Adv Imaging Modalities Flashcards
Advanced Imaging Modalities
(6)
- MDCT
- CBCT
- MRI
- Positive Contrast Examinations
- Nuclear Medicine
- Ultrasound
- Positive Contrast Examinations
(2)
- Arthrography
- Sialography
- Nuclear Medicine
(1)
- PET-CT
Multi-Detector Computed Tomography
(MDCT)
a.k.a.
(3)
- Multidetector Helical CT
- Multislice CT
- Multirow CT
MDCT
older terminology
(6)
- Computerized Axial Tomography (CAT)
- Computerized Reconstruction Tomography
- Computed Tomographic Scanning
- Axial Tomography
- Computerized Transaxial Tomography
- Computerized Axial Transverse Scanning
Electrical and Musical Industries
The Beatles were so successful
that EMI was able to fund other
divisions of the company, in
particular the work of engineer
Godfrey Hounsfield.
Allan Cormack shared the
Nobel Prize in 1979 for the
Development of
CT imaging
Computed Tomography
Robert S. Ledley DDS, MS
DDS -1948, NYU
MS – physics 1950, Columbia U
“Mathematics Used to Keep False Teeth in Place.”
optimize the fitting of dentures by determining the
mean slope of each tooth relative to the surface of the
piece of food being chewed
Robert S. Ledley DDS 1948; MS in physics 1950
The room-sized Standards Eastern Automatic Computer (SEAC) from early 1950s.
Ledley learned to program on this computer
SEAC used to create the
first
scanned image
Computed Tomography
Dr. Ledley (DDS) developed patent for the first
Technically, Ledley’s research resulted in the current
“whole body” CT
scanner for larger patient openings in 1976.
MDCT technology
MDCT
Greater — than conventional
x-ray imaging systems
Demonstrates —
hard tissue object sensitivity
soft tissues
MDCT Technique
uses a — -shaped beam
fan
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.
The greater the #
basis images, the
better the
reconstruction
algorithm
MDCT
* Attenuated beam photon capture in the
solid state — detector
affects (3)
* Electrical charge is assigned a
* Numerical value is assigned a
* (2) information is used
by imaging software to construct images
(visual analogs)
cadmium tungstate
energy, the degree of ionization and electrical charge
numerical value (“digitized”) for a given voxel
gray scale value for the part of the object (voxel)
Spatial and numerical
Images constructed in the anatomic
planes of imaging;
(3)
- Coronal (frontal)
- Axial (transverse)
- Sagittal
Windowing
* Human eye discriminate up to – shades of gray
* Monitors show up to — shades of gray
* CT data has — shades of gray or — 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
40
256 (8 bit)
4096 (12 bit), 17,024 (14 bit)
High contrast resolution yields details of
hard and soft tissue
densitie
Hounsfield (density) Units
Do not translate to
CBCT units
BECAUSE of
variations in
(4)
- FOV
- Exposure
- Position in scanner
- Size of object
the window width can be
narrowed around a selected
window leve
The narrower window width
produces images with —
contras
high
The window level is the
number at the — of the
window
center
A narrow window with
varying window levels
selectively windows
hard
and soft tissue
Disadvantages of C.T.
(3)
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
1 day of background
radiation ~
8.5μSv
Magnetic Resonance Imaging
(MRI)
* One of the most important advantages MR
has is the ability to
separate tissues with
extracellular water from cellular tissues
with intracellular water
Components of
Magnetic Resonance Imaging
(MRI)
(3)
- Magnets
- Resonant energy
- Imaging
MRI System
(2)
Image Capture
Image Processing
MRI Experiences for the Patient
(3)
- Confined space
- “Clanging” noise
- Mild vibration and movement
MRI makes use of the — property found in some of the nuclei present in the human body
resonance
the hydrogen nucleus (proton) is of interest due to its large presence in
water and body molecules
also, only atoms with an – number of protons and or neutrons in the nucleus have the — properties required
odd
magentic
Magnetic moments of MR active nuclei point in — directions
thus they produce no
random
overall magnetic effect
alignment
magnetic moments line up with the magnetic field flux lines
Contrast between soft
tissues
(4)
- Proton density
- T1 relaxation time
- T2 relaxation time
- flow
- T1 weighted images = “
fat images”
(the surrounding fat produces the image
contrast)
- T2 weighted images =
“water images”
(normal or abnormal location of free
water can be evaluated)
Tissue relaxation characteristics
T1
msec
T2
msec
Muscle
860
70
Tissue relaxation characteristics
T1
msec
T2
msec
Fat
750
55
Tissue relaxation characteristics
T1
msec
T2
msec
BRain
220
60
Tissue relaxation characteristics
T1
msec
T2
msec
CSF
3000
2000
Tissue relaxation characteristics
T1
msec
T2
msec
Blood
900
200
Magnetic Resonance Imaging
Advantages of the M.R.I.
(2)
1) No ionizing radiation
2) Best soft tissue imaging
Disadvantages of MRI
(3)
- 1) Sensitive to motion artifacts
- 2) Expensive financial and temporal
demands - 3) Claustrophobia
MRI
DISADVANTAGES
(4)
- Cost
- Availability
- Time to image
- Claustrophobic patients
MRI
ABSOLUTE CONTRAINDICATIONS
General
(1)
Specific
(4)
- Imbedded ferrous metals
- Cardiac pacemakers (depending on model)
- Cerebral aneurysm clips
- Cochlear implants
- Intra-ocular metallic foreign bodies
MRI
Best modality to study
soft tissue disease
MRI
T1 and T2 most common imaging sequences
to evaluate change in
soft tissue structures
MRI
Functional studies of
fluid dynamics in
vascular channels
POSITIVE CONTRAST
EXAMINATIONS:
(5)
● ARTHROGRAPHY
● SIALOGRAPHY
● UROGRAPHY
● PYELOGRAPHY
● BARIUM SERIES
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 the
parotid and
submandibular glands as these glands have a primary duct
amenable for gland infusion
Sialogram
● 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
* — camera takes images of where the
— has collected
* — activity determines degree of
— binding
bone binds a radioisotope Tc99
Gamma, radioisotope
Metabolic, radioisotope
Nuclear Medicine Bone Scan
Advantages
1)
Radioactive isotope concentrates in areas
of rapid bone turnover and gives positive
response with 10% increase of osteoblastic
activity
Nuclear Medicine Bone Scan
Disadvantages
(3)
1) Expensive and invasive
2) Morphologic changes not imaged
3) Findings not specific to any disease process
PET CT
* Combination of
PET
and CT is referred to
as hybrid or fusion
imaging
PET CT
Superior to
plain
nuclear medicine
alone
PET CT
Useful for:
(3)
- 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
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.
PET SCAN
Advantages
(2)
- Allows functional study of a metabolic
process - Provides a visual image that
corresponds with patient anatomy
PET SCAN
Disadvantages
(3)
- Higher dosimetry
- High finances
- Slow imaging; not capable for time
sequences > 30 seconds
Ultrasonography
* aka (2)
– Real-time echography
– Real-time tomography
Ultrasound
* ultrasound uses
* ultrasound examination is less expensive to conduct than (2)
non-ionizing sound waves and has
not been associated with carcinogenesis
CT or MRI
- ultrasound imaging is useful for the evaluation of
physiology as well as anatomy (e.g. vascular lesions
in jaws).
Ultrasound transducer sends ultrasound pulses into tissue and
then receives echoes back with
spatial and contrast information
on a 2D grayscale image
