Purpose: Previous studies have demonstrated how imaging of the breast with patients lying prone using a supportive positioning device markedly facilitates longitudinal and/or multimodal image registration. In this contribution, the authors’ primary objective was to determine if there are differences in the standardized uptake value (SUV) derived from [ 18 F]fluorodeoxyglucose (18F‐FDG) positron emission tomography (PET) in breast tumors imaged in the standard supine position and in the prone position using a specialized positioning device. Methods: A custom positioning device was constructed to allow for breast scanning in the prone position. Rigid and nonrigid phantom studies evaluated differences in prone and supine PET. Clinical studies comprised 18F‐FDG‐PET of 34 patients with locally advanced breast cancer imaged in the prone position (with the custom support) followed by imaging in the supine position (without the support). Mean and maximum values (SUV peak and SUV max , respectively) were obtained from tumor regions‐of‐interest for both positions. Prone and supine SUV were linearly corrected to account for the differences in 18F‐FDG uptake time. Correlation, Bland–Altman, and nonparametric analyses were performed on uptake time‐corrected and uncorrected data. Results: SUV from the rigid PET breast phantom imaged in the prone position with the support device was 1.9% lower than without the support device. In the nonrigid PET breast phantom, prone SUV with the support device was 5.0% lower than supine SUV without the support device. In patients, the median (range) difference in uptake time between prone and supine scans was 16.4 min (13.4–30.9 min), which was significantly—but not completely—reduced by the linear correction method. SUV peak and SUV max from prone versus supine scans were highly correlated, with concordance correlation coefficients of 0.91 and 0.90, respectively. Prone SUV peak and SUV max were significantly lower than supine in both original and uptake time‐adjusted data across a range of index times ( P < < 0.0001, Wilcoxon signed rank test). Before correcting for uptake time differences, Bland–Altman analyses revealed proportional bias between prone and supine measurements (SUV peak and SUV max ) that increased with higher levels of FDG uptake. After uptake time correction, this bias was significantly reduced ( P < 0.01). Significant prone‐supine differences, with regard to the spatial distribution of lesions relative to isocenter, were observed between the two scan positions, but this was poorly correlated with the residual (uptake time‐corrected) prone‐supine SUV peak difference ( P = 0.78). Conclusions: Quantitative 18F‐FDG‐PET/CT of the breast in the prone position is not deleteriously affected by the support device but yields SUV that is consistently lower than those obtained in the standard supine position. SUV differences between scans arising from FDG uptake time differences can be substantially reduced, but not removed entirely, with the current correction method. SUV from the two scan orientations is quantitatively different and should not be assumed equivalent or interchangeable within the same subject. These findings have clinical relevance in that they underscore the importance of patient positioning while scanning as a clinical variable that must be accounted for with longitudinal PET measurement, for example, in the assessment of treatment response.
1123 Objectives Type 2 Diabetes Mellitus (T2DM) is attributed to systemic disturbances in metabolism characterized by impaired insulin action in peripheral tissues. In the current work, preclinical PET imaging with [18F]FDG and [11C]Palmitate in conjunction with kinetic modeling was utilized to identify disturbances in glucose and fatty acid (FA) metabolism and to monitor the effect of PPARγ agonist rosiglitazone (RGZ) in liver, heart, muscle, and brown adipose tissue. Methods Small-animal PET was performed on Lean Zucker (ZL) and Zucker Diabetic Fatty (ZDF) rats assigned to these groups: Controls, age 14wks, no treatment (NT), 1) ZL (N=6), 2) ZDF (N=6); 3) ZDF age 19wks, NT (N=6); and 4) “Treatment group”, ZDF rats treated with 4 mg/kg/day RGZ for 5 weeks (14wks to 19wks) (N=6). A separate group of ZL and ZDF rats (N=4) were used to characterize arterial and portal vein kinetics and to reconstruct liver dual input function. Animals were fasted overnight prior to imaging. The imaging session began with a 20-minute acquisition with [11C]Palmitate followed by a 60-minute [18F]FDG. In each session, 5-6 arterial whole-blood samples were obtained for substrate levels and metabolite analysis. A two compartment kinetic model was used for [18F]FDG and [11C]Palmitate in muscle, brown fat and liver, and a four compartment model for [11C]Palmitate was used in the heart. Results Glucose uptake was impaired in brown fat, muscle, and heart tissues of ZDF rats compared to leans, while RGZ treatment increased glucose uptake compared to untreated ZDF rats. No differences were found in glucose metabolism in the liver. FA uptake decreased, but FA flux increased in brown fat and skeletal muscle of ZDF rats. RGZ treatment resulted in increased uptake of FA in brown fat, but decreased uptake and utilization in liver, muscle and heart. Conclusions Our data indicate tissue-specific mechanisms for glucose and FA disposal as well as differential action of the insulin-sensitizing RGZ to normalize substrate handling. Research Support This work was supported by NIDDK Grant 5R01DK085298.
Microfluidics has received a great deal of attention in the past decade. The ability of modular microfluidic chips to miniaturize integrate chemical and biological systems (µTAS) can be greatly productive in terms of cost and efficiency. During the design of these modular devices, misalignment of materials, geometrical or both is one of the most common problems. These misalignments can have adverse effect in both pressure driven and electrokinetically driven flows. In the present work, Numerical Simulations have been performed to study the effect of material and geometrical mismatch on the flow behavior and species progression in microfluidic interconnects. In the case of electrokinetic flows, simulations were performed for 13%, 50%, 58% and 75% reduction in the available flow area at the mismatch plane. Correlations were developed to predict the flow rate reduction due to the geometrical mismatch in electrokinetic flows. A 13% flow area reduction was found to be insignificant and did not cause an appreciable sample loss. As the amount of geometrical mismatch increases (i.e. area reduction is more than 40%), it can have a significant effect on the sample resolution and on the flow behavior. In the case of pressure driven flows, Numerical Simulations have been performed for three types of interconnection methods: End-to-End, Channel Overlap, and Tube-in- Reservoir interconnection. The effects of geometrical misalignments in these three interconnection methods have been investigated and the results were interpreted in terms of the pressure drop and equivalent length. The amount of misalignment was varied by changing the available flow area ratios. All the configurations were simulated for practically relevant Reynolds numbers ranging from 0.075 to 75. Correlations were developed to predict the pressure drop for any given misalignment area ratio. It was found that for the misalignment area ratio of 2:1 or more, the increase in pressure drop can be drastic. Numerical simulations of Injection and separation were also performed to study the effect of curvatures on the elongation of generated plugs. These end curvatures are commonly encountered during high precision micromilling process as a method to fabricate polymer microfluidic devices. The effect of pinching and pullback voltages on the generation of the sample plugs was investigated and optimum conditions to minimize plug dispersion were found.
Validation of a tolerance analysis for the assembly of modular, polymer microfluidic devices was performed using simulations and experiments. A set of three v-groove and hemisphere-tipped post joints was adopted as a model assembly features. An assembly function with assembly feature dimensions and locations was modeled kinematically. Monte Carlo methods were applied to the assembly function to simulate variation of the assembly. Assembly accuracy was evaluated assuming that the variations of the assembly features were randomly distributed. The estimated mismatches were 118 ± 30 μm and 19 ± 13 μm along the X- and Y-axes, respectively. The estimated vertical gap between the modules at the alignment standards along the X- and Y-axes 312 ± 37 μm and 313 ± 37 μm, compared to the designed value of 287 μm. To validate the tolerance model, two micromilled brass mold inserts containing the assembly features and alignment standards were used to double-sided injection mold polymer parts. The accuracy of the assembly of the modular microdevices was estimated by measuring the mismatch and vertical gaps between alignment standards on each axis. The measured lateral mismatches were 103 ± 6 μm and 16 ± 4 μm along the X- and Y-axes, respectively. The vertical gaps measured for the assemblies were 316 ± 4 μm and 296 ± 9 μm at the X- and Y-axes, compared to the designed distance of 287 μm. Simulation and experimental results were in accordance with each other. The models can be used to predict the assembly tolerance of polymer microfluidic devices and have significant potential for enabling the realization of cost-effective mass production of modular instruments.
