advanced imaging modalities Flashcards
advanced imaging options
- MDCT
- CBCT
- MRI
- Positive Contrast Examinations
- Nuclear Medicine- PET-CT
- Ultrasound
MDCT additional names
- Multidetector Helical CT
- Multislice CT
- Multirow CT
how was MDCT made
beatles made lots of money and it was used by the label’s engineering firm for the work of engineer
Godfrey Hounsfield and Allan Cormack
Dr. Ledley
developed patent for the first “whole body” CT
scanner for larger patient openings in 1976.
Technically, Ledley’s research resulted in the current MDCT technology
MDCT compared to xrays
Greater hard tissue object sensitivity than conventional
x-ray imaging systems
Demonstrates soft tissues
where is the control console for MDCT
behind leaded glass, still visibilty of pt
MDCT beam shape
fan shaped unlike CBCT
detectors of MDCT
multiple present
CT Basis-image Capture
Two basis-image capture sequences as the machine
rotates counterclockwise from Position 1 to Position 2
scans routinely capture in the range of 100 to 600 basis
images per rotational scan
of basis image
The greater the #
basis images, the
better the
reconstruction
algorithm
MDCT mechanism
- 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 (“digitized”) for a given voxel
- Numerical value is assigned a gray scale value for the part of the object (voxel)
- Spatial and numerical information is used by imaging software to construct images (visual analogs)
planes of image reconstruction
- Coronal (frontal)
- Axial (transverse)
- Sagittal
MDCT density units
Hounsfield (density) Units
windowing
- Human eye discriminate up to 40 shades of gray
- Monitors show up to 256 (8 bit) shades of gray
- CT data has 4096 (12 bit) shades of gray or 17,024 (14 bit) shades of gray
- But… the human eye cannot discriminate all the
shades of gray if displayed - So… at the workstation, the window width can be
narrowed around a selected window level
why use windowing
to create different windows to examine different tissues (bone vs soft)
Hounsfield (density) Units
High contrast resolution yields details of hard and soft tissue densities
Hounsfield (density) Units translate to CBCT units?
Do not translate to CBCT units BECAUSE of variations in:
* FOV
* Exposure
* Position in scanner
* Size of objectc
Windowing
* the window width can be?
* The narrower window width produces?
* The window level is the?
* A narrow window with varying window levels
selectively windows?
- the window width can be narrowed around a selected window level
- The narrower window width produces images with high contrast
- The window level is the number at the center of the
window - A narrow window with varying window levels selectively windows hard and soft tissue
which is bone and which is soft tissue window?
R: bone
L: soft
Disadvantages of C.T.
1) High dose of ionizing radiation
2) Expensive and not as readily available as conventional imaging
3) Sensitive to artifacts from metallic restorations and patient movement
One of the most important advantages of MR?
One of the most important advantages MR has is the ability to separate tissues with extracellular water from cellular tissues with intracellular water
good for soft tissues essentially, also no radiation used
Components of
Magnetic Resonance Imaging
(MRI)
- Magnets
- Resonant energy applied to protons which provides a signal to be detected and applied a greyscale value
- Imaging from grey scale values
MRI System components
Image Capture
Image Processing
Experiences for the Patient w MRI
- Confined space
- “Clanging” noise
- Mild vibration and movement
standard vs open MRI
standard is much better open was made to make pts more comfortable (image is less clear)
MRI mechanism
- magentic moments of MR active nuclei point in rnadom directions
- these produce no overall magnetic effect
- magnetic moments line up with the magnetic feild flux lines= alignment
- these nuclei are excited and moved from alignment and then realign, time to realign is the recorded signal
Contrast between soft tissues measurements in MRI
- Proton density
- T1 relaxation time
- T2 relaxation time
- flow
T1 weighted images =
T1 weighted images = “fat images”
(the surrounding fat produces the image
contrast
T2 weighted images =
T2 weighted images = “water images” (normal or abnormal location of free water can be evaluated)
T1? T2?
R: T2
L: T1
where could we used MRI
TMJ
Magnetic Resonance Imaging
Advantages of the M.R.I.
1) No ionizing radiation
2) Best soft tissue imaging
Disadvantages of MRI
- Cost
- Availability
- Time to image
- Claustrophobic patients
ABSOLUTE CONTRAINDICATIONS of MRI
General
* Imbedded ferrous metals
Specific
* Cardiac pacemakers (depending on model)
* Cerebral aneurysm clips
* Cochlear implants
* Intra-ocular metallic foreign bodies
Concluding Comments on MRI
* Best modality to study?
* most common imaging sequences to evaluate change in soft tissue structures?
* Functional studies of ?
- Best modality to study soft tissue disease
- T1 and T2 most common imaging sequences
to evaluate change in soft tissue structures - Functional studies of fluid dynamics in
vascular channels
POSITIVE CONTRAST
EXAMINATIONS uses
● ARTHROGRAPHY
● SIALOGRAPHY
● UROGRAPHY
● PYELOGRAPHY
● BARIUM SERIES
Arthrography Tray Armamentarium
use of LA and dye
epi used to keep dye localized
Arthrography Injection Technique tmj
thru EAM
interpreting Arthrography of TMJ Synovial Spaces
would see two bands of dye seperated by the disk, if not there may be a disk tear
Sialogram
Infusion of a radiopaque dye into a salivary gland’s ductal pattern and evaluating the fill pattern with radiographic imaging
Sialogram
● Technique is used for evaluation of which glands? why?
● Technique is used for evaluation of the parotid and
submandibular glands as these glands have a primary duct amenable for gland infusion
● Sublingual gland lacks a primary duct; it has multiple ducts excreting into the floor of the mouth therefore it is not suitable for sialographic examination
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
Advantages of nuclear medicine
1) Radioactive isotope concentrates in areas of rapid bone turnover and gives positive response with 10% increase of osteoblastic activity
Disadvantages nuclear medicine
1) Expensive and invasive
2) Morphologic changes not imaged
3) Findings not specific to any disease proces
PET CT
- Combination of PET and CT is referred to as hybrid or fusion imaging for both hard and soft tissue
- Superior to plain nuclear medicine alone
PET CT useful for
- location of a tumor
- followup of chemotherapy or surgery
- staging dementia, evaluate stroke
PET - CT FDG Overview
Positron Emission Tomography- Computed Tomography
» Fluorine-18 (18F) is a positron- emitting radioactive isotope that is used with a glucose analogue for quantitative imaging i
» Computed tomography (CT) is fused or co-registered with the PET scan to aid in interpretation
PET scan advantages
Allows functional study of a metabolic process
* Provides a visual image that corresponds with patient anatomy
PET scan disadvantages
- Higher dosimetry
- High finances
- Slow imaging; not capable for time sequences > 30 seconds
ultrasound
* ultrasound uses? not been associated with?
* ultrasound cost?
* ultrasound imaging is useful for the evaluation of?
- ultrasound uses non-ionizing sound waves and has
not been associated with carcinogenesis - ultrasound examination is less expensive to conduct
than CT or MRI - ultrasound imaging is useful for the evaluation of
physiology as well as anatomy (e.g. vascular lesions
in jaws).
Ultrasound mechanism
Ultrasound transducer sends ultrasound pulses into tissue and then receives echoes back with spatial and contrast information on a 2D grayscale image
