The cross-sectional area of visceral and subcutaneous fat in the abdomen was measured with T1-weighted spin-echo images acquired with a 1.5-T magnetic resonance (MR) imager. Four axial images centered on L-4 were acquired in each patient. Outline regions of interest (ROIs) were drawn manually for subcutaneous and visceral fat. The subcutaneous fat cross-sectional area was calculated from the ROIs drawn around the outer and inner margins of subcutaneous fat. Several adaptive processing methods were evaluated for measuring fat in the complex structure of the viscera. These methods were compared with an existing MR imaging measurement method for abdominal fat in 18 patients. The adaptive method that uses the valley between the fat and nonfat distributions in the average histogram curve was judged best for research evaluations because it reduces the effects of volume averaging while using a more natural division between fat and nonfat data. Another adaptive method that yielded comparable measurements was thought to be more suitable for clinical applications. Cross-sectional area measurements of abdominal fat were compared in 18 nonobese and 17 obese women to illustrate the utility of these measurements.
The maximum unit normal component (MUNC) method used for surface area measurement and the divergence theorem algorithm (DTA) used for volume measurement were evaluated. The accuracy and precision of these methods were investigated at varying signal-to-noise ratios (SNRs), sampling, spatial averaging, and orientation. The accuracy of the MUNC measured surface area, as indicated by the mean error, was 2.0% for seven spherical samples, with SNRs ranging from 5:1 to 39:1. The precision, as indicated by the percent coefficient of variation (% CV) for these samples, was less than 3.0%. Likewise, the accuracy and precision of the DTA measured volume for these samples were both less than 1.0%. MUNC surface area measurement from 23 samples of a computed tomography (CT) image of a wooden sphere (51.44-mm diameter) with x,y voxel size ranging from 1 to 10 mm and z voxel size ranging from 2 to 14 mm yielded an accuracy of 1.3% and a precision of 2.2%. The DTA volume measurements from 18 samples of the wooden sphere with x,y vowel size ranging from 1 to 8 mm and z size ranging from 2 to 14 mm provided an accuracy of 1.2% and a precision of 1.8%. Measurement of surface area for a cylindrical rod scanned by CT in five different orientations, ranging from along each axis to between all three axes, yielded an accuracy of 3.7% and a precision of 2.0%. The volume of the cylindrical rod measured by the DTA method for these orientations produced an accuracy of 4.0% and a precision of 3.7%. The volume measured by DTA compared well with the volume measured by a modified voxel counting method. The MUNC surface area method was superior to counting surface voxels. The accuracy and precision for five interactive surface area and volume measurements, using paired cut planes to select subsets of a computer-generated sphere with radius 25 pixels, were both less than 1.0%.
The activity concentrations of (40)K, (226)Ra, (228)Ra and (137)Cs were measured for 14 brands of the powdered milk consumed in Jordan, which are imported from various regions around the world. The activity concentrations of (40)K were found not to vary greatly from one brand to the other with an average of 348 +/- 26 Bq kg(-1). However, the activity concentrations of (137)Cs revealed a geographical distribution being: (i) undetected in any of the samples from Argentina, (ii) uniformly distributed in samples from Europe with an average of 0.43 +/- 0.05 Bq kg(-1), and (iii) widely varying in samples from New Zealand (from being not detected (ND) to 1.55 Bq kg(-1)). (226)Ra and (228)Ra were measured above the detection limits in five brands only and displayed relatively low activity concentrations of 0.50-2.14 and 0.78-1.28 Bq kg(-1) for (226)Ra and (228)Ra, respectively. The total average annual effective doses due to intake of (40)K, (226)Ra, (228)Ra and (137)Cs from the ingestion of the powdered milk for infants, children and adults were estimated to be (in microSv): 332, 138 and 43, respectively. These results indicate no significant radiation dose to the public.
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