A matrix-free algorithm for multiple wavelength fluorescence tomography

In the recent years, there has been an increase in applications of non-contact diffusion optical tomography. Especially when the objective is the recovery of fluorescence targets. The non-contact acquisition systems with the use of a CCD-camera produce much denser sampled boundary data sets than fibre-based systems. When model-based reconstruction methods are used, that rely on the inversion of a derivative operator, the large number of measurements poses a challenge since the explicit formulation and storage of the Jacobian matrix could be in general not feasible. This problem is aggravated further in applications, where measurements at multiple wavelengths are used. We present a matrix-free model-based reconstruction method, that addresses the problems of large data sets and reduces the computational cost and memory requirements for the reconstruction. The idea behind the matrix-free method is that information about the Jacobian matrix could be available through matrix times vector products so that the creation and storage of big matrices can be avoided. We tested the method for multiple wavelength fluorescence tomography with simulated and experimental data from phantom experiments, and we found substantial benefits in computational times and memory requirements. (C) 2009 Optical Society of Americ

Autofluorescence insensitive imaging using upconverting nanocrystals in scattering media

Autofluorescence is a nuisance in the field of fluorescence imaging and tomography of exogenous molecular markers in tissue, degrading the quality of the collected data. In this letter, we report autofluorescence insensitive imaging using highly efficient upconverting nanocrystals (NaYF4: Yb3+ /Tm3+) in a tissue phantom illuminated with near- infrared radiation of 85 mW/cm(2). It was found that imaging with such nanocrystals leads to an exceptionally high contrast compared to traditional downconverting fluorophores due to the absence of autofluorescence. Upconverting nanocrystals may be envisaged as important biological markers for tissue imaging purposes. c 2008 American Institute of Physics. [DOI: 10.1063/1.3005588

Coronary artery surgery: cardiotomy suction or cell salvage?

Coronary artery bypass grafting (CABG) today results in what may be regarded as acceptable levels of blood loss with many institutions avoiding allogeneic red cell transfusion in over 60% of their patients. The majority of cardiac surgeons employ cardiotomy suction to preserve autologous blood during on-pump coronary artery bypass surgery; however the use of cardiotomy suction is associated with a more pronounced systemic inflammatory response and a resulting coagulopathy as well as exacerbating the microembolic load. This leads to a tendency to increased blood loss, transfusion requirement and organ dysfunction. Conversely, the avoidance of cardiotomy suction in coronary artery bypass surgery is not associated with an increased transfusion requirement. There is therefore no indication for the routine use of cardiotomy suction in on-pump coronary artery surgery

Heparin coating and cardiotomy suction in cardiopulmonary bypass

The present thesis addresses various means of reducing inflammatory responses associated with cardiopulmonary bypass (CPB) and retransfusion of pericardial suction blood (PSB) during cardiac surgery. Four (I-IV) prospective randomised controlled clinical trials comprising 475 patients were performed in the following areas: effects of heparin coating on measures of clinical outcome and memory function (I, II), inflammatory reactions in PSB and its systemic effects after retransfusion using cardiotomy suction or cell salvage (III) and effects of retransfusion of PSB on memory function and release patterns of protein S100B (IV). The use of heparin coated CPB-circuits was associated with a decrease of postoperative blood loss (I, II), transfusion requirements (II), shorter stay in hospital (I) decreased postoperative ventilator time (I), lower incidences of atrial fibrillation (II) and neurological deviations (I), reduction in releases of protein S100B (I, II) and lower postoperative creatinine elevation (I, II). PSB contained high concentrations of cytokines, complements, myeloperoxidase, free plasma haemoglobin and protein S100B (III, IV). Retransfusion using cardiotomy suction increased the systemic concentrations of free plasma haemoglobin and protein S100B, whereas retransfusion using cell salvage caused no detectable systemic effects (III, IV). CPB was associated with a small but significant release of protein S100B, despite elimination of PSB-contained protein S100B using cell salvage (IV). Subtle signs of impaired memory function were identified that were not associated with the use of heparin coated CPB-circuits (I, II) or retransfusion of PSB (IV). Key words: cardiopulmonary bypass, oxygenators, heparin, S100 proteins, blood loss, haemostasis, memory, outcome and process assessment

Optical spectroscopy and fluorescence imaging for cancer diagnostics

This work presents optical methods for diagnosing cancer. A complementary method for diagnosing eye cancer was investigated using a technique developed within this work named transscleral optical spectroscopy (TOS). Furthermore, nano-sized crystals doped with lanthanides were exploited as probes for fluorescence imaging with direct applications to preclinical cancer research. Almost all intraocular malignancies can today be correctly diagnosed using techniques like ophthalmoscopy, ultrasonography and fluorescein angiography. Even with the rich flora of tools available, some tumors present non-typical behaviors and are difficult to diagnose. As a complementary diagnostic method, TOS was developed, which exploits the natural optical contrast in tissue for diagnosis. The method is particularly sensitive in identifying physiological changes characteristic of tumors, i.e. tissue hemoglobin (total, oxy- , and deoxy- forms), oxygen saturation, blood volume fraction, water content, melanin content and cellular structure. In a series of experiments on porcine eyes, TOS was successful in quantifying the blood and melanin content of tumor phantoms placed in the choroid. It was also showed that TOS measurements did not cause any visible damage to the sclera, resulted in a significant temperature rise, or led to an unacceptable intra ocular pressure elevation. In further experiments on enucleated human eyes with a predetermined melanoma diagnosis, TOS measurements were found to correlated well with the degree of pigmentation in the melanoma. To summarize, TOS offers a tool to probe the physiology of intraocular tumor, which can be used in a complementary diagnosis. Fluorescence imaging is a versatile tool for studying biology on the nanometer to centimeter length-scale through labeling tissue with fluorescent probes to induce the desired contrast. In this work, upconverting nanoparticles (UPNs) were evaluated as fluorescent probes for deep tissue fluorescence imaging. Efficient upconversion was achieved using a NaYF4 host co-doped with Yb3+ and Tm3+ or Er3+ ions. In comparison to traditional fluorescent probes, UPNs were found to have the follow benefits: 1) they allow autofluorescence insensitive imaging through anti-Stokes shifted 2) they show no signs of photo-damage even at high intensities. 3) for deep tissue imaging, they provide higher resolution images. 4) they emit multiple line emissions with large Stoke shifts. To summarize, UPNs hold unique optical properties which make them attractive as fluorescent probes