Which of the following patients should receive fewer particles than typically administered for lung perfusion imaging?

In lung perfusion imaging, the administration of particles is typically guided by the anatomy and the physiological condition of the patient. In a patient with a right-to-left cardiac shunt, there is an abnormal flow of blood that bypasses the lungs, meaning that particles injected into the pulmonary circulation may avoid the lungs and enter systemic circulation. This can lead to potential complications such as embolization of particles to other organs rather than being effectively utilized for imaging.

In cases of right-to-left shunting, it is crucial to minimize the number of particles administered to mitigate the risk of adverse effects and to ensure adequate imaging quality. Thus, patients with this condition should receive fewer particles than what is typically administered to standard patients.

The other cases listed do not carry the same level of concern regarding particle administration. For example, the elderly woman suspected of having a pulmonary embolism and the man with chronic obstructive pulmonary disease do not have points of significant shunting, and thus the standard doses are appropriate. Similarly, although pregnancy carries considerations regarding radiation exposure, it does not inherently require a decrease in particle quantity specifically related to perfusion imaging unless higher doses are indicated.