Advances in Pediatric Emergency Ultrasound: Procedural Applications in the Adolescent and Child as an Aid to Diagnosis of Traumatic Conditions
Authors: Resa E. Lewiss, MD, RDMS, Director, Division of Emergency Ultrasound, St. Luke’s Roosevelt Hospital Center, Columbia University College of Physicians and Surgeons, New York, NY; and Anthony J. Weekes, MD, RDMS, Associate Medical Director, Emergency Ultrasound Director, Montefiore Medical Center, Bronx, NY
Peer Reviewer: Robert E. Falcone, MD, President, Grant Medical Center, Columbus, OH
Emergency physicians (EPs) increasingly are recognizing the advantages of the use of ultrasound in the emergency department (ED) to aid with clinical diagnosis, management, and disposition of patients.
Applications particularly useful in the pediatric and adolescent patient populations will continue to gain wider recognition and acceptance by the physician community. Most ultrasound examinations are quick and simple to perform, and ED physicians can gain comfort and facility in performing these focused applications.
In two prior issues, the authors have reviewed applications of ultrasound in the nontrauma setting. Safety concerns and the inherent difficulties with pediatric procedures have led to the expansion of ultrasound into this arena. Improved patient safety and ease of performance has resulted in ultrasound being applied routinely to commonly performed procedures in the ED, including central access, lumbar puncture, incision and drainage of abscesses, foreign body removal, and arthrocentesis. — The Editor
Introduction
Bedside ultrasound is recognized as indispensable to the emergency physician (EP). Limited off-hour radiology resources, expanding clinical applications and patient safety have led to ultrasound becoming a mandated part of emergency medicine residency training. Numerous studies substantiate the ability of the EP to perform bedside ultrasound studies, interpret the results accurately, and use the data to answer clinical questions. In doing so, patient length of stay decreases.1-6 The American Academy of Emergency Medicine, American College of Emergency Physicians, and Society for Academic Emergency Medicine have issued policies on the applications of sonography in emergency medicine.7-9 At this time, emergency ultrasound is considered an integral part of emergency medicine training programs in North America, but it is not currently a training requirement for those pursuing a pediatric emergency medicine fellowship. Moreover, ultrasound is increasingly used by pediatric subspecialists in the evaluation of ill or injured children. This article provides an overview of ultrasound-guided procedures; indications, contraindications and techniques for each procedure.
For the definition and explanation of specific sonographic terms used throughout the paper, please refer to the glossary at the end of this article.
Procedural Applications
Vascular Access. Although central vascular access is not a commonly performed procedure in the pediatric and adolescent populations, it is an extremely challenging and critical skill for the EP. Currently, there is increasing emphasis on techniques that decrease medical error; studies support ultrasound guidance for vascular procedures because of time efficiency, and decreased failure rates, complications, and number of attempts needed.10-16 In addition, the U.S. Department of Health and Human Services in its 2001 Agency for Healthcare Research and Quality (AHRQ) report recommended that central venous cannulation be performed under ultrasound-guidance to minimize complications.17 To accurately and efficiently use ultrasound-guided or assisted procedures for an internal jugular or femoral venous catheter requires experience and familiarity with the anatomy present in the area that access is being attempted (Figure 1). The technique for the internal jugular vein is described below and may be extrapolated for access to the femoral vein. The femoral vein technique has been described in the pediatric literature and shows decreased complications and increased successful first-pass rates.18 Ultrasound-guided access to the subclavian vessels will not be discussed in this paper; it is performed rarely by the EP in this population.
Procedure. Position the patient in the usual recommended position and set up the central venous access equipment according to the usual standard sterile technique.
Static one-person technique. For the static one-person technique, place the high frequency linear probe in the transverse plane with the probe marker to the patient’s right just superior to the clavicle between the sternal and clavicular heads of the sternocleidomastoid muscle. Using pulse Doppler waveforms, vessel wall thickness, size, compressibility, distensibility with Valsalva maneuvers, identify the internal jugular vein on the right side of the screen as compared with the carotid artery on the left. Place the internal jugular vein in the center of the screen. The center of the screen corresponds to the center of the probe. Note the hatch marks on the left side of the monitor screen to measure the approximate depth to the vessel. From the center of the probe, measure on the skin that hatchmarked distance in a cephalad direction on the patient. Put down the probe. At this mark, enter the skin at a 45° angle. According to the Pythagorean theorem (rule of right angles), the length of needle penetration path (A) is calculated usingthe formula: A2 = B2 + C2, where B is the depth of the target blood vessel and C is the horizontal distance the needle moves to get to the vessel. Successful vascular access is confirmed with a flashback of dark venous blood.
Dynamic two-person technique. For the dynamic two-person technique, locate the internal jugular vein in a similar fashion to that described above. Create a sterile probe and maintain a strictly sterile field, including a sterile gown and gloves for the sonographer. With the center of the probe corresponding to the center of the screen showing the centered internal jugular vein, the EP should aim the needle toward the center of the probe. The sonographer should concentrate on keeping the vein centered. Visualize the linear hyperechoic needle and/or tenting of the vessel immediately prior to puncturing the vessel (Figures 2A, 2B, 2C). Advancement of the guidewire with the Seldinger technique also will be visible. At this point, the operator should remove the probe from the patient, and the EP should continue the procedure.19
Lumbar Puncture (LP). Ultrasound assisted lumbar puncture may be considered in the care of an obese child or adolescent, especially when the spinous processes are not able to be palpated, making it a blind procedure. Advantages are similar to those for other procedures: most notably time savings and avoiding fluoroscopic radiation exposure. Dynamic sonographic guidance of spinal needle placement has been well described in obstetric patients.20-22 Studies in obstetric patients especially support this application as a means of estimating the depth to reaching the intended spinal space.22-26 Ultrasound also may be used to choose an optimal patient position for widening the space and maximizing the chance of successful LP.27,28 Fewer needle stick attempts are needed, and patients are more satisfied.29 One study described a role in failed LPs in neonates and infants; ultrasound may identify hematomas from failed attempts.30
Procedure. Depending upon the size of the patient, a high frequency linear or medium frequency curvilinear probe may be utilized. Using standard technique, locate the bony landmarks for lumbar puncture. Place the probe in a longitudinal orientation with the probe marker pointing cephalad and identify the L3-L4, and L4-L5 interspaces. Optimal images can be obtained with the probe in a paraspinal location not on top of the spinous processes.23 Note the bony vertebral processes that appear hyperechoic and the more hypoechoic area between the two bright echoes corresponding to the disc interspace (Figure 3). Adjust the probe so that the disc interspace falls in the middle of the screen. Freeze the image on the screen. Mark the skin at the center of the probe. This correlates with the center of the interspace. Estimate the distance to the epidural space by using the hatch marks on the left side of the monitor screen. This measurement correlates with the approximate depth you will need to advance the needle before reaching the space.
Musculoskeletal and Dermatoskeletal Applications. Ultrasound is a quick accessible imaging tool for the EP for patients presenting with traumatic symptoms of the musculoskeletal and dermatoskeletal systems. Although magnetic resonance imaging (MRI) is unprecedented in terms of anatomy and anatomic relationship depiction, this imaging modality often is not readily available to the EP. Moreover, obtaining an MRI scan of an uncooperative child or patient in pain likely will require sedation and unquestionably a time delay. Since the physical examination is not always helpful in directing how to proceed in patient evaluation, sonography can guide toward appropriate radiological testing and consultative services. Ultrasound is fast at the bedside and carries the advantage of image acquisition in conjunction with the physical examination. In addition, ultrasound is a helpful tool in guiding procedures such as arthrocentesis, abscess drainage, and foreign body localization and removal.31, 32
Broadly speaking, swollen structures should be imaged in both longitudinal and transverse planes to clarify the anatomy of interest and neighboring structures. Use of a compression and decompression technique is important when evaluating fluid in a joint or bursa, fluid movement, vascular structures, tendon defects and distinguishing a point of maximal tenderness.33
Abscess. Using a high frequency probe, the EP can learn to distinguish skin layers such as the dermis and epidermis, which appear hyperechoic and bright as a single layer relative to the underlying subcutaneous fat, which appears more hypoechoic. When evaluating superficial structures, consider using an acoustic stand-off pad for better visualization of the skin structures. Sonolucent sonographic stand-off pads lessen the transducer’s near field or dead zone and improve image quality. Stand-off pads are available commercially or can be created with a 500-cc intravenous fluid bag with air pockets removed or alternatively with a gel-filled glove. Systematically scan in two planes and avoid excessive pressure on the probe, which may cause vessel collapse.
Cellulitis appears as nonspecific tissue thickening in subcutaneous tissues layers causing tissue distortion. Essentially, the superficial skin layers are swollen with fluid and may appear hyperechoic. A focused layer of hypoechoic, dark fluid consistent with blood or pus is not visualized. Findings are nonspecific, and comparison with the unaffected side is important.34
Ultrasound also may help locate an abscess within an area of cellulitis or indurated tissue when the clinical findings are ambiguous. Liquid may be distinguished from solid material, and the depth and size of the collection can be measured for drainage. Sonographic evaluation of the skin also helps in localization of an optimal spot for aspiration or incision and drainage.34,35
Utilize a high frequency probe to evaluate presence and extent of the collection. Image the abscess in two planes making note of the depth using the markers on the left side of the screen. Abscess is suggested by fluctuating turbid fluid accumulated in subcutaneous tissue that is distorted. Applying pressure to the fluid collection with the ultrasound probe clarifies the liquid nature of the abscess. Sonographically, the collection may contain hyperechoic debris and appear hypoechoic or isoechoic with posterior enhancement. The surrounding subcutaneous tissue appears hyperechoic. As part of the examination, appreciate surrounding anatomic structures. There should be no vascular flow within the abscess, but surrounding tissue may demonstrate increased flow on Color Doppler.34,35
Foreign Body. Missed foreign bodies (FB) are a leading cause of malpractice suits against emergency physicians. Children and adolescents commonly present to the ED complaining of soft-tissue foreign bodies, most commonly embedded in the hand or foot. For this reason, the EP ought to be familiar with the anatomy of these areas as well as learn the sonoanatomy.37 Sonography is useful for the identification and removal of soft-tissue foreign bodies as well as the skin and inflammatory changes associated with retained foreign bodies.38,39 The larger the object, the more likely the sonographer will successfully locate it. Foreign bodies easily can become imbedded with penetrating injuries. While x-rays are excellent in the detection of metallic and certain glass objects, other materials (e.g., wood and plastic) are radiolucent. Inflammation around the retained object can lead to persistent pain, swelling, and dysfunction. Ultrasound is particularly sensitive for detecting, locating, and aiding in removal of small wooden foreign bodies.34,40-43
Technique for FB visualization. A high frequency probe with stand-off pad is suggested; most foreign bodies are located superficially. Maneuver the probe so the image of interest is centered on the screen with depth and focal zone on optimized settings. Image the foreign body in two planes with the probe held perpendicular to the skin surface.34 The one- or two-person technique may be utilized for foreign body removal.
Foreign material in soft tissue is usually echogenic, but this is dependent upon the material’s inherent acoustic impedance. Inflammation, bleeding, and abscess formation around the object may appear as a hypoechoic rim.43-45 Splinters often are small and produce little echogenicity; relative to surrounding structures, they are often hyperechoic. Artifacts may be present and may help with identifying and locating the foreign material.47 Clean posterior shadowing may be present with objects with a small radius of curvature or an irregular surface. Shadowing is seen behind bone fragments. Reverberation and dirty shadowing artifacts are associated with retained objects that are smooth and/or have a wide radius of curvature and typically are seen with glass and metallic objects. Inflammation, edema, and subcutaneous gas may obscure some of the sonographic features associated with the foreign material but shouldn’t affect localization of the object.47 Metallic objects are associated with ring-down artifact.34
Multiple techniques have been described for dynamic ultrasound-guided foreign body removal. Familiarity with normal sonoanatomy of the hand and foot cannot be overemphasized.
Technique for foreign body removal. Image the object such that it is centered on the screen in its best longitudinal plane. Observe the object’s relationship to other soft-tissue structures (e.g., tendons, bone and blood vessels) (Figure 4). Use the centimeter depth markers at the side of the monitor to determine the objects depth, dimensions, and shape. Anesthetize the skin. A needle or hemostat may be utilized by directly visualizing advancement of the instrument until it touches the foreign body. Once localization has been confirmed sonographically, manipulation of the instrument to extract the object varies based upon the instrument being used. Further discussion of removal technique is described in the literature.34,38,42
Joint Effusion and Arthrocentesis. Any child with an acute arthritis must be evaluated for a septic joint. Septic joints are more common in boys than girls, and most commonly involves the hip, knee, or ankle.48 Joint sonography is more sensitive than blind joint aspiration when there is concern for an effusion.49-51 Sonographic evaluation may be useful, particularly in the obese patient whose physical examination for joint effusion is equivocal. Compared with other radiological modalities, ultrasound has the advantage of immediate bedside evaluation without the need for pediatric sedation. Another clear advantage is the ability to compare the affected joint with the contralateral unaffected joint. This evaluation comparison should be performed each time ultrasound is used.
Although sonography helps answer the question of presence or absence of a joint effusion, it actually is possible to appreciate the fluid content. Consider thinking about acute joint complaints presenting to the ED as traumatic or nontraumatic in etiology. Joint fluid generally appears hypoechoic or dark and will be contained within a capsule; noninflammatory effusions tend to be anechoic. Heterogeneous appearing fluid suggests debris such as fat or clot. Infected joint fluid and hemarthrosis often are hypoechoic with internal echoes.33 It is never recommended to rule out a septic arthritis with ultrasound evaluation alone.
Technique. Depending upon the size of the patient and the size of the joint, a lower frequency curvilinear or higher frequency linear probe may be used. Typically in younger smaller patients, the linear probe is better. The curvilinear is more suited for imaging larger adolescents especially at the hip joint. The ultrasound beam should be directed as perpendicularly as possible to the structure of interest. Important techniques for imaging include examining both the affected and unaffected sides, imaging while moving the joint, and imaging from different sonographic windows. Be familiar with the normal anatomy and sonoanatomy of the joint under evaluation.52 A detailed description of imaging specific joints will be limited to the shoulder, the hip, and the knee in this discussion.
Ultrasound Evaluation for Shoulder Effusion. In the evaluation of a patient with a suspected shoulder effusion, it is best to position the patient sitting up with the arm flexed and supinated at the elbow or lay the patient supine with the arm flexed at the elbow and hand placed on the chest. Fluid often is appreciated within the synovial sheath of the long biceps tendon. Image the shoulder by placing the probe anteriorly obtaining longitudinal and transverse scans using the long head of the biceps as a marker (Figure 5). Alternatively, image the shoulder posteriorly in the transverse plane by placing the probe at the insertion of the infraspinatous tendon onto the humerus. In this case, sit the patient up with arm flexed at the elbow and hand crossed over to the unaffected shoulder.52
Ultrasound Evaluation for Hip Effusion. A limping child or adolescent may be difficult to evaluate, and both the knee and hip joints require a careful, thorough evaluation. Identification of any infectious process in the hip is critical to optimize the care of the patient acutely and minimize the potential future complications. To evaluate for effusion in the hip, place the patient supine with hips slightly flexed and internally rotated. A curvilinear lower frequency probe is suggested. Place the probe parallel to the long axis of the femur anteriorly at the level of the humeral neck. Joint effusion is suggested when the capsule surrounding the femoral head is thicker than 5 mm or there is a greater than 2-mm thickness difference as compared with the normal hip.52 If a hip effusion is appreciated by ED sonographic examination, hip aspiration must be considered, and consultation with the orthopedic surgeon is recommended.
Ultrasound Evaluation for Knee Effusion. An ultrasound scan of the knee may be obtained by positioning the patient supine with the knee flexed approximately 20 degrees. A pillow may be placed below the knee joint for comfort. Place the probe in the longitudinal plane parallel to the long axis of the femur in a suprapatellar position with the patella as an inferior landmark. Because the suprapatellar bursa communicates with the knee joint, fluid there suggests fluid in the knee. Fluid not in the knee joint but next to the suprapatellar region suggests muscle tear or tendon rupture. (See the section on tendon injury.)50,52
Tendon Inflammation and Injury. Ultrasound also may be beneficial in the examination of an active child or teenager that presents to the ED with an acute injury after a jump or a fall or a chronic injury with inflammation from overuse. Sonographic imaging of a normal tendon in the longitudinal plan reveals hyperechoic lines of collagen fibers bundled in parallel. Loss of this geometric pattern suggests inflammation as in tendonitis or tearing as in tendon rupture (Figure 6). In the transverse plane, a fine punctuate pattern of bundles appears and is the best means of measuring tendon thickness.19 Hypoechoic areas within the tendon sheath and disrupting the normal geometry suggests fluid that may represent a partial tendon tear or alternatively tendonitis. Image the tendon in the transverse plane and appreciate the sheath as a hypoechoic rim around the tendon. The best means of imaging these structures is with the sonographic beam at a right angle to the tendon axis. Anisotropy is the false hyperechogenicity that results from the incident ultrasound beam not striking tendon fibers perpendicularly. EPs should be particularly mindful of this pitfall and artifact when evaluating patients for tendonitis and partial tendon tears. Keep the probe as parallel to the long axis of the tendon as possible. Even the most slight malposition or obliqueness to the angle of imaging can cause a hypoechoic artifact.19,34,36,52
The patellar and Achilles tendons may be imaged using a high frequency probe. Consider using an acoustic stand-off pad to maximize image quality. Complete ruptures may be obvious on physical examination based upon the patient’s inability to extend the leg (patellar tendon) or plantar-flex the foot (Achilles tendon). On the skin surface, the area of pressure from the probe may indent infra-patella/supra-patella or supracalcaneous. Place the patient’s knee in 30 degrees of flexion, and scan the patellar tendon in two planes. For scanning the Achilles, place the patient prone with foot hanging over the gurney with foot dorsi- and plantar flexed.33
When there is concern for tendonitis, scan the tendon and look for fluid (surrounding hypoechoic rim) collections within a synovial sheath or nonspecific thickening within the tendon fibers in the absence of synovial sheath (e.g. Achilles tendon).19,33,36 When a tendon is torn partially, the space of torn fibers may be filled with hematoma fluid or fat. In the case of a complete tendon tear, the tendon will be absent with gaps in the fiber bundles on transverse imaging. A hypoechoic clot may be visible, and sometimes an avulsed piece of bone may be visible. Don’t forget to image both affected and unaffected sides (Figure 7).
Peritonsillar Abscess (PTA). Typically, the patient may complain of sore throat, unilateral pain, difficulty swallowing, and perhaps, trismus. On intraoral inspection, one may appreciate a unilateral swelling where the soft palate meets the hard palate, swelling of the tonsils with one side more pronounced, or a bulging peritonsillar area that causes uvular deviation to the contralateral side. On palpation, a fluctuant mass may be appreciated.
Tonsillitis, peritonsillar cellulitis (PTC), and peritonsillar abscess (PTA) fall along a disease entity spectrum and may be difficult to distinguish clinically. Although more common in the older child and adolescent, the incidence of PTA in children is increasing.53 The medical literature supports intraoral ultrasonography as an important and accurate diagnostic tool in distinguishing PTC from PTA with sensitivities between 89% and 92%.54-61 The emergency medicine literature has only a few case reports of intraoral ultrasound that similarly support sonography for locating the presence or absence of fluid.62,63 The advantage to sonographic evaluation is saving the patient the pain and invasive nature of blind-needle aspiration.
Procedure. A high frequency curved-array endocativary probe is utilized. Prepare the probe for sterile procedural technique. Consider spraying the oral cavity with a topical anesthetic for increased patient comfort and procedure tolerance. Identify the carotid artery, which runs posterolaterally in the carotid sheath anterior to the jugular vein. The artery appears hypoechoic as a noncompressible vascular structure, which can be confirmed using color Doppler.34 Sonographically, a peritonsillar abscess commonly demonstrates an isoechoic rim with a hypoechoic center and posterior acoustic enhancement. Less commonly, the entire region appears homogenously isoechoic or hypoechoic.64 In some PTAs, the area of pus accumulation is echogenic. An echogenic mass next to the tonsil is considered positive for a PTA. If the EP does not appreciate a fluid collection, attempts at needle aspiration are not recommended (Figure 8).
Long-Bone Fractures. A newer application for emergency sonography is the evaluation of long-bone fractures in the setting of trauma. Although x-ray remains the standard for fracture detection, studies report the use of emergency ultrasound in the unstable or multiply injured trauma patient for evaluation of long-bone fractures of the femur, humerus, and forearm. Rapid detection of such injuries allows timely immobilization for hemodynamic and pain control. Ultrasound also may be used to evaluate fracture reduction in the ED, thus avoiding the timeliness and radiation exposure of fluoroscopy.65-69
Procedure. After appropriate pain control and sedation is administered, utilize a linear probe and consider an acoustic stand-off pad. Orient the probe in the longitudinal plane and not in parallel to the suspected fracture line. Sonographically, the exterior surface of bone is a highly reflective bright white line. Disruption of the smooth contoured surface easily is appreciated. Look for step-off or displacement of one bone segment from another. Note angulation of the long bone of interest. Proceed with immobilization, reduction, or consultation as deemed appropriate to the injury.67,68
Bladder Assessment and Aspiration. Although suprapubic aspiration of the bladder to obtain sterile urine specimens is no longer routine in the pediatric ED, some scenarios may present where a clean catch is not possible and a bladder aspiration needs to be performed. Suprapubic bladder aspiration may be indicated with inability to pass a catheter, inability to locate the urethral meatus, known anatomic pathology, inconclusive clean catch urine samples, or in multitrauma with urethral damage. The pediatric and infant literature widely reports increased success rates when sufficient bladder volume is known and suprapubic bladder aspiration is performed with ultrasound guidance.70-77
Procedure. Using an abdominal low frequency probe placed just cephalad to the symphysis pubis, image the bladder in both longitudinal and transverse planes to ensure anatomic positioning and relative bladder volume. Consider using an acoustic stand-off pad. The bladder appears as a homogenously hypoechoic fluid-filled structure with a bright hyperechoic rim often demonstrating posterior enhancement. Determine if the bladder is empty or contains a sufficient amount of urine for catheterization. Some authors suggest that a bladder diameter of greater than 2 to 3 cm in the longitudinal plane suggests a sufficient amount of urine for successful catheterization.67-71-73 Similar to its use for vascular access, sonography may be used in static or dynamic fashion for bladder volume evaluation and aspiration.
Using the standardized equipment and technique for bladder aspiration, first confirm bladder location and volume; mark the skin in the center of the probe when the bladder is centered on the screen on a transverse view. From here, perform the one-person technique for aspiration. With two people, the dynamic technique will allow visualization of the needle as it tents the skin with percutaneous introduction followed by entrance into the bladder.19,67
Summary and Pitfalls
The medical literature supports ultrasound-guided assistance for many procedures commonly performed in the pediatric ED. Accurate evaluation and use requires knowledge of the anatomy and directly correlates with the practitioner’s experience and comfort level. Advantages to emergency ultrasound include minimizing discomfort and unnecessary procedures to the patient, minimizing medical error, and maximizing success and time efficiency.
The material contained in this article provides the reader with a comprehensive description for performing most of the procedures described, however, further education is recommended. Hands-on experience with a proctor or as a part of a formal educational process would be appropriate.
Conclusions
Ultrasound is a useful diagnostic and procedural tool for the EP in the evaluation of central vascular access, musculo- and dermatoskeletal complaints, lumbar puncture, long-bone fracture, and bladder aspiration. The EP should remain focused on the limitations and user-dependence of ultrasound when applied to those common pediatric and adolescent ED presentations.
Glossary of Terms
- Acoutic impedance: The density of a tissue and its relative resistance to sound wave propagation
- Acoustic stand-off pad: A commercially available or handmade object used to create distance between the probe and the anatomic structure of imaging interest. The substance contained within the object is anechoic allowing complete through-transmission of sound waves.
- Anistropy: The false hyperechogenicity that results from the incident ultrasound beam not striking tendon fibers at a right angle; caused by suboptimal probe positioning
- Artifacts: The visible sonographic information on the screen that does not correlate with the true anatomy and patient positioning
- Compression technique: Sonographic imaging technique whereby the operator applies gentle steady pressure when imaging a patient; it allows displacement of bowel gas for better visualization of anatomy of interest (e.g. appendix).
- Dynamic ultrasound: One- or two-person use of ultrasound guidance for emergency procedures. The sonographer first performs an ultrasound examination; the probe is prepared for use as a sterile part of the procedure; conducting gel is placed on the probe footprint, a sterile glove or commercially available sterile probe sleeve is applied; air bubbles are removed and sterile conductive gel applied to the relevant anatomic area. In the one-person technique, the operator performs the procedure simultaneously with sonography; in the two-person technique, one operator performs the procedure as a second operator holds the probe and performs the sonogram real-time.
Echogenicity: The amplitude display of echoes
- Anechoic: Without echoes
- Hyperechoic: Brighter than surrounding tissues
- Hypoechoic: Darker than surrounding tissues
Probe: An ultrasound transducer of variable shapes and sizes
- High frequency: A linear footprint probe in the range of 7.5-9 MHz providing high image resolution but poor tissue penetration
- Low frequency: A curvilinear footprint probe in the range of 3.5-5 MHz providing good tissue penetration but less quality image resolution
- Longitudinal plane: Oriented parallel to the long axis of the body
- Probe marker: A reference marker on the transducer that orients the operator to the corresponding orientation of the sonographic image on the screen
- Transverse plane: Oriented perpendicularly to the long axis of the body
- Static ultrasound: One-person use of ultrasound guidance for emergency procedures. Ultrasound is utilized for optimal anatomic localization and marking. The probe then is placed aside, and the operator performs the procedure according to standard technique.
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Applications particularly useful in the pediatric and adolescent patient populations will continue to gain wider recognition and acceptance by the physician community. Most ultrasound examinations are quick and simple to perform, and ED physicians can gain comfort and facility in performing these focused applications.
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