V/Q SPECT: utility for investigation of pulmonary physiology.

Single-photon emission computed tomography (SPECT) is being increasingly used as a tool in respiratory research, in particular ventilation SPECT. Much of the basic understanding of pulmonary physiology has been derived from inhaled radioactive inert gases because, as the lung behaves in an asymmetric manner, the nature of regional differences in ventilation is ideally studied with the use of imaging. It is well known to clinicians that ventilation is patchy in patients who have airways disease. However, the relevance to the disease mechanisms itself only started to be studied with the use of 3-dimensional imaging and with advances in quantitative image analysis. The measurements of both ventilation distribution and nonventilation (airway closure) have become very topical in the study of asthma, and accurate quantification of those parameters is of relevance to disease mechanisms. In chronic obstructive pulmonary disease, the drive is towards better characterization of disease groups ("phenotypes") and, again, description of ventilation patterns may prove to be useful. This is a review, therefore, on pulmonary SPECT imaging in respiratory research which includes a focus on methodology in relation to respiratory physiology. There has been relatively little published in this area but there is great potential for advances in the understanding of airways disease to be gained from SPECT imaging.