Effect of reconstruction algorithm on image quality and identification of ground-glass opacities and partly solid nodules on low-dose thin-section CT: Experimental study using chest phantom

Capability for dose reduction while maintaining nodule detection: Comparison of silver and copper X-ray spectrum modulation filters for chest CT using a phantom study with different reconstruction methods

PURPOSE

To compare the capability of CTs obtained with a silver or copper x-ray beam spectral modulation filter (Ag filter and Cu filter) and reconstructed with FBP, hybrid-type IR and deep learning reconstruction (DLR) for radiation dose reduction for lung nodule detection using a chest phantom study.

MATERIALS AND METHODS

A chest CT phantom was scanned with a 320-detector row CT with Ag filter at 0.6, 1.6 and 2.5 mGy and Cu filters at 0.6, 1.6, 2.5 and 9.6 mGy, and reconstructed with the aforementioned methods. To compare image quality of all the CT data, SNRs and CNRs for any nodule were calculated for all protocols. To compare nodule detection capability among all protocols, the probability of detection of any nodule was assessed with a 5-point visual scoring system. Then, ROC analyses were performed to compare nodule detection capability of Ag and Cu filters for each radiation dose data with the same method and of the three methods for any radiation dose data and obtained with either filter.

RESULTS

At any of the doses, SNR, CNR and area under the curve for the Ag filter were significantly higher or larger than those for the Cu filter (p < 0.05). Moreover, with DLR, those values were significantly higher or larger than all the others for CTs obtained with any of the radiation doses and either filter (p < 0.05).

CONCLUSION

The Ag filter and DLR can significantly improve image quality and nodule detection capability compared with the Cu filter and other reconstruction methods at each of radiation doses used.

Adaptive iterative dose reduction 3D (AIDR 3D) vs. filtered back projection: radiation dose reduction capabilities of wide volume and helical scanning techniques on area-detector CT in a chest phantom study

BACKGROUND

Computed tomography (CT) has important roles for lung cancer screening, and therefore radiation dose reduction by using iterative reconstruction technique and scanning methods receive widespread attention.

PURPOSE

To evaluate the effect of two reconstruction techniques (filtered back projection [FBP] and adaptive iterative dose reduction using three-dimensional processing [AIDR 3D]) and two acquisition techniques (wide-volume scan [WVS] and helical scan as 64-detector-row CT [64HS]) on the lung nodule identifications of using a chest phantom.

MATERIAL AND METHODS

A chest CT phantom including lung nodules was scanned using WVS and 64HS at nine different tube currents (TCs; range, 270-10 mA). All CT datasets were reconstructed with AIDR 3D and FBP. Standard deviation (SD) measurements by region of interest placement and qualitative nodule identifications were statistically compared. 64HS and WVS were evaluated separately, and FBP images acquired with 270 mA was defined as the standard reference.

RESULTS

SDs of all datasets with AIDR 3D showed no significant differences (P > 0.05) with standard reference. When comparing nodule identifications, area under the curve on WVS with AIDR 3D with TC <30 mA, on 64HS with AIDR 3D with TC <40 mA, and on reconstructions with FBP and each scan method with TC <60 mA was significantly lower than with standard reference (P < 0.05). With the same TC and reconstruction, SDs and nodule identifications of WVS were not significantly different from 64HS (P > 0.05).

CONCLUSION

In term of SD of lung parenchyma and nodule identification, AIDR 3D can achieve more radiation dose reduction than FBP and there is no significant different between WVS and 64HS.

Nodule characterization: subsolid nodules

In this review, we focus on the radiologic, clinical, and pathologic aspects primarily of solitary subsolid pulmonary nodules. Particular emphasis will be placed on the pathologic classification and correlative computed tomography (CT) features of adenocarcinoma of the lung. The capabilities of fluorodeoxyglucose positron emission tomography-CT and histologic sampling techniques, including CT-guided biopsy, endoscopic-guided biopsy, and surgical resection, are discussed. Finally, recently proposed management guidelines by the Fleischner Society and the American College of Chest Physicians are reviewed.

Detection of ground-glass opacities by use of hybrid iterative reconstruction (iDose) and low-dose 256-section computed tomography: a phantom study

The detection of ground-glass opacities (GGOs) is an important issue in lung cancer screening with low-dose CT. The iterative reconstruction (IR) technique has the ability to improve the image quality relative to the filtered back projection (FBP) technique with low-dose CT. Our purpose was to investigate the ability to detect GGO in a chest phantom using a low-dose CT and hybrid IR, named iDose. Simulated GGOs in a chest phantom were scanned with 256-section CT at tube current second products of 20, 50, 100, and 200 mAs. Five radiologists visually assessed the detectability of GGOs in the phantom. The contrast-to-noise ratio (CNR) for GGOs was used as an estimate of image quality. Comparison of the detectability and CNR between standard images with 200 mAs-FBP and low-dose images with 20, 50, and 100-mAs FBP/iDose were performed by ANOVA with Dunnett's and Tukey's test. The detectability was significantly lower at 20-mAs FBP/iDose and 50-mAs FBP than that at 200-mAs FBP (p < 0.05). There was no significant difference between 50-mAs iDose and 200-mAs FBP and between 100-mAs iDose/FBP and 200-mAs FBP. The CNR was significantly higher on iDose images than that on FBP images at each mAs value. The CNR at 200-mAs FBP was the same as that at 50-mAs iDose (CNR:1.8). The hybrid IR technique and low-dose CT imaging with 50 mAs enabled noise and to maintain the detectability for GGOs in a chest phantom that is equivalent to the reference acquisitions of 200 mAs with FBP.