Quantitative comparison of ⁹⁹ Tc ^m -aerosol and ⁸¹ Kr ^m ventilation images

Abstract

Quantitative indices are described for assessing the distribution of ventilation imaging agents (radioaerosols, in particular) within the lung. They have been applied to images obtained with 99Tcm aerosol particles (0.5-2.0 micrometer diameter) and with 81Krm gas in 12 patients with a wide range of lung function. In patients with normal lung function aerosol distribution was similar to that of 81Krm. In patients with airways obstruction, the aerosol tended to penetrate less well than 81Krm to the lung periphery and to show a less homogeneous distribution there. Quantitative analysis confirms that the aerosol technique is an effective substitute for 81Krm in patients with normal lung function. When lung function is impaired aerosol images may still be valuable particularly in confirming a diagnosis of pulmonary embolism though they must be interpreted with caution in attempting to exclude that diagnosis. We conclude that small particle radioactive aerosols provide a readily available ventilation technique for clinical ventilation-perfusion imaging.

Methodology for Ventilation/Perfusion SPECT

“…Fifty percent of the radioactivity resides in particles smaller than the MMAD and 50% in larger particles. 17 The MMAD should preferably be smaller than 1.2 m. [18][19][20][21] It is not easy to define the aerodynamic properties of an aerosol. Hydrophilic particles may grow in size as the result of the humid environment of the airways.…”

Physiological imaging of the lung: single-photon-emission computed tomography (SPECT)

“…However, impaction of the aerosol particles in central airways might be a problem, especially in situations with turbulent flow or greater flow velocities (16,20). Several studies using planar imaging have found that the deposition of the radioaerosol differs from the distribution of regional ventilation measured with 81m Kr (1,16,20). We are not aware of studies that used SPECT to compare the distribution of 81m Kr and DTPA aerosol.…”

Tc-99m Technegas scintigraphy to evaluate the lung ventilation in patients with oral corticosteroid-dependent bronchial asthma

“…9 Partial obstruction of a bronchus will lead to increased flow through neighboring bronchi and increased particle deposition caused by impact as well as localized deposit at the site of the obstruction. 5 Various degrees of obstruction may arise from factors such as smooth muscle constriction, submucosal edema or inflammation and mucous hypersecretion with mucous plugging or formation of mucoid strands. 9 Wenzel et al reported that inflammation remains in severe symptomatic asthmatics despite treatment with large doses of glucocorticoids.…”