presentation about ultrasound

Ultrasound (introduction)

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USG (ultrasonography)
Ultrasonography
USS (ultrasound scanning)

Ultrasound ( US ) is an imaging technology that uses high-frequency sound waves to characterize tissue. It is a useful and flexible modality in medical imaging and often provides an additional or unique characterization of tissues when compared to other modalities such as conventional radiography or CT .

Ultrasound is the most common term used for this modality however occasionally ultrasonography (USG), or just sonography are used. When abbreviated, USS, short for ultrasound scanning, may be used as an alternative. Echography is a rare synonym but is seen especially concerning ultrasound of the eye 3 .

For historical reasons, ultrasound of the heart tends to be called echocardiography , or often just echo.

Ultrasound is used in a wide variety of clinical settings to depict pathology and features and has several advantages but also disadvantages compared to other imaging modalities.

ultrasound uses non-ionizing sound waves and has not been associated with carcinogenesis - this is particularly important for the evaluation of the fetal and gonads

in most centers, ultrasound is more readily available than more advanced cross-sectional modalities such as CT or MRI

ultrasound examination is less expensive to perform than CT or MRI

ultrasound is straightforward to perform portably, unlike CT/MRI

there are few (if any) contraindications to the use of ultrasound, compared with MRI or contrast-enhanced CT

the real-time nature of ultrasound imaging is useful for the evaluation of physiology as well as anatomy (e.g. fetal heart rate )

Doppler evaluation of organs and vessels adds a dimension of physiologic data, not available on other modalities (except some MRI sequences)

ultrasound images may not be as adversely affected by metallic objects, as opposed to CT or MRI

an ultrasound exam can easily be extended to cover another organ system or evaluate the contralateral extremity

Disadvantages

training is required to accurately and efficiently conduct an ultrasound exam and there is non-uniformity in the quality of examinations ("operator dependence")

ultrasound is not capable of evaluating the internal structure of tissue types with high acoustical impedance (e.g. bone, air). It is also limited in evaluating structures encased in bone (e.g. cerebral parenchyma inside the calvaria)

the high frequencies of ultrasound result in a potential risk of thermal heating or mechanical injury to tissue at a microscopic level, this is of most concern in fetal imaging

ultrasound has its own set of unique artifacts ( US artifacts ), which can potentially degrade image quality or lead to misinterpretation

some ultrasound exams may be limited by abnormally large body habitus

Physical principles

A sound wave is transmitted through liquids as a longitudinal wave, in which the movements of particles in a medium are parallel to the direction of propagation of the sound wave 2 . Sound wave transmits their energy mechanically, through pressure variations on the particles. Regions of high pressure and density are called "compressions" while regions of low pressure and density are called "rarefactions" 1 .

The frequency of the sound waves used in medical ultrasound is in the range of millions of cycles per second (megahertz, MHz) . In contrast, the upper range of audible frequencies for humans is around 20 thousand cycles per second (20 kHz) 2 .

Ultrasound images are produced by relying on properties of acoustic physics (reflection, refraction, absorption 2 , and scattering). These properties cause attenuation of ultrasound that is used to localize and characterize different tissue types 2 . The amount of attenuation of ultrasound is described by the attenuation coefficient . Acoustic impedance is a physical property of a tissue in which how much resistance it offers to stop the transmission of an ultrasound beam 2 . Differences between the acoustic impedance of the two mediums govern the proportions of reflected and transmitted sound waves 2 .

The angle of the transmitted sound waves (refracted waves) is governed by Snell's law 2 . The velocity of the transmitted wave can be either be higher or slower than the incident wave depending on the type of material it passes through 2 . During the change in velocity, the wavelength changes while the frequency remains constant 2 . The compressibility (or stiffness) of the material and density of the material affects the velocity of the ultrasound wave. The lower the compressibility (or higher the stiffness), or the lower the density, the higher the velocity of ultrasound because the frequency remains constant while the wavelength increases 2 .

The intensity/loudness/amplitude of ultrasound is measured as milliwatts cm -2 or watts cm -2 . Diagnostic and low-intensity ultrasound range from 0.1 to 1 watts cm -2 , while high-intensity ultrasound is more than 10 watts cm -2 4 . Power is energy generated per unit time, measured in joules per second or watts 5 . The intensity or power of the ultrasound is directly proportional to the square of the amplitude 5 . Meanwhile, relative sound intensity is measured by decibels, which compares the relative intensity of two sound beams 2 . The loss of 3 decibels will reduce the sound intensity by half 2 .

Device function

An ultrasound transducer , also known as a probe , operates based on the physical principles of ultrasound . It sends an ultrasound pulse into tissue and then receives echoes back. The echoes contain spatial and contrast information. The concept is analogous to sonar used in nautical applications, but the technique in medical ultrasound is more sophisticated, gathering enough data to form a rapidly moving two-dimensional grayscale image.

Some characteristics of returning echoes from tissue can be selected out to provide additional information beyond a grayscale image. Doppler ultrasound , for instance, can detect a frequency shift in echoes, and determine whether the tissue is moving toward or away from the transducer. This is invaluable for the evaluation of some structures such as blood vessels or the heart ( echocardiography ).

Ultrasound continues to evolve additional functions, including 3D ultrasound imaging , elastography , and contrast-enhanced ultrasound using microbubbles .

Signals from the transducer are fed into a digital scan converter to display them as image on a monitor screen 6 .

Quiz questions

1. Frederick W. Kremkau. Sonography Principles and Instruments. (2015) ISBN: 9780323322713 - Google Books
2. Dowdey, James E., Murry, Robert C., Christensen, Edward E., 1929-. Christensen's Physics of Diagnostic Radiology. (1990). Pages 323-327. ISBN: 9780812113105 - Google Books
3. Graziano M, Biondino D, Fioretto I. Carotid-Cavernous Fistulas: The Utility of Ocular Echography in Their Differentiation [Letter]. Clin Ophthalmol. 2023;17:1421-2. doi:10.2147/OPTH.S420582 - Pubmed
4. Uddin S, Komatsu D, Motyka T, Petterson S. Low-Intensity Continuous Ultrasound Therapies—A Systematic Review of Current State-Of-The-Art and Future Perspectives. JCM. 2021;10(12):2698. doi:10.3390/jcm10122698 - Pubmed
5. Shriki J. Ultrasound Physics. Crit Care Clin. 2014;30(1):1-24. doi:10.1016/j.ccc.2013.08.004 - Pubmed
6. Ophir J & Maklad N. Digital Scan Converters in Diagnostic Ultrasound Imaging. Proc IEEE. 1979;67(4):654-64. doi:10.1109/proc.1979.11289

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What is medical ultrasound?

How does it work, what is ultrasound used for, are there risks, what are examples of nibib-funded projects using ultrasound.

Medical ultrasound falls into two distinct categories: diagnostic and therapeutic.

Diagnostic ultrasound can be further sub-divided into anatomical and functional ultrasound. Anatomical ultrasound produces images of internal organs or other structures. Functional ultrasound combines information such as the movement and velocity of tissue or blood, softness or hardness of tissue, and other physical characteristics, with anatomical images to create “information maps.” These maps help doctors visualize changes/differences in function within a structure or organ.

Therapeutic ultrasound also uses sound waves above the range of human hearing but does not produce images. Its purpose is to interact with tissues in the body such that they are either modified or destroyed. Among the modifications possible are: moving or pushing tissue, heating tissue, dissolving blood clots, or delivering drugs to specific locations in the body. These destructive, or ablative, functions are made possible by use of very high-intensity beams that can destroy diseased or abnormal tissues such as tumors. The advantage of using ultrasound therapies is that, in most cases, they are non-invasive. No incisions or cuts need to be made to the skin, leaving no wounds or scars.

This is a picture of a technician giving a pregnant woman an ultrasound. There is an image of the fetus on the computer monitor.

Ultrasound waves are produced by a transducer, which can both emit ultrasound waves, as well as detect the ultrasound echoes reflected back. In most cases, the active elements in ultrasound transducers are made of special ceramic crystal materials called piezoelectrics. These materials are able to produce sound waves when an electric field is applied to them, but can also work in reverse, producing an electric field when a sound wave hits them. When used in an ultrasound scanner, the transducer sends out a beam of sound waves into the body. The sound waves are reflected back to the transducer by boundaries between tissues in the path of the beam (e.g. the boundary between fluid and soft tissue or tissue and bone). When these echoes hit the transducer, they generate electrical signals that are sent to the ultrasound scanner. Using the speed of sound and the time of each echo’s return, the scanner calculates the distance from the transducer to the tissue boundary. These distances are then used to generate two-dimensional images of tissues and organs.

During an ultrasound exam, the technician will apply a gel to the skin. This keeps air pockets from forming between the transducer and the skin, which can block ultrasound waves from passing into the body.

Click here to watch a short video about how ultrasound works.

Diagnostic ultrasound. Diagnostic ultrasound is able to non-invasively image internal organs within the body. However, it is not good for imaging bones or any tissues that contain air, like the lungs. Under some conditions, ultrasound can image bones (such as in a fetus or in small babies) or the lungs and lining around the lungs, when they are filled or partially filled with fluid. 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. Ultrasound images are displayed in either 2D, 3D, or 4D (which is 3D in motion).

Illustration of a women getting an ultrasound of blood flow in her carotid arteries

Functional ultrasound. Functional ultrasound applications include Doppler and color Doppler ultrasound for measuring and visualizing blood flow in vessels within the body or in the heart. It can also measure the speed of the blood flow and direction of movement. This is done using color-coded maps called color Doppler imaging. Doppler ultrasound is commonly used to determine whether plaque build-up inside the carotid arteries is blocking blood flow to the brain.

Another functional form of ultrasound is elastography, a method for measuring and displaying the relative stiffness of tissues, which can be used to differentiate tumors from healthy tissue. This information can be displayed as either color-coded maps of the relative stiffness; black-and white maps that display high-contrast images of tumors compared with anatomical images; or color-coded maps that are overlayed on the anatomical image. Elastography can be used to test for liver fibrosis, a condition in which excessive scar tissue builds up in the liver due to inflammation.

Ultrasound is also an important method for imaging interventions in the body. For example, ultrasound-guided needle biopsy helps physicians see the position of a needle while it is being guided to a selected target, such as a mass or a tumor in the breast. Also, ultrasound is used for real-time imaging of the location of the tip of a catheter as it is inserted in a blood vessel and guided along the length of the vessel. It can also be used for minimally invasive surgery to guide the surgeon with real-time images of the inside of the body.

Therapeutic or interventional ultrasound. Therapeutic ultrasound produces high levels of acoustic output that can be focused on specific targets for the purpose of heating, ablating, or breaking up tissue. One type of therapeutic ultrasound uses high-intensity beams of sound that are highly targeted, and is called High Intensity Focused Ultrasound (HIFU). HIFU is being investigated as a method for modifying or destroying diseased or abnormal tissues inside the body (e.g. tumors) without having to open or tear the skin or cause damage to the surrounding tissue. Either ultrasound or MRI is used to identify and target the tissue to be treated, guide and control the treatment in real time, and confirm the effectiveness of the treatment. HIFU is currently FDA approved for the treatment of uterine fibroids, to alleviate pain from bone metastases, and most recently for the ablation of prostate tissue. HIFU is also being investigated as a way to close wounds and stop bleeding, to break up clots in blood vessels, and to temporarily open the blood brain barrier so that medications can pass through.

Diagnostic ultrasound is generally regarded as safe and does not produce ionizing radiation like that produced by x-rays. Still, ultrasound is capable of producing some biological effects in the body under specific settings and conditions. For this reason, the FDA requires that diagnostic ultrasound devices operate within acceptable limits. The FDA, as well as many professional societies, discourage the casual use of ultrasound (e.g. for keepsake videos) and recommend that it be used only when there is a true medical need.

The following are examples of current research projects funded by NIBIB that are developing new applications of ultrasound that are already in use or that will be in use in the future:

An illustration of a robotic arm connected to a focused ultrasound transducer that rests above a human chest. A microcatheter injects an ink into a region below the transducer.

3D printing through the skin : Researchers at Duke University have developed a method to 3D print biocompatible structures through thick, multi-layered tissues. The approach entails using focused ultrasound to solidify a special ink that has been injected into the body to repair bone or repair soft tissues, for example. Initial experiments in animal tissue suggest the method could turn highly invasive surgical procedures into safer, less invasive ones. (Image on left courtesy of Junjie Yao (Duke University) and Yu Shrike Zhang (Harvard Medical School and Brigham and Women’s Hospital)).

A graphic shows a mouse before and after an ultrasound device fixed to its head is activated. The mouse is standing prior to activation and is laying down after.

Inducing a hibernation-like state : Researchers at Washington University in St. Louis used ultrasound waves directed into the brain to lower the body temperature and metabolic rates of mice, inducing a hibernation-like state, called torpor. The researchers replicated some of these results in rats, which, like humans, don’t naturally enter torpor. Inducing torpor could help minimize damage from stroke or heart attack and buy precious time for patients in critical care. (Image on right courtesy of Yang et al./Washington University in St. Louis).

A view of the ultrasound probe and the interior of the circuit.

High-quality imaging at home : Brigham and Women’s Hospital researchers compared ultrasound scans acquired by experts with those taken by inexperienced volunteers, finding little difference in the image quality of the two groups. The unconventional approach of having patients take ultrasound images of themselves at home and share them with healthcare professionals could allow for remote monitoring and reduce the need for hospitalization. (Image on right courtesy of Duggan et al./Brigham and Women's Hospital).

Reviewed December 2023

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Diagnostic ultrasounds use sound waves to make pictures of the body. Ultrasound, also called sonography, shows the structures inside the body. The images can help guide diagnosis and treatment for many diseases and conditions.

Most ultrasounds are done using a device outside the body. However, some involve placing a small device inside the body.

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Why it's done

Ultrasound is used for many reasons, including to:

View the uterus and ovaries during pregnancy and monitor the developing baby's health.
Diagnose gallbladder disease.
Evaluate blood flow.
Guide a needle for biopsy or tumor treatment.
Examine a breast lump.
Check the thyroid gland.
Find genital and prostate problems.
Assess joint inflammation, called synovitis.
Evaluate metabolic bone disease.

More Information

Abdominal aortic aneurysm
Acute kidney failure
Acute liver failure
Acute lymphocytic leukemia
Adenomyosis
Adult Still disease
Alcoholic hepatitis
Ambiguous genitalia
Anal cancer
Appendicitis
Arteriosclerosis / atherosclerosis
Arteriovenous fistula
Atelectasis
Autonomic neuropathy
Bladder stones
Blood in urine (hematuria)
Breast cancer
Breast pain
Carotid artery disease
Cerebral palsy
Cholestasis of pregnancy
Chronic exertional compartment syndrome
Chronic kidney disease
Cleft lip and cleft palate
Congenital adrenal hyperplasia
Conjoined twins
Deep vein thrombosis (DVT)
Double uterus
Down syndrome
Ductal carcinoma in situ (DCIS)
Endometrial cancer
Endometriosis
Enlarged breasts in men (gynecomastia)
Enlarged liver
Epididymitis
Erectile dysfunction
Eye melanoma
Fibroadenoma
Fibrocystic breasts
Galactorrhea
Ganglion cyst
Glomerulonephritis
Growth plate fractures
Hamstring injury
High blood pressure in children
Hurthle cell cancer
Incompetent cervix
Infant reflux
Inflammatory breast cancer
Intussusception
Invasive lobular carcinoma
Iron deficiency anemia
Ischemic colitis
Kidney cancer
Knee bursitis
Liver cancer
Liver disease
Liver hemangioma
Male breast cancer
Mammary duct ectasia
Median arcuate ligament syndrome (MALS)
Menstrual cramps
Miscarriage
Morning sickness
Morton's neuroma
Multisystem inflammatory syndrome in children (MIS-C)
Muscle strains
Muscular dystrophy
Myelofibrosis
Neuroblastoma
Nonalcoholic fatty liver disease
Osteoporosis
Ovarian cancer
Ovarian cysts
Painful intercourse (dyspareunia)
Pancreatic cancer
Patellar tendinitis
Pelvic inflammatory disease (PID)
Peripheral artery disease (PAD)
Peyronie disease
Placenta previa
Placental abruption
Polycystic kidney disease
Polymyalgia rheumatica
Post-vasectomy pain syndrome
Precocious puberty
Premature birth
Preterm labor
Prostate cancer
Pulmonary embolism
Pyloric stenosis
Recurrent breast cancer
Residual limb pain
Retinal detachment
Retinoblastoma
Rotator cuff injury
Sacral dimple
Sacroiliitis
Scrotal masses
Secondary hypertension
Solitary rectal ulcer syndrome
Spermatocele
Spina bifida
Swollen knee
Takayasu's arteritis
Tapeworm infection
Testicular cancer
Thrombophlebitis
Thyroid cancer
Thyroid nodules
Torn meniscus
Toxic hepatitis
Toxoplasmosis
Tricuspid atresia
Tuberous sclerosis
Uterine fibroids
Uterine prolapse
Wilms tumor
Zollinger-Ellison syndrome

Diagnostic ultrasound is a safe procedure that uses low-power sound waves. There are no known risks.

Ultrasound is a valuable tool, but it has limitations. Sound waves don't travel well through air or bone. This means ultrasound isn't effective at imaging body parts that have gas in them or are hidden by bone, such as the lungs or head. Ultrasound also may not be able to see objects that are located very deep in the human body. To view these areas, your healthcare professional may order other imaging tests, such as CT or MRI scans or X-rays.

How you prepare

Most ultrasound exams require no preparation. However, there are a few exceptions:

For some scans, such as a gallbladder ultrasound, your healthcare professional may ask that you not eat or drink for a certain period of time before the exam.
Other scans, such as a pelvic ultrasound, may require a full bladder. Your healthcare professional will let you know how much water you need to drink before the exam. Do not urinate until the exam is done.
Young children may need additional preparation. When scheduling an ultrasound for yourself or your child, ask your healthcare professional if there are any specific instructions you'll need to follow.

Clothing and personal items

Wear loose clothing to your ultrasound appointment. You may be asked to remove jewelry during your ultrasound. It's a good idea to leave any valuables at home.

What you can expect

Before the procedure.

Ultrasound of breast cyst

This ultrasound shows a breast cyst.

Ultrasound of liver tumor

An ultrasound uses sound waves to create an image. This ultrasound shows a noncancerous liver tumor.

Ultrasound of gallstones

This ultrasound shows gallstones in the gallbladder.

Ultrasound image showing a needle entering a tumor

Ultrasound of needle-guided procedure

These images show how ultrasound can help guide a needle into a tumor (left), where material is injected (right) to destroy tumor cells.

Transvaginal ultrasound

During a transvaginal ultrasound, a healthcare professional or technician uses a wandlike device called a transducer. The transducer is inserted into your vagina while you lie on your back on an exam table. The transducer emits sound waves that generate images of your pelvic organs.

Before your ultrasound begins, you may be asked to do the following:

Remove any jewelry from the area being examined.
Remove or reposition some or all of your clothing.
Change into a gown.

You'll be asked to lie on an exam table.

During the procedure

Gel is applied to your skin over the area being examined. It helps prevent air pockets, which can block the sound waves that create the images. This safe, water-based gel is easy to remove from skin and, if needed, clothing.

A trained technician, called a sonographer, uses a small, hand-held device called a transducer. The technician presses the transducer against the area being studied and moves it as needed to capture the images. The transducer sends sound waves into your body and collects the ones that bounce back. The images appear on a computer.

Sometimes, ultrasounds are done inside the body. In this case, the transducer is attached to a probe that's inserted into a natural opening in the body. Examples include:

Transesophageal echocardiogram. A transducer, inserted into the esophagus, obtains heart images. It's usually done while under sedation.
Transrectal ultrasound. This test creates images of the prostate by placing a special transducer into the rectum.
Transvaginal ultrasound. A special transducer is inserted into the vagina to look at the uterus and ovaries.

Ultrasound is usually painless. However, you may experience mild discomfort as the sonographer guides the transducer over your body. It may not be comfortable if you're required to have a full bladder or the transducer is inserted it into your body.

A typical ultrasound exam takes from 30 minutes to an hour.

When your exam is complete, a doctor trained to interpret imaging studies, called a radiologist, analyzes the images. The radiologist sends a report to your healthcare professional who will share the results with you.

You should be able to return to usual activities right after an ultrasound.

Clinical trials

Explore Mayo Clinic studies of tests and procedures to help prevent, detect, treat or manage conditions.

Andreas A, et al., eds. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 7th ed. Elsevier; 2021. https://www.clinicalkey.com. Accessed Jan. 15, 2024.
General ultrasound. RadiologyInfo.org. https://www.radiologyinfo.org/en/info/genus. Accessed Jan. 15, 2024.
McKenzie GA (expert opinion). Mayo Clinic. Feb. 1, 2022.
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Introduction to Ultrasound

Physicians in many specialties use ultrasound to confirm diagnoses and to safely guide procedures. Like all diagnostic tests, ultrasound should be applied selectively. Indiscriminate use of ‘screening’ ultrasound has the potential to identify minor abnormalities that would not otherwise have been found, leading to a cascade of costly testing and in some cases, physical or psychological harm.

In the FCM course, we will use ultrasound to identify surface landmarks and correlate physical exam maneuvers with anatomic structures. Our goal is to improve your understanding of both anatomy and the implications of exam findings, and to prepare you for further practice in your clerkships.

In Immersion, you will learn the basics, including how to operate the equipment, and identify key landmarks in the head and neck. We will identify structures in other organ systems in the advanced physical exam sessions in Term 2 and Term 3.

Point of Care Ultrasound Basics

Resources & references:

Ganguli I, Simpkin AL et al. Cascades of Care After Incidental Findings in a US National Survey of Physicians. JAMA Network Open. 2019;2(10):e1913325

Basic Principles of Ultrasound

Jul 20, 2014

720 likes | 1.65k Views

Basic Principles of Ultrasound. Objectives. Define Scope of Practice Understand Principals Understand Physics Understand Transducers Understand Terminology Understand Artifacts. Scope of Practice. eFAST in Trauma Abdomen Chest. Musculoskeletal/Soft tissue Fracture/dislocations.

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Presentation Transcript

Objectives • Define Scope of Practice • Understand Principals • Understand Physics • Understand Transducers • Understand Terminology • Understand Artifacts

Scope of Practice • eFAST in Trauma • Abdomen • Chest • Musculoskeletal/Soft tissue • Fracture/dislocations • Vascular • Access • Blood flow/DVT • Ocular • FB/retinal detachment • Retrobulbar hemorrhage • Genitourinary • Bladder • Ectopic pregnancy • scrotal pain & swelling

3-Tiers • Basic • eFAST, MSK, Skin/Soft Tissue, & Vascular Access • Intermediate • Ocular, Renal, Regional Anesthesia, & DVT • Advanced • OB/Gyn, Testicular, Aorta (AAA), Cardiac (Critical Care), & Pericardiocentesis

Basic Principles • Ultrasound machine and probes create sound waves • Generate waves of vibration from the probe that travel through the tissue of the patient and return to the probe • Received by the machine and interpreted to provide images on screen • Different tissue densities affect the ultrasound beam

Principles • The intensity of the returning echo determines the brightness of the image on the screen • Strong signals = white (hyperechoic) images • Weak signals or lack of signal all together = black (hypoechoic) images • Tissue densities determine the many shades of gray in between

Physics • Diagnostic ultrasound uses sound waves in the frequency range 2-20 MHz • Key properties of sound waves: • Frequency is number of times per second the sound wave is repeated • Wavelength is the distance traveled in 1 cycle • Amplitude is distance between peak and trough

Physics – Parallel Concepts • Conceptually, ultrasound is similar to a laser range finder. • Sound waves sent from the transducer bounce off the object and return. • The ultrasound machine calculates distance to the object from the round-trip time, and creates a grey scale image on the screen.

What does it mean to me? • Lower frequencies image deep structures, but sacrifice resolution. • Higher frequencies provide better resolution, but sacrifice depth. LOWER FREQUENCY Longer wavelength HIGHER FREQUENCY Shorter wavelength

Transducer Function • Ultrasound waves are generated by an electric current -> sent to the crystals -> excites the crystals which vibrate -> creating the resulting wave in the tissue • Beam is ~ 1mm

Transducer Characteristics • The workhorse of the US machine • Sends out sound waves 1% of the time • Listens for echoes 99% of the time • Frequencies are fixed or adjustable • “Footprint” is what touches the patient

Transducer Use • Hold the probe lightly in your hand • Like a pencil • Small movements equal big changes

Transducer Use • Probe marker facing the patient’s right or head • Exceptions: cardiac & procedures

Probe indicator – leading edge Generally to the patient’s head or right side.

Transducer Choices • Curvilinear Array (Curved Probe) • Freq range (5-2 MHz), 30cm depth • Abdomen, FAST, AAA • Linear Sequential Array (Linear Probe) • Freq range (10-5 MHz), 9cm depth • Vascular access, pneumothorax, regional anesthesia • Phased Array (Sector or Cardiac Probe) • Freq range (5-1 MHz), 35cm depth • Cardiac, eFAST, AAA

Transducer directions • Rotating • Fanning/Tilting • Rocking • Sliding • Compression

Transducer directions • Sliding

Transducer directions • Fanning/Tilting • Compression

Transducer directions • Rotation • Rocking

Scanning Planes

Scanning Planes Sagittal Axial

Screen Orientation Near Field Receding Edge Leading Edge Far Field

Image Quality – The 5 P’s • Use Plenty of Gel • Parallel to the table/stretcher • Perpendicular to structure • Pressure (right amount) • Scan in multiple Planes

Gel & Water Stand-offs

Ultrasound transmission gel USE LOTS OF IT!!!

Image Quality - Machine • Depth: Place the object of interest in the center of the screen • Machine will autofocus to the center of the screen giving it the best resolution • Right side markings show depth in cm • Gain: brightness of the image • Can be adjusted for each scan • Be careful not to use too much or too little gain • Autogain

Depth Too Little Too Much

Depth – JUST RIGHT!

Gain Too Little Too Much

Gain – Just Right!

Image Resolution • Spatial Resolution • The ability to distinguish two separate objects close together • Temporal Resolution • The ability to accurately locate structures or events at a specific point in time • Can be improved by decreasing depth & narrowing the sector angle

Spatial Resolution Axial Lateral The ability to distinguish two objects that are laying side-by-side Dependent upon the beam width Two objects cannot be distinguished if they are separated by less than the beam width High freq = narrow width Low freq = wider width • The ability to differentiate two separate objects in the axial plane • Determined by the pulse length • High freq = short length & better axial resolution • Low freq = long length and poor axial resolution

Scanning Modes • B-Mode: • Nearly all of your scans will begin and stay in this mode • Organs appear differently based on their tissue densities

Scanning Modes • M-Mode: • Motion mode provides a reference line on screen • Shows motion towards and away from probe at any depth along that line • Used for detecting fetal heartbeatsand pneumothoracies

Scanning Modes Spectral Doppler Color Flow Doppler Blue – Away : Red – Towards Power Doppler

Attenuation • As the ultrasound beam travels through the body, it looses strength & returns less signal • Certain tissue densities cause this effect: • Slow: Bone, Diaphragm, Pericardium & air = bright (Hyperechoic) images • Moderate: Muscle, Liver, Kidney = gray (Isoechoic) images • Faster: Blood, Ascites, Urine = Darker (Hypoechoic) images

Artifacts • Posterior Enhancement • Reverberation • Edge Artifact • Shadowing • Mirror Image • Comet Tail

Posterior Enhancement Hyperechoic streaking distal to interface of anechoic structure Not a true artifact

Reverberation Bouncing of signal from two reflective surfaces Often seen as a “needle artifact” during procedural ultrasound Called “Ring Down artifact” when seen with air in the bowel or soft tissue

Edge Artifact A distal shadow from the edge of spherical fluid filled structures Scan at different angles to reduce the artifact

Shadowing Anechoic streaking distal to surface with high reflectivity (behaves like light) Stones Bones

Mirror Image Appearance of same image on both sides of highly reflective surface Misinterpretation by machine of signal timing puts image where it thinks it “should be” Often seen on cardiac and around diaphragm

Comet Tail Pathognomonic for excluding pneumothorax

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Ultrasound: Explanation and Examples (KS3/SEN)

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StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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Ultrasound physics and instrumentation.

Scott P. Grogan ; Cristin A. Mount .

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Last Update: March 27, 2023 .

Definition/Introduction

Clinical ultrasound’s maximum utility as a diagnostic tool rests on understanding and manipulating multiple physics principles. The knowledge of ultrasound wave emission, interaction with fluid, tissue, various densities, wave receipt, and machine data processing are integral to ultrasound’s function. Ultrasound machines rely upon different probe types to emit sound waves at variable frequencies, depths, directions, focal points, and power in conjunction with motion and artifact management tools to enhance images obtained.

Understanding the physics of ultrasound is critical to applying clinical ultrasound, particularly as it applies to the optimization, interpretation, and clinical integration of images captured at the bedside. The American Institute of Ultrasound in Medicine has published a full, recommended curriculum to standardize the clinical sonographers’ education on both ultrasound physics principles and the primary clinical applications that depend on them. [1] [2]

Issues of Concern

Primary Ultrasound Physics Principles

The crucial physics principles needed to understand and optimize clinical ultrasound include frequency, propagation speed, pulsed ultrasound, waves’ interaction with tissue, angle of incidence, and attenuation. [3] Sound is mechanical energy that moves via alternating high and low-pressure waves through a medium. A sound source produces longitudinal wave oscillations, allowing the propagation of energy and critical waveforms for a clinical ultrasound. The high-pressure phase of a sound wave is the compression phase, whereas the low-pressure phase is rarefaction. In clinical ultrasound, the media involved are air, water, body fluid, soft tissues, blood, and bone.

Frequency refers to the number of cycles per second emitted by the probe over one second and is expressed in hertz (Hz). A period is the length of time for a complete wave cycle to occur (rarefaction and compression) and is inversely related to frequency. Similarly, the wavelength described is the distance between two adjacent wave peaks. It is important to distinguish the difference between period and wavelength; the former is a distance and the latter a length of time. [4] Ultrasound waves are conducted at a frequency greater than 20MHz, above the upper limit of human hearing. Frequency depends on the emission source and is entirely independent of the tissue that waves are interacting with. [3] Frequencies used in clinical ultrasound range from 1MHz to 20MHz, depending upon the probe used and the application desired. The frequency has a corresponding relationship with resolution and an inverse relationship with depth. The greater the frequency used, the lower the penetration, but the greater the image’s resolution. [5]

Amplitude is the height, or strength, of a wave defined by the distance between the peak and the average of the wave's highest and lowest points. Power in ultrasound refers to the square of wave amplitude, or difference between the maximum and average values, of propagated waves. [6] Both power and amplitude can be controlled by the sonographer and managed with gain adjustment. Power is measured in watts or milliwatts but can be displayed on the ultrasound machine either by decibels (dB) or the total acoustic power percentage. [4]

Intensity refers to the power delivered over a specific area, expressed in watts/cm2 or milliwatts/cm2. [4] The spatial peak is the location where intensity is at its greatest (highest power over the smallest area) and represents the focal point of ultrasound beams.

Decibels (dB) are a logarithmic expression of the ratio of two sound intensities. The dB can be determined by calculating the ratio of the sound source intensity and the least audible intensity, calculating the LOG, and multiplying it by 10. There is a simplified rule of 3dB that states with each 3dB gain. There must be an additional doubling of power delivered. Thus, a 3dB gain requires twice the power, a 6dB gain requires four times the power, and a 9dB gain requires eight times the power.

Propagation speed is the rate at which waves pass through a medium. The ultrasound waves’ speed is accepted to be 1540m/sec in soft tissue, known as acoustic impedance. Propagation speed depends on the characteristics of the medium that waves are traveling through and is independent of the frequency. As tissue density increases, the propagation speed decreases. By contrast, the stiffer the tissue, the higher the propagation speed. [4]

To achieve desired depth and resolution for clinical ultrasound, waves are emitted from the probe as pulses, typically a millisecond in duration and occurring up to several thousand times per second. This principle is referred to as pulsed ultrasound.

Ultrasound waves travel into tissue and are reflected back to the probe at a rate determined by the target tissue’s consistency. Reflections of sound that return to the probe are called echoes and are determined by two different materials' interfaces. [3] Images produced based on the echos give structures and media their varying densities on the screen, referred to as echogenicity. The more significant the difference in the density of two materials (tissue), the stronger the echo that will be produced. [3] Structures with higher density reflect more sound and are considered more echogenic (white). Thus, bone and dense foreign bodies reflect sound fully and appear bright on the screen, whereas fluids such as water or urine reflect no sound to the probe and appear anechoic (black). [6] Weak echos appear gray. When waves echo back to the probe from material such as bone and air, which cannot propagate sound, sound waves cannot pass to deeper tissue and a shadow behind the interface results.

The angle at which ultrasound waves engage with any structure is referred to as the angle of incidence. Structures are ideally imaged with the angle of incidence perpendicular to emitted waves because echoed waves return to the probe in the greatest concentration. [3] When waves interact with a structure obliquely, fewer waves echo back to the probe, decreasing both the structure brightness and resolution. Waves hitting a structure obliquely return to the probe at an angle equal to the angle initially striking the structure’s boundary. [3] If the angle is not directly perpendicular to the incidence angle, the wave will reflect away from the source. [4]

Similarly, waves are deflected from a straight line when waves’ velocity differs between two structures and results in refraction. [3] The original angle of incidence and the difference in the two media’s propagation speed determine the refraction's ultimate angle. Refraction is a source of artifacts in ultrasound, considering that all ultrasound machines operate under the assumption that waves will always travel and return in a straight line. [3]

Different tissue interfaces reflect differently and contribute to image quality. Smooth interfaces are considered specular reflectors and return a high proportion of waves to the transducer. Specular reflectors are contrasted against irregular interfaces called diffuse reflectors, which cause sound waves to reflect away from the transducer and reduce the image’s quality. An important type of scattering, called Rayleigh scattering, occurs when an object is smaller than the ultrasound beam’s wavelength. Red blood cells display this scattering type, resulting in waves scattering in all directions. [4]

Considering that ultrasound waves cannot travel through the air, probes must contact patients’ skin through a coupling medium to engage with tissues. Coupling occurs through the use of ultrasound gel or water baths. As ultrasound waves interact with tissue and reflect the probe, the energy associated with any remaining beams decreases with increasing depth. The strength of penetrating waves is reduced by refraction, scattering, and absorption. [5] When waves are scattered and energy absorbed, it results in vibration energy and heat. All of the processes that contribute to energy reduction are collectively referred to as attenuation.

Wave attenuation, or the decrease in intensity over a given distance, is also measured in decibels (dB) and occurs at a rate per centimeter roughly equal to the frequency emitted initially. Thus, a 5MHz wave will attenuate at approximately 5dB in the first centimeter and another 5bB in the next centimeter. Ultimate wave penetration is determined by the depth at which the intensity of the waves is reduced by 50%, in a reverse fashion used to determine the dB gain described above. Thus, the depth at which 50% of the intensity is attenuated is equivalent to a loss of 3dB. Higher frequency waves and waves for deep imaging are attenuated more quickly than low-frequency waves or waves used for shallow imaging. [4]

Gain (power) can be adjusted over the entire image or, depending on the machine being used, at different depths to visualize structures at those depths best. Additionally, deeper structures must use lower frequencies to become visible. Such visibility comes at the expense of resolution, which is improved with higher frequencies. Sonographers must manage the frequency being used to balance the need for both depth and resolution depending on the ultrasound application for any specific target structure.

Transducers

Transducers are the instruments that emit and receive ultrasound waves by way of electrical signal conversion to sound waves. Ultrasound transducers contain piezoelectric crystals that, when electrical impulses are applied, produce 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. The bandwidth of a particular probe is the range of frequencies at which the probe will operate.

Transducers can both send and receive ultrasound waves by applying energy and, ultimately sound waves, in pulses. The pulsatile nature of ultrasound waves produced facilitates the emission and reception of sound waves. When incident pulses reflect off tissues, producing echoes, the device can detect the strength, direction, and timing of arriving echoes. [3] The number of pulses produced in a single second is the pulsed repetition frequency (PRF), and the pulsed repetition period (PRP) is the time between the start of two pulses. The PRF and PRP, like with period and frequency described above, are inversely related to one another. Higher PRF will equal greater image resolution but shallower depths, whereas higher PRP and increased “listening” time from the transducer will allow greater depth. [4]

Typical transducers used in clinical ultrasound include linear array, phased array, and curvilinear array, which has multiple configurations and frequencies depending on the application needed. The transducer face’s crystals and structure's arrangement determine the area and shape of the image produced. Linear arrays have flat faces that produce a rectangular image. Phased arrays have crystal configurations and power sequences that steer beams from a single point to create a sector image ideal for scanning between ribs. [7] Curvilinear arrays have curved surfaces of various radii that also can be used across multiple bandwidths depending on the application desired. For example, low-frequency curvilinear transducers are often used for abdominal exams because of the deep penetration and wide field of view. In contrast, high-frequency endocavitary curvilinear transducers are used for female pelvic exams due to their high resolution and small footprints.

Managing Images

Selecting a probe with the appropriate bandwidth is an essential consideration to ideal image acquisition. For general scanning presets, machines are often set to “GEN,” or general, typically the middle range for the probe bandwidth. If higher resolution is required to evaluate a structure, the frequency can be increased on the machine directly or using available “RES” for resolution. The increased frequency will sacrifice penetration depth. The reverse is true if greater penetration is needed. Frequency is decreased directly or by using the “PEN” or penetration setting.

When attenuation must be managed, either because a target is too bright or too dark, power can be increased or decreased either throughout the entirety of the image or at specified depths. Gain increases will add power to combat attenuation by increasing the brightness. [5] Gain decreases lower the power and the overall brightness. When images are over-gained or under-gained, the resolution worsens.

Time Gain Compensation

Time gain compensation refers to power controls at specific image depths to combat the attenuation with depth. This helps improve deep structure imaging, mainly if deep tissue is subject to posterior acoustic enhancement. This feature is often seen with “slider bars” seen on the ultrasound console.

Depth of Field

The depth of field is the depth to which sound beams are transmitted and received. Depth is altered on display to optimize the power and temporal resolution of the machine to view target structures. [4] The depth must be significant enough to see deep structures when needed and shallow enough to see shallow structures with adequate resolution. When depth is set too deep for superficial examinations, the target structure image’s quality is degraded.

Focal Point and Resolution

Ultrasound beams leave the transducer at the same width as the face. They travel through the near zone before narrowing at a focal zone and widening in the far zone. The resolution, or the ability to discern two closely situated objects, and lateral resolution is best in the focal zone. Spatial resolution can also be improved with higher frequencies, smaller pulse repetition frequencies, and short pulse duration. The axial resolution, or the ability to discern two structures in the path of the beam, is generally better than lateral resolution, or the ability to distinguish two side-by-side structures due to ultrasound beams being shorter than they are wide. Lateral resolution is greatest at the focal point where the beam width is most narrow. Temporal resolution, or the time the machine takes to create an image, is inversely related to the frame rate. Higher frame rates produce lower resolution images, and lower frame rates have higher resolution images. Frame rates of at least 15 frames per second produce real-time images. [6] Temporal resolution is most important with moving objects, and if the frame rate is too low, supporting a high temporal resolution, the ability to detect motion diminishes. Additional augmentation tools, such as microbubbles, add resolution capability by strongly reflecting ultrasound beams, particularly in vasculature. [8]

Modern ultrasound transducers are created to send ultrasound signals out at multiple angles across the probe’s face. They produce multiple angles of incidence that have multiple angles of reflection back to the probe receiver. This helps to improve image quality, especially around structures that would otherwise be prone to refraction artifacts.

Tissue Harmonics

Tissue harmonics refers to tissue’s tendency to resonate at multiples of the incident frequency transmitted by the probe. For example, when 3MHz waves are transmitted to tissue, the tissue will resonate at 3MHz, 6MHz, and 9MHz. Transducers can be set to receive the incident frequency and the harmonic frequencies, combining them to create a higher resolution image. Using tissue harmonics settings also assists in reducing artifacts.

M-Mode, or time-motion display, allows a single beam to emit from the transducer along a defined track in conjunction with a recorder that captures all motion that occurs along the path. This mode allows high temporal resolution, thus affording the examiner an excellent view of subtle motions. [5] Clinically, this mode is ideal for capturing vessel diameter changes, movement of cardiac valves, and detecting fetal heartbeats.

Artifacts are image errors that are interpreted by the ultrasound machine related to the physics principles discussed previously. They are often the result of assumptions that ultrasound waves always travel in straight lines, that all tissue transmits sound at 1540 m/sec, and that waves are always reflected in the transducer directly. [9] Understanding artifacts' nature is vital to sonographers and those interpreting images because artifacts are often used as clues to detect specific pathologic findings.

Reverberations

Reverberation artifacts result from sound waves bouncing between a smooth reflector and the transducer face. [10] These appear as regularly spaced lines at intervals equal to the distance between the transducer and the structure. Common, normal findings resulting from reverberation artifact are “A lines” in lung fields.

Posterior Acoustic Enhancement

Fluid has a higher propagation rate and less attenuation than soft tissue. As a result, sound waves travel to and return from tissue deep to fluid-filled structures faster than sound waves in adjacent, non-fluid-filled structures. [10] When transducers receive sound more quickly and with higher intensity, the image produced behind the fluid-filled structure will appear bright compared to surrounding tissue. The hyperechoic signal may obscure detail in the tissue. A common application to illustrate posterior acoustic enhancement is bladder ultrasound, where time gain compensation must often be decreased to best evaluate tissues deep into the bladder. Unexpected posterior acoustic enhancement can also be a diagnostic clue that fluid is present in locations representing pathologic processes, such as in the abdomen or pleural space.

Structures of high density are highly reflective, returning the majority of sound waves to the transducer and allowing almost no waves to penetrate deep tissues. [3] The resulting structure image shows a bright, hyperechoic line or density with a dark, hypoechoic shadow behind it. Bone, metal, plastic, wood, glass, and calcium stones are of sufficient density to be so reflective and create “clean” shadows deep. On the other hand, while not dense, air also does not transmit ultrasound waves to deep structures. Air interfaces are also highly reflective but typically create less discernible shadows. Air interfaces with shadowing are typically noted in the lungs and within the bowels and may be referred to as "dirty" shadows.

When sound bounces off a strong, smooth reflector, the transducer may reflect the pulsed wave that causes the machine to believe that the tissue interface is deep and is the same as the tissue interface to the superficial structure. [3] [10] This is commonly seen with viewing the diaphragm through the liver, where machines will display the liver below and above the diaphragm.

Ring down artifacts occurs when tiny bubbles or crystals resonate at the same frequency as the emitted ultrasound frequency, which emits waves of their own. Sound received from these arrives after the original echoes and is interpreted by the machine as deep structures. [3] The resulting artifact appears as a hyperechoic line deep to the offending structure, often referred to as comet tails. Ring down artifacts is of diagnostic utility for cases of adenomyomatosis of the gallbladder when the gallbladder walls are infiltrated with cholesterol crystals. [10]

Refraction artifacts, often referred to as edge artifacts, occur when incident ultrasound waves interact with structure interfaces at angles other than 90 degrees. The difference in structure density promotes the refraction or bending of sound waves off the surface. The result is that echoes do not return to the transducer from an area expected to reflect echoes, and thus a shadow is produced. [9] This artifact is commonly seen when viewing round structures, such as the gallbladder, where shadows will follow the edges, corresponding to the walls as fanning occurs through it.

Clinical Significance

Diagnostic ultrasound is a powerful, minimally-invasive tool that improves the diagnostic accuracy of clinical examinations when employed at the bedside. Understanding ultrasound physics is critical to image acquisition, image optimization, image interpretation, and ultimately clinical integration. Once aware of ultrasound principles and how machines use them to manipulate sound waves, sonographers can best utilize the available tools to optimize the clinical utility of diagnostic ultrasound.

Specifically, the ability to discern normal from pathologic findings also requires understanding how sound waves interact with different tissues and how primary ultrasound functions are used to best display the differentiation. Sonographers who examine patients without applying ultrasound physics principles at the bedside competently will struggle to leverage the technology for timely and accurate diagnosis.

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Gallbladder short axis with stones Contributed by Scott Grogan, DO

Mirror artifact along anterior tibia behind a developing hematoma. Contributed by Scott Grogan, DO

Posterior acoustic enhancement artifact behind the eye. Structures behind a fluid-filled structure appear brighter than the tissue immediately adjacent due to the higher speed of sound waves traveling through fluid. Contributed by Scott Grogan, DO

M-Mode showing motion through a single beam path. In this case, the inferior vena cava shows subtle collapsibility that is more difficult to discern without M-Mode. Contributed by Scott Grogan, DO

Intrauterine device in short axis displaying hyperechoic reflection with deep shadowing. Contributed by Scott Grogan, DO

Disclosure: Scott Grogan declares no relevant financial relationships with ineligible companies.

Disclosure: Cristin Mount declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

Cite this Page Grogan SP, Mount CA. Ultrasound Physics and Instrumentation. [Updated 2023 Mar 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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Ultrasound Etiquette. Introduce yourself to your patient and ask permission to scan. Only expose the area of the body being scanned. Wipe the patient off after the exam is completed. Clean off the probe and cord. Soap and water.
A Beginner's Guide to Ultrasound
Clean the ultrasound probe. 4. Apply a tourniquet. 5. Apply gel to the ultrasound probe. 6. Identify the target vein in the transverse plane: note the depth of the anterior wall of the vein and pay attention to any adjacent structures. 7. Once identified, rotate the probe into the longitudinal plane.
PPT
Physics • Diagnostic ultrasound uses sound waves in the frequency range 2-20 MHz • Key properties of sound waves: • Frequency is number of times per second the sound wave is repeated • Wavelength is the distance traveled in 1 cycle • Amplitude is distance between peak and trough. Physics - Parallel Concepts • Conceptually ...
Basics of Ultrasound
Ultrasound works by using sound waves to create an image of organs and structures inside the body without having to open it up. It can be hard to understand for high school students, but not if you use this creative presentation design full of graphs, charts, illustrations and infographics!
Basics of Ultrasound
This imaging technique uses sound waves to create detailed images of organs, muscles and other inner structures, but how does it work? With these creative slides you can prepare the first introductory class for your engineering students and speak about the ultrasound technology, its fundaments and its applications in the medical field!
Ultrasound: Basic understanding and learning the language
INTRODUCTION. Ultrasound (US) use has rapidly entered the field of acute pain medicine and regional anesthesia and interventional pain medicine over the last decade, and it may even become the standard of practice.[] US guidance for nerve blocks and interventional pain management techniques may have several potential advantages over conventional landmark-based techniques that assume minimal ...
Ultrasound PPT PowerPoint Presentation
Therapeutic Ultrasound and Phonophoresis Chapman University, PT539 Summer 2019 Yvonne B. Brewer, DPT, MPT. Slide 2-. Principles of US Known as the "Reverse Piezoelectric Effect" Converts electrical current to mechanical energy as it passes through a piezoelectric crystal (e.g., quartz, barium titanate, and lead zirconate titanate) housed in ...
Ultrasound: Explanation and Examples (KS3/SEN)
The presentation introduces what ultrasound is and an explanation of what frequency is. There are clearly explained examples such as bat echolocation, SONAR and medical uses. There are learning checks within the PowerPoint, these being opportunities for students to write down information. The main purpose of this presentation is to explain the ...
Ultrasound Physics and Instrumentation
Clinical ultrasound's maximum utility as a diagnostic tool rests on understanding and manipulating multiple physics principles. The knowledge of ultrasound wave emission, interaction with fluid, tissue, various densities, wave receipt, and machine data processing are integral to ultrasound's function. Ultrasound machines rely upon different probe types to emit sound waves at variable ...
Tiger beetles produce anti-bat ultrasound and are probable Batesian
Upon hearing ultrasound, tiger beetles swing their elytra backwards contacting the leading edge of their beating hindwings producing ultrasonic clicks in time with their wingbeat frequency. ... We randomized presentation order of control and experimental species and scored palatability using a 0-6 scale [31,33]. For each insect, we recorded ...
Ultrasonography
Ultrasonography. Apr 20, 2015 • Download as PPTX, PDF •. 21 likes • 4,487 views. Sai Ram. Ultrasonography: Principle, Types and Applications. Education. 1 of 14. Download now. Ultrasonography - Download as a PDF or view online for free.