Philips Microdose Mammography - the Technology and Physics Behind the First FDA Approved Photon Counting X-Ray Imaging System

• Purpose: To validate the use of 4D‐Computed Tomography (4D‐CT) for pre‐treatment evaluation of fractional regional ventilation in patients with lung cancer by benchmarking its performance against scintigraphy V/Q imaging, the current gold‐standard. The second aim is to further corroborate the results of 4D‐CT estimation of lung aeration against the results of Pulmonary Function Testing. Methods: Scintigraphy V/Q and 4D‐CT studies were acquired in four lung cancer patients prior to treatment with radiation therapy. PFTs were acquired in 3 out of the 4 patients. 4D‐CT images were used to create 3D fractional regional ventilation maps by applying a ‘mass correction’ and subtracting the spatially matched end‐exhale and end‐inhale images. Ventilation maps were then collapsed in the anterior‐posterior dimension to create a coronal 2D projection image consistent with the scintigraphy V/Q images. The left and right lung fields were isolated on the projection image and divided into 3 sections of equal height. Summation of the signal intensity in each of the sections was carried out on the maps analogous to the analysis performed on V/Q scans and statistically compared using the Kendall's tau rank correlation. Results: The non‐parametric Kendall's tau estimate ranged between 0.87–0.95 for N=4, with corresponding p‐values ranging between 0.005–0.0002. Mean functional residual capacities (FRC) from the PFTs (N=3) versus calculated FRCs was 2.7 +/− 0.6 L and 2.4 +/− 0.7 L, and the null hypothesis could not be rejected (p = 0.61). The mean fractional regional ventilation versus the ratio of tidal‐volume/FRC was 0.24 +/− 0.11 and 0.22 +/− 0.08, and the null hypothesis could not be rejected (p=0.73). Conclusions: There was a strong correlation between 4D‐CT and scintigraphy V/Q. The similarity between the calculated and measured FRCs further validates the utility of 4D‐CT and supports its use in evaluating lung ventilation in patients with pulmonary neoplasms.

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