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.