TC-99m
Lightest element whose isotopes are ALL radioactive, none are stable. Nearly all TC-99m is artificially created. Used for nuclear scintigraphy, particularly in equine as it is attracted to bone
Define Iodine or I-131
A heavy radioactive isotope of Iodine. Used to treat hyperthyroidism in felines and isnt used for imaging - attracted to thyroid gland
Define gamma rays
Penetrating electromagnetic radioation of a kind arising from the radioactive decay of atomic nuclei. It consists of photons in the highest observed range of photon energy
Define Attenuation coefficient
Characterization of how easily a volume of material can be penetrated by a beam of light or energy
Define Hounsfield unit/CT numbers
A quantitative scale and its units for describing radiodensity. It is the percentage of the change between the HU of water and the HU of the variable.
Define Pitch
Ratio between the table movement in mm and the CT slice thickness
Define Raw data
digital signal collected from the detectors that is sent to the computer to be reconstructed onto an image
Define Interpolation algorithm
calculation of an unknown value based on two known values on either side (this allows the scanner to calculate slice as a straight plane rather than how it would actually appear)
Define matrix
A series of boxes or individual shades of information; a wide matrix results in a pixilated image, small matrix gives clear images
Define volume rendering
A type of 3D imaging; process takes all the range of Hounsfield units and incldues them in a picture. The operator can then select which range of voxels are opaque and which are transparent.
Define Atom
Contains protons, neurons and electrons; spins and wobbles in space; electrons spin around the outside of the atom; can join together to create molecules
Define Echo time
time between responses showing the maximum signal (demonstrates TI response of tissues)
define magnet
exhibiting a magnetic force or field
define magnetic field
region around a magnetic material or a moving electric charge within which the form of magnetism acts
define radio frequency
a frequency or band of frequencies suitable for use in telecommunications
define repetition time
Time between the radio frequency pulses (demonstrates T2 responses of tissues)
define resonance
frequency that results in atoms to jump to a higher energy state
define signal intensity
the relative brilliance of a radiographic image
define precession
the wobble of an atom as it spins
define Gauss and Tesla
Units of measurement of magnetism (1000G = 1T)
define specific absorption rate
calculation made on the bases of mass of the patient
Define radionuclides
Atoms involved in the isotope decay to half its original radioactivity. The radioactive material given to patients to study half life, the atoms that emit particles and energy in order to become stable
Define Algorithm
Mathematical equation, applies on each of the pixels creating the CT image to enhance certain structures
Define analog
During the process of the formation of a CT image, the final phase is the conversion of Digital-to-analog images; analog image involves shades of grey
