Basics of Medical Imaging Technique-Ultrasound

Description

This course is value addition for learners of biomedical sciences , students started  for research  about ultrasonic imaging technique and useful for those who are preparing for GATE in biomedical engineering. This course will be useful for those who operates this imaging modality.  The term ultrasound refers specifically to acoustic waves at frequencies greater than the maximum frequency audible to humans, which is nominally 20 kHz. Diagnostic imaging is generally performed using ultrasound in the frequency range of 2–15 MHz.

The course  includes general information and development of ultrasound such as an ultrasound transducer generates acoustic waves by converting magnetic, thermal, and electrical energy into mechanical energy. The most efficient technique for medical ultrasound uses the piezoelectric effect, which was first demonstrated in 1880 by Jacques and Pierre Curie.  Many significant advances in ultrasound imaging have resulted from innovation in transducer technology. Construction of  transducer materials used with their merits and  demerits. Various aspects which influence on performance of transducer. Q factor , quarter wave matching technique is explained in this course. The transducers used for diagnostic imaging have conventionally been fabricated using the ferroelectric ceramic lead zirconate titanate,

The course gives information about properties of ultrasonic waves and various  display modes available such as A mode which displays only amplitude .B mode  and M mode . 2D and 3D imaging  of ultrasound imaging  linear-array transducers. Previously, ultrasound systems had made an image by manually moving the transducer across the region of interest. Even the faster scanners had required several seconds to generate an ultrasound image, and as a result, only static targets could be scanned.

This course describes modern imaging techniques To implement real-time imaging, researchers developed new types of transducers that rapidly steer the acoustic beam. Piston-shaped transducers were designed to wobble or rotate about a fixed axis to mechanically steer the beam through a sector-shaped region. Linear sequential arrays were designed to electronically focus the beam in a rectangular image region. Linear phased-array transducers were designed to electronically steer and focus the beam at high speed in a sector image format. contrast enhanced ultrasound images is to differentiate echoes produced by microbubbles from echoes produced by tissue, which is typically accomplished by exploiting the non-linear scattering characteristics of microbubbles and Tissue harmonic imaging which generates harmonics to create image.

Imaging using coded excitation pulses is a technique that was developed to increase the penetration depth of ultrasound imaging systems. A coded excitation system transmits a relatively long duration signal such as a chirp (a sinusoid with 323 ULTRASOUND IMAGING increasing or decreasing instantaneous frequency) or a pulse modulated code, in which a sinusoid is switched on and off in a specific temporal sequence to create a binary code.

The last chapter is about Ultrasound which is  is generally assumed to be the safest medical imaging modality, but when a high intensity ultrasound pulse is transmitted through tissue, a substantial amount of energy can be transferred from the pulse to the tissue, thereby increasing the risk of adverse effects to the patient. These biological effects can be used beneficially by therapeutic ultrasound devices but are undesirable during diagnostic imaging. The two most important mechanisms for biological effects of ultrasound are thermal absorption and cavitation.

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