RATIONALE AND OBJECTIVES: The objective of this study was to assess the
feasibility of single-inhalation xenon-enhanced computed tomography (XeCT) to
provide clinically practical, high-resolution pulmonary ventilation imaging to
clinics with access to only a single-energy computed tomography scanner, and to
reduce the subject's overall exposure to xenon by utilizing a higher (70%)
concentration for a much shorter time than has been employed in prior studies.
MATERIALS AND METHODS: We conducted an institutional review board-approved
prospective feasibility study of XeCT for 15 patients undergoing thoracic
radiotherapy. For XeCT, we acquired two breath-hold single-energy computed
tomography images of the entire lung with a single inhalation each of 100% oxygen
and a mixture of 70% xenon and 30% oxygen, respectively. A video biofeedback
system for coached patient breathing was used to achieve reproducible breath
holds. We assessed the technical success of XeCT acquisition and side effects. We
then used deformable image registration to align the breath-hold images with each
other to accurately subtract them, producing a map of lung xenon distribution.
Additionally, we acquired ventilation single-photon emission computed
tomography-computed tomography (V-SPECT-CT) images for 11 of the 15 patients. For
a comparative analysis, we partitioned each lung into 12 sectors, calculated the
xenon concentration from the Hounsfield unit enhancement in each sector, and then
correlated this with the corresponding V-SPECT-CT counts.
RESULTS: XeCT scans were tolerated well overall, with a mild (grade 1) dizziness
as the only side effect in 5 of the 15 patients. Technical failures in five
patients occurred because of inaccurate breathing synchronization with xenon gas
delivery, leaving seven patients analyzable for XeCT and single-photon emission
computed tomography correlation. Sector-wise correlations were strong (Spearman
coefficient >0.75, Pearson coefficient >0.65, P value <.002) for two patients for
whom ventilation deficits were visibly pronounced in both scans. Correlations
were nonsignificant for the remaining five who had more homogeneous XeCT
ventilation maps, as well as strong V-SPECT-CT imaging artifacts attributable to
airway deposition of the aerosolized imaging agent. Qualitatively, XeCT
demonstrated higher resolution and no central airway deposition artifacts
compared to V-SPECT-CT.
CONCLUSIONS: In this pilot study, single-breath XeCT ventilation imaging was
generally feasible for patients undergoing thoracic radiotherapy, using an
imaging protocol that is clinically practical and potentially widely available.
In the future, the xenon delivery failures can be addressed by straightforward
technical improvements to the patient biofeedback coaching system.