Performing a Basic US Examination: Road Map for Radiology Residents

Abstract

This online presentation creates a road map for performing a high-quality gray-scale US examination, revisits fundamental physics concepts for image optimization, and discusses methods to improve image quality and decrease artifacts.

The full digital presentation is available online.

Performing a high-quality US examination is uniquely operator and patient dependent. Obtaining optimal US images is a learned and practiced skill. In the United States, radiologists-in-training are spending less time learning the nuts and bolts of US scanning, while practitioners in other medical specialties are increasingly integrating US training into their programs, including for point-of-care and gynecologic applications. In this online presentation, we review the basic steps for producing an excellent gray-scale US image.

The demand for and application of US is expected to continue to increase given its numerous benefits, including accessibility, cost, portability, and the absence of ionizing radiation. Many procedures are increasingly US guided. In addition, the underlying technology and applications of US continue to increase in complexity, as US becomes the stimulus for research and discovery of novel applications for earlier diagnosis and improved therapeutics for the treatment of many conditions.

A radiologist’s competency in performing US examinations is essential. An expert radiologist interprets images more accurately and is better able to recognize and troubleshoot suboptimal images to overcome operator dependency. He or she is able to teach sonographers, offer valued service to referring colleagues, and provide excellent patient care.

To remain experts in the field, radiologists should be trained to a high standard. However, with increasing demands and requirements for trainees across all imaging subspecialties and owing to the widespread availability of sonographers, opportunities for real-time scanning and hands-on training are limited and varied across radiology residency programs. Moreover, there are inconsistent standards for US training and assessment across all specialties owing to inherent operator dependency.

Currently, there are insufficient data regarding the number of US examinations one must perform and/or interpret to become competent. The American College of Radiology recommends that a radiologist should be involved with the supervision and/or performance, interpretation, and reporting of 500 US examinations in the past 36 months as part of a completed diagnostic or interventional radiology residency program. This number varies by anatomic area per the American Institute of Ultrasound in Medicine guidelines. Other guidelines from specialty-focused societies vary further, including the American College of Emergency Physicians, which recommends that emergency medicine trainees in the United States perform 150–300 examinations.

Although nothing can replace the benefit of hands-on experience, we hope this online presentation serves as a practical reference to guide residents in their US practice. Proper positioning and equipment selection are described, along with transducer selection and orientation, screen display components, and image acquisition and optimization (“knobology”). We review fundamental physics concepts that affect image acquisition and optimization, such as transducer frequency focal zones, overall gain, time-gain compensation, and harmonic and spatial compound–imaging techniques (Figure). Artifacts that result from assumptions about attenuation are briefly covered, and tips for improving image quality and decreasing artifacts are presented. Cases presented in a quiz format at the end of the presentation help reinforce key concepts.

Figure a.

Overall gain setting amplifies all ultrasound signals by a constant factor, regardless of depth. (a) US image obtained with the overall gain set too high at 75% (arrow) shows the liver. Note the brightness of the image. (b) US image obtained with the overall gain set too low at 52% (arrow) shows the liver. Note the darkness of the image. (c) US image obtained with the overall gain optimized at 66% (arrow) shows the liver with improved visualization of the parenchyma. (d) Photograph shows a US machine console and the overall gain knob (circle). Rotating this knob clockwise increases the gain. Adjust the overall gain if the brightness of the entire image needs correction.

Figure b.

Overall gain setting amplifies all ultrasound signals by a constant factor, regardless of depth. (a) US image obtained with the overall gain set too high at 75% (arrow) shows the liver. Note the brightness of the image. (b) US image obtained with the overall gain set too low at 52% (arrow) shows the liver. Note the darkness of the image. (c) US image obtained with the overall gain optimized at 66% (arrow) shows the liver with improved visualization of the parenchyma. (d) Photograph shows a US machine console and the overall gain knob (circle). Rotating this knob clockwise increases the gain. Adjust the overall gain if the brightness of the entire image needs correction.

Figure c.

Overall gain setting amplifies all ultrasound signals by a constant factor, regardless of depth. (a) US image obtained with the overall gain set too high at 75% (arrow) shows the liver. Note the brightness of the image. (b) US image obtained with the overall gain set too low at 52% (arrow) shows the liver. Note the darkness of the image. (c) US image obtained with the overall gain optimized at 66% (arrow) shows the liver with improved visualization of the parenchyma. (d) Photograph shows a US machine console and the overall gain knob (circle). Rotating this knob clockwise increases the gain. Adjust the overall gain if the brightness of the entire image needs correction.

Figure d.

Overall gain setting amplifies all ultrasound signals by a constant factor, regardless of depth. (a) US image obtained with the overall gain set too high at 75% (arrow) shows the liver. Note the brightness of the image. (b) US image obtained with the overall gain set too low at 52% (arrow) shows the liver. Note the darkness of the image. (c) US image obtained with the overall gain optimized at 66% (arrow) shows the liver with improved visualization of the parenchyma. (d) Photograph shows a US machine console and the overall gain knob (circle). Rotating this knob clockwise increases the gain. Adjust the overall gain if the brightness of the entire image needs correction.