From the Guidelines
A pulmonary nodule needs to be larger than the slice thickness of the CT scan to be reliably detected, so with a slice thickness of 3.75mm, the nodule would likely need to be larger than 3mm to be detected. The detection of pulmonary nodules is influenced by the slice thickness of the CT scans, with thinner slices allowing for better detection and characterization of small nodules 1. The use of thinner images has improved the characterization of small lung nodules, and guidelines recommend routine use of contiguous thin sections (1.5 mm) and reconstructed multiplanar images to ensure adequate characterization 1. Some studies suggest that nodules as small as 1-2 mm can be detected with high-resolution CT scans, but the detection of such small nodules is not always reliable and may require additional imaging or follow-up scans 1. In general, the size of the nodule, the slice thickness of the CT scan, and the imaging technique used all play a role in determining the visibility and detectability of a pulmonary nodule. For example, a nodule that is 3mm in size may be detectable with a CT scan that has a slice thickness of 1-2mm, but may not be detectable with a scan that has a slice thickness of 3.75mm 1. Therefore, the size of the nodule and the slice thickness of the CT scan are critical factors in determining the detectability of a pulmonary nodule. It is also important to note that the detection of pulmonary nodules is not just dependent on the size of the nodule, but also on the imaging technique used, the quality of the images, and the expertise of the radiologist interpreting the images 1. In summary, a pulmonary nodule would likely need to be larger than 3mm to be detected with a CT scan slice thickness of 3.75mm, but the detection of such a nodule would also depend on various other factors, including the imaging technique used and the expertise of the radiologist. Some key points to consider when evaluating pulmonary nodules include:
- The size of the nodule: larger nodules are more likely to be detected than smaller ones
- The slice thickness of the CT scan: thinner slices allow for better detection and characterization of small nodules
- The imaging technique used: high-resolution CT scans and reconstructed multiplanar images can improve the detection and characterization of small nodules
- The expertise of the radiologist: experienced radiologists are better able to detect and characterize pulmonary nodules.
From the Research
Detection of Pulmonary Nodules with CT Scans
- The detection of pulmonary nodules using computed tomography (CT) scans depends on various factors, including the size of the nodule and the slice thickness of the CT scan 2, 3, 4.
- According to the Fleischner Society, guidelines for measuring pulmonary nodules at CT are essential for accurate nodule size measurements, which are crucial for nodule management 2, 4.
- A study published in 2024 proposed a deep learning-based 3D super-resolution method for generating thin-slice CT images from heterogeneous thick-slice CT images, which can improve the accuracy of lung nodule volumetry and facilitate more reliable early lung nodule detection 3.
- Another study published in 2025 investigated the localization, visibility, and measurement of lung nodules in digital chest tomosynthesis (DTS) and found that most nodules ≥ 100 mm^3 found on CT can be visualized, correctly localized, and measured in DTS 5.
Nodule Size and Detection
- A study published in 2017 evaluated measurement variability in volumetric assessment of pulmonary nodules on low-dose CT images and found that measurement variability decreased with increasing nodule diameter 6.
- The same study found that the standard deviation (SD) of the percentage of volume change was higher for smaller nodules (< 4 mm) and decreased with increasing nodule diameter 6.
- However, none of the studies directly address the question of whether a pulmonary nodule needs to be larger than 3mm to be detected with a CT scan slice thickness of 3.75mm.