US (Ultrasound imaging)
Anatomical information can be obtained by using high frequency sound waves and the pulse echo effect
Applications: Cardiology, genecology & obstetrics, urology, gastroenterology
• Checking the development of the foetus during pregnancy.
• Imaging most structures of the head and neck, including the thyroid and parathyroid glands, lymph nodes, urinary tract, musculoskeletal system, and salivary glands • Imaging the solid organs of the abdomen such as; the pancreas, aorta, inferior vena cava, liver, gall bladder, bile ducts, kidneys, thyroid, testes, breast, and spleen.
• Guiding the injecting of needles when placing local anaesthetic solutions near nerves.
• Echocardiography used for diagnosing the heart and function of heart entricles and valves.
Prostate, urinary bladder, uterus
• Non-invasive and painless.
• Without using ionizing radiation (particular advantage in pregnancy & paediatrics)
• High resolution.
• Real time information.
• Sensitive to detect flow changes, intra and extra luminal abnormalities.
• Ability to measure velocity.
• Possible control of respiratory phases.
• Colour Doppler shows blood flowing towards the transducer as red, blood flowing away as blue – particularly useful in echocardiography and identifying very small blood vessels
•low equipment price, mobility
• Interactive modality, operator dependent (unlike CT and MRI, which produce cross-sectional images in a reasonably programmed fashion, US relies on the operator to produce and interpret images at the time of examination)
• US cannot penetrate gas or bone. Ultrasound waves are greatly reflected by air-soft tissue and bone-soft tissue interfaces, thus limiting its use in the head, chest and musculoskeletal system
• Doppler’s effect: the influence of a moving object on sound waves
• object travelling towards listener causes compression of sound waves (higher frequency)
• object travelling away from listener gives lower frequency
• flowing blood causes an alteration to the frequency of the sound waves returning to the ultrasound probe, allowing quantitation of blood flow
• No standardized guidelines.
• Time consuming.
• Blinding procedures are challenging.
• Cannot perform global view of the veins.
• Influenced by hydration status.
• Bowel gas may obscure structures deep in the abdomen, such as the pancreas or renal arteries.
•low image quality,
•difficult for interpretation,
The ultrasound transducer is placed against the skin of the patient near the region of interest.
A piezoelectric transducer is used to create high frequency sound waves (3-10 MHz) when electric current is applied to it.
The ultrasonic sound wave emitted travel through human tissues.
Wave is being reflected when it reach an object or surface with different texture or acoustic nature.
Reflected wave will travel back to the piezoelectric transducer to create electric current and a 2d image is produced.
The image formed will be based on how strong the returning signal is.
• The stronger the returning signal, the more white it will be on the grey-scale image (hyperechoic = white or light grey e.g. fat containing tissues)
•hypoechoic = dark grey (e.g. lymphoma, fibro adenoma of the breast)
•pure fluid gives no echoes, appearing black (anechoic)
•acoustic shadow is the opposite effect where tissues distal to e.g. gas containing areas, gallstones, renal stones receive little sound and thus appear as black
Components of ultrasound machine
· Transducer probe
· Central processing unit (CPU)
· Transducer pulse controls
· Disk storage device
· piezoelectric crystal
Flowing blood can alter the frequency of sound waves that are returning to the US probe. The change in the frequency is calculated to estimate the blood flow in the blood vessel.
Duplex US (combination of conventional US imaging with Doppler US)
Colour Doppler is an extension of these principles,
blood flowing towards the transducer- red
blood flowing away from the transducer-coloured blue
The colours superimpose on the cross-sectional image to enable instant assessment of presence and direction of flow. It can be used to confirm blood flow within organs and assess the vascularity of tumours.