Basic ultrasound imaging: Techniques, terminology, and tips





Objectives


On completion of this chapter, you should be able to:




  • Describe the scanning techniques used in abdominal scanning



  • State how to properly label a sonogram



  • List the criteria for identifying abnormalities



  • Explain terminology used to describe the results of ultrasound examinations



  • Define the criteria for an adequate scan



  • Identify abdominal sectional anatomy in the transverse and longitudinal planes



  • Describe the use of Doppler in the abdomen, including Doppler scanning techniques for abdominal vessels





The production of a high-quality sonographic image is an “art” that demands many talents of the sonographer: a high degree of manual dexterity and hand-eye coordination; the ability to conceptualize two-dimensional (2D) information into a three-dimensional (3D) format; and a thorough understanding of anatomy, physiology, pathology, instrumentation, artifact recognition, and transducer characteristics. The sophistication of ultrasound systems requires a greater understanding of the physical principles of ultrasound and computers than ever before. Moreover, sonographers should be able to incorporate Doppler techniques, color flow mapping, tissue harmonics, strain analysis, and 3D imaging to provide an enhanced understanding of anatomy and physiology as it relates to hemodynamic blood flow and reconstruction.


Although one-on-one, hands-on training in a clinical setting is an essential part of the sonographer’s experience of producing high-quality scans, this chapter will take you on a journey toward mastering the foundations of abdominal scanning. Correlation of ultrasound images with sectional anatomy is critical for producing consistent, quality images. The approach to general abdominal ultrasound will be presented in this chapter. Specific organ protocols will be presented in their respective chapters. You may find the protocol for an abdominal scan to differ slightly between ultrasound departments; the key is to develop a protocol that is within the national practice guidelines, such as American Institute of Ultrasound in Medicine (AIUM) or American College of Radiology (ACR) and to consistently maintain such protocol for all patients. The protocol presented here is generic and may be adapted to the particular laboratory situation. Also included in this chapter are special scanning techniques and specific applications of abdominal scanning.




Before you begin to scan patients


Remember that your ultimate goal as a sonographer is to produce diagnostic images that can be interpreted by the physician to answer a clinical question. To create images that are diagnostically useful, you must be familiar with ultrasound instrumentation and the clinical considerations of the patient examination. Clinical considerations include knowing which patient position should be used for specific examinations, transducer selection and scanning techniques, patient breathing techniques, and how to perform a sonographic survey of the abdomen.


Be sure you are very familiar with various types of ultrasound equipment. Know where the operator’s manual is and how to find what you need in the manual. (Every manufacturer places the power supply in a different position, so make sure you know how to turn the machine on and off.) Become familiar with the transducers available for each machine, how to activate the transducers, and how to change transducers; some of the plug-in formats take some practice to master. Know where the critical knobs are that operate the ultrasound instrumentation (e.g., time gain compensation [TGC], power, gain, depth, angle, focus, Doppler, color flow). Know where the annotate text keys are for labeling the image. If the ultrasound equipment is new to you, it may be a good idea for one sonographer to work the controls while the other images the patient until you become comfortable with the equipment.


It is highly recommended that the student sonographer practice in a supervised laboratory setting (away from patients) or with one of the anatomic mannequin/ultrasound models before beginning to work with patients. This way, the student sonographer can become familiar with the ultrasound equipment by scanning phantoms or even “building” his or her own phantoms to be scanned.


The next step should be for one student to scan the other students in the sonography laboratory. This allows the actual experience of feeling how “cold that gel really is” when applied to the abdomen and knowing what the probe feels like with different individual scan techniques. (Most laboratories are equipped with gel warmers to avoid that patient discomfort.) The student can see firsthand how a light touch does not make as pretty an image as a moderate touch with the transducer adjacent to the skin and may experience the agony of the heavy hand as it scrapes across the rib cage. The student will also learn how much scanning gel is the right amount: If it drips down your wrist and onto your clothes, it is too much gel.


Controlled supervised scanning should also emphasize how important it is for the patient to take in a breath or suspend breathing so the highest quality images are obtained. A recommended patient breathing technique tip is to have the patient inhale through the nose to reduce the amount of air going into the stomach. Breathing is probably the weakest learning link for the student. Careful control of respiration is critical for making a beautiful scan versus an image that is not easy to interpret.


The student sonographer should also begin to learn the specific protocols required for each examination. Nationally recognized protocols for all areas of ultrasound have been developed by the American College of Radiology ( www.acr.org ) and the American Institute of Ultrasound in Medicine ( www.aium.org ) for ultrasound examinations. Likewise, the American Congress of Obstetricians and Gynecologists ( www.acog.org ) has developed ultrasound protocols for the female patient. The American Society of Echocardiography ( www.asecho.org ) has developed extensive guidelines for all areas in echocardiography. The Society for Vascular Ultrasound ( www.svt.org ) has established protocols and guidelines for specific vascular examinations. Each of these protocols can be found on the websites of the respective organizations.


Students may be overwhelmed at first with the detail these protocols require and may not completely remember all the steps in the protocols when they first begin their clinical scanning experience. Some equipment manufacturers have built a “Smart Examination Protocol” into the equipment; once activated, the system will direct the sonographer to the next required view. Suggested steps to help the student master the protocols are included in the workbook that accompanies this textbook.


Orientation to the clinical laboratory


A new student in the clinical ultrasound laboratory may be overwhelmed at first with the control panel on the ultrasound system, the hand-eye coordination required to produce an image, and the protocol required for the particular examination. The following suggestions may make your entrance into the clinical world a little smoother:




  • Know all of the ultrasound equipment in your laboratory. This means that every free minute should be spent with the equipment, finding the correct knobs necessary to perform the examination. Know where the depth, gain, 2D, color, M-mode, harmonics, and TGC controls are located.



  • Know where the operator’s manuals are for each piece of equipment so you may have a reference for troubleshooting.



  • Find out what protocols are used for each examination. Most departments have a “Standard Manual of Protocols” for all their examinations.



  • Understand how to read the patient order, find out what question the ordering physician needs to have answered, and know which items in the patient records are relevant for patient identification.



  • When you call for patients, be sure to check their ID with at least two identifiers (i.e., name and birth date, doctor who ordered the examination, type of examination ordered).



  • Introduce yourself and explain briefly the procedure you are going to do. Also explain the procedure the department will follow to notify the patient’s physician of the results of the examination.



  • Always keep your conversation professional. Remember that you need to focus on the examination.



  • Discuss the case only with your mentor or with the physician responsible for interpreting the study.



Written order for the examination


An electronic or written order by the health care provider will indicate the reason for the ultrasound examination. This order should contain the appropriate clinical information relevant to the patient in order to provide the necessary information from the ultrasound procedure to the clinician.


Documentation for the ultrasound examination


Accurate documentation must be made for the ultrasound procedure. There should be a permanent record of the examination and its interpretation available on the electronic medical record or written format. The images obtained from the examination should be recorded in a retrievable format (i.e., PACS system or disc). Communication of the results must be maintained between the providing physician and the ordering physician.


Scanning techniques


Ultrasound can distinguish multiple interfaces between soft tissue structures of different acoustic densities. The strength of the echoes reflected depends on the acoustic interface and the angle at which the sound beam strikes the interface. The sonographer must determine which patient “window” is best to record optimal ultrasound images, and which transducer size best fits into that window. The curved array transducer provides a large field of view, but in some patients this transducer may be too large to fit in between the ribs to provide adequate contact for accurate reflection of the sound wave. The smaller footprint transducer allows the sonographer to scan between intercostal spaces with the patient in a supine, coronal, decubitus, or upright position, but limits the near field of view. It is not unusual to use multiple transducers on one patient to complete the examination, as transducers are available in multiple sizes and frequencies.


Patient preparation


It is recommended that the patient fast for 8 hours before the ultrasound examination of the abdomen. Fasting helps to reduce the interference that may be caused from gas overlying the midline abdominal structures. It will also ensure that the gallbladder will be fully distended. If the patient has eaten, it is still possible to perform the general ultrasound examination; however, visualization of all structures may not be as clear.


Patient positions


The general abdominal examination is performed initially with the patient in the supine position. Additional views may require the oblique, lateral decubitus, prone, and occasionally upright positions for examination of specific areas of interest ( Figure 6-1 ). For example, the gallbladder may be examined with the patient in the supine, oblique, or lateral decubitus positions. These positions will be discussed in more detail in the specific chapters.




FIGURE 6-1


Various standard patient positions for the ultrasound examination.


Transducer selection


Know the various transducers available for each ultrasound system, and know which transducers are used for specific examinations ( Figure 6-2 ). The curved array transducer provides a large pie sector and is used for the survey of the abdomen. The linear array transducer provides a rectangular image of the structure, such as the abdominal aorta or inferior vena cava. The sector array provides a small pie sector of the area. The sector array is useful to find a “window” in between the intercostal spaces to image the liver and biliary system. It is also used extensively to image the cardiac structures. The endocavity or endovaginal transducer is a high-frequency crystal mounted on a longer handle. The transducer is used in female pelvic and male pelvic examinations. If the endocavity transducer is used, the sonographer needs to be familiar with the decontamination process for the transducer. This process is discussed further in Chapter 42 .




FIGURE 6-2


Transducer designs in multiple shapes and sizes are used for specific ultrasound examinations. A, Transducer design ranges from very small to the larger curved array probes. B, An array of transducer sizes and frequencies may be used in a general ultrasound department.


The size of the patient will influence which megahertz transducer will be used. Generally speaking, the lower-frequency transducer has better penetration and is used for the adult abdomen, whereas the high-frequency probe has higher resolution with improved axial resolution and is used for more superficial structures such as the thyroid or breast.


Knobology


The sonographer needs to be familiar with the ultrasound control panel in order to produce an anatomic image ( Figure 6-3 ). The primary controls include the depth, gain (TGC, lateral gain), frequency, focal zone, modes (2D, M-mode, 3D, pulsed wave Doppler, continuous wave Doppler, and color Doppler), annotation, and calculation package. Each of these controls has multiple layers of software (tissue harmonics, dynamic compression range, frame rate, scale, baseline, etc.) that the sonographer will learn to manipulate in order to produce the high-quality image.




FIGURE 6-3


A, Ultrasound system demonstrates portability and ergonomic features for the sonographer. (Philips EPIQ 7 ultrasound system. Used with permission from Philips.) B, Example of the control panel of an ultrasound system. The pods on the right-hand side control the TGC. Other central controls include gain, depth, filter, scale, mode selection, zoom, calipers, and gray-scale maps.


Transducer positions


The sonographer will use multiple wrist actions throughout the study. Remember that the beam is ideally reflected when the transducer is perpendicular to the surface. However, the body has many angles, curves, and rib interferences, causing the sonographer to use intercostal spaces, subcostal windows, multiple degrees of angulation, and many rotations of the transducer to obtain anatomic images ( Figure 6-4 ).




FIGURE 6-4


The sonographer must use a number of different transducer positions and angulations to complete the ultrasound examination.


There are multiple scanning motions that the sonographer needs to master throughout the examination : sweep, slide, rock, fan, and rotate. These movements may be large (macro) or small (micro). The macro movement of the probe is used with the sweep and slide motion in which the probe is moved greater than 1 cm. Macro movement also occurs if the fan or rock motion changes the angle of insonation by more than 15 degrees in either direction. The micro movement of the probe is used with the sweep and slide motion in which the probe is moved less than 1 cm. Micro movement likewise occurs if the fan or rock motion changes the angle of insonation by less than 15 degrees in either direction. It is important to perform only one motion at a time. The movement should be similar every time you have the same scanning window to consistently produce an image.


In a survey of the abdomen, the sonographer will initially use the sweep motion. This requires the transducer to remain in one area while using a large wrist motion with the probe perpendicular to the skin surface to sweep through the abdomen. It is used to locate and interrogate an area of interest or to evaluate the scan windows of abdominal structures before the scan protocol is begun.


The slide motion is used when the transducer is physically moved along the abdomen, such as a longitudinal movement to follow the course of the abdominal aorta into the bifurcation of the iliac arteries.


Once an area of interest is located, the sonographer may pause over the structure and slowly rock or pivot the transducer back and forth or up and down to image the area completely or to follow the anatomic structure. This is when the “cine” frame capture is useful to record the motion. This may be used in demonstrating the junction of the common bile duct and cystic duct or in tracking the communication of the hepatic artery as it arises from the celiac trunk.


A smaller version of the sweep motion is the fan motion, which is used when the transducer is minutely swept, pivoting on a point of interest. This may be useful in the superficial structures such as the breast when differentiation is needed between the duct and the invasive lesion within the duct.


The rotate motion is useful to navigate between the ribs or to change from transverse to longitudinal planes, where the transducer is held in one area and rotated 90 degrees to the opposite plane. Rotate is also used in smaller increments as the transducer is slowly turned around the area of interest.


Annotation


Ultrasound images are labeled as transverse or longitudinal for a specific organ, such as the liver, gallbladder, pancreas, spleen, or uterus. The smaller organs that can be imaged on a single plane, such as the kidney, are labeled as long-midline, -lateral, or -medial, whereas the transverse scans are labeled as transverse-low, middle, or -high.


All transverse supine scans are oriented with the liver on the left of the monitor; this means that the sonographer will be viewing the body from the feet up to the head (“optimistic view”) ( Figure 6-5 ). Longitudinal scans display the patient’s head to the left and feet to the right of the screen and use the xiphoid, umbilicus, or symphysis to denote the midline of the scan plane ( Figure 6-6 ).




FIGURE 6-5


A, The curved array probe is held in a transverse position just under the costal margin with a steep angulation to be perpendicular to the dome of the liver. Patient is supine. B, All transverse supine scans are oriented as looking up from the feet, with the liver on the left side of the screen (right side of the patient is on the left of the screen).



FIGURE 6-6


A, The curved array probe has been rotated 180 degrees to perform a sagittal scan of the abdomen. B, The longitudinal scans for the abdomen and pelvis are oriented with the patient’s head toward the left of the screen and feet toward the right.


All scans should be appropriately labeled for future reference, including the patient’s name, date, and anatomic position. Body position markers are available on many ultrasound machines and may be used in place of written labels.


The position of the patient should be described in relation to the scanning table (e.g., a right decubitus would mean the right side down; a left decubitus would indicate the left side down). If the scanning plane is oblique, the sonographer should merely state that it is an oblique view without specifying the exact degree of obliquity.


Artifacts


Sonographers need to learn about ultrasound artifacts early in their learning curve. There are a few primary artifacts that sonographers should recognize as they begin their scanning experience: reverberation, mirror, side lobe, and shadowing ( Figure 6-7 ). Reverberation artifacts occur between the transducer and a strong reflector such as the rib causing multiple linear lines equidistant apart. A mirror artifact is a form of reverberation that shows structures that exist on one side of a strong reflector as being present on the other side as well; for example, the liver/diaphragm interface may show “liver” tissue in the pleural space. Side lobe artifacts are beams that propagate from a single transducer element in directions different from the primary beam, such as those produced by bone or gas. Shadowing is the reduction in echo amplitude from reflectors that lie behind a strongly reflecting or attenuating structure; for example, calcified gallstone will cause a “shadow” posterior to the stone. Artifacts found in ultrasound images are discussed in more detail in Chapter 7 .




FIGURE 6-7


Artifacts. A, Reverberation artifacts occur between the transducer and a strong reflector such as the rib causing multiple linear lines equidistant apart. B, A mirror artifact is a form of reverberation that shows structures that exist on one side of a strong reflector as being present on the other side as well; for example, the liver/diaphragm interface may show “liver” tissue in the pleural space. C, Side lobe artifacts are beams that propagate from a single transducer element in directions different from the primary beam, such as those produced by bone or gas. D, Shadowing is the reduction in echo amplitude from reflectors that lie behind a strongly reflecting or attenuating structure; for example, calcified gallstone will cause a “shadow” posterior to the stone.




Indications for abdominal sonography


The AIUM has listed multiple indications for an abdominal sonogram that include, but are not limited to, the following:




  • Signs or symptoms that may be referred from the abdominal and/or retroperitoneal region such as jaundice or hematuria



  • Generalized abdominal, flank, or back pain



  • Palpable mass or organomegaly



  • Abnormal laboratory values or abnormal findings on other imaging modalities



  • Follow-up of known or suspected abnormalities in the abdomen or retroperitoneum



  • Search for metastatic disease or occult primary neoplasm



  • Evaluation of suspected congenital abnormalities



  • Trauma to the abdomen or retroperitoneum



  • Pretransplant and posttransplant evaluation



  • Invasive procedure localization



  • Localization for free or loculated peritoneal, pleural, or retroperitoneal fluid



  • Suspicion of hypertrophic pyloric stenosis or intussusception



  • Evaluation of a urinary tract infection



The request for an abdominal or retroperitoneal sonographic examination needs to provide sufficient information to demonstrate the medical necessity of the examination with allowance for proper performance and interpretation.


The documentation that must be met for medical necessity includes the following items: (1) patient signs and symptoms and (2) previous history pertinent to the examination requested. Additional information such as the specific reason for the examination or a provisional diagnosis would be helpful and may aid in the proper performance and interpretation of the examination. This will allow the sonographer to tailor the examination to answer the question from the ordering physician.

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May 29, 2019 | Posted by in ULTRASONOGRAPHY | Comments Off on Basic ultrasound imaging: Techniques, terminology, and tips
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