Lars Thrane

Determination of optical scattering properties of highly-scattering media in optical coherence tomography images

We developed a new algorithm that fits optical coherence tomography (OCT) signals as a function of depth to a general theoretical OCT model which takes into account multiple scattering effects. With use of this algorithm, it was possible to extract both the scattering coefficient and anisotropy factor from a particular region of interest in an OCT image. The extraction algorithm was evaluated against measurements from an integrating sphere on a set of tissue phantoms and yielded valid results. Finally, a preliminary ex vivo OCT investigation on human aortic specimen indicated that the algorithm may contribute importantly to differentiation between normal and atherosclerotic arteries. We conclude that this algorithm may facilitate tissue characterization by OCT.

Enhanced optical coherence tomography imaging by multiple scan averaging

Aims: To describe a method for computerised alignment and averaging of sequences in optical coherence tomography (OCT) B-scans and to present selected clinical observations based on the resulting improvement in retinal imaging. Methods: A methodological study and retrospective investigation of selected cases. Five human subjects were included, one healthy subject, two patients with central serous chorioretinopathy, one patient with branch retinal vein occlusion, and one patient with cilioretinal artery pseudo-occlusion. Based on computerised alignment of sets of B-scans obtained at identical retinal locations, average OCT images were produced and displayed in false colour or grayscale. These enhanced tomograms were compared with other morphological and functional characteristics. Results: Improved retinal imaging enabled assignment of the OCT image to retinal anatomy particularly at the outer layer of the photoreceptors and the retinal pigment epithelium, both in the healthy eye and in pathology. Identification of both post-oedematous structural disorganisation as well as post-ischaemic attenuation of the inner retina was superior to standard OCT images. Conclusions: Averaging of multiple OCT B-scans enhances the quality of retinal imaging sufficiently to reveal new details of retinal pathophysiology. Using the technique on OCT3 scans enables visualisation of details comparable with the results obtained using ultra high resolution OCT.

Optical Coherence Tomography A New High-Resolution Imaging Technology to Study Cardiac Development in Chick Embryos

Background—Optical coherence tomography (OCT) is a depth-resolved, noninvasive, non-destructive imaging modality, the use of which has yet to be fully realized in developmental biology. Methods and Results—We visualized embryonic chick hearts at looping stages using an OCT system with a 22 &mgr;m axial and 27 &mgr;m lateral resolution and an acquisition rate of 4000 A-scans per second. Normal chick embryos from stages 14 to 22 and sham-operated and cardiac neural crest-ablated embryos from stages 15 and 18 were scanned by OCT. Three-dimensional data sets were acquired and processed to create volumetric reconstructions and short video clips. The OCT-scanned embryos (2 in each group) were photographed after histological sectioning in comparable planes to those visualized by OCT. The optical and histological results showing cardiovascular microstructures such as myocardium, the cardiac jelly, and endocardium are presented. Conclusions—OCT is a powerful imaging modality which can provide new insight in assessing and understanding normal and abnormal cardiac development in a variety of animal models.

Assessment of Optical Coherence Tomography Imaging in the Diagnosis of Non-Melanoma Skin Cancer and Benign Lesions Versus Normal Skin: Observer-Blinded Evaluation by Dermatologists and Pathologists

BACKGROUND Optical coherence tomography (OCT) is an optical imaging technique that may be useful in diagnosis of non‐melanoma skin cancer (NMSC). OBJECTIVES To describe OCT features in NMSC such as actinic keratosis (AK) and basal cell carcinoma (BCC) and in benign lesions and to assess the diagnostic accuracy of OCT in differentiating NMSC from benign lesions and normal skin. METHODS AND MATERIALS OCT and polarization‐sensitive (PS) OCT from 104 patients were studied. Observer‐blinded evaluation of OCT images from 64 BCCs, 1 baso‐squamous carcinoma, 39 AKs, two malignant melanomas, nine benign lesions, and 105 OCT images from perilesional skin was performed; 50 OCT images of NMSC and 50 PS‐OCT images of normal skin were evaluated twice. RESULTS Sensitivity was 79% to 94% and specificity 85% to 96% in differentiating normal skin from lesions. Important features were absence of well‐defined layering in OCT and PS‐OCT images and dark lobules in BCC. Discrimination of AK from BCC had an error rate of 50% to 52%. CONCLUSION OCT features in NMSC are identified, but AK and BCC cannot be differentiated. OCT diagnosis is less accurate than clinical diagnosis, but high accuracy in distinguishing lesions from normal skin, crucial for delineating tumor borders, was obtained.

Morphology and Epidermal Thickness of Normal Skin Imaged by Optical Coherence Tomography

Background: Optical coherence tomography (OCT) is an optical imaging technology with a potential in the non-invasive diagnosis of skin cancer. To identify skin pathologies using OCT, it is of prime importance to establish baseline morphological features of normal skin. Aims: The aim of this study is to describe normal skin morphology using OCT and polarization-sensitive OCT (PS-OCT), which is a way of representing birefringent tissue such as collagen in OCT images. Anatomical locations in 20 healthy volunteers were imaged, and epidermal thickness (ET) was measured and compared to age, gender and skin colour. Methods: OCT imaging is based on infrared light reflection/backscatter from tissue. PS-OCT detects birefringence of tissue. Imaging was performed in 12 skin regions. ET was calculated from the OCT images. Results: Normal skin has a layered structure. Layering is less pronounced in adults. In glabrous skin the stratum corneum is visible. Children had larger ET (p < 0.0001). Age had a negative correlation with ET (p < 0.05). No gender- or skin-type-related differences in ET were found. Conclusion: This study contributes to understanding OCT and PS-OCT images of normal skin and indicates that OCT can be used for both the qualitative and quantitative assessment of skin.

In vivo thickness measurement of basal cell carcinoma and actinic keratosis with optical coherence tomography and 20-MHz ultrasound

Background  Accurate assessment of tumour size is important when planning treatment of nonmelanoma skin cancer (NMSC). Imaging with optical coherence tomography (OCT) has the potential to diagnose and measure depth of NMSC.

OCT imaging of skin cancer and other dermatological diseases

Optical coherence tomography (OCT) provides clinicians and researchers with micrometer-resolution, in vivo, cross-sectional images of human skin up to several millimeter depth. This review of OCT imaging applied within dermatology covers the application of OCT to normal skin, and reports on a large number of applications in the fields of non-melanoma skin cancer, malignant melanomas, psoriasis and dermatitis, infestations, bullous skin diseases, tattoos, nails, haemangiomas, and other skin diseases.

The effect of measuring procedure on the apparent rheological properties of self-compacting concrete

Abstract Torque versus time during testing of the rheological properties of fresh concrete has been investigated. The testing was performed in a BML viscometer and on a self-compacting concrete (w/c=0.45, 70% rapid hardening Portland cement, 3% silica fume, 27% fly ash, third generation superplasticizer). The relaxation period needed to obtain steady-state flow may affect the rheological properties estimated and should be taken into account in the selection of measuring procedures. Nonsteady state is likely to cause an overestimation of the plastic viscosity and an underestimation of the yield value. Furthermore, lack of steady state may explain the apparent shear-thickening behaviour of self-compacting concrete reported elsewhere.

Optical coherence tomography for imaging of skin and skin diseases.

Optical coherence tomography (OCT) is an emerging imaging technology based on light reflection. It provides real-time images with up to 2-mm penetration into the skin and a resolution of approximately 10 microm. It is routinely used in ophthalmology. The normal skin and its appendages have been studied, as have many diseases. The method can provide accurate measures of epidermal and nail changes in normal tissue. Skin cancer and other tumors, as well as inflammatory diseases, have been studied and good agreement found between OCT images and histopathological architecture. OCT also allows noninvasive monitoring of morphologic changes in skin diseases and may have a particular role in the monitoring of medical treatment of nonmelanoma skin cancer. The technology is however still evolving and continued technological development will necessitate an ongoing evaluation of its diagnostic accuracy. Several technical solutions are being pursued to further improve the quality of the images and the data provided, and OCT is being integrated in multimodal imaging devices that would potentially be able to provide a quantum leap to the imaging of skin in vivo.

High-resolution in vivo imaging of the cross-sectional deformations of contracting embryonic heart loops using optical coherence tomography

The embryonic heart tube consists of an outer myocardial tube, a middle layer of cardiac jelly, and an inner endocardial tube. It is said that tubular hearts pump the blood by peristaltoid contractions. The traditional concept of cardiac peristalsis sees the cyclic deformations of pulsating heart tubes as concentric narrowing and widening of tubes of circular cross‐section. We have visualized the cross‐sectional deformations of contracting embryonic hearts in chick embryos (HH‐stages 9–17) using real‐time high‐resolution optical coherence tomography. Cardiac contractions are detected from HH‐stage 10 onward. During the cardiac cycle, the myocardial tube undergoes concentric narrowing and widening while the endocardial tube undergoes eccentric narrowing and widening, having an elliptic cross‐section at end‐diastole and a slit‐shaped cross‐section at end‐systole. The eccentric deformation of the endocardial tube is the consequence of an uneven distribution of the cardiac jelly. Our data show that the cyclic deformations of pulsating embryonic heart tubes run other than originally thought. There is evidence that heart tubes of elliptic cross‐section might pump blood with a higher mechanical efficiency than those of circular‐cross section. The uneven distribution of cardiac jelly seems to prefigure the future AV and cono‐truncal endocardial cushions. Developmental Dynamics 237:953–961, 2008.