Adv Imaging Modalities Flashcards by sophie rosen

Advanced Imaging Modalities
(6)

MDCT
CBCT
MRI
Positive Contrast Examinations
Nuclear Medicine
Ultrasound

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Positive Contrast Examinations
(2)

Arthrography
Sialography

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Nuclear Medicine
(1)

PET-CT

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Multi-Detector Computed Tomography
(MDCT)
a.k.a.
(3)

Multidetector Helical CT
Multislice CT
Multirow CT

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MDCT
older terminology
(6)

Computerized Axial Tomography (CAT)
Computerized Reconstruction Tomography
Computed Tomographic Scanning
Axial Tomography
Computerized Transaxial Tomography
Computerized Axial Transverse Scanning

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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

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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

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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

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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

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MDCT
Greater — than conventional
x-ray imaging systems
Demonstrates —

hard tissue object sensitivity
soft tissues

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MDCT Technique
uses a — -shaped beam

fan

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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.

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The greater the #
basis images, the

better the
reconstruction
algorithm

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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

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Images constructed in the anatomic
planes of imaging;
(3)

Coronal (frontal)
Axial (transverse)
Sagittal

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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)

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High contrast resolution yields details of

hard and soft tissue
densitie

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Hounsfield (density) Units
Do not translate to
CBCT units
BECAUSE of
variations in
(4)

FOV
Exposure
Position in scanner
Size of object

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the window width can be
narrowed around a selected

window leve

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The narrower window width
produces images with —
contras

high

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The window level is the
number at the — of the
window

center

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A narrow window with
varying window levels
selectively windows

hard
and soft tissue

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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

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1 day of background
radiation ~

8.5μSv

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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)

1. Magnets 2. Resonant energy 3. 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