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50-918: (Redirected from A-scan ) Diagnostic test used in optometry or ophthalmology [REDACTED] This article needs more reliable medical references for verification or relies too heavily on primary sources . Please review the contents of the article and add the appropriate references if you can. Unsourced or poorly sourced material may be challenged and removed . Find sources:   "A-scan ultrasound biometry"  –  news   · newspapers   · books   · scholar   · JSTOR ( August 2018 ) [REDACTED] Medical diagnostic method A-scan ultrasound biometry Purpose diagnostic test used in optometry A-scan ultrasound biometry , commonly referred to as an A-scan (short for Amplitude scan ), uses an ultrasound instrument for diagnostic testing. A-scan biometry measures

100-489: A price of deeper tissue penetration. In anesthesiology , ultrasound is commonly used to guide the placement of needles when injecting local anesthetic solutions in the proximity of nerves identified within the ultrasound image (nerve block). It is also used for vascular access such as cannulation of large central veins and for difficult arterial cannulation . Transcranial Doppler is frequently used by neuro-anesthesiologists for obtaining information about flow-velocity in

150-500: A specific tumor or calculus is not an imaging mode. However, for positioning a treatment probe to focus on a specific region of interest, A-mode and B-mode are typically used, often during treatment. Compared to other medical imaging modalities, ultrasound has several advantages. It provides images in real-time, is portable , and can consequently be brought to the bedside. It is substantially lower in cost than other imaging strategies. Drawbacks include various limits on its field of view,

200-405: A useful hint to treat patients with symptoms related to pelvic prolapse, double incontinence and obstructed defecation. It is also used to diagnose and, at higher frequencies, to treat (break up) kidney stones or kidney crystals ( nephrolithiasis ). Scrotal ultrasonography is used in the evaluation of testicular pain , and can help identify solid masses. Ultrasound is an excellent method for

250-463: Is a common medical procedure. The need for intravenous access occurs in the outpatient laboratory, in the inpatient hospital units, and most critically in the Emergency Room and Intensive Care Unit. In many situations, intravenous access may be required repeatedly or over a significant time period. In these latter circumstances, a needle with an overlying catheter is introduced into the vein and

300-421: Is an essential tool in cardiology , assisting in evaluation of heart valve function, such as stenosis or insufficiency , strength of cardiac muscle contraction, and hypertrophy or dilatation of the main chambers. ( ventricle and atrium ) Point of care ultrasound has many applications in emergency medicine . These include differentiating cardiac from pulmonary causes of acute breathlessness , and

350-508: Is an unusually high eyelid height that is formed. One of the most troublesome complications of initial eyelid surgery is the surgeon discovering the patient has ptosis or a "drooping" eyelid after the surgery has been performed. It is also possible for a patient to develop ptosis as a result of an initial eyelid surgery operation. Both require eyelid revision surgeries. Since ptosis patients need correction of delicate anatomical tissues and structures, eyelid revision surgery on ptosis patients

400-437: Is called medical ultrasonography or simply sonography , or echography . The practice of examining pregnant women using ultrasound is called obstetric ultrasonography , and was an early development of clinical ultrasonography. The machine used is called an ultrasound machine , a sonograph or an echograph . The visual image formed using this technique is called an ultrasonogram , a sonogram or an echogram . Ultrasound

450-522: Is composed of sound waves with frequencies greater than 20,000 Hz, which is the approximate upper threshold of human hearing. Ultrasonic images, also known as sonograms, are created by sending pulses of ultrasound into tissue using a probe . The ultrasound pulses echo off tissues with different reflection properties and are returned to the probe which records and displays them as an image. A general-purpose ultrasonic transducer may be used for most imaging purposes but some situations may require

500-440: Is curable but must be treated to preserve health and fertility. There are two methods of performing pelvic sonography – externally or internally. The internal pelvic sonogram is performed either trans vaginally (in a woman) or transrectally (in a man). Sonographic imaging of the pelvic floor can produce important diagnostic information regarding the precise relationship of abnormal structures with other pelvic organs and it represents

550-533: Is different from Wikidata Ultrasonography Medical ultrasound includes diagnostic techniques (mainly imaging techniques) using ultrasound , as well as therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal body structures such as tendons , muscles , joints, blood vessels, and internal organs, to measure some characteristics (e.g., distances and velocities) or to generate an informative audible sound. The usage of ultrasound to produce visual images for medicine

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600-620: Is often used as image guidance for renal interventions. Furthermore, novel applications in renal US have been introduced with contrast-enhanced ultrasound (CEUS), elastography and fusion imaging. However, renal US has certain limitations, and other modalities, such as CT (CECT) and MRI, should be considered for supplementary imaging in assessing renal disease. Intravenous access, for the collection of blood samples to assist in diagnosis or laboratory investigation including blood culture, or for administration of intravenous fluids for fluid maintenance of replacement or blood transfusion in sicker patients,

650-499: Is routinely used in urology to determine the amount of fluid retained in a patient's bladder. In a pelvic sonogram, images include the uterus and ovaries or urinary bladder in females. In males, a sonogram will provide information about the bladder, prostate , or testicles (for example to urgently distinguish epididymitis from testicular torsion ). In young males, it is used to distinguish more benign testicular masses ( varicocele or hydrocele ) from testicular cancer , which

700-548: Is the initial imaging choice, avoiding radiation if possible, although it frequently needs to be followed by other imaging methods such as CT . Endoanal ultrasound is used particularly in the investigation of anorectal symptoms such as fecal incontinence or obstructed defecation . It images the immediate perianal anatomy and is able to detect occult defects such as tearing of the anal sphincter . Ultrasonography of liver tumors allows for both detection and characterization. Ultrasound imaging studies are often obtained during

750-476: Is therefore not a true tomographic representation of the body. Three-dimensional imaging is done by combining B-mode images, using dedicated rotating or stationary probes. This has also been referred to as C-mode . An imaging technique refers to a method of signal generation and processing that results in a specific application. Most imaging techniques are operating in B-mode. Therapeutic ultrasound aimed at

800-448: Is used at the bedside or examination table to evaluate a number of different lung abnormalities as well as to guide procedures such as thoracentesis , (drainage of pleural fluid (effusion)), needle aspiration biopsy, and catheter placement. Although air present in the lungs does not allow good penetration of ultrasound waves, interpretation of specific artifacts created on the lung surface can be used to detect abnormalities. Ultrasound

850-488: Is used for imaging flow in the intracerebral arteries. Intravascular ultrasound ( IVUS ) uses a specially designed catheter with a miniaturized ultrasound probe attached to its distal end, which is then threaded inside a blood vessel. The proximal end of the catheter is attached to computerized ultrasound equipment and allows the application of ultrasound technology, such as a piezoelectric transducer or capacitive micromachined ultrasonic transducer , to visualize

900-640: The Focused Assessment with Sonography for Trauma (FAST) exam , extended to include assessment for significant hemoperitoneum or pericardial tamponade after trauma ( EFAST ). Other uses include assisting with differentiating causes of abdominal pain such as gallstones and kidney stones . Emergency Medicine Residency Programs have a substantial history of promoting the use of bedside ultrasound during physician training. Both abdominal and endoanal ultrasound are frequently used in gastroenterology and colorectal surgery . In abdominal sonography,

950-425: The endothelium of blood vessels in living individuals. In the case of the common and potentially, serious problem of blood clots in the deep veins of the leg, ultrasound plays a key diagnostic role, while ultrasonography of chronic venous insufficiency of the legs focuses on more superficial veins to assist with planning of suitable interventions to relieve symptoms or improve cosmetics. Echocardiography

1000-3434: The eyes Anesthesia for eye surgery Eye surgery Oculoplastics Eye examination Adnexa Eyelids Blepharoplasty East Asian blepharoplasty Epicanthoplasty Eyelid revision Hughes procedure Tarsorrhaphy Lacrimal system Dacryocystorhinostomy Punctoplasty Globe Refractive surgery Alpins method Automated lamellar keratoplasty Conductive keratoplasty Corneal inlay Epikeratophakia Epi-LASIK Intrastromal corneal ring segment Keratomileusis Laser blended vision Laser eye surgery Laser thermal keratoplasty LASIK Contoura Vision Limbal relaxing incisions Phakic intraocular lens implantation Photorefractive keratectomy Radial keratotomy SMILE Cataract surgery Capsulorhexis Capsulotomy Glued intraocular lens Hydrodelineation Hydrodissection Intraocular lens scaffold Manual small incision cataract surgery Phacoemulsification Prechop Retinal surgery Ignipuncture Laser photocoagulation Scleral buckle Glaucoma surgery Cyclodestruction Excimer laser trabeculostomy Minimally invasive glaucoma surgery Trabeculectomy Trabeculoplasty Transplantation Whole eye transplantation Corneal transplantation Corneal button Descemet membrane endothelial keratoplasty Pre-Descemet's endothelial keratoplasty Other Anterior chamber paracentesis Boston keratoprosthesis Corneal collagen cross-linking Enucleation Conformer Evisceration Gundersen flap Intravitreal injection Iridectomy Peritomy Photodisruption Phototherapeutic keratectomy Pterygium Sclerotomy Vitrectomy Extraocular muscles Harada–Ito procedure Strabismus surgery Minimally invasive strabismus surgery Botulinum toxin therapy of strabismus Medical imaging Corneal topography Electrodiagnosis Electronystagmography Electrooculography Electroretinography Fluorescein angiography Fundus photography Heidelberg Retinal Tomography Indocyanine green angiography Optical coherence tomography Optical coherence tomography angiography Eye examination A-scan ultrasound biometry Amsler grid Bagolini Striated Glasses Test Color perception test Dilated fundus examination Funduscopy Gonioscopy Ocular tonometry Ophthalmoscopy Retinoscopy Slit-lamp examination Visual field test Radiation therapy Plaque radiotherapy History Couching Cryoextraction Retrieved from " https://en.wikipedia.org/w/index.php?title=A-scan_ultrasound_biometry&oldid=1250637350 " Categories : Diagnostic ophthalmology Medical ultrasonography Hidden categories: Articles with short description Short description matches Wikidata Articles needing additional medical references from August 2018 All articles needing additional references Articles requiring reliable medical sources Short description

1050-440: The transducer at the desired frequency. The frequencies can vary between 1 and 18 MHz , though frequencies up to 50–100 megahertz have been used experimentally in a technique known as biomicroscopy in special regions, such as the anterior chamber of the eye. Older technology transducers focused their beam with physical lenses. Contemporary technology transducers use digital antenna array techniques (piezoelectric elements in

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1100-777: The absence of sonography. It is currently believed that the risk of delayed diagnosis is greater than the small risk, if any, associated with undergoing an ultrasound scan. However, its use for non-medical purposes such as fetal "keepsake" videos and photos is discouraged. Obstetric ultrasound is primarily used to: According to the European Committee of Medical Ultrasound Safety (ECMUS) Ultrasonic examinations should only be performed by competent personnel who are trained and updated in safety matters. Ultrasound produces heating, pressure changes and mechanical disturbances in tissue. Diagnostic levels of ultrasound can produce temperature rises that are hazardous to sensitive organs and

1150-599: The application and interpretation of medical imaging modalities, or by cardiologists in the case of cardiac ultrasonography ( echocardiography ). Sonography is effective for imaging soft tissues of the body. Superficial structures such as muscle , tendon , testis , breast , thyroid and parathyroid glands, and the neonatal brain are imaged at higher frequencies (7–18 MHz), which provide better linear (axial) and horizontal (lateral) resolution . Deeper structures such as liver and kidney are imaged at lower frequencies (1–6 MHz) with lower axial and lateral resolution as

1200-855: The axial length (AL) of the eye prior to cataract surgery in order to assess the refractive power of the intraocular lens that will be implanted. See also [ edit ] B-scan ultrasonography Ultrasonography References [ edit ] ^ Waldron, Rhonda G (2022-08-10). "A-Scan Biometry: Practice Essentials, Ultrasound Principles, Ultrasound Biometry Instrumentation" . Medscape Reference . Retrieved 2024-08-10 . ^ Petrella, Lorena; Perdigão, Fernando; Caixinha, Miguel; Santos, Mário; Lopes, Maria; Gomes, Marco; Santos, Jaime (2021). "A-scan ultrasound in ophthalmology: A simulation tool". Medical Engineering & Physics . 97 : 18–24. doi : 10.1016/j.medengphy.2021.09.005 . PMID   34756334 . v t e Tests and procedures involving

1250-424: The basal cerebral vessels . In angiology or vascular medicine, duplex ultrasound (B Mode imaging combined with Doppler flow measurement) is used to diagnose arterial and venous disease. This is particularly important in potential neurologic problems , where carotid ultrasound is commonly used for assessing blood flow and potential or suspected stenosis in the carotid arteries , while transcranial Doppler

1300-578: The catheter is then inserted securely into the vein while the needle is withdrawn. The chosen veins are most frequently selected from the arm, but in challenging situations, a deeper vein from the neck ( external jugular vein ) or upper arm ( subclavian vein ) may need to be used. There are many reasons why the selection of a suitable vein may be problematic. These include, but are not limited to, obesity, previous injury to veins from inflammatory reaction to previous 'blood draws', previous injury to veins from recreational drug use. In these challenging situations,

1350-415: The chosen vein. Ultrasound training for intravenous cannulation is offered in most ultrasound training programs. The creation of an image from sound has three steps – transmitting a sound wave , receiving echoes , and interpreting those echoes. A sound wave is typically produced by a piezoelectric transducer encased in a plastic housing. Strong, short electrical pulses from the ultrasound machine drive

1400-399: The embryo/fetus. Biological effects of non-thermal origin have been reported in animals but, to date, no such effects have been demonstrated in humans, except when a micro-bubble contrast agent is present. Nonetheless, care should be taken to use low power settings and avoid pulsed wave scanning of the fetal brain unless specifically indicated in high risk pregnancies. Figures released for

1450-464: The evaluation process of Fatty liver disease . Ultrasonography reveals a "bright" liver with increased echogenicity. Pocket-sized ultrasound devices might be used as point-of-care screening tools to diagnose liver steatosis. Gynecologic ultrasonography examines female pelvic organs (specifically the uterus , ovaries , and fallopian tubes ) as well as the bladder , adnexa , and pouch of Douglas . It uses transducers designed for approaches through

1500-415: The head and neck can be differentiated, evaluated, and managed with the help of diagnostic ultrasound and ultrasound-guided procedures. In neonatology , transcranial Doppler can be used for basic assessment of intracerebral structural abnormalities, suspected hemorrhage, ventriculomegaly or hydrocephalus and anoxic insults ( periventricular leukomalacia ). It can be performed through the soft spots in

1550-407: The insertion of a catheter into a vein has been greatly assisted by the use of ultrasound. The ultrasound unit may be 'cart-based' or 'handheld' using a linear transducer with a frequency of 10 to 15 megahertz . In most circumstances, choice of vein will be limited by the requirement that the vein is within 1.5 cms. from the skin surface. The transducer may be placed longitudinally or transversely over

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1600-423: The kidneys is essential in the diagnosis and management of kidney-related diseases. The kidneys are easily examined, and most pathological changes are distinguishable with ultrasound. It is an accessible, versatile, relatively economic, and fast aid for decision-making in patients with renal symptoms and for guidance in renal intervention. Using B-mode imaging , assessment of renal anatomy is easily performed, and US

1650-466: The lateral resolution decreases. Therefore, the wider the transducer width and the higher the frequency of ultrasound, the longer the Fresnel zone, and the lateral resolution can be maintained at a greater depth from the transducer. Ultrasound waves travel in pulses. Therefore, a shorter pulse length requires higher bandwidth (greater number of frequencies) to constitute the ultrasound pulse. As stated,

1700-443: The layers between different tissues or scattered from smaller structures. Specifically, sound is reflected anywhere where there are acoustic impedance changes in the body: e.g. blood cells in blood plasma , small structures in organs, etc. Some of the reflections return to the transducer. The return of the sound wave to the transducer results in the same process as sending the sound wave, in reverse. The returned sound wave vibrates

1750-474: The lower abdominal wall, curvilinear and sector, and specialty transducers such as transvaginal ultrasound . Obstetrical sonography was originally developed in the late 1950s and 1960s by Sir Ian Donald and is commonly used during pregnancy to check the development and presentation of the fetus . It can be used to identify many conditions that could be potentially harmful to the mother and/or baby possibly remaining undiagnosed or with delayed diagnosis in

1800-399: The major organs of the abdomen such as the pancreas , aorta , inferior vena cava , liver , gall bladder , bile ducts , kidneys , and spleen may be imaged. However, sound waves may be blocked by gas in the bowel and attenuated to differing degrees by fat, sometimes limiting diagnostic capabilities. The appendix can sometimes be seen when inflamed (e.g.: appendicitis ) and ultrasound

1850-437: The neck, including the thyroid and parathyroid glands , lymph nodes , and salivary glands , are well-visualized by high-frequency ultrasound with exceptional anatomic detail. Ultrasound is the preferred imaging modality for thyroid tumors and lesions, and its use is important in the evaluation, preoperative planning, and postoperative surveillance of patients with thyroid cancer . Many other benign and malignant conditions in

1900-635: The need for patient cooperation, dependence on patient physique, difficulty imaging structures obscured by bone , air or gases, and the necessity of a skilled operator, usually with professional training. Sonography (ultrasonography) is widely used in medicine . It is possible to perform both diagnosis and therapeutic procedures , using ultrasound to guide interventional procedures such as biopsies or to drain collections of fluid, which can be both diagnostic and therapeutic. Sonographers are medical professionals who perform scans which are traditionally interpreted by radiologists, physicians who specialize in

1950-524: The newborn, respiratory distress syndrome, congenital pneumonia, meconium aspiration syndrome, and pneumothorax. A neonatal lung ultrasound score, first described by Brat et al., has been found to highly correlate with oxygenation in the newborn. In ophthalmology and optometry , there are two major forms of eye exam using ultrasound: Ultrasound is used to assess the lungs in a variety of settings including critical care, emergency medicine, trauma surgery, as well as general medicine. This imaging modality

2000-682: The period 2005–2006 by the UK Government (Department of Health) show that non-obstetric ultrasound examinations constituted more than 65% of the total number of ultrasound scans conducted. Blood velocity can be measured in various blood vessels, such as middle cerebral artery or descending aorta , by relatively inexpensive and low risk ultrasound Doppler probes attached to portable monitors. These provide non-invasive or transcutaneous (non-piercing) minimal invasive blood flow assessment. Common examples are transcranial Doppler , esophageal Doppler and suprasternal Doppler . Most structures of

2050-406: The result of poor wound closure during the procedure. One of the most frequent complications that arise from an initial eyelid surgery is asymmetry, which are often a result of poor markings by the surgeon prior to operation. Unusually high eyelid heights can make the results of an original eyelid revision procedure appear unnatural. Thus, an initial blepharoplasty may need revision if there

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2100-451: The skull of a newborn infant ( Fontanelle ) until these completely close at about 1 year of age by which time they have formed a virtually impenetrable acoustic barrier to ultrasound. The most common site for cranial ultrasound is the anterior fontanelle. The smaller the fontanelle, the more the image is compromised. Lung ultrasound has been found to be useful in diagnosing common neonatal respiratory diseases such as transient tachypnea of

2150-413: The sound is focused either by the shape of the transducer, a lens in front of the transducer, or a complex set of control pulses from the ultrasound scanner, in the beamforming or spatial filtering technique. This focusing produces an arc-shaped sound wave from the face of the transducer. The wave travels into the body and comes into focus at a desired depth. Materials on the face of the transducer enable

2200-408: The sound to be transmitted efficiently into the body (often a rubbery coating, a form of impedance matching ). In addition, a water-based gel is placed between the patient's skin and the probe to facilitate ultrasound transmission into the body. This is because air causes total reflection of ultrasound; impeding the transmission of ultrasound into the body. The sound wave is partially reflected from

2250-409: The study of the penis , such as indicated in trauma, priapism, erectile dysfunction or suspected Peyronie's disease . Musculoskeletal ultrasound is used to examine tendons, muscles, nerves, ligaments, soft tissue masses, and bone surfaces. It is helpful in diagnosing ligament sprains, muscles strains and joint pathology. It is an alternative or supplement to x-ray imaging in detecting fractures of

2300-415: The transducer and the transducer turns the vibrations into electrical pulses that travel to the ultrasonic scanner where they are processed and transformed into a digital image. To make an image, the ultrasound scanner must determine two characteristics from each received echo: Eyelid revision Contour abnormalities are also a common cause of eyelid revision surgery. Contour abnormalities are often

2350-449: The transducer produce echoes at different times) to enable the ultrasound machine to change the direction and depth of focus. Near the transducer, the width of the ultrasound beam almost equals to the width of the transducer, after reaching a distance from the transducer (near zone length or Fresnel zone ), the beam width narrows to half of the transducer width, and after that the width increases (far zone length or Fraunhofer's zone ), where

2400-472: The use of a specialized transducer. Most ultrasound examination is done using a transducer on the surface of the body, but improved visualization is often possible if a transducer can be placed inside the body. For this purpose, special-use transducers, including transvaginal , endorectal, and transesophageal transducers are commonly employed. At the extreme, very small transducers can be mounted on small diameter catheters and placed within blood vessels to image

2450-412: The walls and disease of those vessels. The imaging mode refers to probe and machine settings that result in specific dimensions of the ultrasound image. Several modes of ultrasound are used in medical imaging: Most machines convert two-way time to imaging depth using as assumed speed of sound of 1540 m/s. As the actual speed of sound varies greatly in different tissue types, an ultrasound image

2500-487: The wrist, elbow and shoulder for patients up to 12 years ( Fracture sonography ). Quantitative ultrasound is an adjunct musculoskeletal test for myopathic disease in children; estimates of lean body mass in adults; proxy measures of muscle quality (i.e., tissue composition) in older adults with sarcopenia Ultrasound can also be used for needle guidance in muscle or joint injections , as in ultrasound-guided hip joint injection . In nephrology , ultrasonography of

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