Doppler techniques E. Naredo, I. Monteagudo Department of Rheumatology. Hospital ABSTRACT real time US imaging. In CD mode, General Universitario Gregorio Marañón Over the last decade, there has been a the information from Doppler tech- and Universidad Complutense, Madrid, growing body of evidence on the valid- nique is integrated in the B-mode (i.e. Spain. ity of Doppler ultrasound for assess- grey-scale) image as a colour signal. Esperanza Naredo, MD, PhD ing inflammatory changes in target Real-time flow information as a colour Indalecio Monteagudo, MD, PhD anatomic structures involved in rheu- signal is superimposed on the B-mode Please address correspondence to: matic diseases such as joints, tendons, (i.e. grey-scale) image. Colours indicate Esperanza Nardo, MD, PhD, entheses and vessels. The enhanced Dr Alvarez Sierra 4, 4º A, direction of flow. Red usually indicates 28033 Madrid, Spain. sensitivity for detecting low-velocity flow towards the transducer i.e( . artery) E-mail: [email protected] flow in synovium vessels achieved by and blue indicates flow away from the Received on July 29, 2013; accepted in current Doppler techniques has lead to transducer (i.e. vein). revised form on September 14, 2013. the incorporation of Doppler US in the Power Doppler (PD) mode is the most Clin Exp Rheumatol 2014; 32 (Suppl. 80): assessment of joint and inflammatory recent Doppler mode, which has been S12-S19. enthesis lesions. This review offers an available in US technique since the 90s © Copyright CLINICAL AND overview of the key aspects of current (2-5). While CD displays mean Dop- EXPERIMENTAL RHEUMATOLOGY 2014. applications and limitations of Dop- pler shift, PD displays power of the pler ultrasound in inflammatory rheu- Doppler shift in each cell, represent- Key words: Doppler, ultrasound, matic diseases. The basic principles ing only signal intensity (i.e. amount of synovitis, tenosynovitis, enthesitis, of Doppler modes, Doppler scanning red blood cells flowing). Consequently, rheumatoid arthritis, spondyloarthritis, method, and Doppler artefacts and pit- PD potentially increased the sensitivity vasculitis falls in rheumatology ultrasound are to detect low velocity flow from small also described. vessels such as those involved in in- flammatory processes, which are the Doppler physics and modes key areas in rheumatic diseases (2-5). Doppler ultrasound (US) is based on the In addition, PD is almost angle inde- Doppler effect, which was described by pendent, displays poorer delineation the Austrian physicist Christian Dop- of the flow profile and pursatility and pler in 1842. This physical phenomenon is more vulnerable to motion artefacts consists of a change in the frequency of than CD. In recent years, the sensitiv- a sound wave (i.e. Doppler shift) result- ity of CD mode for detecting flow at ing from motion of either the source or the microvascular level has greatly im- the receiver. In medical Doppler US, proved in many high-end US machines. the Doppler effect allows us to detect Thus, currently the choice of PD versus movement of red blood cells in vessels. CD should be taken for each particular Thus, Doppler US provides information US machine. Nevertheless, PD is still on blood flow, which is related to the recommended for use in rheumatology vascularisation of the anatomic struc- in many mid-range and entry-level US tures (1). machines. Spectral Doppler was the first mode available in Doppler US. In this Dop- Doppler settings pler mode, the spectrum of flow veloci- Optimal adjustment of CD or PD Dop- ties is represented graphically on the pler setting is essential to enhance the Y-axis and time on the X-axis. Thus quality of Doppler US assessment. spectral mode allows us to measure dif- Doppler settings should be adjusted to Competing interests: ferent blood flow parameters, some of obtain the highest sensitivity for detect- E. Naredo has received a research grant which (e.g. resistive index) can be use- ing flow with or without minimal arte- from MSD and speaker fees from AbbVie, ful in rheumatology US. facts. These parameters depend on the Roche Farma, BMS, Pfizer, UCB, General Electric, and Esaote; Later, colour flow imaging or colour US equipment and are different accord- I. Monteagudo has received a research Doppler (CD) mode was developed ing to the depth of the studied anatomic grant from Pfizer and speaker fees from in Doppler US. CD technique is the area. We can create some presets with AbbVie and Roche. combination of the Doppler effect and appropriate Doppler parameters for dif- S-12 Applications of Doppler techniques in rheumatology / E. Naredo & I. Monteagudo ferent anatomic area (e.g. deep, inter- Table I. Principal artefacts in rheumatology Doppler US. mediate and superficial joints), which Artefacts Technical basis How to avoid or minimise are very helpful and save time in daily practice. The principal Doppler settings Motion or random flashes Too low PRF produces detection Adjusting PRF to maximise Doppler that we need to know for rheumatology of slight movements of the sensitivity with no or minimal Doppler US, either CD or PD, are de- patients or the examiner, artery artefacts walls or patient’s voice scribed below (6). – Focusing Ramdon noise Too high Doppler gain Adjusting Doppler gain at or just below the level that generates no or As on B-mode, the focal point should minimal random noise be placed at the level of the target area. – Doppler frequency Mirror Mirror colour images under The real vessel and its mirror image highly reflecting surfaces such under the bone surface are easily In general, high Doppler frequencies as bones recognised should be used for superficial anatomic Blooming Colour beyond the vessel wall This artifact is recognised by areas and low Doppler frequencies for due to high gain temporarily reducing the gain deep anatomic areas. However, optimal Reverberation Superficial vessels produce false This artifact is recognised extending frequencies for different depths depend color signals at deeper locations the colour box to the top of the image on the US machines. such as within synovial spaces – Pulse repetition frequency (PRF) A low PRF enhances the sensitivity US: ultrasound; PRF: pulse repetition frequency. of Doppler to detect low velocity flow from small vessels in inflammatory dis- – Colour priority – Scanning of joints and entheses orders. However, a too low PRF produc- This setting should be maximised over Joints should be scanned in neutral po- es motion artefacts due to movement of grey-scale priority when detecting sition instead of in extended or flexed the patients, probe or artery wall or pa- blood flow is the primary objective of position; overextension or flexion of tient’s voice. These artefacts can make the US investigation. the joint can tighten the joint capsule the interpretation of real flow in the US resulting in compression of vessels images very difficult. Therefore, opti- Doppler scanning method and consequent reduction of detectable mal PRF should be the lowest value that Doppler examination should be per- flow (7). Entheses should be scanned maximises Doppler sensitivity with no formed after morphological B-mode with the joint in neutral position, oth- or minimal motion artefacts. This value examination of the investigated ana- erwise increase in the intratendinous usually ranges from 500 to 900 Hz de- tomic structures. The valuable informa- tension can produce entheseal vessel pending on the US equipment. tion about blood perfusion provided by collapse (8). – Doppler gain Doppler US is always complementary – Scanning pressure A high Doppler gain increases the Dop- to the morphological information pro- Care should be taken not to apply too pler sensitivity but also the noise arte- vided by B-mode US. much pressure with the probe in super- facts. Hence, Doppler gain should be – Training ficial joints so as not to compress the increased until random noise appears. A thorough knowledge of musculoskel- vessels and overlook the colour signal. As stated by Rubin (2), because no etal US on B-mode is necessary before A thick layer of gel should be applied flow should be visualised in the bone, starting the training on Doppler modes. between the probe and the patient’s colour gain should be set just below the The morphological information of the skin which should be visible in the level at which colour noise appeared anatomic structures provided by the US image to ensure minimal scanning underlying bone. Optimal Doppler gain B-mode images allows us to know the pressure. is highly dependent on the machine. location of the vascularisation detected – Knowledge of anatomy – Wall filter by Doppler mode and thus interpret the Knowledge of the location of the feed- Low wall filters enhance the sensitiv- nature, normal (i.e. feeding vessels) or ing vessels of joints, tendon and en- ity of Doppler for detecting flow from pathological, of blood perfusion. theses avoid misinterpretation of these small vessels. – Patient and examiner positioning normal vessels as pathologic vasculari- – Doppler box The patient and the examiner must be sation (Online Fig. 1). The colour box should be adjusted to comfortable to avoid motion artefacts. the region of interest, which should The patient should be quiet because Doppler artefacts include the studied anatomic structure voice can produce motion artefacts. Correct use of Doppler US requires (e.g. joints, entheses), the bony margins The examined area must be relaxed; recognition of artefacts, which can and a variable view of surrounding tis- tension in muscle, tendons and joints lead to misinterpretation of relevant sues. This box can be extended to the produces motion artefacts. The scan- findings in rheumatic diseases (Online top of the image (i.e. patient’s skin) to ning arm and hand of the examiner Figs. 5-8). Table I shows the principal recognise reverberation artefacts pro- must rest in a comfortable way to avoid artefacts in rheumatology Doppler US duced by superficial vessels (6).