Sonodynamics fundamentals

In the absence of road models, we invented the Sonoexam protocols ourselves. The protocols are designed with the intention to provide enough information to enable the experienced sonologist to reveal both subtle and obvious pathology at an Ultrasound dedicated workstation, provided the examiner thoroughly covers the target stuctures. There are two levels of Sonoexams as briefly described below. Detailed descriptions of the proper implementations of the Sonoexams are provided in the guidelines under their respective links in the Sonoexam protocols. The list of published Sonoexams will grow with time. Some technical details are tailor made for our own departments and may not apply to other departments, but the core Sonoexam scanning protocols may be examples for any department to follow, modify or ignore.




Basics: Up

The real strength of Ultrasound (US) and Contrast Enhanced Ultrasound (CEUS) is the examination of well defined organs and structures of limited size. The capture and review of dynamic scans are essential for the interpretation of CEUS exams, as well as for dependable re-evaluation of any US exams. With the introduction of cineloops, small and medium size structures can be depicted for later diagnostic work at workstations with great accuracy according to our experience. Standardized US exams (Sonoexams) of level 1 are designed to be performed by experienced Scanning Techs (Sonotechs), who differ from Sonographers by lacking the skills of pathology of the latter. They are, however, skilled at performing Sonoexams aiming at full diagnostic coverage of the organ or structure of interest. Sonoexams level 1 are fully diagnostic at workstations when performed appropriately. Some Sonoexam protocols are designed toward common diagnoses rather than organs, such as gallstones or Baker cysts. Level 1 Sonoexams are also well suited for use by student sonographers thanks to the possibility to scrutinize their work at a workstation.

Standardized CEUS exams utilise second generation microbubbles that allow continuous real-time scanning without bubble disruption. The CEUS exams are a subset of Sonoexams level 2, which in essence are designed for the aid of experienced ultrasound diagnosticians for increased diagnostic value of their exams by utility of a workstation.

In order to be able to identify the anatomy of the organ and the location of a lesion at the workstation, it is important to follow a predefined standardised scanning acquisition pattern when the series of scans are performed. This also augments parallel comparison of new and old Sonoexams at the workstation regardless of who did the previous exam.

    ·        A Sonoexam consists of Sonoscans, which in turn are built on Sonoloops.

Sonodynamics is the concept of scanning, storing and retrieving fully cine documented exams by use of standardized scanning patterns called Sonoexams. Sonoexams consist of a series of Sonoscans. A Sonoscan basically covers the organ or structure of interest in one direction. A Sonoloop is the extent of one film clip; if the length of a Sonoscan is greater than the machines maximum length of one Sonoloop, the Sonoscan may consist of two or more continuous or overlapping Sonoloops. Sonoscans may also have to be divided into several overlapping Sonoloops if the target can not be fully evaluated in one Sonoloop because of, for instance, gas or ribs.

Documentation: Up

    ·        The basic principle of Sonoexams are: Scans in the transverse plane craniocaudally, and scans in the longitudinal plane from left to right.

This is the principle on which all organ dedicated Sonoexams are built. Hence, the exceptions to the basic principle are all the organs and structures for which we have developed customized Sonoexams, and a few specially designed sonoloops.

    ·        Left-to-right scanning applies universally around the circumference of the body.

This means that a patient in the prone position is still scanned moving the transducer toward the examiner. In this way many misunderstandings are avoided, since it is virtually impossible to keep track of what is "left to right" for the different organs in each possible patient position.

    ·        The transducer marker of the body marker is always placed as seen on the patient.

Example: A point just below the right costal arch is marked when a liver scan is performed with the transducer in that position. The patients position on the bed should also be reflected by the body marker.

    ·        Standard scanning should always be performed at a slow, steady pace in one direction.

One should not alter the scanning speed or direction if unexpected pathology shows up during scanning of the Sonoloop. Such irregular movements are confusing when the scan is viewed off-line at the workstation. Instead, it is possible to take a closer look at the lesion afterwards by using a slow motion review of the data and performing virtual scans back and forth at the workstation. A rule of thumb is to scan a 5-10 cm length in 5-10 seconds depending on the target organ. It is generally better to scan somewhat slower and overlap using a couple of Sonoloops than to rush through the area in one Sonoloop.
Exception to the rule:
“Fanning” Sonoscans in
CEUS arterial phase scanning for characterization of lesion.
“Tracing” Sonoscans along non-linear structures, like a tortuous aorta or the colon.
Still” Sonoscans for documentation of moving structures, such as bowels or dissections.

    ·        Scan entire areas and organs with a margin.

Hence, Sonoscans shall “start outside and end outside” the target areas in each complete target covering scan.

    ·        Additional, well body marked Sonoscans for clarification.

If the examiner finds additional transducer positions or scanning angles that make a difference for the result, additional Sonoscans can be made according to the basic principles of Sonoexams. However, if the pathology or finding is conspicuous on the regular Sonoexam, additional Sonoscans should be used restrictively. As a rule the number of Sonoscans should not exceed the basic Sonoexam protocol by more than 50%. Overlapping Sonoloops are counted as one Sonoscan.


Technique: Up

    ·        The goal of each Sonoexam is to capture cine data from the whole anatomy/organ in accordance with its Sonoexam definition.

The patient position and technique described for each Sonoscan are considered the most appropriate to obtain good consistent results in most patients. Since there are many variations in anatomy as well as accessibility between different individuals, other positions may lead to better conformance with the defined Sonoscan. With experience many different positions and other “tricks” (different breathing positions etcetera) will be learned, each with the goal of presenting the region of interest as well as possible in accordance with each Sonoscan of the Sonoexam protocol.

    ·        Sonoscans are 5-15 second long, full frame rate scans.

Still images are completely replaced by 5-15 second long, full frame rate Sonoscans as defined in these guidelines. The machines are generally set for a high frame rate as a preference over the finest spatial resolution, since much of the sonographic information is interpreted from the motion of the scan plane through eventual pathology. Frame rates should preferably be 15 frames per second or higher. In some special cases of CEUS characterizations, a frame rate of 20 frames per second or above may prove beneficial for the visualization of the actual flow direction of the microbubbles in the initial part of the arterial enhancement. This may be accomplished by zooming in on the lesion.

    ·        Still images only for presentation of measurements.

As a rule, measurements are made side-to-side and up-down on the screen in transverse scans, and side-to-side on the screen on the longitudinal scans, and we describe them in that order for a three-axis measurement. It has proven easier to make consistent comparisons over time that way. Since transverse scans can be made anywhere around the body, side-to-side on the screen is not always equivalent to transverse in the patient, which is why we have chosen to use the screen as the reference.

    ·        Machine settings.

Many machine vendors and examiners set their machines to the highest possible resolution, which unfortunately very often has an inverted correlation to the frame rate. This is of course great for still imaging, but in CEUS and Sonodynamics it is a great disadvantage. Of course one should not exaggerate the frame rate at the expense of diagnostic quality, but a proper balance is desired. In our experience one should really aim hard at having the machine set up to capture at least 15 fps in order to achieve Sonoloop frames that are adjacent to one another at normal Sonodynamics scanning speed. Both concerning the fast arterial flow in CEUS and for any other Sonodynamics scanning, the persistence settings of the machine must be moderate (persistence is the number of consecutive frames added in the image for noise reduction). In the motion of scanning, high persistence blurs the image. We have found a persistence level of 3 to be optimal (Sequoia), while higher values quickly blur the Sonoexams.