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Medical Imaging--Overview
If a correct diagnosis and effective
treatment plan are to be accomplished,
the detection of a hearing abnormality
that, in the judgment of the clinician,
may be caused by a structural lesion,
demands the application of one or
several appropriate radiologic
modalities.
Medical Imaging--Overview
The invention of radiography and the
refined development of tomography
over this past century, have created the
basic components for medical imaging
used today.
Let’s review and contrast the functional
characteristics of radiography and
tomography.
Medical Imaging--Overview
The selection of appropriate radiologic
techniques include four basic
considerations. They are:
1. Which would be the most appropriate
technique to use?
2. Which would be the least invasive?
3. Which would be the most cost-effective?
4. Which would expose the patient/client to
the least amount of radiation?
Medical Imaging--Overview
The four primary radiologic techniques
in use today involve:
1. Radiography (X-ray)
2. Polytomography (high resolution X-ray)
3. Computed tomography (CT-scan)
4. Magnetic resonance imaging (MRI)
Medical Imaging--Overview
Standard Radiography (X-ray)
With this imaging technique, body
tissues absorb or attenuate the imaging
rays.
These differences are reflected upon a
photosensitive plate.
This results in contrasts of bony tissue,
soft tissue, fat, and air within the body.
Medical Imaging--Overview
This tissue-specific absorption of the x-
rays, allows the production of a two-
dimensional image.
This often creates a perceptual problem
because the human body is three-
dimensional.
The angle of projection may also create
an additional perceptual problem.
Medical Imaging--Overview
There are three traditional X-ray views
commonly ordered for the evaluation of
otologic abnormalities. They are:
1. Frontal view
2. Lateral view
3. Towne’s view
Medical Imaging--Overview
Let’ review pages #114 and #115 in
Northern, for a more visually
descriptive presentation of these
three X-ray imaging views.
Medical Imaging--Overview
Despite these multiple views,
interpreting otologic film can be difficult.
An erosion of the internal auditory
canal, large neoplasm (tumor), and
trauma cracks/breaks are usually
detected.
However, more subtle abnormalities
may not be ascertained with standard
radiography.
Medical Imaging--Overview
Polytomography
It is occasionally termed laminagraphy because its imaging involves layers of x-ray images.
This involves movement of the emitting device within a single plane, and provides a very clear image within that imaging area i.e. high resolution imaging.
Medical Imaging--Overview
This high resolution (polytomography)
imaging has great utility in detailing
congenital anomalies of the ear as well
as in early detection of inflammation of
tumors in the temporal bone area.
It also can detect subtle changes in
otosclerosis and trauma to the auditory
canal or ossicles.
Medical Imaging--Overview
Computed Tomography (CT-scan)
This technology uses a small mobile
micro x-ray tube mounted inside a
circular gantry.
Its emission beams are very finely
collimated resulting in extremely high
resolution and detail.
Medical Imaging--Overview
The motion of the micro tube rotates a
full 360 degrees.
The density measurements of the tissue
are then displayed upon a computer
monitor.
This displayed data representation may
be modified by the radiologist so that an
optimal image is achieved.
Medical Imaging--Overview
The measured image appears as a slice
of predetermined thickness in a
projection which is dependent upon the
patient/client’s placement within the
gantry.
Medical Imaging--Overview
Basically, computed tomography (Ct-
scan), is a computer reconstruction of
the absorption density measurements of
human tissue obtained with the use of
“mini-dose” x-rays.
Medical Imaging--Overview
Let’s view the diagram on page
#119 of Northern, for a visual
illustration of computed tomography
function.
Medical Imaging--Overview
The major advantage of computed
tomography (Ct-scans), is that instead
of three of four tissues being imaged,
literally hundreds of tissue conditions
can be revealed.
For example: blood vessels, different
tissue densities within the brain, fresh
blood vs. clotted blood, etc.
Medical Imaging--Overview
Small tumors within the
cerebellopontine angle which have not
yet effected the temporal bone may be
detected.
Perhaps, more importantly, brain lesions
causing otologic symptoms (e.g. stroke,
central nervous system tumor, infection)
can be exposed and localized.
Medical Imaging--Overview
From a radiation exposure standpoint, it
is less hazardous to the radiologist as
well as the patient/client.
However, hazards may be created when
incorporating contrast-enhanced
methods of Ct-scan imaging.
Medical Imaging--Overview
There are certain iodinated compounds that absorb x-rays well. These can be administered to the patient/client to create a contrast-enhanced scan to better visualize the condition.
However, this contrast can cause renal failure or an allergic reaction and result in death to the patient/client. This is rare—but can occur.
Medical Imaging--Overview
This contrast process is referred to as
angiography. It requires passage of
catheters into the arteries or veins that
are to be injected.
Angiography is normally ordered after
abnormalities are revealed through the
conventional Ct-scan process.
Medical Imaging--Overview
Angiography is often used to secure a
precise diagnosis regarding the
presence of an aneurysm, glomus
tumor, or any malignancy of the
neoplasm.
Medical Imaging--Overview
Angiography is highly effective in
delineating the neighboring veins and
arteries in the lesion site.
This is valuable information for the
treating surgeon regarding
contemplation for an operative
approach to the solution/resolution.
Medical Imaging--Overview
Magnetic Resonance Imaging
(MRI)
MRI is based upon the scientific fact
that the nuclei within atoms (with an odd
number of protons or neutrons) possess
an inherent spin, which in turn produces
a magnetic field.
Medical Imaging--Overview
MRI
The movement of a magnet, external to
the spinning nuclei, will tend to orient
the nuclei “magnetic moments”
uniformly in the direction of the external
magnetic field.
Medical Imaging--Overview
MRI
This new “net magnetization” is able to
create a tiny radiofrequency of its own
for a short period of time.
This radiofrequency can be sensed by
coils within the MRI unit, and the
amplitude of this signal can be
mapped—thus creating an image.
Medical Imaging--Overview
MRI
The images require no contrast or
radiation. There are no known health
effects to MRI patients.
However, the use of MRI is not
appropriate for some patients due to
their use of intracranial aneurysm clips,
pacemakers, cochlear implants, etc.
Medical Imaging--Overview
MRI
Unlike other imaging techniques, MRI
images can be produced/constructed in
any desirable plane.
It takes about one hour to complete an
MRI image/examination.
Medical Imaging--Overview
MRI
The patient is placed inside a gantry
and must remain motionless during the
imaging procedure.
Some patient/clients require sedation
due to claustrophobia or inability to
remain motionless for a period of time.
Medical Imaging--Overview
The MRI and CT-scan imaging
procedures may be used to compliment
each other. For example:
MRI—certain neurologic disorders i.e. brain
white matter proliferation, neural
demyelination, closed head injuries.
CT-scan—temporal bone evaluation, sinus
investigation, acute trauma, cholesteatoma.
Medical Imaging--Overview
MRI
Its technology is not over a century old, so continued refinement is anticipated for this revolutionary technique in imaging.
Recently, there has been an injectable contrasting agent called gadolinium.