Full-field laser-Doppler imaging and its physiological significance for tissue blood perfusion

An abnormality in glucocorticoid receptor expression differentiates steroid responders from nonresponders in keloid disease

Background

Glucocorticoids (GCs) are first‐line treatment for keloid disease (KD) but are limited by high incidence of resistance, recurrence and undesirable side‐effects. Identifying patient responsiveness early could guide therapy.

Methods

Nineteen patients with KD were recruited at week 0 (before treatment) and received intralesional steroids. At weeks 0, 2 and 4, noninvasive imaging and biopsies were performed. Responsiveness was determined by clinical response and a significant reduction in vascular perfusion following steroid treatment, using full‐field laser perfusion imaging (FLPI). Responsiveness was also evaluated using (i) spectrophotometric intracutaneous analysis to quantify changes in collagen and melanin and (ii) histology to identify changes in epidermal thickness and glycosaminoglycan (GAG) expression. Biopsies were used to quantify changes in glucocorticoid receptor (GR) expression using quantitative reverse transcriptase polymerase chain reaction, immunoblotting and immunohistochemistry.

Results

At week 2, the FLPI was used to separate patients into steroid responsive (n = 12) and nonresponsive groups (n = 7). All patients demonstrated a significant decrease in GAG at week 2 (P < 0·05). At week 4, responsive patients exhibited significant reduction in melanin, GAG, epidermal thickness (all P < 0·05) and a continued reduction in perfusion (P < 0·001) compared with nonresponders. Steroid‐responsive patients had increased GR expression at baseline and showed autoregulation of GR compared with nonresponders, who showed no change in GR transcription or protein.

Conclusions

This is the first demonstration that keloid response to steroids can be measured objectively using noninvasive imaging. FLPI is a potentially reliable tool to stratify KD responsiveness. Altered GR expression may be the mechanism gating therapeutic response.

What's already known about this topic?

Steroids are used as first‐line treatment for keloid disease, but response is variable with apparent steroid responders and nonresponders.

It remains unclear whether steroid responsiveness is due to an intrinsic difference in the mechanism of the glucocorticoid receptor (GR) action or reduced sensitivity to the steroid itself.

What does this study add?

We show for the first time the utility of noninvasive imaging techniques in stratifying steroid responsiveness in patients treated with steroids.

GR expression increased significantly in keloid tissue. Increased GR expression also correlated with an increased response to steroid treatment.

Steroid responders show a significant decrease in GR transcript and protein 2 weeks after steroid treatment (P < 0·05), which was not evident in steroid‐resistant patients.

Assessing the reliability of diffuse correlation spectroscopy models on noise-free analytical Monte Carlo data

It is shown that an analytical noise-free implementation of Monte Carlo simulations [Appl. Opt.54, 2400 (2015).10.1364/AO.54.002400APOPAI1559-128X] for diffuse correlation spectroscopy (DCS) may be successfully used to check the ability of a given DCS model to generate a reliable estimator of tissue blood flow. As an example, four different DCS models often found in the scientific literature are tested on a simulated tissue (semi-infinite geometry) with a Maxwell-Boltzmann probability distribution function for red blood cell speed. It is shown that the random model is the best model for the chosen speed distribution but that (1) some inaccuracies in the DCS model in taking into account red blood cell concentration and (2) some inaccuracies, probably due to a low-order approximation of the DCS model, are still observed. The method can be easily generalized for other speed/flow probability distribution functions of the red blood cells.

Random numbers free analytical implementation of Monte Carlo for laser-Doppler flowmetry at large interoptode spacing: application to human bone tissue

Classical Monte Carlo (MC) simulations for laser-Doppler flowmetry (LDF) often necessitate too long computation times and specialized hardware. This is particularly true for LDF at large interoptode spacing with low absorption coefficients and large anisotropic factors representing real biological tissues. For this reason, a random numbers free "analytical" implementation of the classical MC (MC_an) is proposed. The MC_an approach allows to obtain noise exempt LDF spectra in a short time and with a simple personal laptop. The proposed MC_an holds for a diffusive regime of light propagation and it is practically implemented for a semi-infinite geometry. Its validity is demonstrated by comparisons with the classical MC.

Predictive value of single photon emission computerized tomography and computerized tomography in osteonecrosis after femoral neck fracture: a prospective study

PURPOSE

Osteonecrosis of the femoral head (ONFH) is a very common complication after femoral neck fracture. The purpose of this study was to assess the femoral head vascularity after femoral neck fracture using single photon emission computerized tomography and computerized tomography (SPECT/CT), and to evaluate its value in predicting ONFH.

METHODS

Between January 2008 and March 2011, 120 patients diagnosed with femoral neck fracture underwent SPECT-CT before the internal fixation. The fracture was classified according to the Garden classification. The ratios of the radionuclide uptake of the fractured femoral head to that of the contralateral femoral head (F/N) were calculated to assess the femoral head vascularity. After a minimum of two years' follow-up, magnetic resonance imaging (MRI) was used as the "gold standard" for the diagnosis of possible ONFH.

RESULTS

A total of 114 patients completed the study. The SPECT/CT examination showed that the F/N ratios of Garden I, II, III and IV were 2.6, 1.8, 0.8, and 0.6, respectively. At the time of the most recent follow-up, osteonecrosis developed in two of the 27 patients who had a Garden Stage-II fracture, in eight of the 34 patients who had a Garden Stage-III fracture, and nine of the 27 patients who had a Garden Stage-VI fracture. With a cutoff of 0.55 from the receiver operating characteristic (ROC) curve, F/N ratio showed a sensitivity of 97%, a specificity of 79%, a positive predictive value of 95%, and a negative predictive value of 19%.

CONCLUSION

SPECT-CT proved to be reliable and valid for predicting ONFH after femoral neck fracture.

FluxEXPLORER: a new high-speed laser Doppler imaging system for the assessment of burn injuries

BACKGROUND

Deep burn assessment made by clinical evaluation has an accuracy varying between 60% and 80% and will determine if a burn injury will need tangential excision and skin grafting or if it will be able to heal spontaneously. Laser Doppler Imaging (LDI) techniques allow an improved burn depth assessment but their use is limited by the time-consuming image acquisition which may take up to 6 min per image.

METHODS

To evaluate the effectiveness and reliability of a newly developed full-field LDI technology, 15 consecutive patients presenting with intermediate depth burns were assessed both clinically and by FluxExplorer LDI technology. Comparison between the two methods of assessment was carried out.

RESULTS

Image acquisition was done within 6 s. FluxEXPLORER LDI technology achieved a significantly improved accuracy of burn depth assessment compared to the clinical judgement performed by board certified plastic and reconstructive surgeons (P < 0.05, 93% of correctly assessed burns injuries vs. 80% for clinical assessment).

CONCLUSION

Technological improvements of LDI technology leading to a decreased image acquisition time and reliable burn depth assessment allow the routine use of such devices in the acute setting of burn care without interfering with the patient's treatment. Rapid and reliable LDI technology may assist clinicians in burn depth assessment and may limit the morbidity of burn patients through a minimization of the area of surgical debridement. Future technological improvements allowing the miniaturization of the device will further ease its clinical application.

A fast time-domain algorithm for the assessment of tissue blood flow in laser-Doppler flowmetry

In this study, we derive a fast, novel time-domain algorithm to compute the nth-order moment of the power spectral density of the photoelectric current as measured in laser-Doppler flowmetry (LDF). It is well established that in the LDF literature these moments are closely related to fundamental physiological parameters, i.e. concentration of moving erythrocytes and blood flow. In particular, we take advantage of the link between moments in the Fourier domain and fractional derivatives in the temporal domain. Using Parseval's theorem, we establish an exact analytical equivalence between the time-domain expression and the conventional frequency-domain counterpart. Moreover, we demonstrate the appropriateness of estimating the zeroth-, first- and second-order moments using Monte Carlo simulations. Finally, we briefly discuss the feasibility of implementing the proposed algorithm in hardware.