Specialized Tech Flashcards
Basic Ideas of Imaging
To measure and map a useful
property of the human tissues.
Non-invasive or minimally-
invasive.
Reflection
Photography,
ultrasound
Transmission
X-rays
Radiation
Pet/spect
Computed Tomography developed in
1971
by Dr. Godfrey N. Hounsfield &was used to image the
brain (Hounsfield, 1980)
Originally all scans were done in the axial plane ,thus
leading to the name
‘Computerized Axial Tomography
“or CAT Scan .
Axial as initial scans are done and these image scan be
reformatted and viewed in the
Axial as initial scans are done and these image scan be
reformatted and viewed in the Coronal plane , Sagittal
plane .
The CT x-ray system
(the gantry) consists of the x-ray source (fan-shaped beam),
radiation detectors and data-acquisition system.
Image Display:
As so called
Image Display:
As so called Soft
Tissue Window is
used to better
visualize the soft
tissues and the Bone
Window is used to
better visualize the
bone tissue.
Image display in term of
2 window
CT scans are mainly
performed in the
CT scans are mainly
performed in the Axial
plane.
The Coronal and Sagittal
cuts can then be calculated
(reconstructed) by the
computer.
Direct coronal and Sagittal
cuts can be also performed
but they require different
patient positioning.
Indications of CT in the Head and
Neck:
- Assessment of tumour size, site and extent, for both
benign and malignant tumours affecting the jaw bones,
maxillary antra, or base of the skull. - Investigation and assessment of extent of any suspected
intracranial and spinal cord damage following trauma to
the head and neck. - Detection of the extent of any diseases in the paranasal
sinuses and their extension into the orbit or base of the
skull. - Investigation of any TMJ pathosis or abnormalities.
- Investigation of the Salivary Glands and detection of any
intrinsic or extrinsic swellings. - Pre-operative assessment of jaw bones height and
thickness before inserting Implants.
Advantages of C.T.:
- Imaging of Hard and Soft tissues.
- The sensitivity of the detector combined with the power of
the computer makes it possible to discriminate between
objects with small differences in density such as blood
and fat or blood and cerebrospinal fluid. - Images can be enhanced by the use of intravenous (IV)
contrast media, providing additional information. - Images can be reformatted to another plane without the
necessity of another scan .Some CT scanners can image
the mandible and the maxilla on one scan . - Eliminates the superimposition of images of structures
superficial or deep to the area in question (Tomography
), and this can be done in any plane.
Disadvantages of C.T.:
The details of a computed tomographic
image are not as fine as in conventional
radiography due to the pixel size which
is greater than the size of the silver
specks that form the image in
conventional radiographs.
2. Metallic objects such as amalgam
fillings produce streak artifacts across
the CT image.
3. The equipment is expensive.
4. Increase radiation dose when compared
with conventional film.
method was introduced that may
prove to be more efficient and economical than
either conventional tomography or CT for oral
diagnosis .
(Cone Beam CT ){(CBCT
CBCT uses a
CBCT uses a round or rectangular cone shaped x-
ray beam centered on 2 &3D x-ray sensor to scan
360 rotations about patients head.
The patient is imaged in normal seated position
as in conventional tomography
Advantages of CBCT :
The scan times usually range between 17
sec. to little more than 1 min.
Excellent image quality :
High resolution
Reduction of artifacts
Distortion free
Excellent contrast resolution
User friendly software making acquisition and
image display simple and accurate
Low radiation dose
less expensive than CT .
It has already been in use in implant therapy.
It helps in clinical assessment of bone graft quality
following alveolar surgery in patients with cleft lip and
palate
These investigations use contrast media
II. Contrast Studies
Contrast Media are:
Radiopaque substances that have been
developed to alter artificially the density
of different parts of the patient i.e.
altering subject contrast.
Certain organs, structures and tissues,
invisible using conventional means can be
seen.
Contrast studies include:
Sialography – Salivary Glands
Arthrography– Joints
Angiography– Blood Vessels
Lymphography– Lymph Nodes and Vessels
Urography– Kidneys
Barium swallow, meal– GI Tract
Contrast media:
Types:
Barium sulphate
Iodine-based aqueous solutions
Iodine-based oil solutions
MR contrast agents
suspensions for GIT investigations.
Barium sulphate
Iodine-based aqueous solutions
water soluble) used for all
other investigations e.g. Urografin
Iodine-based oil solutions
used for lymphography and
sialography e.g. Lipiodol
MR contrast agents e.g
gadolinium.
Contrast media Patients at risk:
Patients at risk:
1. The elderly and very young children.
2. Patient with history of allergy to contrast media.
3. Diabetes, cardiac failure, renal failure or severe pulmonary
disorders.
Sialography: is
radiographic demonstration of the
major salivary glands by introducing a
radiopaque contrast medium into their
ductal system.
Ideal Requirements of Contrast Media
used in Sialography:
- They must posses sufficient radio-opacity provide
good delineation of the anatomic structures. - It must have proper viscosity, not very high as it will
need excessive pressure upon injection, and not very
low as it will escape the gland and will need repeated
injections. - It must be readily excreted from the glands.
- It must be non toxic and non-harmful to the tissues.
Sialography Procedures:
Preoperative phase:
Taking preop. (scout) radiographs:
Parotid gland– lat. oblique, PA and ant. parotid view using
occlusal film
Submandibular gland– lat. oblique, cross-sectional mandibular
occlusal and panoramic
Patient preparation:
Sialography Procedures: Filling phase:
Introducing the contrast medium through a canula in gland duct
orifice
Taking the filling phase radiographs.
Emptying or evacuation phase: sialography
Removal of canula and allowing excretion of contrast media
Taking radiographs after 5minutes
Radiographs can be used to assess gland function
Indications: of sialography ospe
- Chronic inflammation of Salivary Glands (sialectasis):
Obstructive inflammation:
calculi (sialolithiasis)– RL stone
strictures (constriction of the ductal wall near the
orifice)
stenosis (constriction of the ductal wall along the
whole course of the main duct).
Non-obstructive inflammation:
auto-immune diseases as Sjogren’s disease
bacterial infections as acute suppurative parotitis
or recurrent parotitis
viral infections as mumps
inflammation secondary to allergic reactions.
2.Neoplasms of salivary glands :
extrinsic tumours (there is normal architecture of the
gland and its secretary function but there is just
deviation of the ducts due to external pressure of the
tumour)
intrinsic tumour (arising from the gland itself); which
may be benign (encapsulated) or malignant
3.Trauma of salivary glands :
Trauma → haemorrhage → displacement of the gland
→ occlusion by scarring and fibrosis → accumulation
of saliva and contrast media → sialocele.
4.Metabolic diseases of salivary glands : e.g. diabetes
mellitus
Contraindications: of sialography
- Allergy to compounds containing iodine.
- Periods of acute inflammation when there is discharge of
pus from the duct opening because injection may result in
disruption of the epithelium with spread of infection. - When pre-operative radiographs show a calculus close to
the duct opening as injection may push the calculus back
down the main duct where it may be inaccessible. - Patients performing thyroid function test using iodine-
containing materials as there will be interference between
the iodinated contrast media of sialography and those of
the thyroid test resulting in false results of the test so the
test has to be done first followed by sialography.
Radiograph modality of soft tissue
Diagnostic ultrasound is now established as the first
choice imaging modality for soft tissue investigations
of the face and neck, particularly of the salivary
glands.
Frequency of us
It is a non-invasive investigation that uses a very high
frequency (7.5-20 MHz) pulsed ultrasound beam to
produce high resolution images of more superficial
structures.
The use of colour power Doppler allows blood flow to be
detected.
Us image called
If the ultrasound wave is not reflected
but is absorbed by the tissues, no image
will result.
Air, bone and other calcified
materials absorb nearly all the
ultrasound beam so its diagnostic use
is limited in these tissues. resultant image is
a real-time black, white and grey visual echo picture.
It is also a sectional image or tomography that represents a topographical map of the depth of tissue interfaces.
Utilization of Doppler effect
Utilization of Doppler effect– a change in the frequency
of sound reflected from a moving source – allows the
detection of arterial and/or venous blood flow.
Adding appropriate colour to the vascular structures in the
echo picture image makes differentiation between
structures straightforward.
Indications in the Head and Neck:
- Examination of Salivary Glands:
US is valuable in detecting obstructing lesions of S.Gs such as
calculi, cystic lesions and neoplasms.
Benign lesions appear homogenous with US and have a smooth
outline whereas the sonographic appearance of malignant
lesions is of rough and ill-defined margins.
It is the best method for differentiating between solid and
cystic lesions. - Examination of swellings of the neck including lymph nodes and
thyroid gland. - Examination of soft tissues as the lips, cheek and tongue.
- Examination of the maxillary sinus:
It is effective in distinguishing between normal sinus,
chronically inflamed sinus and a sinus obliterated with a tumour
or a fluid. - Assessment of blood flow in the carotid artery thus aiding in
detecting any thrombosis of the carotids as well as carotid body
tumours.
It is the best method for differentiating between solid and
cystic lesions.
Us
Advantages: of us
- Sound waves are not ionizing radiation so it is a
non-invasive technique and is not harmful to the
tissues. - Shows good differentiation between different
soft tissues. - Shows good differentiation between solid and
cystic lesions of salivary glands and neck
swellings. - It is a painless technique.
- It is widely available, rapidly performed and
inexpensive.
Disadvantages:of us
- It has limited use in the head and neck
area because sound waves are absorbed by
bone. - Technique is very operator-dependent.
- Images can be difficult to interpret for
inexperienced operators because image
resolution is very poor.
another specialized modality that does not
involve the use of ionizing radiation. Felix Bloch and Edward M. Purcell
independently describe the nuclear magnetic
resonance (NMR) phenomenon.
Mri
Mri used for
Used for imaging intracranial and soft tissue
lesions.
MRI modality that uses the
response of biologic tissues to an
applied and changing magnetic
field to generate images.
This current is detected by a
computer and converted into a
visual image.
Uses hydrogen atom
Indication of mri in head and neck
Tumour staging: evaluation of the size,
site and extent of soft tissue tumours and
tumour-like lesions.
Investigation of the TMJ to show the hard
and soft tissue components of the joint
including the disc.
Assessment of intra-cranial lesions.
Advantages of mri
- Ionizing radiation is not used. No adverse effects
from MRI have ever been reported. - High-resolution images can be reconstructed in
all planes. - Excellent differentiation between soft tissue is
possible and between normal and abnormal
tissues. - Metallic (amalgam) restorations do not produce
artifacts on the final image as with CT images.
Disadv of mri
Cortical bone is not imaged, signal
obtainable only from bone marrow.
Scanning time is long and very annoying to
the patient.
Equipment is very expensive.
Patients with pacemakers can not be
imaged.
Radioisotope Imaging
(Nuclear Medicine also called
Scintigraphy )
Scintigraphy
It relies upon altering the patient by making
the tissues radioactive and the patient
becoming the source of ionizing
radiation.
Done by injecting certain radioactive
compounds into the patient that have an
affinity for particular tissues – Target
Tissues.
Radioisotope camera
Radioactive compounds
become concentrated in the
target tissue and their
radiation emission are the
detected and imaged,
usually using a stationary
gamma camera.
This investigation allows
the function and/or the
structure of the target tissue
to be examined under both
static and dynamic
conditions.
Radioisotopes :
Typical examples used in conventional nuclear medicine
include:
Technetium (99mTc)– according to its attachment to
different substances .
Indication for conventional isotope
imaging in head and neck
- Tumour staging– assessment of the sites
and extent of bone metastases. - Investigation of salivary gland function.
- Evaluation of bone grafts.
- Assessment of continued growth in
condylar hyperplasia. - Investigation of the thyroid.
- Brain scans.
Advantages: for conventional isotope
- Target tissue function is investigated.
- All similar target tissues can be examined
during one investigation e.g. the whole
skeleton in one bone scan. - Computer analysis and enhancement of
results are available.
Disadv of conventional isotope
- Poor image resolution– minimal
information about anatomy. - Relatively high radiation dose.
- Images are not usually disease-specific.
- Difficult to localize exact anatomical site
of source of emission. - Some investigations take several hours.
- Not widely available.
This enables the exact anatomical site of the
source of the emissions to be determined.
Single Photon Emission Computed
Tomography (SPECT)
Spect
Gamma rays emitted from the patient are detected
by a gamma camera rotating around the
patient.
The distribution of radioactivity is displayed as a
cross-sectional image or SPECT scan.
This enables the exact anatomical site of the
source of the emissions to be determined.
For pregnancy we use
Us
