Novel use of laser Doppler imaging for investigating epicondylitis
W. R. Ferrell,
P. V. Balint and
R. D. Sturrock
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Abstract
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Objective. This investigation evaluated a novel form of tissue perfusion measurement, laser Doppler imaging (LDI), in a case of lateral epicondylitis to establish if it might have applications in assessing soft tissue lesions. LDI was used in conjunction with ultrasonography to provide information about tissue oedema as well as the power Doppler signal as an alternative method of assessing blood flow.
Methods. A laser Doppler imager with a near-infrared (NIR) laser source was used to improve tissue penetration and yield measurements of perfusion (flux) from structures under the skin. Skin temperature over the lateral epicondylar region was also measured. Ultrasonography was used in both grey-scale and power Doppler modes. LDI, temperature measurements and ultrasonographic data were obtained before treatment and serially after local injection of methylprednisolone.
Results. Before treatment there was increased perfusion and skin temperature and the presence of a power Doppler sign associated with the right lateral epicondyle as well as oedema at the extensor origin. None of these was present at the asymptomatic contralateral epicondylar region. Twenty-four hours after methylprednisolone administration, both perfusion and skin temperature had increased, and they declined over the subsequent 48 h. Although skin temperature had declined to normal (referenced to the contralateral epicondyle) by the third day after injection, it took until the eleventh day after injection for perfusion to normalize.
Conclusions. LDI using an NIR laser source appears to be an effective non-invasive method for the examination of inflammatory responses in soft tissue, with greater sensitivity than thermally based methods. In addition, LDI was found to correlate with power Doppler ultrasonography.
KEY WORDS: Laser Doppler imaging, Ultrasonography, Epicondylitis.
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Introduction
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Objective investigation of soft tissue injury or inflammation is difficult, as there are few techniques which adequately permit the non-invasive assessment of tissue perfusion. Infrared thermography has been used to investigate soft tissue lesions, including epicondylitis [1], and although it is useful it requires careful control of environmental temperature and acclimatization of the subject before measurement. Laser Doppler flowmetry is a non-invasive technique based on the well-known Doppler shift principle for detecting changes in skin blood flow (perfusion) at a single point [2]. Laser Doppler imaging (LDI) extends this technique by scanning a laser beam across the tissue to generate a spatial map of perfusion [3] with hundreds or thousands of measurement points per scan, depending on the area scanned. This technique has proved to be of value in assessing burns [4], and when a near-infrared (NIR) laser is used hyperaemia in inflamed finger joints is detectable in patients with rheumatoid arthritis [5]. In this preliminary study we describe the novel use of laser Doppler imaging (LDI) in conjunction with ultrasonography to investigate a case of lateral epicondylitis.
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Materials and methods
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Following overuse, one of the authors (WRF) developed lateral epicondylitis of the right elbow, characterized by localized pain and tenderness over the epicondyle and increased pain on resisted wrist extension. These symptoms had remained stable over the 8 weeks before examination. The left elbow was asymptomatic.
A laser Doppler imager (Moor Instruments, Axminster, UK) scanned a laser beam across the elbow, producing a two-dimensional perfusion map of 256 x 256 measurement points. The instrument incorporated an NIR laser (830 nm), although on each occasion a scan was also taken using a red (635 nm) HeNe laser. The optical properties of skin are such that wavelengths longer than the visible spectrum penetrate more deeply [6], and previous work indicates that hyperaemia associated with inflamed [5] or injured [7] finger joints is readily detectable using the NIR laser. Measurements were performed in a room relatively free of draughts and an ambient temperature of 2225°C, but no subject acclimatization was employed. Both the affected right elbow and the asymptomatic left elbow were scanned periodically before and after treatment, the left side being an internal control. We had demonstrated previously that within- and between-day variability for LDI measurements of proximal interphalangeal joints was between 3 and 4% [5]. Skin surface temperature over both epicondyles was also measured on the same occasions as scans were taken, using thermocouples connected to a monitor (Harvard Inc, MA, USA) with a resolution of 0.1°C.
An ATL (WA, USA) HDI 3000 ultrasound machine with a compact linear 105 MHz, 26 mm probe was used to obtain 2D grey-scale and power Doppler images and to detect altered structure of the origin of the common extensors and blood flow in a coronal plane (Fig. 1
). A previously described technique was used to avoid artefacts [8]. Colour noise was set before examination, it was checked that there was no signal under the cortical bone, and the contralateral side was also examined. Pulse repetition frequency setup was at 500 Hz and low-flow optimum was selected from the software. Using grey-scale ultrasonography, we had examined the thickness of the iliofemoral ligament previously and found intra- and inter-observer error to be 6.1 and 10.6% respectively [9]. To avoid errors [10] we examined the contralateral asymptomatic side with the same settings.

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FIG. 1. Colour panels showing progressive LDI near infrared scans from the affected right and unaffected left elbows on various days before (0) and after injection of methylprednisolone. Scans are colour-coded: dark blue represents the lowest degree of perfusion, and increasing perfusion values are represented by green, yellow, red and white. Power Doppler scans are shown at the appropriate time points along with photographic images of the elbows and diagrams of the bony structure. CE, common extensor origin; LEC, left edge of the capitulum; RH, radial head; LEH, left edge of humerus. The position of the ultrasonic transducer over the lateral epicondyle of the right arm is also shown.
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Ultrasound scans were taken before injection and 11 days after the injection of 10 mg methylprednisolone at the site of maximal tenderness, close to the extensor origin.
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Results and discussion
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Skin temperature over the affected epicondyle was initially elevated (by 1.1°C) compared with the unaffected side and was associated with the LDI perfusion value being more than three times higher over the epicondylar region (Figs 1
and 2A
and 2B
). Power Doppler ultrasonography localized the increased blood flow volume to deeper structures, with only weak signals in the tendon (Fig. 1
). Grey-scale ultrasonographic examination revealed a hypoechogenic region associated with the common extensor origin on the affected side, suggestive of oedema.

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FIG. 2. Temperature (A) and perfusion (flux) (B) values measured over the inflamed (right) and control (left) epicondyles as a function of time before and after steroid injection. Although skin temperature normalized by the third day after injection, a further 7 days was required for perfusion to normalize. (C) Skin temperature and perfusion were poorly correlated below a skin temperature of 33°C. Data points for both the affected right (filled circles) and unaffected left (open circles) elbows are plotted, but R2 refers to the combined data sets. No significance was obtained when the individual data sets were assessed statistically.
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Methylprednisolone administration resulted in an inflammatory response 24 h later. Concurrently there was an increase in epicondylar temperature (Fig. 2A
) and perfusion (Figs 1
and 2
B), which had declined by 48 h after injection (Figs 1
and 2
B). Epicondylar temperature also fell and became equivalent to that on the unaffected side by 72 h after injection (Fig. 2A
). However, perfusion remained elevated compared with the unaffected side and took a further 7 days to approximate the value on the unaffected side (Fig. 2B
), even though the symptoms had resolved completely by the third day after injection. On the eleventh day, when the LDI signal approximated the unaffected side, the power Doppler sign was virtually absent (Fig. 1
). At this time the grey-scale ultrasonogram showed reduced hypoechogenic features. The correlation between skin temperature and LDI perfusion proved to be non-significant below a skin temperature of 33°C (Fig. 2C
), although there was some correspondence at higher skin temperatures in the 48 h after the administration of methylprednisolone.
This investigation is novel in two respects: LDI has never previously been used to examine a case of epicondylitis and, although ultrasonography has been used to investigate normal elbow joint structure [11, 12] and lateral epicondylitis [13, 14], there has never previously been an investigation combining the two techniques. The results from this longitudinal case study indicate that LDI is sufficiently sensitive to detect hyperaemia associated with epicondylitis. Although both techniques are based on the Doppler shift principle, there are differences in the signals obtained with these two techniques. The LDI perfusion signal is the product of the velocity and the concentration of blood cells within a volume of tissue. However, the power Doppler technique creates a colour flow map through a sample volume based on the total integrated power of the Doppler spectrum, but all velocity information is sacrificed [8]. Further work is required to establish the reproducibility and repeatability of grey-scale and power Doppler ultrasonography at the lateral epicondyle of the humerus in asymptomatic and symptomatic individuals.
An important issue is whether LDI penetrates sufficiently to detect hyperaemia of structures under the skin. There is indirect evidence to support the concept that the laser penetrates to deeper structures, as subcutaneous veins were clearly imaged with the 830 nm laser but not with the less penetrating red source (not shown). In animal experiments, in which variables can be controlled more tightly, it has been demonstrated that changes in synovial perfusion are detectable through intact skin [15].
Our grey-scale findings of a hypoechoic region at the insertion of the extensor carpi radialis brevis confirm previous observations [13, 14]. On power Doppler examination, a stronger signal was observed at the periosteum than in the tendon itself, which correlates with the tendon being poorly vascularized, whereas periosteum has a rich vascular network.
Over the basal physiological (
33°C) range of perfusion and skin temperatures encountered, there was no significant correlation between these two variables. This may indicate that thermally based techniques involving the measurement of surface temperature are less sensitive than LDI. Although there was correspondence between LDI and temperature initially, as the inflammation resolved and the surface temperature dropped below 33°C this association diminished (Fig. 2A
and B
). Thus LDI can detect hyperaemic areas associated with injury or inflammation with greater sensitivity than thermally based methods. LDI has the potential to be an effective diagnostic tool for the non-invasive assessment of soft tissue injuries such as epicondylitis, and may prove to be particularly useful for monitoring progress after symptoms have resolved. This may have predictive value in determining when exercise can be resumed and could provide objective parameters for evaluating the effectiveness of interventions in clinical research.
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Acknowledgments
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The authors gratefully acknowledge the support of the Arthritis Research Campaign (ICAC award S0590).
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Notes
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Correspondence to: W. R. Ferrell. 
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Submitted 24 January 2000;
revised version accepted 9 June 2000.