Structure and Classification of Medical X-ray Equipment

 

I. Structure of an X-ray Machine

X-rays are produced when a beam of high-speed electrons strikes a target material and is suddenly decelerated. To generate X-rays, the following conditions must be met:

• A stream of high-speed electrons
• A target material capable of withstanding the impact of those electrons
• A high-vacuum and high-voltage environment necessary to accelerate the electrons

A medical X-ray machine is a comprehensive medical device designed and manufactured according to these physical requirements and the needs of clinical diagnosis and treatment. It converts electrical energy into X-ray energy. Although there are many models and structural variations, an X-ray system generally consists of two main parts: the X-ray generating unit and auxiliary facilities.

1. X-ray Generating Unit

This is the part that produces and controls the X-rays, composed of four components:

(1) Control console – Regulates the exposure time and adjusts the quality and quantity of X-rays, providing various operational indicators.
(2) High-voltage generator – Supplies direct high voltage to the X-ray tube. It also contains the filament transformer, which provides heating current to the X-ray tube filament.
(3) X-ray tube – The core component that converts electrical energy into X-ray energy. It consists of the X-ray tube housing and the tube insert.
(4) High-voltage cables – Multi-core insulated cables that connect the high-voltage generator to the X-ray tube.

2. Auxiliary Facilities

These are supporting systems designed to meet clinical diagnostic and therapeutic needs, including:

• Mechanical supporting structures for the X-ray tube, such as ceiling rails, floor rails, columns, and suspension arms;
• Patient positioning and examination tables, such as radiographic or fluoroscopic tables;
• Image intensifiers and X-ray television systems that convert fluoroscopic images into video images;
• Specialized accessories for cardiovascular examinations and interventional procedures.

II. Classification of X-ray Equipment

Medical X-ray equipment is generally divided into diagnostic and therapeutic categories according to their intended use.

1. Diagnostic X-ray Machines

These use X-ray transmission through the human body to create images for diagnostic purposes. They can be classified in several ways:

(1) By structural form:
① Portable type – Compact, lightweight, easy to assemble and transport; components can be stored in carrying cases or backpacks, suitable for field or mobile examinations.
② Mobile type – Compact and integrated, with both X-ray generation and application systems mounted on a wheeled base. It can be moved manually or electrically, enabling bedside fluoroscopy and radiography in wards. When equipped with an image intensifier and X-ray TV, it can be used for monitoring and interventional procedures.
③ Fixed type – Large, heavy, and complex systems that must be installed in a dedicated X-ray room. They have strict requirements for power supply, room setup, installation, and calibration.

(2) By output power:
This classification is based on the nominal power of the X-ray tube (e.g., 10 kW, 20 kW, 50 kW). In China, it is usually determined by the maximum allowable tube current:
① Small machines: Maximum tube current below 100 mA.
② Medium machines: Maximum tube current between 200–500 mA.
③ Large machines: Maximum tube current above 500 mA.

(3) By application range:
① General-purpose X-ray machines – Equipped for both fluoroscopy and radiography, suitable for examinations of various organs and diseases.
② Special-purpose X-ray machines – Designed for specific medical fields, such as dental X-ray units, mammography systems, and cardiovascular angiography machines.

2. Therapeutic X-ray Machines

These devices utilize the biological effects of X-rays for disease treatment. They can be classified into three types according to application:
(1) Contact therapy units – Used for treating skin surface or shallow cavity lesions.
(2) Superficial therapy units – Used for treating relatively large skin areas or shallow-seated lesions.
(3) Deep therapy units – Used for treating deep-seated pathological tissues.

III. Different Functions of Diagnostic X-ray Machines

Diagnostic X-ray machines vary in structure and power output, thus offering different functions. Taking a medium-sized X-ray machine as an example, its functions include:

1. X-ray Fluoroscopy

Fluoroscopy utilizes two main properties of X-rays—penetration and fluorescence—to visualize internal structures through a fluorescent screen.
(1) Conventional fluoroscopy – Based on density differences between tissues or morphological differences between normal and pathological tissues to form contrast images for diagnosis.
(2) Gastrointestinal (barium) fluoroscopy – Since soft tissues in the digestive tract have little natural density contrast, patients ingest barium sulfate, a radiopaque agent, to create distinct contrast images for diagnosis.

2. X-ray Radiography

Radiography records the X-ray image of the examined area onto a film for diagnostic interpretation.
(1) Conventional radiography – X-rays pass through the body directly onto a film in a cassette, creating a latent image that becomes visible after processing.
(2) Grid radiography – A technique used to improve image sharpness. As X-rays pass through the body, scattered radiation is generated, which can blur the image and reduce contrast. A grid device (anti-scatter grid) is installed in the X-ray system to filter out scattered radiation, thereby improving image quality.

3. Gastrointestinal Radiography

Also called spot radiography, this method is designed to visualize the digestive tract in detail.

4. Tomography

Also known as layer imaging or sectional radiography, this technique focuses on a specific internal plane of the body. In standard radiography, overlapping tissue shadows may obscure important pathological details, making diagnosis difficult. Tomography minimizes this problem by imaging a single layer or section, enhancing diagnostic accuracy.