Cystic Lung Phantom to Validate Clinical CT Protocols.

In CT-based evaluation of the extent of cystic changes in the lungs of patients with cystic lung diseases, such as Lymphangioleiomyomatosis (LAM), there is a lack of a lung phantom containing air-filled cavities that mimic pulmonary cysts to calibrate the measurement of cystic volumes from CT scans. Here we describe a simple, easy-to-replicate cystic lung phantom consisting of basic structures of a trachea and two lung compartments. The lung compartments contain air cavities of varying sizes to mimic cystic lesions. The lung volumes are equal to those of typical adults. The lung compartments are made of a foam material recommended by NIST to simulate the radiodensity of human lung parenchyma. In tests performed on a clinical scanner using two types of lung analysis software, the various structures in the lung phantom were correctly recognized by the software. The resulting cystic volume measurements revealed the relationship between the size of the cysts and the accuracy of the measurement. A significant finding is that the volumes of individual cysts were underestimated for small cysts. The error increased with decreasing cyst sizes. Such underestimation has not been mentioned previously and deserves the attention of clinicians using CT scans to assess the cyst burden in the lungs, particularly in patients presenting with numerous small pulmonary cysts.