Compound analysis of gallstones using dual energy computed tomography—Results in a phantom model

Dual-Energy, Spectral and Photon Counting Computed Tomography for Evaluation of the Gastrointestinal Tract

The use of dual-energy computed tomography (CT) allows for reconstruction of energy- and material-specific image series. The combination of low-energy monochromatic images, iodine maps, and virtual unenhanced images can improve lesion detection and disease characterization in the gastrointestinal tract in comparison with single-energy CT.

Making the invisible visible: improving conspicuity of noncalcified gallstones using dual-energy CT

PURPOSE

To determine whether virtual monochromatic imaging (VMI) increases detectability of noncalcified gallstones on dual-energy CT (DECT) compared with conventional CT imaging.

MATERIALS AND METHODS

This retrospective IRB-approved, HIPAA-compliant study included consecutive patients who underwent DECT of the abdomen in the Emergency Department during a 30-month period (July 1, 2013-December 31, 2015), with a comparison US or MR within 1-year. 51 patients (36F, 15M; mean age 52 years) fulfilled the inclusion criteria. All DECT were acquired on a dual-source 128 × 2 slice scanner using either 80/Sn140 or 100/Sn140 kVp pairs. Source images at high and low kVp were used for DE post-processing with VMI. Within 3 mm reconstructed images, regions of interest of 0.5 cm² were placed on noncalcified gallstones and bile to record hounsfield units (HU) at VMI energy levels ranging between 40 and 190 keV.

RESULTS

Noncalcified gallstones uniformly demonstrated lowest HU at 40 keV and increase at higher keV; the HU of bile varied at higher keV. Few of the noncalcified stones are visible at 70 keV (simulating a conventional 120 kVp scan), with measured contrast (bile-stone HU difference) <10 HU in 78%, 10-20 HU in 20%, and >20 HU in 2%. Contrast was maximal at 40 keV, where 100% demonstrated >20 HU difference from surrounding bile, 75% >44 HU difference, and 50% >60 HU difference. A paired t test demonstrated a significant difference (p < 0.0001) between this stone-bile contrast at 40 vs. 70 keV and 70 vs. 190 keV.

CONCLUSION

Low keV virtual monochromatic imaging increased conspicuity of noncalcified gallstones, improving their detectability.

Single- and dual-energy CT of the abdomen: comparison of radiation dose and image quality of 2nd and 3rd generation dual-source CT

OBJECTIVES

To compare single-energy (SECT) and dual-energy (DECT) abdominal CT examinations in matched patient cohorts regarding differences in radiation dose and image quality performed with second- and third-generation dual-source CT (DSCT).

METHODS

We retrospectively analysed 200 patients (100 male, 100 female; mean age 61.2 ± 13.5 years, mean body mass index 27.5 ± 3.8 kg/m²) equally divided into four groups matched by gender and body mass index, who had undergone portal venous phase abdominal CT with second-generation (group A, 120-kV-SECT; group B, 80/140-kV-DECT) and third-generation DSCT (group C, 100-kV-SECT; group D, 90/150-kV-DECT). The radiation dose was normalised for 40-cm scan length. Dose-independent figure-of-merit (FOM) contrast-to-noise ratios (CNRs) were calculated for various organs and vessels. Subjective overall image quality and reader confidence were assessed.

RESULTS

The effective normalised radiation dose was significantly lower (P < 0.001) in groups C (6.2 ± 2.0 mSv) and D (5.3 ± 1.9 mSv, P = 0.103) compared to groups A (8.8 ± 2.3 mSv) and B (9.7 ± 2.4 mSv, P = 0.102). Dose-independent FOM-CNR peaked for liver, kidney, and portal vein measurements (all P ≤ 0.0285) in group D. Subjective image quality and reader confidence were consistently rated as excellent in all groups (all ≥1.53 out of 5).

CONCLUSIONS

With both DSCT generations, abdominal DECT can be routinely performed without radiation dose penalty compared to SECT, while third-generation DSCT shows improved dose efficiency.

KEY POINTS

• Dual-source CT (DSCT) allows for single- and dual-energy image acquisition. • Dual-energy acquisition does not increase the radiation dose in abdominal DSCT. • Third-generation DSCT shows improved dose efficiency compared to second-generation DSCT. • Dose-independent figure-of-merit image contrast was highest with third-generation dual-energy DSCT. • Third-generation DSCT shows improved dose efficiency for SECT and DECT.

Comparison of Virtual Unenhanced Images Derived From Dual-Energy CT With True Unenhanced Images in Evaluation of Gallstone Disease

OBJECTIVE

The aim of this study was to compare gallstones on virtual unenhanced images and true unenhanced images acquired with dual-energy CT (DECT).

MATERIALS AND METHODS

We enrolled 112 patients with right upper quadrant pain and clinically suspected acute cholecystitis or gallstone who underwent DECT--including unenhanced, arterial, and portal phases. Eighty-three gallstones with composition proven by semiquantitative Fourier transform infrared spectroscopy from 45 patients who had undergone cholecystectomy (40 cholesterol gallstones from 21 patients, 43 calcium gallstones from 24 patients) were included. CT images were retrospectively evaluated for stone size, contrast-to-noise ratio (CNR) of gallstone to bile, and visibility and density of gallstones for each image set. The visibility of each type of stone was compared with a paired t test.

RESULTS

Both cholesterol and calcium stones measured smaller on virtual unenhanced images than on true unenhanced images, yielding a lower sensitivity of virtual unenhanced images for detecting small gallstones. Mean CNR of cholesterol stones was 2.45 ± 1.32 versus 1.67 ± 1.55 (p < 0.032) and that of calcium stones was 10.59 ± 7.15 and 14.11 ± 9.81 (p < 0.001) for virtual unenhanced and true unenhanced images, respectively. For calcium stones, two readers found 43 of 43 (100%) on true unenhanced images; one reader found 41 of 43 (95%) and the other, 37 of 43 (86%) on virtual unenhanced images. For cholesterol stones, one reader found 20 of 40 (50%) and the other 19 of 40 (47%) on true unenhanced images versus 34 of 40 (85%) and 30 of 40 (75%), respectively, on virtual unenhanced images. The visibility of cholesterol stones was higher on virtual unenhanced images, but that of calcium stones was lower.

CONCLUSION

Virtual unenhanced images at DECT allow better visualization of cholesterol gallstones, but true unenhanced images allow better visualization of calcium and small gallstones.

Spectral CT with metal artifacts reduction software for improvement of tumor visibility in the vicinity of gold fiducial markers

PURPOSE

To evaluate spectral computed tomography (CT) with metal artifacts reduction software (MARS) for reduction of metal artifacts associated with gold fiducial seeds.

MATERIALS AND METHODS

Thirteen consecutive patients with 37 fiducial seeds implanted for radiation therapy of abdominal lesions were included in this HIPAA-compliant, institutional review board-approved prospective study. Six patients were women (46%) and seven were men (54%). The mean age was 61.1 years (median, 58 years; range, 29-78 years). Spectral imaging was used for arterial phase CT. Images were reconstructed with and without MARS in axial, coronal, and sagittal planes. Two radiologists independently reviewed reconstructions and selected the best image, graded the visibility of the tumor, and assessed the amount of artifacts in all planes. A linear-weighted κ statistic and Wilcoxon signed-rank test were used to assess interobserver variability. Histogram analysis with the Kolmogorov-Smirnov test was used for objective evaluation of artifacts reduction.

RESULTS

Fiducial seeds were placed in pancreas (n = 5), liver (n = 7), periportal lymph nodes (n = 1), and gallbladder bed (n = 1). MARS-reconstructed images received a better grade than those with standard reconstruction in 60% and 65% of patients by the first and second radiologist, respectively. Tumor visibility was graded higher with standard versus MARS reconstruction (grade, 3.7 ± 1.0 vs 2.8 ± 1.1; P = .001). Reduction of blooming was noted on MARS-reconstructed images (P = .01). Amount of artifacts, for both any and near field, was significantly smaller on sagittal and coronal MARS-reconstructed images than on standard reconstructions (P < .001 for all comparisons). Far-field artifacts were more prominent on axial MARS-reconstructed images than on standard reconstructions (P < .01). Linear-weighted κ statistic showed moderate to perfect agreement between radiologists. CT number distribution was narrower with MARS than with standard reconstruction in 35 of 37 patients (P < .001).

CONCLUSION

Spectral CT with use of MARS improved tumor visibility in the vicinity of gold fiducial seeds.