I was fortunate to work with/for Dr Britton Chance as his postdoctoral fellow, in the Biochemistry and Biophysics Department at the University of Pennsylvania, between August 1991 and January 1994. As anyone who worked for him, I had a sufficient dosage of \Britton Chance" over the years. Initially, to me, I felt that he was someone who was above regular people and far away to reach. Then I became to know him as a person, who was simple and complicated at the same time, with a persistent pursuit for his life interests, i.e., the advancement in science related to human health. As far as it goes to science (and perhaps with sailing), he had few boundary: He communicated with any age group, any one from any country with any cultural background. Any scientists were welcomed to his lab, his own house, and even his boat. He was happy with minimal material things. He kept his friendship faithfully. From him, I came to know how much one person can actually do during a life time. I am very grateful that I got to know him during my life path. In this paper, I list some of my experiences with him scientifically and also how and what I learned from him impacted my research and personal life.

Dedicated to the memory of Professor Britton Chance on the occasion of his 100th birthday (July 24th, 2013), and remembering many exciting discussions on the oxygenation of breast cancer, on tumor hypoxia in general and imaging of the oxygenation status of malignant tumors. Hypoxic tissue subvolumes are a hallmark feature of solid malignant tumors, relevant for cancer therapy and patient outcome because they increase both the intrinsic aggressiveness of tumor cells and their resistance to several commonly used anticancer strategies. Pathogenetic mechanisms leading to hypoxia are diverse, may coexist within the same tumor and are commonly grouped according to the duration of their effects. Chronic hypoxia is mainly caused by diffusion limitations resulting from enlarged intercapillary distances and adverse diffusion geometries and — to a lesser extent — by hypoxemia, compromised perfusion or long-lasting microregional flow stops. Conversely, acute hypoxia preferentially results from transient disruptions in perfusion. While each of these features of the tumor microenvironment can contribute to a critical reduction of oxygen availability, the delivery of imaging agents (as well as nutrients and anticancer agents) may be compromised or remain unaffected. Thus, a critical appraisal of the effects of the various mechanisms leading to hypoxia with regard to the blood-borne delivery of imaging agents is necessary to judge their ability to correctly represent the hypoxic phenotype of solid malignancies.

Britton Chance pursued his research and sailing until his death at age 97. His 100th anniversary was memorialized in this paper from longevity viewpoint. His lifelong work was very creative. His life was very colorful. His aging was very successful. He has lived a longevity.

Upconverting lanthanide nanoparticles overcome many of the problems associated with more traditionally used luminescent contrast agents, such as photobleaching, autofluorescence, cytotoxicity and phototoxicity. For this reason, they are an attractive choice for biomedical imaging applications, particularly for imaging in living tissues. The last decade has seen numerous improvements to these nanocrystals, but a comprehensive guide to the synthesis of upconverting lanthanide nanoparticles has not yet been written. Methods vary from paper to paper and from group to group, and results vary between research groups for each method. For this reason, development of these nanoparticles remains a significant endeavor for any research group interested in joining the field. In this review, we look at the varying synthetic methods employed over the last decade and detail methodology for a select few that have been favored in the field.

At present, there are no methods that determine the total microbial load on an abiotic substrate in real time. The utility of such a capability ranges from sterilization and medical diagnostics to the search for new microorganisms in the environment and study of their ecological niches. We report the development of a hand-held, fluorescence detection device and demonstrate its applicability to the field detection of Arctic bacteria. This technology is based on the early pioneering work of Britton Chance which elucidated the intrinsic fluorescence of a number of metabolites and protein cofactors in cells, including reduced pyridine nucleotides, cytochromes and flavins. A PDA controls the device (fluorescence excitation and data collection) and processes the multiwavelength signals to yield bacterial cell counts, including estimates of live cells, dead cells and endospores. Unlike existing methods for cell counting, this method requires no sample contact or addition of reagents. The use of this technology is demonstrated with in situ measurements of two sub-glacial microbial communities at sites in Palander and colonized surface rocks in the Bockfjord Volcanic Complex during AMASE 2008 (Arctic Mars Analog Svalbard Expedition). The total bacterial load on the interrogated sample surfaces ranged from < 20 cells/ cm² to > 10⁹ cells/cm².

The ability to resolve the spatio-temporal complexity of intracellular O₂ distribution is the \Holy Grail" of cellular physiology. In an effort to obtain a minimally invasive approach to the mapping of intracellular O₂ tensions, two methods of phosphorescent lifetime imaging microscopy were compared in the current study and gave similar results. These were two-photon confocal laser scanning microscopy with pinhole shifting, and picosecond time-resolved epi-phosphorescence microscopy using a single 0.5 μm focused spot. Both methods utilized Ru coordination complex embedded nanoparticles (45 nm diameter) as the phosphorescent probe, excited using pulsed outputs of a titanium–sapphire Tsunami lasers (710–1050 nm).

The heart requires continuous ATP availability that is generated in the mitochondria. Although studies using the cell culture and perfused organ models have been carried out to investigate the biochemistry in the mitochondria in response to a change in substrate supply, mitochondrial bioenergetics of heart under normal feed or fasting conditions has not been studied at the tissue level with a sub-millimeter spatial resolution either in vivo or ex vivo. Oxidation of many foodderived metabolites to generate ATP in the mitochondria is realized through the NADH/NAD＋ couple acting as a central electron carrier. We employed the Chance redox scanner — the lowtemperature fluorescence scanner to image the three-dimensional (3D) spatial distribution of the mitochondrial redox states in heart tissues of rats under normal feeding or an overnight starvation for 14.5 h. Multiple consecutive sections of each heart were imaged to map three redox indices, i.e., NADH, oxidized flavoproteins (Fp, including flavin adenine dinucleotide (FAD)) and the redox ratio NADH/Fp. The imaging results revealed the micro-heterogeneity and the spatial distribution of these redox indices. The quantitative analysis showed that in the fasted hearts the standard deviation of both NADH and Fp, i.e., SD NADH and SD Fp, significantly decreased with a p value of 0.032 and 0.045, respectively, indicating that the hearts become relatively more homogeneous after fasting. The fasted hearts contained 28.6% less NADH (p = 0.038). No signi ficant change in Fp was found (p = 0.4). The NADH/Fp ratio decreased with a marginal p value (0.076). The decreased NADH in the fasted hearts is consistent with the cardiac cells' reliance of fatty acids consumption for energy metabolism when glucose becomes scarce. The experimental observation of NADH decrease induced by dietary restriction in the heart at tissue level has not been reported to our best knowledge. The Chance redox scanner demonstrated the feasibility of 3D imaging of the mitochondrial redox state in the heart and provides a useful tool to study heart metabolism and function under normal, dietary-change and pathological conditions at tissue level.

Recently, the simplified spherical harmonics equations (SPN) model has attracted much attention in modeling the light propagation in small tissue geometries at visible and near-infrared wavelengths. In this paper, we report an efficient numerical method for fluorescence molecular tomography (FMT) that combines the advantage of SPN model and adaptive hp finite element method (hp-FEM). For purposes of comparison, hp-FEM and h-FEM are, respectively applied to the reconstruction process with diffusion approximation and SPN model. Simulation experiments on a 3D digital mouse atlas and physical experiments on a phantom are designed to evaluate the reconstruction methods in terms of the location and the reconstructed fluorescent yield. The experimental results demonstrate that hp-FEM with SPN model, yield more accurate results than h-FEM with diffusion approximation model does. The phantom experiments show the potential and feasibility of the proposed approach in FMT applications.

Development of the use of flavin and nicotinamide-adenine nucleotide fluorescence in monitoring the redox state of the free mitochondrial NADH/NADt couple in cells, tissues and organs is reviewed. A break-through was the identification of dihydrolipoamide dehydrogenase (FpL) as the major NAD-linked fluorescent flavoprotein of mitochondria. This mitochondrial matrix flavoprotein is in equilibrium with the free NADH/NAD＋ pool and its mid-potential is sufficiently near to that of NADH/NAD＋ so that its percentage reduction follows that of the latter. Possibilities of monitoring mitochondrial and cytosolic NADH depend on the population density of mitochondria and thus are tissue-dependent. Upon a shift toward reduction, fluorescence intensities of NADH and flavins swing to reciprocal directions, so that the NADH/flavin fluorescence ratio can be used to increase the sensitivity of redox monitoring. This method is attaining widening use in studies on metabolic regulation under normal and pathological conditions.

Acute tubular necrosis (ATN) induced by ischemia is the most common insult to donor kidneys destined for transplantation. ATN results from swelling and subsequent damage to cells lining the kidney tubules. In this study, we demonstrate the capability of optical coherence tomography (OCT) to image the renal microstructures of living human donor kidneys and potentially provide a measure to determine the extent of ATN. We also found that Doppler-based OCT (i.e., DOCT) reveals renal blood flow dynamics that is another major factor which could relate to posttransplant renal function. All OCT/DOCT observations were performed in a noninvasive, sterile and timely manner on intact human kidneys both prior to (ex vivo) and following (in vivo) their transplantation. Our results indicate that this imaging model provides transplant surgeons with an objective visualization of the transplant kidneys prior and immediately post transplantation.

As near-infrared spectroscopy (NIRS) broadens its application area to different age and disease groups, motion artifacts in the NIRS signal due to subject movement is becoming an important challenge. Motion artifacts generally produce signal fluctuations that are larger than physiological NIRS signals, thus it is crucial to correct for them before obtaining an estimate of stimulus evoked hemodynamic responses. There are various methods for correction such as principle component analysis (PCA), wavelet-based filtering and spline interpolation. Here, we introduce a new approach to motion artifact correction, targeted principle component analysis (tPCA), which incorporates a PCA filter only on the segments of data identified as motion artifacts. It is expected that this will overcome the issues of filtering desired signals that plagues standard PCA filtering of entire data sets. We compared the new approach with the most effective motion artifact correction algorithms on a set of data acquired simultaneously with a collodion-fixed probe (low motion artifact content) and a standard Velcro probe (high motion artifact content). Our results show that tPCA gives statistically better results in recovering hemodynamic response function (HRF) as compared to wavelet-based filtering and spline interpolation for the Velcro probe. It results in a significant reduction in mean-squared error (MSE) and significant enhancement in Pearson's correlation coefficient to the true HRF. The collodion-fixed fiber probe with no motion correction performed better than the Velcro probe corrected for motion artifacts in terms of MSE and Pearson's correlation coefficient. Thus, if the experimental study permits, the use of a collodion-fixed fiber probe may be desirable. If the use of a collodion-fixed probe is not feasible, then we suggest the use of tPCA in the processing of motion artifact contaminated data.

To celebrate the scientific legacy and spirit of the late Dr. Britton Chance (1913–2010) and his 100th birthday, the Britton Chance International Symposium on Metabolic Imaging and Spectroscopy was held at the Perelman School of Medicine, University of Pennsylvania on June 18–19th, 2013. The symposium brought together over 200 physicists, engineers, biologists and clinicians from all over the world including Europe, Asia and North America. The latest research innovations and clinical progresses by optical, nuclear magnetic resonance (NMR) and nuclear medicine methods were presented and discussed extensively.

NAD+/NADH redox state has been implicated in many diseases such as cancer and diabetes as well as in the regulation of embryonic development and aging. To fluorimetrically assess the mitochondrial redox state, Dr. Chance and co-workers measured the fluorescence of NADH and oxidized flavoproteins (Fp) including flavin–adenine–dinucleotide (FAD) and demonstrated their ratio (i.e. the redox ratio) is a sensitive indicator of the mitochondrial redox states. The Chance redox scanner was built to simultaneously measure NADH and Fp in tissue at submillimeter scale in 3D using the freeze-trap protocol. This paper summarizes our recent research experience, development and new applications of the redox scanning technique in collaboration with Dr. Chance beginning in 2005. Dr. Chance initiated or actively involved in many of the projects during the last several years of his life. We advanced the redox scanning technique by measuring the nominal concentrations (in reference to the frozen solution standards) of the endogenous fluorescent analytes, i.e., [NADH] and [Fp] to quantify the redox ratios in various biological tissues. The advancement has enabled us to identify an array of the redox indices as quantitative imaging biomarkers (including [NADH], [Fp], [Fp]/([NADH]+[Fp]), [NADH]/[Fp], and their standard deviations) for studying some important biological questions on cancer and normal tissue metabolism. We found that the redox indices were associated or changed with (1) tumorigenesis (cancer versus non-cancer of human breast tissue biopsies); (2) tumor metastatic potential; (3) tumor glucose uptake; (4) tumor p53 status; (5) PI3K pathway activation in premalignant tissue; (6) therapeutic effects on tumors; (7) embryonic stem cell differentiation; (8) the heart under fasting. Together, our work demonstrated that the tissue redox indices obtained from the redox scanning technique may provide useful information about tissue metabolism and physiology status in normal and diseased tissues. The Chance redox scanner and other redox imaging techniques may have wide-ranging potential applications in many fields, such as cancer, diabetes, developmental process, mitochondrial diseases, neurodegenerative diseases, and aging.

Britton Chance was a pioneer in many scientific fields such as enzymatic reaction kinetics, bioenergetics, metabolism, in vivo NMR, and biophotonics. As an engineer, physical chemist, physicist, physiologist, biophysicist, biochemist, innovator and educator, he had worked in diversified fields over extended periods between 1926 until his death in 2010, at the age of 97. In order to illustrate his scientific career and great impact on research from a new perspective, we employ scientometric analysis tools to analyze the publications of Britton Chance with data downloaded from the ISI Citation Indexes in April 2013. We included articles, reviews and proceeding papers but excluded meeting abstracts. In total, we obtained 1023 publication records with 1236 authors in 266 journals with 17,114 citations from 1945 to 2013. We show the annual publications and citations that Britton Chance received from 1945 to 2013, and generate HistCite maps on the basis of the global citations (GCS) and local (self) citations (LCS) to show the citation relationships among the top-30 publications of Britton Chance. Metabolism and the development of physical methods to probe it appear to be the connecting thread of the lifelong research of Britton Chance. Furthermore, we generate the journal map and co-authorship map to show the broad scope of research topics and collaborators and the high impacts of the scientific oeuvre of Britton Chance ranging from physics, engineering, chemistry and biology to medicine.

In obstructive sleep apnea syndrome (OSA) the periodic reduction or cessation of breathing due to narrowing or occlusion of the upper airway during sleep leads to an impaired cerebral vascular autoregulation that is associated with an increased cardiovascular risk, including stroke. Continuous positive airways pressure (CPAP) therapy at night is the most effective treatment for OSA and has been shown to reduce the cardiovascular risk in OSA patients. However, there is no suitable bedside monitoring method evaluating the recovery of cerebral hemodynamics during CPAP therapy. Near-infrared spectroscopy (NIRS) is ideally suited for non-invasive monitoring the cerebral hemodynamics during sleep due to its properties of local measurement, totally safe application and good tolerance to motion. In this pilot study, we monitored cerebral hemodynamics during standard CPAP therapy at night in three patients with severe OSA using NIRS. We found periodic oscillations in HbO2, HHb, tissue oxygenation index (TOI) and blood volume (BV) associated with periodic apnea events without CPAP in all OSA patients. These oscillations were eliminated under the optimal CPAP pressures in all patients. These results suggested that the recovery of cerebral hemodynamics impaired by apnea events can be evaluated by bedside NIRS measurements in real time during all night CPAP therapy. NIRS is a useful bedside monitoring tool to evaluate the treatment efficacy of CPAP therapy in patients with OSA.

Hypoxia is closely related to many diseases and often leads to death. Early detection and identification of the hypoxia causes may help to promptly determine the right rescue plan and reduce the mortality. We proposed a new multiparametric monitoring method employing mitochondrial reduced nicotinamide adenine dinucleotide (NADH) fluorescence, regional reflectance, regional cerebral blood flow (CBF), electrocardiography (ECG), and respiration under six kinds of acute hypoxia in four categories to investigate a correlation between the parameter variances and the hypoxia causes. The variation patterns of the parameters were discussed, and the combination of NADH and CBF may contribute to the identification of the causes of hypoxia.