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Int Poster J Dent Oral Med 14 (2012), No. 1     15. Mar. 2012

Int Poster J Dent Oral Med 2012, Vol 14 No 1, Poster 576

SDF imaging for assessing mucosal microcirculation and its correlation with OSMF

A review

Language: English
 

Authors:
Senior lecturer Prashant Gupta, Prof Dr Ashok L, HOD, Senior Lecturer Dr Shantala R Naik,
MJP Rohilkhand University, Institute of Dental Sciences, Dept of Oral Medicine and Radiology, Bareilly, Uttar Pradesh, India

Date/Event/Venue:
17th, 18th and 19th December, 2010
22nd national conference of Indian academy of Oral Medicine and Radiology
New Delhi
 

Introduction

Tissue oxygenation is important for organ function. An important approach in understanding tissue dysoxia and the proper choice of treatment is to measure the oxygenation status of the microcirculation. Oral and maxillofacial compartments are highly vascularized areas and offer a very approachable site for noninvasively monitoring and assessing the microcirculation. Recently intravital microscopy has been miniaturized and developed for clinical conditions by the implementation of orthogonal polarization spectral (OPS) imaging in a hand held microscope type device.1 Since it has few drawbacks microvision medical introduced another novel approach as side stream dark field (SDF) imaging.2
 

Principle of SDF imaging

SDF is a stroboscopic LED ring based imaging modality. In SDF imaging illumination is provided by surrounding a central light guide by concentrically placed light emitting diodes (LEDs) to provide sidestream dark field illumination. The lens system in the core of the light guide is optically isolated from the illuminating outer ring thus preventing the microcirculatory image from contamination by tissue surface reflections. Light from the illuminating outer core of the SDF probe, which penetrates the tissue embedded microcirculation by scattering. The LEDs emit a central wavelength of 530nm, chosen to correspond to an isobestic point in the absorption spectra of deoxy and oxyhemoglobin (i.e at 530nm) to ensure optimal optical absorption by the hemoglobin in the RBCs, independent of its oxygenation state. This leads to an image where RBCs are imaged as dark moving globules against a white / grayish background. To improve the imaging of moving structures such as flowing RBCs, the LEDs provide pulsed illumination in synchrony with the CCD frame rate to perform intravital stroboscopy. This stroboscopic imaging partially prevents smearing of moving features, such as flowing RBCs and motion induced blurring of capillaries due to the short illumination intervals.1

Advantages:3,4
• Non invasive and hence makes SDF a attractive and patient friendly instrument
• Provides stroboscopic illumination
• Superior image quality when compared with OPS imaging
• Low power LED illumination allows computer operation and thereby improved clinical applicability

Shortcomings:3,4
• Limited penetration depth limits its use to superficial epithelial layers (upto 500 µm)
• > 1 area is required
• Detectable RBC velocity is physically limited
• Pressure induced microcirculatory alterations occur due to pressure from probe. This leads to false interpretation of actual microcirculatory perfusion.

Fig. 1: illustration of SDF imaging probe Fig. 2: SDF imaging device
 
Fig. 3: SDF imaging device
 
 

Material and Methods

The SDF imaging technology is incorporated into a portable hand held video microscopy instrument for performing noninvasive real time intravital microcirculatory observations on mucosal surfaces.4 SDF imaging is a microscan video microscope (Microvision Medical, Amsterdam, The Netherlands). It is fitted with a 5x objective lens system. The CCD chip is axially translated with respect to the fixed lens system in the tip of SDF probe. It is covered by a sterile disposable cap, the probe can be placed on organ and tissue surfaces to investigate microcirculatory morphology and perfusion under different clinical conditions. To prevent microcirculatory perfusion alterations by applying pressure on imaged area, the probe is placed onto tissue and gently pulled back until contact is lost. Then probe is advanced again slowly to point at which contact was regained and microcirculation is in focus of lens system contained in probe.4
Investigation is done bedside with backrest inclined upright. Instrument is placed on buccal mucosa inferior to the 1st and 2nd molar without applying pressure and gently pivoting the SDF imaging probe wedged between molars. A 2 minute video recording of different adjacent sites is obtained.4 Microcirculation studies requires multiple measurements per time point. Current microcirculatory guidelines dictate that measurements has to be done at 3-5 sites / time point to allow adequate interpretation of results. Length of each image sequence should be > 20 sec.5 All imaging is captured with a 720 × 576 pixel resolution video camera resulting in a 1.0 × 0.75mm imaged mucosal segment. All measurements are recorded for 2 minutes on a video camera and then transferred on monitor.4
Video output is visualized on a monitor and connected to a computer via signal converter to directly and digitally record images onto a hard drive to enable offline analysis of images. The device is mounted in a specifically engineered universal holder.3

Fig. 4: placement of probe on oral mucosa
 
Fig. 5: SDF imaging probe

Interpretation of images

SDF evaluates fuctional state of circulation (perfusion), morphological characteristics of microcirculation such as capillary density and microvessel morphology. Homogeneous perfusion of capillaries is a prerequisite for normal function. Offline image analysis is performed by counting the number of perfused capillaries in each frame. Baseline capillary density is 18.9 ± 2.4 cpll/mm2.3,4

Fig. 6: offline images of capillary diameter Fig. 7: capillary loop showing individual RBCs and plasma gaps
Fig. 8: pulsatile flow observed during during SDF probing to calculate the RBC velocity
 
Fig. 9: leucocyte visualization using SDF

Conclusions

Correlation with the therapy of OSMF: Oral submucous fibrosis still remains enigmatic. The degree of vascularity of diseased mucosa has always been a matter of dispute. Atrophy in OSMF is based on assumption of ischemic epithelium resulting in poorly vascularized stroma. Vasodilators such as Pentoxifylline has also been used in the therapy and found to be an effective adjunct in the treatment of OSMF.6

 
Fig. 10: flow chart correlating SDF imaging with OSMF
 
 

References

  1. D M Milstein, J A H Lindeboom and C Ince: Sidestream dark field imaging and image analysis of oral microcirculation under clinical conditions. AIPCE proceedings of 20th post graduation course in critical care, 2005, Nov 18-21.
  2. C Ince: Sidestream dark field imaging: an important technique to observe sublingual microcirculation. Critical care 2005, 9 (suppl 1), p72.
  3. P T Goedhart, M Khalizada, R Bezemer, J Merza and C Ince: SDF imaging: a novel stroboscopic LED ring based imaging modality for clinical assessing of the microcirculation. Optic express 2007, 15(23), 15101-15114.
  4. D M J Milstein, L C J te Boome, Yuk Wang Chung, J A H Lindeboom, H P van der Akker, B J Biemond and C Ince: Use of sidestream dark field (SDF) imaging for assessing the effects of high dose melphalan and autologous stem cell transplantation on oral mucosal microcirculation in myeloma patients. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010, 109, 91-97.
  5. G M Balestra, R Bezemer, E C Boerma, Ze - Yie Yong, Krishan D Sjauw, A E Engstrom, M Koopmans and C Ince: Improvement of SDF imaging with image acquisition stabilizer. BMC Medical Imaging 2010, 10, 15.
  6. R Rajendran, Vidya Rani and Saleem Shaikh: Pentoxifylline therapy: A new adjunct in the treatment of oral submucous fibrosis. Indian J Dent Res 2006, 17, 190-8.
     

Abbreviations

SDF: side stream dark field
OSMF: oral submucous fibrosis
 

This Poster was submitted by Prashant Gupta.
 

Correspondence address:
Senior lecturer Prashant Gupta
MJP Rohilkhand University
Institute of Dental Sciences, Dept of Oral Medicine and Radiology
Suresh sharma Nagar, Pilibhit bypass road
Bareilly, Uttar Pradesh
India