Medical imaging normal anatomy

X-ray

• Standard x-ray is posteroanterior ± lateral, with various additional views as required

• Depicts various different densities

  • Air

  • Fat

  • Fluid (soft tissues)

  • Bone

  • Metal

• It is good for loking at bones and distinguishing air-filled structures from fluid filled/soft tissue

• Adjacent tissues of the same density cannot be distinguished form each other. therefore it does not distinguish different types of soft tissues, such as the heart and blood

Posteroanterior (PA) View (standard)

• Standard outpatient chest X-ray

• Beam passes back → front (posterior to anterior)

• Patient stands upright, chest against detector

• Heart size accurately represented (minimal magnification)

• Best for general lung, cardiac, and mediastinal assessment

Anteroposterior (AP) View

• Used in bedridden or ICU patients

• Beam passes front → back

• Patient lying or sitting upright with back against detector

• Heart appears artificially enlarged

• Less optimal for lung detail; clavicles appear higher

Lateral View

• Taken with left side of chest against detector

• Used to:

  • Localise lesions (anterior vs posterior)

  • Assess behind the heart or diaphragm

  • Evaluate lower lobes, retrosternal and retrocardiac space

Lateral Decubitus View

• Patient lying on side with horizontal beam

• Detects:

  • Pleural effusion (fluid layers down)

  • Pneumothorax (air rises)

• Side down = fluid; side up = air

• Helpful when erect film not possible

Expiratory View

• Taken at end expiration

• Used to detect:

  • Small pneumothorax (air stands out better)

  • Air trapping (e.g. in bronchiolitis, foreign body)

• Lungs appear denser, heart looks larger

Computed tomography

• CT (Computed Tomography) uses X-ray beams rotated around the body and computer algorithms to create cross-sectional images.

• Modern scanners use helical (spiral) scanning and multidetector arrays for rapid, high-resolution imaging.

• Image planes: axial, with reformatted coronal/sagittal views.

• IV or oral contrast may be used depending on target structures.

Standard CT (Conventional CT)

• Non-contrast or contrast-enhanced

• General assessment: lungs, pleura, mediastinum, lymph nodes, masses

• Thicker slices (~5 mm)

• Less detail than HRCT but broader coverage

High-Resolution CT (HRCT)

• Thin slices (≤1.5 mm), high spatial resolution

• Best for interstitial lung disease, fibrosis, bronchiectasis

• Often no contrast

• Uses specific inspiratory/expiratory and prone views

CT angiography (CTA)

• IV contrast timed to image arterial phase

• Assesses arteries: e.g., aorta (aortic dissection), carotids, mesenteric arteries

• Requires good IV access, ECG-gated if for coronary/aorta

CT Pulmonary Angiography (CTPA)

• Type of CTA focused on pulmonary arteries

• Gold standard for pulmonary embolism

• Requires:

  • Rapid contrast injection

  • Timing to pulmonary artery opacification

  • Patient cooperation (breath-hold)

CT Coronary angioplasty

• Specialised ECG-gated CTA of coronary arteries

• Evaluates coronary artery disease, plaques, stenosis

• Requires:

  • Beta-blockers for HR < 60 bpm

  • Sublingual GTN for coronary vasodilation

  • IV contrast

Magnetic Resonance Imaging (MRI)

• Basic principles

  • Uses strong magnetic field and radiofrequency pulses

  • Aligns hydrogen protons (mainly from water)

• Key Points

  • Superior soft tissue resolution

  • Uses magnetic fields — no ionising radiation

  • Can produce 4D dynamic imaging

• Uses

  • Cardiac MRI – wall motion, function, infarction

  • Chest wall pathology

  • Mediastinal mass characterisation

• Limitations

  • Slower, expensive, not always available

  • Limited use cases in acute settings

Digital subtraction Angiography (DSA)

• Basic Principle

  • X-ray based imaging of blood vessels

  • Involves injecting contrast into arteries

  • Pre-contrast image subtracted from contrast-filled image → enhances vessel visibility

• Key Points

  • Best for visualising vessel lumens

  • Subtracts pre-contrast image from contrast-filled image → clear view of vasculature

  • Commonly used in angiography, e.g. cerebral, coronary, or pulmonary

• Advantages

  • High-resolution vessel imaging

  • Enables interventions (e.g. angioplasty, stenting)

• Limitations

  • Invasive

  • Limited information about surrounding soft tissues

  • Radiation exposure + iodinated contrast risks