Ultrasonography is an imaging technique used in medicine for the imaging of subcutaneous body structures, blood vessels, joints, and internal organs to exclude structural pathologies. This technique is based on the utilization of ultrasound (or high-frequency, inaudible sound waves). In medical imaging, the sound waves have a frequency of 2–18 megahertz (MHz). The equipment utilizes a transducer acting as the emitter and receptor Receptor Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors of sound waves, and a central computer processes the electrical signals to generate the image. The general advantages of this type of imaging is its low cost, availability, and safety. Some specialties that rely heavily on ultrasound examination are cardiology, nephrology, general surgery, gastroenterology, emergency medicine, and obstetrics.
Last updated: 6 May, 2022
Types of transducers:
Note that decreasing the frequency increases the depth to which the ultrasound wave travels. However, this comes at the cost of image resolution.
An ultrasound machine and different probes
Image: “Photos of a sonography Sonography The visualization of deep structures of the body by recording the reflections or echoes of ultrasonic pulses directed into the tissues. Use of ultrasound for imaging or diagnostic purposes employs frequencies ranging from 1. 6 to 10 megahertz. Diagnostic Procedures in Gynecology system and typical transducers.” by Kieran Maher. License: Public DomainThe main principle behind ultrasound imaging is the transmission and reflection of sound waves through the tissues.
Ultrasound waves and the tissues:
The diagram shows that as the ultrasound wave beam (blue horizontal bar) penetrates the tissues, a percentage is reflected back (left arrows) toward the transducer while another continues to go deeper into the tissues (right arrow), losing some energy to the parenchyma as it goes.
Imaging planes:
Types of images:
Image definition or sharpness of the image generated can be characterized in terms of:
Image definition is also determined by how close objects are to the transducer; according to their frequencies, probes have a near and a far field of “ vision Vision Ophthalmic Exam”:
Near and far fields of a transducer in ultrasound imaging:
Note how, in the near field, the transducer has an adequate lateral definition, being able to distinguish between 2 points. On the other
hand
Hand
The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves.
Hand: Anatomy, in the far field, increasing
axial
Axial
Computed Tomography (CT) definition (depth) sacrifices lateral definition.
Different planes of fetal ultrasound imaging:
Top left:
Sagittal
Sagittal
Computed Tomography (CT) plane
Top right:
Coronal
Coronal
Computed Tomography (CT) plane
Bottom left:
Axial
Axial
Computed Tomography (CT) plane
Bottom right: Non–fetal facial standard plane (FFSP)
Doppler ultrasound (or just “Doppler”) is a widely used ultrasound method based on the principle of sound-wave compression Compression Blunt Chest Trauma and dilation relative to the receptor Receptor Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors. Doppler ultrasound is most commonly used to visualize blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure.
The interpretation of ultrasound images is done in real time, while the examination is being performed.
A: Urinary ultrasound showing right-sided
hydronephrosis
Hydronephrosis
Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients.
Hydronephrosis and the irregular upper section of the right ureter
B: Gynecologic ultrasound showing a
cystic
Cystic
Fibrocystic Change
mass
Mass
Three-dimensional lesion that occupies a space within the breast
Imaging of the Breast (8.8  X 7.5  X  8.6  cm) in the right rear
uterus
Uterus
The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina.
Uterus, Cervix, and Fallopian Tubes: Anatomy
Note that both findings are hypoechoic to anechoic because of their liquid content
Transvaginal ultrasound
Transvaginal Ultrasound
Obstetric Imaging showing a polycystic ovary:
Note the multiple
cysts
Cysts
Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues.
Fibrocystic Change on the periphery of the ovary (white arrow)
Example of a nonspecific hypoechoic structure on an ultrasound of the right breast, which could represent a malignancy Malignancy Hemothorax, an abscess Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease, or a benign Benign Fibroadenoma tumor Tumor Inflammation, depending on the clinical scenario
Image by Hetal Verma.Example of a thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy nodule Nodule Chalazion containing internal calcifications, depicted as hyperechoic foci on an ultrasound of the thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy gland
Image by Hetal Verma.By convention, in color Doppler:
Color Doppler and spectral Doppler examination of the left internal carotid artery Internal carotid artery Branch of the common carotid artery which supplies the anterior part of the brain, the eye and its appendages, the forehead and nose. Carotid Arterial System: Anatomy revealing stenoses of about 70%
Image: “Color Doppler and spectral Doppler examination of the left ICA ICA Diabetes Mellitus” by Christian Arning et al AL Amyloidosis. License: CC BY 2.0Doppler ultrasound of the
carotid arteries
Carotid Arteries
Either of the two principal arteries on both sides of the neck that supply blood to the head and neck; each divides into two branches, the internal carotid artery and the external carotid artery.
Carotid Arterial System: Anatomy showing
carotid stenosis
Carotid stenosis
Narrowing or stricture of any part of the carotid arteries, most often due to atherosclerotic plaque formation. Ulcerations may form in atherosclerotic plaques and induce thrombus formation. Platelet or cholesterol emboli may arise from stenotic carotid lesions and induce a transient ischemic attack; cerebrovascular accident; or temporary blindness (amaurosis fugax).
Transient Ischemic Attack (TIA):
A
plaque
Plaque
Primary Skin Lesions can be seen obstructing < 40% of the lumen, and hyperechoic foci within the vessel wall can be seen, probably due to calcification
Doppler ultrasound of the right testicle:
Note the difference in color for
flow
Flow
Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.
Vascular Resistance, Flow, and Mean Arterial Pressure coming toward the transducer (red) and
flow
Flow
Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.
Vascular Resistance, Flow, and Mean Arterial Pressure away from the transducer (blue).
Spectral Doppler ultrasound of the right testicle:
A graph of the
flow
Flow
Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls.
Vascular Resistance, Flow, and Mean Arterial Pressure appears at the bottom of the image.
Artifacts are artificial objects produced by the equipment’s misinterpretation of sound-wave data coming back from the tissues that do not represent actual structures.
Some examples of artifacts are:
Ultrasound from a patient with
acute cholecystitis
Acute cholecystitis
Acute inflammation of the gallbladder wall. It is characterized by the presence of abdominal pain; fever; and leukocytosis. Gallstone obstruction of the cystic duct is present in approximately 90% of the cases.
Cholecystitis:
Multiple
gallstones
Gallstones
Cholelithiasis (gallstones) is the presence of stones in the gallbladder. Most gallstones are cholesterol stones, while the rest are composed of bilirubin (pigment stones) and other mixed components. Patients are commonly asymptomatic but may present with biliary colic (intermittent pain in the right upper quadrant).
Cholelithiasis are visualized within the
gallbladder
Gallbladder
The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile.
Gallbladder and Biliary Tract: Anatomy lumen with
gallbladder
Gallbladder
The gallbladder is a pear-shaped sac, located directly beneath the liver, that sits on top of the superior part of the duodenum. The primary functions of the gallbladder include concentrating and storing up to 50 mL of bile.
Gallbladder and Biliary Tract: Anatomy wall thickening and
pericholecystic fluid
Pericholecystic Fluid
Imaging of the Liver and Biliary Tract. Shadowing can be seen behind the gallstone.
Pros | Cons CoNS Staphylococcus |
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Indications:
There are no contraindications Contraindications A condition or factor associated with a recipient that makes the use of a drug, procedure, or physical agent improper or inadvisable. Contraindications may be absolute (life threatening) or relative (higher risk of complications in which benefits may outweigh risks). Noninvasive Ventilation for ultrasound imaging.
Radiography | CT | Ultrasound | MRI | |
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Mechanism of acquisition | Ionizing radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma | Ionizing radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma | Acoustic energy | Ferromagnetic pulses |
Relative cost | Inexpensive | Expensive | Inexpensive | Very expensive |
Portable | Yes | No | Yes | No |
Length of exam | Seconds | < 1 minute | Seconds | Approximately 1 hour |
Contrast | No | May be needed | May be needed | May be needed |