Korean J Radiol.  2008 Jun;9(3):219-225. 10.3348/kjr.2008.9.3.219.

A New Method of Measuring the Amount of Soft Tissue in Pulmonary Ground-Glass Opacity Nodules: a Phantom Study

• Lee KW
• Im JG
• Kim TJ
• Dae CM

• KMID: 1758455
• DOI: http://doi.org/10.3348/kjr.2008.9.3.219

Abstract

OBJECTIVE
To devise a new method to measure the amount of soft tissue in pulmonary ground-glass opacity nodules, and to compare the use of this method with a previous volumetric measurement method by use of a phantom study. MATERIALS AND METHODS: Phantom nodules were prepared with material from fixed normal swine lung. Forty nodules, each with a diameter of 10 mm, were made with a variable mean attenuation. The reference-standard amount of soft tissue in the nodules was obtained by dividing the weight by the specific gravity. The imaging data on the phantom nodules were acquired with the use of a 16-channel multidetector CT scanner. The CT-measured amount of soft tissue of the nodules was calculated as follows: soft tissue amount = volume x (1 + mean attenuation value / 1,000). The relative percentage error (RPE) between the CT-measured amount of the soft tissue and the reference-standard amount of the soft tissue was also measured. The RPEs determined with use of the new method were compared with the RPEs determined with the current volumetric measurement method by the use of the paired t test. RESULTS: The CT-measured amount of soft tissue showed a strong correlation with the reference-standard amount of soft tissue (R(2) = 0.996, p < 0.01). The mean RPE of the CT-measured amount of soft tissue in the nodules was -7.79 +/- 1.88%. The mean RPE of the CT-measured volume was 114.78 +/- 51.02%, which was significantly greater than the RPE of the CT-measured amount of soft tissue (p < 0.01). CONCLUSION: The amount of soft tissue measured by the use of CT reflects the reference-standard amount of soft tissue in the ground-glass opacity nodules much more accurately than does the use of the CT-measured volume.

Keyword

Lung, nodule; Computed tomography (CT), volumetry

MeSH Terms

Animals
Lung Neoplasms/*radiography
Phantoms, Imaging
Reference Standards
Swine
*Tomography, X-Ray Computed

Figure

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  Fig. 1 Phantom nodules made of fixed swine lung (A). Forty nodules were placed in wells with diameter of approximately 10 mm of 5 cm-thick Styrofoam plate (B).

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  Fig. 2 CT image of 40 ground-glass opacity nodules. Mean attenuation values of nodules range from -754 HU to -352 HU.

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  Fig. 3 Scatterplots of linear regression.A. Regression of STARS on STACT of nodules at -900 HU lower threshold level. Scatterplot shows very strong correlation between STACT and STARS. Resulting linear equation was as follows: STARS = 1.036 × STACT + 21.199 (R2 = 0.996, p < 0.01).B. Regression of STARS on VCT of nodules at -900 HU lower threshold level. Scatterplot shows poor correlation between VCT and STARS (R2 = 0.294, p < 0.01).C. Regression of relative percent error of VCT on attenuation values of nodules at 900 HU lower threshold level. Scatterplot shows negative strong correlation between mean attenuation value of nodules and VCT (R2 = 0.941, p < 0.01).RPE = relative percentage error; STACT = CT-measured amount of soft tissue in nodules; STARS = reference-standard amount of soft tissue in nodules; VCT = CT-measured volume of nodules; MHU = mean attenuation value of nodules

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