Imaging Methods in Radiology

Imaging Methods

• Radiography, Roentgenoscopy, Scintigraphy, Computed tomography (CT), Magnetic Resonance Imaging (MRI), Ultrasonography, Thermography are all imaging methods.

Main Imaging Methods

• X-ray, Computed Tomography, Magnetic Resonance Imaging, Ultrasonography, Radionuclide Imaging are the main imaging methods used today.

Imaging Principles

• Imaging methods are based on different physical principles: Emission, Transmission, Reflection (Reflection).

Emission Imaging

• The energy source is within the body.
• Energy released from the body is received and processed to create an image.
• Radio-nuclide materials are delivered to tissues and organs for signal generation (as in radio-nuclide imaging)
• In MRI, radiofrequency waves stimulate tissues to create an image.

Transmission Imaging

• The energy in the method passes through the organism to reach the receiver on the opposite side.
• This principle is valid in X-ray and computed tomography methods.

Reflection Imaging

• The energy source and receiver are in the same location.
• After sending the energy to the organism, the reflected energy is collected to create an image.
• Ultrasound works on this principle.

Radiography Indications

• Identification of specific body formations,
• Evaluating disease spread,
• Follow-up of progressive lesions or healing,
• Evaluation of pathological formations are all indications of radiography.

Ultrasonography

• An image is formed by transmitting and receiving sound waves from a probe to and from the patient.
• Ultrasonography is used to evaluate soft tissues, abdominal structures, and the heart.
• The image displays structures, including size, shape, echogenicity (bright/dark spots), and position.
• Ultrasonography images are moving, unlike other imaging techniques.
• Ultrasonography waves cannot penetrate air or bone.
• Physician experience and anatomical knowledge are crucial.

Computed Tomography (CT)

• X-rays are used to create images (transmission).
• Multiple detectors produce cross-sectional images of the body.
• Scan times are short.
• Size, shape, density, location, and superposition of structures are documented.
• Computer manipulation is needed to review the images.

Magnetic Resonance Imaging (MRI)

• Only uses radiofrequency waves (no ionizing radiation).
• Stimulating hydrogen atoms within the body creates an image.
• Creates cross-sectional images similar to CT (as in BT).
• MRI is ideal for imaging soft tissues, particularly the central nervous system.

Diagnostic Radiology

• Uses various imaging techniques to diagnose diseases and conditions.
• Techniques include X-rays, computed tomography (CT), magnetic resonance imaging (MRI), and ultrasonography (US).

X-Ray Machines

• Enable X-ray production with desired duration, quality, and quantity.
• X-rays are ionizing radiation.
• X-rays penetrate different thicknesses and densities of tissues at varying rates.

X-rays and the Body

• The human body comprises tissues with varying atomic weights, thicknesses, and densities.
• X-rays reflect through these tissues at different rates.
• This reflection creates a grayscale image from black to white.
• A method to obtain an image by passing X-rays through the body and projecting them onto film is called radiography.

Imaging Modalities (Black and White)

• Roentgenogram: Radiolucent (black) vs. Radiopaque (white)
• CT: Hypodense (black) vs. Hyperdense (white)
• MRI: Hypointense (black) vs. Hyperintense (white).

Computed Tomography (CT) Principles

• Developed by Cormack in 1963, CT is a cross-sectional imaging technique.
• Based on X-ray principles, CT utilizes X-rays to create cross-sectional images of the body.
• CT produces 3D images of the body.
• Useful for thoracic and abdominal imaging, allowing visualization of masses and their spread through tissues.

Magnetic Resonance Imaging (MRI) Principles

• MRI images organs, soft tissues, and bones without ionizing radiation.
• A tube-shaped magnet creates a magnetic field around the patient.

Ultrasonography (US), Doppler US Principles

• Ultrasonography converts sound energy into images using high-frequency sound waves.
• The reflection of ultrasound waves creates images of internal body structures.

Important Advantages of Ultrasonography (US)

• It does not involve ionizing radiation.
• Safe for infants and pregnant women.

Interventional Radiology

• Includes diagnostic and therapeutic procedures.
• Involves entering the body (e.g., through needle puncture) without major incisions.
• Diagnostic procedures include biopsies, drainage, and angiography.
• Imaging procedures use harmful ionizing radiation and often utilize X-rays.

Radiation Principles

• Radiation is emitted energy (electromagnetic waves or particles) from a source.
• Major types: electromagnetic and particulate radiation.
• Radiation interacts with, and transfers energy to matter.

Ionizing Radiation

• Capable of creating ion pairs by interacting with matter.
• Primary types are X-rays and gamma rays. Also includes alpha, beta particles, neutrons, and charged nuclei.
• Biologically significant as it can alter DNA, causing cell death or mutations.

X-rays: What are they?

• High-energy electromagnetic waves.
• Shorter wavelengths and higher energy than visible light.
• Ionizing radiation, meaning they can remove electrons from atoms.

X-Rays in the Electromagnetic Spectrum

• Located between ultraviolet light and gamma rays.
• Have shorter wavelengths than visible light.
• Classified as 1. soft X-rays (lower energy, 0.12-12 kV), and 2. hard X-rays (higher energy, 12 kV and above).

Radiation/Exposure Protection Principles in Diagnostic Radiology (ALARA)

• Exposure to radiation should be as low as reasonably achievable (ALARA).
• The main principles are time, distance, and shielding.
• Time, distance and shielding protect from harmful radiating sources.

Personal Dosimeters

• Radiation dosimeters are personal dose-measuring devices.

Personal Protective Equipment (PPE) for Radiation

• PPE includes lead aprons, gloves, thyroid shields, glasses, lead screens, and gonad protectors.

Methods of Radiation Dose Reduction

• Regular calibration and quality checks of radiation emitting devices are necessary.
• Properly calibrated devices prevent overexposure to both the worker and the patient.
• Lead aprons should be checked and maintained for optimal safety.

Computed Tomography (CT) Scans

• Combines X-rays and computer technology for detailed cross-sectional images.
• Useful for diagnosing conditions like internal bleeding, tumors, and organ damage.
• Provides 3D images of soft tissues, bones, and blood vessels (essential for trauma).
• Widely used in cancer diagnosis and monitoring.

X-ray Properties

• Electromagnetic radiations composed of energy packets called photons.
• Travel at the speed of light and in straight lines.
• High penetrating power.
• Invisible to the naked eye.
• Blacken radiographic films.
• Produce scattered radiation.

Transmission and Attenuation

• Transmission is the amount of X-ray passing through a patient.
• Absorption is the amount of X-ray held or absorbed by a patient.
• Attenuation occurs during transmission; some X-rays are held/absorbed, reducing the amount passing through.

Radiation Therapy

• High-energy X-rays (hard X-rays) used in cancer treatment to target and destroy cancer cells while minimizing damage to surrounding tissues.
• X-ray therapy used in radiation oncology to treat tumors and cancers.
• Modern radiation therapy uses precise CT scans for guidance.

Security Applications of X-rays

• X-rays used in security screenings (airport baggage scans) to detect hidden objects, contraband, weapons, and explosives.