Ultra-High-Resolution Computed Tomography of the Lung: Image Quality of a Prototype Scanner

Purpose: The image noise and image quality of a prototype ultra-high-resolution computed tomography (U-HRCT) scanner was evaluated and compared with those of conventional high-resolution CT (C-HRCT) scanners. Materials and Methods: This study was approved by the institutional review board. A U-HRCT scanner prototype with 0.25 mm × 4 rows and operating at 120 mAs was used. The C-HRCT images were obtained using a 0.5 mm × 16 or 0.5 mm × 64 detector-row CT scanner operating at 150 mAs. Images from both scanners were reconstructed at 0.1-mm intervals; the slice thickness was 0.25 mm for the U-HRCT scanner and 0.5 mm for the C-HRCT scanners. For both scanners, the display field of view was 80 mm. The image noise of each scanner was evaluated using a phantom. U-HRCT and C-HRCT images of 53 images selected from 37 lung nodules were then observed and graded using a 5-point score by 10 board-certified thoracic radiologists. The images were presented to the observers randomly and in a blinded manner. Results: The image noise for U-HRCT (100.87 ± 0.51 Hounsfield units [HU]) was greater than that for C-HRCT (40.41 ± 0.52 HU; P <.0001). The image quality of U-HRCT was graded as superior to that of C-HRCT (P <.0001) for all of the following parameters that were examined: margins of subsolid and solid nodules, edges of solid components and pulmonary ves sels in subsolid nodules, air bronchograms, pleural indentations, margins of pulmonary vessels, edges of bronchi, and interlobar fissures. Conclusion: Despite a larger image noise, the prototype U-HRCT scanner had a significantly better image quality than the C-HRCT scanners

Comparison of Scores for U-HRCT and 16-row C-HRCT Findings.

<p>§: Score was rounded to the first decimal place.</p><p>U-HRCT: ultra-high-resolution CT, C-HRCT: conventional high-resolution CT.</p

Example of CT images for the observer test.

<p>(A) An example of an ultra-high-resolution CT image with different colored dots and annotations used for the observer test. The X and Y coordinates of each dot are shown in parentheses. The image shows a lepidic-predominant invasive adenocarcinoma with a tumor size of 1.2 x 0.9 x 0.9 cm located in segment 2 of the right upper lobe in a 73-year-old man. The blue dot indicates the edge of a solid nodule. The green dot indicates a cavity. The yellow dot indicates pleural indentation of the interlobar fissure. The white dot indicates a fissure between the right upper lobe and the right lower lobe. The red dot indicates the margin of the pulmonary vessel. The purple dot indicates the edge of a bronchiole. The gray dot indicates an interlobular septum. (B) Ultra-high-resolution CT image in which the dots and annotations are hidden.</p

CT-pathologic correlation of an adenocarcinoma in situ.

<p>The patient was a 58-year-old female with adenocarcinoma in situ (size, 18 x 16 mm; pT1aN0M0, stage IA). The part-solid nodule was located in segment 6 of the right lower lobe. (A) Loupe view of the pathology specimen (Scale: 1 cm) (H & E, original magnification x1.25). (B) Multiplanar reconstruction (MPR) image from the ultra-high-resolution CT (U-HRCT) data corresponding to the pathology specimen. (C) MPR image from the conventional high-resolution CT (C-HRCT) data corresponding to the pathology specimen. U-HRCT image (Fig B) clearly depicting the solid component (§) immediately adjacent to the bronchial wall (¶) and low-attenuation areas, indicated by a white arrowhead and a white star, in the GGO component of the part-solid nodule. Collapse of the alveolar spaces (§) in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137165#pone.0137165.g005" target="_blank">Fig 5A</a> corresponds to the solid component (§) of the part-solid nodule on the U-HRCT and C-HRCT images (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137165#pone.0137165.g005" target="_blank">Fig 5B and 5C</a>), and the nlarged bronchiole (black arrowhead) and enlarged alveolar air spaces (black stars) in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137165#pone.0137165.g005" target="_blank">Fig 5A</a> correspond to the low-attenuation areas (white arrowhead and white star) in the GGO component of the part-solid nodule on the U-HRCT and C-HRCT images (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137165#pone.0137165.g005" target="_blank">Fig 5B and 5C</a>). The lepidic component indicated by the black dots in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137165#pone.0137165.g005" target="_blank">Fig 5A</a> corresponds to the GGO component (black dot) of the part-solid nodule on the U-HRCT and C-HRCT images (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137165#pone.0137165.g005" target="_blank">Fig 5B and 5C</a>). (D) Maximum intensity projection (MIP) image (2 cm thick) of the pulmonary vessels obtained from the U-HRCT data. (E) MIP image (4 cm thick) of the pulmonary vessels obtained from the C-HRCT data. Fine pulmonary vessels are depicted on the MIP image reconstructed from the U-HRCT data (black arrows). The size of the fine pulmonary vessels, as indicated by the black arrows (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137165#pone.0137165.g005" target="_blank">Fig 5D</a>), was 0.2 mm. The black star in each MIP image indicates the part-solid nodule of the adenocarcinoma in situ. (F) 3D curved-MPR image of the pulmonary bronchi from the U-HRCT data. (G) 3D curved-MPR image of the pulmonary bronchi from the C-HRCT data. U-HRCT image (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137165#pone.0137165.g005" target="_blank">Fig 5F</a>) clearly depicting the part-solid opacity (black arrowhead) immediately adjacent to the bronchial wall (white star) with traction bronchiectasis caused by the collapse of the alveoli in the tumor. A: pulmonary artery. V: pulmonary vein.</p

Interobserver Agreement for U-HRCT and C-HRCT Finding.

<p>U-HRCT: ultra-high-resolution CT, C-HRCT: conventional high-resolution CT.</p

Appearance and geometry of channel direction of the prototype ultra-high-resolution CT scanner.

<p>(A) External appearance of the prototype ultra-high-resolution CT scanner. The bore size was 72 cm in diameter. (B) Image showing the directions of the slices and the channels of the CT detector. (C) Geometry of channel direction of the prototype ultra-high-resolution CT scanner. The maximal field of view was 250 mm and number of the channels was 896. (D) Geometry of channel direction of the conventional high-resolution CT scanner. The maximal field of view was 500 mm and number of the channels was 896. U-HRCT: ultra-high-resolution CT, C-HRCT: conventional high-resolution CT.</p

Comparison of Scores for U-HRCT and 64-row C-HRCT Findings.

<p>§: Score was rounded to the first decimal place.</p><p>U-HRCT: ultra-high-resolution CT, C-HRCT: conventional high-resolution CT.</p