Single-photon emission computed tomography (SPECT) imaging is being increasingly used to assess inhaled aerosol deposition. This study uses simulation to evaluate the errors involved in such measurements and to compare them with those from conventional planar imaging. SPECT images of known theoretical distributions of radioaerosol in the lung have been simulated using lung models derived from magnetic resonance studies in human subjects. Total lung activity was evaluated from the simulated images. A spherical transform of the lung distributions was performed, and the absolute penetration index (PI) and a relative value expressed as a fraction of that in a simulated ventilation image were calculated. All parameters were compared with the true value used in the simulation, and the errors were assessed. An iterative method was used to correct for the partial volume effect, and its effectiveness in improving errors was evaluated. The errors were compared with those of planar imaging. The precision of measurements was significantly better for SPECT than planar imaging (2.8 vs 6.3% for total lung activity, 6 vs 20% for PI, and 3 vs 6% for relative PI). The method of correcting for the influence of the partial volume effect significantly improved the accuracy of PI evaluation without affecting precision. SPECT is capable of accurate and precise measurements of aerosol distribution in the lung, which are improved compared with those measured by conventional planar imaging. A technique for correcting the SPECT data for the influence of the partial volume effect has been described. Simulation is demonstrated as a valuable method of technique evaluation and comparison.
"The values obtained depend quite significantly on the size of the areas chosen. This dependency can be considerably reduced by normalising the central to peripheral ratios to lung volume [11,12]. Lung volume is often estimated using transmission scanning or ventilation imaging. "
[Show abstract][Hide abstract] ABSTRACT: Background
Determination of regional lung air volume has several clinical applications. This study investigates the use of mid-tidal breathing CT scans to provide regional lung volume data.
Low resolution CT scans of the thorax were obtained during tidal breathing in 11 healthy control male subjects, each on two separate occasions. A 3D map of air volume was derived, and total lung volume calculated. The regional distribution of air volume from centre to periphery of the lung was analysed using a radial transform and also using one dimensional profiles in three orthogonal directions.
The total air volumes for the right and left lungs were 1035 +/− 280 ml and 864 +/− 315 ml, respectively (mean and SD). The corresponding fractional air volume concentrations (FAVC) were 0.680 +/− 0.044 and 0.658 +/− 0.062. All differences between the right and left lung were highly significant (p < 0.0001). The coefficients of variation of repeated measurement of right and left lung air volumes and FAVC were 6.5% and 6.9% and 2.5% and 3.6%, respectively. FAVC correlated significantly with lung space volume (r = 0.78) (p < 0.005). FAVC increased from the centre towards the periphery of the lung. Central to peripheral ratios were significantly higher for the right (0.100 +/− 0.007 SD) than the left (0.089 +/− 0.013 SD) (p < 0.0001).
A technique for measuring the distribution of air volume in the lung at mid-tidal breathing is described. Mean values and reproducibility are described for healthy male control subjects. Fractional air volume concentration is shown to increase with lung size.
BMC Medical Imaging 07/2014; 14(1):25. DOI:10.1186/1471-2342-14-25 · 1.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Planar gamma camera scintigraphy is a well-established technique for characterising the deposition and clearance of radiolabelled aerosols. While single-photon emission tomography (SPET) can offer superior assessment of radioaerosol deposition and better differentiation between peripheral and central deposition, the long acquisition times of single-headed SPET have largely prevented its use for measuring clearance or deposition of fast-clearing radioaerosols. This study investigated the feasibility of fast dynamic SPET imaging (1 min/frame) using a three-headed gamma camera to assess the regional and total deposition and clearance of different radioaerosols over a period of 26 min. Six subjects inhaled nebulised technetium-99m diethylene triamine penta-acetic acid radiolabelled aerosols with small and large droplet sizes [mass median aerodynamic diameter (MMAD) 3.2ǂ.2 and 6.5ǂ.2 m, span 1.8 and 1.7, respectively] and in normal (0.9%) or hypertonic (7%) saline with controlled breathing on four separate occasions. The penetration indices (PIs) calculated from the SPET data for normal saline were 0.50ǂ.04 and 0.36ǂ.02 for the small and large droplet sizes, respectively. Consistent with the hygroscopic growth of the hypertonic aerosols, the PIs for hypertonic saline were lower, at 0.43ǂ.02 and 0.34ǂ.02 for the small and large droplet sizes, respectively. PIs calculated from the planar data showed similar trends, but failed to detect the significant difference seen with SPET between small normal and small hypertonic saline radioaerosols. In conclusion, the feasibility of using fast dynamic SPET for imaging radioaerosol deposition and associated radiolabel clearance in the lung has been successfully demonstrated. The fast SPET was able to reveal important differences in aerosol deposition that were not detected by planar imaging.
European journal of nuclear medicine and molecular imaging 01/2001; 28(9):1365-1372. DOI:10.1007/s002590100586 · 5.38 Impact Factor
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