E4790. Noncontrast Fluoroscopy for Evaluation of Pulmonary Blood Flow: Comparison With Clinical Gold Standard Pulmonary Angiography
  1. Matthew Smith; Vanderbilt University Medical Center
  2. Jared Grice; Vanderbilt University Medical Center
  3. Jared O'Leary; Vanderbilt University Medical Center
  4. Gary Smith; Vanderbilt University Medical Center
Time-dependent x-ray attenuation in the lungs provides an opportunity to evaluate pulmonary blood flow without iodinated contrast using fluoroscopy. The purpose of this study was to compare the perfusion map obtained without contrast using spectral analysis with the clinical gold standard of pulmonary angiography.

Materials and Methods:
Volunteers suspected of chronic thromboembolic pulmonary hypertension (CTEPH) based on pulmonary scintigraphy and/or CTA were enrolled in the IRB-approved prospective study. Fluoroscopic acquisition (70 kV, 30 frames/s) over an 8-second breath hold was performed in either RAO (30°) or LAO (40°) for the right and left lung, respectively. The temporal signal from each pixel was decomposed into individual frequency components using Fourier transformation. Signal oscillating at the heart rate was isolated using a band-pass filter and the amplitude (x-ray pulsatility index [XPI]) mapped to form an image. Immediately following each fluoroscopic acquisition for spectral analysis, digital subtraction pulmonary angiography was performed using catheter-injected contrast in the same projection using standard clinical protocol for comparison. Perfusion maps were segmented using a blinded manual technique as well as a semi-automated threshold and region-growing method. Segmentation maps were compared using the Dice similarity coefficient, a statistical measurement of overlap.

Noncontrast (XPI) and contrast pulmonary angiography images were obtained in 11 different lungs. All patients were able to perform satisfactory breath hold, despite moderate to severe disease. Direct comparison of segmentation maps revealed an average Dice score of 0.77, suggesting excellent agreement between XPI and pulmonary angiography maps in depicting regions of blood flow and more importantly, lack of blood flow.

Pulmonary angiography is an invasive, time-consuming, costly procedure that exposes the patient to sedation, iodinated contrast, and procedural risk. The noncontrast XPI method to evaluate and monitor pulmonary blood flow could improve clinical efficiency as a screening or diagnostic test, provide substantial financial benefits, and improve patient satisfaction. Additionally, this easy-to-implement method can be performed by an x-ray technologist in an outpatient setting.