Introduction to Computed Tomography (CT) - Computed Tomography (Ct)

This topic will cover the history, principles, and basic concepts of computed tomography, including how CT scans are used in medical imaging.

Introduction to Computed Tomography (CT)
Designed as a concise, study‑friendly overview.

1. What Is Computed Tomography?

Definition: A medical imaging modality that creates cross‑sectional (tomographic) images of the body by reconstructing multiple X‑ray projections taken around the patient.
Key Idea: Instead of a single 2‑D X‑ray image, CT provides a series of thin “slices” that can be stacked to form a 3‑D representation.
Typical Uses:
- Trauma assessment (head, chest, abdomen)
- Oncology (tumor detection, staging, treatment monitoring)
- Vascular imaging (angiography, pulmonary embolism)
- Surgical planning and guidance

Concept	Description	Relevance to CT
X‑ray Attenuation	Photons are absorbed or scattered as they pass through matter; attenuation depends on density and atomic number.	Determines contrast between different tissues.
Beer‑Lambert Law	(I = I_0 , e^{-\mu x}) where (I) = transmitted intensity, (I_0) = incident intensity, (\mu) = linear attenuation coefficient, (x) = path length.	Basis for converting raw detector signals to attenuation values.
Radon Transform	Mathematical operation that integrates a function over straight lines; each X‑ray projection is a line integral of attenuation.	The set of projections collected at many angles constitutes the Radon data used for reconstruction.
Filtered Back‑Projection (FBP)	Classical reconstruction algorithm: each projection is filtered (high‑frequency boost) then back‑projected across the image space.	Fast, widely used in clinical scanners.
Iterative Reconstruction (IR)	Starts with an initial guess, simulates projections, compares to measured data, and updates the guess repeatedly.	Reduces noise and radiation dose; increasingly common.

X‑ray Tube
- Generates a fan‑ or cone‑shaped beam.
- Adjustable tube voltage (kVp) and current (mA) to control photon energy and flux.
Gantry
- Rotating frame that holds the X‑ray tube and detector array.
- Typical rotation speeds: 0.3–1.0 s per rotation (fast for cardiac CT).
Detector Array
- Scintillator + photodiodes (or solid‑state detectors) that convert X‑ray photons to electrical signals.
- Number of detector rows defines “slices per rotation” (e.g., 64‑row, 128‑row, 256‑row, 320‑row, or > 640 for ultra‑high‑resolution).
Patient Table (Couch)
- Moves the patient longitudinally (helical/spiral scanning) or steps between rotations (axial scanning).
Computer System
- Controls acquisition parameters.
- Performs raw data correction (gain, offset, scatter, beam‑hardening).
- Executes reconstruction algorithms and displays images.

Mode	Description	Typical Applications
Axial (Step‑and‑Shoot)	Table stops; a single rotation acquires one slice.	High‑resolution brain, temporal bone imaging.
Helical (Spiral)	Table continuously translates while the gantry rotates, producing

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