Computed Tomography (CT)

What is computed tomography (CT)?

An imaging technique that uses rotating X-rays and computer processing to produce cross-sectional (transverse) images of the body.

What do CT images resemble?

Transverse anatomical sections (cross-sectional slices) of the body.

How are CT images produced?

An X-ray tube rotates around the body while detectors measure the amount of radiation passing through different tissues. A computer reconstructs these measurements into images.

What rotates around the patient during a CT scan?

• X-ray tube

• X-ray detectors

What determines how much X-ray radiation is absorbed during CT?

The tissue composition, particularly the amount of:

• Bone

• Fat

• Water

Why do different tissues appear differently on CT?

Different tissues absorb different amounts of X-rays based on their density and composition.

What does a computer do in CT imaging?

It reconstructs the measured X-ray data into:

• 2D cross-sectional images

• 3D reconstructions

What are the two main image formats produced by CT?

• Two-dimensional slices

• Three-dimensional reconstructions

What orientation are CT images usually displayed in?

As if you are standing at the patient’s feet looking toward their head.

Patient’s right = your left.

What is one major advantage of CT over conventional radiography?

CT eliminates much of the superimposition of structures by producing cross-sectional images.

Why is CT considered superior to plain radiography for many conditions?

Because it provides detailed cross-sectional anatomy and allows 3D reconstruction.

What type of beam is used in CT?

A fan-shaped beam of X-rays.

What is reconstructed from CT slices?

Three-dimensional images of anatomical structures.

Complete the CT process:

X-ray tube → ______ → Computer → ______

X-ray tube

↓

Detectors measure transmitted X-rays

↓

Computer reconstruction

↓

2D slices and/or 3D images

Give 3-4 differences between conventional radiography and CT

Conventional radiography

• Single projection

• 2D image

• Superimposition of structures

CT

• Rotating X-ray beam

• Cross-sectional slices

• Minimal superimposition

• Can produce 3D reconstructions

Label

Remember:

• CT = transverse (cross-sectional) image

• Right side of image = patient’s right

• Left side of image = patient’s left

Oki

CT reconstructed into 3D model

Perf

CT Cheat Sheet

Uses X-rays ✔

Rotating X-ray tube

Produces transverse slices

Excellent anatomical detail

Computer reconstructs:

• 2D slices

• 3D images

Little superimposition

Patient viewed from feet toward head