Developing Single-Laser Sources for Multimodal Coherent Anti-Stokes Raman Scattering Microscopy

Coherent anti-Stokes Raman scattering (CARS) microscopy has developed rapidly and is opening the door to new types of experiments. This work describes the development of new laser sources for CARS microscopy and their use for different applications. It is specifically focused on multimodal nonlinear optical microscopy—the simultaneous combination of different imaging techniques. This allows us to address a diverse range of applications, such as the study of biomaterials, fluid inclusions, atherosclerosis, hepatitis C infection in cells, and ice formation in cells. For these applications new laser sources are developed that allow for practical multimodal imaging. For example, it is shown that using a single Ti:sapphire oscillator with a photonic crystal fiber, it is possible to develop a versatile multimodal imaging system using optimally chirped laser pulses. This system can perform simultaneous two photon excited fluorescence, second harmonic generation, and CARS microscopy. The versatility of the system is further demonstrated by showing that it is possible to probe different Raman modes using CARS microscopy simply by changing a time delay between the excitation beams. Using optimally chirped pulses also enables further simplification of the laser system required by using a single fiber laser combined with nonlinear optical fibers to perform effective multimodal imaging. While these sources are useful for practical multimodal imaging, it is believed that for further improvements in CARS microscopy sensitivity, new excitation schemes are necessary. This has led to the design of a new, high power, extended cavity oscillator that should be capable of implementing new excitation schemes for CARS microscopy as well as other techniques. Our interest in multimodal imaging has led us to other areas of research as well. For example, a fiber-coupling scheme for signal collection in the forward direction is demonstrated that allows for fluorescence lifetime imaging without significant temporal distortion. Also highlighted is an imaging artifact that is unique to CARS microscopy that can alter image interpretation, especially when using multimodal imaging. By combining expertise in nonlinear optics, laser development, fiber optics, and microscopy, we have developed systems and techniques that will be of benefit for multimodal CARS microscopy.

Differences in Abdominal and Liver Fat Accumulation Between Obesity-Matched Adults With and Without Type 2 Diabetes

Despite attempts to identify the mechanisms by which obesity leads to the development of Type 2 Diabetes (T2D), it remains unclear why some but not all adults with obesity develop T2D. Given the established associations between visceral adipose tissue (VAT) and liver fat with insulin resistance, we hypothesized that compared to age and obesity matched adults who were non-diabetic (NT2D), adults with T2D would have greater amounts of VAT and liver fat. The International Study of Prediction of Intra-Abdominal Adiposity and Its Relationship with Cardiometabolic Risk/Intra-Abdominal Adiposity (INSPIRE ME IAA) aims to study the associations between VAT and liver fat and risk of developing T2D and cardiovascular disease. Four thousand, five hundred and four participants were initially recruited; from this, 2383 White and Asian adults were selected for this ancillary analysis. The NT2D and T2D groups were matched for age, body mass index (BMI) and waist circumference (WC). The T2D and NT2D groups were also compared to participants with either impaired fasting glucose (IFG) or impaired glucose tolerance (IGT; IFG/IGT)). Abdominal adipose tissue was measured by computed tomography; liver fat was estimated using computed tomography-derived mean attenuation. Secondary analysis determined whether differences existed between NT2D and T2D groups in VAT and liver fat accumulation within selected BMI categories for Whites and Asians. We report across sex and race, T2D and IFG/IGT groups had elevated VAT and liver fat compared to the NT2D group (p<0.05). VAT was not different between IFG/IGT and T2D groups (p>0.05), however liver fat was greater in the T2D group compared to the IFG/IGT group in both Whites and Asians (p<0.05). Within each BMI category, the T2D group had elevated VAT and liver fat compared to the age and anthropometrically matched NT2D group in both Whites and Asians (p<0.05). With few exceptions, abdominal subcutaneous adipose tissue was not different in the T2D or IFG/IGT groups compared to the NT2D group independent of sex and race. Compared to age and obesity-matched adults who are NT2D, we observe that White and Asian adults with T2D, and those with IFG/IGT, present with greater levels of both VAT and liver fat.