Final; Advanced Imaging Modalities Flashcards
This was invented in 1972 by Sir Godfrey Hounsfield and Dr. Allan Cormack sharing the Nobel Prize; it produced non-superimposed images for the first ime
CT; computed tomography
What three things make CT superior to conventional radiographs
multiplanar and cross sectional images and 3D viewing
no superimposition of structures
many times higher sensitivity to subtle differences
What is the principle of a CT scanner
internal structures of an object can be reconstructed from multiple projections of the object
What are the three steps to image isolation of a CT scanner
x-ray tube is rotated around the patient
radiation transmitted through the patient is absorbed by a ring of detectors
absorbed radiation is converted to an image
What are some current standards for the multi director CT
up to 64 slice scanner available
isotropic (clear, realistic) resolution
true 3D
What are three limitations of fan beam CT in dentistry
expensive
substantial size; occupy large space
high radiation dose
This was developed in the lat 1900’s using rotating gantry to which an x-ray source and detector are attached
cone beam computed tomography
A cone-shaped x-ray beam is directed though the middle of the area os interest and onto what
an area x-ray detector (sensor) on the opposite side
During the rotation os a cbct, multiple sequential planar projection images of what are acquired in a complete or sometimes partial arc
field of view (FOV)
This type of field of view is approximately 5cm or less; dentoalveolar/TMJ
small; localized region
This type of field of view is 5 to 7cm; maxilla/amndible
medium; single arch
This type of field of view is 7-10cm; inferior concha to mandible
medium; interacrh
This type of field of view is 10-15cm; nation to mandible
large; maxillofacial
this type of field of view is greater tun 15cm; vertex of skull to inferior border of mandible
large; craniofacial
What are some advantages to cbct in dental/maxillofacial imaging
1/4-1/5 cost of fan beam CT
significantly reduced patient exposure
segmentation
What are some limitations and disadvantages to cbct
artifacts
image noise
poor soft tissue contrast
What can cbct be used for in dental and maxillofacial applications
analysis of available bone for implant impacted teeth assessment bony and dental pathologic conditions maxillofacial deformities TMJ evaluation of root canal system and nasopharyngeal airway
This was discovered in 1946 and was used for diagnostic imaging in the 70s and 80s; introduced by Lauterbur and Mansfield; Damadian = father of modern
MRI and NMR
What are the three steps to an MRI
magnetic field
radio-frequency pulse
relaxation
This step of MRI; nuclei of many atoms, particularly hydrogen align with an external magnetic field (MRI machine)
magnetic field
This step of MRI; generated by “transmitter coil” directed at patient cause some hydrogen atoms to absorb energy
radio-frequency pulse
This step of MRI; when RF pulse is turned off, the stored energy is released from the body and detected as a signal in “receiver coil”
relaxation
What is the signal in an MRI
essentially a map of hydrogen ion distribution in the body
What are some relative brightness of tissued in the body in an MRI
white = fat, marrow, brain grey = muscle, body fluid black = TMJ disc, cortical bone, air
