Estimation of optimal number of gates in dual gated 18F-FDG cardiac PET.

Gating of positron emission tomography images has been shown to reduce the motion effects, especially when imaging small targets, such as coronary plaques. However, the selection of optimal number of gates for gating remains a challenge. Selecting too high number of gates results in a loss of signal-to-noise ratio, while too low number of gates does remove only part of the motion. Here, we introduce a respiratory-cardiac motion model to determine the optimal number of respiratory and cardiac gates. We evaluate the model using a realistic heart phantom and data from 12 cardiac patients (47-77 years, 64.5 on average). To demonstrate the benefits of our model, we compared it with an existing respiratory model. Based on our study, the optimal number of gates was determined to be five respiratory and four cardiac gates in the phantom and patient studies. In the phantom study, the diameter of the most active hot spot was reduced by 24% in the dual gated images compared to non-gated images. In the patient study, the thickness of myocardium wall was reduced on average by 21%. In conclusion, the motion model can be used for estimating the optimal number of respiratory and cardiac gates for dual gating.

NEMA NU 4-2008 and in vivo imaging performance of RAYCAN trans-PET/CT X5 small animal imaging system.

The RAYCAN Trans-PET/CT X5 is a preclinical positron emission tomography and computed tomography (PET/CT) system intended for in vivo imaging of rats and mice, featuring all-digital readout electronics for PET data acquisition. The National Electrical Manufacturers Association (NEMA) NU 4-2008 performance evaluation was conducted on the RAYCAN Trans-PET/CT X5 in addition to assessing in vivo imaging performance of the system on live animals. The performance characteristics of the system were evaluated, including system spatial resolution, count rate performance, sensitivity and image quality. The system imaging performance is assessed in dynamic in vivo PET imaging. The system resolution defined as full width half maximum (FWHM) was 2.07 mm, 2.11 mm and 1.31 mm for the tangential, radial and axial resolution, respectively, at the center of the field of view. The peak noise equivalent count rate (NECR) values measured were 61 kcps at 0.19 MBq ml-1 for the rat size phantom and 126 kcps at 1.53 MBq ml-1 for the mouse size phantom. Scatter fractions were 24% and 14% for the rat and mouse phantom. The measured peak sensitivity of the system was 1.70%. Image quality in static imaging was deemed sufficient based on the image quality phantom study, with average activity concentration of 155 ± 8.6 kBq ml-1 and image uniformity of 5.57% when using two-dimensional filtered backprojection algorithm (2D-FBP). Rods in the image quality phantom were visualized easily up to 2 mm in size. In dynamic in vivo PET imaging, time-activity-curves from several regions were successfully measured, characterizing the radioactivity distribution in myocardial blood pool, liver, left ventricle and the lung. In conclusion, the RAYCAN Trans-PET/CT X5 system can be considered a suitable option for basic imaging needs in preclinical imaging.

Brain ß-Amyloid and Atrophy in Individuals at Increased Risk of Cognitive Decline.

BACKGROUND AND PURPOSE: The relationship between brain ß-amyloid and regional atrophy is still incompletely understood in elderly individuals at risk of dementia. Here, we studied the associations between brain ß-amyloid load and regional GM and WM volumes in older adults who were clinically evaluated as being at increased risk of cognitive decline based on cardiovascular risk factors. MATERIALS AND METHODS: Forty subjects (63-81 years of age) were recruited as part of a larger study, the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability. Neuroimaging consisted of PET using 11C Pittsburgh compound-B and T1-weighted 3D MR imaging for the measurement of brain ß-amyloid and GM and WM volumes, respectively. All subjects underwent clinical, genetic, and neuropsychological evaluations for the assessment of cognitive function and the identification of cardiovascular risk factors. RESULTS: Sixteen subjects were visually evaluated as showing cortical ß-amyloid (positive for ß-amyloid). In the voxel-by-voxel analyses, no significant differences were found in GM and WM volumes between the samples positive and negative for ß-amyloid. However, in the sample positive for ß-amyloid, increases in 11C Pittsburgh compound-B uptake were associated with reductions in GM volume in the left prefrontal (P = .02) and right temporal lobes (P = .04). CONCLUSIONS: Our results show a significant association between increases in brain ß-amyloid and reductions in regional GM volume in individuals at increased risk of cognitive decline. This evidence is consistent with a model in which increases in ß-amyloid incite neurodegeneration in memory systems before cognitive impairment manifests.

Exercise training alters lipoprotein particles independent of brown adipose tissue metabolic activity.

INTRODUCTION: New strategies for weight loss and weight maintenance in humans are needed. Human brown adipose tissue (BAT) can stimulate energy expenditure and may be a potential therapeutic target for obesity and type 2 diabetes. However, whether exercise training is an efficient stimulus to activate and recruit BAT remains to be explored. This study aimed to evaluate whether regular exercise training affects cold-stimulated BAT metabolism and, if so, whether this was associated with changes in plasma metabolites. METHODS: Healthy sedentary men (n = 11; aged 31 [SD 7] years; body mass index 23 [0.9] kg m-2; VO2 max 39 [7.6] mL min-1 kg-1) participated in a 6-week exercise training intervention. Fasting BAT and neck muscle glucose uptake (GU) were measured using quantitative [18F]fluorodeoxyglucose positron emission tomography-magnetic resonance imaging three times: (1) before training at room temperature and (2) before and (3) after the training period during cold stimulation. Cervico-thoracic BAT mass was measured using MRI signal fat fraction maps. Plasma metabolites were analysed using nuclear magnetic resonance spectroscopy. RESULTS: Cold exposure increased supraclavicular BAT GU by threefold (p < 0.001), energy expenditure by 59% (p < 0.001) and plasma fatty acids (p < 0.01). Exercise training had no effect on cold-induced GU in BAT or neck muscles. Training increased aerobic capacity (p = 0.01) and decreased visceral fat (p = 0.02) and cervico-thoracic BAT mass (p = 0.003). Additionally, training decreased very low-density lipoprotein particle size (p = 0.04), triglycerides within chylomicrons (p = 0.04) and small high-density lipoprotein (p = 0.04). CONCLUSIONS: Although exercise training plays an important role for metabolic health, its beneficial effects on whole body metabolism through physiological adaptations seem to be independent of BAT activation in young, sedentary men.

Nickel penetration in allergic individuals: bioavailability versus X-ray microanalysis detection.

Development of local allergic reactions after different application times with Finn Chambers was recorded in 34 nickel-sensitive patients. Biologically significant amounts of nickel seemed to penetrate the skin within a few hours, although physical penetration was minimal. Nickel was detected only in the upper keratin cell layer with an X-ray microanalysis method.