Physiology for the pulmonary functional imager

Abstract

As pulmonary functional imaging moves beyond the realm of the radiologist and physicist, it is important that imagers have a common language and understanding of the relevant physiology of the lung. This review will focus on key physiological concepts and pitfalls relevant to functional lung imaging.

Respiratory Invariant Textures From Static Computed Tomography Scans for Explainable Lung Function Characterization

“…The sliding window size setting for FM generation (21×21×21 mm 3 ) was primarily based on lung physiological considerations in this work. During feature distribution mapping, each sliding window was expected to cover multiple lung minimum gas exchange units with a measured size slightly >10×10×10 mm 3 , due to the demonstrated tendency of lung function to be spatially clustered 47,48 . A sliding window too small in size could subject the calculated FM to noise, while a window too large would reduce function-correlated information capture sensitivity and significantly increase computational complexity.…”

Spatial Comparison of CT-Based Surrogates of Lung Ventilation With Hyperpolarized Helium-3 and Xenon-129 Gas MRI in Patients Undergoing Radiation Therapy

“…While it is often desirable to perform anatomic lung imaging at higher spatial resolutions, this is not necessarily the case for functional lung imaging. As noted by Levin et al [32], functional lung images need only be acquired at the resolution of the smallest gas exchange unit, namely, the acinus (estimated to be on the order of 10x10x10mm 3 ), and that an even lower spatial resolution such as 20x20x20mm 3 is adequate for most applications due to functional defects demonstrating a tendency to be spatially clustered.…”

Treatment planning based on lung functional avoidance is not ready for clinical deployment

“…In fact, gas exchange is proportional to the ratio of alveolar ventilation (V a ) = the delivery of fresh gas, to perfusion (Q). 1 V a is non-linearly related to V s , and can be computed using regional density. 2 However, these corrections are not applied in current LFA planning.…”

“…Lung cancer patients frequently present with comorbidities (COPD, pulmonary hypertension), which can cause significant V/Q mismatches. 1,3 Thus, regions showing high ventilation but poor perfusion (and vice versa) may be incorrectly classified as “highly-functional”. Furthermore, regional ventilation and perfusion exhibit significant gravitational dependence and therefore vary with body position.…”