Quantitative indices of radionuclide uptake in an object of interest provide a useful adjunct to qualitative interpretation in the diagnostic application of radionuclide imaging. This note describes a new measure of total uptake of an organ, the specific uptake size index (SUSI). It can either be related in absolute terms to the total activity injected or to the specific activity in a reference region. As it depends on the total activity in the object, the value obtained will not depend on the resolution of the imaging process, as is the case with some other similar quantitative indices. This has been demonstrated in an experiment using simulated images. The application of the index to quantification of dopamine receptor SPECT imaging and parathyroid-thyroid subtraction planar scintigraphy is described. The index is considered to be of potential value in reducing variation in quantitative assessment of uptake in objects with applications in all areas of radionuclide imaging.

Planar gamma camera imaging of inhaled aerosol deposition is extensively used to assess the total deposition in the lung. However, validation of the measurements is not straightforward, as gold standard measurements of lung activity against which to compare are not readily available. Quantitative SPECT imaging provides an alternative method for comparison. Four different methods for planar image quantification are compared. Two attenuation correction techniques, thickness measurement and transmission measurement, have been combined with two scatter correction techniques, reduced attenuation coefficient and line-source scatter function convolution subtraction. Each technique has been applied to 10 studies of aerosol deposition of a fine aerosol (mass median aerodynamic diameter 1.8 microm) and 10 studies using a coarse aerosol (mass median aerodynamic diameter 6.5 microm). The total activity in the right lung for each measurement has been compared to the value determined from SPECT imaging on the same subjects. When the thickness measurement and transmission techniques were applied with scatter compensation using a reduced attenuation coefficient, activity was systematically overestimated by 5% in both cases. The corresponding random errors (coefficient of variation) were 8.6% and 6.6%. Separate scatter correction reduced these systemic errors significantly to -1.5% and 2.7%, respectively. The random errors were not affected. All techniques provided assessment of total lung activity with an accuracy and precision that differed by less than 10% compared to the SPECT values. Planar gamma camera imaging provides a good method of assessing total lung deposition of inhaled aerosol.

These findings illustrate the capability of statistical parametric mapping to demonstrate reliable abnormalities in the majority, but not all, patients with either mild Alzheimer's disease or DLB. Precuneal hypoperfusion is not specific to Alzheimer's disease and is equally likely to be found in DLB. In this study, medial temporal hypoperfusion was significantly more common in Alzheimer's disease than in DLB. Statistical parametric maps appear to be considerably more reliable than simple visual interpretation of 99mTc-HMPAO images for these regions.

Three-dimensional (3D) radionuclide imaging provides detailed information on the distribution of inhaled aerosol material within the body. Analysis of the data can provide estimates of the deposition per airway generation. Information on regional distribution of deposited aerosol can also be obtained from 24-hour clearance measurements. In this study, a nebulizer was used to deliver a radiolabeled aerosol to nine human subjects. Single photon emission computed tomography (SPECT) has been used to assess the distribution of aerosol deposition per airway generation. The deposition pattern was also estimated using measurements of the aerosol remaining in the lung 24 h after inhalation. The error in the SPECT value was assessed by simulation and that in the 24-h clearance value by repeat analysis. The mean fraction of lung deposition in the conducting airway (CADF) from SPECT was 0.21. The corresponding 24-h clearance value was 0.23. These values were not significantly different. There was a weak but non-significant correlation between the SPECT and 24-h measurements (r = 0.49). The standard error of the difference was 0.11. The corresponding errors on the SPECT and 24-h clearance measurements were 0.04 and 0.05, respectively. There was no systematic difference between the values of conducting airways deposition obtained from 24-h measurements and SPECT. However, there were random differences on individual subjects, which were larger than the estimated measurement errors.

To further validate a stochastic particle deposition model, threedimensional deposition patterns predicted by that model were compared with corresponding spatial particle deposition data obtained from SPECT measurements. In the in vivo inhalation experiments, two different polydisperse aerosols with mass median aerodynamic diameters of 1.6 µm and 6.8 µm were inhaled by 12 test subjects, using different nebulizers. Predicted and measured deposition data were compared on three different levels: (1) total lung deposition, (2) deposition per hemispherical shell, and (3) deposition per airway generation. First, experimental and theoretical total lung deposition data showed good agreement for both the fine (65 ± 9% vs. 55 ± 21%) and the coarse aerosols (55 ± 8% vs. 46 ± 4%). Second, predicted deposition per hemispherical shell also corresponded well with the experimental data, both exhibiting small deposition fractions in the inner shells and a roughly quadratic increase in the outer shells. Third, fair agreement was observed for the deposition fractions per airway generation, both experimental data and modelling predictions exhibiting relatively small deposition fractions in central bronchial airway generations, followed by a steep increase in the peripheral respiratory airways. While the overall agreement between measured SPECT data and computed deposition fractions demonstrates that SPECT data can indeed be used for model validation, the current spatial resolution of the SPECT method allows only a limited validation of model predictions at the single airway generation level.