Rationale and Objective
This study aimed to investigate the clinical value of spectral computed tomography (CT) in the detection of cholesterol gallstones from surrounding bile.
Materials and Methods
This study was approved by the institutional review board. The unenhanced spectral CT data of 24 patients who had surgically confirmed cholesterol gallstones were analyzed. Lipid concentrations and CT numbers were measured from fat-based material decomposition image and virtual monochromatic image sets (40–140 keV), respectively. The difference in lipid concentration and CT number between cholesterol gallstones and the surrounding bile were statistically analyzed. Receiver operating characteristic analysis was applied to determine the diagnostic accuracy of using lipid concentration to differentiate cholesterol gallstones from bile.
Results
Cholesterol gallstones were bright on fat-based material decomposition images yielding a 92% detection rate (22 of 24). The lipid concentrations (552.65 ± 262.36 mg/mL), CT number at 40 keV (−31.57 ± 16.88 HU) and 140 keV (24.30 ± 5.85 HU) for the cholesterol gallstones were significantly different from those of bile (−13.94 ± 105.12 mg/mL, 12.99 ± 9.39 HU and 6.19 ± 4.97 HU, respectively). Using 182.59 mg/mL as the threshold value for lipid concentration, one could obtain sensitivity of 95.5% and specificity of 100% with accuracy of 0.994 for differentiating cholesterol gallstones from bile.
Conclusions
Virtual monochromatic spectral CT images at 40 keV and 140 keV provide significant CT number differences between cholesterol gallstones and the surrounding bile. Spectral CT provides an excellent detection rate for cholesterol gallstones.
Introduction
Gallstones are a common disease in the gallbladder with an incidence rate of about 10% and occur mostly in middle-aged women. There are three common gallstones: cholesterol, bile pigment, and mixed stone . Cholesterol stone is the main type of gallstone, and is iso- or slightly hypoattenuating relative to bile. The experiment by Brakel et al. proved that the computed tomography (CT) value of the stones negatively correlated with cholesterol content and positively with calcium content. The cholesterol stone has CT attenuation similar to the surrounding bile under the normal X-ray or CT examination and is often difficult to detect. Cholesterol stones are therefore often referred to as negative stones and are easily missed in conventional CT using CT number alone . The recently introduced dual-energy spectral CT imaging uses information from two different energy spectrums to provide additional material density and effective atomic number information for different materials such as different stones , as well as a set of virtual monochromatic images at different photon energy levels. This multiparameter (photon energy-dependent CT number and material density value) approach should improve the separation of materials that have similar CT attenuation value using polychromatic energy beams but different intrinsic material densities such as the cholesterol gallstone and bile. The purpose of this study was to investigate the clinical value of dual-energy spectral CT imaging in the detection of cholesterol gallstones.
Materials and Methods
I. General Information
This retrospective study was approved by the institutional review board. The authors retrospectively analyzed the CT imaging data of 24 patients from July 2013 to June 2014 who underwent unenhanced spectral CT scans for upper abdominal pain in our hospital. Because cholesterol gallstones are easily missed in the conventional CT imaging, the study population was limited to patients who had only this type of stone confirmed by surgery. These patients included 10 men and 14 women with mean age of 48 years (32–67 years), mean body mass index (BMI) of 24.40 ± 4.11 kg/m 2 , no history of biliary surgery, and no fatty diet in the week before the CT examination.
II. CT Scan Technique
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III. Image Analysis
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IV. Statistical Analysis
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Results
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Table 1
CT Number Measurements of Bile and Cholesterol Gallstones and CNR Values for Cholesterol Gallstones as Function of Photon Energy ( x¯±s x
¯
±
s ± s)
keV CT Number (HU) Measurement_Z_ Value_P_ Value Contrast-to-Noise Ratio for Gallstones Bile Gallstone Gallstone 40 12.99 ± 9.39 −31.57±16.88 −5.68 <.001 1.38 ± 0.38 50 10.50 ± 6.01 −10.62±9.35 −5.34 <.001 0.87 ± 0.42 60 7.85 ± 4.32 7.67 ± 4.04 −0.42 .673 0.01 ± 0.03 70 8.57 ± 2.51 8.58 ± 2.58 −0.12 .907 0.00 ± 0.01 80 8.91 ± 2.05 9.28 ± 2.16 −0.81 .418 0.03 ± 0.06 90 6.84 ± 4.30 15.18 ± 4.18 −5.09 <.001 0.73 ± 0.48 100 6.52 ± 4.58 19.37 ± 4.94 −5.63 <.001 1.22 ± 0.62 110 6.39 ± 4.71 21.34 ± 5.30 −5.68 <.001 1.49 ± 0.68 120 6.30 ± 4.80 22.51 ± 5.49 −5.68 <.001 1.69 ± 0.72 130 6.25 ± 4.90 23.25 ± 5.58 −5.68 <.001 1.82 ± 0.75 140 6.19 ± 4.97 24.30 ± 5.85 −5.68 <.001 2.00 ± 0.75
CNR, contrast-to-noise ratio; CT, computed tomography; HU; Hounsfield unit.
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Discussions
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Conclusions
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Acknowledgments
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