ULTRASOUND Flashcards
consists of many components, each of which has a separate operation to perform. This starts with transmitting and receiving ultrasound signals which are then processed to form the images that we see on screen.
diagnostic ultrasound machine
The internal components that make up a typical ultrasound machine are the following:
- Transducer
- Pulser
- Beam former
- Receiver
- Processor
- Display
- Digital storage
- Hard copy printer devices
Diagnostic transducers are made from __
piezoelectric materials
As a consequence of this they can act as a transmitter and receiver of ultrasound. They are able to produce beams which can be directed in various ways which are controlled by the ultrasound machine to improve image quality.
Transducer
materials and are able to convert electrical energy into ultrasound energy and vice versa.
Transducer
Changes in the applied __ to the transducer changes the strength and intensity of the ultrasound beam, and affects the overall brightness of the B-mode image.
voltage
The ___ produces the electric voltage that drives the transducer. This driving voltage governs the output power of the ultrasound machine and can be adjusted by the operator through the power or output control
pulser
Increasing the applied voltage to the transducer increases the ultrasound pulse intensity, resulting in an increase in the overall ___ of the image.
brightness
The greater the applied voltage, the stronger the ultrasound pulse and the higher the __
pulse intensity
The ___ controls the shape and direction of the ultrasound beam and the scanning patterns used to form the images that we see.
beam former
As a consequence of attenuation the returning echo amplitudes and intensities are___
decreased
beam former: this enables the operator to have indirect control of:
- depth
- focus
- sector width
- zoom
job is to to combat attenuation, i.e. the energy lost from the beam a sit propagates through soft tissue.
Receiver
energy is lost from the beam through absorption which is mainly converted into __
heat.
The ultrasound machine can compensate for the effects of attenuation by amplifying the received signals in two ways, using the ___ and __
overall gain and the time-gain compensation (TGC) controls.
The processor can be divided into two individual parts, each having very different tasks to fulfil, and consists of:
signal processor and image processor
converts echo voltages to video signals
signal processor
formats the many scan line data into image form.
image processor
cleans up the signal, removing unwanted noise, and also controls the signal bandwidth
Filtering in Processor
performs a process of demodulation which means it converts the received signal voltages into video form, retaining the amplitude information required for B-mode imaging
Amplitude detection in Processor
controls the dynamic range of the B-mode image (the number of shades of gray displayed in the image)
Compression in Processor
Once the signals have passed through the signal processor they are fed into the ___
image processor
The ___ performs operations such as scan conversion which reformats the scan line data into two-dimensional images, i.e. either___
image processor; linear or sector form.
There is a range of processing performed on the image data prior to and following storage into memory before they are finally sent to the display. Functions such as edge enhancement are known as ___ because they are performed before being stored.
pre-processing functions
stores a number of sequentially acquired and processed static image frames every second which are rapidly sent to the display to provide dynamic real-time ultrasound.
Image memory
This process can be interrupted by activating the___ which stops any further acquisition and processing of data from the transducer.
freeze control
In freeze mode only ___ in the memory is displayed. The numerous frames of image data held and stored can be reviewed in turn using the machine’s __ function.
one static image; cine loop control
There are only two controls that can be adjusted on most displays, which are ___
brightness and contrast
The images displayed on screen can be sent out to an external hard copy device such as ___ and __
radiographic film or thermal paper printers.
The images displayed on screen can be sent out to an external hard copy device such as radiographic film or thermal paper printers. Alternatively, the images, which can also consist of short cine loop review video clips, can be digitally stored on the machine’s hard disc or alternatively burnt to CD or DVD.
Hard Copy and Soft Copy Storage
Many ultrasound departments are linked into a __ This enables images such as X-rays and ultrasound scans to be stored electronically and viewed on any __display monitor around the hospital at the touch of a button.
picture archiving and communications system, more commonly known as PACS.
Different types of ultrasound transducers:
Linear array, Curvilinear array, Phased array
type of transducer: Produces a rectangular field of view
Linear array
type of transducer: Produces a wide “sector” field of view
Curvilinear array
type of transducer: small footprint Produces a “sector” field of view
Phased array
Ultrasound transducers are described by their type and operating frequency which can range from __ and are selected based on their ‘fitness for purpose’.
2MHz up to 20 MHz
We need to be aware that there is a trade-off between image resolution and the penetrating depth of ultrasound which is governed by its __
frequency.
In general use, the ___ which will reach the required depth should always be employed.
highest frequency transducer
An ultrasound transducer converts __ and ___ and back again, based on the piezoelectric effect.
electrical energy into mechanical (sound) energy
It is the hand-held part of the ultrasound machine that is responsible for the production and detection of ultrasound waves.
ultrasound transducer
The main components of a typical ultrasound transducer consist of:
- physical housing assembly
- electrical connections
- piezoelectric element
- backing material
- acoustic lens
- impedance matching layer.
This contains all the individual components including the crystal, electrodes, matching layer, and backing material. This housing provides the necessary structural support and acts as an electrical and acoustic insulator.
Physical housing
Two electrical connections are formed on the front and back face of the crystal by plating a thin film of gold or silver on these surfaces. These electrodes are connected to the ultrasound machine which generates the short burst of electrical pulses to excite the crystal and through the piezoelectric effect generates a pulse of ultrasound energy.
Electrical connections
They also discovered that the converse was true, i.e. if a short electrical burst was applied to these crystals it would cause them to__. The term ‘piezoelectric’ was derived from the Greek word__, meaning to press or squeeze.
vibrate; ‘piezein’
Piezoelectric element is made of ___
Quartz
__ is a naturally occurring material with piezoelectric properties and was extensively used in the development of early machines. This has now been superseded by man-made ceramics such as __ which are more efficient, have better sensitivity, and can easily be shaped.
Quartz; lead-zirconate-titanate (PZT)
The operating frequency of a transducer is critically governed by the __. For maximum efficiency the crystal should be operating at its___ frequency. This occurs when the thickness of the crystal corresponds to half a wavelength (λ/2).
thickness of the piezoelectric crystal; ‘natural’ or ‘resonant’
Typical diagnostic ultrasound elements are between ___
0.2 mm and 1 mm thick
To try and eliminate the vibrations from the back face, and to control the length of vibrations from the front face a ___ is used.
backing or damping material
This damping material, which typically consists of __ and __ , is attached to the back face of the piezoelectric crystal.
tungsten powder; plastic or epoxy resin
A refractive element such as plastic or rubber lens placed in front of a flat crystal to focus the ultrasound beam.
Acoustic Lens
Sandwiched between the PZT crystals and the patient’s skin is a __ and __
matching layer and acoustic coupling.
is fashioned to be one-quarter wavelength and of intermediate acoustic impedance between that of the piezoelectric crystals and soft tissue.
matching layer
Acoustic coupling between the transducer and the patient’s skin consists of copious amounts of___
gel or mineral oil.
