Medical Ultrasound Imaging
Thursday, 21 November 2024
 Info Sheets  Out- side     | 'Contrast Resolution' p3 Searchterm 'Contrast Resolution' found in 23 articles 7 definitions [ • ] - 16 booleans [• ]Result Pages : •
(CHI) Contrast harmonic imaging is an ultrasound technique to improve the measurement of blood perfusion or capillary blood flow. Based on the nonlinear properties of contrast agents, CHI transmits at the fundamental frequency but receives at the second harmonic. Contrast enhanced echo signals contain significant energy components at higher harmonics (bubbles acts as harmonic oscillators), while tissue echoes do not. Caused by that contrast signal can be separated from tissue echoes by the characteristic signal. In combination with the pulse inversion technique, CHI promises very high contrast agent sensitivity with high spatial resolution. See also Ultrasound Contrast Agent Safety and Hemoglobin.  Further Reading: Basics:
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(PII) Pulse inversion imaging (also called phase inversion imaging) is a non-linear imaging method specifically made for enhanced detection of microbubble ultrasound contrast agents. In PII, two pulses are sent in rapid succession into the tissue; the second pulse is a mirror image of the first. The resulting echoes are added at reception. Linear scattering of the two pulses will give two echoes which are inverted copies of each other, and these echoes will therefore cancel out when added. Linear scattering dominates in tissues. Echoes from linear scatterers such as tissue cancel, whereas those from gas microbubbles do not. Non-linear scattering of the two pulses will give two echoes which do not cancel out completely due to different bubble response to positive and negative pressures of equal magnitude. The harmonic components add, and the signal intensity difference between non-linear and linear scatterers is therefore increased. The resulting images show high sensitivity to bubbles at the resolution of a conventional image. In harmonic imaging, the frequency range of the transmitted pulse and the received signal should not overlap, but this restriction is less in pulse inversion imaging since the transmit frequencies are not filtered out, but rather subtracted. Broader transmit and receive bandwidths are therefore allowed, giving shorter pulses and improved axial resolution, hence the alternative term wideband harmonic imaging. Many ultrasound machines offer some form of pulse inversion imaging. See also Pulse Inversion Doppler, Narrow Bandwidth, Dead Zone, Ultrasound Phantom. •
A liver sonography is a diagnostic tool to image the liver and adjoining upper abdominal organs such as the gallbladder, spleen, and pancreas. Deeper structures such as liver and pancreas are imaged at a lower frequency 1-6 MHz with lower axial and lateral resolution but greater penetration. The diagnostic capabilities in this area can be limited by gas in the bowel scattering the sound waves. The application of microbubbles may be useful for detection of liver lesions and for lesion characterization. Some microbubbles have a liver-specific post vascular phase where they appear to be taken up by the reticuloendothelial system (RES). Dynamic contrast enhanced scans in a similar way as with CT or MRI can be used to studying the arterial, venous and tissue phase. After a bolus injection, early vascular enhancement is seen at around 30sec in arterialized lesions (e.g., hepatocellular carcinomas (HCC), focal nodular hyperplasia (FNH)). Later enhancement is typical of hemangiomas with gradually filling towards the center. In the late phase at around 90sec, HCCs appear as defects against the liver background. Most metastases are relatively hypovascular and so do not show much enhancement and are seen as signal voids in the different phases. Either with an intermittent imaging technique or by continuous scanning in a nondestructive, low power mode, characteristic time patterns can be used to differentiate lesions. See also Medical Imaging, B-Mode, High Intensity Focused Ultrasound, Ultrasound Safety and Contrast Medium. Further Reading: Basics:
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Bubble specific imaging methods rely usually on non-linear imaging modes. These contrast imaging techniques are designed to suppress the echo from tissue in relation to that from a microbubble contrast agent. Stimulated acoustic emission (SAE) and phase / pulse inversion imaging mode (PIM) are bubble specific modes, which can image the tissue specific phase. In SAE mode bubble rupture is seen as a transient bright signal in B-mode and as a characteristic mosaic-like effect in velocity 2D color Doppler. PIM are Doppler modes and detect non-linear echoes from microbubbles. In pulse inversion imaging modes the transducer bandwidth extends, resulting in improved spatial resolution and more contrast. See also Contrast Pulse Sequencing, Microbubble Scanner Modification, Narrow Bandwidth, Contrast Medium, Dead Zone. Further Reading: Basics:
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Conventional, CT and MR imaging technologies are limited in their availability, to depict soft tissue, or to show dynamic activity, like cardiac muscle contractility and blood flow. Easy applicability, real-time sonography and biopsy facilitation are important advantages in veterinarian medicine. Veterinary ultrasound has a very high sensitivity to show the composition of soft tissues, but the low specificity is a disadvantage. High ultrasound system performance includes Doppler techniques, contrast enhanced ultrasound, 3D ultrasound, and tissue harmonic imaging to improve resolution. Technical and physical requirements of veterinary ultrasound are the same as in human ultrasonography. The higher the sound frequency, the better the possible resolution, but the poorer the tissue penetration. Image quality is depended of the ultrasound equipment. For example, a 10 MHz transducer is excellent for imaging of superficial structures; a 3.5 or 5.0 megahertz transducer allows sufficient penetration to see inner structures like the liver or the heart. In addition, the preparation and performing of the examination is similar to that of humans. The sound beam penetrates soft tissue and fat well, but gas and bone impede the ultrasonic power. Fluid filled organs like the bladder are often used as an acoustic window, and an ultrasound gel is used to conduct the sound beam. Result Pages : | Share This Page     Look Ups |
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[last update: 2023-11-06 01:42:00]