A comparison of emulsifiers for the formation of oil-in-water emulsions: stability of the emulsions within 9 h after production and MR signal properties

Objective

To provide a basis for the selection of suitable emulsifiers in oil-in-water emulsions used as tissue analogs for MRI experiments. Three different emulsifiers were investigated with regard to their ability to stabilize tissue-like oil-in-water emulsions. Furthermore, MR signal properties of the emulsifiers themselves and influences on relaxation times and ADC values of the aqueous phase were investigated.

Materials and methods

Polysorbate 60, sodium dodecyl sulfate (SDS) and soy lecithin were used as emulsifiers. MR characteristics of emulsifiers were assessed in aqueous solutions and their function as a stabilizer was examined in oil-in-water emulsions of varying fat content (10, 20, 30, 40, 50%). Stability and homogeneity of the oil-in-water emulsions were evaluated with a delay of 3 h and 9 h after preparation using T₁ mapping and visual control. Signal properties of the emulsifiers were investigated by ¹H-MRS in aqueous emulsifier solutions. Relaxometry and diffusion weighted MRI (DWI) were performed to investigate the effect of various emulsifier concentrations on relaxation times (T₁ and T₂) and ADC values of aqueous solutions.

Results

Emulsions stabilized by polysorbate 60 or soy lecithin were stable and homogeneous across all tested fat fractions. In contrast, emulsions with SDS showed a significantly lower stability and homogeneity. Recorded T₁ maps revealed marked creaming of oil droplets in almost all of the emulsions with SDS. The spectral analysis showed several additional signals for polysorbate and SDS. However, lecithin remained invisible in ¹H-MRS. Relaxometry and DWI revealed different influences of the emulsifiers on water: Polysorbate and SDS showed only minor effects on relaxation times and ADC values of aqueous solutions, whereas lecithin showed a strong decrease in both relaxation times (r_1,lecithin = 0.11 wt.%⁻¹ s⁻¹, r_2,lecithin = 0.57 wt.%⁻¹ s⁻¹) and ADC value (Δ(ADC)_lecithin =  − 0.18 × 10^–3 mm²/s⋅wt.%) with increasing concentration.

Conclusion

Lecithin is suggested as the preferred emulsifier of oil-in-water emulsions in MRI as it shows a high stabilizing ability and remains invisible in MRI experiments. In addition, lecithin is suitable as an alternative means of adjusting relaxation times and ADC values of water.

     

Comparison of T1-weighted 2D TSE, 3D SPGR,and two-point 3D Dixon MRI for automated segmentation of visceral adipose tissue at 3 Tesla

Objectives

To evaluate and compare conventional T1-weighted 2D turbo spin echo (TSE), T1-weighted 3D volumetric interpolated breath-hold examination (VIBE), and two-point 3D Dixon-VIBE sequences for automatic segmentation of visceral adipose tissue (VAT) volume at 3 Tesla by measuring and compensating for errors arising from intensity nonuniformity (INU) and partial volume effects (PVE).

Materials and methods

The body trunks of 28 volunteers with body mass index values ranging from 18 to 41.2 kg/m² (30.02 ± 6.63 kg/m²) were scanned at 3 Tesla using three imaging techniques. Automatic methods were applied to reduce INU and PVE and to segment VAT. The automatically segmented VAT volumes obtained from all acquisitions were then statistically and objectively evaluated against the manually segmented (reference) VAT volumes.

Results

Comparing the reference volumes with the VAT volumes automatically segmented over the uncorrected images showed that INU led to an average relative volume difference of ?59.22 ± 11.59, 2.21 ± 47.04, and ?43.05 ± 5.01 % for the TSE, VIBE, and Dixon images, respectively, while PVE led to average differences of ?34.85 ± 19.85, ?15.13 ± 11.04, and ?33.79 ± 20.38 %. After signal correction, differences of ?2.72 ± 6.60, 34.02 ± 36.99, and ?2.23 ± 7.58 % were obtained between the reference and the automatically segmented volumes. A paired-sample two-tailed t test revealed no significant difference between the reference and automatically segmented VAT volumes of the corrected TSE (p = 0.614) and Dixon (p = 0.969) images, but showed a significant VAT overestimation using the corrected VIBE images.

Conclusion

Under similar imaging conditions and spatial resolution, automatically segmented VAT volumes obtained from the corrected TSE and Dixon images agreed with each other and with the reference volumes. These results demonstrate the efficacy of the signal correction methods and the similar accuracy of TSE and Dixon imaging for automatic volumetry of VAT at 3 Tesla.

     

Morning to evening changes of intramyocellular lipid content in dependence on nutrition and physical activity during one single day: a volume selective 1H-MRS study

Object  

Intramyocellular lipids (IMCL) were shown to be metabolically highly active. In order to get insight into short-term regulation of IMCL and to reveal related problems with standardization in metabolic studies using the common signal ratio IMCL/Cr3, relative concentration changes from morning to evening in the same day were examined under four different nutritional and exercise conditions.     

Improved clinical echo-planar MRI using spatial-spectral excitation

The feline immunodeficiency virus (FIV) model of vertical human immunodeficiency virus type 1 transmission was used to explore the timing and tissue tropisms associated with intrauterine lentivirus infection. Cats chronically infected with FIV-B-2542 and their cesarean-derived fetuses and placentas were assayed by polymerase chain reaction and coculture at defined gestational intervals. Prevalence of fetal FIV infection was 0 at 3 weeks, 5% at 5 weeks, 38% at 7 weeks, and 60% at 9 weeks (term). Fetal tissues exhibiting the highest viral tropism were blood mononuclear cells and brain (each containing virus in 60% of FIV-positive fetuses) and thymus (47%). Maternal hematologic and virus load markers did not vary substantially with gestational stage. Therefore, fetal and/or placental maturation may determine the timing of lentivirus transmission. FIV infection prevalence in term fetuses was equivalent to that seen previously in vaginally delivered offspring, suggesting that most vertical FIV transmission occurs late in utero rather than intrapartum.     

Highly selective water and fat imaging applying multislice sequences without sensitivity to B1 field inhomogeneities

1. Homocysteine is an independent risk factor for cardiovascular disease. The mechanisms by which elevated plasma concentrations of homocysteine are related to the pathogenesis of atherosclerosis are not fully understood. Therefore, we examined the effect of homocysteine on cell replication of rat cultured vascular smooth muscle cells (VSMCs) at concentrations similar to those observed in clinical studies. 2. The incorporation of [3H]-thymidine was used as a marker of mitosis. Homocysteine (250-500 microM) was a weak mitogen as compared to platelet-derived growth factor-BB (PDGF-BB, 1 nM) and serum (10%), but it potentiated the mitogenic effect of PDGF-BB four fold at 500 microM. This enhancement of mitogenesis was blunted by the addition of the scavenging enzyme catalase or the antioxidant N-acetyl-L-cysteine. 3. Furthermore, stimulation of VSMC with homocysteine (25-500 microM) decreased the glutathione peroxidase activity of the cells to 50% of control at 500 microM. Inversely, homocysteine enhanced the superoxide dismutase (SOD) activity to 137% of control at 500 microM, but it had no effect on the catalase activity. 4. Homocysteine decreased the activity of bovine purified liver cytosolic glutathione peroxidase in a time- and dose-dependent manner. The maximum decrease was 50%. 5. In summary, homocysteine has a weak mitogenic effect on VSMC, but it dramatically enhances the mitogenic response of PDGF-BB, presumably by disturbing the activity of antioxidant enzymes.     

Age and gender related effects on adipose tissue compartments of subjects with increased risk for type 2 diabetes: a whole body MRI / MRS study

Quantitative measurement of adipose tissue (AT) compartments in the entire body and of lipids in muscle and liver cells by means of MRI and MRS. Assessment of ageand gender related differences in AT compartments and determination of cross-correlations between AT compartments in a heterogeneous cohort at increased risk for metabolic diseases. One hundred and fifty healthy volunteers with increased risk to type 2 diabetes were examined. T1-weighted MRI was applied for whole-body adipose tissue quantification. Adipose tissue compartments were subdivided in lower extremities, trunk (abdominal subcutaneous (SCAT) and visceral (VAT) adipose tissue), and upper extremities. Intrahepatocellular lipids (IHCL) and intramyocellular lipids (IMCL) in tibialis anterior and soleus muscle were determined by volume selective MRS. Females are characterized by lower %VAT (2.8±1.3% vs. 4.6±1.4% ,p<0.001) and higher %SCAT (14.7±3.9% vs. 9.3±2.9% ,p<0.001). There is a strong correlation between %VAT and age (r=0.64/0.60 for females/males), whereas %SCAT remained virtually unchanged in males (r=-0.09) and was only slightly increaseding in females (r =0.30,p<0.01). For IHCL, age related differences were observed in females with significantly increased IHCL in the older women, but not in males. IMCL contents in both muscles were found almost independent of age in both, males and females. Furthermore, VAT and IHCL show significant correlations in both groups. Assessed age and gender related differences, especially the age related significant increase of VAT and IHCL, as well as cross-correlations between different lipid compartments might contribute to a better understanding of the lipid metabolism under normal and pathologic metabolic conditions in humans.Supported through a grant from the Deutsche Forschungsgemeinschaft (DFG, KFO 114/1)