data acquisition

Gantry: Consists of hardware and components used to create and detect X-rays.
- Structure: Ring-shaped part of the scanner.
- Aperture: Center of the gantry.
- Dimensions: Varies in diameter from 70 to 90 cm.
- Mobility: Can tilt forward or backward.
- Positioning Aids: Laser light for positioning.
- Control Interface: Control panel, microphone, and speakers present.
X-ray Generator: Provides the necessary power and generates X-rays.
Computer: Processes the data acquired from the scans.
Operators Console: Interface for the technician to operate the scanner.
Physician Viewing Console: Interface for physicians to view the scans.

Functionality: Contains hardware and components for creating and detecting X-rays.
- Design: Ring-like structure that allows rotation.

Evolution: First-generation CT scanners utilized cables to rotate the gantry frame, known as the step-and-shoot technique.
Current Design: Newer CT scanners employ slip rings, which are electromechanical brushes.
- Function: Provides continuous electrical power and communication.
- Result: Allow for continuous rotation of the gantry, enabling helical (spiral) scanning.

Type: High-frequency generators are the most commonly used in CT.
Functionality: Houses within the gantry, producing high voltages to send to the X-ray tube for generating X-ray beams.
Power Capacity: Measured in kilowatts (kW), determines operational range of kV (kilovolt) and mA (milliamps).
- High kV Effects: Increases the penetrating power and radiation dose but allows for lower mA settings which limits heat load on the tube.

Purpose: CT components generate significant heat that must be dissipated.
Types: Various cooling systems employ blowers, filters, or oil-to-air exchanges. Newer designs may use cooling oil in direct contact with the anode for efficient heat dissipation.

Components: Consists of a cathode (which includes a filament wire) and a tungsten target (anode).
Thermionic Emission: The cathode heats the filament wire (measured in mA), releasing electrons.
Acceleration: Electrons are propelled towards the target due to the electrical potential difference (measured in kV), causing X-ray production upon interaction with the anode.

CT Tubes: Generally have multiple focal spots, common sizes are 0.5 mm and 1.0 mm.
Resolution: Smaller focal spots provide higher spatial resolution but cannot withstand as much heat as larger spots.
Advanced Technology: Some tubes utilize multiple focal spots to produce overlapping beams, effectively doubling the number of slices possible.

Compensating Filters Function: Shape the X-ray beam to reduce radiation dose and minimize imaging artifacts (e.g., beam hardening).
- Usage: Different filters applied for the head versus the body due to density differences (body filters reduce intensity at periphery).
- Bow Tie Filters: Specifically designed for body imaging to account for density differences.

Purpose of Collimators: Reduce scatter radiation which can adversely affect image quality and increase patient dosage.
Control of Slice Thickness: Collimators directly influence the slice thickness of the scans.
- Types of Collimators:
- Prepatient (Source) Collimator: Positioned near the X-ray tube, controls X-ray emergence and affects patient dose and profile.
- Postpatient (Predetector) Collimator: Located right before the detector array to ensure correct beam width, preventing scatter from reaching the detector.

Detector Types: Categories include single detectors and detector arrays (comprehensive systems containing multiple detectors).
Optimal Characteristics for CT Detectors: Include high efficiency, minimal afterglow, high scatter suppression, and stability.

Efficiency: Considered low; the gas is pressurized in aluminum casings.
- Mechanics: Absorption of X-rays by aluminum leads to reduced efficiency.
- Electric Field Production: The detector contains tungsten plates creating an electric field, ionization from X-rays generates electric current.

Comparison to Nuclear Medicine: Similar technology used; photomultiplier tubes (PMT) replaced by photodiodes.
Performance: Capable of absorbing approximately 100% of photons; configured in an arc shape allowing uniform spacing between detectors to enhance spatial resolution and minimize scatter rejection.

First Generation: Employed a narrow X-ray beam; utilized a single detector that rotated slightly to cover a 180° arc.
Second Generation: Similar to the first but used a fan-shaped beam, improving scan time albeit still relatively long.
Third Generation: Predominantly used in modern practice, utilizing a fan-shaped beam covering the entire field of view (FOV), allowing for continuous rotation.
Fourth Generation: Incorporated 360° detectors with an X-ray tube that rotates around the patient.
Sixth Generation: Characterized by dual-source scanners with 360° detectors; uses two X-ray sources that may operate at the same or different kVp settings. Dual energy refers to different kVp settings during scanning.

Location: Inside the gantry near the detectors, crucial for measuring X-ray photons, converting signals, and transmitting to the computer.
- Signal Conversion: Managed by the Analog to Digital Converter (ADC); detectors can operate at sampling rates up to 1000 Hz to prevent artifacts from insufficient sampling.
- Sampling Efficiency: Important for maintaining quality images at each table position throughout scans.

Scannable Range: The table's position relative to the gantry is significant, using anatomical landmarks for reference.
- Zero Setting: The table is calibrated to a zero reference point; attachments may be utilized based on protocols and procedures.