Chest tomosynthesis images of pulmonary nodule. Source: Radiology 2012; 265: 273-282

Measurements of pulmonary nodule size on chest tomosynthesis are comparable to those attained with CT, potentially offering a low-dose alternative when planning follow-up strategies, according to a study published in the October issue of Radiology.

There is one caveat: while there is no bias between the modalities and the repeatability of measurements is similar, the limits of agreement (LOA) between chest tomosynthesis and CT are wider than the LOA for intraobserver variability for each modality. This calls into question whether measurements from chest tomosynthesis and CT can be used interchangeably, according to study authors Åse A. Johnsson, MD, PhD, of Sahlgrenska Academy at University of Gothenburg in Sweden, and colleagues.

A total of 36 segmented nodules in 20 patients were included in the study. Eight observers, using chest tomosynthesis and CT images, measured the left-to-right, inferior-to-superior and longest nodule diameters. Johnsson and colleagues then assessed intra- and interobserver repeatability and agreement between measurements on chest tomosynthesis and CT images.

“Manual measurements on both CT and chest tomosynthesis images underestimated the left-to-right and inferior-to-superior diameter compared with the segmentation process,” wrote the authors. Results showed the mean difference for left-to-right diameter was -2.3 mm on axial CT and -2.2 mm on chest tomosynthesis images. The mean difference for inferior-to-superior diameter was -2.2 mm on coronal CT and -2.6 mm on chest tomosynthesis images.

Intraobserver 95 percent LOA for the longest diameter ranged from a lower limit of -1.1 mm and an upper limit of 1.0 mm to -1.8 and 1.8 mm for chest tomosynthesis and from -0.6 and 0.9 mm to ?3.1 and 2.2 mm for axial CT, according to the authors. The 95 percent LOA for different observers between the modalities ranged from -2.2 and 1.6 mm to -3.2 and 2.8 mm.

The fact that the intraobserver variability is less than the LOA between the modalities “calls for caution” when considering using the measurement interchangeably, according to the authors.

Johnsson and colleagues noted that the study did not include nodule detection, and they suspect some nodules may not have been detected if only chest tomosynthesis was used. They explained that in a clinical situation, follow-up with chest tomosynthesis would be suggested only for clearly observable nodules.