Question

expalin in brief and in detailed

1. Ultrasound imaging: Doppler imaging
2. Ultrasound imaging: image quality, artefacts, biologic effects and safety

3 Optical imaging: Optical coherence tomography

Answer 1

Ultrasound imaging (Sonography) uses sound waves to produce pictures of the inside of the body. It is used to help diagnose the causes of pain, swelling and infection in the body's internal organs and to examine a baby in pregnant women and the brain and hips in infants.It also helps to diagnose heart conditions and assess damage after a heart attack.It uses a small probe called a transducer and gel placed directly on the skin. High-frequency sound waves travel from the probe through the gel into the body. The probe collects the sounds that bounce back. A computer uses those sound waves to create an image. Ultrasound exams do not use radiation (as used in x-rays). Because images are captured in real-time, they can show the structure and movement of the body's internal organs. They can also show blood flowing through blood vessels.Advancement in ultrasound includes 3-D ultrasound that formats sound waves in to 3-D images.

Doppler ultrasound is a special type of ultrasound which is used to look at blood flow.It is a special ultrasound technique that evaluates movement of materials in the body. It allows the doctor to see and evaluate blood flow through arteries and veins in the body.

A Doppler ultrasound machine has a hand held scanner which is connected to a computer. It uses soundwaves to make pictures of the blood flow in your major arteries and veins. 3 Types of Doppler Ultrasound;

• Color Doppler ; uses a computer to convert Doppler measurements into an array of colors to show the speed and direction of blood flow through a blood vessel.
• Power Doppler ; is a newer technique that is more sensitive than color Doppler and capable of providing greater detail of blood flow, especially when blood flow is little or minimal. This, however, does not help the radiologist determine the direction of blood flow, which may be important in some situations.
• Spectral Doppler ; displays blood flow measurements graphically, in terms of the distance traveled per unit of time, rather than as a color picture. It can also convert blood flow information into a distinctive sound that can be heard with every heartbeat.

Doppler ultrasound images can help the physician to see and evaluate:

• blockages to blood flow (such as clots)
• narrowing of vessels
• tumors and congenital vascular malformations
• reduced or absent blood flow to various organs, such as the testes or ovary
• increased blood flow, which may be a sign of infection.

Ultrasound imaging: image quality, artefacts, biologic effects and safety;

Image quality ; Since the advanced modes are aimed at improving image quality, image contrast, and high‐contrast spatial resolution (HCSR) are usually evaluated for these modes. The image contrast test is aimed at establishing the ability of the UltraSound imaging system to detect subtle differences in the echogenicity of two targets.Performance evaluation or quality assurance (QA) of ultrasound (US) equipment is necessary, as for any other medical imaging equipment,for ensuring the safety of the patient and operator, for maintaining the image quality. Currently the QA of US inaging is done in B-mode and Doppler imaging.B- mode testing methods are well documented in many literature. These tests usually include: visual inspection of the components of the US system (scanner/probes), display monitor performance, image uniformity, sensitivity (maximum depth of visualization, signal‐to‐noise ratio), geometric accuracy, spatial resolution, and contrast resolution..

Artefacts ; An Ultrasound artifact is a structure in an image which does not directly similar with the real tissue being scanned.Artifacts assumes different forms; Struacture in the image not actually present, Objects that should be represented but missing from the image, and structures that are misregistered on the image.Ultrasound artifacts are commonly encountered and familiarity is necessary to avoid false diagnoses. Artifacts can be broken down into two categories: those from violation of ultrasound system assumptions and those from interference by external equipment and devices.

Biological effects and safety ; The ultrasound has a remarkable record for patient safety with no significant adverse bioeffects reported in literature.The biological effects of ultrasound refer to the potential adverse effects the imaging modality has on human tissue. These are primarily via two main mechanisms: thermal and mechanical.

Thermal ; Due to the law of the conservation of energy, all the sound energy have being reduced in force by tissues must be converted to other forms of energy. The majority of this is turned into heat. So, it is possible for ultrasound to raise tissue temperature by up to 1.5°C. For sensitive tissues like fetal tissues , this rise in temperature may have deleterious effects if present for an extended period of time.

Mechanical; The mechanical bioeffect of ultrasound refers to damage caused by the actual oscillation of the sound wave on tissue. The most common is referred to as cavitation and is caused by the oscillation of small gas bubbles within the ultrasound field. In certain circumstances, these bubbles may grow in size or collapse generating very high energies to adjacent tissue. This can increase tissue temperature by more than 1000°C.

Ultrasound imaging has been used for over 20 years and has an excellent safety record. It is based on non-ionizing radiation, so it does not have the same risks as X-rays or other types of imaging systems that use ionizing radiation.It is important, as ultrasound imaging techniques and applications evolve and new devices become available, to be ever vigilant and to provide ongoing assessment of diagnostic ultrasound usage to ensure that its use can continue to be justified on safety grounds.

3 Optical Imaging; a technique for non-invasively looking inside the body, as done with x-rays. But, unlike x-rays, which use ionizing radiation, optical imaging uses visible light and the special properties of photons to obtain detailed images of organs and tissues as well as smaller structures including cells and even molecules. These images are used by scientists for research and by clinicians for disease diagnosis and treatment. As optical imaging uses no ionizing radiations reduces risk and harmful exposure to patients. It is particularly used gor visualizing softer tissues.It can obtain images of structures in a wide range of sizes and types, optical imaging can be combined with other imaging techniques, such as MRI or x-rays, to provide enhanced information for doctors monitoring complex diseases or researchers working on experiments.

Optical Coherence Tomography (OCT): A type of Optical Imaging . Optical coherence tomography is a technique for obtaining sub-surface images such as diseased tissue just below the skin. OCT is a well-developed technology with commercially available systems now in use in a variety of applications, including art conservation and diagnostic medicine. For example, ophthalmologists use OCT to obtain detailed images from within the retina. Cardiologists also use it to help diagnose coronary artery disease.It is the technology for the future because it can enhance patient care. It has the ability to detect problems in the eye prior to any symptoms being present in the patient.It uses light waves instead of sound waves.There are two main categories of OCT instrumentation: Time-Domain OCT (TDOCT) and Spectral-Domain OCT (SDOCT). Time-Domain OCT technology is more intuitive to understand, and most early reasearch and commercial instrumentation was based on this technology. Spectral-Domain OCT is rapidly replacing the Time-Domain technology in most applications because it offers significant advantages in sensitivity and imaging speed.