Effect of surrounding materials on iterative reconstruction-based line-source response function, and annihilations outside the source assessed by a small animal PET scanner.

OBJECTIVE: The aims of this study were (1) to evaluate the effect of surrounding materials on the iterative reconstruction-based line-source response function (IR-RF) of (18)F, (11)C, (13)N, and (15)O using a preclinical PET system, and (2) to determine whether and how annihilation outside the source can be visualized experimentally. METHODS: We performed all the measurements using the LabPET-8 PET/CT subsystem built-in the Triumph II platform (TriFoil Imaging, Inc., Northridge, CA, USA). IR-RF was measured for (18)F, (11)C, (13)N, and (15)O, and was expressed as full-width at half-maximum (FWHM) and full-width at tenth maximum (FWTM) using a glass capillary phantom mounted in materials of various densities, which were chosen to cover the wide range of real tissues. To determine whether and how annihilation outside the source can be visualized, we designed a concentric ring paper phantom, which consisted of a source at the center with 4 ring-like paper layers. RESULTS: When the radionuclides were placed in air (material density 0 g/cm(3)), IR-RFs were similar among the radionuclides tested. As the surrounding material density increased, IR-RFs for higher energy-emitting radionuclides ((11)C, (13)N, and (15)O) became worse, whereas those of (18)F remained relatively constant over the range of surrounding material densities (0-2.17 g/cm(3)). Both FWHM and FWTM values were closely correlated with mean energy of radionuclides at middle to high material densities (material density 0.94-2.17 g/cm(3)). The FWTM/FWHM ratio of high energy-emitting radionuclides such as (15)O increased as a function of material density, which was followed by subsequent decrease at high material densities (1.2-2.17 g/cm(3)). Using a concentric ring paper phantom, annihilations outside the source were visible and measurable. The innermost layer was visible with all radionuclides, whereas the outer layers only with high energy positron emitters. CONCLUSIONS: The results indicate that surrounding material affects IR-RF particularly for high energy positron emitters. Furthermore, annihilation outside the radio-active source can be visualized with some circumstances such as those seen with a concentric ring paper phantom.

Performance evaluation of the eXplore speCZT preclinical imaging system.

OBJECTIVE: The eXplore speCZT is a recently introduced cadmium zinc telluride-based preclinical SPECT system that has a stationary detector design with interchangeable rotating collimators. Our aim was to evaluate the performance of the eXplore speCZT using 99mTc-sources. In particular, the image quality was assessed using the National Electrical Manufacturers Association NU-4 image quality phantom as well as an in vivo mouse. METHODS: Energy resolution, sensitivity and spatial resolution were measured using 99mTc sources. Image quality was assessed using NU-4 image quality phantom. The measurements were performed for 4 available collimators: (1) mouse 7-pinhole collimator (mouse PH); (2) mouse 8-slit collimator (mouse SL); (3) rat 5-pinhole collimator (rat PH); and (4) rat 5-slit collimator (rat SL). Furthermore, a mouse bone imaging study was performed using mouse PH and mouse SL. RESULTS: The system achieved the energy resolution of 5.5% in full-width at half maximum (FWHM) at 140 keV using a 99mTc source. Without resolution recovery function, the system provided a near millimeter transaxial and axial spatial resolution using mouse PH. Mouse SL and rat SL provided reasonably good transaxial (1.79-2.00 mm in FWHM), but much worse axial resolutions (4.55-4.96 mm in FWHM). The use of resolution recovery significantly improved spatial resolution by in average 31±3 or 35±4% in FWHM or full-width at tenth maximum, respectively. In particular, a sub-millimeter resolution of 0.71 mm in FWHM was achieved in either transaxial or axial direction with mouse PH. Using NU-4 phantom, the uniformity of slit collimators as expressed as percentage standard deviation was generally better than that of pinhole collimators. The use of resolution recovery substantially improved uniformity for all the collimators tested, but caused some overestimation in recovery coefficient. Reconstruction settings such as iteration or subset number significantly affected image quality measures. Finally, bone images of acceptable quality were obtained in in vivo mouse using mouse PH with resolution recovery. CONCLUSIONS: The overall performance shows that the eXplore speCZT system is suitable for preclinical imaging-based research using small-animals.

Adipogenetic effects of retrofractamide A derivatives in 3T3-L1 cells.

In a previous study, retrofractamide A from the fruit of Piper chaba was shown to promote adipogenesis in 3T3-L1 cells. In the present study, retrofractamide A and its derivatives were synthesized, and their adipogenetic effects in 3T3-L1 cells were examined. Among the tested compounds, an amide composed of 9-(3',4'-methylenedioxyphenyl)-nona-2E,4E,8E-trienoic acid and an n-butyl or n-pentyl amine showed strongest activity. Moreover, the amide with the n-pentyl amine moiety significantly increased the uptake of 2-deoxyglucose into the cells, and also increased the mRNA levels of adiponectin, peroxisome proliferator-activated receptor γ2 (PPARγ2), glucose transporter 4 (GLUT4), fatty acid-binding protein (aP2), and CCAAT/enhancer-binding protein (C/EBP) α and ß in a similar manner as the PPARγ agonist troglitazone, although it had less agonistic activity against PPARγ.

Myocardial sympathetic innervation, function, and oxidative metabolism in non-infarcted myocardium in patients with prior myocardial infarction.

OBJECTIVE: The purpose of this study was to investigate the relationship between sympathetic innervation, contractile function, and the oxidative metabolism of the non-infarcted myocardium in patients with prior myocardial infarction. METHODS: In 19 patients (14 men, 5 women, 65 ± 9 years) after prior myocardial infarction, sympathetic innervation was assessed by (11)C-hydroxyephedrine (HED) positron emission tomography (PET). Oxidative metabolism was quantified using (11)C-acetate PET. Left ventricular systolic function was measured by echocardiography with speckle tracking technique. RESULTS: The (11)C-HED retention was positively correlated with left ventricular ejection fraction (LVEF) (r = 0.566, P < 0.05), and negatively with peak longitudinal strain in systole in the non-infarcted myocardium (r = -0.561, P < 0.05). Kmono, as an index of oxidative metabolism, was significantly correlated with rate pressure product (r = 0.649, P < 0.01), but not with (11)C-HED retention (r = 0.188, P = 0.442). Furthermore, there was no significant correlation between Kmono and LVEF (r = 0.106, P = 0.666) or peak longitudinal strain in systole (r = -0.256, P = 0.291) in the non-infarcted myocardium. When the patients were divided into two groups based on the median value of left ventricular end-systolic volume index (LVESVI) (41 mL), there were no significant differences in age, sex, and rate pressure product between the groups. However, the large LVESVI group (>41 mL) was associated with reduced (11)C-HED retention and peak longitudinal strain in systole, whereas Kmono was similar between the groups. CONCLUSIONS: This study indicates that remodeled LV after myocardial infarction is associated with impaired sympathetic innervation and function even in the non-infarcted myocardial tissue. Furthermore, oxidative metabolism in the non-infarcted myocardium seems to be operated by normal regulatory mechanisms rather than pre-synaptic sympathetic neuronal function.