LECTURE – 1 – RHPT – 485READING IN MEDICAL IMAGING

LEVEL - 8

INTRODUCTIONX-RAY

Discovered and named by Dr. W. C. Röentgen at University of Würzburg, 1895

Awarded first Nobel prize for physics, 1901

• In 1895 Wilhelm Conrad Roentgen discovered X-rays, so paving the way for the development of a new branch of medicine called radiology.

• Initially, radiology was the science of 'X-rays', but today it involves a variety of imaging techniques to study and investigate patients so that a diagnosis can be achieved.

• In addition, therapeutic procedures are performed by radiologists under image guidance, a branch also known as interventional radiology.

FIRST X-RAY

Roentgen’s wife's hand

What are the Different Imaging Modalities Radiography “plain films”

Computed axial tomography “CT”

Magnetic resonance imaging “MRI”

Ultrasound “US”

Interventional radiology “angio”

RADIOLOGY TOOLS

6

X- RAY

ULTRASOUND

NUCLEAR MEDICINE

MAGNETIC RESONANCE

COMPUTED TOMOGRAPHY

HOW IS IMAGING DONE?

IONIZING RADIATION

X-ray, CT, Nuclear Medicine

SOUND WAVES

Ultrasound

MAGNETIC FIELDS / RADIO WAVES

Magnetic Resonance

To image the patient a energy source is directed into a volume of tissue and an image is created of the tissue interaction.

How to Approach Reading any Image

Identify the patient

When was the image taken

Are these the proper images

The five densities

Are the images technically adequate

Radiography – X - Ray Also called “plain films” or “standard films”

Image formed using broad beam ionizing radiation

The image formed is related to the subjects density

May involve the use of contrast agentsIodinated BariumAir

High Energy Photon --Kilo Electron Volts

Ionizing Radiation

Exposes Film / Detector

Projection Data

X-RAY

detector

X-ray beam

X-rays are short-wave electromagnetic radiation produced by accelerating electrons across an evacuated tube onto a tungsten anode using a high voltage.

• An X-ray tube is similar to a light bulb with a filament and a current to heat the filament.

• There is also a high voltage to accelerate the electrons from the filament at a target.

• This collision releases the x-ray radiation that is used to image the patient.

X-RAYS PLAIN FILM RADIOGRAPHY - Clinical uses

Chest Bones Spine / Extremities / Skull Soft tissue Mammography / Abdomen

These are typical body regions that plain x-ray is used to evaluate.

Air / Gas

Soft Tissue / Fluid filled space

Bone

Fat

Metal

X - RAY --- FIVE BASIC DENSITIES

• The x-rays can traverse tissue to create the image.

• We can only separate the 5 basic densities noted. Air / Gas, Soft tissue / Fluid filled space, Bone, Fat & Metal.

• Here we see the Air in the lungs, the soft tissue of the heart and the bone density of the ribs.

• Water will appear of the same density as soft tissue and cannot be separated. Fat is difficult to see on the chest and better noted on abdominal x-rays

Plain film projections

• There are a number of projections or views commonly used when taking plain films.

• If a beam passes through the patient's ventral (anterior) surface first then through the dorsal (posterior) surface to reach the film, it is called an anteroposterior projection.

• Similarly, if the beam passes from dorsal to ventral through the body then a posteroanterior view is obtained.

Advantages • cheap

• good first line imaging test

• readily available

• low radiation dose

• non-invasive

• standardized techniques

Disadvantages

• two-dimensional imaging• no cross section imaging• poor soft tissue contrast• poor for individual organs

CONTRAST RADIOGRAPHY

Injection, ingestion, or other placement of opaque material within the body.

Improves visualization and tissue separation.

Can demonstrate functional anatomy and pathology.

• Administering a contrast agent modifies the image to give more information.

Clinical uses :-

• Typical ones are barium, an inert particulate contrast used in GI tract evaluation.

• Iodine, a water soluble agent which can be injected into the vascular tree.(ANGIOGRAPHY) + intravenous agents to visualize the renal tract (intravenous pyelogram - IVP)

• Interventional procedures

UPPER GI--(GASTRO INTESTINAL)ORAL BARIUM CONTRAST

ARTERIOGRAM INTRAARTERIAL IODINE CONTRAST

• The contrast agent -Barium- will outline the GI tract, determine size and show patency or obstruction.

• The contrast agent-Iodine can be injected and is water soluble.

• In the blood stream, it will outline the vessel and demonstrate anatomy.

• Iodine is also filtered by the kidney and can show information about tissue function.

Reactions and side effects

• slight nausea or sensation of heat, • to anaphylactoid shock and death. • The mechanism of idiosyncratic reactions, such

as urticaria, angioneurotic oedema, bronchospasm, vasomotor collapse and respiratory arrest, is poorly understood.

Risk factors

• asthma, • allergies, • renal or cardiac impairment, • diabetes and myeloma.

Contrast agent administration

• Intra-arterial and intravenous contrast agents• These water soluble non-ionic contrast agents. • used for evaluation of the venous and arterial

systems.• Injected either directly into the veins (eg for

intravenous pyelography, venography, or CT) or intra-arterially (eg for evaluation of carotid, renal, coronary, abdominal and limb arteries)

• Their excretion is via the renal tract.

• Intrathecal (water soluble) contrast agents

Water soluble intrathecal contrast agents are used for evaluation of the cervical, thoracic and lumbar subarachnoid space.

• Oral and rectal contrast

Barium sulphate is the agent used for the detailed evaluation of the gastrointestinal tract.

It is derived from mineral barites. Barium sulphate preparations are not water soluble and are rarely associated with any contrast reactions.