اساسيات الموجات فوق الصوتية

موضوع: radiology key notes الإثنين أبريل 08, 2024 7:06 pm

Ultrasound is an important technique for tomographic imaging of soft tissues. It provides images in real time and so can also be used to interrogate the movement of structures such as cardiac valves and biopsy needles and, using Doppler, the patterns of blood flow in both large and small vessels.
Contrast agents in the form of microbubbles are invaluable in cardiology and the liver, but images are generally obtained without them and thus are not dependent on organ function.
Elastography adds information on tissue stiffness, an extension of manual palpation.
Ultrasound at diagnostic intensities does not cause damage to tissues and, although complete safety is difficult to prove, it can be used for ovarian follicles and in the developing fetus.
Despite its very wide application in obstetrics, cardiology, abdominal and small parts imaging, the parts of the body that can be imaged with ultrasound are limited because ultrasound does not cross tissue–gas or tissue–bone boundaries so that structures lying deeper to them are obscured. Thus, ultrasound is not generally useful for the lungs and is difficult to use in the head—except in the neonate, as the open fontanelles provide an excellent ‘window’.
In other areas, overcoming the barrier caused by the bony skeleton and gassy viscera requires technical expertise. Ultrasound is also subject to many artefactual signals, which complicate interpretation and add to the operator skills required.
Patient acceptance is high and preparation is minimal: bladder filling is required for pelvic imaging and fasting is helpful for the gallbladder. Mobile imaging systems for theatre and emergency point-of-care use are widely available and are being miniaturised while retaining their quality, so that in the future they may become used by all medical practitioners, though training will have to be made available.
Ultrasound is the ideal technique for biopsy and interventional guidance because it operates in real time. Real-time ultrasound can be fused with previously acquired 3D CT or MR data sets to improve the precision of biopsies and tumour ablation. A position sensor then adjusts the CT or MR image to match the ultrasound slice, thus combining the strengths of each technique.

موضوع: radiology key notes الإثنين أبريل 08, 2024 7:13 pm

Nature of Ultrasound
Ultrasound is a coherent, mechanical vibration at high frequencies. In most diagnostic applications, frequencies in the 2–20 MHz (megahertz = million cycles per second) range are used, corresponding to wavelengths of 1–0.1 mm in tissue.
Ultrasonic Transducers
Ultrasound is generated by piezoelectric materials which have the property of changing thickness when a voltage is applied across them. Lead zirconate titanate (PZT) is the most widely used.
The piezoelectric effect derives from movements of a heavy, charged atom that is loosely bound within a complex crystal; when an electrical field is applied, the atom moves and distorts the crystal. PZT is a ceramic that is cast as a thin plate that may be disc-shaped or more usually is formed into a strip that is then sliced into several hundred tiny elements as an array, with metal electrodes on the two surfaces.
It is polarised by heating it above a critical temperature (the Curie point, which is around 200°C) and then allowing it to cool in an electric field, a process similar to that used to polarise a magnet.
When electrically pulsed, the crystal rings like a bell at a resonant frequency which is mainly determined by its thickness. Higher-frequency crystals are thinner and thus more difficult to manufacture.
The piezoelectric effect is symmetrical, so that the same or a similar crystal is used as the receiver to produce small electrical signals when struck by an ultrasound wave.
The crystal is mounted in a conveniently shaped holder which contains the electrodes and any associated electronics as well as the lenses and matching layers required to improve the beam shape and enable efficient transfer of acoustic energy between the crystal and the patient (see later). The whole assembly is known as the probe or transducer.
The development of single crystal piezoelectric materials is improving the sensitivity and the bandwidth of transducers because the piezo domains are more truly aligned than in a traditional amorphous ceramic material. Manufacture is similar to silicon chip technology, seeding a molten pot of the material in a crucible and slowly cooling it to allow crystallization. The material is then machined to the required shape (usually as a multi-element array).

Propagation in Tissue
Ultrasound travels through tissue as a beam, which, for most clinical applications, is focused to around 1 mm or less in diameter at the focal zone.
It propagates as a sequence of compression and rarefaction waves which are transmitted by the elastic forces between adjacent tissue particles.
The particles move in the same direction as the wave—thus ultrasound is a longitudinal wave unlike the transverse waves that occur at the surface of water where the particles move up and down as the wave travels horizontally.
The frequency of the oscillations is inversely proportional to the wavelength ( f = c/λ, where f is frequency, c is the velocity of ultrasound and λ is the wavelength).
The way in which the ultrasound wave is transmitted varies with the strength of the elastic forces between adjacent particles (which relates to the elasticity of the tissue and thus to the velocity of ultrasound) and with the masses of the particles (which determines density). These two factors determine the acoustic impedance (Z) of the tissue (Z ≅ ρc, where ρ is density and c is the velocity of ultrasound). When the particles are heavy, a given amount of energy is transmitted with small movements of the particles; when they are light, larger excursions occur, though it should be understood that the actual distance a particle is moved at diagnostic ultrasound intensities is less than a nanometre.
In clinical practice, since the velocity of ultrasound in tissue is almost constant (at 1540 m s⁻¹), changes in impedance are mainly attributable to differences in density.
The constant speed of ultrasound in soft tissues allows the depth of reflectors to be calculated by measuring the delay in the return of echoes after the ultrasound pulse has been transmitted. This is the essence of the pulse-echo method used in both ultrasound imaging and most forms of Doppler ultrasound. (Note that the position of reflectors across the imaged plane is determined in a quite different manner, by the direction in which the ultrasound beam is transmitted; see below.)

موضوع: radiology key notes الإثنين أبريل 08, 2024 7:17 pm

Attenuation
Provided that the constituent particles of a tissue are small enough to move as a single entity, the acoustical vibrations are transmitted in an orderly and efficient manner. However, when very large molecules are involved, the vibrations become disorganised, one part of the molecule responding more or less than another. While coherent vibration is what we know as sound, chaotic vibration is heat. This loss of coherence, the most important cause of dissipation of ultrasound energy, is known as absorption and is approximately proportional to the concentration of large molecules which correlates fairly well with viscosity.
Absorption is also highly dependent on the ultrasound frequency, higher frequencies being more strongly absorbed.

For average soft tissues the loss, amounts to approximately 1 dB per cm tissue depth for each megahertz. Thus, when using a 3-MHz probe, for every 2 cm of tissue penetration there will be a loss of 6 dB, which is a halving of the pressure amplitude of the signal.
The noise floor (produced by random vibrations in the tissue and the transducer as well as by imperfections in the electronics) lies some 60–90 dB below the peak signal; so the penetration of such a probe would be limited to about 20 cm depth and to 10 cm for a 6-MHz probe.
Ultrasound energy is also lost to the receiving transducer when it is reflected or refracted away from the returning line of sight or if the beam diverges. The total loss from all these mechanisms is called attenuation.
High-frequency ultrasound gives better resolution because of the shorter wavelength, but the frequency dependence of attenuation in tissue is the limiting factor to the maximum that can be used in any given clinical application.
Frequencies as high as 20 MHz can be used when only a few millimetres of tissue are to be traversed, such as for examining the eye and skin and for intravascular ultrasound (IVUS).
For superficial tissues, such as the thyroid, breast and scrotum, 10–18 MHz is appropriate.
For the heart, abdomen and second and third trimester obstetrics, 3–7 MHz is optimal, while for some difficult applications, such as the abdomen in obese subjects, and for transcranial studies (most of which use Doppler), one has to resort to 1.5- or 2.5-MHz transducers. This frequency limitation can be reduced by the use of longer-duration coded transmit pulses, which essentially impose a signature on the pulse (for example, by making the frequency increase during the pulse, so-called chirp encoding). This approach allows the spatial resolution to be maintained while using longer transmit pulses and improving the sensitivity of the system to weak echoes.
Obviously a way to compensate for this rapid reduction in signal intensity is required if the image is to display similar reflectors as equal in brightness over a range of tissue depths. This is achieved by applying progressively increasing amplification (gain) to later echoes in proportion to their depth using a time-varying amplifier that is triggered when each ultrasound pulse is sent. This is the TGC (time gain compensation), an important user control that must be set to equalise the image brightness for superficial and deep structures.
Most imaging now incorporates automatic gain and TGC correction which makes it easier to set the imaging parameters correctly.

موضوع: radiology key notes الإثنين أبريل 08, 2024 7:27 pm

Different Types of Ultrasound

The ultrasound that we have described so far presents a two-dimensional image, or "slice," of a three-dimensional object (fetus, organ). Two other types of ultrasound are currently in use, 3-D ultrasound imaging and Doppler ultrasound.
Ultrasound machines capable of three-dimensional imaging have been developed. In these machines, several two-dimensional images are acquired by moving the probes across the body surface or rotating inserted probes. The two-dimensional scans are then combined by specialized computer software to form 3-D images.
3-D imaging allows you to get a better look at the organ being examined and is best used for:

Early detection of cancerous and benign tumors (examining the prostate gland for early detection of tumors, looking for masses in the colon and rectum, detecting breast lesions for possible biopsies).
Visualizing a fetus to assess its development, especially for observing abnormal development of the face and limbs.
Visualizing blood flow in various organs or a fetus.

Doppler ultrasound is based upon the Doppler Effect. When the object reflecting the ultrasound waves is moving, it changes the frequency of the echoes, creating a higher frequency if it is moving toward the probe and a lower frequency if it is moving away from the probe. How much the frequency is changed depends upon how fast the object is moving. Doppler ultrasound measures the change in frequency of the echoes to calculate how fast an object is moving. Doppler ultrasound has been used mostly to measure the rate of blood flow through the heart and major arteries

موضوع: radiology key notes الإثنين أبريل 08, 2024 7:31 pm

The Ultrasound Machine

A basic ultrasound machine has the following parts:

Transducer probe - probe that sends and receives the sound waves
Central processing unit (CPU) - computer that does all of the calculations and contains the electrical power supplies for itself and the transducer probe
Transducer pulse controls - changes the amplitude, frequency and duration of the pulses emitted from the transducer probe
Display - displays the image from the ultrasound data processed by the CPU
Keyboard/cursor - inputs data and takes measurements from the display
Printer - prints the image from the displayed data

The transducer probe is the main part of the ultrasound machine. The transducer probe makes the sound waves and receives the echoes. It is, so to speak, the mouth and ears of the ultrasound machine. The transducer probe generates and receives sound waves using a principle called the piezoelectric (pressure electricity) effect, which was discovered by Pierre and Jacques Curie in 1880. In the probe, there are one or more quartz crystals called piezoelectric crystals. When an electric current is applied to these crystals, they change shape rapidly. The rapid shape changes, or vibrations, of the crystals produce sound waves that travel outward. Conversely, when sound or pressure waves hit the crystals, they emit electrical currents. Therefore, the same crystals can be used to send and receive sound waves. The probe also has a sound-absorbing substance to eliminate back reflections from the probe itself, and an acoustic lens to help focus the emitted sound waves.

موضوع: radiology key notes الإثنين أبريل 08, 2024 7:34 pm

Transducer probes come in many shapes and sizes, as shown in the photo above. The shape of the probe determines its field of view, and the frequency of emitted sound waves determines how deep the sound waves penetrate and the resolution of the image.
Transducer probes may contain one or more crystal elements; in multiple-element probes, each crystal has its own circuit. Multiple-element probes have the advantage that the ultrasonic beam can be steered by changing the timing in which each element gets pulsed; steering the beam is especially important for a cardiac ultrasound. In addition to probes that can be moved across the surface of the body, some probes are designed to be inserted through various openings of the body (vagina, rectum, esophagus) so that they can get closer to the organ being examined (uterus, prostate gland, stomach); getting closer to the organ can allow for more detailed views.
The parts of an ultrasound machine
The CPU is the brain of the ultrasound machine. The CPU is basically a computer that contains the microprocessor, memory, amplifiers and power supplies for the microprocessor and transducer probe. The CPU sends electrical currents to the transducer probe to emit sound waves, and also receives the electrical pulses from the probes that were created from the returning echoes. The CPU does all of the calculations involved in processing the data. Once the raw data are processed, the CPU forms the image on the monitor. The CPU can also store the processed data and/or image on disk.
The transducer pulse controls allow the operator, called the ultrasonographer, to set and change the frequency and duration of the ultrasound pulses, as well as the scan mode of the machine. The commands from the operator are translated into changing electric currents that are applied to the piezoelectric crystals in the transducer probe.

موضوع: radiology key notes الإثنين أبريل 08, 2024 7:37 pm

What is the wavelength of an ultrasound?
Ultrasound is defined by the American National Standards Institute as "sound at frequencies greater than 20 kHz" (above human hearing). In air at atmospheric pressure, ultrasonic waves have wavelengths of 1.9 cm or less.
What are 4 uses of an ultrasound?
What is medical ultrasound?
One of the most common uses of ultrasound is during pregnancy, to monitor the growth and development of the fetus, but there are many other uses, including imaging the heart, blood vessels, eyes, thyroid, brain, breast, abdominal organs, skin, and muscles.
What are the four primary components of an ultrasound system?
Ultrasound waves are transmitted inside the body, and the waves reflected back by organs and tissues (echoes) are received and used to create images based on this information. Diagnostic ultrasound system comprises four main components: a transducer, monitor, operating panel and processing unit.Feb 16, 2023
Why is ultrasound safe?
Because ultrasound uses sound waves instead of radiation, it's safer than X-rays. Providers have used ultrasound for more than 30 years, and they have not found any dangerous risks.

ESWL
Extracorporeal Shock Wave Lithotripsy (ESWL) is the use of low-frequency, high-energy shock waves, externally sent through the skin to target kidney stones – causing the stones to break down into fragments until they become "stone dust", small enough to pass
What are the three common contraindications for ultrasound
ESWL - Infection, stone burden greater than 2.5 cm; coagulopathies, untreated hypertension, pregnancy-ESWL.
Magnetic Resonance-guided Focused Ultrasound Surgery (MRgFUS) - Cardiac pacemaker or other implantable devices.
Which ultrasound is most important in pregnancy?
Ultrasound scans during pregnancy - benefits, about ...
A morphology scan (also known as a 'fetal anomaly scan') is an ultrasound usually done between 18 and 22 weeks of pregnancy. It checks your baby's body organs, specifically looking at their structure and growth, their gestational age and size will also be estimated based on these measurements.

موضوع: radiology key notes الإثنين أبريل 08, 2024 7:45 pm

What is the physics of ultrasound?
Ultrasound transducers contain piezoelectric crystals that, when electrical impulses are applied, produce mechanical sound waves at frequencies determined by the crystal's propagation speed, divided by two times the thickness of the crystal layer. The typical thickness of crystal layers is between 0.2mm and 2mm.Mar 27, 2023
What is nature of ultrasound?
Ultrasonic waves are waves of frequency above the audible frequencies of the human ear. In medical diagnostics are used ultrasound frequencies between 3 and 18 MHz
.Because the speed of sound (cs) is orders of magnitude lower than the speed of light, the wavelength (λ) of US radiation λ = cs/f in tissue higher than the frequency (f) range of interest (0.5–10 MHz) is 0.1 to 3 mm. With such small wavelengths, US beams are easily focused into very small volumes at depth.
Ultrasound is defined by the American National Standards Institute as "sound at frequencies above those audible to the human hearing (greater than 20 kHz").
In air at atmospheric pressure, ultrasonic waves have wavelengths of 1.9 cm or less
Ultrasound typically used in clinical settings has frequencies between 2 and 12 MHz..

US waves are
Typically 1 or 3 MHz.
WAVELENGTH - this is the distance
between two equivalent points on the waveform in the particular medium
In an 'average tissue' the wavelength is : @ 1MHz would be 1.5mm and @ 3 MHz would be 0.5 mm.
The frequencies used in ultrasonic diagnosis are in the range of 1 to 10 MHz. The speed of sound waves in the tissues of the human body averages about 1540 m/s (close to that for water). So, the wavelength of a 1 MHz wave is about λ=v/f=1540/1∙106=1.5∙10–3m=1.5mm
6 Mhz - 6 x 10 *6/s........

موضوع: radiology key notes الإثنين أبريل 08, 2024 7:46 pm

Frequencies used in USG range from 2 to 18 MHz. Frequency ( f ) is inversely proportional to wavelength ( λ ) and varies according to the specific velocity of sound in a given tissue ( c ) according to the formula: λ = c / f
What is the formula for wavelength frequency in US?
What is the formula for US waves ?
Velocity of ultrasonic waves in a medium (V):
(V) = f x l OR Where f = is Number of cycles per second & is called frequency. Measured in 'Hertz'. Abbreviated as 'Hz'.
One Hertz is equivalent to One cycle per second l = Distance covered in one cycle is wavelength V= Velocity of Ultrasonic wave inside the medium in 'mm/s' 2.
What is the formula of ultrasound wave?
The product of the frequency (ν) and the wavelength (λ) is the velocity of the wave; that is, c = νλ. In most soft tissues, the velocity of ultrasound is about 1540 m/sec. Frequencies of 1 MHz and greater are required to furnish ultrasound wavelengths suitable for diagnostic imaging.
What is the frequency and wavelength of ultrasound?
The velocity of sound in biologic tissue is a constant at approximately 1540 meters/second. Applying a frequency of 2 MHz of ultrasound energy will result in a wavelength of 0.77 mm, whereas applying a frequency of 8 MHz of ultrasound energy will result in a wavelength of 0.19 mm.

موضوع: radiology key notes الإثنين أبريل 08, 2024 8:08 pm

What are the modes of ultrasound?
These are:
    A-mode: A-mode is the simplest type of ultrasound. ...
    B-mode: In B-mode ultrasound, a linear array of transducers simultaneously scans a plane through the body that can be viewed as a two-dimensional image on screen.
    M-mode: M stands for motion.
Basic physics for generation of US image

Brightness mode (B mode) is the basic mode that is usually used. Ultrasound waves are emitted from piezoelectric crystals of the ultrasound transducer. Depending on the acoustic impedance of different materials, which depends on their density, different grades of white and black images are produced
The speed of US : In diagnostic ultrasound imaging the speed of sound is assumed to be 1540 m/s in soft tissues ;
330 m/s in air

موضوع: Anatomical planes الإثنين أبريل 15, 2024 6:17 pm

Introduction

Anatomical planes are imaginary planes/2D surfaces used to divide the body to facilitate descriptions of location and movement.
The anatomical position is used as a reference when describing locations of structures and movements. It is an upright position with arms by the side and palms facing forward. Feet are parallel with toes facing forward

Anatomical terms

To understand anatomical planes, it is important to be familiar with basic anatomical terms:

Proximal: towards the main trunk of the body
Distal: away from the main trunk of the body
Superior: upper
Inferior: lower
Superficial: near the surface of the body
Deep: away from the surface of the body
Medial: towards the midline
Lateral: away from the midline

Additional terms which are more commonly used in embryology and neuroanatomy:

Ventral: front, anterior
Dorsal: back, posterior
Cranial: towards the head
Caudal: towards the ‘tail’ end

اساسيات الموجات فوق الصوتية - صفحة 2 Figure-3-4th-Digit-Laceration-1-e1635430810456

Clinical relevance: describing injuries
It is important to become familiar with anatomical terms to describe locations of bodily structures and injuries as well as for describing movements.
For example, Figure 3 shows a laceration located on the medial aspect of the 4^th digit of the left hand immediately distal to the proximal interphalangeal joint

The Sagittal plane is a longitudinal plane, dividing the body into right and left parts. These are not necessarily equal but if they are equal the plane is termed a midsagittal or median plane
The Coronal plane is a longitudinal plane, dividing the body into anterior (front) and posterior (back) sections
Sagittal and Coronal are also terms used to describe the sutures of the skull. The original meaning of sagittal is ‘arrow
and coronal means ‘crown’. It can be helpful to remember this when describing the anatomical planes
sagittal is ‘arrow (سهمي)
The Axial (or Transverse plane) is a horizontal plane dividing the body into superior (upper) and inferior (lower) sections.
Planes that are NOT parallel to any of the three planes above are termed oblique planes

Anatomical terms and planes help to describe locations of body structures and movements.
Understanding the anatomical planes enables you to correctly orientate prosections and scans (e.g. CT).
https://geekymedics.com/anatomical-planes/

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