SESSION TITLE: Imaging Posters
SESSION TYPE: Original Investigation Poster
PRESENTED ON: Wednesday, October 28, 2015 at 01:30 PM - 02:30 PM
PURPOSE: Quantitative CT (QCT) imaging uses the voxel density histogram to measure the emphysema surrogates low attenuation area% (LAA%) and lung density (LD). QCT is carried out with careful attention to quality control including scanner make and model, calibration, lung volume and acquisition protocol, and bears a financial and radiation cost. We wished to determine if CT scans acquired for clinical indications on a variety of scanners with varying calibration frequency, acquisition protocols and only simple breath holding instructions could yield reproducible data.
METHODS: 52 subjects (42 COPD, 10 asthma) from a community respirology practice had had 2 CT scans judged free of significant infiltrates, performed on 3 models of scanner in 5 different community hospitals for clinical indications within a 12 month period and had available spirometry and lung volumes performed respecting ATS criteria within 12 months of CT scans. Images were analyzed with AirwayInspector (airwayinspector.acil-bwh.org) for LAA%<-950HU, LD at 15th percentile + 1000HU and total lung volume (TLV). 30 pairs of non-contrast scans (NC/NC) and 26 contrast/non-contrast scans (C/NC, 15 CT angio, 11 routine contrast) were used to construct identity plots for TLV, LAA%, LD and LD corrected for both predicted (LDpTLC) and measured TLC (LDmTLC). Slopes of regression lines were determined and Spearman rank correlations were calculated for TLV, LAA% and LD. Significance was set at p<0.05.
RESULTS: NC/NC inter-scan and CT-PFT intervals were 3.93 months±0.41SEM and 4.53±0.76, and C/NC were 4.34±0.54 and 5.30±0.78. NC/NC slope and r were; TLV 0.96, 0.95; LAA% 1.06, 0.97; LD 1.01, 0.95; LDpTLC 1.01, 0.96, LDmTLC 1.02, 0.97. Results did not differ between CT angio and routine contrast, and data were pooled yielding C/NC slope and r of; TLV 0.83, 0.90; LAA% 1.37, 0.94; LD 0.80, 0.93; LDpTLC 0.85, 0.93; LDmTLC 0.86, 0.97. P was always <0.0001.
CONCLUSIONS: Community acquired, non-contrast chest CT scans if properly selected, can generated reproducible QCT data. CT angio and routine contrast scans have similar and predictable effects on QCT metrics decreasing LAA% by 37% and increasing LD by 14%.
CLINICAL IMPLICATIONS: If validated by other centres, these findings suggest that the pool of observational QCT data could be vastly expanded at little dollar and no radiation cost.
DISCLOSURE: The following authors have nothing to disclose: Ronald Dandurand, Myriam Dandurand, Raul Estepar, Jean Bourbeau, David Eidelman
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