Sonography, also known as ultrasound imaging, employs several techniques to visualize internal body structures and assess various physiological functions. These techniques are designed to optimize image quality and provide specific diagnostic information based on the type of tissue and clinical requirements. Here are the main imaging techniques used in sonography:
1. B-Mode (Brightness Mode) Imaging
- Basic Principle: B-mode is the most common ultrasound imaging technique. It produces two-dimensional images by converting the amplitude of echo signals into varying shades of gray.
- Applications: Used for general anatomical imaging, including organs like the liver, kidneys, thyroid, and for assessing fetal development in obstetrics.
2. M-Mode (Motion Mode) Imaging
- Basic Principle: M-mode captures a single line of B-mode imaging over time, displaying motion as a graph. This technique is particularly useful for evaluating the movement of structures.
- Applications: Primarily used in cardiology to assess heart valve motion and cardiac chamber size and function.
3. Doppler Ultrasound
- Basic Principle: Doppler ultrasound measures the change in frequency of sound waves reflected off moving objects, such as blood cells, to assess blood flow.
- Types of Doppler Ultrasound:
- Continuous Wave (CW) Doppler: Uses two transducers to continuously transmit and receive sound waves. It measures high-velocity blood flow but cannot determine the exact location of the flow.
- Pulsed Wave (PW) Doppler: Uses a single transducer that alternates between sending and receiving sound waves, allowing for precise measurement of blood flow at specific locations. However, it is limited in measuring very high velocities.
- Color Doppler: Provides a color-coded map of blood flow direction and velocity superimposed on a B-mode image, aiding in the visualization of blood flow within vessels.
- Power Doppler: More sensitive than Color Doppler, it detects the presence of blood flow and is useful for assessing low-velocity or small vessel flow, but does not provide directional information.
4. 3D and 4D Ultrasound
- 3D Ultrasound:
- Basic Principle: Acquires multiple two-dimensional images from different angles and reconstructs them into a three-dimensional image.
- Applications: Used for detailed anatomical studies, such as fetal face imaging in obstetrics, and for assessing structural abnormalities.
- 4D Ultrasound:
- Basic Principle: Similar to 3D ultrasound but adds the element of real-time movement, essentially providing a “live” three-dimensional image.
- Applications: Allows dynamic visualization of moving structures, such as fetal movements and cardiac function.
5. Elastography
- Basic Principle: Measures tissue stiffness or elasticity by observing the deformation of tissue in response to an applied force, typically using ultrasound waves.
- Applications: Used for detecting and characterizing tumors, such as in the breast, liver, and thyroid, as cancerous tissues often differ in stiffness from normal tissues.
6. Contrast-Enhanced Ultrasound (CEUS)
- Basic Principle: Uses microbubble contrast agents that enhance the reflectivity of blood or tissues, providing improved imaging of vascular structures and blood flow.
- Applications: Useful in liver imaging to detect and characterize lesions, in cardiac imaging to assess myocardial perfusion, and in other organs for detailed vascular studies.
7. Intravascular Ultrasound (IVUS)
- Basic Principle: A specialized form of ultrasound where a miniature transducer is inserted into blood vessels to provide detailed images of the vessel walls.
- Applications: Primarily used in cardiology to assess the extent of atherosclerosis and to guide interventions like angioplasty and stent placement.
8. Intraoperative Ultrasound
- Basic Principle: Performed during surgical procedures using specialized transducers to provide real-time imaging that guides surgical decisions.
- Applications: Used in neurosurgery, liver surgery, and other procedures to locate lesions, guide resections, and ensure complete removal of tumors.
