Quantitative CT of lung nodules: Dependence of calibration on patient body size, anatomic region, and calibration nodule size for single- and dual-energy techniques

• Published in: Medical physics (Lancaster) 2009-07, Vol.36 (7), p.3107-3121
• Main Authors: Goodsitt, Mitchell M., Chan, Heang-Ping, Way, Ted W., Schipper, Mathew J., Larson, Sandra C., Christodoulou, Emmanuel G.
• Format: Article
• Language: English
• Subjects: ACCURACY; Algorithms; ATOMIC NUMBER; Body Size; CALCIUM; Calcium Carbonate - analysis; CALCIUM CARBONATES; CALIBRATION; Cancer; CAT SCANNING; CHEST; Computed tomography; Computer aided diagnosis; computerised tomography; dual energy; Humans; Image Processing, Computer-Assisted; lung; Lung - chemistry; Lung - diagnostic imaging; Lung - pathology; Lung Neoplasms - chemistry; Lung Neoplasms - diagnostic imaging; Lung Neoplasms - pathology; lung nodule; LUNGS; Medical imaging; Muscles; PATIENTS; PHANTOMS; Phantoms, Imaging; quantitative CT; Radiation Imaging Physics; RADIOLOGY AND NUCLEAR MEDICINE; Rings; SKELETON; Software; Tomography Scanners, X-Ray Computed; Tomography, X-Ray Computed - methods; Units and standards; X RADIATION; X‐ray spectra
• ISSN: 0094-2405; 2473-4209; 0094-2405
• DOI: 10.1118/1.3148536

Calcium concentration may be a useful feature for distinguishing benign from malignant lung nodules in computer-aided diagnosis. The calcium concentration can be estimated from the measured CT number of the nodule and a CT number vs calcium concentration calibration line that is derived from CT scans of two or more calcium reference standards. To account for CT number nonuniformity in the reconstruction field, such calibration lines may be obtained at multiple locations within lung regions in an anthropomorphic phantom. The authors performed a study to investigate the effects of patient body size, anatomic region, and calibration nodule size on the derived calibration lines at ten lung region positions using both single energy (SE) and dual energy (DE) CT techniques. Simulated spherical lung nodules of two concentrations (50 and 100 mg/cc CaCO 3 ) were employed. Nodules of three different diameters (4.8, 9.5, and 16 mm) were scanned in a simulated thorax section representing the middle of the chest with large lung regions. The 4.8 and 9.5 mm nodules were also scanned in a section representing the upper chest with smaller lung regions. Fat rings were added to the peripheries of the phantoms to simulate larger patients. Scans were acquired on a GE-VCT scanner at 80, 120, and 140 kVp and were repeated three times for each condition. The average absolute CT number separations between the calibration lines were computed. In addition, under- or overestimates were determined when the calibration lines for one condition (e.g., small patient) were used to estimate the CaCO 3 concentrations of nodules for a different condition (e.g., large patient). The authors demonstrated that, in general, DE is a more accurate method for estimating the calcium contents of lung nodules. The DE calibration lines within the lung field were less affected by patient body size, calibration nodule size, and nodule position than the SE calibration lines. Under- or overestimates in CaCO 3 concentrations of nodules were also in general smaller in quantity with DE than with SE. However, because the slopes of the calibration lines for DE were about one-half the slopes for SE, the relative improvement in the concentration estimates for DE as compared to SE was about one-half the relative improvement in the separation between the calibration lines. Results in the middle of the chest thorax section with large lungs were nearly completely consistent with the above generalization. On the other ha