Advanced Imaging Modalities Flashcards
what are the advanced imaging modalities
- MDCT
- CBCT
- MRI
- positive contrast examinations- arthrography, sialography
- nuclear medicine- PET CT
- ultrasound
what are the advanced imaging modalities that use CT
- MDCT
- CBCT
- MRI
- PET-CT
- ultrasound
what are the other names for MDCT
- multidetector helical CT
- multislice CT
- multirow CT
what does MDCT stand for
multi detector computed tomography
what are the older terms for MDCT
- CAT
who developed CT imaging
Godfrey Hounsfield and Allan Cormack
what did Dr. Ledley do
developed patent for the first whole body CT scanner for larger patient openings
what does the MDCT image
greater hard tissue object sensitivity than conventional XR systems
- demonstrates soft tissues
MDCT technique uses a _____ beam
fan-shaped
how many detector arrays are in MDCT
4
describe the CT basis image capture and how many images are captures
- two basis image capture sequences as the machine rotates counterclockwise
- scans routinely capture in the range of 100-600 basis images per rotational scan
how does MDCT work
- attenuated beam photon capture in the solid state cadmium tungstate detector affects energy, the degree of ionization and electrical charge
- electrical charge is assigned a numerical value for a given voxel
- numerical value is assigned a gray scaled value for the part voxel
- spatial and numerical information is used by imaging software to construct images
what planes of images does MDCT construct
coronal
- axial
- sagittal
human eye can discriminate up to _____ shades of gray
40
monitors show up to ____ shades of gray
256
most CT data have _____ shades of gray
4096
a 14 bit system has _____ shades of gray
17,024
what units are used for density in MDCT
hounsfield units
hounsfield units do not translate to CBCT because of variations in:
- FOV
- exposure
- position in scanner
- size of object
the narrower window width produced images with ____ contrast
high
a narrow window with varying window levels selectively windows:
hard and soft tissue
where is the window level number
at the center of the window
what are the disadvantages of CT
- high dose of radiation
- expensive and not as readily available as conventional imaging
- sensitive to artifacts from metallic restorations and patient movement
what is the dose for head MDCT
960-1500
one of the most important advantages MRI has is:
the ability to separate tissues with extracellular water from cellular tissues with intracellular water
what are the components of MRI
- magnets
- resonant energy
- imaging
what are the MRI experiences for the patient
- confined space
- clanging noise
- mild vibration and movement
What does MRI target in cells
- uses the resonance property found in some of the nuclei present in the human body
- the hydrogen nucleus is of interest due to its large presence in water and body molecules
- only atoms with an odd number of protons and/or neutrons in the nucleus have the mangetic properties required
magnetic moments of MR active nuclei point in____ so they _____
random directions; produce no overall magnetic effect
what is alignment in magnetic moments
magnetic moments line up with the magnetic field flux lines
what is the contrast between soft tissues in MRI-
- proton density
- T1 relaxation time
- T2 relaxation time
- flow
what are T1 weighted images
- “fat images”
- the surrounding fat produces the image contrast
what are T2 weighted images
-“water images”
- normal or abnormal location of free water can be evaluated
what are the advantages of the MRI
- no ionizing radiation
- best soft tissue imaging
what are the disadvantages of MRI
- sensitive to motion artifacts
- expensive financial and temporal demands
- claustrophobia
- cost
- availability
- time to image
- claustrophobic patients
what are the absolute contraindications for MRI
- imbedded ferrous metals
- cardiac pacemakers- not always
- cerebral aneurysm clips
- cochlear implants
- intra ocular metallic foreign bodies
what is the best modality to study soft tissue disease
MRI
what are the most common imaging sequences to evaluate change in soft tissue structures
T1 and T2
what are the positive contrast examinations
- arthrography
- sialography
- urography
- pyelography
- barium series
what is arthrography used for
synovial spaces
what is done in a sialogram
infusion of a radiopaque dye into a salivary glands ductal pattern to evaluate the fill pattern
what is the sialogram used for in dentisry and why
evaluation of the parotid and submandibular glands because these glands have a primary duct amendable for gland infusion
why cant you do a sialogram on the sunlingual gland
it lacks a primary duct, it has multiple ducts excreting into the floor of the mouth so its not suitable
describe the nuclear medicine bone scan
- imaging technique where bone binds a radioisotope Tc99
- gamma camera takes images of where the radioisotope has collected
- metabolic activity determines degree of radioisotope binding
what are the advantages of nuclear medicine bone scan
radioactive isotope concentrates in areas of rapid bone turnover and gives positive response with 10% increase in osteoblastic activity
what are the disadvantages of nuclear medicine bone scan
- expensive and invasive
- morphologic changes not imaged
- findings not specific to any disease process
what does PET -CT
positron emission tomography - computer tomography
combination of PET and CT is referred to:
as hybrid or fusion imaging
PET CT is superior to:
plain nuclear medicine alone
what is the PET CT useful for
- location of a tumor
- followup of chemotherapy or surgery
- staging dementia, evaluate stroke
describe PET-CT
- fluorine-18 is a positron emitting radioactive isotope that is used with glucose analogue for quantitative imaging
- CT is fused or co-registered with the PET scna to aid in interpretation
Describe FDG uptake
increased FDG uptake is evident as increased brightness in left condyle laterally and superiorly. comparison of left and right condyles joints illustrates difference in FDG uptake
what are the advantages and disadvantages of PET scan
-A: allows functional study of a metabolic process. provides a visual image that corresponds with patient anatomy
-D: higher dosimetry, high finances, slow imaging;not capable for time sequences greater than 30 seconds
what does ultrasound use and is it associated with carcinogenesis
uses non ionizing sound waves and has not been associated with carcinogenesis
ultrasound is _____ expensive to conduct than CT or MRI
less
ultrasound imaging is useful for:
the evaluation of physiology as well as anatomy
how does ultrasound work
sends ultrasound pulses into tissue and then receives echoes back with spatial and contrast information on a 2D grayscale image
