Conventional Radiography & Imaging Principles

What is the purpose of medical imaging?

To visualize internal body structures and recognize abnormalities such as congenital anomalies, tumors, and fractures.

What does the introduction of contrast media allow us to study?

Luminal or vascular organs and potential or actual spaces, including:

• Digestive tract

• Blood vessels

• Kidneys

• Synovial cavities

• Subarachnoid space

What are the five common diagnostic imaging techniques?

• Conventional radiography (X-ray)

• Computed tomography (CT)

• Ultrasonography (US)

• Magnetic resonance imaging (MRI)

• Positron emission tomography (PET)

What is conventional radiography?

An imaging technique in which a highly penetrating beam of X-rays passes through the body, producing an image based on differences in tissue density.

How does conventional radiography produce different shades on an image?

Different tissues absorb different amounts of X-rays depending on their density. Dense tissues absorb more X-rays, while less dense tissues allow more X-rays to reach the detector.

Why does compact bone appear white on an X-ray?

Because it is very dense and absorbs many X-rays (radiopaque), so few X-rays reach the detector.

Why does air appear black on an X-ray?

Because it absorbs very few X-rays (radiolucent), allowing most X-rays to reach the detector.

Define radiopaque.

A substance that absorbs many X-rays and appears white or light on a radiograph

Define radiolucent.

A substance that absorbs few X-rays and appears dark or black on a radiograph.

Arrange the following from most radiolucent → most radiopaque:

Water/soft tissue, Fat, Air, Compact bone, Spongy bone

Air

↓

Fat

↓

Water & soft tissue

↓

Spongy bone

↓

Compact bone

Which tissue is more radiopaque: compact bone or spongy bone?

Compact bone.

Which tissue absorbs more X-rays: compact bone or soft tissue?

Compact bone.

Why is the body part placed close to the detector during radiography?

To maximize image sharpness and minimize magnification

Why are radiographs considered two-dimensional representations?

Because they compress a three-dimensional structure into a two-dimensional image, causing structures to overlap.

Why are at least two radiographic projections usually obtained?

Because a single radiograph cannot accurately localize abnormalities due to superimposition of structures.

What does PA stand for?

Posteroanterior projection.

The X-ray beam passes posterior → anterior.

In a PA projection, where are the X-ray tube and detector?

• X-ray tube = posterior

• Detector = anterior

What does AP stand for?

Anteroposterior projection

The X-ray beam passes anterior → posterior.

In an AP projection, where are the X-ray tube and detector?

• X-ray tube = anterior

• Detector = posterior

How are PA and AP radiographs viewed?

As if you are facing the patient.

The patient’s right side appears on your left.

What do the radiopaque letters “R” and “L” indicate on lateral radiographs?

The side of the patient that was closest to the detector.

Why are contrast media used in radiography?

To visualize structures that are not visible on plain radiographs.

Give two examples of commonly used radiopaque contrast media.

• Iodine compounds

• Barium

Name four structures commonly examined using contrast media. (+an extra one)

• Digestive tract

• Blood vessels

• Kidneys

• Synovial cavities

(Also: subarachnoid space)

Why can abnormalities be missed if only one radiographic projection is taken?

Because overlapping anatomical structures in a 2D image can hide or obscure pathology. Multiple projections improve localization and detection.

Label chest X-ray

Memorise

Good