X-Ray Technology Overview

X-Ray Tube Components

• Stationary anode tube with a 1-mm focal spot has a target area of 4 mm².
• Rotating anode tube with a 15-cm diameter can have a target area of approximately 1800 mm².
• Rotating anode tubes increase the heating capacity of the tube by a factor of nearly 500 compared to stationary anode tubes.
• The tube housing contains expansion bellows, an evacuated tube envelope, cooling dielectric oil, a rotor, an induction stator, and a tube window.

X-Ray Control Panel

• Control panel has three primary controls:
  • kVp (kilovoltage peak) - controls the quality of the x-ray beam.
  • mA (milliamperage) - controls the quantity of x-ray beam.
  • Time - controls the duration of x-ray exposure.
• Control panel also includes auxiliary controls, such as anatomical programs and automatic exposure control (AEC).
• AEC is used to automatically adjust the x-ray exposure based on the patient's anatomy.

X-Ray Image Quality

• Higher kVp and lower mAs reduces patient dose.
• High kVp and low mAs results in a high-energy, penetrating x-ray beam and a small patient dose.
• Low kVp and high mAs results in a low-energy x-ray beam, most of which is easily absorbed by the patient.

Medical Imaging Overview

• Medical imaging is concerned with the interaction of all forms of radiation with tissues in the body.
• Medical imaging uses technology to extract clinically useful information from observation of this interaction.
• Medical imaging allows for non-invasive visualization of internal organs, tissues, and body parts.
• The overall objective of medical imaging is to acquire useful information about physiological processes or organs of the body using external or internal sources of energy.

Sources of Energy in Medical Imaging

• External sources of energy:
  • Reflected energy (e.g., ultrasound)
  • Penetrated energy (e.g., x-rays)
• Internal sources of energy:
  • Emit energy (e.g., nuclear medicine)

Major Types of Medical Imaging Modalities

• X-ray imaging:
  • Conventional X-ray + Film processing
  • Digital X-ray + Film processing
  • Fluoroscopy (guided process, diagnostic or therapeutic) with image intensifier and Flat Panel Detector (FPD)
  • Mammography
  • Bone densitometry (DXA)
  • Computed Tomography (CT) + Film processing
• Nuclear Imaging:
  • Gamma camera
  • Positron Emission Tomography (PET)
• Ultrasound Imaging
• Fundus images

Evolution of Medical Imaging

• Photographic film has been used in medical imaging for nearly 100 years.
• Intensifying screens have been used with x-ray films for over 60 years to obtain high-quality images with lower radiation doses.
• Digital radiography (CR and DR) has become possible in recent years.
• Film-screen technology still accounts for about 65% of all diagnostic examinations.

Radiography

• Radiography was the first medical imaging technology.
• Radiography uses an x-ray source on one side of the patient and an x-ray detector on the other side.
• A short-duration pulse of x-rays is emitted by the x-ray tube.
• A large fraction of the x-rays interact with the patient, and some of the x-rays pass through the patient and reach the detector, forming a radiographic image.
• Radiography is performed with an x-ray source on one side of the patient and a (typically flat) x-ray detector on the other side.

Radiographic Image Formation

• The homogeneous distribution of x-rays entering the patient is modified by scattering and absorption within the tissues.
• The attenuation properties of different tissues (bone, soft tissue, and air) create a heterogeneous x-ray distribution.
• The radiographic image is a visualization of this x-ray distribution.
• The detector used in radiography can be photographic film or an electronic detector system.

Transmission and Projection Imaging

• Transmission imaging involves an external energy source on one side of the body and detection on the other side.
• Projection imaging relates each image point to information along a straight line through the patient.
• Radiographic images are useful for various medical indications, including diagnosis of broken bones, lung cancer, and cardiovascular disorders.

Image Properties

• Contrast: The difference in luminance or color that makes an object distinguishable. X-ray contrast is related to tissue composition, MRI contrast is related to proton density and relaxation phenomena, and ultrasound contrast is determined by acoustic properties of the tissues.
• Spatial resolution: The ability to resolve fine details in the body parts. The spatial resolution of medical images depends on the size of the smallest object that an imaging system can resolve. This is influenced by factors such as wavelength in ultrasound imaging. There are also concepts of depth resolution and lateral resolution to consider.